Gearboxes for gas turbine engines
An epicyclic power gear box for a gas turbine engine delivers torque from a low speed shaft to the primary fan. The gear box includes a planet gear, a bearing pin for the planet gear, sun gear and ring gear. The planet gear and bearing pin are arranged so that a clearance between the two is maintained during a takeoff condition for the gas turbine engine. The planet gear can be characterized by a pin clearance parameter, a ratio of bending stress neutral axis radius to rim thickness, a gear pinch ratio, and/or a ratio of average rim radius to rim thickness.
1 . A gas turbine engine comprising:
an epicyclic gear train mechanically coupled to an LP shaft of the gas turbine engine, wherein the epicyclic gear train comprises a sun gear, a ring gear, a carrier, and a plurality of planet gears arranged in a planetary configuration, wherein each of the plurality of planet gears comprises:
a bearing pin comprising a pin outer surface;
an annular planet gear rim comprising:
an inner surface, wherein the inner surface and the pin outer surface define a clearance, and wherein the clearance is greater than zero when a radial component force, a pinch component force, a tangential component force, and a centrifugal component force are applied to the planet gear; and
an outer surface, wherein the outer surface and the inner surface define a rim thickness therebetween;
a planet gear bending stress neutral axis radius, wherein the planet gear bending stress neutral axis radius is a radius where stresses and strains within the annular planet gear rim are zero when the radial component force, the pinch component force, the tangential component force, and the centrifugal component force are applied to the planet gear; and
a pin clearance parameter defined by:
PCP
=
K
1
c
r
GR
GR
-
2
r
p
2
[
K
2
r
p
3
Ω
fan
3
-
HP
fan
N
p
(
GR
-
2
GR
)
2
]
wherein “PCP” is the pin clearance parameter in rpm, “c r ” is the clearance in inches, “GR” is a gear ratio of the epicyclic gear train, “r p ” is the planet gear bending stress neutral axis radius in inches, “N p ” is a number of the plurality of planet gears, “HP fan ” is a fan power of the gas turbine engine in horsepower at takeoff conditions, “Ω fan ” is a fan speed of the gas turbine engine in rpm at takeoff conditions, K 1 is a first constant of 1.96×10 −5 per horsepower-minute-inch, and K 2 is a second constant of 4.91×10 −9 horsepower-minutes cubed per cubic inch,
wherein the pin clearance parameter is greater than or equal to zero rpm and less than or equal to 3,334 rpm, and
wherein the planet gear bending stress neutral axis radius and the rim thickness define a ratio in a range from 3 to 10.
2 . The gas turbine engine of claim 1 , 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.
3 . The gas turbine engine of claim 1 , wherein the pin clearance parameter includes values in a range from zero rpm to 3,000 rpm.
4 . The gas turbine engine of claim 1 , wherein the pin clearance parameter includes values in a range from 48 rpm to 1,334 rpm.
5 . The gas turbine engine of claim 1 , wherein the pin clearance parameter includes values in a range from 80 rpm to 1,300 rpm.
6 . The gas turbine engine of claim 1 , wherein the gas turbine engine is configured to produce the fan power in a range from 7,000 horsepower to 80,000 horsepower at takeoff 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 1,600 rpm to 3,334 rpm at takeoff conditions.
8 . The gas turbine engine of claim 1 , wherein each of the plurality of planet gears further comprises a bearing, and wherein the planet gear rim is disposed circumferentially around the bearing.
9 . A gas turbine engine comprising:
an epicyclic gear train mechanically coupled to an LP shaft of the gas turbine engine, wherein the epicyclic gear train comprises a sun gear, a ring gear, a carrier, and a plurality of planet gears arranged in a planetary configuration, wherein each of the plurality of planet gears comprises:
a bearing pin comprising a pin outer surface;
an annular planet gear rim comprising:
an inner surface, wherein the inner surface and the pin outer surface define a clearance, and wherein the clearance is greater than zero when a radial component force, a pinch component force, a tangential component force, and a centrifugal component force are applied to the planet gear; and
an outer surface, wherein the outer surface and the inner surface define a rim thickness of the planet gear rim therebetween;
a planet gear bending stress neutral axis radius, wherein the planet gear bending stress neutral axis radius is a radius where stresses and strains within the annular planet gear rim are zero when the radial component force, the pinch component force, the tangential component force, and the centrifugal component force are applied to the planet gear;
a pin clearance parameter defined by:
PCP
=
K
1
c
r
GR
GR
-
2
r
p
2
[
K
2
r
p
3
Ω
fan
3
-
HP
fan
N
p
(
GR
-
2
GR
)
2
]
wherein “PCP” is the pin clearance parameter in rpm, “c” is the clearance in inches, “GR” is a gear ratio of the epicyclic gear train, “r p ” is the planet gear bending stress neutral axis radius in inches, “N p ” is a number of the plurality of planet gears, “HP fan ” is a fan power of the gas turbine engine in horsepower at takeoff conditions, “Ω fan ” is a fan speed of the gas turbine engine in rpm at takeoff conditions, K 1 is a first constant of 1.96×10 −5 per horsepower-minute-inch, and K 2 is a second constant of 4.91×10 −9 horsepower-minutes cubed per cubic inch,
wherein the pin clearance parameter is greater than or equal to zero rpm and less than or equal to 3,334 rpm; and
a gear pinch ratio defined by:
Γ
=
[
r
p
3
·
F
r
T
3
·
w
·
c
r
]
·
[
3
(
π
2
-
8
)
E
·
2
π
]
wherein “Γ” is the gear pinch ratio, “F r ” is the radial component force in pounds-force, “T” is the rim thickness in inches, w is an axial length of the planet gear rim in inches, and “E” is a Young's modulus of a material forming the planet gear rim 306 in pounds-force per square inch, and
wherein the gear pinch ratio is less than or equal to 1.
10 . The gas turbine engine of claim 9 , wherein the number of the plurality of planet gears is three, four, five, or six.
11 . The gas turbine engine of claim 9 , wherein the gas turbine engine has a bypass ratio in a range from 12 to 15.
12 . The gas turbine engine of claim 9 , wherein each of the plurality of planet gears further comprises a journal bearing, and wherein the planet gear rim is disposed circumferentially around the journal bearing.
13 . The gas turbine engine of claim 9 , wherein the gear pinch ratio is in a range from 0.1 to 0.9.
14 . The gas turbine engine of claim 13 , wherein the gear pinch ratio is in a range from 0.25 to 0.75.
15 . A gas turbine engine comprising:
an epicyclic gear train mechanically coupled to an LP shaft of the gas turbine engine, wherein the epicyclic gear train comprises a sun gear, a ring gear, a carrier, and a plurality of planet gears arranged in a planetary configuration, wherein each of the plurality of planet gears comprises:
a bearing pin comprising a pin outer surface;
an annular planet gear rim comprising:
an inner surface having an inner radius, wherein the inner surface and the pin outer surface define a clearance, and wherein the clearance is greater than zero when a radial component force, a pinch component force, a tangential component force, and a centrifugal component force are applied to the planet gear;
an outer surface having an outer radius;
a rim thickness between the inner surface and the outer surface; and
an average rim radius at a radial location halfway between the inner radius and the outer radius, wherein the average rim radius and the rim thickness define a ratio in a range from 4 to 9;
a planet gear bending stress neutral axis radius, wherein the planet gear bending stress neutral axis radius is a radius where stresses and strains within the annular planet gear rim are zero when the radial component force, the pinch component force, the tangential component force, and the centrifugal component force are applied to the planet gear; and
a pin clearance parameter defined by:
PCP
=
K
1
c
r
GR
GR
-
2
r
p
2
[
K
2
r
p
3
Ω
fan
3
-
HP
fan
N
p
(
GR
-
2
GR
)
2
]
wherein “PCP” is the pin clearance parameter in rpm, “c r ” is the clearance in inches, “GR” is a gear ratio of the epicyclic gear train, “Ip” is the planet gear bending stress neutral axis radius in inches, “N p ” is a number of the plurality of planet gears, “HP fan ” is a fan power of the gas turbine engine in horsepower at takeoff conditions, “Ω fan ” is a fan speed of the gas turbine engine in rpm at takeoff conditions, K 1 is a first constant of 1.96×10 −5 per horsepower-minute-inch, and K 2 is a second constant of 4.91×10 −9 horsepower-minutes cubed per cubic inch,
wherein the pin clearance parameter is greater than or equal to zero rpm and less than or equal to 3,334 rpm.
16 . The gas turbine engine of claim 15 , wherein the gas turbine engine further comprises:
a fan shaft coupled to the carrier of the epicyclic gear train; and
a fan coupled to the fan shaft, wherein the fan comprises a fan diameter that ranges from 80 inches to 95 inches.
17 . The gas turbine engine of claim 16 , wherein the fan diameter ranges from 85 inches to 90 inches.
18 . The gas turbine engine of claim 15 , wherein each of the plurality of planet gears further comprises a bearing, and wherein the annular planet gear rim is disposed circumferentially around the bearing.
19 . The gas turbine engine of claim 18 , wherein the bearing comprises a journal bearing.
20 . The gas turbine engine of claim 15 , wherein the annular planet gear rim has a constant inner radius.