Note: Descriptions are shown in the official language in which they were submitted.
TEMPER~TURE TRIM/SYNCHRONIZER SYSTEM
Background of the Invention
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This invention relates to a temperature trim and fan
speed synchronizer control system for a multiple engine air-
craft. The control system automatically compensates for engine
efficiency, deterioration and the effects of changes in alti-
tude during the climh and cruise phases of flight.
The U. S. Patent 3,368,346 to Warne titled Synchron-
izing Control Means for Multiple Gas Turbine Engine Installa-
tions discloses one method known in the art for speed synchron-
ization. In the system disclosed by Warne speed of the engines
is synchronized by monitoring and comparing the compressor
pressures of the several engines. Instrumentation on that
engine having the lowest pressure being developed will cause
a valve member to move to permit an increase in fuel delivery
to the combustor of the under performing engine.
The U. S. Patent 3,854,287 to Rembold titled Self-
trimming Control for Turbofan Engines discloses means for con-
trolling a twin spool turbofan engine to compensate for such
things as deterioration with operating hours, increased alti-
tude, or increased power extraction. Control is achieved by the
use of an electronic supervisory unit which monitors engine
inlet temperature, pressure in the combustor, fan rotor speed
and high rotor speed.
The prior art systems implemented on aircraft having
at least one pair of gas turbine engines concern only speed
synchronization. Usually, speed synchronization is achieved
by sensing the fan speed of each engine and comparing the mea-
surements. If a differential is present, a signal is generated
which adjusts the speed of one engine so as to eliminate the
difference. Often this is done by designating one engine as
the master and the other engine/s as slave/s.
With my system a similar closed loop speed synchroni-
zing system is used, but each engine is provided with a throttle
adjustment which may be actuated by electronic signal. Also,
the interturbine temperature of each engine is sensed and
compared to a preselected operating temperature which is gener-
ally chosen according to the engine rating. When the temperature
of an engine varies from the preselected value, a signal is
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generated which adjusts the throttle of that engine to maintain
the desired temperature. The speed of the other engine is then
synchronized accordingly.
In operation the pilot will manually adjust the
throttle to obtain rated engine power and it is at this point
that the temperature is selected and stored. The temperature
control and speed synchronizer system is then energized and
from then on the rated temperature will be maintained through-
out the cruise portion of the flight.
Summary of the Invention
The temperature trim/synchronizer (TT/S) system moni-
ters and provides closed loop control of the gas temperatures
measured at the first turbine stage of each aircraft engine
while at the same time keeping engine fan speeds synchronized.
The principles of the invention will be described with reference
to a twin engine aircraft. However, aircraft having more than
two engines could be instrumented using the same disclosed
concepts.
The TT/S system functions by transmitting fan speed and
turbine temperature signals to an electronic type master control
unit. Acting on the incoming signal data, the master control
unit pulses throttle actuators which move each engine fuel
control lever a cmall amount in either direction to correct speed
and temperature. The system has limited authority and the pilot
can override at any time by simple movement of the throttles.
To operate the system, the pilot makes use of a multi-
plicity of switches and gages. Included are: a cockpit control
switch having three positions, namely, "off", "set" and "engage";
a pair of dual indicator lamps which advise the pilot whether
the engines are going too fast or too slow; a temperature
selector control which the pilot presets to the desired first
turbine gas temperature to be used for the flight; and gages
which provide turbine temperature readouts for each engine
(measured gas temperature or MGT).
During takeoff the pilot keeps the TT/S system
switched "off". After takeoff power is reduced and the throttles
are reset to the cruise/climb condition, the cockpit control
switch is moved to the "set" condition. In the "set" mode, the
pilot manually trims the throttle levers while observing both
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the temperature gages and the dual indicator lamps. The turbine
temperature gages are monitored so that the measured gas temper-
ature (MGT) of each engine is at or below the value preset on
the temperature selector. Secondly, the pilot reduces the speed
of the faster engine as indicated by the dual indicator lamps
to get the engines within synchronizing range. With these tasks
accomplished, the pilot switches the cockpit control switch to
the "engage" position.
In the "engage" mode, the master control unit takes
over. The automatic system automatically establishes the last
sensed temperature of each engine as a set point not to be
exceeded. Further, throttle settings are incrementally trimmed
to achieve fan speed synchronization.
The master control unit accomplishes this task by use
15 of an 8-bit microcomputer having 27 input/output lin~s, a 1024
word program memory, a 64 x 8 RAM data memory, an on-board
oscillator and clock circuit, an 8-bit timer/event counter and
an 8-bit central processor unit.
Output of the master control unit consists of signals
which drive the throttle actuators. There is a throttle actua-
tor serially connected between the pilot'sthrottle lever and the
fuel control valve on each turbine engine. Each throttle actua-
tor is capable of increasing or decreasing the effective preset
value on the pilot's throttle lever by a small amount, typically
6 degrees in either direction. For aircraft using mechanical
linkage type fuel control systems, trim of throttle settings can
be effectively obtained by use of solenoid actuated cams.
Using my invention, the pilot may dial in a desired
climb or cruise temperature, set the throttle, and the system
will maintain the temperature constant as well as keep both
engines synchronized. As in the case of the single synchroni-
zer system, the throttle maintains full authority at all times,
whether the trim system is on or off. The advantages of this
system of controlling a multiengine aircraft by means of a
temperature trim/synchronizer system include the following:
1. No charts or computers are required for normal
piloting after take-off.
2. The thrust level relative to the max. allowable
level is evident at a glance. (MGT set vs. MGT max)
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3. The effects of varying quantities of power extraction
and bleed air (as when anti-icing air is turned on)
will automatically appear on the temperature gage and
can be compensated for by a throttle movement.
Thus, in accordance with the present invention there
is provided apparatus for trimming the operating temperatures
and synchronizing the fan speeds of the turbine engines used to
power a muIti-engine aircraft, each of said turbine engines
including an air inlet, gas stream discharge means, a low
pressure compressor having a fan stage, a high pressure com
pressor driven by a first turbine stage, a second turbine stage
for driving the fan stage and a combustor to which fuel is
supplied for generating hot gases to drive said turbines, each
combustor including a fuel control valve for controlling the
fuel supply thereto, the fuel supply to each engine being
responsive to the setting of a pilot's throttle lever, said
apparatus comprising means for measuring the fan speed of each
engine and generating a first set of electronic signals indica-
tive thereof; means responsive to the temperature of the gas
stream at the first turbine stage of each engine including the
generation of a second set of electronic signals indicative of
the measurement thereof; means for scheduling a third electronic
signal indicative of a not-to-be-exceeded first turbine stage
temperature; throttle actuator means serially connected between
the pilot's throttle lever and the fuel control valve of each
turbine engine, said throttle actuator being capable of
increasing and decreasing the preset value of said throttle
sufficient to maintain speed synchronization and temperature
control of the associated engine during the cruise phase of the
flight of said aircraft; and a master control unit for pulsing
the throttle actuators to trim the fuel supply to each turbine
in response to electronic signal data indicative of engine fan
speed, the measured gas temperature at each first turbine stage
and the scheduled not-to-be-exceeded first turbine stage
temperatures.
Brief Descr_ption of the Drawings
Fig. 1 is a schematic diagram, partially in block
diagram form, of a dual turbine engine control system incor-
porating the invention.
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Fig. 2 is a schematic diagram of the master control
section of system shown in Fig~ 1.
Fig. 3 is a schematic representation of the throttle
actuator portion of the system shown in Fig. 1.
Description of_the Preferred Embodiment
Referring to Fig. 1 there is shown a temperature
trim/synchronizer system used to simultaneously control two
turbine engines 50 and 52. Engine 50 is typically of the bypass
type having an inlet fan stage 54 rotating in annular duct 56.
~0 The stream of incoming air accelerated by fan stage 54 divides.
Primary air enters passageway 58 while secondary air flows rear-
ward through annular bypass duct 60, eventually discharging out
the rear of the engine as a cool gas stream. The primary air
stream in passageway 58 is compressed in compressor stage 62 and
after traversing a diffuser enters combustor 64 where fuel is
added to achieve hot products of combustion. The hot gases
flowing outward from the combustor 64 drive first turbine stage
66. Power absorbed at first turbine stage 66 serves to drive
the compressor section of the engine. The hot gas stream flowing
rearward from the first turbine stage 66 powers second turbine
stage 68. Second turbine stage 68 is connected by shaft 70 and
gears 72 to fan stage 54. The configuration of engine 52 is
shown as being identical to that of engine 50.
To implement my invention, two sensors are added to
each turbine engine 50 and 52. One is a sensor which counts the
rpm (Nl) of fan stage 54. In the unit reduced to practice speed
sensor 74 was a magnetic pickup device. The second sensor
monitors the gas temperatur~ at the first fan turbine (TTl).
This is shown as temperature sensor 76 which can typically be
a thermocouple.
Engine 52 is similarly instrumented. Speed (N2) of
the fan stage of engine 52 is monitored by speed sensor 78.
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~as temperature (TT2) at the first turbine stage is monitored
by temperature sensor 80.
The electronic signals representing the fan speeds
and the first turbine temperatures of the two engines serve as
inputs to master control 82. The signals are generated by
transducers well known in the art with signal conditioning
amplifiers added as necessary.
The master control section operates under the control
of the aircraft pilot. The pilot will, prior to takeoff, select
the desired maximum temperature operating limit for the engines
on temperature selector 84. This can typically be a calibrated
trimpot device. Then, leaving the master control 82 in the
"off" condition, the pilot will execute aircraft takeoff using
manual control of engine throttles 86 and 88. Engine fan rpm
and the measured gas temperature (MGT) at the first -turbine
stage will have been determined in advance in terms of ambient
temperature, aircraft weight, field altitude, and runway length.
A set of charts may be used, or the information may be stored in
a computer. The concept used is aimed at conserving engine life
by not using more takeoff thxust than necessary. It has been
called "flexible thrust" or "managed thrust". The maximum
thrust rating must be obtained at a measured gas temperature
below the redline value.
Following the first power reduction after takeoff, the
pilot will activate the temperature trim/synchronization (TT/S)
system. This accomplishes two things, First, fan speeds N1 and
N2 are synchronized. Secondly, the MGT of both engines is moni-
tored and controlled so as not to exceed the value preset in
temperature selector 84, Master control 82 accomplishes this
task in combination with throttle actuators 90 and 92. Master
control 82 signals instructions to throttle actuators 90 and 92
via trim signal lines PLj and PL2 respectively. The throttle
actuators under command of the trim signals will adjust, by a
small amount, the throttle settings preset into engine throttles
35 86 and 88 by the pilot. Thus, if TC1 is the preset value of
throttle 85, the fuel control signal 94 forwarded to engine 50
will be acted UpOil by throttle actuator 90 under instructions
from trim signal PL1 to cover a range
TC1 + ~ TC1
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~n the unit reduced to practice the ~TC1 covered the range
~6 to -6 throttle lever angle which is equivalent to + 10
percent power.
Trim signal PL2 provides a similar input to enable
throttle actuator 92 to vary throttle setting TC2 either up or
down by a small amount. ~n this way the two engines are kept
synchronized in speed and at the same time their measured gas
temperatures are kept below the value preset in temperature
selector 84.
The manner in which master control 82 and throttle
actuator 90 accomplish these tasks will be explained by reference
to Fig. 2 and 3. Fig. 2 is a schematic of master control 82
together with the units with which it cooperates. A micro-
computer 100 forms the heart of the master control unit. In
the unit reduced to practice, microcomputer 100 was a single
component 8-bit Intel type 8748. The 8748 is a user programmable
and erasable EPROM program memory intended for prototype and
preproduction systems. The pin-compatible Intel type 8048 with
factory programmed mask ROM would be more suitable for production
20 quantities. The numbers 12-38 shown in Fig. 2 refer to the
microcomputer pin numbers (See p. 365 of Microcomputer D.A.T.A.
Book, Edition 5, published by Cordura Publications, Inc.,
Pinebrook, N. J. 07058).
Prime power is fed to master control 82 through termi-
25 nal 98 which is connected with energizing switch 102. Energiz-
ing switch 102 has three positions, namely 0 signifying - "off",
S signifying - "set", and E signifying - "engage". Logic module
104 routes the "set" and "engage" commands to the various
elements within the master control console and the double arrows
30 shown connecting logic module 104 with microcomputer 100 are
intended as only symbolic of the routing of these commands. A
stream of pulses representing the speed of the fan stage of
engine 50 enters at terminal 106. The pulse stream representing
the speed of the fan stage of engine 52 enters at terminal 108.
An anolog voltage representing the temperature of the first tur-
bine stage of engine 50 enters at terminal 110. Similarly, an
anolog voltage representing temperatures of the first turbine
stage of engine 52 enters at terminal 112. The anolog voltages
entering on -terminals 110 and 112 are converted to digital bit
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reams in A-to-D converters 111 and 113 respectively, prior
to entry in microcomputer 100. Comparators 114 and 116 furnish
step function inputs to the microcomputer when the temperature
from either engine 50 or 52 equates with the value preset by the
pilot on temperature selector 84.
The speed status of both engines is presented visually
to the pilot by means of four indicator lamps 118, 120, 122 and
124. If indicator lamp 118 is on so that an upward - pointing
arrow is illuminated, the pilot knows that engine 50 should be
10 speeded up. If lamp 120 is illuminated, the speed of engine 50
should be decreased. Likewise, if lamp 122 is illuminated,
engine 52 should be speeded up. If lamp 124 is lit, engine 52
should be slowed down. For the system reduced to practice, the
programming of the microcomputer was set such that when engine
fan speeds are matched within one-half percent, the indicator
lamps will go out. It will be understood that indicator lamps
118,120, 122 and 124 include the necessary DC-drivers so that
the low output signal from microcomputer 100 is able to elimi-
nate the lamps.
Throttle actuators 90 and 92 receive instructions from
the microcomputer via lines 21, 22, 23 and 24. Feedback signals
from the throttle actuators are sent over lines 16 and 17 for
throttle actuator 90 and on lines 12 and 13 for throt-tle actuator
92.
Functionally the temperature trim/synchronizer (TT/S)
System operates as follows. After the initial climb out phase
of flight, the pilot will turn cockpit switch 102 to the "setl'
position. This setting enables master control 82 to monitor
each engine's fan speed and the actual measured gas temperature
status resulting from the setting of throttle control levers 86
and 88. During this phase the throttle actuator 90 and 92 are
driven to and remain in their center or null position. Simul-
taneously, the cockpit indicator lamps 118,120, 122 and 124
advise the pilot regarding whe-ther the fan speeds of the two
engines are within the pull-in range of the TT~S System.
After the pilot has adjusted the throttle control
levers to achieve the desired MGT value preset on temperature
selector 84 and has the fan speeds within the pull-in range of
the synchronizer (plus or minus half a percent in the unit
reduced to practice), he will move switch 102 to the "engage"
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In the "engage" mode, the TT/S System, under -the direc-
tion of master control 82 will establish the last monitored MGT
values as references and drive the throttle actuators ~0 and 92
in either direction to properly adjust each fuel control's power
lever shafts. Whenever the fan speeds N1 and N2 are not
synchronized at the reference temperatures, the TT/S System will
always decrease the power setting of the faster operating engine
to match the fan speed of the slower operating engine in order
to achieve fan speed synchronization. This may reduce the tem-
perature of this engine below its referenced value. ~owever,
in no case will the operating temperature of either engine be
allowed to exceed, within the authority limits of the TT/S System,
the established reference value.
Fig. 3 shows how the throttle actuator functions with
a mechanical fuel control system. The pilot's power lever 86
is connected via mechanical linkage 126 to the fuel control valve
128 of engine 50. At some convenient point along linkage 126,
there is a break where oppositely positioned push rod ends are
held against a wedge shaped cam 130 by spring 132. It will be
seen that movement of the wedge shaped cam 130 is at right angles
to linkage 126. Thus, movement of cam 130 into linkage 126 serves
to lengthen the distance between throttle lever 86 and fuel con-
trol valve 128 while withdrawal of cam 130 tends to shorten the
linkage. Positioning of cam 130 is under the control of solenoid
actuator 134.
When energizing switch 102 (See Fig. 2) is in the "set"
condition, the solenoid actuator is commanded to position wedge
shaped cam 130 such that its centerline ( ~ ) or null condition
is in line with the push rod ends of mechanical linkage 126.
With cam 130 in its null position, the pilot can then proceed to
adjust throttle lever 86 to achieve temperature and fan speed
criteria as monitored on temperature gage 136 and an RPM gage
(not shown). With the manually set criteria established, the
pilot will then rotate switch 102 to the "engage" position.
Master control 82 will then take over, Under direction of master
control,soleno d actuator 134 will step forward or back in order
to move wedge shaped cam 130 away from the null position an amount
just sufficient to control speed and temperature characteristics.
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The four communicating lines between master control 82
and solenoid actuator 134 can be better described by reference
to Fig. 2. Signals coming out of microcomputer 100 on line 21
advise throttle actuator 90 to increase the fuel supply to
engine 50. Signals emitted on line 23 advise throttle actuator
90 to decrease the fuel supply of engine 50. When master control
82 is in the "set" condition, feedback from throttle actuator 90
along lines 12 and 13 provides intelligence concerning the null
condition of wedge cam 130 (See Fig. 3). A step signal on line 12
signifies the cam has been moved far enough in the direction of
increasing thickness while a step signal on line 13 signifies
sufficient movement in the direction of decreasing wedge thickness.
~ ovement of throttle actuator 92 is accomplished in a
similar manner. Data coming from microcomputer 100 along line 22
signals throttle actuator 92 to increase the fuel supply of
engine 52. Signals on line 24 signify that throttle actuator 92
should decrease the fuel supply of engine 52. Feedback signals
on lines 16 and 17 advise the microcomputer when throttle actu-
ator 92 has reached the null position from an initial condition
on either side of centerline. It will be understood that signal
conditioners and/or line drivers may be required for the micro-
computer module to properly interface with the throttle actuator
modules which will most often be attached directly on the aircraft
engines.
While the present invention has been described in terms
of a preferred embodiment, it is apparent that modifications
may be made without departing from the scope intended. For
example, implementation on engines equipped with electronic fuel
control equipment would require changes only in the way that the
throttle actuators accomplish their functions. It will thus be
understood that various changes in details, steps and arrange-
ment of parts will occur to and may be made by those skilled in
the art upon a reading of this disclosure within the principles
of the inventlon.
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