FUNDAMENTAL GEAR SYSTEM ARCHITECTURE
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of United States Application No.
5 131557,614 filed July 25, 2012 that in turn claims priority to Provisional Application
No. 61/653,73 1 filed May 3 1,2012.
BACKGROUND
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
10 compressed and delivered into the combustion section where it is mixed with fuel
and ignited to generate a high-speed exhaust gas flow. The high-speed 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 typically includes at least a fan drive turbine.
15 The fan drive turbine may drive a first compressor through an inner shaft to
form a low spool. A speed reduction device such as an epicyclical gear assembly
may be utilized to drive the fan section such that the fan section may rotate at a speed
different than the fan drive turbine so as to increase the overall propulsive efficiency
of the engine. The efficiency at which the gear assembly transfers power is a
20 consideration in the development of a gear driven fan. Power or energy not
transferred through the gearbox may result in the generation of heat that may be
removed with a lubrication system. Typically, the more heat generated, the larger
and heavier the lubrication system.
Although geared architectures can provide improved propulsive efficiency,
25 other factors including heat removal and lubrication can detract from the improved
propulsive efficiency. Accordingly, turbine engine manufacturers continue to seek
further improvements to engine performance including improvements to thermal,
transfer and propulsive efficiencies.
SUMMARY
A gas turbine engine, according to an exemplary embodiment of this
disclosure, among other possible things includes a fan that includes a plurality of fan
5 blades rotatable about an axis, a compressor section, a combustor that is in fluid
communication with the compressor section, and a fan drive turbine that is in
communication with the combustor. The fan drive turbine has a first exit area at a
first exit point and is configured to rotate at a first speed. A second turbine section
includes a second exit area at a second exit point and is configured to rotate at a
10 second speed that is faster than the first speed. A first performance quantity is
defined as a product of the first speed squared and the first area. A second
performance quantity is defined as a product of the second speed squared and the
second area. A ratio of the first performance quantity to the second performance
quantity is between about 0.5 and about 1.5. A gear system is configured to provide
15 a speed reduction between the fan drive turbine and the fan, and to transfer shaft
power input from the fan drive turbine to the fan at efficiency greater than about 98%
and less than 100%. A mount flexibly supports portions of the gear system. The
mount extends from a static structure of the engine to accommodate at least radial
movement between the gear system and the static structure. A lubrication system is
20 configured to provide lubricant to the gear system and to remove thermal energy
from the gear system.
In a further embodiment of the above, the lubrication system includes a
capacity for removing an amount of energy that is greater than zero and less than
about 2% of the energy input into the gear system during operation of the gas turbine
25 engine.
In a further embodiment of any of the above, the fan delivers a portion of air
into a bypass duct. A bypass ratio is defined as the portion of air delivered into the
bypass duct divided by the amount of air delivered into the compressor section. The
bypass ratio is greater than about 6.0.
3 0 In a further embodiment of any of the above, the mouiit includes a load
limiter for liliiitiiig liiove~~ienotf tlie gear systeii~r esponsive to a11 unbalallced
condition.
In a further embodiment of any of the above, the bypass ratio is greater than
about 10.0.
In a further embodiment of any of the above, the ratio is above or equal to
about 0.8.
5 In a further embodiment of any of the above, a pressure ratio across the fan
drive turbine is greater than about 5: 1.
In a further embodiment of any of the above, a ratio of a sea level take-off
flat-rated static thrust is provided by the gas turbine engine, to a combined volume of
the fan drive turbine. The second turbine that is greater than or equal to about 1.5
10 lbf/inch3 and less than or equal to about 5.5 lbf/inch3.
A gas turbine engine, according to an exemplary embodiment of this
disclosure, among other possible things includes a fan including a plurality of fan
blades rotatable about an axis, a compressor section, a combustor that is in fluid
communication with the compressor section, and a turbine section including a fan
15 drive turbine and a second turbine that is in communication with the combustor. A
ratio of sea level take-off flat-rated static thrust is provided by the gas turbine engine
to a volume of the turbine section is greater than or equal to about 1.5 lbf/inch3 and
less than about 5.5 lbf/inch3. A gear system is configured to provide a speed
reduction between the fan drive turbine and the fan, and to transfer power input from
20 the fan drive turbine to the fan at an efficiency greater than about 98% and less than
100%. A mount flexibly supports portions of the gear system. The mount extends
from a static structure of the engine to accommodate at least radial movement
between the gear system and the static structure. A lubrication system is configured
to provide lubricant to the gear system and to remove thermal energy from the gear
25 system.
In a further embodiment of the above, the lubrication system includes a
capacity for removing an amount of energy that is greater than zero and less than
about 2% of the energy input into the gear system during operation of the gas turbine
engine.
3 0 In a further embodiment of any of the above, the mount includes a load
limiter for limiting moveinel~t of the gear system responsive to an unbalanced
condition.
In a further embodiment of any of the above, the fan delivers a portion of air
into a bypass duct. A bypass ratio is defined as the portion of air delivered into the
bypass duct divided by the amount of air delivered into the compressor section. The
bypass ratio is greater than about 6.0.
5 In a further embodiment of any of the above, the ratio is greater than or equal
to about 2.0 lbf/inch3.
In a further embodiment of any of the above, the ratio is greater than or equal
to about 4.0 lbf/inch3.
A gas turbine engine, according to an exemplary embodiment of this
10 disclosure, among other possible things includes a fan including a plurality of fan
blades rotatable about an axis, a compressor section, a combustor that is in fluid
communication with the compressor section, and a fan drive turbine that is in
communication with the combustor. A gear system is configured to provide a speed
reduction between the fan drive turbine and the fan, and to transfer power input from
15 the fan drive turbine to the fan at an efficiency greater than about 98% and less than
100%. A mount flexibly supports portions of the gear system. The mount extends
from a static structure of the engine to accommodate at least radial movement
between the gear system and the static structure. A lubrication system is configured
to provide lubricant to the gear system and to remove thermal energy from the gear
20 system.
In a further embodiment of the above, the lubrication system includes a
capacity for removing an amount of energy that is greater than zero and less than
about 2% of energy input into the gear system during operation of the gas turbine
engine.
2 5 In a further embodiment of any of the above, the fan delivers a portion of air
into a bypass duct. A bypass ratio is defined as the portion of air delivered into the
bypass duct divided by the amount of air delivered into the compressor section. The
bypass ratio is greater than about 6.0.
In a further embodiment of any of the above, the mount includes a load
30 limiter for limiting movement of the gear system responsive to an unbalanced
condition.
In a further embodiment of any of the above, the bypass ratio is greater than
about 10.0.
In a further embodiment of any of the above, a pressure ratio across the fan
drive turbine is greater than about 5: 1.
5 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.
10 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
Figure 1A is a schematic view of an example gas turbine engine.
15 Figure 1B is a schematic view of a feature of the example gas turbine engine.
Figure 1C is a schematic view of another feature of the example gas turbine
engine.
Figure 2 is a schematic view of an example fan drive gear system including
star epicyclical geared architecture.
2 0 Figure 3 is a schematic view of an example fan drive gear system including
planetary epicyclical geared architecture.
DETAILED DESCRIPTION
Figure 1A schematically illustrates an example gas turbine engine 20 that
25 incIudes a fan section 22, a compressor section 24, a combustor section 26 and a
turbine section 28. Alternative engines might include an augmenter section (not
shown) among other systems or features. The fan section 22 drives air along a bypass
flow path B while the compressor section 24 draws air in along a core flow path C
where air is compressed and communicated to a combustor section 26. In the
30 combustor section 26, air is mixed with fuel and ignited to generate a high pressure
exhaust gas stream that expands through the turbine section 28 where energy is
extracted and utilized to drive the fan section 22 and the compressor section 24.
Although the disclosed non-limiting embodiment depicts a turbofan gas
turbine engine, it should be understood that the concepts described herein are not
limited to use with turbofans and the teachings also may be applied to other types of
turbine engines; for example a turbine engine including a three-spool architecture in
5 which three spools concentrically rotate about a common axis and where a low spool
enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that
enables an intermediate pressure turbine to drive a first compressor of the compressor
section, and a high spool that enables a high pressure turbine to drive a high pressure
compressor of the compressor section.
10 The example 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.
15 The low speed spool 30 generally includes an inner shaft 40 that connects a
fan 42 and a low pressure (or first) compressor section 44 to a low pressure (or first)
turbine section 46. The inner shaft 40 drives the fan 42 through a speed change
device, such as 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
20 interconnects a high pressure (or second) compressor section 52 and a high pressure
(or second) turbine section 54. The inner shaft 40 and the outer shaft 50 are
concentric and rotate via the bearing systems 38 about the engine central longitudinal
axis A.
A combustor 56 is arranged between the high pressure compressor 52 and
25 the high pressure turbine 54. In one example, the high pressure turbine 54 includes at
least two stages to provide a double stage high pressure turbine 54. In another
example, the high pressure turbine 54 includes only a single stage. As used herein, a
"high pressure" compressor or turbine experiences a higher pressure than a
corresponding "low pressure" compressor or turbine.
30 The example low pressure turbine 46 has a pressure ratio that is greater than
about 5. The pressure ratio of the example low pressure turbine 46 is measured prior
to an inlet of the low pressure turbine 46 as related to the pressure measured at the
outlet of the low pressure turbine 46 prior to an exhaust nozzle.
A mid-turbine frame 58 of the engine static structure 36 is arranged
generally between the high pressure turbine 54 and the low pressure turbine 46. The
5 mid-turbine frame 58 further supports bearing systems 38 in the turbine section 28 as
well as setting airflow entering the low pressure turbine 46.
Airflow through the core flow path C is compressed by the low pressure
compressor 44 then by the high pressure compressor 52 mixed with fuel and ignited
in the combustor 56 to produce high speed exhaust gases that are then expanded
10 through the high pressure turbine 54 and low pressure turbine 46. The mid-turbine
frame 58 includes vanes 60, which are in the core airflow path and function as an
inlet guide vane for the low pressure turbine 46. Utilizing the vane 60 of the midturbine
frame 58 as the inlet guide vane for low pressure turbine 46 decreases the
length of the low pressure turbine 46 without increasing the axial length of the mid-
15 turbine frame 58. Reducing or eliminating the number of vanes in the low pressure
turbine 46 shortens the axial length of the turbine section 28. Thus, the compactness
of the gas turbine engine 20 is increased and a higher power density may be
achieved.
The disclosed gas turbine engine 20 in one example is a high-bypass geared
20 aircraft engine. In a further example, the gas turbine engine 20 includes a bypass
ratio greater than about six (6), with an example embodiment being greater than
about ten (10). The example geared architecture 48 is an epicyclical gear train, such
as a planetary gear system, star gear system or other known gear system, with a speed
reduction ratio of greater than about 2.3. In some embodiments, the speed reduction
25 ratio may be greater than about 2.6 and in other embodiments the speed reduction
ratio may be greater than about 3.0.
In one disclosed embodiment, the gas turbine engine 20 includes a bypass
ratio greater than about ten (1 0: 1) and the fan diameter is significantly larger than an
outer diameter of the low pressure compressor 44. It should be understood, however,
30 that the above parameters are only exemplary of one embodiment of a gas turbine
engine including a geared architecture and that the present disclosure is applicable to
other gas turbine engines.
A significant amount of thrust is provided by tlie 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
5 consumption - also known as "bucket cruise Thrust Specific Fuel Consumption
('TSFC')" - is the industry standard parameter of pound-mass (lbm) of fuel per hour
being burned divided by pound-force (lbf) of thrust the engine produces at that
minimum point.
"Low fan pressure ratio" is the pressure ratio across the fan blade alone,
10 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 SO.
In another non-limiting embodiment the low fan pressure ratio is less than about
1.45.
"Low corrected fan tip speed" is the actual fan tip speed in ftlsec divided by
15 an industry standard temperature correction of [(Tram OR) / 51 8.71 '. The "Low
corrected fan tip speed", as disclosed herein according to one non-limiting
embodiment, is less than about 11 50 ftlsecond.
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
20 expanded over the high pressure turbine 54 and low pressure turbine 46. The
turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed
spool 32 in response to the expansion of the airflow passing therethrough.
The amount of thrust that can be produced by a particular turbine section
compared to how compact the turbine section is, is referred to in this disclosure as
25 the power density, or the force density, of the turbine section, and is derived by the
flat-rated Sea Level Take-Off (SLTO) thrust divided by the volume of the entire
turbine section. The example volume is determined from an inlet of the high pressure
turbine 54 to an exit of the low pressure turbine 46. In order to increase the power
density of the turbine section 28, each of the low pressure and high pressure turbines
30 46, 54 is made more compact. That is, the high pressure turbine 54 and the low
pressure turbine 46 are made with a shorter axial length, and the spacing between
each of the turbines 46, 54 is decreased, thereby decreasing the volume of the turbine
section 28.The power density in the disclosed gas turbine engine 20 including the
gear driven fan section 22 is greater than the power density provided in prior art gas
turbine engine including a gear driven fan. Eight disclosed exemplary engines,
which incorporate turbine sections and fan sections driven through a reduction gear
5 system and architectures as set forth in this application, are described in Table I as
follows:
TABLE 1
10 In some embodiments, the power density (also referred to as "thrust density")
is greater than or equal to about 1.5 lbf /in3. In further embodiments, the power
density is greater than or equal to about 2.0 lbf /in3. In further embodiments, the
power density is greater than or equal to about 3.0 lbf/in3. In further embodiments,
10
Engi Turbine section
ne
I
Thru Thrust/turbine
st ST,TO
(lbf)
17,O
00
the power density is greater than or equal to about 4.0 lbf /in3. In further
embodiments, the power density is less than or equal to about 5.5 lbf /in3.
Engines made with the disclosed gear driven fan architecture, and including
turbine sections as set forth in this application, provide very high efficiency
5 operation, and increased fuel efficiency.
Referring to Figure lB, the example turbine section 28 volume is
schematically shown and includes first, second and third stages 46A, 46B and 46C.
Each of the stages 46A, 46B and 46C includes a corresponding plurality of blades
21 2 and vanes 2 14. The example turbine section further includes at least one example
10 air-turning vane 220 between the high and low turbines 54, 46 that has a modest
camber to provide a small degree of redirection and achieve a desired flow angle
relative to blades 212 of the first stage 46a of the low pressure turbine 46. The
disclosed vane 220 could not efficiently perform the desired airflow function if the
high and pressure turbines 54,46 rotated in a common direction.
15 The example mid-turbine frame 58 includes multiple air turning vanes 220
arrayed circumferentially in a row that direct air flow exiting the high pressure
turbine 54 and ensure that air is flowing in the proper direction and with the proper
amount of swirl. Because the disclosed turbine section 28 is more compact than
previously utilized turbine sections, air has less distance to travel between entering
20 the mid-turbine frame 58 and entering the low pressure turbine 46. The smaller axial
travel distance results in a decrease in the amount of swirl lost by the high-speed
airflow during the transition from the mid-turbine frame 58 to the low pressure
turbine 46, and allow the vanes 220 of the mid-turbine frame 58 to function as inlet
guide vanes of the low pressure turbine 46. The mid-turbine frame 58 also includes a
25 strut 221 providing structural support to both the mid-turbine frame 58 and to the
engine housing. In one example, the mid-turbine frame 58 is much more compact by
encasing the strut 221 within the vane 220, thereby decreasing the length of the midturbine
frame 58.
At a given fan tip speed and thrust level provided by a given fan size, the
30 inclusion of the speed change device 48 (shown in Figure 1A) provides a gear
reduction ratio, and thus the speed of the low pressure turbine 46 and low pressure
compressor 44 components may be increased. More specifically, for a given fan
diameter and fan tip speed, increases in gear ratios provide for a faster turning turbine
that, in turn, provides for an increasingly compact turbine and increased thrust to
volume ratios of the turbine section 28. By increasing the gear reduction ratio, the
speed at which the low pressure compressor 44 and the low pressure turbine 46 turn,
5 relative to the speed of the fan 42, is increased.
Increases in rotational speeds of the gas turbine engine 20 components
increases overall efficiency, thereby providing for reductions in the diameter and the
number of stages of the low pressure compressor 44 and the low pressure turbine 46
that would otherwise be required to maintain desired flow characteristics of the air
20 flowing through the core flow path C. The axial length of each of the low pressure
compressor 44 and the low pressure turbine 46 can therefore be further reduced due
to efficiencies gained from increased speed provided by an increased gear ratio.
Moreover, the reduction in the diameter and the stage count of the turbine section 28
increases the compactness and provides for an overall decrease in required axial
15 length of the example gas turbine engine 20.
In order to further improve the thrust density of the gas turbine engine 20,
the example turbine section 28 (including the high pressure turbine 54, the midturbine
frame 58, and the low pressure turbine 46) is made more compact than
traditional turbine engine designs, thereby decreasing the length of the turbine
20 section 28 and the overall length of the gas turbine engine 20.
In order to make the example low pressure turbine 46 compact, make the
diameter of the low pressure turbine 46 more compatible with the high pressure
turbine 54, and thereby make the air-turning vane 220 of the mid-turbine frame 58
practical, stronger materials in the initial stages of the low pressure turbine 46 may be
25 required. The speeds and centrifugal pull generated at the compact diameter of the
low pressure turbine 46 pose a challenge to materials used in prior art low pressure
turbines.
Examples of materials and processes within the contemplation of this
disclosure for the air-turning vane 220, the low pressure turbine blades 212, and the
30 vanes 2 14 include materials with directionally solidified grains to provided added
strength in a span-wise direction. An example method for creating a vane 220, 214
or turbine blade 212 having directionally solidified grains can be found in U.S.
Applications No. 131290667, and U.S. Patent Nos. 7338259 and 7871247, each of
which is incorporated by reference. A further, engine embodiment utilizes a cast,
hollow blade 212 or vane 214 with cooling air introduced at the leading edge of the
bladelvane and a trailing edge discharge of the cooling air. Another embodiment
5 uses an internally cooled blade 212 or vane 214 with film cooling holes. An
additional engine embodiment utilizes an aluminum lithium material for construction
of a portion of the low pressure turbine 46. The example low pressure turbine 46
may also be constructed utilizing a powdered metal disc or rotor.
Additionally, one or more rows of turbine blades 212 of the low pressure
10 turbine 46 can be constructed using a single crystal blade material. Single crystal
constructions oxidize at higher temperatures as compared to non-single crystal
constructions and thus can withstand higher temperature airflow. Higher temperature
capability of the turbine blades 2 12 provide for a more efficient low pressure turbine
46 that may be further reduced in size.
15 While the illustrated low pressure turbine 46 includes three turbine stages
46a, 46b, and 46c, the low pressure turbine 46 can be modified to include up to six
turbine stages. Increasing the number of low pressure turbine stages 46a, 46b, 46c at
constant thrust slightly reduces the thrust density of the turbine section 28 but also
increases power available to drive the low pressure compressor and the fan section
20 22.
Further, the example turbine blades may be internally cooled to allow the
material to retain a desired strength at higher temperatures and thereby perform as
desired in view of the increased centrifugal force generated by the compact
configuration while also withstanding the higher temperatures created by adding low
25 pressure compressor 44 stages and increasing fan tip diameter.
Each of the disclosed embodiments enables the low pressure turbine 46 to be
more compact and efficient, while also improving radial alignment to the high
pressure turbine 54. Improved radial alignment between the low and high pressure
turbines 46, 54, increases efficiencies that can offset any increases in manufacturing
30 costs incurred by including the air turning vane 220 of the mid-turbine frame 58.
In light of the foregoing embodiments, the overall size of the turbine section
28 has been greatly reduced, thereby enhancing the engine's power density. Further,
as a result of the improvemeilt in power density, the engine's overall propulsive
efficiency has been improved.
An exit area 400 is shown, in Figure 1C and Figure lA, at the exit location
for the high pressure turbine section 54. An exit area for the low pressure turbine
5 section is defined at exit 401 for the low pressure turbine section. As shown in
Figure lC, the turbine engine 20 may be counter-rotating. This means that the low
pressure turbine section 46 and low pressure compressor section 44 rotate in one
direction, while the high pressure spool 32, including high pressure turbine section
54 and high pressure compressor section 52 rotate in an opposed direction. The gear
10 reduction 48, which may be, for example, an epicyclic transmission (e.g., with a sun,
ring, and star gears), is selected such that the fan 42 rotates in the same direction as
the high spool 32. With this arrangement, and with the other structure as set forth
above, including the various quantities and operational ranges, a very high speed can
be provided to the low pressure spool. Low pressure turbine section and high
15 pressure turbine section operation are often evaluated looking at a performance
quantity which is the exit area for the turbine section multiplied by its respective
speed squared. This performance quantity ("PQ") is defined as:
Equation 1: PQlpt = (Alpt x VI,,?)
Equation 2: PQllpt = (AIIpt x vhp?)
2 0 where Alpt is the area of the low pressure turbine section at the exit thereof
(e.g., at 401), where Vlpt is the speed of the low pressure turbine section, where AIIpt
is the area of the high pressure turbine section at the exit thereof (e.g., at 400), and
where Vllpti s the speed of the high pressure turbine section.
Thus, a ratio of the performance quantity for the low pressure turbine section
25 compared to the performance quantify for the high pressure turbine section is:
Equation 3: (Apt x VI~:)/(AIx~ v~r~P ?) = PQI~JPQII~~
In one turbine embodiment made according to the above design, the areas of
the low and high pressure turbine sections are 557.9 in2 and 90.67 in2, respectively.
Further, the speeds of the low and high pressure turbine sections are 10179 rpm and
30 24346 rpm, respectively. Thus, using Equations 1 and 2 above, the performance
quantities for the low and high pressure turbine sections are:
Equalion 1: PQIpt = (Alpt x VI,,?) = (557.9 in2)(10179 rpm)2 =
57805 157673.9 in2 rpm2
Equation 2: PQrpt = (Ahpt x v,:) = (90.67 in2)(24346 rpm12 =
53742622009.72 in2 rpm2
5 and using Equation 3 above, the ratio for the low pressure turbine section to
the high pressure turbine section is:
Ratio = PQlpt/PQllp=t 57805 157673.9 in2 rpm2 1 53742622009.72 in2 rpm2 =
1.075
In another embodiment, the ratio was about 0.5 and in another embodiment
10 the ratio was about 1.5. With PQlpt/PQhprt atios in the 0.5 to 1.5 range, a very
efficient overall gas turbine engine is achieved. More narrowly, PQlpt/PQllprat tios of
above or equal to about 0.8 are more efficient. Even more narrowly, PQlpt/PQllpt
ratios above or equal to 1.0 are even more efficient. As a result of these PQIpt/PQl,pt
ratios, in particular, the turbine section can be made much smaller than in the prior
15 art, both in diameter and axial length. In addition, the efficiency of the overall engine
is greatly increased.
The low pressure compressor section of the example gas turbine engine 20 is
improved with this arrangement and resembles a high pressure compressor section as
it is more efficient and can do more compression work in fewer stages. The low
20 pressure compressor section may be made smaller in radius and shorter in length
while contributing more toward achieving the overall compression pressure ratio
design target of the engine.
As appreciated, improvements to the low pressure turbine 46 that increase
rotational speed and torque result in an increased load on the geared architecture 48.
25 The increased loads on the geared architecture 48 include increases in lubricant
requirements. Moreover, the increased speed and torques provided by the low
pressure turbine 46 may only be fully realized if that power can be efficiently
transferred through the geared architecture 48 and not lost as heat. Accordingly, the
transfer efficiency of the geared architecture 48 and the capability of a corresponding
30 lubricant system provide for the realization of the efficiencies gained from the
improved turbine configuration.
Referring to Figure la, the example gas turbine engine iilcludes the fan 42
that comprises in one non-limiting embodiment less than about 26 fan blades. In
another non-limiting embodiment, the fan section 22 includes less than about 20 fan
blades. Moreover, in one disclosed embodiment the low pressure turbine 46 includes
5 no more than about 6 turbine rotors schematically indicated at 34. In another nonlimiting
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
10 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.
Referring to Figure 2 with continued reference to Figure lA, the example
gas turbine engine includes a lubrication system 98. The lubrication system 98
15 provides lubricant flow to the rotating components of the gas turbine engine
including the bearing assemblies 38 and the geared architecture 48. The lubrication
system 98 further provides for the removal of heat generated in the various bearing
systems and the geared architecture 48.
The example lubrication system 98 includes a main system 80 that provides
20 lubrication during normal operating conditions of the gas turbine engine. An
auxiliary system 82 is also included to supplement operation of the main lubrication
system 80. The size and weight of the lubrication system 90 is directly related to its
capacity for removing heat from the geared architecture 48. The greater the need for
removal of heat, the larger and heavier the lubrication system 98 becomes. The
25 amount of heat generated by the geared architecture 48 is therefore an important
consideration in the configuration of a fan drive gear system.
The example geared architecture 48 is part of a fan drive gear system 70.
The example geared architecture 48 comprises a gear assembly 65 that includes a sun
gear 62 driven by a fan drive turbine 46. In this example, the fan drive turbine is the
30 low pressure turbine 46. The sun gear 62 in turn drives intermediate gears 64
mounted on a carrier 74 by jourllal bearings. The carrier 74 is grounded to the static
engine structure 36 and therefore the interniediate gears 64 do not orbit about the sun
gear 62. The intermediate gears 64 intermesh and drive a ring gear 66 coupled to a
fan shaft 68 to drive the fan 42.
The gear assembly 65 is flexibly mounted such that it may be isolated from
vibrational and transient movement that could disturb alignment between the gears
5 62, 64 and 66. In this example, flexible mounts 76 support the carrier 74 and
accommodate relative movement between the gear assembly 65 and the static
structure 36. The example flexible mount 76 includes a spring rate that
accommodates deflections that occur during normal operation of the fan drive gear
system 70.
10 Power input through the inner shaft 40 of the fan drive turbine 46 is
transmitted through a flexible coupling 72. The flexible coupling 72 also includes a
spring rate that allows a defined amount of deflection and misalignment such that
components of the gear assembly 65 are not driven out of alignment.
Although some relative movement is compensated by the flexible coupling
15 72 and the flexible mounts 76, movement beyond a desired limitation can
detrimentally affect meshing engagement between the gears and therefore a load
limiting device 78 is provided as part of the gear box mounting structure. The load
limiter 78 constrains movement of the gear box 65. The limiter 78 further provides a
stop that reacts to unbalanced loads on the gear box 65. Accordingly, the limiter
20 prevents radial unbalanced loads and/or torsional overloads from damaging the gas
turbine engine 20.
The example fan drive gear system 70 is sustained by a lubrication system
98. The lubrication system 98 provides for lubrication and cooling of the gears 62,
64 and 66 along with bearings supposting rotation of the gears. It is desirable to
25 circulate lubricant as quickly as possible to maintain a desired temperature. Power
transmission efficiency through the gear box 65 is detrimentally affected by elevated
temperatures.
In this example, the lubricant system 98 includes a main system 80 that
provides the desired lubricant flow through a plurality of conduits schematically
30 illustrated by the line 88 to and from the gear box 65. The ~naino il system 80 also
transmits heat, schematically by arrows 92, away from the gear box 65 to maintain a
desired temperature.
The lubrication system 98 also includes the auxiliary oil system 82 that
supplies oil flow to the gear box 65 in response to a temporary interruption in
lubricant flow from the main oil system 80.
The efficiency of the example gear box 65 and overall geared architecture 48
5 is a function of the power input, schematically indicated by arrow 94, through the
shaft 40 relative to power output, schematically indicated by arrows 96, to the fan
shaft 68. Power input 94 compared to the amount of power output 96 is a measure of
gear box efficiency. The example gear box 65 operates at an efficiency of greater
than about 98%. In another disclosed example the example gear box 65 operates at
10 efficiency greater than about 99%.
The disclosed efficiency is a measure of the amount of power 94 that is
specifically transferred to the fan shaft 68 to rotate the fan 42. Power that is not
transmitted through the gear box 65 is lost as heat and reduces the overall efficiency
of the fan drive gear system 70. Any deficit between the input power 94 and output
15 power 96 results in the generation of heat. Accordingly, in this example, the deficit
of between about 1-2% between the input power 94 and output power 96 generates
heat. In other words, between about 1% and 2% of the input power 94 is converted
to heat energy that must be accommodated by the lubrication system 98 to maintain a
working lubricant temperature within operational limits.
20 The example lubricant system 98 provides for the removal of thermal energy
equal to or less than about 2% of the input power 94 from the low speed spool 30 that
includes the fan drive turbine 46. In another non-limiting embodiment of the
example fan drive gear system 70, the efficiency of the gear box 65 is greater than
about 99% such that only about 1% of power input from the low speed spool 30 is
25 transferred into heat energy that must be handled by the lubricant system 98. In
another non-limiting embodiment of the example fan drive gear system 70 is an
example turbine engine including three-spool architecture in which three spools
concentrically rotate about a common axis and where a low spool enables a low
pressure turbine 46 to drive a fan via a gearbox 65.
3 0 The larger the capacity for handling and removing thermal energy, the larger
and heavier the lubricant system 98. In this example, the main oil system includes a
heat exchanger 90 that accommodates heat 92 that is generated within the' gear box
65. The heat exchanger 90 is an example of one element of the lubrication system 98
that is scaled to the desired capacity for removing ther~nal energy. As appreciated,
other elements, such as for example lubricant pumps, conduit size along with overall
lubricant quantity within the lubrication system 98 would also be increased in size
5 and weight to provide increased cooling capacity. Accordingly, it is desirable to
increase power transfer efficiency to reduce required overall heat transfer capacity of
lubrication system 98.
In this example, the high efficiency of the example gear box 65 enables a
relatively small and light lubricant system 98. The example lubricant system 98
10 includes features that can accommodate thermal energy generated by up to about 2%
of the input power 94. In other words, the lubrication system 98 has an overall
maximum capacity for removing thermal energy up to about 2% of the input power
provided by the low pressure turbine 46.
Referring to Figure 3 with continued reference to Figure lA, another
15 example epicyclical gear box 85 is disclosed and comprises a planetary
configuration. In a planetary configuration, planet gears 84 are supported on a carrier
86 that is rotatable about the engine axis A. The sun gear 62 remains driven by the
inner shaft 40 and the low pressure turbine 46. The ring gear 66 is mounted to a
fixed structure 36 such that it does not rotate about the axis. Accordingly, rotation of
20 the sun gear 62 drives the planet gears 84 within the ring gear 66. The planet gears
84 are supported on the rotatable carrier 86 that in turn drives the fan shaft 68. In this
configuration, the fan shaft 68 and the sun gear 62 rotate in a common direction,
while the planet gears 84 individually rotate in a direction opposite to the sun gear 62
but collectively rotate about the sun gear 62 in the same direction as the rotation of
25 the sun gear 62.
The example planetary gear box illustrated in Figure 3 includes the ring gear
66 that is supported by flexible mount 76. The flexible mount 76 allows some
movement of the gearbox 85 to maintain a desired alignment between meshing teeth
of the gears 62, 84, 66. The limiter 78 prevents movement of the planetary gear box
30 85 beyond desired limits to prevent potential damage caused by radial imbalances
and/or torsional loads.
The example low pressure turbine 46 inputs power 94 to drive the gear box
85. As in the previous example, the example gear box 85 transmits more than about
98% of the input power 94 to the fan drive shaft 68 as output power 96. In another
example, the gear box 85 transmits more than about 99% of the input power 94 to the
5 fan drive shaft 68 as output power 96.
The difference between the input power 94 and the output power 96 is
converted into heat energy that is removed by the lubrication system 98. In this
example, the lubrication system 98 has a capacity of removing no more heat 92 than
is generated by about 2% of the input power 94 from the low speed spool 30 that
10 includes the low pressure turbine 46. In another example. The lubrication system 98
has a capacity of removing no more heat 92 than is generated by about 1% of tlie
input power 94. Accordingly, the efficiency provided by the example gear box 85
enables the lubrication system 98 to be of size that does not detract from the
propulsive efficiency realized by turning the fan section 22 and low pressure turbine
15 46 at separate and nearer optimal speeds.
Accordingly the example fan drive gear system provides for the
improvement and realization of propulsive efficiencies by limiting losses in the form
of thermal energy, thereby enabling utilization of a lower capacity and sized
lubrication system.
2 0 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 this disclosure. For that reason, the following claims should be studied to
determine the scope and content of this disclosure.
CLAIMS
We claim:
1. A gas turbine engine comprising:
a fan including a plurality of fan blades rotatable about an axis;
a compressor section;
a combustor in fluid communication with the compressor section;
a fan drive turbine in communication with the combustor, wherein the fan
drive turbine has a first exit area at a first exit point and is configured to rotate at a
first speed;
10 a second turbine section including a second exit area at a second exit point
and being configured to rotate at a second speed that is faster than the first speed,
wherein a first performance quantity is defined as a product of the first speed squared
and the first area, a second performance quantity is defined as a product of the second
speed squared and the second area; and a ratio of the first performance quantity to the
15 second performance quantity is between about 0.5 and about 1.5;
a gear system configured to provide a speed reduction between the fan drive
turbine and the fan, and to transfer shaft power input from the fan drive turbine to the
fan at an efficiency greater than about 98% and less than 100%;
a mount flexibly supporting portions of the gear system, the mount extending
20 from a static structure of the engine to accommodate at least radial movement
between the gear system and the static structure; and
a lubrication system configured to provide lubricant to the gear system and to remove
thermal energy from the gear system.
25 2. The gas turbine engine as recited in claim 1, wherein the lubrication system
includes a capacity for removing an amount of energy that is greater than zero and
less than about 2% of the energy input into the gear system during operation of the
gas turbine engine.
30 3. The gas turbine engine as recited in claim 1, wherein said fan delivers a
portion of air into a bypass duct, and a bypass ratio being defined as the portion of air
delivered into the bypass duct divided by the amount of air delivered into the
compressor section, with the bypass ratio being greater than about 6.0.
4. The gas turbine engine as recited in claim I , wherein the mount includes a
5 load limiter for limiting movement of the gear system responsive to an unbalanced
condition.
5. The gas turbine engine as recited in claim 3, wherein the bypass ratio is
greater than about 10.0.
10
6. The gas turbine engine as recited in claim 1, wherein the ratio is above or
equal to about 0.8.
7. The gas turbine engine as recited in claim 1, wherein a pressure ratio across
15 the fan drive turbine is greater than about 5: 1.
8. The gas turbine engine as recited in claim 1, including a ratio of a sea level
take-off flat-rated static thrust provided by the gas turbine engine, to a combined
volume of the fan drive turbine and the second turbine that is greater than or equal to
20 about 1.5 lbf/inch3 and less than or equal to about 5.5 lbf/inch3.
9. A gas turbine engine comprising:
a fan including a plurality of fan blades rotatable about an axis;
a compressor section;
2 5 a combustor in fluid communication with the compressor section;
a turbine section including a fan drive turbine and a second turbine in
communication with the combustor, wherein a ratio of sea level take-off flat-rated
static thrust provided by the gas turbine engine to a volume of the turbine section is
greater than or equal to about 1.5 lbf/inch3 and less than about 5.5 lbf/inch3;
3 0 a gear system configured to provide a speed reduction between the fan drive
turbine and the fan, and to transfer power input from the fan drive turbine to the fan
at an efficiency greater than about 98% and less than 100%;
a mount flexibly supporting portions of the gear system, the mount extending
from a static structure of the engine to accommodate at least radial movement
between the gear system and the static structure; and
a lubrication system configured to provide lubricant to the gear system and to remove
5 thermal energy from the gear system.
10. The gas turbine engine as recited in claim 9, wherein the lubrication system
includes a capacity for removing an amount of energy that is greater than zero and
less than about 2% of the energy input into the gear system during operation of the
10 gas turbine engine.
11. The gas turbine engine as recited in claim 9, wherein the mount includes a
load limiter for limiting movement of the gear system responsive to an unbalanced
condition.
15
12. The gas turbine engine as recited in claim 9, wherein said fan delivers a
portion of air into a bypass duct, and a bypass ratio being defined as the portion of air
delivered into the bypass duct divided by the amount of air delivered into the
compressor section, with the bypass ratio being greater than about 6.0.
2 0
13. The gas turbine engine as recited in claim 9, wherein the ratio is greater than
or equal to about 2.0 lbf/inch3.
14. The gas turbine engine as recited in claim 9, wherein the ratio is greater than
25 or equal to about 4.0 lbf/inch3.
1 5. A gas turbine engine comprising:
a fan including a plurality of fan blades rotatable about an axis;
a compressor section;
a combustor in fluid communication with the compressor section;
a fan drive turbine in communication with the combustor;
a gear system collfigured to provide a speed reduction between the fan drive
turbine and the fan, and to transfer power input from the fan drive turbine to the fan
at an efficiency greater than about 98% and less than 100%;
a mount flexibly supporting portions of the gear system, the mount extending
5 from a static structure of the engine to accommodate at least radial movement
between the gear system and the static structure; and
a lubrication system configured to provide lubricant to the gear system and to remove
thermal energy from the gear system.
10 16. The gas turbine engine as recited in claim 15, wherein the lubrication system
includes a capacity for removing an amount of energy that is greater than zero and
less than about 2% of energy input into the gear system during operation of the gas
turbine engine.
15 17. The gas turbine engine as recited in claim 15, wherein said fan delivers a
portion of air into a bypass duct, and a bypass ratio being defined as the portion of air
delivered into the bypass duct divided by the amount of air delivered into the
compressor section, with the bypass ratio being greater than about 6.0.
20 18. The gas turbine engine as recited in claim 15, wherein the mount includes a
load limiter for limiting movement of the gear system responsive to an unbalanced
condition.
19. The gas turbine engine as recited in claim 17, wherein the bypass ratio is
25 greater than about 10.0.
20. The gas turbine engine as recited in claim 15, wherein a pressure ratio across
the fan drive turbine is greater than about 5: 1.