CN117469347A - Planetary gear lash in epicyclic gearbox - Google Patents

Abstract

An epicyclic power gearbox for a gas turbine engine transfers torque from a low speed shaft to a main fan. The gearbox includes planet gears and bearing pins for the planet gears, a sun gear, and a ring gear. The planet gears and the bearing pins are arranged such that a gap between the two is maintained during take-off conditions of the gas turbine engine.

Description

Planetary gear lash in epicyclic gearbox

Cross Reference to Related Applications

The present application claims the benefit of indian patent application No. 202211043036 filed on 7.27, 2022, which is incorporated herein by reference.

Technical Field

The present application relates generally to gas turbine engines used in aircraft.

Background

Aircraft engines typically include a fan, a low pressure compressor, and a low pressure turbine rotationally coupled in a series configuration by a low pressure shaft. The low pressure shaft is rotationally coupled to the low pressure turbine and the power gearbox. The power gearbox includes a plurality of gears and is rotationally coupled to the low pressure fan and the low pressure compressor. The gears surround journal bearings or oil film bearings. The journal bearing includes a fixed pin surrounded by a fluid film. The fluid film provides lubrication to allow the gear rim to rotate about the fixed pin.

Drawings

FIG. 1 illustrates a schematic view of an exemplary gas turbine engine according to one example.

FIG. 2 illustrates a schematic diagram of an exemplary epicyclic gear train for use with a gas turbine engine according to one example.

FIG. 3 illustrates a partial schematic diagram of an epicyclic gear train according to one example.

Fig. 4 shows a schematic view of the planetary gear shown in fig. 3 according to an example, which generates tangential forces, radial forces, pressing forces and centrifugal forces that cause deformation of the planetary gear rim.

FIG. 5 illustrates exemplary pin clearance parameters for an exemplary epicyclic gear train according to one example.

FIG. 6 illustrates an exemplary range of values for epicyclic gear train characteristics according to one example.

Detailed Description

For purposes of this description, certain aspects, advantages, and novel features of the embodiments of the disclosure are described herein. The disclosed methods, apparatus, and systems should not be construed as limiting in any way. Rather, the present disclosure is directed to all novel and nonobvious features and aspects of the various embodiments disclosed, both alone and in various combinations and subcombinations with one another. The methods, apparatus and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved.

Features and characteristics described in connection with a particular aspect, embodiment or example are to be understood as applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Although the operations of some of the disclosed methods are described in a particular sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular order is required by particular language. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Furthermore, descriptions sometimes use terms such as "provide" or "implement" to describe the disclosed methods. These terms are high-level summaries of the actual operations performed. The actual operations corresponding to these terms may vary depending on the particular implementation and are relatively discernable to one of ordinary skill in the art.

The terms "a," "an," and "at least one" as used herein, include one or more of the specified elements. That is, if there are two particular elements, then one of those elements is also present, so there is "one" element. The terms "plurality" and "a plurality" mean two or more of the specified elements. As used herein, the term "and/or" as used between the last two of a list of elements means any one or more of the listed elements. For example, the phrase "A, B and/or C" means "a", "B", "C", "a and B", "a and C", "B and C" or "A, B and C". As used herein, the term "coupled" generally refers to a physical, chemical, electrical, magnetic, or otherwise coupled or linked, and does not exclude the presence of intermediate elements between coupled items that are not specifically and contrary language.

FIG. 1 is a schematic cross-sectional view of a gas turbine engine 110 according to one example of the present disclosure. In this example, the gas turbine engine 110 may be a high bypass turbofan jet engine, which may also be referred to as a turbofan engine. As shown in FIG. 1, gas turbine engine 110 defines an axial direction A (extending parallel to a longitudinal centerline 112 for reference) and a radial direction R. The gas turbine engine 110 includes a fan section 114 and a core turbine engine 116 disposed downstream of the fan section 114.

The depicted example core turbine engine 116 includes a substantially tubular outer casing 118 defining an annular inlet 120. The outer casing 118 encloses a compressor section 123 in serial flow relationship, the compressor section 123 including a booster or Low Pressure (LP) compressor 122 and a High Pressure (HP) compressor 124; a combustion section 126; a turbine section including a High Pressure (HP) turbine 128 and a Low Pressure (LP) turbine 130; and an injection exhaust nozzle section 132. A High Pressure (HP) shaft or spool 134 drivingly connects HP turbine 128 to HP compressor (HPC) 124. A Low Pressure (LP) shaft or spool 136 drivingly connects LP turbine 130 to LP compressor 122. The compressor section 123, the combustion section 126, the turbine section, and the injection exhaust nozzle section 132 together define a core air flow path 137.

In the illustrated example, the fan section 114 includes a fan 138, which may be a variable pitch or a fixed pitch, and a plurality of fan blades 140 coupled to a disk 142 in a spaced apart manner. The plurality of fan blades 140 and the disk 142 may be rotated together about the longitudinal axis 112 by the LP shaft 136 across the power gearbox 146. The fan 138 defines a fan diameter (dashed line "D" in fig. 1), which is the radial distance between the radially outermost tip portions of two opposing fan blades 140. The fan diameter ranges from 80 inches to 95 inches. In other examples, the fan diameter ranges from 85 inches to 95 inches. The power gearbox 146 includes a plurality of gears for adjusting the rotational speed of the fan 138 relative to the LP shaft 136 to a more efficient rotational fan speed.

A rotatable front hub 148 covers the disk 142, the rotatable front hub 148 having an aerodynamic profile to facilitate airflow through the plurality of fan blades 140. Further, the fan section 114 includes an annular fan casing or nacelle 150 that circumferentially surrounds at least a portion of the fan 138 and/or the core turbine engine 116. A plurality of circumferentially spaced outlet guide vanes 152 support the outer nacelle 150 relative to the core turbine engine 116. A downstream section 154 of outer nacelle 150 extends over an outer portion of core turbine engine 116 to define a bypass airflow passage 156 therebetween.

During operation of the gas turbine engine 110, a volume of air 158 enters the gas turbine engine 110 through the outer nacelle 150 and/or an associated inlet 160 of the fan section 114. As the volume of air 158 passes through the plurality of fan blades 140, a second portion 164 of the air is directed or channeled to core air flow path 137 or, more specifically, into LP compressor 122. The ratio of the first portion 162 of air to the second portion 164 of air directed through the bypass airflow channel 156 is referred to as the "bypass ratio". The gas turbine engine 110 has a bypass ratio in the range from 12 to 15. The pressure of the second portion 164 of air increases as it is channeled through HP compressor 124 and into combustion section 126, wherein second portion 164 of air is mixed with fuel and combusted in combustion section 126 to provide combustion gases 166.

HP compressor 124 includes a plurality of HP compressor stages ("HPC stages"), with combustion gases 166 channeled through a plurality of HP compressor stages, wherein each HP compressor stage includes a plurality of HP compressor rotor blades 125 arranged in a single row and coupled to HP shaft 134. Each HP compressor stage further includes a plurality of HP compressor stator vanes 127 arranged in a single row aft of the single row HP compressor rotor blades 125 and coupled to outer casing 118. The number of the plurality of HP compressor stages ranges from eight to ten stages. In some examples, the HP compressor 124 may have eight, nine, or ten HP compressor stages.

The combustion gases 166 are channeled through HP turbine 128 wherein a portion of the thermal and/or kinetic energy from combustion gases 166 is extracted via a series of HP turbine stator vanes 168 and a plurality of HP turbine rotor blades 170, which HP turbine stator vanes 168 may be coupled to outer casing 118. A plurality of HP turbine rotor blades 170, which may be coupled to HP shaft 134, rotate HP shaft 134 and, thus, support the operation of HP compressor 124. The combustion gases 166 are then channeled through LP turbine 130 wherein thermal energy and a second portion of the kinetic energy may be extracted from combustion gases 166 via a series of LP turbine stator vanes 172 and a plurality of LP turbine rotor blades 174, LP turbine stator vanes 172 being coupled to outer-casing 118. LP turbine rotor blade 174 coupled to LP shaft or spool 136 rotates LP shaft 136. The rotating LP shaft 136 causes a power gearbox 146 to rotate the LP compressor 122 and/or the fan 138. The LP turbine 130 includes a plurality of LP turbine stages ("LPT stages"), each of which includes a series of rows of LP turbine stator vanes 172 disposed aft of a row of LP turbine rotor blades 174. The number of LP turbine stages is in the range of three to six. This means that the LP turbine 130 may include three, four, five, or six LP turbine stages.

Combustion gases 166 are then channeled through injection exhaust nozzle section 132 of core turbine engine 116 to provide propulsion thrust. At the same time, as the first portion 162 of air is channeled through bypass airflow passage 156 before it is discharged from fan nozzle exhaust section 176 of gas turbine engine 110, the pressure of first portion 162 of air increases substantially, also providing thrust. The HP turbine 128, the LP turbine 130, and the injection exhaust nozzle section 132 at least partially define a hot gas path 178 for directing the combustion gases 166 through the core turbine engine 116.

The gas turbine engine 110 generates power (referred to herein as "fan power") in the range from 7,000 horsepower (inclusive) to 80,000 horsepower (inclusive) under takeoff conditions. As used herein, "takeoff conditions" refers to operating conditions of the gas turbine engine 110 at sea level altitude, standard pressure, extremely hot weather temperature, and at flight speeds up to about mach 0.25. As used herein, the term "extreme hot weather temperature" refers to the extreme hot weather temperature specified for a particular gas turbine engine. This may include extremely hot weather temperatures for engine certification. The extremely hot weather temperature may additionally or alternatively include a temperature of about 130-140°f.

The gas turbine engine 110 rotates the LP shaft 136 at a rate from 8,000rpm to 10,000rpm under take-off conditions.

In some examples, the rotational rate of the LP shaft 136 may be proportional to the rotational rate of the fan 138. The rotational speed of the fan 138 (referred to herein as "fan speed") ranges from 1,600rpm to 3,336 rpm.

The example gas turbine engine 110 depicted in FIG. 1 should not be construed to exclude other suitable configurations of gas turbine engines. It should also be appreciated that aspects of the present disclosure may be incorporated into any other suitable gas turbine engine in other examples. In some of these other examples, the present disclosure may be incorporated into a turboprop engine.

The gas turbine engine 110 generates a significant load on the LP shaft 136, and the LP shaft 136 transfers torque to the plurality of fan blades 140 via the fan shaft 208a. The power gearbox 146 translates the high speed rotation in the LP shaft 136 to the slower rate required to maintain the desired tip speed in the plurality of fan blades 140, while the LP shaft 136 rotates at a higher rate to increase the extraction power from the LP turbine 130. The load on the LP shaft 136 may exert significant forces on the gears within the power gearbox 146. These loads include unevenly distributed loads on journal bearings within the gear. Accordingly, the load on the power gearbox 146 needs to be managed to ensure that the power gearbox 146 is operating safely and reliably.

Fig. 2 is a schematic diagram of an epicyclic gear train 200. In the example shown, the epicyclic gear train 200 is housed within the power gearbox 146 of fig. 1. In other examples, epicyclic gear train 200 may be adjacent to power gearbox 146 (fig. 1) and may be mechanically coupled to power gearbox 146. The epicyclic gear train 200 includes a sun gear 202, a plurality of planet gears 204, a ring gear 206 and a planet carrier 208. Although the epicyclic gear train 200 is depicted in fig. 2 as including three planet gears 204, the epicyclic gear train 200 may include any number of planet gears 204 such that the epicyclic gear train 200 is capable of operating as described herein. The number of planet gears 204 ranges from three planet gears 204 to six planet gears 204. In some examples, the number of planet gears 204 may be three, four, five, or six planet gears 204.LP shaft 136 (FIG. 1) is coupled to sun gear 202. The sun gear 202 engages the plurality of planet gears 204 through a plurality of complementary sun gear teeth 210 and a plurality of planet gear teeth 212 circumferentially spaced about the radial outer circumference of the sun gear 202 and the radial outer circumference of each of the plurality of planet gears 204, respectively. The plurality of planet gears 204 are held in position relative to one another by a planet carrier 208. The plurality of planet gears 204 engage the ring gear 206 through a plurality of ring gear teeth 214 that are complementary to the planet gear teeth 212. The ring gear teeth 214 are circumferentially spaced about the radially inner circumference of the ring gear 206, and the planet gear teeth 212 are circumferentially spaced about the radially outer circumference of each of the plurality of planet gears 204. The planet carrier 208 is rotationally coupled to the plurality of fan blades 140 by a fan shaft 208a, the fan shaft 208a driving the fan 138 by torque transferred from the power gearbox 146. LP turbine 130 is coupled to LP compressor 122.

The sum of the number of ring gear teeth 214 and sun gear teeth 210 divided by the number of sun gear teeth 210 is defined herein as the Gear Ratio (GR) of the epicyclic gear train 200. The gear ratio is dimensionless and can be a value from 2.5 to 5, 3.2 to 4.0 or 3.5 to 4.0.

The epicyclic gear train 200 is a planetary configuration in which the ring gear 206 remains stationary while the sun gear 202, the plurality of planet gears 204 and the planet carrier 208 rotate. The LP shaft 136 drives the sun gear 202, which rotates the plurality of planet gears 204, resulting in rotation of the planet carrier 208. The planet carrier 208 drives the plurality of fan blades 140 via a fan shaft 208a. When the epicyclic gear train 200 is in the planetary configuration, the sun gear 202 and the planet carrier 208 rotate in the same direction.

Fig. 3 is a partial schematic view of epicyclic gear train 200 in a planetary configuration, showing the ring gear rim of ring gear 206 and the planet gear rim 306 of planet gears 204, bearing pins 302 and the sun gear rim of sun gear 202. In this figure, the meshing engagement of sun gear 202, planet gears 204, and ring gear 206 in fig. 3 is replaced by a similar arrangement of these respective rims, which may be considered to be the gear portion that does not include sun gear teeth 210, planet gear teeth 212, and ring gear teeth 214. It is shown that each of sun gear 202, planet gears 204, and ring gear 206 are represented by a "rim" having an inner radius and an outer radius measured from the center of the planet gears.

Bearing pins 302 are located within the planet gears 204. A lubricant or fluid film 304 is disposed between the bearing pin 302 and the planet gear 204 to provide lubrication between the outer surface of the bearing pin 302 (i.e., the outer surface of the pin located at a radial distance 316 from the center of the bearing pin 302) and the inner surface of the planet gear 204 (located at a radial distance 312 from the center of the planet gear 204). Planetary gear rim 306 is defined as a planetary gearA portion of the planet gears 204 from the inner surface of the planet gears 204 to a portion of the planet gears 204 located at a radial distance 310 from the center of the planet gears 204 corresponds to the gear root radius (i.e., the radial position of the root of the planet gear teeth 212). The planet wheel rim 306 has a thickness 314 and a neutral axis of curvature (as shown by the dashed line) located at a radial distance 308 from the center of the planet wheel 204. Radial distance 308, hereinafter referred to as bending stress neutral axis radius (r _p ) Is the radial position of the normal stress in the planet wheel rim 306 associated with bending of the planet gears 204 in the plane of fig. 3, e.g., the compression of the planet gears 204 between the sun gear 202 and the ring gear 206 is equal to zero. In accordance with the present disclosure, the planetary gear bending stress neutral axis radius (r _p ) 308 is determined to be a value in the range from 1.5 inches to 4.0 inches.

The planet carrier 208 (fig. 2) is coupled to the bearing pin 302 such that rotation of the sun gear 202, in turn, causes rotation of the planet gears 204, which causes rotation of the planet carrier 208 coupled to the fan shaft 208a. Accordingly, torque from the LP shaft 136 is transferred via the sun gear 202, the planet gears 204, and the planet carrier 208 to a fan shaft 208a coupled to the plurality of fan blades 140. This torque transfer causes significant loads on the epicyclic gear train 200, as explained in more detail below, in terms of the load created by the torque transfer and the associated off-axis load. In view of this significant load on such power gearboxes, it is desirable to design the power gearbox components to ensure that metal-to-metal contact is avoided under high load conditions (i.e., at takeoff) without placing unacceptable burden on the architecture in terms of weight, size, and thermal management systems to support proper operation.

Referring again to fig. 3, the load generated by epicyclic gear train 200 when torque is transferred from LP shaft 136 through power gearbox 146 and output to fan shaft 208a pushes planet gears 204 (represented in fig. 3 as rims 306) towards the outer surface of bearing pins 302, which in some examples may comprise journal bearings without any rolling elements. A fluid film 304 is disposed between the inner surface of the planet gear 204 and the outer surface of the bearing pin 302 to avoid metal-to-metal contact between the parts and to allow the planet gear 204 to wrap around the bearing pin302 are free to rotate. Bearing pin 302 includes a bearing pin radius 316. Gap (c) _r ) 318 is the minimum radial distance between the bearing pin 302 and the planetary gear rim 306 when the power gearbox 146 is under load (i.e., when torque is transferred from the LP shaft 136 to the fan shaft 208 a). The inventors have determined that in order to reliably maintain operating conditions through an appropriate number of cycles, taking into account the different aircraft mission requirements, the clearance (c _r ) Should be in the range of.00075 inches to 0.012 inches. If the clearance (c) _r ) Less than.00075 inches, it is more likely to result in at least some metal-to-metal contact (resulting in higher friction, significant heating, and possibly failure of the gearbox). On the other hand, too large a gap (over 0.012 inches) can also reduce bearing performance. The inventors found that if the clearance exceeds 0.012 inches, the required oil pressure between the pin and the gear cannot be reliably maintained. If the gap is too large, the bearing stiffness may decrease.

The planet gears 204 may comprise at least one material selected from a variety of alloys including, but not limited to, ANSI M50 (AMS 6490, AMS6491, and ASTM a 600), M50 Nil (AMS 6278), pyroweb 675 (AMS 5930), pyroweb 53 (AMS 6308), pyroweb 675 (AMS 5930), ANSI9310 (AMS 6265), 32CDV13 (AMS 6481), ceramic (silicon nitride), ferrium C61 (AMS 6517), and Ferrium C64 (AMS 6509). Further, in some examples, the metal material may be a nitride to improve lifetime and resistance to particle damage. The planet gears 204 may include any combination of alloys and any weight percent range of those alloys that facilitates operation of the planet gears 204 as described herein, including, but not limited to, the combination of M50 Nil (AMS 6278), pyrospar 675 (AMS 5930), and ferroum C61 (AMS 6517). The planet gears 204 may have a young's modulus of elasticity that depends on the material used to construct the planet gears 204. The young's modulus of elasticity can be defined as the ratio of stress along an axis (force per unit area) to strain along that axis (deformation to initial length ratio) over the stress range for which hooke's law applies.

During operation, when epicyclic gear train 200 is in the planetary configuration, LP shaft 136 (FIG. 1) rotates, applying torque to sun gear 202 in a clockwise direction, as indicated by first arrow 320. The rotation of the sun gear 202, in turn, causes the planet gears 204 to rotate in a counterclockwise direction, as indicated by the second arrow 322. The planet gears 204, in turn, cause the planet carrier 208 (fig. 2) to rotate in a clockwise direction, as indicated by the third arrow 324.

Fig. 4 is a schematic diagram of a planetary gear 204 that generates radial, compressive, lateral, and centrifugal forces that cause deformation 400 of the planetary gear rim 306. Torsional input from LP shaft 136 (FIG. 1) causes sun gear 202 (FIG. 2) to exert a compressive component 404 and a tangential component 406 on planetary gear rim 306. The compressive component 404 and the tangential component 406 are caused by radial and tangential components of the force applied on one side from the sun gear 202 and on the other side from the ring gear 206 (FIG. 2) through the planetary gear teeth 212 (FIG. 2), respectively. The compressive force component 404 is directed radially inward at the location where the planet gears 204 contact the sun gear 202 (FIG. 2) and the ring gear 206 (FIG. 2). Tangential component 406 is tangential to planetary gear rim 306 at the location where planetary gear 204 contacts sun gear 202 (FIG. 2) and ring gear 206 (FIG. 2).

The radial component 408 extends radially outward from the center of the planet gear 204 due to the radial component of the force exerted on the planet gear 204 by the rotation of the planet gear 204 about the bearing pin 302. Centrifugal force component 410 is the force generated by the precession of planet gear 204 about sun gear 202 (fig. 2). In some examples, centrifugal force component 410 is greater in magnitude than compression force component 404 and tangential force component 406.

The resulting compressive, tangential, radial and centrifugal force components 404, 406, 408, 410 result in deformation 400 of the planetary gear rim 306. The compressive force component 404 deforms the planetary gear rim 306 inwardly toward the bearing pin 302. Tangential force component 406 elongates planetary gear rim 306 in a direction opposite the path of planetary gears 204. Radial force component 408 deforms planetary gear rim 306 in a radially outward direction. Centrifugal force component 410 lengthens planetary gear rim 306 in a direction radially outward from sun gear 202. The deformation 400 causes the gap 318 to decrease due to the change in the gap 414, the gap 414 being the radial distance between the inner radius 312 and the deformed inner radius 412.

When the gap 318 is greater than the variation of the gap 414, enhanced performance of the epicyclic gear train 200 (fig. 2) may be achieved. In other words, when the planetary gear rim 306 is not deformed or bent, an enhanced result may be achieved such that when the generated radial force component 408, compressive force component 404, tangential force component 406, and centrifugal force component 410 are applied to the planetary gear rim 306, the planetary gear rim 306 contacts the surface of the bearing pin 302.

Desirably, the epicyclic gear train 200 (FIG. 2) is designed to maintain the minimum clearance 318 during high load conditions of the gas turbine engine 110, such as during takeoff, as this advantageously minimizes metal-to-metal contact within the planet gears 204.

The inventors have discovered that by identifying specific conditions of the gas turbine engine 110 that may result in maximum deformation of the planet gears 204 and correlating those conditions to the gearbox design, a minimum clearance may be maintained. The inventors have discovered a relationship that enables them to determine the proper size of the planet gears 204 for a given number of planet gears 204 and gear ratios (in particular, the planet gear bending stress neutral axis radius (r _p ) 308) based on the load conditions of the gearbox during take-off conditions so that a minimum clearance may be maintained. The relationship found, referred to by the inventors as the Pin Clearance Parameter (PCP) in revolutions per minute (rpm), is given in equation (1):

wherein "c _r "is the clearance 318 of the bearing pin 302 (journal bearing) measured in inches," GR "is a gear ratio defined as the ratio of the sum of the number of ring gear teeth 214 and sun gear teeth 210 divided by the number of sun gear teeth 210," r _p "is the planetary bending stress neutral axis radius 308 measured in inches," N _p "is the number of planetary gears 204," HP _fan "is the measured fan power in horsepower of the gas turbine engine 110 based on takeoff conditions, and" Ω _fan "is the fan speed measured in rpm for the gas turbine engine 110 measured in rpm at takeoff conditions. First constant K ₁ Has a value of 1.96x10 ^-5 Per horsepower-minute-inch (hp) ^-1 ·min ^-1 ·in. ^-1 ). Second constant K ₂ Has a value of 4.91x10 ^-9 Horsepower-minute cubic per cubic inch (hp-min) ³ /in. ³ ). The inventors have found that a minimum gap can be maintained during takeoff conditions if the following inequality is satisfied:

0rpm≤PCP≤3,334rpm (2)

in other examples, where the design space is more limited by the engine architecture or gearbox design, the range in (2) may be greater than or equal to 0rpm and less than or equal to 3,000rpm, greater than or equal to 48rpm and less than or equal to 1, 336 rpm, or greater than or equal to 80rpm and less than or equal to 1,300rpm.

Fig. 5 discloses gear ratios, fan power, fan speed, number of gears, planetary bending stress neutral axis radius 308 (fig. 4), clearance 318 (fig. 4), and pin clearance parameters for a plurality of exemplary epicyclic gear trains 200 (fig. 2).

Fig. 6 discloses units and exemplary ranges for gear ratios, fan power, fan speed, number of gears, planetary gear bending stress neutral axis radius 308 (fig. 4), clearance 318 (fig. 4), and pin clearance parameters.

In view of the foregoing embodiments of the disclosed subject matter, the present application discloses additional examples listed below. It should be noted that one feature of an isolated example or a combination of more than one feature of an example with one or more features of one or more further examples, and optionally a combination of one or more features of one or more further examples, are also further examples that fall within the scope of the disclosure of the present application.

A gas turbine engine, comprising: an epicyclic gear train mechanically coupled to the LP shaft of the gas turbine engine, wherein the epicyclic gear train comprises a sun gear, a ring gear, a planet carrier, and a plurality of planet gears arranged in a planetary configuration, wherein each planet gear of the plurality of planet gears comprises: a bearing pin, the bearing pin comprising a pin outer surface; a ring-shaped planetary gear rim comprising an inner surface, wherein the inner surface and the pin outer surface define a gap, wherein the gap is greater than 0 when a radial component, a compressive component, a tangential component, and a centrifugal component are applied to the planetary gear; a planetary gear bending stress neutral axis radius, wherein the planetary gear bending stress neutral axis radius is a radius at which stress and strain within the annular planetary gear rim are both 0 when the radial force component, the compressive force component, the tangential force component, and the centrifugal force component are applied to the planetary gear; and a pin clearance parameter, the pin clearance parameter defined as:

wherein "PCP" is the pin clearance parameter in rpm, "c _r "is the gap in inches," GR "is the ratio of the epicyclic gear train," r _p "is the neutral axis radius of bending stress of the planetary gear in inches," N _p "is the number of the plurality of planetary gears," HP _fan "is the fan power in horsepower of the gas turbine engine under take-off conditions," Ω _fan "is the fan speed, K, of the gas turbine engine in rpm under take-off conditions ₁ Is a first constant of 1.96x10 ^-5 K per horsepower-min-inch ₂ Is a second constant of 4.91x10 ^-9 Horsepower-minutes cubic per cubic inch, and wherein the pin clearance parameter is greater than or equal to 0rpm and less than or equal to 3,336 rpm.

The gas turbine engine of any of the preceding clauses, wherein the sun gear further comprises a plurality of sun gear teeth, the ring gear further comprises a plurality of ring gear teeth, and the gear ratio of the epicyclic gear train is a sum of the number of the plurality of ring gear teeth and the number of the plurality of sun gear teeth divided by the number of the plurality of sun gear teeth.

The gas turbine engine according to any one of the preceding clauses, wherein the pin clearance parameter comprises a value in a range from 0rpm to 3,000 rpm.

The gas turbine engine as claimed in any one of the preceding clauses, wherein the pin clearance parameter comprises a value in a range from 48rpm to 1, 336 rpm.

The gas turbine engine according to any one of the preceding clauses, wherein the pin clearance parameter comprises a value in a range from 80rpm to 1,300rpm.

The gas turbine engine of any of the preceding clauses, wherein the gas turbine engine is configured to produce the fan power in a range from 7,000 horsepower to 80,000 horsepower under takeoff conditions.

The gas turbine engine according to any one of the preceding claims, wherein the gas turbine engine is configured to produce the fan speed in a range from 1,600rpm to 3,336 rpm under takeoff conditions.

The gas turbine engine according to any one of the preceding clauses, wherein the number of the plurality of planet gears is three, four, five or six.

The gas turbine engine according to any one of the preceding clauses, wherein the gas turbine engine has a bypass ratio in the range from 12 to 15.

The gas turbine engine of any of the preceding clauses, wherein the gas turbine engine further comprises an HP compressor disposed aft of the epicyclic gear train, wherein the HP compressor comprises eight, nine, or ten HP compressor stages.

The gas turbine engine of any of the preceding clauses, wherein the gas turbine engine further comprises an LP turbine coupled to the LP shaft and comprising a plurality of LP turbine stages, wherein the number of the plurality of LP turbine stages is three, four, five, or six.

The gas turbine engine according to any one of the preceding clauses, wherein the gas turbine engine further comprises: a fan shaft coupled to the planet carrier of the epicyclic gear train; and a fan coupled to the fan shaft, wherein the fan comprises a fan diameter ranging from 80 inches to 95 inches.

The gas turbine engine of any of the preceding clauses, wherein the fan diameter ranges from 85 inches to 90 inches.

The gas turbine engine as recited in any preceding claim, wherein each of the plurality of planet gears further comprises a bearing, and wherein the annular planet gear rim is disposed circumferentially about the bearing.

The gas turbine engine according to any one of the preceding clauses, wherein the bearing comprises a journal bearing.

In view of the many possible examples to which the principles of this disclosure may be applied, it should be recognized that the examples shown are only preferred examples and should not be taken as limiting the scope. Rather, the scope is defined by the appended claims. Accordingly, we claim all that comes within the scope and spirit of these claims.

Claims (10)

1. A gas turbine engine, comprising:

an epicyclic gear train mechanically coupled to the LP shaft of the gas turbine engine, wherein the epicyclic gear train comprises a sun gear, a ring gear, a planet carrier, and a plurality of planet gears arranged in a planetary configuration, wherein each planet gear of the plurality of planet gears comprises:

a bearing pin, the bearing pin comprising a pin outer surface;

a ring-shaped planetary gear rim comprising an inner surface, wherein the inner surface and the pin outer surface define a gap, wherein the gap is greater than 0 when a radial component, a compressive component, a tangential component, and a centrifugal component are applied to the planetary gear;

a planetary gear bending stress neutral axis radius, wherein the planetary gear bending stress neutral axis radius is a radius at which stress and strain within the annular planetary gear rim are both 0 when the radial force component, the compressive force component, the tangential force component, and the centrifugal force component are applied to the planetary gear; and

a pin clearance parameter defined as:

wherein "PCP" is the pin clearance parameter in rpm, "c _r "is the gap in inches," GR "is the ratio of the epicyclic gear train," r _p "is the neutral axis radius of bending stress of the planetary gear in inches," N _p "is the number of the plurality of planetary gears," HP _fan "is the fan power in horsepower of the gas turbine engine under take-off conditions," Ω _fan "is the fan speed, K, of the gas turbine engine in rpm under take-off conditions ₁ Is a first constant of 1.96x10 ^-5 Per horsepower-minute-inch, and K ₂ Is a second constant of 4.91x10 ^-9 Horsepower-minute cubic per cubic inch, and

wherein the pin clearance parameter is greater than or equal to 0rpm and less than or equal to 3,336 rpm.

2. The gas turbine engine of claim 1, wherein:

the sun gear further includes a plurality of sun gear teeth,

the ring gear further includes a plurality of ring gear teeth, an

The gear ratio of the epicyclic gear train is a sum of the number of the plurality of ring gear teeth and the number of the plurality of sun gear teeth divided by the number of the plurality of sun gear teeth.

3. The gas turbine engine of claim 1, wherein the pin clearance parameter comprises a value in a range from 0rpm to 3,000 rpm.

4. The gas turbine engine of claim 1, wherein the pin clearance parameter comprises a value in a range from 48rpm to 1,336 rpm.

5. The gas turbine engine of claim 1, wherein the pin clearance parameter comprises a value in a range from 80rpm to 1,300rpm.

6. The gas turbine engine of claim 1, wherein the gas turbine engine is configured to generate the fan power in a range from 7,000 horsepower to 80,000 horsepower under take-off conditions.

7. The gas turbine engine of claim 1, wherein the gas turbine engine is configured to produce the fan speed in a range from 1,600rpm to 3,336 rpm under takeoff conditions.

8. The gas turbine engine of claim 1, wherein the number of the plurality of planet gears is three, four, five, or six.

9. The gas turbine engine of claim 1, wherein the gas turbine engine has a bypass ratio in a range from 12 to 15.

10. The gas turbine engine of claim 1, wherein the gas turbine engine further comprises an HP compressor disposed aft of the epicyclic gear train, wherein the HP compressor comprises eight, nine, or ten HP compressor stages.