Patent GB-741352-A (GB)
Title: Control system for gas turbine engines
IPC: F02C9/16
Filed: 1950-12-14
Abstract: 741,352. Automatic speed control systems. BENDIX AVIATION CORPORATION. Dec. 14, 1950 [Dec. 23, 1949], No. 30571/50. Class 38 (4). [Also in Groups XXVI and XXXVIII] A fuel supply system for a gas turbine engine has an actuator for the fuel rate varying means controlled by, or its range of movement limited by, one or more devices responsive to a function of engine speed and to a function of one or more engine operating conditions. The fuel supply to a burner manifold 14, Fig. 1, is controlled by a throttle valve 27 provided with a series of metering restrictions 27<SP>1</SP>. The pressure drop across the valve 27 is maintained constant by a valve 24 actuated by a diaphragm 23 so that rotation of the valve 27 will vary proportionally the fuel flow. The valve 27 is rotated by a motor 31 which is of the twophase reversing type. The variable phase 32 is supplied with current from an amplifier 34 fed from a convertor 35. The convertor 35 is energized by a polarized relay 37 consisting of an armature 36, an automatic governing contact 40, a contact 38 forming part of a deceleration circuit and a contact 39 forming part of an acceleration circuit. Under steady running conditions, the armature 36 is spring urged into engagement with the contact 40, which is connected to a pilot-operated wiper arm 42 of a potentiometer 43. The potentiometer 43 has a resistance 44 in series with a suitable reference voltage such as a battery 45. A tachometer generator 47 driven by the engine is connected to the potentiometer 43 so that the voltage generated by it, E 2 , opposes that of the potentio - meter E 1 . Under steady running conditions, the resultant voltage in the circuit will be zero and no current will flow through the polarized relay 37 and the armature 36 will remain in engagement with the contact 40. As the relay 37 is constructed so that it operates only when the current through it exceeds a certain value, small differences of the voltages E 1 , E 2 , due to small variations of engine speed, will cause current to flow through contact 40 and armature 36 to the convertor 35 and actuate the valve 27 to bring the speed back to the value pre-set by the pilot's lever 46. If the pilot desires to accelerate or decelerate the engine, the lever 46 and consequently the wiper 42 is moved to cause the voltage E 1  to be increased or decreased. Since the voltage E 2  is unchanged this will cause a current to flow through the polarized relay 37 and urge the armature 36 into engagement with deceleration contact 38 or acceleration contact 39. The voltages E 9 , E 10  applied to the convertor 35 through the contacts 38 or 39 and consequently the amounts by which the fuel supply is varied, are determined by cams 55, 56 and 57. These cams are mounted on a shaft 58 which is rotated by a motor 60 similar to the motor 31. The convertor 72 controlling the motor 60 is fed by the tachometer generator 47 through a follow-up potentiometer 65. When the pilot varies the speed of the engine, the voltage E 2  of the generator 47 is also varied. This causes a current to flow through the convertor 72 and the motor 60 to rotate the wiper arm 64 until the voltage E 3 across the potentiometer to equal the voltage E 2 . For each speed of the engine there is thus one position of the cams 55, 56 and 57. The cam followers 75 and 76 are positioned axially of the cams 55, 56 by means of a bar 78 which is actuated by a motor 84 of similar construction to the motors 31, 60. The convertor 88 of the motor 84 is fed with current from a potentiometer 89, the voltage output of which is determined by a capsule or bellows 92 located at a point subject to air intake or ram pressure. The follow-up potentiometer 96 operates in a similar manner to the follow-up potentiometer 65 described above so that for each value of the air intake or ram pressure there is a given axial position of the cam followers 75, 76. The cam follower 77 is positioned axially of the cam 57 by means of a rack gear 108 operated by a motor 111. The motor 111 is operated by the voltage generated by a thermocouple 115 located at a point where it is subjected to temperatures affecting surge of the compressor of the gas turbine plant, e.g. the compressor inlet temperature. The motor 111 is similar to the motors 60, 84 and has a follow-up potentiometer 121 so that there is a given axial position of the cam follower 77 for each value of the air inlet temperature. The cam follower 75 controls the wiper arm 132 of a potentiometer resistance 131 and determines the voltage E 9  across the deceleration circuit comprising contact 38 and follow-up potentiometer 136. If the voltage E 9  differs from the voltage E 8  across the follow-up potentiometer, a current will flow through the convertor 35 and cause the motor 31 to vary the fuel supply. At the same time the motor 31 will move the wiper arm 138 over the potentiometer resistance 137 until the voltage E 8  equals E 9  when the motor 31 will stop. The resulting deceleration of the engine will then cause cam 55 to be repositioned. The cam follower 75 thus limits the rate of deceleration according to the engine speed and the density of the air flowing to the engine. The camfollowers 76, 77 are connected through gearing 150, 151 and a differential gear 152 to the wiper arm 147 of a potentiometer resistance 146 and thus determine the voltage E  10  across the acceleration circuit comprising the contact 39 and follow-up potentiometer 136. If the voltage E 10  differs from the voltage E 8  across the follow-up potentiometer 136, the motor 31 will operate as described above. The resulting acceleration of the engine will then cause cams 56, 57 to be re-positioned. The cam followers 76, 77 thus limit the rate of acceleration of the engine according to the engine speed, the density of the air flowing to the engine and the compressor inlet temperature. In a modification the battery 45 is replaced by a potentiometer, the output of which is determined by density responsive bellows.