GB2132384A - Control for aircraft gas turbine engines - Google Patents

Abstract

Automatic power reserve control for multiple engine aircraft for providing increased fuel flow to each remaining operating engine in response to the detection of a failure of an engine during the takeoff phase of operation. The fuel flow is increased in response to an error signal derived from the actual power of the failed engine after the failure and a stored value of its power before the failure.

Description

SPECIFICATION Control for aircraft gas turbine engines The present invention relates to aircraft engine control and, more particularly, to control for gas turbine engines in multiple engine aircraft.

Background of the invention Control systems adapted to provide general control of aircraft engines are known in the art. For example, certain of such systems include means for sensing the output shaft torque of an aircraft engine. Other known systems sense parameters proportional to the power of the aircraft engine.

An example of a control system which senses shaft torque is disclosed in U.S- Patent No.

3,106,062 to Rosenberg, et al., which patent is assigned to the assignee of the present application, and is hereby incorporated by reference herein.

In order to protect against possible failure of one or more engines in a multiple engine aircraft during takeoff, it is desirable to provide means to increase the power setting of the remaining operating engines during such failure conditions.

However, under conventional operating practices, the power setting of each engine must be initially adjusted by the pilot prior to takeoff without further manual adjustment during takeoff even in the event of failure of one of the engines.

One solution to this problem is to set each engine's takeoff power level at a level greater than that which would be required if all the engines were operating. This would provide for the contingency of failure of one or more of the engines. However, an appreciable decrease in engine life occurs when power level settings are continuously increased to such levels.

Objects of the invention It is a primary object of the present invention to provide new and improved control for aircraft engines responsive to the failure of one or more engines forming the power system.

It is another object of the present invention to provide a new and improved control for aircraft gas turbine engines having means for automatically increasing the power settings of one or more of the engines during takeoff when the failure of one or more engines occurs.

Yet an additional object of the present invention is to provide a new and improved control for gas turbine aircraft engines wherein the control includes memory means responsive to input parameters of respective engines and is adapted to continuously memorize the value of the output shaft torque of each engine.

Summary of the invention In one form of the invention, a control is provided for a plurality of gas turbine engines.

Each of the engines includes an output shaft. The control includes automatic power reserve switching means for developing a switching output signal responsive to power failure of at least one of the engines. Means is provided for developing a first signal representative of the substantially instantaneous value of power, e.g., torque, at the output shaft of the one engine.

Memory means is responsive to the switching output signal for receiving and storing the first signal and developing a memory means output signal. The memory means output signal equals the first signal when the switching output signal is in an OFF condition and equals a stored value of the first signal when the switching output signal is in an ON condition. Means is provided for receiving the memory means output signal and developing a second signal representative of a desired power at the output shaft of at least one of the engines. Means is provided for receiving the first and second signals and developing a third signal representative of the difference therebetween. Means is provided for receiving the third signal and increasing the power at the output shaft of at least one of the engines when the third signal does not meet predetermined criteria.

The foregoing and other objects of the present invention, together with the features and advantages thereof, will become apparent from the following detailed specification when read in conjunction with the accompanying drawings.

Brief description of the drawings Figure 1 illustrates a block diagram of one form of the control of the present invention in combination with two gas turbine engines.

Figure 2 illustrates a detailed block diagram of a portion of the control shown in Figure 1.

Figure 3A and 3B illustrate a more detailed diagram of the memory circuit shown in block form in Figure 2.

Detailed description of the invention The block diagram of Figure 1 illustrates one embodiment of a control system in which the present invention is used in an aircraft (not shown) having two gas turbine engines 1 OA, 1 OB, which engines, may, for example, be conventional turboprop engines. For simplicity, although two engines are depicted in Figure 1, only one engine 1 OA and the control therefor will be described in detail.

As is well known, each turboprop engine includes a gas generator and a free power turbine.

The gas generator includes a combustor section disposed between a compressor section and a high pressure turbine section. Following combustion and rotation of the high pressure turbine, exhaust gases are directed through the low pressure free power turbine. This power turbine is generally coaxial with the gas generator although generally not mechanically coupled thereto. The power turbine transmits the power developed by the engine to drive the propeller through a reduction gear. In view of its function, the power turbine may be referred to as an output power shaft of the engine.

The control system of engine 1 OA includes: electronic control unit 22A of the present invention; hydromechanical fuel control mechanism 24A; and engine power failure detection circuit 26A. Hydromechanical fuel control 24A (HMU) is of the well known type which controls fuel flow (Wf) to the engine 1 OA in response to a plurality of input signals (not specifically identified in Figure 1) sensed from the engine 1 OA; and a biasing signal 21 from control unit 22A.The input signals to hydrnmechanical control circuit 24A (not specifically identified in Figure 1) typically include: command signals of power lever position (PLA) and condition Lever position (CLA) received from the aircraft; and signals representative of prevailing conditions of engine 1 OA such as gas generator speed (we), compressor discharge pressure (P > ) and compressor inlet temperature (T2). As is well known, hydromechanical control 24A is a mechanism comprising mainly hydraulic and mechanical subassemblies with a minor number of electromechanical parts which are advantageously utilized to communicate with the electronic control 22A.

Failure detection circuit 26A is also electrically coupled (through conduits 27A, 27B) to substantially identical failure detection circuit 26B in the control system for gas turbine engine 1 OB, and each circuit 26A, 26B is respectively coupled to the engines 1 0A, 1 OB, for detection of operational failure of the respective engine.

Automatic power reserve (APR) switching means 28A, also referred to as power reserve circuit, is coupled to control unit 22A, failure detection circuit 26A and activation means or control lever 33A. Power reserve circuit 28A is effective for developing a switching output signal APR, which signal is sensed by control unit 22A.

in one simple form, power reserve circuit 28A includes two normally open switches 30A and 32A which are arranged in series relationship.

Switch 30A is coupled to failure detection circuit 26A. Switch 32 is coupled to control lever 33A disposed in the cockpit of the aircraft and is manually activated by the pilot to arm the power reserve circuit 28A in accordance with standard takeoff procedures.

Generally, whenever engine 1 OA (or 1 OB) fails, i.e., loses a predetermined degree of power as determined by detection circuit 26A, in the course of takeoff, switch 30A is activated by detection circuit 26A and closed in response to the failure.

When both switches 30A, 32A are closed, the APR circuit 28A is in an "ON" condition.

Conversely, when one or both switches are not closed, the APR circuit is in the "OFF" condition. If both switches are closed, i.e., when there has been an engine failure and the APR switch has been set by the pilot, the control unit 22A is activated and begins to trim the power settings of the engine 1 0A (and the remaining operating engine 1 OB) upward through control of the fuel flow Wf to the remaining engine or engines.

One embodiment of the electronic control unit 22A is illustrated in block form in Figure 2. In addition to the APR signal, the input to electronic control unit 22A comprises a plurality of well known and available signals including power turbine speed (Np) and engine output shaft torque (QES). Input signals Np and QES are sensed from the engine 1 OA whereas the APR signal is sensed from the power reserve circuit 28A (see Figure 1).

Control 22A of the present invention includes means for receiving a first signal (QES) representative of the substantially instantaneous value of torque at the output shaft, i.e., power turbine shaft, of engine 1 OA. Memory means 42, also referred to as memory circuit, is responsive to switching signal APR and is adapted for both receiving and storing the first signal (QES).

Memory circuit 42 further provides a memory means output signal OEM. Signal QEM equals the first signal (QES) when the APR circuit 28 is in an OFF condition. Alternatively, OEM equals a stored value of the first signal (QES) when the APR circuit 28 is first placed in an ON condition.

The control 22A further includes means for receiving signal QEM and developing a second signal (OEM[Xj), which signal is the product of OEM and a predetermined power factor X. The signal QEM(X) is representative of a desired value of shaft torque. One exemplary device well known in the art which performs the above function is multiplier 44. Multiplier 44 simply multiplies the value QEM by the predetermined power factor X.

For example, in one embodiment, the value of the power factor X may be from about 1.05 to about 1.50, preferably about 1.10.

Means is provided for receiving the first signal (QES) and second signal (OEM[X]) and for developing a third signal 47 representative of the difference therebetween, i.e., (OEM[X]--OES). The third signal 47 functions as an error signal and is ultimately fed to the hydromechanical fuel control 24A (see Figure 1). An example of a circuit known in the art for developing tha third signal 47 in accordance with the present invention is summer 46.

Assuming that the APR circuit 28A of Figure 1 is in the "ON" condition, the control 22A of Figure 2 also includes means for receiving the third or error signal 47 and for increasing the value of torque at the output shaft of the engine 1 OA (and the remaining operating engine 10B) whenever the third signal does not meet predetermined criteria. The predetermined criteria requires that the value of the first signal (QES) equal the value of the second signal (QEM[X]) at summer 46; otherwise, the third or error signal 47 is generated.

In a preferred embodiment of electronic control unit 22A, the receiving means for the third signal 47 includes conventional dynamic compensation circuit 48 which functions to integrate to force the determined error to zero when such error occurs. Such integrator circuits are well known and readily available.

The circuitry of electronic control unit 22A additionally includes conventional underspeed governor circuit 40 which receives signal Np. A control mode selector circuit 50 is provided which includes two interconnected switches 52 and 54.

When APR circuit 28A is in the OFF condition, the signal 41 at the output of governor circuit 40 is fed directly through selector circuit 50 to a conventional torque motor circuit 53.

Alternatively, when the APR circuit 28 is in the ON condition, the signal 49 at the output of dynamic compensation circuit 48 will be fed through selector circuit 50 to torque motor circuit 53.

It is believed that a presentation of a specific design of underspeed governor circuit 40, torque motor circuit 53 and dynamic compensation circuit 48 is not necessary for an understanding of the present invention. Generally, however, underspeed governor circuit 40 receices the signal Np from engine 1 OA and is of a type which amplifies signal Np and generates a DC reference threshold signal 41 representative of 82% of Np.

Those skilled in the art will recognize that there are many known circuits suitable for generating this reference signal.

With APR 28A off, this threshold signal 41 is fed to control mode selector circuit 50, and therethrough to torque motor circuit 53, which generates DC current signal X. Under these conditions, signal X serves as the input signal 21 from the electronic control unit 22A to the hydro mechanical unit 24A for providing a predetermined minimum power turbine speed (see Figure 1). With APR 28A on (not shown in Figure 2), torque motor circuit 53 ultimately receives the third or error signal 47 referred to above, which signal is first passed through compensation circuit 48, resulting in signal 49. Signal 49 is passed through control mode selector circuit 50, and therethrough to torque motor circuit 53, which generates a DC current signal Y.Under these conditions, signal Y serves as th-e input signal 21 from the electronic control unit 22A to the hydromechanical control 24A for increasing fuel flow to the engines 1 OA and 1 OB in accordance with the present invention (see Figure 1 ) A representation of the specific design of engine failure detection circuit 26A and APR circuit 28A above that which is provided hereinabove is not necessary for an understanding of the invention. However, to reduce the likelihood of a false trip of the APR 28a, a plurality of engine failure parameters should be monitored, e.g., shaft torque (QES) and power turbine inlet temperature (T4 s) Circuits of the relevant kind are also readily available in the art and thus the present invention is not limited to any particular embodiment thereof.

The operation of the control of the present invention during takeoff will now be described in greater detail. With reference again to Figures 1 and 2, automatic power reserve control is achieved when an increased torque signal 21 (signal Y) is developed by control unit 22A and additional fuel is fed to the engine 1 OA via the hydromechanical unit 24A. The APR circuit 28A preferably operates only during the takeoff phase of aircraft operation and the position of power lever 33A must be first manually set by the pilot to a position consistent with the takeoff ratings of engine 1OA.

In the normal course of takeoff operation, electronic control unit 22A continuously senses the shaft torque (QES) of the engine 1 OA. In the event that electronic control unit 22A receives an APR ON condition signal, the control unit 22A memorizes the then current value of torque (QES) and signal 21 (Y) is developed instead of signal 21(X). Signal 21(Y) is fed to the HMU circuit 24A and is effective for increasing the gas generator speed until the shaft torque of the engine 1 OA has increased by a preselected increment. As described previously, the APR OFF position results in modification of fuel flow to engine 1 OA as required to maintain power turbine speed at or above its minimum governing limit.However, while APR circuit 28 is in its OFF condition, memory circuit 42 of electronic control unit 22A continuously revisits or updates its output OEM which is substantially equal to its input QES.

When the APR circuit switches to the ON condition in response to engine 1 OA failure, the then present value of OEM becomes fixed in memory circuit 42. Concurrently, the control mode selector circuit 50 is activated and switches 52 and 54 are automatically set to their APR ON position. In this position, the signal 49 received from dynamic compensation circuit 48, rather than the signal 41 from underspeed governor circuit 40, is passed to torque motor circuit 53.

In the APR ON condition, control in accordance with the present invention is effective to modify fuel flow Wf to engine 1 OA whenever the then present value of the first signal (QES) does not equal the value of the second signal (QEM[X]).

When the third signal 47 is developed, i.e, when the first signal is not equal to the second signal, the value of the difference is ultimately passed to control mode selector circuit 50, to torque motor circuit 53, to be further passed to HMU circuit 24A in order to increase the amount of fuel flowing to engine 1 OA, and therefore to increase the shaft torque of the engine 1 OA.

As the value of the first signal (QES) is increased, the value of the third signal 47 is decreased until eventually the second signal equals the first. When the magnitude of the first and second signals become equal, the third signal is forced to zero. Thus, the increase in fuel flow generated by electronic control circuit 22A is halted and the incidence of fuel flowing to engine 1 OA is now no longer directly controlled by the automatic power reserve of the present invention.

In the present arrangement, for a given application and power factor X, the value of the second signal is a constant entering summer 46 however, the value of the first signal (QES) is variable simply because an increase in fuel flow produces a proportional and corresponding increase in the value of the first signal entering electronic control unit 22A.

Although, for purposes of clarity, the present invention has been described primarily in connection with engine 1 OA, and the failure and increased fuel flow Wf therefor, the invention also includes provision for increasing the fuel flow Wf of operating engine 1 OB upon failure of engine 1 or. For example, referring to Figure 1, in one form of the invention, detection circuit 26A develops detection output signal 27A which is received by detection circuit 26B, wherein detection circuit 26B is actuated thereby. Thus failure of engine 1 OA with APR 28B and lever 33B in ON condition, results in control 28B causing a predetermined increase in fuel flow Wf to engine 1 OB.In this connection, if desired, the control of the present invention can also be utilized in applications where, following failure of one or more engines, the fuel flow Wf to some or all of the remaining engines is increased.

The magnitude of increased fuel flow should be selected to provide a significant increase in engine life but not so large as to result in an uncontrollable condition of asymmetric thrust on the multiple engine aircraft. Of course, in increasing fuel flow Wf to any one or more of the engines, appropriate limits must be set to prevent excessive trim beyond turbine temperature or turbine shaft torque limits.

The control of the present invention is generally applicable to multiple gas turbine engines, not simply turboprop engines. For example, the control can be utilized for turbofan engines although the power failure measurement may be different than for turboprop applications.

In addition, for convenience, the controlled variable QES would preferably be replaced with fan speed N,. The low pressure turbine in such turbofans is coupled to drive the fan. Thus, the low pressure turbine may be referred to as an output shaft of the turbofan.

Memory circuit Referring to Figures 3A and 3B an embodiment of the memory circuit 42 of Figure 2 is illustrated in which the DC analog of QES is passed to a unity gain amplifier 50 (part number LM 108 by National Semiconductor Company, hereinafter referred to as NSC) via input 52 connected to an RC circuit. The RC circuit comprises resistors 54 and 56 with a capacitor 58 connected therebetween, the other extremity of which capacitor is connected to ground. Another input 60 to amplifier 50 is connected to ground through a resistor 62. Disposed between input 52 and the output 64 is a parallel circuit arrangement comprising a capacitor 66 and resistor 68. Two other inputs 70 and 72 are connected to positive and negative sources of a supply voltage respectively. Lastly, a capacitor 74 is coupled between two additional inputs 76 and 78 of amplifier 50.

The output from amplifier 50 serves as one input to a torque limit (-selector) circuit 80. A second input to the torque limit circuit 80 is coupled to output 82 of a unity gain amplifier 84.

With regard to the torque limit circuit 80, a third input 94 connects to a positive source of supply voltage. The output 95 from torque limit circuit 80 serves as input to torque limit circuit (+ selector) 96. A second input to torque limit 96 is connected through a junction 98 to a voltage divider network formed by resistors 100 and 1 02.

The voltage at junction 98 is equivalent to the minimum torque that the memory circuit is allowed to set. The free end of resistor 100 is connected to a positive source of supply whereas the free end of resistor 102 is connected to ground. A third input 104 of torque limit circuit (+ selector) 96 is tied to a negative source of supply voltage.

Amplifier 84 (NSC part number LM 741), referenced above, establishes a voltage equivalent to tha maximum torque allowed. This maximum torque reference voltage is established via resistors 86 and 88. Two additional inputs 90 and 92 are connected to a positive and negative source of supply respectively. An input 93 is tied directly to the output 82 of amplifier 84 in a feedback fashion.

The output 106 from torque limit circuit 96 provides an input to a comparator 108 (NSC part number LM 111) via one end of resistor 110 with the other end thereof bypassed to ground through capacitor 11 2. A second input 114 to comparator 108 is coupled to a positive source of supply, the supply being bypassed to ground through capacitor 116. Two additional inputs 11 8 and 120 to comparator 108 are tied together. A further input 122 is connected to a negative source of supply and then to the negative side of a bypass capacitor 124 with the other side of said capacitor 124 being connected to ground.

Another input 126 is connected to ground.

Input 111 of comparator 108 is connected through load resistor 11 5 to ground and is coupled to the output of an amplifier 362 (NSC part number LM 108) via resistor 382, which amplifier will be further described hereinbelow in connection with Figure 3B.

The output 121 of comparator 108 is connected to a positive source of supply via resistor 130 and further to input 136 of a 14-pin D-type dual-edge triggered flip-flop 132 (Type 7474). In flip-flop 132, pins 136, 148 and 152 are inputs and pins 142, 144 and 1 62 are outputs. Pins 138 and 1 54 are the clocking pins. Pins 134 and 1 50 are status clear pins. Pins 140 and 1 58 are presets while pin 146 is common.

Pin 140 of flip-flop 132 is coupled to pin 134 and further to pins 150 and 1 56 via a junction 1 70. Junction 1 70 additionally connects to a positive source of supply through a resistor 1 72 with the supply being coupled directly to input pin 148 of flip-flop 132. Pin 138 connects to pin 1 54 of flip-flop 132 and also to pin 202 via a junction 203 to a 14-pin quad 2-input NAND gate 1 74.

Output pin 142 and common pin 146 of flip-flop 132 are left open and connected to ground respectively. With regard to the remaining pins of flip-flop 132, output pin 1 62 connects to input pins 228 and 264 of up/down counters 220 and 256 respectively. Output pin 1 58 is unused in the present embodiment, whereas input pin 1 52 is connected to the respective APR circuit 28 which is located outside the memory circuit 42.

The quad 2-input NAND gate 1 74 (Type 7400) of memory circuit 42 has input pins 176, 1 78, 1 82, 1 84, 192, 198 and 200. The outputs from NAND gate 174 comprise pinsl 180, 186, 196 and 202. Pin 188 is common and is suitably grounded. Pins 180, 182 and 1 84 are tied together and coupled to one end of a resistor 204 while the other end of resistor 204 is connected to pins 1 76 and 178. Pin 186 connects to pins 1 76 and 1 78 via capacitor 206 through junction 207.

An input to NAND gate 174 through pin 1 90 is connected to a positive source of supply. Pins 1 92 and 194 are tied together at junction 210.

Junction 210 further couples to one end of a resistor 212 and capacitor 214, the other end of which resistor and capacitor are respectively connected to pins 196,198 and 200 of gate 174 and to a junction 203. Junction 203 further connects to pin 202.

The memory circuit 42 further comprises two identical (Type 74LS 191) 16-pin presettable up/down counters 220 and 256. Counter 220 has inputs 222, 228, 230, 238, 240, 242, 248, 250 and 252; outputs 224, 226, 232, 234, 244 and 246: and ground pin 236. Counter 256 comprises inputs 258, 264, 266, 274, 276, 278, 286 and 288; and outputs 260, 264,268, 270, 280 and 282. Pin 272 is ground for counter 256.

Inputs pins 228 and 264 of counters 220 and 256, respectively, are connected together and further couples to pin 1 62 of flip-flop 132 as described above. Similarly, pins 230 and 266 of counters 220 and 256, respectively, are connected to each other andre coupled to pin 144 of flip-flop 132. Pin 242 if counter 220 is connected to pin 286 via junction 207. Pins 244 and 248 of counter 220 are fed to pins 278 and 284, respectively, of counter 256. Pin 284 of counter 256 connects to a positive source of supply through a resistor 290. A capacitor 292 is connected at one end to the supply end and the other extremity is connected to ground. Pins 222, 240, 246, 250 and 252 of counter 220 remain unused in the embodiment of memory circuit 42 shown in Figure 3.Similarly, pins 258, 276, 280, 282, 286 and 288 of counter 256 remain unused.

As in the case of counter 220, counter 256 is also powered by a positive source of supply (pin 274).

Pins 224, 226, 232 and 234 of counter 220 are connected to pins 312, 310, 314 and 316, respectively, of a 1 6-pin digital-to-analog (D/A) converter 300. Pins 236 and 272 of counters 220 and 256, respectively, are coupled to ground.

D/A converter 300 (Type DAC-08) has inputs 308,310,312,314,316,326,328,330 and 332 and an analog output at pin 324. Pins 302, 304, 306 and 322 provide means for stabilizing converter 300 and pins 318 and 320 are ground.

Pin 302 is connected to pin 322 via capacitor 340, with the negative terminal of the capacitor connected to a negative source of supply. Pin 304 is connected to ground through a resistor 342.

Pin 306 connects to resistor 344 and to a grounded parallel arrangement comprising a resistor 346 and capacitor 348 via a junction 350. Junction 350 is further coupled to a positive source of supply via resistor 352. The D/A converter 300 is powered by a positive source of supply voltage at pin 308. In the present embodiment for D/A converter 300, pins 318 and 320 are tied together and grounded. Pins 326, 328, 330 and 332 are connected respectively to pins 270, 268, 260 and 262 of counter 256. The output of D/A converter 300 at pin 324 is coupled to pin 360 of a unity gain amplifier 326.

Amplifier 362 (Type LM 108) has several inputs and one output. A resistor 364 is connected between input pin 360 and the output of amplifier 362. Another input 366 is connected to a positive voltage source, which source is bypassed to ground via a capacitor 368. An additional input 370 is coupled to ground through a capacitor 372. A further input 374 is coupled to a negative source of supply which supply is bypassed to ground via capacitor 376. Still another input 378 is connected to ground via a resistor 380. The output from amplifier 362 is fed back to comparator 108 of Figure 3A at pin 111 via a divider arrangement comprising resistors 382 and 11 5.

The operation of the embodiment of memory circuit 42, illustrated in Figures 3A and 3B, is considered below. Initially, NAND gate 1 74 provides clock pulses to flip-flop 1 32 and to up/down counters 220 and 256. These clock pulses are used to create an eight-bit binary number in the up/down counters corresponding to the analog torque value. A DC reference voltage proportional to the first signal (QES) is fed to pin 52 of amplifier 50 and any ripple in the signal is filtered by means of the RC combination of resistors 54 and 56 and capacitor 58. The output from amplifier 50 is first fed through the maximum torque limit circuit 80 which is preset to limit the value of torque to a first predetermined value. This limit is a minimum torque limit, i.e., the memory does nowt hold a torque value below this limit.The signal is then fed through the minimum torque limit circuit 96 whose value is preset to a second predetermined value. This limit is the highest torque value that the engine to be controlled is permitted to operate in order to prevent damage to aircraft gear drives and other engine related systems and components. The resulting signal at the output of torque limit circuit 96 provides an input to comparator 108.

When the value of the signal at pin 111 of comparator 1 08 is less than the value of the signal at pin 113, the output at pin 121 is driven high and is fed to pin 1 36 of flip-flop 132. Output signals from flip-flop 132 at pins 144 and 1 62 are fed to pins 230 and 228, respectively, of up/down counter 220 and pins 266 and 264 of up/down counter 256. When the APR circuit 28 (individually and collectively referring to 28A, 28B of Figures 1, 2) is in the OFF condition, the value of the input signals to pins 228 and 264 of up/down counter 220 and 256, respectively, equal zero and the counters are in the "enable" mode. The input to pins 230 and 266 of up/down counters 220 and 256, respectively, will set the binary outputs from the counters to be converted to a DC signal at pin 324 of the D/A converter 300.

When the APR circuit 28 switches to the ON condition, the output of flip-flop 1 32 at pin 1 62 changes from a low to a high value and up/down counters 220 and 256 are switched to the "inhibit" mode. The then present binary value in the counters at the time that APR is switched to the ON condition will be held and retained until APR is no longer activated. This retained signal provides a reference, i.e., signal QEM, for determining the increased fuel to one or more engines 1 OA, 1 or.

From the foregoing, it will be apparent that the invention lends itself to numerous modifications, changes, substitutions and equivalents, all of which will be obvious to those skilled in the art.

The digital logic used herein is preferably the transistor-transistor logic type, but other logic types will be obvious to those skilled in the art.

Accordingly, it is intended that the scope of the invention be limited only by the spirit and scope of the appended claims.

Claims (23)

Claims

1. Control for a plurality of gas turbine engines, each of the engines having an output shaft, which control comprises: (a) automatic power reserve switching means for developing a switching output signal responsive to power failure 9f at least one of said engines; (b) means for developing a first signal representative of the substantially instantaneous value of power at the output shaft of said one engine; (c) memory means responsive to said switching output signal for receiving and storing said first signal and developing a memory means output signal, said memory means output signal comprising said first signal when said switching output signal is in an OFF condition, and said memory means output signal comprising a stored value of said first signal when said switching output signal is in an ON condition;; (d) means for receiving said memory means output signal and developing a second signal representative of a desired power at said output shaft of at least one of said engines; (e) means for receiving said first signal and said second signal and developing a third signal representative of the difference there between; and (f) means for receiving said third signal and increasing the power at said output shaft of at least one of said engines when said third signal does not meet predetermined criteria.

2. A control in accordance with claim 1 wherein said first signal is representative of the substantially instantaneous value of torque.

3. A control in accordance with claim 2 wherein said engines comprise turboprop engines.

4. A contro! in accordance with claim 1 wherein said engines comprise turbofan engines.

5. A control in accordance with claim 4 wherein each of said engines include a fan section and in which said first signal is representative of the substantially instantaneous value of fan speed.

O. H conrroi In accordance witn claim I wherein said stored value of said first signal comprises the value of power at said output shaft of said one engine when said automatic power reserve switching means develops said switching output signal.

7. A control in accordance with claim 6 wherein said engines are coupled for control purposes and wherein a plurality of said first signals of (b) are developed, each of said plurality representative of the substantially instantaneous value of power at said output shaft of respective ones of said engines.

8. A control in accordance with claim 7 wherein said means of (f) includes means for increasing the power-at said output shaft of said one engine.

9. A control in accordance with claim 8 wherein said means of (f) includes means for increasing the power at said output shaft of each remaining operating engine.

1 0. Automatic power reserve control for multiple engine aircraft, said engines each having an output shaft and operated responsive to fuel flow, said engines each having coupling means for comparable operation; said aircraft including means for turning said control to an operative condition and means for generating a signal responsive to the failure of any one of said engines during takeoff, said aircraft having switching means effective for developing an automatic power reserve switching output signal, said control being responsive to said switching output signal, said control comprising:: (a) means for developing a first signal representative of the substantially instantaneous value ot torque of the output shaft of each of said operating engines; (b) memory means responsive to said switching output signal for receiving and storing said first signal and developing a memory means output signal, said memory means output signal comprising said first signal when said switching output signal is in an OFF condition, and said memory means output signal comprising a stored value of said first signal when said switching output signal is in an ON condition; (c) means for receiving said memory means output signal and developing a second signal representative of a desired torque at said output shaft of any remaining operating engine;; (d) means for receiving said first signal and said second signal and developing a third signal representative of the difference there between; and (e) means for receiving said third signal and utilizing said third signal for increasing the value of torque at said output shaft of said remaining operating engines when said third signal does not meet predetermined criteria.

11. A control in accordance with claim 10 wherein said gas turbine engines comprise turboprop engines.

12. A control in accordance with claim 6 or 10 wherein said second signal comprises said stored value of said first signal multiplied by a predetermined power factor.

1 3. A control in accordance with claim 12 wherein said predetermined constant is from about 1.05 to about 1.50.

14. A control in accordance with claim 6 or 10 wherein said memory means includes counter means.

1 5. A method of control for a plurality of gas turbine engines, each of said engines having an output shaft, the method comprising the steps of: (a) developing a switching output signal responsive to the failure of at least one of said engines; (b) developing a first signal representative of the substantially instantaneous value of power at the output shaft of at least said one engine; (c) receiving and storing said first signal in memory means; (d) developing a memory means output signal, said memory means output signal comprising said first signal when said switching output signal is in an OFF condition, and said memory means output signal comprising a stored value of said first signal when said switching output signal is in an ON condition;; (e) receiving said memory means output signal and developing a second signal representative of a desired torque at said output shaft of at least one of said engines; (f) receiving said first signal and said second signal and developing a third sional representative of the difference there between; and (g) receiving said third signal and increasing the value of torque at said output shaft of at least one of said engines when said third signal does not meet predetermined criteria.

1 6. A method in accordance with claim 1 5 wherein said first signal is representative of the substantially instantaneous value or torque.

1 7. A method in accordance with claim 1 6 wherein said second signal comprises said stored value of said first signal multiplied by a predetermined power factor.

1 8. A method in accordance with claim 1 7 wherein said predetermined constant is from about 1.05 to about 1.50.

19. A method in accordance with claim 16 wherein said engines comprise turboprop engines.

20. A method in accordance with claim 15 wherein said engines comprise turbofan engines.

21. A method in accordance with claim 15 in which said engines comprise two turboprop engines wherein when one of said engines has failed step (g) includes increasing the value of torque at the remaining operating engine.

22. A control substantially as hereinbefore described with reference to and as illustrated in the drawings.

23. A method of control substantially as hereinbefore described with reference to the drawings.