Epicyclic gear system housing assembly

Abstract

The present invention discloses an epicyclic gear system housing assembly. A planetary gear housing assembly in an epicyclic gear system of a gas turbine engine, the planetary gear housing assembly comprising: a rear planetary gear carrier assembly; a front planetary gear carrier assembly; and a plurality of planetary gears. The planetary gear housing assembly comprises one or more of the following features: a strengthening member positioned between the front planetary gear carrier assembly and the rear planetary gear carrier assembly; a static bending joint that couples the front planetary gear carrier assembly and the rear planetary gear carrier assembly; a plurality of roller element bearings for supporting the plurality of planetary gears; and one or more bearing springs disposed between the bearings and the gear carrier housing to accommodate relative movement.

Description

[0001] Cross - reference to related applications

[0002] This application is related to the following co - filed and co - pending U.S. patent applications: U.S. Patent Application No. XXXXX, titled “BEARING SPRING FOR EPICYCLICAL GEAR SYSTEM HOUSING ASSEMBLY” (agent docket number G2640 - 00404 / RCA12400); U.S. Patent Application No. 16 / 592,498, titled “STIFFENING MEMBER FOR EPICYCLICAL GEAR SYSTEM HOUSING ASSEMBLY” (agent docket number G2640 - 00406 / RCA12401); and U.S. Patent Application No. 16 / 592,499, titled “STATIC CURVIC JOINT FOR EPICYCLICAL GEAR SYSTEM HOUSING ASSEMBLY” (agent docket number G2640 - 00408 / RCA12402). The entire contents of each of the above - mentioned documents are hereby incorporated by reference. Background of the Invention

[0003] Epicyclic gear systems can be used in rotating machinery to transfer energy from one component (such as a rotatable shaft) to another. By changing certain variables (such as the number, size, and tooth count of the gears), an epicyclic gear system can be designed to transfer energy between components at a desired ratio and typically convert a high - speed, low - torque input into a lower - speed, higher - torque output.

[0004] Epicyclic gear systems can be suitable for a wide range of applications, including transferring energy from a turbine shaft to a fan rotor in a geared turbofan engine. However, in such dynamic applications, the epicyclic gear system must be designed to allow a certain degree of relative movement between the parts of the system to avoid excessive wear and system failure under extreme conditions. Summary of the Invention

[0005] According to some aspects of the present disclosure, a planetary gear housing assembly in an epicyclic gear assembly includes: a rear planetary carrier assembly; a front planetary carrier assembly; a plurality of planetary gears; a bearing assembly; and a strengthening member. The rear planetary carrier assembly includes: a rear flange that defines a central orifice; and a plurality of gear shaft cavities that are circumferentially disposed around the central orifice and radially outside the central orifice, each cavity having a cylindrical wall. The front planetary carrier assembly includes: a front flange that defines a central orifice; and a plurality of gear shaft cavities that are circumferentially disposed around the central orifice and radially outside the central orifice, each cavity having a cylindrical wall. Each of the plurality of planetary gears includes a cylindrical shaft having: a front end portion that is disposed in one of the gear shaft cavities of the front planetary carrier assembly and is coaxial with the cylindrical wall of the cavity; a rear end portion that is disposed in one of the gear shaft cavities of the rear planetary carrier assembly and is coaxial with the cylindrical wall of the cavity; and one or more gears that are carried by the bearing between the front end portion and the rear end portion. The bearing assembly includes: a bearing that is disposed on at least a portion of one of the rear end portion and the front end portion of the gear shaft; and an annular spring that is disposed on at least a portion of the bearing. The strengthening member is positioned between the rear planetary carrier assembly and the front planetary carrier assembly. The strengthening member includes: an annular body that defines a central orifice; and a plurality of radial flanges that extend radially outward from the annular body, each of the plurality of radial flanges partially defining a gear-facing surface.

[0006] In some embodiments, the bearing is a roller bearing. In some embodiments, the shaft and the gear form a compound star gear in an epicyclic gear system. In some embodiments, the annular spring includes an annular body and a plurality of mufflers spaced circumferentially around the body.

[0007] In some embodiments, the rear planetary carrier assembly is coupled to the front planetary carrier assembly. In some embodiments, the rear planetary carrier assembly further includes an annular mounting flange extending from the rear flange, the annular mounting flange being positioned in front of and coaxial with the central orifice, the mounting flange forming a front-facing mounting surface that includes a curved structure. In some embodiments, the front planetary carrier assembly further includes an annular mounting flange extending from the front flange, the annular mounting flange being positioned behind and coaxial with the central orifice, the mounting flange forming a rear-facing mounting surface that includes a curved structure. In some embodiments, the mounting surfaces are positioned relative to each other to thereby form a static curved joint.

[0008] In some embodiments, each of the plurality of planetary gears includes a sun gear engaging gear and a ring gear engaging gear that are carried by the bearing between the front end portion and the rear end portion.

[0009] According to a further aspect of the present disclosure, an epicyclic gear assembly for a gas turbine engine includes three flexible joints, each flexible joint having a different radial dimension from the other flexible joints, and at least one of the flexible joints being a static flexible joint. In some embodiments, the radial dimension of the static flexible joint is the smallest radial dimension among the radial dimensions. In some embodiments, a first flexible joint among the three flexible joints couples a ring gear to a ring gear assembly. In some embodiments, a second flexible joint among the three flexible joints couples the ring gear assembly to an output shaft. In some embodiments, a third flexible joint among the three flexible joints couples a front planetary carrier assembly to a rear planetary carrier assembly. In some embodiments, the third flexible joint among the three flexible joints is the static flexible joint.

[0010] According to yet some further aspects of the present disclosure, a planetary gear housing assembly in an epicyclic gear assembly includes: a rear planetary carrier assembly; a front planetary carrier assembly; a plurality of planetary gears; and a strengthening member. The rear planetary carrier assembly includes a rear flange and an annular mounting flange. The rear flange defines a central orifice and a plurality of gear shaft recesses that surround the central orifice and are positioned radially outward of the central orifice, each recess having a cylindrical wall. The annular mounting flange is positioned in front of the central orifice and is coaxial with the central orifice, and forms a forward-facing mounting surface that includes a curved structure. The front planetary carrier assembly includes a front flange and an annular mounting flange. The front flange defines a central orifice and a plurality of gear shaft recesses that surround the central orifice and are positioned radially outward of the central orifice, each recess having a cylindrical wall. The annular mounting flange is positioned behind the central orifice and is coaxial with the central orifice, and forms a rearward-facing mounting surface that includes a curved structure. Each of the plurality of planetary gears includes a cylindrical shaft having: a front end portion that is disposed in a gear shaft recess of the front planetary carrier assembly and is coaxial with the cylindrical wall of the recess; a rear end portion that is disposed in a gear shaft recess of the rear planetary carrier assembly and is coaxial with the cylindrical wall of the recess; and one or more gears that are carried by the bearing between the front end portion and the rear end portion. The strengthening member is positioned between the rear planetary carrier assembly and the front planetary carrier assembly. The strengthening member includes: an annular body that defines a central orifice; and a plurality of radial flanges that extend radially outward from the annular body, each of the plurality of radial flanges partially defining a gear-facing surface. The curved structures of the mounting surfaces are positioned relative to each other such that a static flexible joint is formed.

[0011] In some embodiments, the shaft and the gear form a compound star gear in an epicyclic gear system. In some embodiments, the epicyclic gear assembly is part of a gas turbine engine having an engine casing, and wherein the rear flange is coupled to the engine casing to define a rear torsional stiffness, and the front flange is coupled to the rear planetary housing assembly to define a front torsional stiffness. In some embodiments, the front torsional stiffness is between 60% and 80% of the rear torsional stiffness. In some embodiments, the front torsional stiffness is between 65% and 75% of the rear torsional stiffness.

[0012] In some embodiments, the planetary gear housing assembly further includes a bearing assembly. The bearing assembly includes: a bearing disposed on at least a portion of one of the rear end and the front end of the gear shaft; and an annular spring disposed on at least a portion of the bearing. In some embodiments, the bearing is a roller bearing. In some embodiments, the annular spring includes an annular body and a plurality of mufflers spaced apart around the perimeter of the body. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Referring to the elements of the drawings provided for illustrative purposes, the following will become apparent.

[0014] Figure 1 is a cross-sectional side view of a gas turbine engine.

[0015] Figure 2 is a close-up cross-sectional side view of an upstream portion of a gas turbine engine.

[0016] Figure 3 is a partial cross-sectional view of a gearbox of a gas turbine engine.

[0017] Figure 4 is a schematic cross-sectional view of an epicyclic gear system according to some embodiments of the present disclosure.

[0018] Figure 5 is a detailed schematic cross-sectional view of a planetary gear disposed in an epicyclic gear system according to some embodiments of the present disclosure.

[0019] Figure 6 is an isometric view of a front planetary gear carrier assembly, a strengthening member, and a rear gear carrier housing assembly of a planetary gear housing assembly according to some embodiments of the present disclosure.

[0020] Figure 7 is a partial cross-sectional view of a strengthening member coupled between a front planetary gear carrier assembly and a rear planetary gear carrier assembly of a planetary gear housing assembly according to some embodiments.

[0021] Figure 8A is an isometric view of a strengthening member according to some embodiments.

[0022] Figure 8B Is an isometric view of a reinforcement member according to some embodiments.

[0023] Figure 9 Is a flowchart of a method according to some embodiments of the present disclosure.

[0024] Figure 10 Is an isometric view of a front planet carrier assembly of a planetary gear housing assembly according to some embodiments of the present disclosure.

[0025] Figure 11 Is an isometric view of a rear planet carrier assembly of a planetary gear housing assembly according to some embodiments of the present disclosure.

[0026] Figure 12 Is a partial cross-sectional view of a front planet carrier assembly coupled to a rear planet carrier assembly of a planetary gear housing assembly according to some embodiments.

[0027] Figure 13 Is a partial isometric view of a front planet carrier assembly coupled to a rear planet carrier assembly of a planetary gear housing assembly according to some embodiments.

[0028] Figure 14 Is a partial isometric view of a bent structure of a front planet carrier assembly of a planetary gear housing assembly according to some embodiments.

[0029] Figure 15 Is a partial isometric view of a bent structure of a rear planet carrier assembly of a planetary gear housing assembly according to some embodiments.

[0030] Figure 16 Is a flowchart of a method according to some embodiments of the present disclosure.

[0031] Figure 17 Is a schematic cross-sectional view of a part of an epicyclic gear system according to some embodiments of the present disclosure.

[0032] Figure 18 Is a partial cross-sectional view of a spring according to some embodiments.

[0033] Figure 19 Is a flowchart of a method according to some embodiments of the present disclosure.

[0034] Figure 20 Is a partial schematic cross-sectional view of an epicyclic gear system according to some embodiments of the present disclosure.

[0035] This application discloses illustrative (i.e., exemplary) embodiments. The claimed invention is not limited to the illustrative embodiments. Accordingly, many implementations of the claims will differ from the illustrative embodiments. Various modifications may be made to the claimed invention without departing from the spirit and scope of this disclosure. The claims are intended to cover embodiments having such modifications. Detailed Description

[0036] To facilitate understanding of the principles of this disclosure, reference will now be made to several illustrative embodiments shown in the accompanying drawings, and specific language will be used to describe these illustrative embodiments.

[0037] As noted elsewhere herein, this disclosure may relate to a gas turbine engine. Such a gas turbine engine may include an engine core that includes a turbine, a combustor, a compressor, and a core shaft that connects the turbine to the compressor. Such a gas turbine engine may include a fan (with fan blades) located upstream of the engine core.

[0038] The arrangements of this disclosure are particularly advantageous for a fan driven via a gearbox, but not exclusively. Thus, a gas turbine engine may include a gearbox that receives an input from the core shaft and outputs a drive to the fan to drive the fan at a lower speed than the core shaft. The input to the gearbox may come directly from the core shaft or indirectly from the core shaft, such as via a spur gear shaft and / or gears. The core shaft may rigidly connect the turbine and the compressor such that the turbine and the compressor rotate at the same speed (where the fan rotates at a lower speed).

[0039] The gas turbine engines described and / or claimed herein may have any suitable general architecture. For example, a gas turbine engine may have any desired number of shafts connecting the turbine and the compressor, such as one, two, or three shafts. By way of example only, the turbine connected to the core shaft may be a first turbine, the compressor connected to the core shaft may be a first compressor, and the core shaft may be a first core shaft. The engine core may also include a second turbine, a second compressor, and a second core shaft that connects the second turbine to the second compressor. The second turbine, the second compressor, and the second core shaft may be arranged to rotate at a higher speed than the first core shaft.

[0040] In such an arrangement, the second compressor may be located axially downstream of the first compressor. The second compressor may be arranged to receive (e.g., directly receive, such as via a generally annular duct) an airflow from the first compressor.

[0041] The gearbox can be arranged to be driven by a spindle configured to rotate at a minimum speed (e.g., in use) (e.g., the first spindle in the above example). For example, the gearbox can be arranged to be driven only by a spindle configured to rotate at a minimum speed (e.g., in use) (e.g., only the first spindle in the above example and not the second spindle). Alternatively, the gearbox can be arranged to be driven by any one or more shafts, e.g., by the first shaft and / or the second shaft in the above example.

[0042] The gearbox can be a reduction gearbox (where the rotational speed of the output to the fan is lower than the rotational speed of the input from the spindle). Any type of gearbox can be used. For example, the gearbox can be a "planetary" or "star" gearbox as described in more detail elsewhere herein. The gearbox can have any desired reduction ratio (defined as the rotational speed of the input shaft divided by the rotational speed of the output shaft), e.g., greater than 2.5, e.g., in the range of 3 to 4.2 or 3.2 to 3.8, e.g., about 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 transmission ratio can be between any two values in, for example, the previous sentence. By way of example only, the gearbox can be a "star" gearbox with a transmission ratio in the range of 3.1 or 3.2 to 3.8. In some arrangements, the transmission ratio can be outside of these ranges.

[0043] In any gas turbine engine described and / or claimed herein, the burner can be disposed axially downstream of the fan and the compressor. For example, in the case where a second compressor is provided, the burner can be located directly downstream of the second compressor (e.g., at the outlet of the second compressor). As a further example, in the case where a second turbine is provided, the airflow at the burner outlet can be supplied to the inlet of the second turbine. The burner can be disposed upstream of the turbine.

[0044] The compressor or each compressor (e.g., the first compressor or the second compressor above) can include any number of stages, e.g., multiple stages. Each stage can include a row of rotor blades and a row of stator blades, and the stator blades can be variable stator blades (where their angle of attack can be variable). The row of rotor blades and the row of stator blades can be axially offset from each other.

[0045] The turbine or each turbine (e.g., the first turbine and the second turbine above) can include any number of stages, e.g., multiple stages. Each stage can include a row of rotor blades and a row of stator blades. The row of rotor blades and the row of stator blades can be axially offset from each other.

[0046] Each fan blade can be defined as having a radial span that extends from a root (or hub) or 0% span location at a radially inner gas-washing position to a tip at the 100% span position. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip can be less than (or approximately) any of the following values: 0.4, 0.39, 0.38, 0.37, 0.36, 0.35, 0.34, 0.33, 0.32, 0.31, 0.3, 0.29, 0.28, 0.27, 0.26, or 0.25. The ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip can be within an inclusive range delimited by any two values in the previous sentence (i.e., these values can form an upper or lower limit), e.g., in the range from 0.28 to 0.32. These ratios are generally referred to as hub-tip ratios. The radius at the hub and the radius at the tip can both be measured at the leading edge (or axially most forward) portion of the blade. The hub-tip ratio, of course, refers to the gas-washing portion of the fan blade, i.e., that part of the blade that is radially outside of any platform.

[0047] The radius of the fan can be measured between the engine centerline and the tip at the leading edge of the fan blade. The fan diameter (which can simply be twice the fan radius) can be greater than (or approximately) any of the following values: 220 cm, 230 cm, 240 cm, 250 cm (about 100 inches), 260 cm, 270 cm (about 105 inches), 280 cm (about 110 inches), 290 cm (about 115 inches), 300 cm (about 120 inches), 310 cm, 320 cm (about 125 inches), 330 cm (about 130 inches), 340 cm (about 135 inches), 350 cm, 360 cm (about 140 inches), 370 cm (about 145 inches), 380 cm (about 150 inches), 390 cm (about 155 inches), 400 cm, 410 cm (about 160 inches), or 420 cm (about 165 inches). The fan diameter can be within an inclusive range delimited by any two values in the previous sentence (i.e., these values can form an upper or lower limit), e.g., in the range from 240 cm to 280 cm or from 330 cm to 380 cm.

[0048] The rotational speed of the fan may change during use. Generally, for a fan with a larger diameter, the rotational speed is lower. By way of non-limiting example only, the rotational speed of the fan under cruise conditions can be less than 2500 rpm, for example less than 2300 rpm. By way of a further non-limiting example, for an engine with a fan diameter in the range of 220 cm to 300 cm (such as 240 cm to 280 cm or 250 cm to 270 cm), the rotational speed of the fan under cruise conditions can be in the range of 1700 rpm to 2500 rpm, for example in the range of 1800 rpm to 2300 rpm, for example in the range of 1900 rpm to 2100 rpm. By way of a further non-limiting example, for an engine with a fan diameter in the range of 330 cm to 380 cm, the rotational speed of the fan under cruise conditions can be in the range of 1200 rpm to 2000 rpm, for example, in the range of 1300 rpm to 1800 rpm, for example in the range of 1400 rpm to 1800 rpm.

[0049] When using a gas turbine engine, the fan (with associated fan blades) rotates about an axis of rotation. This rotation causes the tips of the fan blades to move at a speed Utip. The work done by the fan blades 13 on the air flow causes the enthalpy of the air flow to increase by dH. The tip loading of the fan can be defined as dH / Utip2, where dH is the increase in enthalpy across the fan (such as the 1-D (one-dimensional) average increase in enthalpy), and Utip is the (translational) speed at the tip of the fan, for example the speed at the leading edge of the tip (which can be defined as the tip radius of the fan at the leading edge multiplied by the angular velocity). The tip loading of the fan under cruise conditions can be greater than (or approximately) any of the following values: 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39 or 0.4 (all units in this paragraph are Jkg-1K-1 / (ms-1)2). The tip loading of the fan can be within an inclusive range bounded by any two of the values in the previous sentence (i.e., these values can form an upper or lower limit), for example in the range of 0.28 to 0.31 or 0.29 to 0.3.

[0050] A gas turbine engine according to the present disclosure may have any desired bypass ratio, where the bypass ratio is defined as the ratio of the mass flow rate of the airflow through the bypass duct to the mass flow rate of the airflow through the engine core under cruise conditions. In some arrangements, the bypass ratio may be greater than (or approximately) any of the following values: 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, or 20. The bypass ratio may be within an inclusive range bounded by any two values in the previous sentence (i.e., these values may form an upper or lower limit), for example, in the range from 12 to 16, 13 to 15, or 13 to 14. The bypass duct may be generally annular. The bypass duct may be located radially outside the engine core. The radially outer surface of the bypass duct may be defined by the engine nacelle and / or the fan casing.

[0051] The overall pressure ratio of a gas turbine engine 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 outlet of the highest pressure compressor (before entering the combustor). As a non-limiting example, the overall pressure ratio of a gas turbine engine described and / or claimed herein at cruise may be greater than (or approximately) any of the following values: 35, 40, 45, 50, 55, 60, 65, 70, 75. The overall pressure ratio may be within an inclusive range bounded by any two values in the previous sentence (e.g., these values may form an upper or lower limit), for example, in the range from 50 to 70.

[0052] The specific thrust of the engine may be defined as the net thrust of the engine divided by the total mass flow rate through the engine. Under cruise conditions, the specific thrust of an engine described and / or claimed herein may be less than (or approximately) any of the following values: 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 within an inclusive range bounded by any two values in the previous sentence (e.g., these values may form an upper or lower limit), for example, in the range from 80 Nkg-1s to 100 Nkg-1s, or 85 Nkg-1s to 95 Nkg-1s. Such an engine may be particularly efficient compared to conventional gas turbine engines.

[0053] The gas turbine engines described and / or claimed herein can have any desired maximum thrust. By way of non-limiting example only, the gas turbines described and / or claimed herein may be capable of producing a maximum thrust of at least (or about) any of the following values: 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 can be within an inclusive range bounded by any two of the values in the previous sentence (i.e., these values can form an upper or lower limit). By way of example only, the gas turbines described and / or claimed herein may be capable of producing a maximum thrust within the range of 330 kN to 420 kN (e.g., 350 kN to 400 kN). The thrust mentioned above can be the maximum net thrust at sea level plus 15 degrees Celsius (ambient pressure 101.3 kPa, temperature 30 degrees Celsius) under standard atmospheric conditions, with the engine in a stationary state.

[0054] In use, the temperature of the airflow at the high-pressure turbine inlet can be particularly high. This temperature, which can be referred to as TET, can be measured at the outlet of the combustor, e.g., immediately upstream of the first turbine blade, which itself can be referred to as a nozzle guide vane. During cruise, the TET can be at least (or about) any of the following values: 1400 K, 1450 K, 1500 K, 1550 K, 1600 K, or 1650 K. The TET during cruise can be within an inclusive range bounded by any two of the values in the previous sentence (i.e., these values can form an upper or lower limit). The maximum TET during engine operation can be, for example, at least (or about) any of the following values: 1700 K, 1750 K, 1800 K, 1850 K, 1900 K, 1950 K, or 2000 K. The maximum TET can be within an inclusive range bounded by any two of the values in the previous sentence (i.e., these values can form an upper or lower limit), e.g., within the range of 1800 K to 1950 K. The maximum TET can occur, for example, under high-thrust conditions, e.g., under maximum takeoff (MTO) conditions.

[0055] The fan blades and / or airfoils described herein and / or claimed may be made of any suitable material or combination of materials. For example, at least a portion of the fan blade and / or airfoil may be at least partially made of a composite material, such as a metal matrix composite and / or an organic matrix composite, such as carbon fiber. As a further example, at least a portion of the fan blade and / or airfoil may be at least partially made of a metal, such as a titanium-based metal or an aluminum-based material (such as an aluminum-lithium alloy) or a steel-based material. The fan blade may include at least two regions made of different materials. For example, the fan blade may have a protective leading edge that may be made of a material that is more resistant to impact (e.g., resistant to impact from birds, ice, or other materials) than the remainder of the blade. Such a leading edge may be made, for example, of titanium or a titanium-based alloy. Thus, by way of example only, the fan blade may have a carbon fiber or aluminum (such as an aluminum-lithium alloy) body with a titanium leading edge.

[0056] The fan described herein and / or claimed may include a central portion from which the fan blades may extend, for example, in a radial direction. The fan blades may be attached to the central portion in any desired manner. For example, each fan blade may include a fixing device that may engage a corresponding slot in the hub (or disc). By way of example only, such a fixing device may be in the form of a dovetail that may be inserted along the slot and / or engage a corresponding slot in the hub / disc to secure the fan blade to the hub / disc. As a further example, the fan blade may be integrally formed with the central portion. Such an arrangement may be referred to as a bladed disc or a bladed ring. Any suitable method may be used to manufacture such a bladed disc or bladed ring. For example, at least a portion of the fan blade may be machined from a billet, and / or at least a portion of the fan blade may be attached to the hub / disc by welding (such as linear friction welding).

[0057] The gas turbine engine described herein and / or claimed may or may not be provided with a variable area nozzle (VAN). Such a variable area nozzle may allow the exit area of the bypass duct to vary during use. The general principles of the present disclosure may apply to engines with or without a VAN.

[0058] The fan of the gas turbine described herein and / or claimed may have any desired number of fan blades, such as 14, 16, 18, 20, 22, 24, or 26 fan blades.

[0059] The cruise conditions used in this document have their ordinary meanings, and those skilled in the art will readily understand them. Thus, for a given gas turbine engine for an aircraft, those skilled in the art will immediately recognize that the cruise conditions mean the operating point of the engine during the mid-cruise of the given mission (referred to in the industry as the "economic mission") of the aircraft to which the gas turbine engine is designed to be attached. In this regard, mid-cruise refers to the time point when 50% of the total fuel burned between the climb apex and the start of descent has been burned during the aircraft flight cycle (which can be approximated as the midpoint in terms of time and / or distance between the climb apex and the start of descent). Thus, the cruise conditions define the following operating point of the gas turbine engine, that is: considering the number of engines provided to the aircraft, the thrust provided at this operating point will ensure that the aircraft to which the gas turbine engine is designed to be attached operates in a steady state during mid-cruise (i.e., maintains a constant altitude and a constant Mach number). For example, in the case where the engine is designed to be attached to an aircraft with two engines of the same type, under cruise conditions, the engine provides half of the total thrust required for the aircraft to operate in a steady state during mid-cruise.

[0060] In other words, for a given gas turbine engine for an aircraft, the cruise conditions are defined as the engine operating point that provides a specified thrust (the specified thrust refers to the thrust required for the given gas turbine engine to be combined with any other engine on the aircraft to enable the aircraft to which the given gas turbine engine is designed to be attached to operate in a steady state at a given mid-cruise Mach number) under mid-cruise atmospheric conditions (defined by the International Standard Atmosphere at the mid-cruise altitude according to ISO 2533). For any given gas turbine engine for an aircraft, the mid-cruise thrust, atmospheric conditions, and Mach number are known, thus clearly defining the operating point of the engine under cruise conditions.

[0061] Merely by way of example, the forward speed under cruise conditions can be from 0.7 to 0.9 Mach, such as from 0.75 to 0.85 Mach, such as from 0.76 to 0.84 Mach, such as from 0.77 to 0.83 Mach, such as from 0.78 to 0.82 Mach, such as any point within the range from 0.79 to 0.81 Mach, such as approximately 0.8 Mach, approximately 0.85 Mach or within the range from 0.8 to 0.85 Mach. Any single speed within these ranges can be part of the cruise conditions. For a certain aircraft, the cruise conditions may not be within these ranges, such as below 0.7 Mach or above 0.9 Mach.

[0062] By way of example only, the cruise conditions can correspond to standard atmospheric conditions (according to the International Standard Atmosphere, ISA) at an altitude in the range from 10,000 m to 15,000 m, for example in the range from 10,000 m to 12,000 m, for example in the range from 10,400 m to 11,600 m (about 38,000 feet), for example in the range from 10,500 m to 11,500 m, for example in the range from 10,600 m to 11,400 m, for example in the range from 10,700 m (about 35,000 feet) to 11,300 m, for example in the range from 10,800 m to 11,200 m, for example in the range from 10,900 m to 11,100 m, for example at an altitude of about 11,000 m. The cruise conditions can correspond to standard atmospheric conditions at any given altitude within these ranges.

[0063] By way of example only, the cruise conditions may correspond to the following operating points of the engine, namely: the operating point provides a known required thrust level (e.g., a value in the range from 30 kN to 35 kN) at an altitude of 38,000 feet (11,582 m), at a forward Mach number of 0.8 and standard atmospheric conditions (according to the International Standard Atmosphere). By way of further example only, the cruise conditions can correspond to the following operating points of the engine, namely: the operating point provides a known required thrust level (e.g., values from 50 kN to 65 kN) at an altitude of 35,000 feet (10,668 m), at a forward Mach number of 0.85 and standard atmospheric conditions (according to the International Standard Atmosphere).

[0064] In use, the gas turbine engine described and / or claimed herein can operate under cruise conditions defined elsewhere herein. Such cruise conditions can be determined by the cruise conditions (e.g., mid - cruise conditions) of an aircraft on which at least one (e.g., 2 or 4) gas turbine engines can be installed to provide propulsion thrust.

[0065] According to one aspect, there is provided an aircraft including the gas turbine engine described and / or claimed herein. The aircraft according to this aspect is an aircraft such that the gas turbine engine has been designed to be attached thereto. Thus, the cruise conditions according to this aspect correspond to the mid - cruise of the aircraft defined elsewhere herein.

[0066] According to one aspect, there is provided a method of operating the gas turbine engine described and / or claimed herein. The operation can be under cruise conditions (e.g., in terms of thrust, atmospheric conditions, and Mach number) defined elsewhere herein.

[0067] According to one aspect, a method of operating a gas turbine engine as described and / or claimed herein is provided. The operation according to this aspect can include (or can be) an operation under mid-cruise of an aircraft as defined elsewhere herein.

[0068] Figure 1 There is shown a gas turbine engine 10 having an engine main rotational axis 9. The engine 10 includes an air intake 12 and a propelling fan 23 which generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 includes a core 11 which receives the core airflow A. The engine core 11 includes an axial low-pressure compressor 14, a high-pressure compressor 15, a combustor 16, a high-pressure turbine 17, a low-pressure turbine 19, and an engine core split exhaust nozzle 20. An engine nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass split exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The propelling fan 23 is attached to and driven by the low-pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0069] In use, the core airflow A is accelerated and compressed by the low-pressure compressor 14 and introduced into the high-pressure compressor 15 where further compression takes place. The compressed air discharged from the high-pressure compressor 15 is introduced into the combustor 16 where the compressed air is mixed with fuel and the mixture is burned. The resulting hot combustion products then expand through the high-pressure turbine 17 and the low-pressure turbine 19 and thereby drive the high-pressure turbine 17 and the low-pressure turbine 19 before being discharged through the engine core split exhaust nozzle 20 to provide some propulsive thrust. The high-pressure turbine 17 drives the high-pressure compressor 15 via a suitable interconnecting shaft 27. The propelling fan 23 generally provides most of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0070] In Figure 2 there is shown an exemplary arrangement for a geared fan gas turbine engine 10. The low-pressure turbine 19 (see Figure 1 ) drives a shaft 26 which is connected to a sun wheel or sun gear 28 of an epicyclic gear arrangement 30. Radially outwardly of and meshing with the sun gear 28 are a plurality of planet gears 32 which are connected together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 so that they travel synchronously around the sun gear 28 while enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is connected via a link 36 to the propelling fan 23 so as to drive its rotation about the engine main rotational axis 9. Radially outwardly of and meshing with the planet gears 32 is an annulus gear or ring gear 38 which is connected via a link 40 to a stationary support structure 24.

[0071] It should be noted that the terms "low-pressure turbine" and "low-pressure compressor" as used herein can mean the lowest-pressure turbine stage and the lowest-pressure compressor stage, respectively (i.e., excluding the propulsive fan 23), and / or the turbine stage and the compressor stage connected together by an interconnecting shaft 26 having the lowest rotational speed in the engine (i.e., excluding the gearbox output shaft driving the propulsive fan 23). In some literature, the "low-pressure turbine" and "low-pressure compressor" referred to herein can be alternatively referred to as "intermediate-pressure turbine" and "intermediate-pressure compressor". In the case of using these alternative designations, the propulsive fan 23 can be referred to as the first compression stage or the lowest-pressure compression stage.

[0072] In Figure 3 as an example, the epicyclic gearbox 30 is shown in more detail. The sun gear 28, the planet gears 32, and the ring gear 38 each include teeth around their perimeters to mesh with other gears. However, for clarity, only an exemplary portion of the teeth is shown in Figure 3 . Four planet gears 32 are shown, but those skilled in the art will appreciate that more or fewer planet gears 32 can be provided within the scope of the claimed invention. The practical application of the planetary epicyclic gearbox 30 typically includes at least three planet gears 32.

[0073] In Figure 2 and Figure 3 the epicyclic gearbox 30 shown as an example is of the planetary type, where the planet carrier 34 is coupled to the output shaft via a link 36 and the ring gear 38 is fixed. However, any other suitable type of epicyclic gearbox 30 can be used. As a further example, the epicyclic gearbox 30 can be of a star arrangement, in which the planet carrier 34 is held fixed, allowing the ring gear (or annulus gear) 38 to rotate. In such an arrangement, the propulsive fan 23 is driven by the ring gear 38. As a further alternative example, the gearbox 30 can be a differential gearbox, in which both the ring gear 38 and the planet carrier 34 are allowed to rotate.

[0074] It should be understood that Figure 2 and Figure 3 the arrangements shown are only examples, and various alternatives are within the scope of the present disclosure. Only as an example, any suitable arrangement can be used to position the gearbox 30 in the engine 10 and / or connect the gearbox 30 to the engine 10. As a further example, the connections between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft, and the support structure 24), such as Figure 2The connecting rods 36, 40) in the example can have any desired degree of stiffness or flexibility. As a further example, any suitable bearing arrangement can be used between the rotating and stationary parts of the engine (e.g., between the input and output shafts of the gearbox and a fixed structure such as the gearbox housing), and the present disclosure is not limited to Figure 2 the exemplary arrangement of. For example, in the case where the gearbox 30 has a star arrangement (as described above), those skilled in the art will readily understand that the arrangement of the output connecting rod and the support connecting rod and the bearing positions will generally be different from those Figure 2 shown by way of example in.

[0075] Thus, the present disclosure extends to gas turbine engines having any arrangement of gearbox styles (e.g., star or planetary), support structures, input and output shaft arrangements, and bearing positions.

[0076] Optionally, the gearbox can drive additional and / or alternative components (e.g., an intermediate pressure compressor and / or a booster compressor).

[0077] Other gas turbine engines to which the present disclosure can be applied can have alternative configurations. For example, such an engine can have an alternative number of compressors and / or turbines, and / or an alternative number of interconnected shafts. As a further example, Figure 1 the gas turbine engine shown in has a bypass split exhaust nozzle 18 and an engine core split exhaust nozzle 20, which means that the airflow through the bypass duct 22 has its own bypass split exhaust nozzle 18 that is separate from and radially outside of the engine core split exhaust nozzle 20. However, this is not restrictive, and any aspect of the present disclosure can also be applied to an engine in which the airflow through the bypass duct 22 and the airflow through the engine core 11 are mixed or combined before (or upstream of) a single nozzle, which can be referred to as a mixed flow nozzle. One or both nozzles (whether mixed flow or split) can have a fixed or variable area.

[0078] The geometry of the gas turbine engine 10 or its components is defined by a conventional axis system that includes an axial direction (which is aligned with the main engine rotation axis 9), a radial direction (in the Figure 1 upward direction in), and a circumferential direction (perpendicular to Figure 1 the plane of the view). The axial, radial, and circumferential directions are mutually perpendicular.

[0079] Figure 4A schematic diagram of an epicyclic gear system 100 in accordance with some embodiments of the present disclosure is provided. The epicyclic gear system 100 may be a compound star gear system. The sun gear 101 is coupled to and driven by a first rotatable shaft 103. The sun gear 101 engages one or more planet gears 105 such that rotation of the sun gear 101 causes rotation of the one or more planet gears 105. The planet gears 105 may be star gears such that the planet gears 105 rotate about an axis fixed relative to the axis of rotation of the sun gear 101.

[0080] Each of the one or more planet gears 105 engages a ring gear 107. The ring gear 107 is coupled to a second rotatable shaft 109 via a ring gear hub 108. Thus, rotation of the first rotatable shaft 103 drives rotation of the second rotatable shaft 109 via rotation of the sun gear 101, the one or more planet gears 105, and the ring gear 107. In some embodiments, the first rotatable shaft 103 may be a turbine shaft of a turbine engine (i.e., a high or low speed spool), and the second rotatable shaft 109 may be a fan shaft or a fan rotor.

[0081] Figure 5 A detailed schematic diagram of a housing assembly 111 of the epicyclic gear system 100 in accordance with some embodiments of the present disclosure is provided. Each of the one or more planet gears 105 includes a cylindrical gear shaft 123, a sun gear engagement portion 125, and a ring gear engagement portion 127. The sun gear engagement portion 125 and the ring gear engagement portion 127 may be carried by the cylindrical gear shaft 123. Each of the one or more planet gears 105 is carried by the housing assembly 111. The planet gears 105 may be compound star gears of the epicyclic gear system 100.

[0082] The housing assembly 111 may include a front housing member 113 and a rear housing member 115. In some embodiments, the housing assembly 111 further includes an intermediate housing member 114. One or more of the housing members 113, 114, 115 may be joined together. Each of the front housing member 113 and the rear housing member 115 defines a plurality of gear shaft cavities 116 having a cylindrical wall 120. The intermediate housing member 114 may define a plurality of holes 118.

[0083] The cylindrical gear shaft 123 of the planetary gear 105 can have a front end portion 141 disposed within one of the plurality of gear shaft cavities 116 formed by the front housing member 113. The cylindrical gear shaft 123 of the same planetary gear 105 can have a rear end portion 142 disposed within one of the plurality of gear shaft cavities 116 formed by the rear housing member 115. The cylindrical gear shaft 123 can be coaxially disposed within each gear shaft cavity 116 with the cylindrical wall 120 of the gear shaft cavity 116. The cylindrical gear shaft 123 can extend through the hole 118 defined by the intermediate housing member 114. The sun gear engagement portion 125 and the ring gear engagement portion 127 of the planetary gear 105 can be carried by the cylindrical gear shaft 123 between the front end portion 141 and the rear end portion 142.

[0084] The housing assembly 111 can further include a bearing assembly 117. The housing assembly 111 can include a front bearing assembly and a rear bearing assembly. The bearing assembly 117 can include bearings. For example, the front bearing 119 can be disposed on at least a portion of the front end portion 141 of the cylindrical gear shaft 123, and the rear bearing 121 can be disposed on at least a portion of the rear end portion 142 of the cylindrical gear shaft 123. Each bearing 119, 121 can rotatably carry the planetary gear 105. Each bearing 119, 121 can be a roller element bearing.

[0085] During operation of the epicyclic gear system 100, the components of the epicyclic gear system 100, as described above and including the additional gear carrier assembly, housing, and bearings, can move relative to each other. Even a small change in the relative positioning between one component and another can have a significant impact on the performance of the epicyclic gear system 100. For example, misalignment of the meshing gear teeth and / or bearings can cause uneven gear and / or bearing loads, resulting in deterioration or damage of the gear teeth. For example, misalignment of the meshing gear teeth and / or bearings can cause uneven gear and / or bearing loads, resulting in deterioration or damage of the gear teeth and reducing bearing life and bearing stability.

[0086] Particular attention needs to be paid to the front-to-back alignment of the cylindrical gear shaft 123 of each planetary gear 105. Since each planetary gear 105 is carried by the cylindrical gear shaft 123 that is partially disposed within the gear shaft cavity 116 of the front housing member 113 and the gear shaft cavity 116 of the rear housing member 115, a change in the relative movement or relative positioning between the front housing member 113 and the rear housing member 115 can cause misalignment of the planetary gear 105. Similarly, a change in the relative movement or relative positioning between the intermediate housing member 114 and one or both of the front housing member 113 and the rear housing member 115 can cause misalignment of the planetary gear 105.

[0087] Such misalignment may in turn result in uneven load distribution among the planetary gears 105, gear degradation, and shortened service life of the planetary gears 105 and / or the planetary bearings 119, 121. Factors that may cause misalignment of the planetary gears include misaligned forces between the front bearing 119 and the rear bearing 121, manufacturing inaccuracies in the positions of the gear shaft cavities 116 and the holes 118, the ability to reassemble the front housing and the rear housing to the same position where they were machined, gear tolerances, and non-flexibility and / or relative rigidity between each of the housing members 113, 114, 115 of the housing.

[0088] Accordingly, the present disclosure relates to systems and methods for improving and maintaining alignment of planetary gears in an epicyclic gear system, and to systems and methods for reducing relative movement between static components in an epicyclic gear system. More specifically, the present disclosure relates to a planetary gear housing assembly for an epicyclic gear system, the planetary gear housing assembly having one or more of the following features: a strengthening member positioned between a front planetary carrier assembly and a rear planetary carrier assembly; a static flexure joint coupling the front planetary carrier assembly and the rear planetary carrier assembly; a roller element bearing; and a bearing spring disposed between the bearing and the carrier housing to accommodate relative movement between the bearing and the carrier housing.

[0089] As Figure 4 shown in FIGS. 8 and Figures 10 to 12 as described below, the planetary gear housing assembly 111 may include: a rear planetary carrier assembly 131; a front planetary carrier assembly 161; a strengthening member 171; and a plurality of planetary gears 105, each of the plurality of planetary gears 105 being carried by the rear planetary carrier assembly 131 and the front planetary carrier assembly. Figure 6 is an isometric view of a front planetary carrier assembly, a strengthening member, and a rear planetary carrier assembly of a planetary gear housing assembly according to some embodiments of the present disclosure. Figure 7 is a partial cross-sectional view of a strengthening member coupled between a front planetary carrier assembly and a rear planetary carrier assembly of a planetary gear housing assembly according to some embodiments. Figure 8A and Figure 8B provide an isometric view of a strengthening member according to some embodiments. Figure 10 is an isometric view of a front planetary carrier assembly of a planetary gear housing assembly according to some embodiments of the present disclosure. Figure 11 is an isometric view of a rear planetary carrier assembly of a planetary gear housing assembly according to some embodiments of the present disclosure. Figure 12 is a partial cross-sectional view of a front planetary carrier assembly coupled to a rear planetary carrier assembly of a planetary gear housing assembly according to some embodiments.

[0090] The rear planetary carrier assembly 131 may include one or both of an intermediate housing member 114 and a rear housing member 115. The rear planetary carrier assembly 131 may include a rear flange 136. The rear flange 136 may be the intermediate housing member 114, the rear housing member 115, or another flange member. The rear flange 136 may include more than one flange, as Figure 6 shown, and has a first rear flange 136A and a second rear flange 136B. The rear flange 136 may define a central aperture 132 and a plurality of gear shaft cavities 137 that surround the central aperture 132 and are located radially outward of the central aperture 132. Each gear shaft cavity 116 may have a cylindrical wall 138. In some embodiments, the rear flange 136 may further include a radially outer mounting surface 139 for coupling the rear planetary carrier assembly 131 to the engine housing.

[0091] The rear planetary carrier assembly 131 may further include an annular mounting flange 133. The annular mounting flange 133 may be positioned in front of the central aperture 132 and coaxial with the central aperture 132. The annular mounting flange 133 may extend substantially perpendicularly from the rear flange 136. The annular mounting flange 133 may form a forward-facing mounting surface 134 that may include a curved structure 135.

[0092] The front planetary carrier assembly 161 may include a front flange 162 and an annular mounting flange 143. The front planetary carrier assembly 161 may be the front housing member 113. The front flange 162 may define a central aperture 144 and a plurality of gear shaft cavities 145 that surround the central aperture 144 and are located radially outward of the central aperture 144. Each gear shaft cavity 145 may have a cylindrical wall 146. The annular mounting flange 143 may be positioned behind the central aperture 144 and coaxial with the central aperture 144. The annular mounting flange 143 may form a rear-facing mounting surface 147 that may include a curved structure 148. The annular mounting flange 143 may extend substantially perpendicularly from the front flange 162.

[0093] A plurality of planetary gears 105 may be carried by the front planetary carrier assembly 161 and the rear planetary carrier assembly 131. Each of the planetary gears 105 may include a cylindrical gear shaft 123 having a front end portion 141 disposed in one of the gear shaft cavities 145 of the front flange 162. The front end portion 141 may be disposed in the gear shaft cavity 145 and coaxial with the cylindrical wall 146 that defines the gear shaft cavity 145. The cylindrical shaft may have a rear end portion 142 disposed within one of the gear shaft cavities 137 of the rear flange 136 and may be disposed in the gear shaft cavity 137 coaxial with the cylindrical wall 138.

[0094] Each planetary gear 105 may further include one or more gears carried by a cylindrical gear shaft 123 between a front end portion 141 and a rear end portion 142. These gears may be, for example, the sun gear engagement portion 125 of the planetary gear 105 and / or the ring gear engagement portion 127 of the planetary gear 105.

[0095] The curved structures 135, 148 of the rear planetary carrier assembly 131 and the front planetary carrier assembly 161 may be positioned relative to each other to form a static curved joint 165. In Figure 14 an isometric view shows a portion of the curved structure 148 of the front planetary carrier assembly 161. In Figure 15 an isometric view shows a portion of the curved structure 135 of the rear planetary carrier assembly 131. Figure 13 A partial isometric view of the curved joint 165 is provided.

[0096] In some embodiments, the curved structure 148 of the front planetary carrier assembly 161 may include a plurality of teeth 152 defined by a rear-facing mounting surface 147 and extending away from the rear-facing mounting surface 147. The rear-facing mounting surface 147 may also define a plurality of fastener holes 153, each fastener hole 153 being positioned between a pair of adjacent teeth 152. The teeth 152 may be shaped and sized to form a curved joint 165 with the curved structure 135 of the rear planetary carrier assembly 131.

[0097] In some embodiments, the curved structure 135 of the rear planetary carrier assembly 131 may include a plurality of teeth 151 defined by a front-facing mounting surface 134 and extending away from the front-facing mounting surface 134. The front-facing mounting surface 134 may also define a plurality of fastener holes 154, each fastener hole 154 being positioned between a pair of adjacent teeth 151. The teeth 151 may be shaped and sized to form a curved joint 165 with the curved structure 148 of the front planetary carrier assembly 161.

[0098] Fasteners 155 may be positioned in the fastener holes of each associated set of fastener holes 153, 154 that align when the curved structures 135, 148 are positioned to form the curved joint 165. In Figure 13 the illustrated embodiment, the fasteners 155 are bolts and nuts. Fasteners 155 may be provided for each associated pair of fastener holes 153, 154.

[0099] The planetary gear housing assembly 111 and / or the front planetary gear carrier assembly 161 may further include a reinforcement member 171. The reinforcement member 171 may include an annular body 172 defining a central aperture 173. The reinforcement member 171 may further include a plurality of radial flanges 174 extending radially outward from the annular body 172. Each radial flange 174 may at least partially define a gear-facing surface 175. In some embodiments, the reinforcement member 171 includes seven radial flanges 174 and defines seven gear-facing surfaces 175.

[0100] The reinforcement member 171 may be positioned between the rear planetary gear carrier assembly 131 and the front planetary gear carrier assembly 161. In some embodiments, the reinforcement member 171 may abut one or both of the front flange 162 and the rear flange 136. In some embodiments, the reinforcement member 171 is coupled to one or both of the front flange 162 and the rear flange 136 by a plurality of bolts, pins, or other fasteners 176.

[0101] When the epicyclic gear system 100 is fully assembled, the respective planetary gears 105 may be carried by the front flange 162 and the rear flange 136 and may have a gear portion, such as a ring gear engagement portion 127 positioned adjacent to the gear-facing surface 175 of the reinforcement member 171. The reinforcement member 171 may be coupled between the front flange 162 and the rear flange 136 to increase the torsional stiffness of the front planetary gear carrier assembly 161 relative to the rear planetary gear carrier assembly 131.

[0102] The epicyclic gear system 100 may be an epicyclic gear system of a gas turbine engine. The gas turbine engine may include an engine housing 177, a portion of which is shown in Figure 7 section. The rear flange 136 may be coupled to the engine housing 177 to define a rear torsional stiffness. The front flange 162 may be coupled to the rear flange 136 to define a front torsional stiffness. The front flange 162 may be coupled to the rear flange 136, for example, in the case where the forward-facing mounting surface 134 of the mounting flange 133 is positioned relative to the rearward-facing mounting surface 147 of the mounting flange 143. The front flange 162 may be coupled to the rear flange 136 by a static bending joint.

[0103] In some embodiments, the front torsional stiffness may be between 60% and 80% of the rear torsional stiffness. Since the radius at which the rear flange 136 is mounted to the engine housing 177 is greater than the radius at which the front flange 162 is mounted to the rear flange 136, the rear torsional stiffness may be greater. More generally, the front torsional stiffness may be between 50% and 90% of the rear torsional stiffness. In other embodiments, the front torsional stiffness may be between 65% and 75% of the rear torsional stiffness.

[0104] The planetary gear housing assembly 111 may further include a bearing assembly 117. Figure 17 A schematic cross-sectional view of a portion of an epicyclic gear system 100 in accordance with some embodiments of the present disclosure is provided. Figure 17 The cross-section shown is taken normal to the axis of rotation of the first shaft 103 and / or the second shaft 109, while Figure 4 and Figure 5 the cross-section shown is taken along the axis of rotation. Although Figure 17 is labeled to illustrate the front housing member 113, it is equally applicable to illustrate the rear housing member 115 and / or the intermediate housing member 114.

[0105] As Figure 17 shown, the bearing assembly 117 may include an annular spring 181 disposed on at least a portion of the bearing 119. The spring 181 may be positioned between the bearing 119 and the front housing member 113. The spring 181 may be at least partially positioned within the gear shaft recess 116, between the front housing member 113 and the bearing 119. The spring 181 may be coaxial with one or both of the cylindrical wall 120 of the gear shaft recess 116 and / or the bearing 119. The spring 181 may be adapted to accommodate relative movement between the front housing member 113 and the bearing 119. The spring 181 may effectively prevent, reduce or minimize the fore-and-aft misalignment of the cylindrical gear shaft 123.

[0106] The spring 181 may be customized to achieve a desired deflection and / or stiffness. Figure 18 A partial cross-sectional view of a spring in accordance with some embodiments is provided. The spring 181 may include an annular body 183 and a plurality of dampers 185 spaced apart around one or both of the inner and outer peripheries of the annular body 183. The shape, size (e.g., radial depth, circumferential length, etc.) and spacing of the dampers 185 may be varied to achieve a desired deflection and / or stiffness of the spring 181, and thus a desired reduction or possible reduction in the fore-and-aft misalignment of the cylindrical gear shaft 123.

[0107] In Figure 18 embodiments, the spring 181 includes a plurality of dampers 185 spaced apart around both the inner and outer peripheries of the annular body 183. The dampers 185 are shaped to have straight side edge surfaces 186 and arcuate radially outer surfaces 187. In other embodiments, the dampers 185 may be shaped to be arcuate, parabolic, curved or straight.

[0108] In Figure 18In [the device], the muffler 185 along the outer periphery has a radial dimension D2 that is approximately half of the radial dimension D1 of the body 183. In other embodiments, the radial dimension D2 of the muffler 185 along the outer periphery can be between 0.25 and 1.25 times the radial dimension D1 of the body 183. The muffler 185 along the inner periphery has a radial dimension D3 that is approximately half of the radial dimension D1 of the body 183. In other embodiments, the radial dimension D3 of the muffler 185 along the inner periphery can be between 0.25 and 1.25 times the radial dimension D1 of the body 183. All mufflers 185 along the outer or inner periphery can have the same radial dimensions D2, D3 as other mufflers 185 along the same periphery. However, in some embodiments, the muffler 185 can have varying radial dimensions D2, D3 when compared to other mufflers 185 along the same periphery of the body 183. In some embodiments, the radial dimensions D2, D3 of the muffler 185 along the inner and / or outer periphery can be between 0.8 and 1.0 times the radial dimension D1 of the body 183.

[0109] In Figure 18 [the device], the peripheral length L1 of the muffler 185 along the outer periphery is approximately equal to the peripheral length L2 between the mufflers 185. In other words, the mufflers 185 are spaced apart by a distance L2 that is equal to the length L1 of the muffler 185. In other embodiments, the peripheral length L1 of the muffler 185 along the outer periphery can be between 0.25 and 1.25 times the circumferential length L2, where the circumferential length L2 is the length by which adjacent mufflers 185 are separated. The peripheral length L3 of the muffler 185 along the inner periphery is likewise approximately equal to the peripheral length L4 between the mufflers 185. In other embodiments, the circumferential length L3 of the muffler 185 along the inner periphery can be between 0.25 and 1.25 times the peripheral length L4, where the circumferential length L4 is the length by which adjacent mufflers 185 are separated. In some embodiments, the peripheral lengths L1, L3 of the muffler 185 along the inner and / or outer periphery can be between 0.8 and 1.0 times the peripheral lengths L2, L4 between the mufflers 185.

[0110] The radial dimension D1 of the spring 181 can be sized to achieve the desired stiffness and / or deflection of the spring 181. The radial dimension D1 of the spring 181 can be uniform or non-uniform around the circumference of the spring 181. First, for example, the radial dimension D1 of the front spring 181 can be different from or the same as the radial dimension D1 of the second, for example, the rear spring 181.

[0111] The number of silencers 185 spaced around the inner and / or outer periphery of spring 181 can also vary to achieve the desired stiffness and / or deflection of spring 181. The silencers 185 can be spaced evenly or unevenly around the periphery. First, for example, the number of silencers 185 of the front spring 181 can be different from or the same as the number of silencers 185 of the second, for example, the rear spring 181.

[0112] In some embodiments, one or more housing bushings (not shown) can be positioned in gear shaft recess 116. The housing bushings can be positioned between spring 181 and front housing member 113, and / or can be located between spring 181 and bearing 119.

[0113] In some embodiments, spring 181 can be disposed on at least a portion of one of bearings 119 or 121. In other words, spring 181 can be positioned between only one of front bearing 119 and front housing member 113 or rear roller element bearing 121 and rear housing member 115. For example, to achieve the desired deflection of cylindrical gear shaft 123, an embodiment can include spring 181 positioned between rear roller element bearing 121 and rear housing member 115 without spring 181 positioned between front bearing 119 and front housing member 113.

[0114] In some embodiments, spring 181 positioned between front bearing 119 and front housing member 113 can differ from spring 181 positioned between rear roller element bearing 121 and rear housing member 115 in shape, size, and silencers. In some embodiments, spring 181 positioned between front bearing 119 and front housing member 113 can have a first stiffness, while spring 181 positioned between rear roller element bearing 121 and rear housing member 115 can have a second stiffness. The first stiffness can be greater than, equal to, or less than the second stiffness.

[0115] During operation of epicyclic gear system 100, forces from bearing 119 are applied to spring 181, causing local deflection of spring 181 unless and until the spring contacts housing member 113. Spring 181 allows the portion of cylindrical gear shaft 123 that is loaded more than other portions to deflect gradually more than those other portions, thus effecting an averaging of load sharing among the plurality of cylindrical gear shafts 123 within the limits of spring stiffness.

[0116] In some embodiments, epicyclic gear system 100 can include three flex joints. Figure 20 A partial schematic cross-sectional view of an epicyclic gear system 100 according to some embodiments is provided.

[0117] The first flexure joint 165 may have a first radial dimension r1 and may couple the front planetary carrier assembly 161 to the rear planetary carrier assembly 131. The first flexure joint 165 may be a static flexure joint. The second flexure joint 192 may have a second radial dimension r2 and may couple the ring gear assembly 193 to an output shaft such as the second shaft 109. The second shaft 109 may include an output shaft coupler 194 between the second shaft 109 and the ring gear assembly 193. The third flexure joint 195 may have a third radial dimension r3 and may couple the ring gear 107 to the ring gear assembly 193.

[0118] As Figure 20 shown, the epicyclic gear system 100 may have three flexure joints 165, 192, 195, each having a radial dimension different from the radial dimensions of the other flexure joints (r1, r2, and r3, respectively). The three flexure joints 165, 192, 195 may include one static flexure joint 165 and two dynamic, i.e., rotating, flexure joints 192, 195.

[0119] Figure 20 A general overview of many features of the presently disclosed systems and methods is additionally provided. The epicyclic gear system 100 may include one or more of the following features: a reinforcement member 171 positioned between the front planetary carrier assembly 161 and the rear planetary carrier assembly 131; a static flexure joint 165 that couples the front planetary carrier assembly 161 and the rear planetary carrier assembly 131; a plurality of roller element bearings 119, 121 for carrying the plurality of planetary gears 105; and one or more bearing springs 181 disposed between the bearings 119, 121 and the front flange 162, rear flange 136 to accommodate relative movement between the bearings 119, 121 and the front flange 162, rear flange 136.

[0120] The present disclosure additionally provides several methods for reducing relative movement between static components of an epicyclic gear system and / or improving the front-to-back alignment of the planetary gears of an epicyclic gear system. Figure 9 is a flowchart of a method 900 for reducing relative movement between static components of an epicyclic gear system according to some embodiments of the present disclosure. Method 900 begins at block 901. The steps of method 900 presented in blocks 901 through 919 may be performed in the Figure 9 order presented or in another order. One or more steps of method 900 may not be performed.

[0121] At block 903, a static front planetary carrier assembly 161 and a static rear planetary carrier assembly 131 may be provided. The front planetary carrier assembly 161 may include a front flange 162 that defines a central aperture 144, and a plurality of gear shaft cavities 145 that are positioned around the perimeter of the central aperture 144. The front planetary carrier assembly 161 may further include an annular mounting flange 143 that extends from the front flange 162, the annular mounting flange 143 being positioned rearward of and coaxial with the central aperture 144. The mounting flange 143 may form a rear-facing mounting surface 147.

[0122] The rear planetary carrier assembly 131 may include: a rear flange 136 that defines a central aperture 132; and a plurality of gear shaft cavities 137 that are positioned around the perimeter of and radially outward of the central aperture 132. The rear planetary carrier assembly 131 may further include an annular mounting flange 133 that extends from the rear flange 136, the annular mounting flange 133 being positioned forward of and coaxial with the central aperture 132. The mounting flange 133 may form a front-facing mounting surface 134.

[0123] At block 905, a strengthening member 171 may be positioned between the rear planetary carrier assembly 131 and the front planetary carrier assembly 161. The strengthening member 171 may include an annular body 172 that defines a central aperture 173, and a plurality of radial flanges 174 that extend radially outward from the annular body 172. Each of the plurality of radial flanges 174 may partially define a gear-facing surface 175.

[0124] At block 907, bearings 119, 121 may be at least partially positioned in the gear shaft cavities 145, 137 of the front planetary carrier assembly 161 and / or the rear planetary carrier assembly 131.

[0125] At block 909, a planetary gear 105 among the plurality of planetary gears 105 may be positioned in each pair of axially aligned gear shaft cavities formed between cavities 145, 137 of the front planetary gear carrier assembly 161 and / or the rear planetary gear carrier assembly 131. Each planetary gear 105 may include a cylindrical gear shaft 123 having a front end portion 141 disposed in a gear shaft cavity 145 of the front planetary gear carrier assembly 161 and coaxial with the cylindrical wall 146 of the cavity 145, and a rear end portion 142 disposed within a gear shaft cavity 137 of the rear planetary gear carrier assembly 131 and coaxial with the cylindrical wall 138 of the cavity 137. The planetary gear 105 may further include one or more sun gear engagement portions 125 and ring gear engagement portions 127 carried by the cylindrical gear shaft 123 between the front end portion 141 and the rear end portion 142.

[0126] At block 911, a portion of the cylindrical gear shaft 123 of the planetary gear 105 may be carried by bearings 119, 121.

[0127] At block 913, the method may further include positioning the mounting surface 134 of the rear planetary gear carrier assembly 131 relative to the mounting surface 147 of the front planetary gear carrier assembly 161.

[0128] At block 915, the front planetary gear carrier assembly 161 may be coupled to the rear planetary gear carrier assembly 131.

[0129] At block 917, the cylindrical gear shaft 123 of each planetary gear 105 may be rotated. This rotation may be driven by the sun gear 101 of the compound star epicyclic gear system 100.

[0130] Method 900 ends at block 919.

[0131] Figure 16 is a flowchart of a method 120 for reducing relative motion between static components of an epicyclic gear system according to some embodiments of the present disclosure. Method 1200 begins at block 1201. The steps of method 1200 presented in blocks 1201 through 1217 may be performed Figure 16 in the order presented or in another order. One or more steps of method 1200 may not be performed.

[0132] At block 1203, a static rear planetary carrier assembly 131 may be provided. The rear planetary carrier assembly 131 may include: a rear flange 136 that defines a central aperture 132; and an annular mounting flange 133 that is positioned forward of the central aperture 132 and is coaxial with the central aperture 132. The annular mounting flange 133 may form a forward-facing mounting surface 134 that includes a curved structure 135. The rear flange 136 may further define a plurality of gear shaft cavities 137 that surround the central aperture 132 and are positioned radially outward of the central aperture 132, each cavity having a cylindrical wall 138.

[0133] At block 1205, a static front planetary carrier assembly 161 may be provided. The front planetary carrier assembly 161 may include: a front flange 162 that defines a central aperture 144; and an annular mounting flange 143 that is positioned rearward of the central aperture 144 and is coaxial with the central aperture 144. The annular mounting flange 143 may form a rear-facing mounting surface 147 that includes a curved structure 148. The front flange 162 may further define a plurality of gear shaft cavities 145 that surround the central aperture 144 and are positioned radially outward of the central aperture 144, each cavity having a cylindrical wall 146.

[0134] At block 1207, the rear planetary carrier assembly 131 and the front planetary carrier assembly 161 may be coupled. The coupling may be achieved by mating the curved structure 135 of the forward-facing mounting surface 134 with the curved structure 148 of the rear-facing mounting surface 147, thereby forming a static curved joint 165. The coupling of the rear planetary carrier assembly and the front planetary carrier assembly may form a plurality of axially aligned pairs of gear shaft cavities.

[0135] At block 1209, one of the plurality of planetary gears, a planetary gear 105, may be positioned in each pair of the plurality of axially aligned gear shaft cavities. Each planetary gear 105 may include a cylindrical gear shaft 123 that has: a front end portion 141 that is disposed in a gear shaft cavity 145 of the front planetary carrier assembly 161 and is coaxial with the cylindrical wall 146 of the cavity 145; and a rear end portion 142 that is disposed within a gear shaft cavity 137 of the rear planetary carrier assembly 131 and is coaxial with the cylindrical wall 138 of the cavity 137. Each planetary gear 105 may have one or more gears (e.g., a sun gear engagement portion 125 and a ring gear engagement portion 127) that are carried by the cylindrical gear shaft 123 between the front end portion 141 and the rear end portion 142.

[0136] At block 1211, bearings 119, 121 can be positioned such that they are at least partially within gear shaft cavities 137, 145. At block 1213, a portion of the cylindrical gear shaft 123 of the planetary gear 105 can be carried by bearings 119, 121.

[0137] At block 1215, each cylindrical gear shaft 123 of the planetary gear 105 can be rotated while maintaining the flexure joint 165 stationary. This rotation can be driven by the sun gear 101 of the compound star gear assembly.

[0138] Method 1200 ends at block 1217.

[0139] Figure 19 is a flowchart of a method 500 for accommodating relative motion between components of an epicyclic gear system 100 in accordance with some embodiments of the present disclosure. Method 500 begins at block 501. The steps of method 500 presented in blocks 501 - 513 can be performed Figure 19 in the order presented or in another order. One or more steps of method 500 may not be performed.

[0140] At block 503, bearing 119 can be at least partially positioned within a gear shaft cavity 116 defined by the housing member 113 of the epicyclic gear system 100. At block 505, bearing 119 can carry at least a portion of the cylindrical gear shaft 123 of the planetary gear 105 of the epicyclic gear system 100. Bearing 119 can be disposed on at least a portion of the end 141 of the cylindrical gear shaft 123.

[0141] At block 507, an annular spring 181 can be at least partially positioned within the gear shaft cavity 116. The annular spring 181 can be positioned between bearing 119 and the planetary gear housing member 113. The annular spring 181 can be disposed on at least a portion of bearing 119. The annular spring 181 can be generally as described above with reference to Figure 17 and Figure 18 described.

[0142] At block 509, the cylindrical gear shaft 123 can be rotated, for example, by the rotation of the sun gear 101 or the ring gear 107 that engages the planetary gear 105. Rotation of the cylindrical gear shaft 123 and / or operation of the epicyclic gear system 100 may cause deflection of the cylindrical gear shaft 123 and / or misalignment of the cylindrical gear shaft 123 in the front - to - back direction.

[0143] At block 511, the annular spring 181 can buckle or deflect in response to relative motion between bearing 119 and the planetary gear housing member 113. Buckling or deflection of the annular spring 181 can accommodate all or some of the relative motion between bearing 119 and the planetary gear housing member 113.

[0144] Method 500 ends at block 513.

[0145] The presently disclosed systems and methods provide many advantages over prior art systems. By providing a strengthening member positioned between and coupling a front planetary carrier assembly and a rear planetary carrier assembly, the disclosed planetary gear housing assembly reduces the fore-aft misalignment of the planetary gear shafts caused by relative movement between the front planetary carrier assembly and the rear planetary carrier assembly. The rear planetary carrier assembly may be rigidly mounted to the engine block at the outer diameter of the rear flange. Since the front flange may be mounted to the rear flange at the inner diameter, the front-to-rear coupling of the flanges may inherently be less rigid, thus allowing greater torsional deflection under equal bearing reaction loads.

[0146] By coupling the rear planetary carrier assembly and the front planetary carrier assembly with a strengthening member between the rear planetary carrier assembly and the front planetary carrier assembly, the front planetary carrier assembly may be held to the rear planetary carrier assembly, and the relative movement between the two is less than the relative movement between the two in the case of a standard coupling. While a typical epicyclic gear system may have a front torsional stiffness that is 25%-40% of the rear torsional stiffness, the disclosed strengthening member provides a front torsional stiffness that is increased to 60%-80% of the rear torsional stiffness. Less relative movement is advantageous during assembly and during the operation of the epicyclic gear system.

[0147] By providing a static (i.e., non-rotating) flexure joint to couple the front planetary carrier assembly and the rear planetary carrier assembly, the disclosed planetary gear housing assembly reduces the fore-aft misalignment of the planetary gear shafts caused by relative movement between the front planetary carrier assembly and the rear planetary carrier assembly. The rear planetary carrier assembly may be rigidly mounted to the engine block. Through the static flexure joint, the front planetary carrier assembly may be held to the rear planetary carrier assembly, and the relative movement between the two is less than the relative movement between the two in the case of a standard coupling. Less relative movement is advantageous during assembly and during the operation of the epicyclic gear system.

[0148] The disclosed static flexure joint is additionally advantageous during the assembly of the epicyclic gear system. One cause of fore-aft misalignment of the gear shafts of each planetary gear may be the difficulty of reassembling the housing in the same alignment, orientation, and position in which they were machined. While machining accuracy may be improved by machining the housings together (e.g., line boring), the static flexure joint improves fore-aft alignment through reaction torque during the reassembly process, thus ensuring precise accuracy of hole alignment through the manufacture, machining, and assembly of the epicyclic gear system.

[0149] The present disclosure may be used in combination with the disclosures of one or more of the related applications listed above. The disclosed static bending joint ensures hole-to-hole alignment during machining and assembly, but may reduce the front torsional stiffness. The reinforcing member described herein can counteract this reduction in front torsional stiffness, such that the combination of the static bending joint and the reinforcing member in an epicyclic gear system is advantageous. This combination can ensure hole-to-hole alignment during manufacturing, machining, assembly, and operation.

[0150] Since the life of a bearing is proportional to the cube of the bearing load, the disclosed bearing assembly with a spring can greatly improve the life of the associated bearings by ensuring a more uniform load distribution. The disclosed spring can accommodate the deflection of the planetary gear shaft to improve the load distribution, and the spring can be customized to achieve a desired effect on the front-to-back alignment of the planetary gear shaft.

[0151] Although examples are illustrated and described herein, the embodiments are not limited to the details shown, because various modifications and structural changes may be made by those skilled in the art within the scope and breadth of equivalents of the claims.

Claims

1. A planetary gear housing assembly in an epicyclic gear assembly, comprising: A rear planetary carrier assembly, the rear planetary carrier assembly comprising: a rear flange that defines a central orifice; and a plurality of gear shaft cavities that are circumferentially around the central orifice and are positioned radially outward of the central orifice, each cavity having a cylindrical wall; A front planetary carrier assembly, the front planetary carrier assembly comprising: a front flange that defines a central orifice; and a plurality of gear shaft cavities that are circumferentially around the central orifice and are positioned radially outward of the central orifice, each cavity having a cylindrical wall; A plurality of planetary gears, each of the plurality of planetary gears comprising a cylindrical shaft having: a front end portion that is disposed in a gear shaft cavity of the front planetary carrier assembly and is coaxial with the cylindrical wall of the cavity; a rear end portion that is disposed in a gear shaft cavity of the rear planetary carrier assembly and is coaxial with the cylindrical wall of the cavity; and one or more gears that are carried by the cylindrical shaft between the front end portion and the rear end portion; A bearing assembly, comprising: A bearing that is disposed on at least a portion of one of the rear end portion and the front end portion of the gear shaft; and An annular spring that is disposed on at least a portion of the bearing; And A strengthening member that is positioned between the rear planetary carrier assembly and the front planetary carrier assembly, the strengthening member comprising: An annular body that defines a central orifice; and A plurality of radial flanges that extend radially outward from the annular body, Each of the plurality of radial flanges partially defines a gear-facing surface.

2. The planetary gear housing assembly according to claim 1, wherein, The bearing is a roller bearing.

3. The planetary gear housing assembly according to claim 1, wherein, The cylindrical shaft and the gear form a compound star gear in an epicyclic gear system.

4. The planetary gear housing assembly according to claim 1, wherein, The annular spring includes an annular body and a plurality of silencers that are spaced apart circumferentially around the body.

5. The planetary gear housing assembly according to claim 1, wherein, The rear planetary carrier assembly is coupled to the front planetary carrier assembly.

6. The planetary gear housing assembly according to claim 5, Among them, The rear planetary carrier assembly further includes an annular mounting flange that extends from the rear flange, the annular mounting flange being positioned in front of the central orifice and coaxial with the central orifice, and the mounting flange forms a forward-facing mounting surface that includes a curved structure; Wherein, the front planetary carrier assembly further includes an annular mounting flange that extends from the front flange, the annular mounting flange being positioned behind the central orifice and coaxial with the central orifice, and the mounting flange forms a rearward-facing mounting surface that includes a curved structure; and Wherein, the mounting surfaces are positioned relative to each other, thereby forming a static curved joint.

7. The planetary gear housing assembly according to claim 1, wherein, Each of the plurality of planetary gears includes a sun gear engaging gear and a ring gear engaging gear that are carried by the bearing between the front end portion and the rear end portion.

8. An epicyclic gear assembly for a gas turbine engine, comprising three flex joints, each flex joint having a different radial dimension from the other flex joints, and at least one of said flex joints being a static flex joint.

9. The epicyclic gear assembly according to claim 8, wherein, The radial dimension of the static flex joint is the smallest radial dimension among the radial dimensions.

10. The epicyclic gear assembly according to claim 8, wherein, A first flex joint of the three flex joints couples a ring gear to a ring gear assembly.

11. The epicyclic gear assembly according to claim 8, wherein, A second flex joint of the three flex joints couples the ring gear assembly to an output shaft.

12. The epicyclic gear assembly according to claim 8, wherein, A third flex joint of the three flex joints couples a front planetary carrier assembly to a rear planetary carrier assembly.

13. The epicyclic gear assembly according to claim 12, wherein, The third flex joint of the three flex joints is the static flex joint.

14. A planetary gear housing assembly in an epicyclic gear assembly, comprising: A rear planetary carrier assembly, the rear planetary carrier assembly comprising: A rear flange defining a central orifice and a plurality of gear shaft cavities, the plurality of gear shaft cavities surrounding the central orifice and positioned radially outward of the central orifice, each cavity having a cylindrical wall; and An annular mounting flange positioned in front of the central orifice and coaxial with the central orifice, and the mounting flange forming a forward-facing mounting surface including a curved structure; A front planetary carrier assembly, the front planetary carrier assembly comprising: A front flange defining a central orifice and a plurality of gear shaft cavities, the plurality of gear shaft cavities surrounding the central orifice and positioned radially outward of the central orifice, each cavity having a cylindrical wall; and An annular mounting flange positioned behind the central orifice and coaxial with the central orifice, and the mounting flange forming a rearward-facing mounting surface including a curved structure; A plurality of planetary gears, each of the plurality of planetary gears comprising a cylindrical shaft having: a front end portion disposed in a gear shaft cavity of the front planetary carrier assembly and coaxial with the cylindrical wall of the cavity; a rear end portion disposed in a gear shaft cavity of the rear planetary carrier assembly and coaxial with the cylindrical wall of the cavity; and one or more gears carried by the cylindrical shaft between the front end portion and the rear end portion; and A strengthening member positioned between the rear planetary carrier assembly and the front planetary carrier assembly, the strengthening member comprising: An annular body defining a central orifice; and A plurality of radial flanges extending radially outward from the annular body, Each of the plurality of radial flanges partially defining a gear-facing surface; Wherein the curved structures of the mounting surfaces are positioned relative to each other, thereby forming a static flex joint.

15. The planetary gear housing assembly according to claim 14, wherein, The cylindrical shaft and the gears form a compound star gear in the epicyclic gear system.

16. The planetary gear housing assembly according to claim 14, wherein, The epicyclic gear assembly is part of a gas turbine engine having an engine casing, and wherein the rear flange is coupled to the engine casing to define a rear torsional stiffness, and the front flange is coupled to the planetary gear housing assembly to define a front torsional stiffness, and wherein the front torsional stiffness is between 60% and 80% of the rear torsional stiffness.

17. The planetary gear housing assembly according to claim 16, wherein, The front torsional stiffness is between 65% and 75% of the rear torsional stiffness.

18. The planetary gear housing assembly according to claim 14, further comprising: A bearing assembly, the bearing assembly comprising: A bearing disposed on at least a portion of one of the rear end and the front end of the gear shaft; and An annular spring disposed on at least a portion of the bearing.

19. The planetary gear housing assembly according to claim 18, wherein, The bearing is a roller bearing.

20. The planetary gear housing assembly according to claim 19, wherein, The annular spring includes an annular body and a plurality of mufflers spaced apart around the periphery of the body.

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