US3080712A - Compressor anti-surge control for a gas turbine engine - Google Patents

Description

March 12, 1963 H. J. WOOD 3,

COMPRESSOR ANTI-SURGE CONTROL FOR A GAS TURBINE ENGINE Filed Feb. 5, 1959 5 Sheets-Sheet 1 TO OTHER AIR RS Fl 61 INVENTOR. 26 HOMER J.WOOD

ATTORNEYS March 12, 1963 H. J. WOOD 3,080,712

COMPRESSOR ANTI-SURGE CONTROL FOR A GAS TURBINE ENGINE Filed Feb. 5, 1959 5 Sheets-Sheet 2 FiG.3.

Consmni Speed Lines INVENTOR. w J'' Q I43 HOMER J. wooo Compressor Airflow BY MQAQJ;

ATTORNEYS March 12, 1963 H. J. WOOD 3,080,712

COMPRESSOR ANTI-SURGE CONTROL FOR A GAS TURBINE ENGINE Q Filed Feb. 5, 1959 5 Sheets-Sheet 3 FIGS.

Constant Speed Lines Sens or Pa rumeter a/ t Compressor Pressure Ratio FIG.6.

INVENTOR. HOMER J.WOOD

ATTOR NEYS March 12, 1963 H. J. WOOD 3,080,712

COMPRESSOR ANTI-SURGE CONTROL FOR A GAS TURBINE ENGINE Filed Feb. 5, 1959 5 Sheets-Sheet 4 INVENTOR.

HOMER J. W0 OD BY %A 1 J51?! 1 ATTORNEY COMPRESSOR ANTI-SURGE CONTROL FOR A GAS TURBINE ENGINE 5 Sheets-Sheet 5 Filed Feb. 5, 1959 FIG.9.

I1 I w l KJI a INVENTOR.

HOMER J.WOOD

ATTORNEYS Patented Mar. 12, 1963 3,080,712 COMPRESSUR ANTI-SURGE CONTROL FGR A GAS TURBINE ENGENE Homer J. Wood, Sherman Oaks, Califi, assignor to Continental Aviation and Engineering Corporation, Detroit, Mich, a corporation of Virginia Filed Feb. 5, 1959, Ser. No. 791,447 18 Claims. (Cl. 641-3919) This invention relates to control systems for gas turbine engines, and more particularly to a pneumatic surge control sensor system operable to prevent compressor surge by discharging controlled amounts of compressor airflow.

Compressor surge in gas turbine engines results in violent pulsations of gas flow and pressure. These upset the operating cycle to the extent that gross deterioration of engine performance immediately occurs, and excessive gas temperatures are likely to result. In addition, the pressure variations are so violent that physical damage to the engine may result. Although it is possible to build engines which can withstand surge conditions, or which develop only mild pressure pulsations, undesirable increases in weight and cost are involved. It is a further characteristic of many gas turbines that the most efficient operating point occurs quite close to the compressor surge range, and to avoid surging difiiculties by moving the operating point results in undesirable deterioration of performance.

For gas turbine engines used primarily for compressing air for use by other equipment, certain special problems are involved in addition to those encountered in other gas turbines with respect to compressor surge difliculties. In particular, such engines must face very abrupt shutoil of the compressed air demand flow. This results in the very rapid establishment of a condition tending to produce surge. This condition is often called shock surge, in recognition of the shock efie'ct of a sudden shut-oil of air delivery.

Heretofore, little has been accomplished in finding an efiective, yet inexpensive and simplified method of avoiding compressor surge conditions.

An object of the present invention is to improve performance of gas turbine engines by preventing compressor operation from reaching surge conditions.

Another object of the invention is to control gas turbine engine operation by providing a system for controlling compressor pressure ratios and airflow.

A further object of the invention is to prevent compressor surge in a gas turbine engine by providing a new pressure sensitive control system operable to discharge controlled amounts of compressor airflow.

Yet another object of the invention is to simplify gas turbine engine controls by providing an automatically operating compressor surge prevention system.

Still a further object of the invention is to prevent compressor surge conditions in a gas turbine engine by providing an automatic pressure sensitive pneumatic valve system operated through a surge sensor which is responsive to compressor operation.

Yet a further object of the invention is to increase the operating efficiency of gas turbine compressors by providing a control system enabling the compressor to operate at the highest effective pressure ratio at all operating ranges.

Still another object of the invention is to prevent surge conditions in gas turbine engines by providing a new pressure sensitive control system operable to modify fuel flow to the engine.

For a more complete unedrstanding of the invention, reference may be had to the accompanying drawings illustrating a preferred embodiment of the invention in which like reference characters refer to like parts throughout the several views and in which FIG. 1 is a diagrammatic view of a preferred control system embodying the invention as applied to a preferred gas turbine engine.

FIG. 2 is a longitudinal cross-sectional view of a preferred pneumatic sensor construction as embodied in the system of FIG. 1.

FIG. 3 is a longitudinal cross-sectional view of a preferred servo valve construction as embodied in the system of FIG. 1.

FIG. 4 is a compressor map for purposes of explaining the surge control concept of the invention.

FIG. 5 is another compressor map utilizing different parameters.

FIG. 6 is a diagram illustrating the aerodynamic relationship of two orifices in series.

FIG. 7 is a diagrammatic cross-section of a portion of a chamber in the sensor of FIG. 2.

FIG. 8 is a diagrammatic view of another preferred modification of the invention using the sensor of FIG. 2

for controlling engine fuel flow.

FIG. 9 is a cross-sectional view of a preferred fuel control valve as used in the modification of FIG. 8.

In the embodiment of the invention represented in FIG. 1 a preferred gas turbine engine 10 is illustrated as comprising a housing 11 having an air inlet 12, a combustion chamber or combustor 13, an exhaust nozzle 14, and a compressor air chamber 15, the housing 11 supporting a turbine 16 and a compressor 17 operable to supply compressed air to the chamber 15, the compressed air being used in the turbine and also stored for selective delivery through a discharge pipe 18 having a butterfly valve 18a for delivery to any compressed air consumer. It will be noted that the compressor is operable to deliver more air than is consumed by the turbine 16. Connected with the discharge pipe 18 is a bypass pipe 19 having a discharge stack 20 for exhausting excess compressed air as controlled by a servo valve 21, shown in more detail in FIG. 3 as will be described later.

The servo valve is generally controlled by a surge control sensor 22 illustrated more fully in FIG. 2, as will also be described later. Suitable pressure probes and communicating pressure conduits are also provided.

In order to fully comprehend the function and operation of the present system, an understanding of the known theoretical operating characteristics of an air compressor, such as is utilized in a gas turbine engine, is first necessary. FIG. 4 illustrates, generally, a compressor map on which operation of any compressor may be diagrammed in terms of corrected compressor airflow and compressor pressure ratio, where:

P /P is the pressure ratio across the compressor; that is, compressor discharge pressure (P per compressor inlet total pressure (P and W,, /0/6 is corrected compressor airflow, where W,, is uncorrected compressor airflow, 0 is ambient temperature correction to NACA std., and 5 is barometric correction to NACA std.

Note-In gas turbine engines not in motion, as where used solely to compress air for use by other equipment, compressor inlet total pressure would be equivalent to atmospheric pressure.

With compressor operation described in terms of corrected parameters, the compressor map of FIG. 4 then fixes compressor performance for all inlet conditions and enables one to predict compressor performance for varying inlet conditions.

Compressor surge is a phenomenon associated with the operation of all compressors. For example, assuming NACA standard ambient temperature and barometric conditions, a compressor operating at a given speed, regardless of its power source, to deliver a certain airflow W at some given pressure ratio P /P (point 1 on the map), and a large air valve downstream of the compressor, a partial closing of the air valve while maintaining compressor speed will reduce compressor airflow W and the operating point of the compressor will shift to point (2) on the map. Upon continued closing of the air valve and consequent reduction of airflow, the compressor will reach a state of unstable operation, commonly called compressor surge, and on the compressor map will substantially occur when the operating point reaches a line such as the solid line of FIG. 4. To the left of this line is the unstable operating line, and to the right will be seen typical lines of ditferent constant speeds of the compressor.

With the compressor as part of the compressed air producing gas turbine engine 10 shown in FIG. 1, the combustor 13 and turbine 16 will act on the compressor 17 in a similar manner asthe theoretical valve mentioned above; for example, at a given speed, held by any means such as a governor (not shown), an increase in fuel flow to the combustor 13 will raise the temperature of the air (and consequently its volume) and thereby act to decrease compressor air flow, moving the operating point on the compressor map of FIG. 4 toward the surge line. Opening of the butterfly valve 18a would increase compressor air flow, moving the operating point on the compressor map away from the surge line. Closing of the butterfly valve 18a would again decrease compressor air flow, again moving the operating point on the compressor map toward the surge line.

It will be apparent, then, that a control system operable to bleed off the proper controlled amounts of air will function to maintain compressor operation somewhere to the right of the surge line, and preferably no closer to the surge line than a predetermined value, such as is illustrated by a dash line in FIG. 4. In other words, the control system will function in such a manner that any tendency of the compressor to operate at, Surge will immediately be offset by increasing compressor airflow so that the operating point of the compressor will remain to the right of the surge line of FIG. 4.

Thus it is seen that corrected compressor airflow is the critical determining factor with which the control system is concerned. In seeking to develop a suitable control system, it was found that corrected compressor airflow could be sensed by measuring static and total pressure at the inlet to the compressor.

Mathematically,

where P zCompressor inlet total pressure P =Compressor inlet static pressure W =Compressor airflow =Ambient temperature correction to NACA std. 6=Barometric correction to NACA std.

In other words, for any given value of corrected compressor airflow there exists One and only one value of the compressor inlet ratio P -P t Thus it is possible to construct a compressor map using P -P Pt This map is illustrated in FIG. 5, and illustrates the concept that it will be possible by making a mechanical com parison of compressor pressures, to establish an operating or modulation line (dotted line in FIG. 5), since in place of for any operation of the compressor.

Referring to FIGS. 1, 2 and 3, the preferred control system comprises the sensor 22 and the servo 21, a compressor inlet total pressure (P sensing conduit 25, a compressor inlet static pressure (P sensing conduit 26, and a compressor discharge pressure (P sensing conduit 27, the signal from the sensor 22 to the servo 21 being transmitted through a signal pressure (S) conduit 28.

The sensor 22 preferably comprises a multiple part housing 29 having a sensor chamber 30 divided by a compressor inlet pressure sensing diaphragm 31 of area A a second sensor chamber 32 divided by a compressor pressure ratio sensing diaphragm 33 of area A and a control chamber 34. The diaphragms 31 and 33 are connected to a control pin 35 operable to control the opening of a port 36, connecting the control chamber 34 with the signal pressure (S) conduit 28, in proportion to the magnitude of pressure area differential existing across the stacked diaphragms 31 and 33. The pin 35 is preferably biased toward the closed position by a relatively weak spring 40 hearing between a plate 41, adjustable by any means such as an adjusting screw 42, and a plate 43 connected to the control pin 35. For purposes of the following explanatiointhe small force of the spring 40 will not be included.

One side of the chamber 30 is openly connectedthrough a port 44 to a branch 25a of the conduit 25, and the other side of the chamber 30 is openly connected through a port 45 with the conduit 26, suchthat the diaphragm 31 will be responsive to the diiferential between compressor inlet total pressure P, and static pressure P to a degree dependent on the diaphragm area A One side of the chamber 32 is openly connected through a port 46 with another branch 25b of the conduit 25. The other side of the chamber 32 is subject to an intermediate pressure P developed between series-connected orifices 47 (openly connected with the conduit 27) and 48 (openly connected with a third branch 250 of the conduit 25).

The area a of the orifice 48 is preferably adjustable by means of a needle valve 49, while the area a of the orifice 47 is preferably fixed. Thus the diaphragm 33 will be responsive to the differential between compressor inlet total pressure P, and the intermediate pressure P to a degree dependent on the diaphragm area A It can be shown that the sensor operation is in accord with the conditions required by the compressor map FIG. 5; that is, if properly constructed, the sensor will axially actuate the pin to open and close the port 36 in correspondence to the parameter aphragms 31 and 33, the force balance equation (P,P )A (P P )A describes the function of the sensor 22. Dividing by P, and A t t A2 Since any constant may be selected for the ratio it remains only to show that e) Pt 1 P,

t on, 5 P2 2 P,

age e a P. P, 2 Pt 3 P,

By choosing the proper values of a and a ea Pt P.

In constructing the sensor 22,

can be made to equal so that 1 and are selected so that, for values of it is possible to determine the value of that the sensor will regulate to, which will be the selected modulation line in FIG. 5.

In accomplishing this function, the servo Valve 21, shown in FIG. 3, operates to bleed excess compressor air from the by-pass pipe 19 through the stack 20 in response to the signal from the sensor 22.

The servo valve preferably comprises a housing 55 having an inlet chamber 56 openly connected with the bypass pipe 19 and terminating in an annular valve seat 57. A poppet valve 58 having an annular closure memher 57 adapted to seat on the valve seat 57 is positioned in a control chamber 60. A diaphragm 61 is secured to the poppet valve 53 and the housing 55 so that the valve 58 will operate axially as determined by a pressure differential existing between the chambers 56 and 60 to open and close the valve. A tube element 62 is carried by the poppet valve 58 and slides axially within a sleeve 63 supported by the housing 55. The sleeve 63 carries a needle valve element 64 which extends into the end of the tube element 62, acting to open and close an orifice 65 as determined by the position of the poppet valve 58. The tube 62 thus variably communicates the inner end of the chamber 60 with the discharge pressure P of the compressor. The chamber 60 communicates at all times with the conduit 28 which is connected with the sensor 22 and transmits the sensor signal S.

In substance, when the sensor valve port 36 is open, pressure in the chamber 60 is bled out through the conduit 28 relativeto the degree to which the sensor signal port 36 is opened by the pin 35 (see FIG. 2), permitting the poppet valve 58 to open and bleed compressor discharge air out the stack 20. As the poppet valve 58 opens, however, the area of the orifice 65 will increase to bleed compressor discharge pressure P through the tube 62 into the chamber 6t) tending to close the poppet valve 58, the eifective area on the chamber 60 side of the diaphragm 61 being greater than the effective area on the chamber 56 side as shown.

In efiect, the pressure existing in the chamber 66 will take an intermediate pressure valve between S and P which is a function of the degree to which the sensor port 36 is opened. Consequently, the position of the poppet valve 58 in the servo is a function of the bleed area of the port 36 in the sensor, Which in turn, due to the pressure differential existing across the stack diap-hragms of the sensor 22, will take on values such as to maintain in accordance with the discussion given previously, tending to maintain operation of the compressor on the control line shown in the compressor map of FIG. 4.

It will be apparent that when the butterfly valve 1? (FIG. 1) is opened for delivery of compressed air to the user, compressor airflow will increase, the surge sensor 22 will operate to cut-off bleed through the port 36, the poppet valve 58 of the servo valve 21 will close fully, and no air will bleed through the by-pass pipe 19. Thus the compressor will be able to operate to the right of the control line of FIG. 4 to produce the required airflow. However, as the butterfly valve 18a is closed, compressor airflow decreases, and when an imbalance is sensed by the sensor 22, indicating an approach toward surge conditions, the sensor port 36 will open to bleed the servo chamber 69 and open the poppet valve 58 to the necessary degreeas described above.

The servo valve 21 also preferably performs the additional function of preventing shock surge due to rapid closing of the buterfiy valve 18a. For most purposes, a compressor delivery valve such as that illustrated should be operable to move from full open to full closed in about 0.2 second. A second control chamber 70 is provided in the servo valve housing 55, and is divided by a diaphragm 71 which carries a needle valve element 72 extending into a port 73 which communicates the chamber 60 with atmosphere via a passage 74. A conduit 75 connects with a passage 76 in the housing 55, the passage 76 opening .to the inner end of the chamber 70.

' The conduit 75 is connected, as shown in FIG. 1, with the pipe 18 upstream of the butterfly valve 18a. Upon suddent closing of the butterfly valve, an immediate presvalve 58 as previously described, providing for an immediate increase in compressor airflow to prevent sudden operation toward the surge line of the compressor map FIG. 4, which the sensor 22 would not have time to counteract. A passage 77 connects the passage 76 with the outer end of the chamber 70, the passage 77 being provided with an adjustable orifice 78 so that the increased pressure P will be subsequently transmitted to the outerside of the diaphragm 71 to shortly equalize pressures and permit the diaphragm 71 to be urged inward by a spring 79 or other means to close the port 73 as the sensor 22 takes over control of the poppet valve 58.

Although it is practical to use a control system of the general idea illustrated in FIG. 1 for shaft power or jet engines, a more likely modification utilizes the basic surge sensor 22 to modulate a fuel servo valve rather than an air valve. In FIG. 8 a preferred gas turbine jet engine 85 illustrating such a modification comprises a housing 86 having an air inlet 87, a combustion chamber or combustor 88, a jet exhaust nozzle 89, and a compressed air chamber 90, the housing 36 supporting a turbine 91 and a compressor 92 operable to supply compressed air to the chamber 90 for use in the combustor 88 only.

The sensor 22 is the same as that previously described, as well as the compressor inlet total pressure ('P sensing conduit 25 with its branches 25a, 25b and 25c, the compressor inlet static pressure (P sensing conduit 26, the compressor discharge pressure (P sensing conduit 27, and the sensor signal pressure conduit 28. However, the conduit 28 is suitably connected to and transmits the sensor signal to a fuel servo valve 93 which is preferably constructed on the lines suggested in FIG. 9, having a fuel inlet 94 suitably connected with the supply of a fuel pump (not shown) and a fuel outlet 95 delivering metered fuel to the engine, the fuel flowing through passages 96 and 97 in the valve 93 and modulated by means of a poppet valve 98.

The valve 93 is provided with a pair of compartments 100 and 101 respectively divided by diaphragms 102 and 103 into respective control chambers 164, 105, 106 and 107. Chamber 104 is connected by a passage 110 with the fuel passage 97, chambers 105 and 107 are connected respectively by passages 1 1-1 and 112 with the sensor signal pressure conduit 28, and chamber 106 is connected by a passage 113 with a branch conduit 25d sensing compressor inlet total pressure P, from the conduit 25. A conduit 27a connects the passages 111 and 112 with the compressor discharge pressure (P sensing conduit 27, and includes a restricted orifice 114.

The poppet valve 98 is operably connected by means of a pin 115 with the diaphragm 102, being urged toward the closed position by a relatively weak spring 116. The two diaphragms 102 and 103 are operably connected in series by means of a pin 117.

It will be apparent that the diaphragm 102 balances fuel pressure against a pressure intermediate the surge sensor signal pressure (S) and the compressor discharge pressure (P The diaphragm 103 balances compressor inlet total pressure against the same intermediate pressure. In essence, the position of the poppet valve will be determined by the surge sensor signal pressure which varies relative to the opening of the sensor valve port 36.

Thus, when the compressor approaches surge conditions, the sensor 22 operates as previously explained to open the valve port 36. This decreases the pressure in the fuel valve chambers 105 and 107 and the poppet valve 98 moves toward a closed position to reduce fuel flow. Thermodynamically, reduced fuel flow to a turbine engine operates to reduce compressor discharge pressure and hence increases compressor ainflow, and the operating point on the compressor map of FIG. 4 will move away from the surge line. Thus the result of reducing fuel flow is in substance, as far as its effect on the engine is 8 concerned, the same as bleeding off excess compressed air as is done in the first modification described.

As the fuel poppet valve 98 closes, the fuel pressure in the chamber 104 will decrease correspondingly, so that, since the diaphragm 102 balances fuel pressure with a pressure depending on surge signal pressure (S), the poppet valve 98 will seek a stable position to provide that fuel flow which will not cause surge conditions.

It is apparent also that the present system will prevent excess fuel flow during acceleration. Since increased fuel flow on acceleration causes a rise in the temperature of the combustion mixture, its volume also increases, resulting in a decrease of compressor airflow. The surge sensor, as previously explained, operates to open the valve port 36 on such a decrease as the operating point moves toward surge conditions, and this again will cause the fuel poppet valve 93 to move toward a closed position to decrease fuel flow.

Although I have described only two preferred embodiments of my invention, it will be apparent to one skilled in the art to which the invention pertains that various changes and modifications may be made therein without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. A control system for a gas turbine engine having a fuel system and an air compressor characterized by a predictable tendency to develop compressor surge conditions at operating ranges producing a predetermined reduction of compressor airflow, an air inlet and an air discharge for said compressor, said control system comprising first means variably increasing compressor airflow to avoid said surge conditions a servo means operating said first means and a sensing means automatically controlling operating of said servo means in response to varying compressor airflow, said sensing means comprising an actuating means operably connected with said servo means and a pressure responsive means adjusting said actuating means in response to changes in the balance of two pressure differentials, one of said pressure differentials being the diflerential between compressor inlet total pressure and compressor inlet static pressure, the other of said pressure differentials being the differential between compressor inlet total pressure and a pressure intermediate compressor discharge pressure and compressor inlet total pressure.

2. A control system for a gas turbine engine having a fuel system and an air compressor characterized by a predictable tendency to develop compressor surge conditions at operating ranges producing a predetermined reduction of compressor airflow, an air inlet and an air discharge for said compressor, said control system comprising first means variably increasing compressor airflow to avoid said surge conditions a servo means operating said first means and a sensing means automatically controlling operation of said servo means in response to varying compressor airflow, said sensing means comprising a housing having two pressure sensitive elements, a movable actuator operably connecting said pressure sensitive elements with said ser-vo means, one of said pressure sensitive elements moving said actuator in response to changes in pressure differential between a compressor inlet total pressure and compressor inlet static pressure, and the other of said pressure sensitive elements moving said actuator in response to changes in pressure differential between compressor inlet total pressure and a pressure intermediate compressor total pressure and compressor discharge pressure.

3. The control system as defined in claim 2 and in which said pressure sensitive elements are balanced in accordance with the force-balance equation t 0 2 equals b"" t) 1 in which P represents compressor inlet total pressure, P, represents pressure-inlet static pressure, P represents the pressure intermediate compressor total pressure and compressor discharge pressure, A represents the total effective area of the first mentioned pressure sensitive element, and A represents the total efifective area of the second mentioned pressure sensitive element.

4. A control system for a gas turbine engine having a fuel system and an air compressor characterized by a predictable tendency to develop compressor surge conditions at operating ranges producing a predetermined reduction of compressor airflow, an air inlet and an air discharge for said compressor, said control system comprising first means variably increasing compressor airflow to avoid said surge conditions a servo means operating said first means and a sensing means automatically controlling operation of said servo means in response to varying compressor airflow, said sensing means comprising a housing having a first pressure chamber and a second pressure chamber, a movable pressure sensitive element disposed in each of said chambers and each element having a predetermined total effective area, a movable actuator operably connecting said pressure sensitive ele ments with said servo means, a compressor inlet total pressure sensing means, a compressor inlet static pressure sensing means, and a compressor discharge pressure sens ing means, means connecting said first pressure chamber on one side of the pressure sensitive element with said total pressure sensing means and means connecting said first pressure chamber on the other side of the pressure sensitive element with said static pressure sensing means, means connecting said second pressure chamber on one side of the pressure sensitive element with said total pressure sensing means, means connecting said second pressure chamber on the other side of the pressure sensitive ele ment with said total pressure sensing means and including a restricted orifice having a predetermined area, and means connecting said second pressure chamber on said other side of the pressure sensitive element with said discharge pressure sensing means and including a second restricted orifice, the pressure in said other side of the last mentioned pressure sensitive element being the intermediate pressure measured between said orifices and dependent on the ratio of the areas of said orifices.

5. The control system as defined in claim 4 in which said pressure sensitive elements comprise axially movable diaphragm members, and said actuator axially connecting said diaphragm members in series.

6. The control system as defined in claim 4 and having means variably adjusting the area of one of said orifices to vary said intermediate pressure and thereby adjust the operating pressure differential acting on the last mentioned pressure sensitive element.

7. A control system for a gas turbine engine haViIlg a fuel and an air compressor characterized by a predictable tendency to develop compressor surge conditions at operating ranges producing a predetermined reduction of compressor airflow, an air inlet and an air discharge for said compressor, said control system comprising first means variably increasing compressor airflow to avoid said surge conditions a servo means operating said first means and a sensing means automatically controlling operation of said servo means in response to varying compressor airflow, said servo means comp-rising a housing having a bleed air outlet, an air inlet openly con nected with said compressor discharge, a bleed valve means operable to bleed controlled amounts of compressed air from said air outlet and disposed intermediate said outlet and inlet, a pressure control chamber, and a pressure sensitive element operably connected with said bleed valve and disposed intermediate said inlet and said control chamber, said pressure sensitive element actuating said bleed valve in response to changes in pressure differential between compressor discharge pressure and the pressure in said control chamber, and said sensing means comprising means transmitting a variable pressure to said control chamber relative to changes in compressor airflow.

8. The control system as defined in claim 7 and in which said servo means includes means variably openly connecting said control chamber to compressor discharge pressure, said last mentioned means being operable relative to bleed valve operation to modify relative to the position of said bleed valve the control chamber pressure as transmitted from said sensing means.

9. A control system for a gas turbine engine having a fuel system and an air compressor characterized by a predictable tendency to develop compressor surge conditions at operating ranges producing a predetermined reduction of compressor airflow, an air inlet and an air discharge for said compressor, said control system comprising first means variably increasing compressor airflow to avoid said surge conditions a servo means operating said first means and a sensing means automatically controlling operation of said servo means in response to varying compressor airflow, and a second sensing means automatically operating said servo means in response only to a sudden decrease in compressor airflow.

10. The control system as defined in claim 9 and in which said servo means com-prises an air bleed valve means operable to bleed controlled amounts of compres-sed air from said air outlet and pressure responsive means operably connected with said air bleed valve means, said second sensing means comprising a variable pressure transmitting means actuating said pressure responsive means only upon a sudden decrease in compressor airflow.

11. The control system as defined in claim 10 and in which said pressure responsive means comprises a pressure sensitive element actuating said air bleed valve in response to changes in a pressure diiferential between compressor discharge pressure and a pressure intermediate compressor discharge pressure and the pressure of said pressure transmitting means.

12. The control system as defined in claim 9 and in which said servo means comprises a housing having a bleed air outlet, an air inlet openly connected with said compressor discharge, a bleed valve means operable to bleed controlled amounts of compressed air from said air outlet and disposed intermediate said outlet and inlet, a pressure control chamber, and a pressure sensitive element operably connected with said bleed valve and dis posed intermediate said inlet and said control chamber, said pressure sensitive element actuating said bleed valve in response to changes in pressure diflerent-ial between compressor discharge pressure and the pressure in said control chamber, and said second sensing means comprising means transmitting a variable pressure to said control chamber relative only to a sudden decrease in compressor airflow.

13. The control system as defined in claim 12 and in which said second sensing means comprises a housing having a pressure chamber, a valve means variably connecting said servo means pressure control chamber with atmosphere, a pressure sensitive element operably connected with said valve means and disposed in said pressure chamber, means openly connecting said pressure chamber on one side of said pressure sensitive element with compressor discharge pressure such as will open said valve means upon increase of compressor discharge pressure, and a second means openly connecting said pressure chamber on the other side of said pressure sensitive element with compressor discharge pressure such as will equalize pressure on said pressure sensitive element, said second means including a restricted orifice operable to delay the aforesaid pressure equalization only after a sudden change of compressor discharge pressure and to permit the aforesaid pressure equalization upon other more gradual changes of compressor discharge pressure.

14. A control system for a gas turbine engine having a fuel system and an air compressor characterized by a predictable tendency to develop compressor surge conditions at operating ranges producing a predetermined reduction of compressor airflow, and air inlet and an air discharge for said compressor, said control system comprising first means variably increasing compressor airflow to avoid said surge conditions a servo means operating said first means and a sensing means automatically controlling operation of said servo means in response to varying compressor airflow said sensing means comprising an actuating means operably connected with said servo means and a pressure responsive means adjusting said actuating means in response to changes in the balance of two pressure differentials one of said pressure differentials being the differential between compressor inlet total pressure and compressor inlet static pressure, the other of said pressure differentials being the differential between compressor inlet total pressure and a pressure intermediate compressor discharge pressure and compressor inlet total pressure, said first means comprising a fuel control valve means operable to vary fuel flow to said engine and pressure responsive means actuated by said servo means and operably connected with said fuel control valve means whereby compressor airflow will be varied by varying fuel flow to said engine.

15. The control system as defined in claim 14 and in which said last mentioned pressure responsive means comprises a pressure sensitive element actuating said fuel control valve means in response to changes in a pressure differential between fuel pressure and a pressure intermediate compressor discharge pressure and the pressure of said first mentioned pressure responsive means.

16. The control system as defined in claim 15 and in which the aforesaid fuel pressure is taken downstream of said fuel control valve means.

17. The control system as defined in claim 16 and in which said second mentioned pressure responsive means includes a second pressure sensitive element modifying actuation of said fuel control valve means in response to changes in pressure differential between compressor inlet total pressure and the aforesaid intermediate pressure.

18. A control system for a gas turbine engine having a fuel system and an air compressor characterized by a predictable tendency to develop compressor surge conditions at operating ranges producing a predetermined reduction of compressor airflow, and air inlet and an air discharge for said compressor, said control system comprising first means variably increasing compressor airflow to avoid said surge conditions a servo means operating said first means and a sensing means automatically controlling operation of said servo means in response to varying compressor airflow said sensing means comprising an ac tuating means operably connected with said servo means and a pressure responsive means adjusting said actuating means in response to changes in the balance of two pressure differentials one of said pressure differentials being the differential between compressor inlet total pressure and compressor inlet static pressure, the other of said pressure differentials being the differential between compres-sor inlet total pressure and a pressure intermediate compressor discharge pressure and compressor inlet total pressure, said first means comprising a housing having a fuel inlet and a fuel outlet, a fuel control valve operable to vary fuel flow to said engine and disposed intermediate said inlet and outlet, a pressure control chamber, a pressure sensitive element operably connected with said fuel control valve and disposed in said pressure control chamber, and means openly connecting said fuel outlet with said control chamber on one side of said pressure sensitive element, said servo means being operable to transmit a variable pressure to said control chamber on the other side of said pressure sensitive element relative to changes in compressor airflow.

References Cited in the file of this patent UNITED STATES PATENTS 2,463,865 Gilfillan Mar. 8, 1949 2,618,431 Walker Nov. 18, 1952 2,645,240 Drake July 14, 1953 2,767,725 Long Oct. 23, 1956 2,813,672 Long et a1. Nov. 19, 1957 2,846,846 Mock Aug. 12, 1958 2,851,855 Gamble Sept. 16, 1958 2,858,700 Rose Nov. 4, 1958 2,863,601 Torell Dec. 9, 1958 2,886,968 Johnson May 19, 1959 em mam

Claims (1)

14. A CONTROL SYSTEM FOR A GAS TURBINE ENGINE HAVING A FUEL SYSTEM AND AN AIR COMPRESSOR CHARACTERIZED BY A PREDICTABLE TENDENCY TO DEVELOP COMPRESSOR SURGE CONDITIONS AT OPERATING RANGES PRODUCING A PREDETERMINED REDUCTION OF COMPRESSOR AIRFLOW, AND AIR INLET AND AN AIR DISCHARGE FOR SAID COMPRESSOR, SAID CONTROL SYSTEM COMPRISING FIRST MEANS VARIABLY INCREASING COMPRESSOR AIRFLOW TO AVOID SAID SURGE CONDITIONS A SERVO MEANS OPERATING SAID FIRST MEANS AND A SENSING MEANS AUTOMATICALLY CONTROLLING OPERATION OF SAID SERVO MEANS IN RESPONSE TO VARYING COMPRESSOR AIRFLOW SAID SENSING MEANS COMPRISING AN ACTUATING MEANS OPERABLY CONNECTED WITH SAID SERVO MEANS AND A PRESSURE RESPONSIVE MEANS ADJUSTING SAID ACTUATING MEANS IN RESPONSE TO CHANGES IN THE BALANCE OF TWO PRESSURE DIFFERENTIALS ONE OF SAID PRESSURE DIFFERENTIAL BEING

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