Patent GB-814077-A (GB)
Title: Improvements relating to controls for gas turbine jet propulsion engines
IPC: F02K1/16
Filed: 1955-09-26
Abstract: 814,077. Gas turbine jet propulsion engines; centrifugal governors. CURTISS-WRIGHT CORPORATION. Feb. 26, 1955 [Sept. 24, 1954], No. 27352/55. Classes 57 and 110 (3). A gas turbine jet propulsion engine has a variable area for controlling inlet air or exhaust gases in response to a function of engine operation which is adjusted through a direct mechanical drive driven by the engine. The invention is described with reference to a gas turbine jet propulsion having a single turbine-compressor rotor and a variable area propulsion nozzle comprising a plurality of leaves pivoted to the end of the tail pipe having cam-slotted tabs extending outwardly which co-operate with studs attached to an axially slidable ring. This ring is positioned axially by mechanism which converts the rotary motion of a shaft 26, Fig. 2, into linear motion. The shaft 26 is driven from a shaft 50 driven by the engine through gearing 120-126 and hydraulically operated couplings 102, 103, 104 to which pressure oil is supplied by a pump 109 through a valve 98 rotatable to any one of three positions by a differential gear D4 through a snap action 100. A pressure oil inlet 23 is connected to a passage 114, Fig. 3, in the core of the valve 98 and a drain 24 to the passage 115. The arrangement is such that when one of the passages 105, 106, 107 is connected to the pressure oil supply the other two passages are connected to the drain. The passages 105, 106, 107 are connected to the hydraulic couplings 102, 103, 104. The coupling 102 is used to engage a brake to prevent rotation of the shaft. 26 and the couplings 103, 104 are used to drive the shaft in one direction or the other. The differential D4 operates in response to any differences in the actual position of the variable area nozzle as determined by the shaft 26 and the desired position of the nozzle as determined by the shaft 162. The shaft 26 is connected to the differential gear-wheel 94 through shafts 92, 93 and the shaft 162 is connected to the gearwheel 95 through a slipping coupling 144 and shaft 138. The shaft 162 is positioned by a differential gear D3 which algebraically adds the difference between a reference speed and the actual speed and the integrated difference of these speeds relative to time. This is effected in the following manner. A flyweight governor 52, driven by the engine shaft 50, swings a yoke 57 angularly in response to speed variations. The yoke carries a ball 58, mounted on a spindle 60, which engages a pair of coaxial discs 61, 62. The disc 61 is driven from the shaft 50 and the disc 62 drives the shafts 64, 64<SP>1</SP>. Movements of the yoke change the ratio of the speeds of the discs 61, 62 so that the variable engine speed 61 is changed to a constant reference speed 62. This reference speed may be predetermined by varying the loading of the governor speeder spring 54. As a safety measure the loading of the speeder spring 54 may be lessened by the action of a piston 66 in a cylinder 65 which is connected, to the compressor discharge by the conduit 64. A stiff spring 67 normally holds the speeder spring 54 in the position for the desired constant speed. Excess compressor discharge pressure moves the piston 66 to the left and thereby lowers the loading of the spring 54 reducing the speed setting. Shaft 50 drives a gear 69 and shaft 64<SP>1</SP> a gear 70 of a differential D1 so that the output gear 71, rotates in a direction and at a speed in accordance with the difference in speed between the shafts 50 and 64<SP>1</SP> and the total rotation of this output gear represents the integrated speed difference with respect to time. Shaft 50 also drives a disc 73 of a speed changer SC2 which includes a shiftable ball 74 and an output disc 75. The output disc 75 drives an input gear 76 of a differential D2, the other input gear 77 of which is driven at the reference speed by the shaft 64<SP>1</SP>. The output gear 79 drives through a gear 80 a shaft 81 and slip clutch 82 a worm 83 which engages a wormwheel teeth on the yoke 84 which carries the ball 74. As a result the shaft 81 assumes a position corresponding to the speed difference. The shafts 81 and 71 are connected to the differential D3 which. algebraically sums the two differences. When fuel is burnt in the tail pipe, it is ignited by injecting additional fuel into the combustion equipment. This additional fuel is controlled by a valve 130 operated by a cam 134 driven by a gear 135 on a shaft 93 connected to the shaft 26 so that the valve 130 is opened or closed in accordance with the area of the variable area nozzle. Preferably the valve 130 is closed when the nozzle area is substantially greater than the minimum as then the ignition of the reheat fuel can be considered as certain due to the increase of nozzle area necessary to prevent a decrease of speed. Should the reheat, fuel be extinguished the nozzle area will automatically be decreased and the supply of igniter fuel automatically restarted. Shutting off of the reheat fuel will also shut off the supply of igniter fuel. The variable area nozzle mechanism may have stops to limit the maximum and minimum area. The shaft 138 carries a lug 140, Fig. 5, which engages a fixed stop 142 when the nozzle is at its minimum allowable area. Should the differential D3 call for a smaller area, the coupling 144 slips. The maximum nozzle area stop 146 has two positions. In normal operation of the engine without reheat, the stop is in the position shown in full lines. When the reheat fuel is turned on, it is necessary to increase this maximum area. The stop 146 is carried by a ring 148 which is rotatable by a spring-loaded piston 152 in a cylinder 154. The fuel supply pipe 132 to the reheat igniter is connected to the left-hand end of the cylinder so that the pressure on the piston 152 is increased when the reheat is switched on. This causes the piston 152 to move to the left and move the stop 146 to the dotted line or increased area position. The invention may be used in a compound engine or an engine having a separate power turbine. In this case, the control system described may be used to control the speed of one of the rotors and the speed of the other rotor would be controlled by the normal fuel regulating system.