U.S. patent application number 16/157581 was filed with the patent office on 2020-04-16 for accessory gearbox with superposition gearbox.
The applicant listed for this patent is United Technologies Corporation. Invention is credited to Nicholas D. Leque, Joseph H. Polly.
Application Number | 20200116085 16/157581 |
Document ID | / |
Family ID | 68387122 |
Filed Date | 2020-04-16 |
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United States Patent
Application |
20200116085 |
Kind Code |
A1 |
Polly; Joseph H. ; et
al. |
April 16, 2020 |
ACCESSORY GEARBOX WITH SUPERPOSITION GEARBOX
Abstract
A turbofan engine includes a first spool including a first
turbine; a second spool including a second turbine disposed axially
forward of the first turbine, a first tower shaft engaged to the
first spool, a second tower shaft engaged to the second spool and
an accessory gearbox supporting a plurality of accessory components
and a superposition gear system disposed within the accessory
gearbox. The superposition gear system includes a plurality of
intermediate gears engaged to the sun gear and supported in a
carrier and a ring gear circumscribing the intermediate gears. The
second tower shaft is engaged to drive the sun gear; a starter
selectively coupled to the sun gear through a starter clutch; a
first clutch for selectively coupling the first tower shaft to the
ring gear; a second clutch for selectively coupling the ring gear
to a static structure of the engine.
Inventors: |
Polly; Joseph H.; (Tolland,
CT) ; Leque; Nicholas D.; (Vernon, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
United Technologies Corporation |
Farmington |
CT |
US |
|
|
Family ID: |
68387122 |
Appl. No.: |
16/157581 |
Filed: |
October 11, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02K 3/06 20130101; F05D
2260/40311 20130101; F02C 7/32 20130101; F16H 37/065 20130101 |
International
Class: |
F02C 7/32 20060101
F02C007/32; F16H 37/06 20060101 F16H037/06; F02K 3/06 20060101
F02K003/06 |
Claims
1. A turbofan engine comprising: a first spool including a first
turbine; a second spool including a second turbine disposed axially
forward of the first turbine; a first tower shaft engaged to the
first spool; a second tower shaft engaged to the second spool; an
accessory gearbox supporting a plurality of accessory components; a
superposition gear system disposed within the accessory gearbox,
the superposition gear system including, a plurality of
intermediate gears engaged to the sun gear and supported in a
carrier and a ring gear circumscribing the intermediate gears,
wherein the second tower shaft is engaged to drive the sun gear; a
starter selectively coupled to the sun gear through a starter
clutch; a first clutch for selectively coupling the first tower
shaft to the ring gear; a second clutch for selectively coupling
the ring gear to a static structure of the engine.
2. The turbofan engine as recited in claim 1, wherein a first
output of the superposition gear system comprises a carrier shaft
attached to the carrier.
3. The turbofan engine as recited in claim 2, wherein the carrier
shaft is coupled to drive a first gear system within the accessory
gearbox for driving a first group of the plurality of accessory
components.
4. The turbofan engine as recited in claim 3, including a sun gear
shaft supporting the sun gear, the sun gear shaft coupling the
second tower shaft to the starter through the starter clutch.
5. The turbofan engine as recited in claim 2, wherein a second
output of the superposition gear system includes a ring gear shaft
driven by the first tower shaft, wherein the second output is
coupled to drive a second group of the plurality of accessory
components.
6. The turbofan engine as recited in claim 5, wherein a third
output of the superposition gear system includes a drive gear
coupled to the sun gear shaft to drive a third group of the
plurality of accessory components.
7. The turbofan engine as recited in claim 1, wherein the first
turbine comprises a low pressure turbine and the second turbine
comprises a high pressure turbine.
8. The turbofan engine as recited in claim 1, wherein the first
tower shaft and the second tower shaft are concentric about a
common axis.
9. The turbofan engine as recited in claim 1, wherein the first
tower shaft and the second tower shaft are disposed about different
axes.
10. The turbofan engine as recited in claim 1, wherein the starter
clutch, first clutch and the second clutch comprise one-way
mechanical clutches.
11. The turbofan engine as recited in claim 1, wherein the first
clutch couples the first tower shaft to the ring gear and the
second tower shaft drives the sun gear in a first operating
condition such that both the first tower shaft and the second tower
shaft combine to drive the output.
12. The turbofan engine as recited in claim 11, wherein the second
clutch couples the ring gear to the static engine structure and the
starter clutch couples the starter to the sun gear such that the
starter drives the sun gear and thereby the second tower shaft and
the second spool in a starting operating condition.
13. The turbofan engine as recited in claim 12, wherein the second
clutch decouples the ring gear from the static structure and
couples the first clutch in response to rotation of the first tower
shaft driven by the first spool.
14. An accessory gearbox for a turbofan engine, the accessory
gearbox comprising: a superposition gear system including a sun
gear coupled to a second tower shaft of the turbofan engine; a
plurality of intermediate gears engaged to the sun gear and
supported in a carrier; a ring gear circumscribing the intermediate
gears; a starter selectively coupled to the sun gear through a
starter clutch; a first means for selectively coupling the ring
gear to a first tower shaft of the turbofan engine; a second means
for selectively coupling the ring gear to a fixed structure; a
first output coupled to the carrier shaft for driving a first group
of accessory components; and a second output coupled to the first
tower shaft for driving a second group of accessory components.
15. The accessory gearbox as recited in claim 14, wherein the first
output comprises a carrier shaft attached to the carrier that is
coupled to a first gear system driving the first group of accessory
components.
16. The accessory gearbox as recited in claim 15, wherein the
second output comprises a ring gear shaft driven by the first tower
shaft that is coupled to a second gear system for driving the
second group of accessory components.
17. The accessory gearbox as recited in claim 14, wherein each of
the first means for selectively coupling the ring gear to the first
tower shaft and the second means for selectively coupling the ring
gear to the fixed engine structure are one-way mechanical
clutches.
18. The accessory gearbox as recited in claim 14, wherein the first
means couples the first tower shaft to the ring gear and the second
tower shaft drives the sun gear in a first operating condition such
that both the first tower shaft and the second tower shaft combine
to drive the carrier shaft.
19. The accessory gearbox as recited in claim 14, wherein the
second means couples the ring gear to the fixed structure when the
starter is driving the sun gear to rotate an engine spool through
the second tower shaft in a starting operating condition.
20. A method of operating an accessory gearbox for a turbofan
engine comprising: coupling a first tower shaft to engage a first
spool; coupling a second tower shaft to engage a second spool;
coupling a sun gear of a superposition gear system supported within
the accessory gearbox to the second tower shaft, wherein the
superposition gear system includes the sun gear, a plurality of
intermediate gears engaged to the sun gear and supported in a
carrier and a ring gear circumscribing the intermediate gears;
selectively coupling a starter to the sun gear; and selectively
coupling the ring gear to an engine static structure; and driving
the second spool with the starter through the sun gear to rotate
the second spool and start the turbofan engine.
21. The method as recited in claim 20, including coupling the first
tower shaft to the ring gear such that the first tower shaft drives
the ring gear and the second tower shaft drives the sun gear once
both the first spool and the second spool are rotating independent
of rotation of the starter such that both the first tower shaft and
the second tower shaft combine to drive a first output coupled to
the carrier and a second output coupled to the ring gear.
22. The method as recited in claim 21, wherein the first output
drives a first group of accessory components at a first speed and
the second output drives a second group of accessory components at
a second speed different than the first speed.
23. The method as recited in claim 22, wherein a third output
coupled to sun gear drives a third group of accessory components at
a third speed that is different that both the first speed and the
second speed.
Description
BACKGROUND
[0001] A gas turbine engine typically includes a fan section, a
compressor section, a combustor section and a turbine section. Air
entering the compressor section is compressed and delivered into
the combustion section where it is mixed with fuel and ignited to
generate a high-energy exhaust gas flow. The high-energy exhaust
gas flow expands through the turbine section to drive the
compressor and the fan section. The compressor section typically
includes low and high pressure compressors, and the turbine section
includes low and high pressure turbines.
[0002] A high pressure turbine drives the high pressure compressor
through an outer shaft to form a high spool, and the low pressure
turbine drives the low pressure compressor through an inner shaft
to form a low spool. The fan section may also be driven by the low
pressure turbine through the inner shaft.
[0003] The engine is typically started by driving the high spool
through a tower shaft with a starter through an accessory gearbox.
Once the high spool is up to speed, the low spool follows and the
engine is brought to an idle condition. When the engine is
operating, the accessory gearbox is driven through the same tower
shaft to drive accessory components such as hydraulic pumps and
electric generators.
[0004] Turbine engine manufacturers continue to seek further
improvements to engine performance including improvements to
thermal, transfer and propulsive efficiencies.
SUMMARY
[0005] A turbofan engine according to an exemplary embodiment of
this disclosure includes, among other possible things, a first
spool including a first turbine; a second spool including a second
turbine disposed axially forward of the first turbine; a first
tower shaft engaged to the first spool; a second tower shaft
engaged to the second spool and an accessory gearbox supporting a
plurality of accessory components and a superposition gear system
disposed within the accessory gearbox. The superposition gear
system includes a plurality of intermediate gears engaged to the
sun gear and supported in a carrier and a ring gear circumscribing
the intermediate gears. The second tower shaft is engaged to drive
the sun gear; a starter selectively coupled to the sun gear through
a starter clutch; a first clutch for selectively coupling the first
tower shaft to the ring gear; a second clutch for selectively
coupling the ring gear to a static structure of the engine.
[0006] In a further embodiment of the foregoing turbofan engine, a
first output of the superposition gear system comprises a carrier
shaft attached to the carrier.
[0007] In another embodiment of any of the foregoing turbofan
engines, the carrier shaft is coupled to drive a first gear system
within the accessory gearbox for driving a first group of the
plurality of accessory components.
[0008] In another embodiment of any of the foregoing turbofan
engines, a sun gear shaft supports the sun gear. The sun gear shaft
is coupled the second tower shaft to the starter through the
starter clutch.
[0009] In another embodiment of any of the foregoing turbofan
engines, a second output of the superposition gear system includes
a ring gear shaft driven by the first tower shaft, wherein the
second output is coupled to drive a second group of the plurality
of accessory components.
[0010] In another embodiment of any of the foregoing turbofan
engines, a third output of the superposition gear system includes a
drive gear coupled to the sun gear shaft to drive a third group of
the plurality of accessory components.
[0011] In another embodiment of any of the foregoing turbofan
engines, the first turbine comprises a low pressure turbine and the
second turbine comprises a high pressure turbine.
[0012] In another embodiment of any of the foregoing turbofan
engines, the first tower shaft and the second tower shaft are
concentric about a common axis.
[0013] In another embodiment of any of the foregoing turbofan
engines, the first tower shaft and the second tower shaft are
disposed about different axes.
[0014] In another embodiment of any of the foregoing turbofan
engines, the starter clutch, first clutch and the second clutch
comprise one-way mechanical clutches.
[0015] In another embodiment of any of the foregoing turbofan
engines, the first clutch couples the first tower shaft to the ring
gear and the second tower shaft drives the sun gear in a first
operating condition such that both the first tower shaft and the
second tower shaft combine to drive the output.
[0016] In another embodiment of any of the foregoing turbofan
engines, the second clutch couples the ring gear to the static
engine structure and the starter clutch couples the starter to the
sun gear. The starter drives the sun gear and thereby the second
tower shaft and the second spool in a starting operating
condition.
[0017] In another embodiment of any of the foregoing turbofan
engines, the second clutch decouples the ring gear from the static
structure and couples the first clutch in response to rotation of
the first tower shaft driven by the first spool.
[0018] An accessory gearbox for a turbofan engine according to an
exemplary embodiment of this disclosure includes, among other
possible things, a superposition gear system including a sun gear
coupled to a second tower shaft of the turbofan engine; a plurality
of intermediate gears engaged to the sun gear and supported in a
carrier; a ring gear circumscribing the intermediate gears; a
starter selectively coupled to the sun gear through a starter
clutch; a first means for selectively coupling the ring gear to a
first tower shaft of the turbofan engine; a second means for
selectively coupling the ring gear to a fixed structure; a first
output coupled to the carrier shaft for driving a first group of
accessory components. A second output is coupled to the first tower
shaft for driving a second group of accessory components.
[0019] In a further embodiment of the foregoing accessory gearbox
for a turbofan engine, the first output comprises a carrier shaft
attached to the carrier that is coupled to a first gear system
driving the first group of accessory components.
[0020] In another embodiment of any of the foregoing accessory
gearboxes for a turbofan engine, the second output comprises a ring
gear shaft driven by the first tower shaft that is coupled to a
second gear system for driving the second group of accessory
components.
[0021] In another embodiment of any of the foregoing accessory
gearboxes for a turbofan engine, each of the first means for
selectively coupling the ring gear to the first tower shaft and the
second means for selectively coupling the ring gear to the fixed
engine structure are one-way mechanical clutches.
[0022] In another embodiment of any of the foregoing accessory
gearboxes for a turbofan engine, the first means couples the first
tower shaft to the ring gear and the second tower shaft drives the
sun gear in a first operating condition. Both the first tower shaft
and the second tower shaft combine to drive the carrier shaft.
[0023] In another embodiment of any of the foregoing accessory
gearboxes for a turbofan engine, the second means couples the ring
gear to the fixed structure when the starter is driving the sun
gear to rotate an engine spool through the second tower shaft in a
starting operating condition.
[0024] A method of operating an accessory gearbox for a turbofan
engine according to an exemplary embodiment of this disclosure
includes, among other possible things, coupling a first tower shaft
to engage a first spool; coupling a second tower shaft to engage a
second spool; coupling a sun gear of a superposition gear system
supported within the accessory gearbox to the second tower shaft.
The superposition gear system includes the sun gear, a plurality of
intermediate gears engaged to the sun gear and supported in a
carrier and a ring gear circumscribing the intermediate gears;
selectively coupling a starter to the sun gear; selectively
coupling the ring gear to an engine static structure; and driving
the second spool with the starter through the sun gear to rotate
the second spool and start the turbofan engine.
[0025] In a further embodiment of operating an accessory gearbox
for a turbofan engine, the first tower shaft is coupled to the ring
gear. The first tower shaft drives the ring gear and the second
tower shaft drives the sun gear once both the first spool and the
second spool are rotating independent of rotation of the starter.
Both the first tower shaft and the second tower shaft combine to
drive a first output coupled to the carrier and a second output
coupled to the ring gear.
[0026] In another embodiment of any of the foregoing methods of
operating an accessory gearbox for a turbofan engine, the first
output drives a first group of accessory components at a first
speed. The second output drives a second group of accessory
components at a second speed different than the first speed.
[0027] In another embodiment of any of the foregoing methods of
operating an accessory gearbox for a turbofan engine, a third
output coupled to sun gear drives a third group of accessory
components at a third speed that is different that both the first
speed and the second speed.
[0028] Although the different examples have the specific components
shown in the illustrations, embodiments of this invention are not
limited to those particular combinations. It is possible to use
some of the components or features from one of the examples in
combination with features or components from another one of the
examples.
[0029] These and other features disclosed herein can be best
understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a schematic view of an example gas turbine engine
embodiment.
[0031] FIG. 2 is a schematic representation of the example gas
turbine engine and accessory gearbox.
[0032] FIG. 3 is schematic illustration of the accessory gearbox in
a starting operating condition.
DETAILED DESCRIPTION
[0033] 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. The
fan section 22 drives air along a bypass flow path B in a bypass
duct defined within a nacelle 18, and also drives air along a core
flow path C for compression and communication into the combustor
section 26 then expansion through the turbine section 28. Although
depicted as a two-spool 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 two-spool
turbofans as the teachings may be applied to other types of turbine
engines including three-spool architectures.
[0034] The exemplary 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, and the location of bearing systems 38
may be varied as appropriate to the application.
[0035] The low speed spool 30 generally includes an inner shaft 40
that interconnects, a first (or low) pressure compressor 44 and a
first (or low) pressure turbine 46. The inner shaft 40 is connected
to a fan section 22 through a speed change mechanism, which in
exemplary gas turbine engine 20 is illustrated as a geared
architecture 48 to drive fan blades 42 at a lower speed than the
low speed spool 30. The high speed spool 32 includes an outer shaft
50 that interconnects a second (or high) pressure compressor 52 and
a second (or high) pressure turbine 54. A combustor 56 is arranged
in exemplary gas turbine 20 between the high pressure compressor 52
and the high pressure turbine 54. A mid-turbine frame 58 of the
engine static structure 36 may be arranged generally between the
high pressure turbine 54 and the low pressure turbine 46. The
mid-turbine frame 58 further supports 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.
[0036] The core airflow 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 58 includes airfoils 60 which are in the core airflow path C.
The turbines 46, 54 rotationally drive the respective low speed
spool 30 and high speed spool 32 in response to the expansion. It
will be appreciated that each of the positions of the fan section
22, compressor section 24, combustor section 26, turbine section
28, and fan drive gear system 48 may be varied. For example, gear
system 48 may be located aft of the low pressure compressor 44 and
the fan blades 42 may be positioned forward or aft of the location
of the geared architecture 48 or even aft of turbine section
28.
[0037] 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 about ten (10), the geared architecture 48 is an
epicyclic gear train, such as a planetary 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 five. 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 five 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. The geared architecture 48 may be an
epicycle gear train, such as a planetary gear system or other gear
system, with a gear reduction ratio of greater than about 2.3:1 and
less than about 5:1. 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.
[0038] 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 (10,668 meters). The
flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with
the engine at its best fuel consumption--also known as "bucket
cruise Thrust Specific Fuel Consumption (`TSFC`)"--is the industry
standard parameter of lbm of fuel being burned divided by lbf of
thrust the engine produces at that minimum point. "Low 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 .degree. R)/(518.7.degree. R)].sup.0.5. The
"Low corrected fan tip speed" as disclosed herein according to one
non-limiting embodiment is less than about 1150 ft/second (350.5
meters/second).
[0039] The example gas turbine engine includes the fan section 22
that comprises in one non-limiting embodiment less than about 26
fan blades 42. In another non-limiting embodiment, the fan section
22 includes less than about 20 fan blades 42. Moreover, in one
disclosed embodiment the low pressure turbine 46 includes no more
than about 6 turbine rotors schematically indicated at 34. In
another non-limiting example embodiment, the low pressure turbine
46 includes about 3 turbine rotors. A ratio between the number of
fan blades 42 and the number of low pressure turbine rotors is
between about 3.3 and about 8.6. The example low pressure turbine
46 provides the driving power to rotate the fan section 22 and,
therefore, the relationship between the number of turbine rotors 34
in the low pressure turbine 46 and the number of blades 42 in the
fan section 22 disclose an example gas turbine engine 20 with
increased power transfer efficiency.
[0040] The example engine 20 includes an accessory drive system 62
that receives power from both the high speed spool 32 and the low
speed spool 30. The accessory drive system 62 includes an accessory
gearbox 68 for driving a plurality of accessory components 72, 74,
75, 77, 80, and 82. The accessory components 72, 74, 75, 77, 80,
and 82 support operation of the gas turbine engine 20 and include
pumps, generators and other devices driven to enable operation of
different engine and aircraft systems. The accessory gearbox 68 is
also coupled to a starter 70. The starter 70 is capable of driving
the accessory drive system 62 to start the engine 20. In this
example, a tower shaft assembly 64 including first and second tower
shafts 76, 78 is coupled to both the low speed spool 30 and the
high speed spool 32 to distribute power extraction between the two
spools 30, 32.
[0041] Excessive power extraction from a single spool, such as the
high speed spool 32, can limit operation and degrade overall
performance and engine efficiency. Accordingly, the example
accessory drive system 62 extracts power from both the low speed
spool 30 and the high speed spool 32 to meet the overall power
demands of the engine 20 and the aircraft associated with the
engine. The power extracted from the spools 30, 32 is combined in a
superposition gear system 66 disposed within the accessory gearbox
68.
[0042] Referring to FIG. 2, with continued reference to FIG. 1, the
superposition gear system 66 is an epicyclic gearbox that includes
a sun gear 102 that rotates about an axis 118. A plurality of
intermediate gears 104 are engaged with the sun gear 102 and
supported by a carrier 106. A ring gear 108 circumscribes and is
engaged with the plurality of intermediate gears 104.
[0043] In the disclosed example, the tower shaft assembly 64
includes the first tower shaft 76 that is driven by a gear 85
disposed on the low speed spool 30. A first gear 86 on the tower
shaft 76 is coupled to the gear 85. A second gear 88 is disposed on
a second end of the tower shaft 76 and engages a drive gear 90
disposed on a ring gear shaft 92.
[0044] A second tower shaft 78 is coupled to a drive gear 84 that
is driven by the high speed spool 32. The second tower shaft 78
includes a first gear 94 driven by the gear 84 on the high speed
spool 32. A second gear 96 of the second tower shaft 78 is engaged
to drive gear 98 disposed on a sun gear shaft 100. In this example,
the first tower shaft 76 and the second tower shaft 78 are disposed
concentrically about a common axis 83. Moreover, the axis 83 is
disposed at an angle relative to the engine longitudinal axis A and
the axis 118 of the superposition gear system 66. It should be
appreciated that although the specific disclosed embodiment
includes concentric tower shafts 76, 78, other configurations and
orientations of tower shafts are within the contemplation and scope
of this disclosure.
[0045] First tower shaft 76 is coupled to the ring gear shaft 92
that is selectively coupled to the ring gear 108. The second tower
shaft 78 is coupled to the sun gear shaft 100 that is coupled to
drive the sun gear 102. The sun gear shaft 100 is directly coupled
to the sun gear 102 and extends past the sun gear 102 to the
starter 70.
[0046] The superposition gear system 66, therefore, has a first
input provided by the first tower shaft 76 through the ring gear
shaft 92 to drive the ring gear 108 and a second input provided by
the second tower shaft 78 to drive the sun gear shaft 100 and,
thereby, the sun gear 102. A first output from the superposition
gear system 66 is provided by a carrier shaft 110 that is coupled
to the carrier 106. The carrier shaft 110 drives a first group of
the accessories in the disclosed example embodiment. The ring gear
shaft 92 provides a second output to drive a second group of
accessories.
[0047] The sun gear shaft 100 provides both another input into the
gear system 66 by being driven by the starter 70 and a third output
to drive at least one accessory component as is schematically
indicated at 77. The starter 70 provides a driving input to the sun
gear 102 through the sun gear shaft 100.
[0048] Referring to FIG. 3, with continued reference to FIG. 2, the
example superposition gear system 66 includes a direct connection
between the starter 70 and the sun gear shaft 100 to provide for
direct driving of the high speed spool 32. The sun gear shaft 100
is coupled to the starter 70 through a starter clutch 112. The
starter clutch 112 in this example is a mechanical one-way clutch
that enables direct driving of the high speed spool 32 during
starting operations. Once the high speed spool 32 is operating, the
starter clutch 112 prevents back driving or over driving of the
starter 70. The sun gear shaft 100 is directly connected to the
starter rather than being driven through a gear system. The direct
drive of the high speed spool 32 through the direct connection
simplifies operation and the mechanical connections.
[0049] Moreover, the example superposition gear system 66 provides
the first output through the carrier shaft 110 that drives a first
group of accessory components 128 through a first gear system 122.
In this example the first group of accessory components 72, 74, 75
and 80 are driven at a first speed. Once the engine is started, the
first output through the carrier shaft 110 provides the driving
input required to power the first group 128 of accessory components
72, 74, 75 and 80 through the first gear system 122.
[0050] A second group 130 of accessory components 130 is driven by
the ring gear shaft 92 through a second gear system 124. In this
example, only one accessory component 82 is shown as being driven
by the second gear system 124, however, other components could be
included.
[0051] A third group 132 of accessory components 77 is driven by a
third gear system 126 coupled to the sun gear shaft 100. The third
gear system 126 is operable to rotate at the speed of the sun gear
shaft 100 during engine operation and when driven by the starter 70
during starting operations.
[0052] The superposition gear system 66 includes a first clutch 114
that couples the ring gear shaft 92 to the ring gear 108. A second
clutch 116 couples the ring gear 108 to a static engine structure
36. In this example, both the first clutch 114 and second clutch
116 are mechanical one-way clutches. Moreover, in this example, the
first and second mechanical one-way clutches 114, 116 are sprag
clutches. It should be appreciated that although sprag clutches are
disclosed by way of example, other mechanical clutch systems could
be utilized and are within the contemplation of this
disclosure.
[0053] The second clutch 116 couples the ring gear 108 to the
engine static structure 36 during a starting operation to prevent
rotation of the ring gear 108 and thereby the first tower shaft 76
and the low speed spool 30. When the ring gear 108 is fixed, the
starter 70 will drive the sun gear shaft 100 such that it will be
the only driving output back to the high speed spool 32.
[0054] During a starting operation, the starter 70 will drive the
sun gear shaft in a first direction. The starter clutch 112 will
engage and enable driving of the sun gear shaft 100 by the starter
70. The same rotation provided by the starter 70 will engage the
ring gear 108 such that the second clutch 116 will lock the ring
gear 108 to the static structure to prevent rotation of the ring
gear 108. The first clutch 114 is not locked in this direction, but
does not receive a driving input and therefore does not rotate the
corresponding first tower shaft 76. The starter 70 thereby directly
drives the high speed spool 32 to start the engine.
[0055] Once the engine has started and the high speed spool 32 is
rotating at speed, the starter 70 will be stopped. The high speed
spool 32 will begin driving the second tower shaft 78 and thereby
the sun gear shaft 100. The higher speed provided by the driving of
the high speed spool 32 will disengage the starter 70.
Additionally, once the low speed spool 30 begins operation, the
first tower shaft 76 will being rotating. The first clutch 114 will
then engage to couple the ring gear shaft 92 to the ring gear 108.
In this operating condition, both the low speed spool 30 and the
high speed spool 32 will drive portions of the superposition gear
system 66.
[0056] The first clutch 114 will couple power from the first tower
shaft 76 to the ring gear 108. The second clutch 116 will free
wheel and allow rotation of the ring gear 108. The second tower
shaft 78 will drive the sun gear 102 and thereby the intermediate
gears 104 and the carrier 106. The carrier 106 will in turn drive
carrier shaft 110 to drive the first gear system 122, within the
accessory gearbox 68. Power from each of the high spool 32 and the
low spool 30 will be split to drive the carrier shaft 110 and power
the first group 128 of accessory components 72, 74, 75, and 80
throughout engine operation.
[0057] The second group 124 includes the accessory component 82 and
is driven by a gear coupling 136 to the ring gear shaft 92. The
third group 132 of accessory components 77 is driven by a gear
coupling 138 to the sun gear shaft 100. Each of the ring gear shaft
92, sun gear shaft 100 and carrier shaft 110 rotate at different
speeds and therefore the accessory components 72, 74, 75, 77, 80
and 82 are driven by the shaft 92, 100 and 110 that best
corresponds with a desired speed and operation of each accessory
component.
[0058] In the disclosed example embodiment, the fuel pump 77 is
driven by the sun gear shaft 100 that is in turn driven by the high
speed spool 32. Fuel flow requirements are tied closely to the
speed of the high speed spool 32. Coupling the fuel pump 77 to the
sun gear shaft 100 enables driving of the fuel pump 77 by only the
high speed spool 32 at a speed that corresponds and changes
proportionally with operation of the engine 20 to provide a more
desirable corresponding variation in operation. Moreover, the gear
coupling 138 can be set to generate the desired proportional speed
of the fuel pump in direct relationship to the speed of the high
speed spool 32.
[0059] The first group 128 including the main oil pump 80,
generator 72, deoiler 74 and hydraulic pump 75 all demand
significant power without a strong tie or correlation to a speed of
either of the spools 30, 32. Accordingly, the first group 128 of
accessories is driven through the gear coupling 134 by the carrier
shaft 110. The carrier shaft 110 is driven by power extracted from
both spools 30, 32 to provide a steady consistent power output.
[0060] The third group 130 of accessory components in this example
includes the auxiliary oil pump 82 that is driven through the gear
coupling 136 by the ring gear shaft 92. The ring gear shaft 92 is
coupled to the low speed spool 30. The auxiliary oil pump 82 is
desired to operate during low and negative G environments as well
as operate when the engine is not operating but the fan is rotating
to drive the low speed spool 30. In configurations where the
accessory components are driven only by the high speed spool 32,
the auxiliary oil pump 82 is not engaged and therefore does not
produce an output flow of oil 68. However, the third output from
the superposition gear system 66 enables direct driving by the low
speed spool 30 as needed to provide the desired operation.
[0061] The gear couplings 134, 136 and 138 are each defined in
consideration of the accessory component driven. Each of the gear
couplings drive corresponding gear systems 122, 124 and 126 that
are tailored to provide the most efficient speeds for each
accessory component 72, 74, 75, 77, 80, and 82.
[0062] It should be understood that although disclosed groups of
accessory components are driven by specific gear couplings to
specific locations and features of the superposition gear system
66, each accessory component could be configured to be driven by
gear couplings in combinations that differ from the disclosed
examples. Each accessory component could be driven by any of the
outputs provided by the superposition gear system 66. Moreover, not
all the outputs need to drive an accessory component to be
considered within the contemplation of this disclosure. Any
configuration of the example superposition gear system 66 will be
determined by the design and operational requirements for each
accessory.
[0063] According, the example accessory drive system 62 includes
the superposition gear system 66 that automatically distributes
input driving torque between the low speed spool 30, the high speed
spool 32 as required during engine operation. The selective
operation of the superposition gear system 66 is enabled by one-way
mechanical clutches that provide different combinations of inputs
and outputs that are automatically couple based on engine operating
conditions. Moreover, the direct starting input is enabled by
coupling of the starter directly to the sun gear shaft 100 along
with fixing of the ring gear by a one-way mechanical clutch.
Additionally, the superposition gear system 66 enables driving of
different accessory components through different outputs at
differing speeds to tailor each individual speed to each accessory
component.
[0064] Although an example embodiment has been disclosed, a worker
of ordinary skill in this art would recognize that this disclosure
is not just a material specification and that certain modifications
would come within the scope of this disclosure. For that reason,
the following claims should be studied to determine the scope and
content of this disclosure.
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