U.S. patent application number 10/679262 was filed with the patent office on 2004-07-22 for control system.
Invention is credited to Garner, Stephen G., Horswill, Michael A..
Application Number | 20040139727 10/679262 |
Document ID | / |
Family ID | 9945994 |
Filed Date | 2004-07-22 |
United States Patent
Application |
20040139727 |
Kind Code |
A1 |
Horswill, Michael A. ; et
al. |
July 22, 2004 |
Control system
Abstract
A control apparatus 50 for a gas turbine engine for an aircraft
includes engine control means 52 forming part of an outer fuel
control loop and fuel control means/overthrust protector 76 forming
part of an inner fuel control loop. Overthrust protection is
provided within each of the engine control means 52 and the fuel
control means/overthrust protector 76, which are powered and housed
separately. Thus, a failure within one of these systems could not
result in overthrust and demonstrably reliable overthrust
protection is provided within a single channel.
Inventors: |
Horswill, Michael A.;
(Chester, GB) ; Garner, Stephen G.; (Derby,
GB) |
Correspondence
Address: |
MANELLI DENISON & SELTER
2000 M STREET NW SUITE 700
WASHINGTON
DC
20036-3307
US
|
Family ID: |
9945994 |
Appl. No.: |
10/679262 |
Filed: |
October 7, 2003 |
Current U.S.
Class: |
60/233 |
Current CPC
Class: |
F05D 2270/094 20130101;
F02C 9/46 20130101; F02C 9/28 20130101; F02C 9/48 20130101 |
Class at
Publication: |
060/233 |
International
Class: |
F02K 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 16, 2002 |
GB |
0224039.8 |
Claims
I claim:
1. Control apparatus for an aircraft engine, the control apparatus
including: engine control means including; means for receiving a
signal representative of a desired thrust for the engine; means for
receiving a signal representative of the actual thrust of the
engine; and means for analysing the above signals and for producing
a signal representative of a desired fuel flow for the engine; and
fuel control means including: means for receiving a signal
representing a desired fuel flow; means for providing a signal to a
fuel monitoring means for regulating the flow of fuel to the
engine; means for receiving a feedback signal from the fuel
monitoring means; and means for analysing the signal representing
desired fuel flow and the feedback signal from the fuel monitoring
means and adjusting the signal to the fuel monitoring means for
achieving the desired fuel flow; wherein the engine control means
and the fuel control means are separately powered such that a
failure of the power supply to one of them will not necessarily
result in a failure of the power supply to the other.
2. Control apparatus according to claim 1, wherein the engine
control means and the fuel control means are physically
separated.
3. Control apparatus according to claim 2, wherein the engine
control means and the fuel control means are provided within
separate housings allowing limited communication of data
therebetween.
4. Control apparatus according to claim 1, further including
selection means for receiving first and second signals each
representing desired fuel flow and selecting the lower of the
two.
5. Control apparatus according to claim 4, wherein the fuel control
means receives the selected lower desired fuel flow signal.
6. Control apparatus according to claim 4, wherein the first signal
representing desired fuel flow is produced by the engine control
means.
7. Control apparatus according to claim 4, wherein the second
signal representing desired fuel flow is produced by a protector
means, which is powered separately from the engine control
means.
8. Control apparatus according to claim 7, wherein the protector
means includes means for receiving a signal representing engine
thrust and a signal indicating whether a throttle of the aircraft
is idle or in reverse and the thrust reversers not deployed and
means for calculating a maximum desired fuel flow demand
appropriate for the above conditions.
9. Control apparatus according to claim 8 wherein the signal
representing engine thrust comprises a signal reprsenting engine
speed.
10. Control apparatus according to claim 1, wherein the engine
control means includes means for determining whether the
comparative values of the signals representing actual thrust of the
engine and the desired thrust of the engine suggest overthrust and
means for reducing or preventing fuel flow to the engine in such
circumstances.
11. Control apparatus according to claim 1, further including fuel
monitoring means which may be controlled by the signal from the
fuel control means.
12. Control apparatus according to claim 11, wherein the fuel
monitoring means comprises a fuel metering valve which may be
adjusted by a torque motor.
13. Control apparatus according to claim 12, wherein the fuel
metering valve position controls the fuel flow to burners of the
combustor of the gas turbine engine, thereby controlling the thrust
of the engine.
Description
[0001] The invention relates to a control apparatus for protecting
against overthrust in an engine for an aircraft.
[0002] Overthrust is a condition in which an aircraft engine
produces excessive thrust which cannot be alleviated by movement of
the throttle. The condition can occur in respect of thrust level or
thrust direction (where the engine produces forward thrust even
though the thrust reversers have been commanded to deploy but have
failed).
[0003] Overthrust is a condition at the engine level that leads to
an event at the aircraft level which is defined as catastrophic.
This means that new control systems are obliged to be designed such
that a single physical or functional failure cannot result in
overthrust and such that there is an extremely remote likelihood of
the occurrence of overthrust due to multiple failures.
[0004] In a typical dual channel control system, it is difficult to
demonstrate satisfactorily that a single failure could not produce
overthrust. This is primarily due to the lack of adequate
independence between control of thrust and protection against
overthrust.
[0005] In view of the above, an aircraft cannot safely operate on a
single channel because it is necessary that each channel
effectively cover for any faults in the other channel.
[0006] In a single channel control system, it is not possible to
demonstrate that a single failure could not produce overthrust.
[0007] According to the invention there is provided a control
apparatus for an aircraft engine, the control apparatus
including:
[0008] engine control means including:
[0009] means for receiving a signal representative of a desired
thrust for the engine;
[0010] means for receiving a signal representative of the actual
thrust of the engine; and
[0011] means for analysing the above signals and for producing a
signal representative of a desired fuel flow for the engine;
and
[0012] fuel control means including:
[0013] means for receiving a signal representing a desired fuel
flow;
[0014] means for providing a signal to a fuel monitoring means for
regulating the flow of fuel to the engine;
[0015] means for receiving a feedback signal from the fuel
monitoring means; and
[0016] means for analysing the signal representing desired fuel
flow and the feedback signal from the fuel monitoring means and
adjusting the signal to the fuel monitoring means, for achieving
the desired fuel flow;
[0017] wherein the engine control means and the fuel control means
are separately powered such that a failure of the power supply to
one of them will not necessarily result in a failure of the power
supply to the other.
[0018] Preferably the engine control means and the fuel control
means are also physically separated. The physical separation may
take the form of a physical barrier such as a metal plate. The
engine control means and the fuel control means may be provided
within separate housings allowing limited communication of data
therebetween.
[0019] The control apparatus may further include selection means
for receiving first and second signals each representating a
desired fuel flow and selecting the lower of the two. The fuel
control means may receive the selected lower desired fuel flow
signal.
[0020] The first signal representing desired fuel flow may be
produced by the engine control means.
[0021] The second signal representing desired fuel flow may be
produced by a protector means. The protector means is preferably
powered separately from the engine control means. The protector
means preferably includes means for receiving a signal representing
engine thrust, which may comprise a single representing engine
speed, and a signal indicating whether a throttle of the engine is
at idle or in reverse and the thrust reversers not deployed. The
protector means preferably further includes means for calculating a
maximum desired fuel flow demand appropriate for the above
conditions.
[0022] The signal representing desired thrust, received by the
engine controller, may be a signal indicating a desired engine
speed, for example a desired low pressure shaft speed.
Alternatively, the signal may be a pressure signal and/or a
temperature signal.
[0023] The signal representing actual thrust, received by the
engine controller, may be indicative of engine speed, for example
low pressure shaft speed, or of pressure and/or temperature within
the gas turbine engine.
[0024] The engine control means may include means for determining
whether the comparative values of the signals representing actual
thrust of the engine and the desired thrust of the engine suggest
overthrust, possibly caused by failure of the fuel control means.
Preferably the engine control means includes means for reducing or
preventing fuel flow to the engine in such circumstances. These
means may include means for closing a shut-off valve. The engine
control means may electrically drive the shut-off valve.
[0025] The control apparatus may further include fuel monitoring
means, which may comprise a fuel metering valve, the position of
which may be controlled by the signal from the fuel control means.
The protector means may electrically drive the fuel metering valve.
The fuel metering valve may be adjusted by a torque motor. The
control apparatus may further include means for monitoring the
position of the fuel metering valve. These means may include a
linear variable differential transformer, which may produce a
feedback signal representative of the position of the fuel metering
valve. This feedback signal may be the feedback signal received by
the fuel control means.
[0026] The fuel metering valve position preferably controls the
fuel flow to the engine, thereby controlling the thrust of the
engine.
[0027] According to the invention there is further provided an
aircraft including a control apparatus as defined in any of the
preceding ten paragraphs.
[0028] An embodiment of the invention will be described for the
purpose of illustration only with reference to the accompanying
drawings in which:--
[0029] FIG. 1 is a diagrammatic cross-section through a gas turbine
engine suitable for control by a system according to the
invention;
[0030] FIG. 2 is a block diagram representating a single channel,
prior art control system;
[0031] FIG. 3 is a highly simplified block diagram representating a
single channel control system according to the invention; and
[0032] FIG. 4 is a block diagram representating a single channel
control system according to the invention, illustrating the
interaction between the inner and outer fuel flow control loops and
engine thrust in detail but omitting the interaction between the
engine controller and the shut off valve.
[0033] With reference to FIG. 1 a ducted fan gas turbine engine
generally indicated at 10 comprises, in axial flow series, an air
intake 12, a propulsive fan 14, an intermediate pressure compressor
16, a high pressure compressor 18, combustion equipment 20, a high
pressure turbine 22, an intermediate pressure turbine 24, a low
pressure turbine 26 and an exhaust nozzle 28.
[0034] The gas turbine engine 10 works in the conventional manner
so that air entering the intake 12 is accelerated by the fan 14 to
produce two air flows, a first air flow into the intermediate
pressure compressor 16 and a second airflow which provides
propulsive thrust. The intermediate pressure compressor 16
compresses the air flow directed into it before delivering the air
to the high pressure compressor 18 where further compression takes
place.
[0035] The compressed air exhausted from the high pressure
compressor 18 is directed into the combustion equipment 20 where it
is mixed with fuel and the mixture combusted. The resultant hot
combustion products then expand through and thereby drive the high,
intermediate and low pressure turbines 22, 24 and 26 before being
exhausted through the nozzle 28 to provide additional propulsive
thrust. The high, intermediate and low pressure turbines 22, 24 and
26 respectively drive the high and intermediate pressure
compressors 16 and 18 and the fan 14 by suitable interconnecting
shafts.
[0036] The thrust produced by the engine is controlled by adjusting
the flow of fuel to burners (not illustrated) of the combustion
equipment 20. FIG. 2 illustrates a known engine control system 50,
including engine control means 52 and fuel control means 54.
[0037] Referring to FIG. 2 the engine controller 52 has inputs
including a throttle position 56 and air data and rating 58. These
are the basic inputs which enable the engine controller to
determine the fuel flow required by the engine. The engine
controller also includes a throttle at idle input 60, this being a
simple on/off signal indicating whether or not the throttle is at
idle, and a low pressure shaft speed signal 62. The function of
these signals will be described below.
[0038] The fuel controller 54 includes a fuel metering valve
("FMV") which is able to control the amount of fuel being passed to
the burners of the aircraft engine combustor. The fuel controller
also includes a shut-off valve ("SOV") 66, being a simple on/off
valve which is open during operation but which is moved into the
closed position at the end of a flight or, for example, in the
event of a malfunction of the fuel metering valve.
[0039] Various signals pass between the engine controller and the
fuel controller. These include an FMV demand signal 68 and an FMV
feedback signal 70. In addition an SOV demand signal 72 and an SOV
feedback signal 74 pass between the engine controller and the
shut-off valve.
[0040] In operation, the engine controller 52 analyses the throttle
position and the air data and rating to determine the rate of fuel
required by the engine. The engine controller produces a resulting
FMV demand signal 68 which passes to the fuel metering valve 64
within the fuel controller 54. The fuel metering valve is moved to
an appropriate position for this rate of fuel and the fuel is then
supplied to the burners, via the shut-off valve 66 which is open in
operation. The FMV feedback signal is continually monitored by the
engine controller and the FMV demand signal adjusted
accordingly.
[0041] The control system 50 has certain adaptations to protect
against overthrust. As described previously, overthrust is a
condition in which the engine produces excessive thrust which
cannot be alleviated by movement of the throttle. The engine
controller checks the low pressure shaft speed signal 62 and the
throttle at idle signal 60. If the throttle is at idle, the low
pressure shaft speed should respond to the throttle and should be
reducing or below a threshold and not increasing and above a
threshold. The threshold is idle plus a margin. If the low pressure
shaft speed is not reducing, this indicates an overthrust situation
and the engine controller therefore sends a signal along line 72
demanding the shut-off valve to move into the closed position. This
stops fuel flowing to the burners.
[0042] It may be seen that in the above system, the engine
controller 52 provides the FMV demand signal 68 and also the SOV
demand signal 72. Therefore an error in the engine controller which
resulted in overthrust could theoretically also result in the
engine controller not providing the SOV demand signal correctly.
Thus, it cannot be demonstrated that a single failure in the above
system, for example in the power supply to the engine controller,
could not cause an overthrust situation.
[0043] FIGS. 3 and 4 illustrate a control system 50 according to
the invention, FIG. 3 providing abroad overview and FIG. 4 being
more detailed but omitting the interaction between the engine
controller and the fuel controller sov. Referring initially to FIG.
3, it may be seen that the engine controller 52 is provided with
control system inputs 58, a low pressure shaft speed signal 62 and
a throttle position signal 56. The engine controller 52 may be
regarded as forming part of an outer fuel control loop.
[0044] An overthrust protector 76 includes a throttle at idle input
60 and a low pressure shaft speed signal 63. The low pressure shaft
speed signal 63 for the overthrust protector is independent of the
low pressure shaft speed signal 62 of the engine controller. The
overthrust protector 76 may be regarded as forming part of an inner
fuel control loop. The inner fuel control loop includes an FMV
demand signal 68, passing between the overthrust protector 76 and a
fuel metering valve 64, and an FMV feedback signal 70 passing from
the fuel metering valve 64 to the overthrust protector 76.
[0045] The fuel metering valve 64 is provided within fuel control
means 54, which also includes a shut-off valve 66. The shut-off
valve is controlled from the engine controller 52 via an SOV demand
signal 72.
[0046] In operation, the engine controller 52 monitors the throttle
position signal 56 and the low pressure shaft speed signal 62,
together with the control system inputs 58, to provide a signal 78
representative of the fuel flow required by the engine. This signal
passes to the overthrust protector 76. In normal operation, the
fuel flow demand signal 78 is translated by the overthrust
protector 76 into an FMV demand signal 68. However, the overthrust
protector 76 also monitors the throttle at idle signal 60 and its
low pressure shaft speed signal 63. If the throttle is at idle, the
low pressure shaft speed should be decreasing or below a threshold,
as mentioned previously. If this is not the case, the overthrust
protector detects an overthrust situation and overrides the fuel
flow demanded by the engine controller. In this case the overthrust
protector 76 provides an FMV demand signal in line with a
reasonable demand based on the low pressure shaft speed and
throttle at idle signal.
[0047] Should there be a failure in the overthrust protector 76,
resulting in overthrust, the engine controller 52 will detect this
by monitoring the low pressure shaft speed signal 62 and the
throttle position signal 56. If the throttle is at idle, the low
pressure shaft speed should be decreasing or below a threshold and,
if this is not the case, the engine controller is able to detect
overthrust and send a signal down line 72 to operate the shut-off
valve. This therefore prevents fuel from flowing to the
burners.
[0048] FIG. 4 illustrates part of the above system in somewhat more
detail. It may be seen that the engine controller 52 is provided
with a speed or pressure demand signal 80 resulting from a thrust
demand, represented by the arrow 82. This is generally equivalent
to the throttle position signal 56 in FIG. 3. The engine controller
52 also receives a speed or pressure voltage signal 84 which it
converts into a speed or pressure feedback signal 86. The speed or
pressure voltage signal is derived from a speed or pressure sensor
88 provided within the aircraft engine.
[0049] The engine controller uses the speed or pressure demand
signal 80 and the speed or pressure feedback signal 86 to calculate
a fuel flow demand, which is output as a first fuel flow demand
signal 78.
[0050] The first fuel flow demand signal 78 is input into a
comparitor 92 within the overthrust protector 76. The comparitor 92
is also provided with a second fuel flow demand signal 94
indicative of a fuel flow limit. The second fuel flow demand signal
94 is provided by the overthrust protector. The overthrust
protector includes a throttle at idle signal 96, a speed at idle
signal 98 and a speed at red line signal 100. In addition, a speed
feedback signal 102 is provided, this resulting from a speed signal
voltage 104 in turn derived from a speed sensor 106 provided within
the engine. The overthrust protector is able to compare these
various signals to provide a maximum fuel flow demand which the
engine controller should be requesting for these conditions. This
is the fuel flow demand signal 94.
[0051] The comparitor 92 chooses the lower one of the two fuel flow
demand signals 78 and 94. Therefore, provided that the fuel flow
demand signal 78 (produced by the engine controller 52) is below
the perceived maximum fuel flow demand signal 90 (as calculated by
the overthrust protector 76), the fuel flow demand signal 78 is
chosen by the comparitor. The fuel flow demand signal 78 is then
used by the overthrust protector to determine an FMV demand signal
68. The FMV demand signal 68 is compared with an FMV position
feedback signal 74 an FMV position error which is used to control a
drive current for a fuel metering valve torque motor 108. The
torque motor 108 drives the fuel metering valve 64 into a desired
position. A fuel metering valve linear variable differential
transformer 110 converts the position of the fuel metering valve
into a voltage signal 112 which is used to derive the FMV feedback
signal 74. This provides a closed loop control for the fuel
metering valve position.
[0052] The position of the fuel metering valve 64 dictates the fuel
flow to the burners of the combustion equipment (indicated by 114)
and thereby controls the thrust of the aircraft engine. The thrust
in turn affects the speed or pressure sensor 88 and the speed
sensor 106.
[0053] It will be appreciated that if the engine controller 52
malfunctions and demands too high a fuel flow along the fuel flow
demand signal line 78, this will be overridden by the fuel flow
demand signal 94 (which represents a fuel flow limit) if
appropriate. In this way, overthrust protection is built into this
system.
[0054] Should the overthrust protector 76 malfunction, the engine
controller 52 is able to detect this by monitoring the low pressure
shaft speed and the signals representative of demanded thrust. If
these signals indicate an overthrust situation, the engine
controller sends a signal to the shut-off valve 66 (not illustrated
in FIG. 4) in order to stop fuel passing to the burners.
[0055] The circuitry making up the engine controller 52 is powered
by a separate power supply to the circuitry making up the
overthrust protector 76. In addition, the engine controller
circuitry is housed in a separate housing from the overthrust
protector circuitry. The fuel flow demand signal 78 which passes
between the engine controller 52 and the overthrust protector 76 is
a serial digital transmission which is received by a suitably
buffered input on the overthrust protector. The signal could
alternatively be a parallel digital or an analogue signal.
[0056] There is thus provided a control system for an aircraft
engine in which overthrust protection is provided both by the
engine controller and the separate overthrust protector.
[0057] Because of the independence of the engine controller and the
overthrust protector, a single failure will not result in the
malfunctioning of both these systems. Both systems have overthrust
protection built into them. Thus, the malfunctioning of a single
one of the engine controller and the overthrust protector will not
result in overthrust. This means that overthrust protection is
provided fully within a single channel. Therefore, an aircraft
could fly on a single channel and nevertheless have sufficient
overthrust protection. In addition, because overthrust problems are
generally dealt with by the comparitor 92 providing an appropriate
FMV demand signal, rather than by shutting off the fuel flow
completely via the shut off valve, such situations may be dealt
with more safely than was the case with the prior art system.
[0058] Various modifications may be made to the above described
embodiment without departing from the scope of the invention. In
particular, more sophisticated implementations could incorporate
the calculation of a maximum limit for fuel flow in the overthrust
protector for all throttle positions and also for a thrust reverser
position.
[0059] Whilst endeavouring in the foregoing specification to draw
attention to those features of the invention believed to be of
particular importance it should be understood that the Applicant
claims protection in respect of any patentable feature or
combination of features hereinbefore referred to and/or shown in
the drawings whether or not particular emphasis has been placed
thereon.
* * * * *