U.S. patent application number 16/815737 was filed with the patent office on 2021-03-18 for secondary fuel flow demand fuel pumping system.
The applicant listed for this patent is United Technologies Corporation. Invention is credited to Peter Cocks, Michael K. Ikeda.
Application Number | 20210079848 16/815737 |
Document ID | / |
Family ID | 1000005292562 |
Filed Date | 2021-03-18 |
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United States Patent
Application |
20210079848 |
Kind Code |
A1 |
Cocks; Peter ; et
al. |
March 18, 2021 |
SECONDARY FUEL FLOW DEMAND FUEL PUMPING SYSTEM
Abstract
A fuel system for a gas turbine engine includes a main fuel pump
generating a main fuel flow into a main fuel passage and a
secondary pump generating a secondary fuel flow into a secondary
flow passage. A first control valve is disposed in a passage
between the main fuel passage and the secondary flow passage. The
first control valve selectively directs an excess portion of the
main fuel flow to the secondary flow passage to provide at least a
portion of the secondary fuel flow.
Inventors: |
Cocks; Peter; (South
Glastonbury, CT) ; Ikeda; Michael K.; (West Hartford,
CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
United Technologies Corporation |
Farmington |
CT |
US |
|
|
Family ID: |
1000005292562 |
Appl. No.: |
16/815737 |
Filed: |
March 11, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62821066 |
Mar 20, 2019 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02C 7/36 20130101; F05D
2240/35 20130101; F05D 2220/32 20130101; F02C 7/236 20130101; F02C
9/26 20130101; F04D 13/06 20130101; F02C 3/13 20130101 |
International
Class: |
F02C 7/236 20060101
F02C007/236; F02C 9/26 20060101 F02C009/26; F02C 3/13 20060101
F02C003/13; F02C 7/36 20060101 F02C007/36; F04D 13/06 20060101
F04D013/06 |
Claims
1. A fuel system for a gas turbine engine comprising: a main fuel
pump generating a main fuel flow into a main fuel passage; a
secondary pump generating a secondary fuel flow into a secondary
flow passage; and a first control valve disposed in a passage
between the main fuel passage and the secondary flow passage,
wherein the first control valve selectively directs an excess
portion of the main fuel flow to the secondary flow passage to
provide at least a portion of the secondary fuel flow.
2. The fuel system as recited in claim 1, including a boost pump
drawing fuel from a fuel supply and directing fuel flow to the main
fuel pump and the secondary pump.
3. The fuel system as recited in claim 2, including an electric
motor driving the secondary pump.
4. The fuel system as recited in claim 2, including a second
control valve disposed between the boost pump and the secondary
pump, the second control valve selectively reducing fuel flow to
the secondary pump in response to communication of excess fuel flow
from the main passage to the secondary flow passage.
5. The fuel system as recited in claim 4, including a common shaft
driving each of the boost pump, main pump and secondary pump.
6. The fuel system as recited in claim 5, including a selectively
actuated clutch for decoupling the secondary pump from the common
shaft.
7. The fuel system as recited in claim 5, wherein the main pump is
disposed between the boost pump and the secondary pump.
8. The fuel system as recited in claim 1, wherein the secondary
pump provides the secondary fuel flow to an ejector pump disposed
within a fuel tank.
9. The fuel system as recited in claim 1, wherein the secondary
pump provides the secondary fuel flow to operate an actuator.
10. The fuel system as recited in claim 1, wherein the main pump
comprises a constant volume gear pump.
11. A gas turbine engine comprising: a fan rotatable within a fan
nacelle; a core engine including a compressor communicating
compressed air to a combustor where compressed air is mixed with
fuel and ignited to generate a high-energy gas flow expanded
through a turbine; an accessory gearbox driven by a mechanical link
to the turbine; and a fuel system including; a fuel tank including
an ejector pump; a main fuel pump drawing fuel from the fuel tank
and generating a main fuel flow into a main fuel passage; a
secondary pump generating a secondary fuel flow within a secondary
flow passage in communication with the ejector pump; and a first
control valve disposed in a passage between the main fuel passage
and the secondary flow passage, wherein the first control valve
selectively directs an excess portion of the main fuel flow to the
secondary flow passage to provide the secondary fuel flow.
12. The gas turbine engine as recited in claim 11, including a
boost pump drawing fuel from the fuel tank and directing fuel flow
to the main fuel pump and the secondary pump.
13. The gas turbine engine as recited in claim 12, including a
second control valve disposed between the boost pump and the
secondary pump, the second control valve selectively shutting off
fuel flow to the secondary pump in response to communication of
excess fuel flow from the main passage to the secondary flow
passage.
14. The gas turbine engine as recited in claim 12, including a
common shaft driving each of the boost pump, main pump and
secondary pump.
15. The gas turbine engine as recited in claim 14, wherein the
common shaft is driven by an output of the accessory gearbox.
16. The gas turbine engine as recited in claim 14, including a
selectively actuated clutch for decoupling the secondary pump from
the common shaft.
17. The gas turbine engine as recited in claim 12, including an
electric motor for driving the secondary pump.
18. A method of supplying fuel to a combustor of a gas turbine
engine comprising: generating a main fuel flow with a main fuel
pump and communicating the main fuel flow to a main fuel passage in
communication with the combustor; generating a secondary flow with
a secondary pump and communicating the secondary flow to a
secondary flow passage; and bypassing an excess fuel flow from the
main fuel passage into the secondary flow passage to generate at
least a portion of the secondary flow.
19. The method as recited in claim 18, including supplying fuel
flow from a boost pump to the secondary pump and the main fuel pump
during a first engine operating condition requiring a first fuel
flow and stopping fuel flow to the secondary fuel pump during a
second engine operating condition requiring a second fuel flow,
wherein the second fuel flow includes the excess fuel flow.
20. The method as recited in claim 18, including deactivating the
secondary fuel pump such that the secondary fuel pump stops running
in response to excess fuel flow from the main fuel passage
generating a predefined fuel flow that is sufficient to meet
secondary fuel flow demands.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 62/821,066 which was filed on Mar. 20, 2019.
BACKGROUND
[0002] 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.
[0003] A mechanical pump driven by an accessory gearbox or other
rotating shaft of the engine provides fuel flow at a predefined
pressure to the combustor. The mechanical pump is reliable and
supplies fuel in proportion to engine speed. The minimum capacity
of the mechanical pump is sized such that sufficient fuel is
provided for high power and low power conditions. Excess fuel not
needed is recirculated back to the fuel tank. The energy used on
the excess fuel is essentially lost, reducing the overall
efficiency of the engine, and reducing the ability to use fuel as a
heat sink for thermal management.
[0004] Turbine engine manufacturers continuously seek improvements
to engine performance including improvements to thermal, transfer
and propulsive efficiencies.
SUMMARY
[0005] A fuel system for a gas turbine engine according to an
exemplary embodiment of this disclosure includes, among other
possible things, a main fuel pump generating a main fuel flow into
a main fuel passage and a secondary pump generating a secondary
fuel flow into a secondary flow passage. A first control valve is
disposed in a passage between the main fuel passage and the
secondary flow passage. The first control valve selectively directs
an excess portion of the main fuel flow to the secondary flow
passage to provide at least a portion of the secondary fuel
flow.
[0006] In a further embodiment of the foregoing fuel system for a
gas turbine engine, a boost pump is drawing fuel from a fuel supply
and directing fuel flow to the main fuel pump and the secondary
pump.
[0007] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, an electric motor drives the secondary
pump.
[0008] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, a second control valve is disposed
between the boost pump and the secondary pump. The second control
valve selectively reduces fuel flow to the secondary pump in
response to communication of excess fuel flow from the main passage
to the secondary flow passage.
[0009] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, a common shaft drives each of the boost
pump, main pump and secondary pump.
[0010] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, a selectively actuated clutch is for
decoupling the secondary pump from the common shaft.
[0011] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, the main pump is disposed between the
boost pump and the secondary pump.
[0012] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, the secondary pump provides the secondary
fuel flow to an ejector pump disposed within a fuel tank.
[0013] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, the secondary pump provides the secondary
fuel flow to operate an actuator.
[0014] In another embodiment of any of the foregoing fuel systems
for a gas turbine engine, the main pump comprises a constant volume
gear pump.
[0015] A gas turbine engine according to an exemplary embodiment of
this disclosure includes, among other possible things, a fan
rotatable within a fan nacelle, and a core engine that includes a
compressor communicating compressed air to a combustor where
compressed air is mixed with fuel and ignited to generate a
high-energy gas flow expanded through a turbine. An accessory
gearbox driven by a mechanical link to the turbine. A fuel system
includes a fuel tank with an ejector pump and a main fuel pump
drawing fuel from the fuel tank and generating a main fuel flow
into a main fuel passage. A secondary pump generates a secondary
fuel flow within a secondary flow passage in communication with the
ejector pump. A first control valve is disposed in a passage
between the main fuel passage and the secondary flow passage. The
first control valve selectively directs an excess portion of the
main fuel flow to the secondary flow passage to provide the
secondary fuel flow.
[0016] In a further embodiment of any of the foregoing gas turbine
engines, a boost pump draws fuel from the fuel tank and directing
fuel flow to the main fuel pump and the secondary pump.
[0017] In another embodiment of any of the foregoing gas turbine
engines, a second control valve is disposed between the boost pump
and the secondary pump. The second control valve selectively shuts
off fuel flow to the secondary pump in response to communication of
excess fuel flow from the main passage to the secondary flow
passage.
[0018] In another embodiment of any of the foregoing gas turbine
engines, a common shaft drives each of the boost pump, main pump
and secondary pump.
[0019] In another embodiment of any of the foregoing gas turbine
engines, the common shaft is driven by an output of the accessory
gearbox.
[0020] In another embodiment of any of the foregoing gas turbine
engines, a selectively actuated clutch is for decoupling the
secondary pump from the common shaft.
[0021] In another embodiment of any of the foregoing gas turbine
engines, an electric motor is for driving the secondary pump.
[0022] A method of supplying fuel to a combustor of a gas turbine
engine according to an exemplary embodiment of this disclosure
includes, among other possible things, generating a main fuel flow
with a main fuel pump and communicating the main fuel flow to a
main fuel passage in communication with the combustor, and
generating a secondary flow with a secondary pump and communicating
the secondary flow to a secondary flow passage. An excess fuel flow
bypasses from the main fuel passage into the secondary flow passage
to generate at least a portion of the secondary flow.
[0023] In a further embodiment of the foregoing method of supplying
fuel to a combustor of a gas turbine engine, fuel flow is supplied
from a boost pump to the secondary pump and the main fuel pump
during a first engine operating condition requiring a first fuel
flow. Fuel flow to the secondary fuel pump is stopped during a
second engine operating condition requiring a second fuel flow. The
second fuel flow includes the excess fuel flow.
[0024] In another embodiment of any of the foregoing methods of
supplying fuel to a combustor of a gas turbine engine, the
secondary fuel pump is deactivated such that the secondary fuel
pump stops running in response to excess fuel flow from the main
fuel passage, generating a predefined fuel flow that is sufficient
to meet secondary fuel flow demands.
[0025] 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.
[0026] 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
[0027] FIG. 1 is a schematic view of an example gas turbine
engine.
[0028] FIG. 2 is a schematic view of an example fuel system
embodiment.
[0029] FIG. 3 is a schematic view of another example fuel system
embodiment.
[0030] FIG. 4 is a schematic view of yet another example fuel
system embodiment.
DETAILED DESCRIPTION
[0031] 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.
[0032] 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 the
various bearing systems 38 may alternatively or additionally be
provided at different locations, and the location of bearing
systems 38 may be varied as appropriate to the application.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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).
[0037] 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.
[0038] Fuel is delivered to the combustor 56 by a fuel system 62.
The example fuel system 62 includes a boost pump 68 that draws fuel
from a fuel tank 66. The boost pump 68 communicates fuel at a low
pressure to a main pump 70. The main pump 70 increases the pressure
of a fuel flow 64 and communicates that fuel to the combustor 56. A
heat exchanger 82 may be included to use the fuel flow 64 as a heat
sink to cool flows from other engine systems schematically
indicated at 84. The engine system 84 may be any system that
generates heat such as for example a lubricant system. Lubricant
from the lubricant system is cooled by fuel flow 64 that is then
communicated to the combustor 56.
[0039] The main pump 70 and boost pump 68 are mechanically driven
by a connection to one of the inner and outer shafts 40, 50. In
this example, an accessory gearbox 78 is driven through a tower
shaft 80 by the outer shaft 50. The accessory gearbox 78 includes
outputs that drive the boost pump 68 and the main pump 70. It
should be appreciated, that other drive connections could be
utilized and are within the contemplation and scope of this
disclosure.
[0040] The example fuel system 62 further includes a secondary pump
72 that may also be driven by the accessory gearbox 78. The
secondary pump 72 generates a secondary fuel flow 88 that is
utilized as motive flow to drive an ejector pump 86 within the fuel
tank 66. The ejector pump 86 provides for movement of fuel within
the fuel tank 66 to prevent starvation of fuel to the boost pump
68. The secondary flow 88 may also be utilized for other devices
that utilize fuel flow for actuation.
[0041] The main pump 70 is sized to provide flow for high power
(such as take-off and climb) and low power (such as start) engine
operating conditions. However, most engine operating time is
conducted at intermediate power conditions such as cruise or
decent. Accordingly, during the intermediate power conditions, some
portion of fuel flow that is not needed is recirculated to a
location upstream from the main pump 70 or back to the fuel tank
66. Work that is performed to increase the fuel flow pressure is
wasted with regard to the recirculated fuel flow and this work also
increases the recirculated fuel flow temperature. The recirculated
fuel flow is also hotter than fuel from the fuel tank 66 and may
reduce the available heat acceptance capacity.
[0042] The disclosed example fuel system 62 utilizes the excess
fuel flow to provide at least a portion, if not all of the
secondary flow. Once the engine begins operation at a lower power
level where a portion of the fuel flow 64 is not needed, control
valves 74 and 76 will be actuated to stop flow to the secondary
pump 72 and communicate excess flow to provide the desired
secondary flow 88. Utilizing the excess flow to provide at least a
portion of the secondary flow 88 reduces engine work extraction and
reduces the generation of waste heat thereby improving the heat
acceptance capability of the fuel while also increasing overall
engine operating efficiency.
[0043] Referring to FIG. 2 with continued reference to FIG. 1, the
example fuel system 62 is schematically shown and includes the
boost pump 68, main pump 70 and secondary pump 72 all driven by a
common shaft 94. In one disclosed example, the shaft 94 is an
output of the accessory gearbox 78 that rotates about a common axis
96. Each of the boost pump 68, main pump 70 and the secondary pump
72 are constant volume mechanical gear pumps of a known
configuration.
[0044] The main fuel pump 70 includes an inlet 102 and an outlet
104 and generates the main fuel flow 64 into a main fuel passage
114. The secondary pump 72 includes an inlet 106 and an outlet 108
and generates the secondary fuel flow 88 within a secondary flow
passage 118. A control valve 76 is disposed in a bypass passage 120
between the main fuel passage 114 and the secondary flow passage
118. The control valve 76 selectively directs an excess fuel flow
110 of the main fuel flow 64 to the secondary flow passage 118 to
provide at least a portion of the secondary fuel flow 88. A
controller 92 is in communication with the control valves 74, 76 to
govern operation and direct fuel flow according to engine operating
conditions.
[0045] The boost pump 68 draws fuel from the fuel tank 66 and
directs boost fuel flow 98 through an outlet 100 into a boost
passage 116. The boost passage 116 is in communication with the
inlet 102 of the main pump 70 and the inlet 106 of the secondary
pump 72. The control valve 74 is disposed between the boost pump 68
and the secondary pump 72 to control flow to the secondary pump 72.
The control valve 74 selectively shuts off fuel flow 98 to the
secondary pump 72 in response to communication of excess fuel flow
from the main passage 114 to the secondary flow passage 118. The
secondary pump 72 is thereby starved of fuel and runs dry while the
excess fuel flow from the main pump 70 is used to generate the
secondary flow 88.
[0046] The secondary flow 88 is supplied as motive flow to the
ejector pump 86 disposed within the fuel tank 66. The ejector pump
86 provides for balancing the amount of fuel within the fuel tank
66 as well as maintaining sufficient fuel at an outlet to the boost
pump 68. The example ejector pump 86 is disclosed as an example of
how the secondary flow 88 is utilized. It should be appreciated
that other uses for the secondary fuel flow 88 are within the
contemplation of this disclosure. For example, the secondary fuel
flow 88 may be communicated to actuators 112 that use the
pressurized fuel flow for operation.
[0047] During initial engine operation at higher power levels, all
the fuel from the main pump 70 is utilized by the combustor 56 to
generate engine power. At the higher power levels, the control
valve 76 is off to prevent flow through the bypass passage 120. The
control valve 74 is open to communicate fuel flow 98 to the
secondary pump 72. The secondary pump 72 generates the secondary
flow 88 within the secondary passage 118. The secondary flow 88 is
communicated to the ejector pump 86 and/or the actuators 112. Other
control valves or systems may be included to operate the actuators
112 and ejector pump 86.
[0048] At the intermediate power operating conditions where excess
main pump flow exists, the control valve 76 will open to direct
excess fuel flow 110 through the bypass passage 120 to the
secondary flow passage 118. The control valve 76 may be an on/off
valve or a proportional valve to tailor the flow of fuel from the
main passage 114 to engine fuel demand. The shutoff valve 74 is
concurrently operated to reduce and/or stop flow to the secondary
pump 72. The shutoff valve 74 may also be an on/off valve or a
proportional valve. As the excess fuel flow 110 from the main pump
70 increases, the amount of flow needed from the secondary pump 72
will decrease and eventually stop. Accordingly, excess fuel flow
from the main pump 70 will take over the generation of the
secondary flow 88 and the secondary pump 72 will run dry.
[0049] Upon a subsequent increase in fuel demand, the control
valves 74, 76 will operate to again communicate flow to the
secondary pump 72 and stop flow through the bypass passage 120.
[0050] Referring to FIG. 3, with continued reference to FIG. 1,
another example fuel system embodiment is shown schematically and
indicated at 62'. The example fuel system 62' includes a clutch 90
that is operable by the controller 92. The operation of the fuel
system 62' is as disclosed above with the addition of shutting down
the secondary pump 72 when not receiving fuel flow. The clutch 90
enables the secondary pump 72 to be shut down to reduce energy use
and prevent dry running when the main pump 70 is generating
sufficient excess fuel flow to provide the secondary flow 88.
[0051] Referring to FIG. 4, with continued reference to FIG. 1,
another example fuel system 62''. The example fuel system 62''
includes an electric motor 122 that is operable by the controller
92. The operation of the fuel system 62'' is as disclosed above
with the addition of shutting down the secondary pump 72 through
control of the electric motor 122 when not receiving fuel flow. The
electric motor 122 enables the secondary pump 72 to be shut down to
reduce energy use and prevent dry running when the main pump 70 is
generating sufficient excess fuel flow to provide the secondary
flow 88. Moreover, the electric motor 122 enables diving the pump
72 at a variable speed to match the secondary flows needed for
motive flow and to power the actuators 112.
[0052] Accordingly, the disclosed fuel systems utilize excess fuel
flow to generate the required secondary flow to reduce excess heat
within the fuel and increase engine efficiency.
[0053] 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.
* * * * *