GB2095755A - Multiple gas turbine speed/temperature response control system - Google Patents

Abstract

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 temperature for the turbines and secondly, adjust the throttles to bring engine fan speeds within the pull-in range of the synchronizer. This done, the pilot engages the closed loop control system which functions by having fan speed 78 and turbine temperature data 80 signals transmitted to an electronic type master control unit 82. Acting on the incoming signal data, the master control unit pulses power lever actuators 90, 92. There is a power lever actuator serially connected between each throttle lever 86, 88 and the fuel control valve associated therewith. Each power lever actuator is capable of increasing and decreasing the effective preset value of a power lever 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. <IMAGE>

Description

SPECIFICATION Temperature trim/synchronizer system Background of the invention This invention relates to a temperature trim and fan speed synchronizer control system for a multiple engine aircraft. The control system automatically compensates for engine efficiency, deterioration and the effects of changes in altitude during the climb and cruise phases of flight.

The U.S. Patent 3,368,346 to Warne titled "Synchronizing Control Means for Multiple Gas Turbine Engine Installations" discloses one method known in the art for speed synchronization. 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 controlling a twin spool turbofan engine to compensate for such things as deterioration with operating hours, increased altitude, 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 measurements. 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 our other engine/s as slave/s.

With our system a similar closed loop speed synchronizing 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 generally chosen according to the engine rating. When the temperature of an engine varies from the preselected value, of a pulse signal is generated which adjusts the power lever on the fuel control 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 throughout the cruise portion of the flight.

The temperature trim/synchronizer (TT/S) system monitors and provides closed loop control of the gas temperatures measured at the first power 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 twd 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 power lever actuators which move each engine fuel control lever a small 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 is generally provided with a multiplicity of switches and gauges, 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 turbine gas temperature to be used for the flight; and gauges 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, pdwer 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 the temperature gauges and the dual indicator lamps. The turbine temperature gauges are monitored so that the measured gas temperature (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, power lever settings are incrementally trimmed to achieve fan speed synchronization.

The master control unit preferably accomplishes this task by use of an 8-bit microcomputer having 27 input/output lines, a 1024 word program memory, a 64x8 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 power lever actuators.

There is a power lever actuator seriaily connected between the pilot's throttle lever and the fuel control valve on each turbine engine. Each power lever actuator is capable of increasing or decreasing the effective preset value of the fuel control power lever by a small amount, typically 6 degrees in either direction. For aircraft using mechanical linkage type fuel control systems, trim of power lever angle settings can be effectively obtained by use of solenoid actuated cams.

Using our 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 synchronizer 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 multi-engine 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.).

3. The effects of varying quantities of power extraction and bleed air (as when anti-icing air is turned on) will appear on the temperature gauge and can be compensated for automatically by the TT/S.

Brief description of the drawings Fig. 1 is a schematic diagram, partially in block diagram form, of a dual turbine engine control system incorporating the invention.

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 power lever 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. The stream of incoming air accelerated by fan stage 54 divides. Primary air enters passageway 58 while secondary air flows rearward 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 gas producer 66.Power absorbed at first turbine gas producer 66 serves to drive the compressor section of the engine. The hot gas stream flowing rearward from the first turbine gas producer 66 energizes power turbine 68. Power turbine 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 our invention, two sensors are added to each turbine engine, 50 and 52. One is a sensor 74 which counts the rpm (N1) of fan stage 54, and, in the present embodiment is a magnetic pickup device. The second sensor monitors the gas temperature at the first fan turbine (TT,). 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. Gas temperature (TT2) at the first power turbine stage is monitored by temperature sensor 80.

The electronic signals representing the fan speeds and the power 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 power 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 thrust 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 N, and N2 are synchronized. Secondly, the MGT of both engines is monitored and controlled so as not to exceed the value preset in temperature selector 84. Master control 82 accomplishes this task in combination with power lever actuators 90 and 92. Master control 82 signals instructions to power lever actuators 90 and 92 via trim signal lines PL, and PL2 respectively. The power lever actuators under command of the trim signals will adjust, by a small amount, fuel control power lever angle settings preset into engine throttles 86 and 88 by the pilot. Thus, if TC, is the power lever preset by throttle 86, the fuel control signal 94 forwarded to engine 50 will be acted upon by power lever actuator 90 under instructions from trim signal PL, to cover a range TC,+ATC, In the embodiment shown, the ATC, covers the range +6 to --60 power lever angle which is equivalent to +10 percent powder.

Trim signal PL2 provides a similar input to enable power lever actuator 92 to vary fuel control power lever setting TC2 either up or down by a small amount. In 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 power lever actuator 90 accomplish these tasks will be explained by reference to Figs. 2 and 3.

Fig. 2 is a schematic of master control 82 together with the units with which it cooperates.

A microcomputer 100 forms the heart of the master control unit, and in the embodiment shown 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 pincompatible Intel type 8048 with factory programmed mask ROM would be more suitable for production 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 terminal 98 which is connected with energizing switch 102. Energizing 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 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 analog voltage representing the temperature of the first power turbine stage of engine 50 enters at terminal 110. Similarly, an analog voltage representing temperatures of the first power turbine stage of engine 52 enters at terminal 112.

The analog voltages entering on terminals 110 and 112 are converted to digital bit streams in Ato-D converters 111 and 11 3 respectively, prior to entry in microcomputer 100. Comparators 114 and 11 6 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 speeded up. If lamp 120 is illuminated, the speed of engine 50 should be decreased.

Likewise, if lamp 122 is illustrated, engine 52 should be speeded up. If lamp 124 is lit, engine 52 should be slowed down. For the system shown 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 11 8, 120, 122 and 124 include the necessary DC-drivers so that the low output signal from microcomputer 100 is able to illuminate the lamps.

Throttle actuators 90 and 92 receive instructions from the microcomputer via lines 21, 22, 23 and 24. Feedback signals from the bottle actuators are sent over lines 1 6 and 1 7 for throttle actuator 90 and on lines 12 and 13 for throttle 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 "set" 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 power level actuator 90 and 92 are driven to and remain in their center or null position. Simultaneously, the cockpit indicator lamps 118, 120, 122 and 124 advise the pilot regarding whether 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 embodiment shown, he will move switch 102 to the "engage" position.

In the "engage" mode, theft/S System, under the direction of master control 82 will establish the last monitored MGT values as references and drive the power lever actuators 90 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 aiways 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 temperature of this engine below its referenced value. However, 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 referenced value.

Fig. 3 shows how the power lever actuator functions with a mechanical fuel control system.

The pilot's throttle lever 86 is connected via mechanical linkage 126 to the fuel control valve power lever 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 1 32. 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 control valve power lever 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 ( i ) 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 gauge 136 and an RPM gauge (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, solenoid actuator 134 will step forward or back in order to move wedge shaped cam 1 30 away from the null position an amount just sufficient to control speed and temperature characteristics.

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 power lever 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 1 3 signifies sufficient movement in the direction of decreasing wedge thickness.

Movement of power lever 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 power lever actuator 92 should decrease the fuel supply of engine 52. Feedback signals on lines 16 and 17 advise the microcomputer when power lever actuator 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 microcomputer module to interface properly with the power lever actuator modules which will most often be attached directly on the aircraft engines.

When the engines are throttled back prior to landing of the aircraft, the power lever actuators automatically return to the null position. This is important from the standpoint of safety. For example, if the actuator of one engine were displaced from null in the direction of reduced speed, the result would be that the engine would operate at dangerously low rpm during letdown along the glideslope. By having the power actuators automatically return to the null condition whenever the pilot throttles back his engines, positive control of the aircraft is assured during final approach.

While the present invention has been described in terms of a preferred embodiment, it S 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 power lever actuators accomplish their functions. It will thus be understood that various changes in details, steps and arrangement 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 invention as defined by the appendant claims.

Claims (11)

Claims

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 compressor 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 indicative 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 power turbine stage temperature; power lever actuator means serially connected between the pilot's throttle lever and the fuel control valve of each turbine engine, said power lever actuator being capable of increasing and decreasing the preset value of said power lever 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 operating the power level 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 power turbine stage and the scheduled not-to-be-exceeded first power turbine stage temperatures.

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

3. Apparatus as claimed in Claim 1 or 2, wherein the means responsive to the temperature of the gas stream at the first turbine stage of each engine includes a thermocouple sensor and an analog-to-digital converter.

4. Apparatus as claimed in any of Claims 1 to 3, wherein the power lever actuator means includes solenoid driven cams.

5. Apparatus as claimed in any of Claims 1 to 4, wherein the power lever actuators are capable of trimming the present value of a throttle lever by as much as +6 degrees.

6. Apparatus as claimed in any of Claims 1 to 5, wherein said apparatus provides temperature trim and speed synchronization for aircraft having two turbofan engines.

7. Apparatus as claimed in any of claims 1 to 6, wherein the power level actuator means is arranged to return to the null condition whenever the pilot's throttle levers are cut back preparatory to landing.

8. Apparatus for trimming the operating temperatures and synchronising the fan speeds of the turbine engines used to power a multi-engine aircraft, substantially as hereinbefore described with reference to the accompanying drawings.

9. An aircraft having a plurality of turbine engines to power it, which includes an apparatus according to any one of the preceding claims.

1 0. An aircraft having a plurality of turbine engines to power it, which includes a closed loop control system for automatically trimming the temperature of and automatically synchronising the fan speeds of the turbine engines.

11. The features hereinbefore disclosed, or their equivalents, in any novel selection.