U.S. patent application number 13/481006 was filed with the patent office on 2013-10-03 for geared architecture with speed change device for gas turbine engine.
The applicant listed for this patent is Daniel Bernard Kupratis, Frederick M. Schwarz. Invention is credited to Daniel Bernard Kupratis, Frederick M. Schwarz.
Application Number | 20130259654 13/481006 |
Document ID | / |
Family ID | 49233027 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130259654 |
Kind Code |
A1 |
Kupratis; Daniel Bernard ;
et al. |
October 3, 2013 |
GEARED ARCHITECTURE WITH SPEED CHANGE DEVICE FOR GAS TURBINE
ENGINE
Abstract
A gas turbine engine includes first and second shafts rotatable
about a common axis. The gas turbine engine includes a fan, and
first and second gear trains interconnected to one another and
coupling the first shaft to fan.
Inventors: |
Kupratis; Daniel Bernard;
(Wallingford, CT) ; Schwarz; Frederick M.;
(Glastonbury, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kupratis; Daniel Bernard
Schwarz; Frederick M. |
Wallingford
Glastonbury |
CT
CT |
US
US |
|
|
Family ID: |
49233027 |
Appl. No.: |
13/481006 |
Filed: |
May 25, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13437448 |
Apr 2, 2012 |
|
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|
13481006 |
|
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Current U.S.
Class: |
415/122.1 |
Current CPC
Class: |
F02C 7/36 20130101; F05D
2260/40311 20130101; F02K 3/06 20130101 |
Class at
Publication: |
415/122.1 |
International
Class: |
F01D 15/12 20060101
F01D015/12 |
Claims
1. A gas turbine engine comprising: first and second shafts
rotatable about a common axis and rotationally decoupled from one
another, the first and second shafts respectively provide low and
high spools; first and second turbine sections respectively mounted
on the first and second shafts, first and second compressor
sections respectively driven through the first and second shafts,
the first compressor and turbine sections are low pressure
compressor and turbine sections, and the second compressor and
turbine sections are high pressure compressor and turbine sections;
a fan arranged fluidly upstream from a core nacelle; and an
epicyclic gear train and a speed change device interconnected to
one another and coupling the first shaft to the fan such that the
fan is driven through the first shaft by both the epicyclic gear
train and the speed change device, wherein the fan is configured to
rotate at a different speed than the low pressure compressor.
2. (canceled)
3. The gas turbine engine according to claim 1, wherein the speed
change device is configured to provide a speed reduction.
4. The gas turbine engine according to claim 3, wherein the
epicyclic gear train is arranged between the first shaft and the
speed change device.
5. The gas turbine engine according to claim 3, wherein the speed
change device is arranged between the first shaft and the epicyclic
gear train.
6. The gas turbine engine according to claim 3, wherein the
epicyclic gear train is a differential gear train that includes a
sun gear, planetary gears arranged about and intermeshing with the
sun gear, and a ring gear circumscribing and intermeshing with the
planetary gears.
7. The gas turbine engine according to claim 6, wherein the
planetary gears are supported by a carrier, the carrier is
configured to receive rotational input from one of the first shaft
and the speed change device.
8. The gas turbine engine according to claim 6, wherein the speed
change device is configured to receive rotational input from the
sun gear.
9. The gas turbine engine according to claim 3, wherein the first
compressor section is coupled to the epicyclic gear train.
10. The gas turbine engine according to claim 9, comprising an
inducer coupled to the speed change device.
11.-21. (canceled)
22. The gas turbine engine according to claim 1, wherein rotational
drive from the first shaft is provided sequentially through the
epicyclic gear train and the speed change device to the fan.
23. The gas turbine engine according to claim 1, wherein rotational
drive from the first shaft is provided sequentially through the
speed change device and the epicyclic gear trains to the fan.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 13/437,448, filed on Apr. 2, 2012.
BACKGROUND
[0002] This disclosure relates to a geared architecture for a gas
turbine engine.
[0003] One type of geared turbofan engine includes a two-spool
arrangement in which a low spool, which supports a low pressure
turbine section, is coupled to a fan via a planetary gear train. A
high pressure spool supports a high pressure turbine section. Low
and high pressure compressor sections are respectively supported by
the low and high spools.
[0004] The planetary gear train includes a planetary gear set
surrounding and intermeshing with a centrally located sun gear that
is connected to the low spool. A ring gear circumscribes and
intermeshes with the planetary gears. A fan shaft supports the fan.
The fan shaft is connected to either the planetary gears or the
ring gear, and the other of the planetary gears and ring gear is
grounded to the engine static structure. This type of planetary
gear arrangement can limit the design speeds of and configuration
of stages in the low and high pressure turbine sections.
SUMMARY
[0005] In one exemplary embodiment, a gas turbine engine includes
first and second shafts rotatable about a common axis. The gas
turbine engine includes a fan, and first and second gear trains
interconnected to one another and coupling the first shaft to
fan.
[0006] In a further embodiment of any of the above, the first gear
train is an epicyclic gear train.
[0007] In a further embodiment of any of the above, the second gear
train is configured to provide a speed reduction.
[0008] In a further embodiment of any of the above, the first gear
train is arranged between the first shaft and the second gear
train.
[0009] In a further embodiment of any of the above, the second gear
train is arranged between the first shaft and the first gear
train.
[0010] In a further embodiment of any of the above, the epicyclic
gear train is a differential gear train that includes a sun gear.
Planetary gears are arranged about and intermesh with the sun gear.
A ring gear circumscribes and intermeshes with the planetary
gears.
[0011] In a further embodiment of any of the above, the planetary
gears are supported by a carrier. The carrier is configured to
receive rotational input from one of the first shaft and the second
gear train.
[0012] In a further embodiment of any of the above, the second gear
train is configured to receive rotational input from the sun
gear.
[0013] In a further embodiment of any of the above, the gas turbine
engine includes a first turbine section that is supported on the
first shaft. Second compressor and turbine sections are supported
on the second shaft, and a first compressor section is coupled to
the first gear train.
[0014] In a further embodiment of any of the above, the gas turbine
engine includes an inducer that is coupled to the second gear
train.
[0015] In a further embodiment of any of the above, first and
second shafts respectively provide low and high spools. The first
compressor and turbine sections are low pressure compressor and
turbine sections. The second compressor and turbine sections are
high pressure compressor and turbine sections.
[0016] In one exemplary embodiment, a gas turbine engine includes
first and second shafts rotatable about a common axis. The gas
turbine engine includes a fan. First and second gear trains are
interconnected to one another and couple the first shaft to fan.
The first gear train is an epicyclic gear train. A first turbine
section is supported on the first shaft. Second compressor and
turbine sections are supported on the second shaft, and a first
compressor section coupled to the first gear train. First and
second shafts respectively provide low and high spools. The first
compressor and turbine sections are low pressure compressor and
turbine sections. The second compressor and turbine sections are
high pressure compressor and turbine sections.
[0017] In a further embodiment of any of the above, the second gear
train is configured to provide a speed reduction.
[0018] In a further embodiment of any of the above, the first gear
train is arranged between the first shaft and the second gear
train.
[0019] In a further embodiment of any of the above, the second gear
train is arranged between the first shaft and the first gear
train.
[0020] In a further embodiment of any of the above, the epicyclic
gear train is a differential gear train that includes a sun gear.
Planetary gears are arranged about and intermesh with the sun gear.
A ring gear circumscribes and intermeshes with the planetary
gears.
[0021] In a further embodiment of any of the above, the planetary
gears are supported by a carrier. The carrier is configured to
receive rotational input from one of the first shaft and the second
gear train.
[0022] In a further embodiment of any of the above, the second gear
train is configured to receive rotational input from the sun
gear.
[0023] In a further embodiment of any of the above, an inducer is
coupled to the second gear train.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The disclosure can be further understood by reference to the
following detailed description when considered in connection with
the accompanying drawings wherein:
[0025] FIG. 1 schematically illustrates a gas turbine engine
embodiment.
[0026] FIG. 2 is a schematic view of a geared architecture
embodiment for the engine shown in FIG. 1.
[0027] FIG. 3 is a schematic view of another geared architecture
embodiment.
[0028] FIG. 4 is a schematic view of a geared architecture
embodiment with an inducer.
[0029] FIG. 5 is a schematic view of yet another geared
architecture embodiment.
[0030] FIG. 6 is a schematic view of another geared architecture
embodiment with an inducer.
[0031] FIG. 7 is a schematic view of yet another geared
architecture embodiment with an inducer.
[0032] FIG. 8 is a schematic view of still another geared
architecture embodiment with an inducer.
[0033] FIG. 9A is a schematic view of an epicyclic gear train
having a first example geometry ratio.
[0034] FIG. 9B is a schematic view of an epicyclic gear train
having a second example geometry ratio.
[0035] FIG. 9C is a schematic view of an epicyclic gear train
having a third example geometry ratio.
[0036] FIG. 10 is a nomograph depicting the interrelationship of
speeds of epicyclic gear train components for a given geometry
ratio.
[0037] FIG. 11A is a schematic view of an epicyclic gear train
having the first geometry ratio with a carrier rotating in the
opposite direction to that shown in FIG. 9A.
[0038] FIG. 11B is a schematic view of an epicyclic gear train
having the second geometry ratio with a carrier rotating in the
opposite direction to that shown in FIG. 9B.
[0039] FIG. 11C is a schematic view of an epicyclic gear train
having the third geometry ratio with a carrier rotating in the
opposite direction to that shown in FIG. 9C.
DETAILED DESCRIPTION
[0040] FIG. 1 schematically illustrates a gas turbine engine 20.
The gas turbine engine 20 is disclosed herein as a two-spool
turbofan that generally incorporates a fan section 22, a compressor
section 24, a combustor section 26 and a turbine section 28.
Alternative engines might include an augmentor section (not shown)
among other systems or features. The fan section 22 drives air
along a bypass flowpath B while the compressor section 24 drives
air along a core flowpath C for compression and communication into
the combustor section 26 then expansion through the turbine section
28. Although depicted as a turbofan gas turbine engine in the
disclosed non-limiting embodiment, it should be understood that the
concepts described herein are not limited to use with turbofans as
the teachings may be applied to other types of turbine engines
including three-spool architectures.
[0041] The engine 20 generally includes a low speed spool 30 and a
high speed spool 32 mounted for rotation about an engine central
longitudinal axis A relative to an engine static structure 36 via
several bearing systems 38. It should be understood that various
bearing systems 38 at various locations may alternatively or
additionally be provided.
[0042] The low speed spool 30 generally includes an inner shaft 40
that interconnects a fan 42, a low pressure (or first) compressor
section 44 and a low pressure (or first) turbine section 46. The
inner shaft 40 is connected to the fan 42 through a geared
architecture 48 to drive the fan 42 at a lower speed than the low
speed spool 30. The high speed spool 32 includes an outer shaft 50
that interconnects a high pressure (or second) compressor section
52 and high pressure (or second) turbine section 54. A combustor 56
is arranged between the high pressure compressor 52 and the high
pressure turbine 54. A mid-turbine frame 57 of the engine static
structure 36 is arranged generally between the high pressure
turbine 54 and the low pressure turbine 46. The mid-turbine frame
57 supports one or more bearing systems 38 in the turbine section
28. The inner shaft 40 and the outer shaft 50 are concentric and
rotate via bearing systems 38 about the engine central longitudinal
axis A, which is collinear with their longitudinal axes. As used
herein, a "high pressure" compressor or turbine experiences a
higher pressure than a corresponding "low pressure" compressor or
turbine.
[0043] The core airflow C is compressed by the low pressure
compressor 44 then the high pressure compressor 52, mixed and
burned with fuel in the combustor 56, then expanded over the high
pressure turbine 54 and low pressure turbine 46. The mid-turbine
frame 57 includes airfoils 59 which are in the core airflow path.
The turbines 46, 54 rotationally drive the respective low speed
spool 30 and high speed spool 32 in response to the expansion.
[0044] The engine 20 in one example is a high-bypass geared
aircraft engine. In a further example, the engine 20 bypass ratio
is greater than about six (6), with an example embodiment being
greater than ten (10), the geared architecture 48 is an epicyclic
gear train, such as a star gear system or other gear system, with a
gear reduction ratio of greater than about 2.3 and the low pressure
turbine 46 has a pressure ratio that is greater than about 5. In
one disclosed embodiment, the engine 20 bypass ratio is greater
than about ten (10:1), the fan diameter is significantly larger
than that of the low pressure compressor 44, and the low pressure
turbine 46 has a pressure ratio that is greater than about 5:1. Low
pressure turbine 46 pressure ratio is pressure measured prior to
inlet of low pressure turbine 46 as related to the pressure at the
outlet of the low pressure turbine 46 prior to an exhaust nozzle.
It should be understood, however, that the above parameters are
only exemplary of one embodiment of a geared architecture engine
and that the present invention is applicable to other gas turbine
engines including direct drive turbofans.
[0045] A significant amount of thrust is provided by the bypass
flow B due to the high bypass ratio. The fan section 22 of the
engine 20 is designed for a particular flight condition--typically
cruise at about 0.8 Mach and about 35,000 feet. The flight
condition of 0.8 Mach and 35,000 ft, with the engine at its best
fuel consumption--also known as "bucket cruise Thrust Specific Fuel
Consumption ("TSFCT")"--is the industry standard parameter of lbm
of fuel being burned per hour divided by lbf of thrust the engine
produces at that minimum point. "Fan pressure ratio" is the
pressure ratio across the fan blade alone, without a Fan Exit Guide
Vane ("FEGV") system. The low fan pressure ratio as disclosed
herein according to one non-limiting embodiment is less than about
1.45. "Low corrected fan tip speed" is the actual fan tip speed in
ft/sec divided by an industry standard temperature correction of
[(Tram deg R)/518.7) 0.5]. The "Low corrected fan tip speed" as
disclosed herein according to one non-limiting embodiment is less
than about 1150 ft/second.
[0046] An example geared architecture 48 for the engine 20 is shown
in FIG. 2. Generally, the engine static structure 36 supports the
inner and outer shafts 40, 50 for rotation about the axis A. The
outer shaft 50 supports the high pressure compressor section 52 and
the high pressure turbine section 54, which is arranged upstream
from the mid turbine frame 59.
[0047] The inner shaft 40 is coupled to the geared architecture 48,
which is an epicyclic gear train 60 configured in a differential
arrangement. The gear train 60 includes planetary gears 64
supported by a carrier 62, which is connected to the inner shaft 40
that supports the low pressure turbine 46. A sun gear 66 is
centrally arranged relative to and intermeshes with the planetary
gears 64. A ring gear 70 circumscribes and intermeshes with the
planetary gears 64. In the example, a fan shaft 72, which is
connected to the fan 42, is rotationally fixed relative to the ring
gear 70. The low pressure compressor 44 is supported by a low
pressure compressor rotor 68, which is connected to the sun gear 66
in the example.
[0048] The carrier 62 is rotationally driven by the low pressure
turbine 46 through the inner shaft 40. The planetary gears 64
provide the differential input to the fan shaft 72 and low pressure
compressor rotor 68 based upon the geometry ratio, which is
discussed in detail in connection with FIGS. 9A-10.
[0049] Another example geared architecture 148 for the engine 120
is shown in FIG. 3. The engine static structure 136 supports the
inner and outer shafts 140, 150 for rotation about the axis A. The
outer shaft 150 supports the high pressure compressor section 152
and the high pressure turbine section 154, which is arranged
upstream from the mid turbine frame 159.
[0050] The inner shaft 140 is coupled to the geared architecture
148, which is an epicyclic gear train 160 configured in a
differential arrangement. The gear train 160 includes planetary
gears 164 supported by a carrier 162, which is connected to the
inner shaft 140 that supports the low pressure turbine 146. A sun
gear 166 is centrally arranged relative to and intermeshes with the
planetary gears 164. A ring gear 170 circumscribes and intermeshes
with the planetary gears 164. In the example, a fan shaft 172,
which is connected to the fan 142, is rotationally fixed relative
to the ring gear 170. The low pressure compressor 144 is supported
by a low pressure compressor rotor 168, which is connected to the
sun gear 166 in the example.
[0051] The carrier 162 is rotationally driven by the low pressure
turbine 146 through the inner shaft 140. The planetary gears 164
provide the differential input to the fan shaft 172 and low
pressure compressor rotor 168 based upon the geometry ratio. The
geared architecture 148 includes an additional speed change device
74 interconnecting the inner shaft 140 and the gear train 160.
Higher low pressure turbine section rotational speeds are
attainable with the additional speed change device 74, enabling the
use of fewer turbine stages in the low pressure turbine section.
The speed change device 74 may be a geared arrangement and/or a
hydraulic arrangement for reducing the rotational speed from the
low pressure turbine section 146 to the fan 142 and low pressure
compressor section 144.
[0052] Another example geared architecture 248 for the engine 220
is shown in FIG. 4. The engine static structure 236 supports the
inner and outer shafts 240, 250 for rotation about the axis A. The
outer shaft 250 supports the high pressure compressor section 252
and the high pressure turbine section 254, which is arranged
upstream from the mid turbine frame 259.
[0053] The inner shaft 240 is coupled to the geared architecture
248, which is an epicyclic gear train 260 configured in a
differential arrangement. The gear train 260 includes planetary
gears 264 supported by a carrier 262, which is connected to the
inner shaft 240 that supports the low pressure turbine 246. A sun
gear 266 is centrally arranged relative to and intermeshes with the
planetary gears 264. A ring gear 270 circumscribes and intermeshes
with the planetary gears 264. In the example, a fan shaft 272,
which is connected to the fan 242, is rotationally fixed relative
to the ring gear 270. The low pressure compressor 244 is supported
by a low pressure compressor rotor 268, which is connected to the
sun gear 266 in the example.
[0054] The carrier 262 is rotationally driven by the low pressure
turbine 246 through the inner shaft 240. The planetary gears 264
provide the differential input to the fan shaft 272 and low
pressure compressor rotor 268 based upon the geometry ratio. The
geared architecture 248 includes an additional speed change device
274 interconnecting the inner shaft 240 and the gear train 260.
[0055] An inducer 76 is fixed for rotation relative to the ring
gear 270. The inducer 76 is arranged in the core flow path C to
provide some initial compression to the air before entering the low
pressure compressor section 244. The inducer 76 rotates at the same
rotational speed as the fan 242 and provides some additional
thrust, which is useful in hot weather, for example, where engine
thrust is reduced.
[0056] Another example geared architecture 348 for the engine 320
is shown in FIG. 5. The engine static structure 336 supports the
inner and outer shafts 340, 350 for rotation about the axis A. The
outer shaft 350 supports the high pressure compressor section 352
and the high pressure turbine section 354, which is arranged
upstream from the mid turbine frame 359.
[0057] The inner shaft 340 is coupled to the geared architecture
348, which is an epicyclic gear train 360 configured in a
differential arrangement. The gear train 360 includes planetary
gears 364 supported by a carrier 362, which is connected to the
inner shaft 340 that supports the low pressure turbine 346. A sun
gear 366 is centrally arranged relative to and intermeshes with the
planetary gears 364. A ring gear 370 circumscribes and intermeshes
with the planetary gears 364. In the example, a fan shaft 372 is
connected to the fan 342. The low pressure compressor 344 is
supported by a low pressure compressor rotor 368, which is
rotationally fixed relative to the ring gear 370 in the
example.
[0058] The carrier 362 is rotationally driven by the low pressure
turbine 346 through the inner shaft 340. The planetary gears 364
provide the differential input to the fan shaft 372 and low
pressure compressor rotor 368 based upon the geometry ratio. The
geared architecture 348 includes an additional speed change device
374 interconnecting the inner shaft 340 and the gear train 360. The
speed change device 374 receives rotational input from the sun gear
366 and couples the fan shaft 372 to the gear train 360, which
enables slower fan speeds.
[0059] Another example geared architecture 448 for the engine 420
is shown in FIG. 6. The engine static structure 436 supports the
inner and outer shafts 440, 450 for rotation about the axis A. The
outer shaft 450 supports the high pressure compressor section 452
and the high pressure turbine section 454, which is arranged
upstream from the mid turbine frame 459.
[0060] The inner shaft 440 is coupled to the geared architecture
448, which is an epicyclic gear train 460 configured in a
differential arrangement. The gear train 460 includes planetary
gears 464 supported by a carrier 462, which is connected to the
inner shaft 440 that supports the low pressure turbine 446. A sun
gear 466 is centrally arranged relative to and intermeshes with the
planetary gears 464. A ring gear 470 circumscribes and intermeshes
with the planetary gears 464. In the example, a fan shaft 472 is
connected to the fan 442. The low pressure compressor 444 is
supported by a low pressure compressor rotor 468, which is
rotationally fixed relative to the ring gear 470 in the
example.
[0061] The carrier 462 is rotationally driven by the low pressure
compressor 446 through the inner shaft 440. The planetary gears 464
provide the differential input to the fan shaft 472 and low
pressure compressor rotor 468 based upon the geometry ratio. The
geared architecture 448 includes an additional speed change device
474 interconnecting the inner shaft 440 and the gear train 460. The
speed change device 474 receives rotational input from the sun gear
466 and couples the fan shaft 472 to the gear train 460, which
enables slower fan speeds.
[0062] The inducer 476 is fixed for rotation relative to the fan
shaft 472. The inducer 476 is arranged in the core flow path C to
provide some initial compression to the air before entering the low
pressure compressor section 444. The inducer 476 rotates at the
same rotational speed as the fan 442.
[0063] Another example geared architecture 548 for the engine 520
is shown in FIG. 7. The engine static structure 536 supports the
inner and outer shafts 540, 550 for rotation about the axis A. The
outer shaft 550 supports the high pressure compressor section 552
and the high pressure turbine section 554, which is arranged
upstream from the mid turbine frame 559.
[0064] The inner shaft 540 is coupled to the geared architecture
548, which is an epicyclic gear train 560 configured in a
differential arrangement. The gear train 560 includes planetary
gears 564 supported by a carrier 562, which is connected to the
inner shaft 540 that supports the low pressure turbine 546. A sun
gear 566 is centrally arranged relative to and intermeshes with the
planetary gears 564. A ring gear 570 circumscribes and intermeshes
with the planetary gears 564. In the example, a fan shaft 572 is
connected to the fan 542. The low pressure compressor 544 is
supported by a low pressure compressor rotor 568, which is
rotationally fixed relative to the ring gear 570 in the
example.
[0065] The carrier 562 is rotationally driven by the low pressure
turbine 546 through the inner shaft 540. The planetary gears 564
provide the differential input to the fan shaft 572 and low
pressure compressor rotor 568 based upon the geometry ratio. The
geared architecture 548 includes an additional speed change device
574 interconnecting the inner shaft 540 and the gear train 560. The
speed change device 574 receives rotational input from the sun gear
566 and couples the fan shaft 572 to the gear train 560, which
enables slower fan speeds.
[0066] The inducer 576 is fixed for rotation relative to the fan
shaft 572. The inducer 576 is arranged in the core flow path C to
provide some initial compression to the air before entering the low
pressure compressor section 544. In one example, the sun gear 566
rotates at the same speed as one of the fan shaft 572 and the
inducer 576, and the other of the fan shaft 572 and the inducer 576
rotate at a different speed than the sun gear 566. In another
example, the inducer 576, sun gear 566 and fan shaft 572 rotate at
different rotational speeds than one another through the speed
change device 574, which is another epicyclic gear train, for
example.
[0067] Another example geared architecture 648 for the engine 620
is shown in FIG. 8. The engine static structure 636 supports the
inner and outer shafts 640, 650 for rotation about the axis A. The
outer shaft 650 supports the high pressure compressor section 652
and the high pressure turbine section 654, which is arranged
upstream from the mid turbine frame 659.
[0068] The inner shaft 640 is coupled to the geared architecture
648, which is an epicyclic gear train 660 configured in a
differential arrangement. The gear train 660 includes planetary
gears 664 supported by a carrier 662, which is connected to the
inner shaft 640 that supports the low pressure turbine 646. A sun
gear 666 is centrally arranged relative to and intermeshes with the
planetary gears 664. A ring gear 670 circumscribes and intermeshes
with the planetary gears 664. In the example, a fan shaft 672 is
connected to the fan 642. The low pressure compressor 644 is
supported by a low pressure compressor rotor 668, which is
rotationally fixed relative to the ring gear 670 in the
example.
[0069] The carrier 662 is rotationally driven by the low pressure
turbine 646 through the inner shaft 640. The planetary gears 664
provide the differential input to the fan shaft 672 and low
pressure compressor rotor 668 based upon the geometry ratio. The
geared architecture 648 includes an additional speed change device
674 interconnecting the inner shaft 640 and the gear train 660. The
speed change device 674 receives rotational input from the sun gear
666 and couples the fan shaft 672 to the gear train 660, which
enables slower fan speeds.
[0070] The inducer 676 is arranged in the core flow path C to
provide some initial compression to the air before entering the low
pressure compressor section 644. The inducer 676 is fixed to the
sun gear 666 for rotation at the same rotational speed.
[0071] In the arrangements shown in FIGS. 2-8, the relative
rotational directions are shown for each of the fan, low pressure
compressor section, high pressure compressor section, high pressure
turbine section, low pressure turbine section and inducer. The
geared architectures may be configured in a manner to provide the
desired rotational direction for a given engine design.
[0072] The example geared architectures enable large fan diameters
relative to turbine diameters, moderate low pressure turbine to fan
speed ratios, moderate low pressure compressor to low pressure
turbine speed ratios, high low pressure compressor to fan speed
ratios and compact turbine section volumes. The low pressure
turbine section may include between three and six stages, for
example.
[0073] The rotational speeds of the sun gear, ring gear and carrier
are determined by the geometry ratio of the differential gear
train. The interrelationship of these components can be expressed
using the following equation:
X carrier X ring = GR 1 + GR , where ( Equation 1 )
##EQU00001##
[0074] X.sub.carrier is the nomograph distance of the planetary
rotational axis from the sun gear axis,
[0075] X.sub.ring is the nomograph radius of the ring gear, and
[0076] GR is the geometry ratio. Thus, for a geometry ratio of
3.0.
X carrier X ring = 0.75 . ##EQU00002##
[0077] The relative sizes amongst the sun gear, planetary gears and
ring gear for several different geometry ratios are schematically
depicted in FIGS. 9A-9C. Referring to FIG. 9A, the epicyclic gear
train 760 includes a sun gear 766, planetary 764, carrier 762 and
ring gear 770 that are sized to provide a geometry ratio of 3.0.
Referring to FIG. 9B, the epicyclic gear train 860 includes a sun
gear 866, planetary 864, carrier 862 and ring gear 870 that are
sized to provide a geometry ratio of 2.0. Referring to FIG. 9C, the
epicyclic gear train 960 includes a sun gear 966, planetary 964,
carrier 962 and ring gear 970 that are sized to provide a geometry
ratio of 1.5. In the examples, the ring gear radius remains
constant.
[0078] FIG. 10 graphically depicts effects of the geometry ratio on
the rotational speeds and directions of the sun and ring gears and
the carrier. The upper, lighter shaded bars relate to FIG. 9A-9C.
Assuming a rotational input from the low pressure turbine to the
carrier of 10,000 RPM, the sun gear would be driven at 15,000 RPM
and the ring gear would be driven at 8,333 RPM for a geometry ratio
of 3.0. In an arrangement in which the fan is coupled to the ring
gear and the sun gear is coupled to the low pressure compressor,
like the arrangement shown in FIG. 2, the following speed ratios
would be provided: LPT:fan=1.2, LPC:LPT=1.5, and LPC:fan=1.8.
[0079] The lower, darker shaded bars relate to FIGS. 11A-11C. The
carrier and ring gear rotate in the opposite direction than
depicted in FIG. 9A-9C.
[0080] Although an example embodiment has been disclosed, a worker
of ordinary skill in this art would recognize that certain
modifications would come within the scope of the claims. For that
reason, the following claims should be studied to determine their
true scope and content.
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