CA1161527A

CA1161527A - Temperature trim/synchronizer system

Info

Publication number: CA1161527A
Application number: CA000394263A
Authority: CA
Inventors: Thomas A. Dickey
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1981-03-30
Filing date: 1982-01-15
Publication date: 1984-01-31
Also published as: DE3201010A1; FR2502697A1; IT8220466A0; BR8201832A; SE8107800L; IT1151860B; GB2095755A; JPS57165632A

Abstract

ABSTRACT OF THE DISCLOSURE
A closed loop control system is presented which trims fuel flow to the turbine engines of a multi-engine aircraft in response to fan speed and turbine temperature measurements. The closed loop system is activated after the initial climb out phase of flight. To engage -the automatic control system the pilot will first preset a not-to-exceed measured gas tempera-ture for the turbines and secondly, adjust the throttles to bring engine fan speeds within the pull-in range of the synchro-nizer. This done, the pilot engages the closed loop control system which functions by having fan speed and turbine tempera-ture data signals transmitted to an electronic type master control unit. Acting on the incoming signal data, the master control unit pulses throttle actuators, There is a throttle actuator serially connected between each throttle lever and the fuel control valve associated therewith. Each throttle actuator is capable of increasing and decreasing the effective preset value of a throttle by an amount just sufficient to maintain speed synchronization and temperature control of the associated engine during the cruise phases of flight, The automatic system has limited authority and the pilot can override at any time by simply moving the throttle levers.

Description

TEMPER~TURE TRIM/SYNCHRONIZER SYSTEM
Background of the Invention . ~
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 , .~

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

2 7 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) I 161~27 ~,~

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.

. 5 2 7 -4a-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.

.; , . ~ J

'7 ~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 ` :

~ ~is~

~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 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"

~sition. -8-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.
. . .

_9_ 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.

"

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for trimming the operating temperatures and synchronizing the fan speeds of the turbine engines used to power a multi-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 sup-plied 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 indicative thereof;
means responsive to the temperature of the gas stream at the first turbine stage of each engine including the genera-tion of a second set of electronic signals indicative of the measurement thereof;
means for scheduling a third electronic signal indica-tive 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 increas-ing 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 actua-tors 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.

2. The invention as described in Claim 1 wherein the means for measuring the fan speed of each engine includes a magnetic pickup.

3. The invention as described in Claim 1 wherein the means responsive to the temperature of the gas stream at the first tur-bine stage of each engine includes a thermocouple sensor and an analog-to-digital converter.

4. The invention as described in Claim 1 wherein the throttle actuator means includes solenoid driven cams.

5. The invention as described in Claim 1 wherein the master control unit includes a microcomputer having 27 input/
output lines, an 8-bit central processor, a 1024 word program memory and a 64 x 8 RAM memory.

6. The invention as described in Claim 1 wherein the throttle actuators are capable of trimming the preset value of a throttle lever by as much as ? 6 degrees.

7. The invention as described in Claim 1 wherein said apparatus provides temperature trim and speed synchronization for an aircraft having two turbofan engines.