Patent GB-1055389-A (GB)
Title: Engine speed control
IPC: F02C9/28
Filed: 1964-06-03
Abstract: 1,055,389. Fluid pressure servomoter system; pure fluid amplifiers; regulating fluid flow. BENDIX CORPORATION. June 3, 1964 [June 25, 1963J, No. 23013/64. Headings G3H and G3P. [Also in Division F1]. The fuel supply to a gas turbine engine is controlled, under normal conditions, by comparing pressure pulse signals representing the actual engine speed and a manually adjustable throttle control and using the comparison to actuate a throttle valve in the fuel supply line to the burners there being an override control to prevent excessive fuel if surge is imminent. Pressure pulse generator. The pressure pulse signal responsive to actual engine speed is produced by a gear 68, Fig. 5 (not shown) which is rotated at a speed proportional to the engine to control flow from a nozzle 62 supplied from a fluid source 58 through a restriction 64. The gear teeth 70 restrict flow from the nozzle to provide a pulsing pressure in the space C which has an outlet passage 66. The pressure pulse signal representing the manually adjustable throttle is produced by a tuning fork 78, Fig. 7 (not shown) which restricts flow from the nozzle 80 to provide the pulse in outlet passage 88 as above. The frequency of vibration of the tuning fork is adjustable by a slug 90, movable by a rod 92, to vary the effective length of the vibrating arms of the fork 78. To provide a pressure pulse signal when surge is imminent, a steady pulse signal from a tuning fork is supplied through passage 214, Fig. 10B (not shown) to the surface of a compressor stator blade 210. When surge is not imminent, the pressure pulse has no effect on the flow of air past the blade and the pressure in a passage 212 is constant. When surge is imminent, the pressure pulses cause the fluid flowing past the blade to be separated and thus produce a pulse signal in the passage 212. Fluid error computer. The comparison of the pressure pulse signals representing the throttle demand and actual speed is made by a computer 24, Fig. 8, which comprises a fluid source 90 supplying a nozzle 92 which normally discharges into a passage 102 leading to a chamber 106 having an outlet 108. The throttle demand signal "A" is fed to a passage 138 leading to a nozzle 142 and the actual speed signal "B" is fed to a passage 140 leading to a nozzle 144. If the frequencies of the two pulse signals vary, the flow from the nozzle 92 is deflected to passages 114 or 116 to cause a differential between the pressures in bellows 118, 120 which produces an output movement of a lever 124 proportional to the difference in the frequencies of the signals. A feed back is provided from the bellows through passages 126, 128 containing restrictions 130, 132 to provide a signal acting on the jet in opposition to the input signal. Fuel control system. The fuel control system comprises a fuel pump 152, Fig. 9, supplies fuel through a metering valve 176 to a passage 150 leading to the burners, a valve 158 responsive to the pressures upstream and downstream of the metering valve maintains the pressure arop across the metering valve constant. Fuel is also supplied through a passage 184 to a chamber 186 which is connected through a passage 190 containing a restriction 188 to a chamber 180 above a piston 178 of the metering valve. Flow from the chamber 186 to the space 182 below the piston is controlled by a valve 202 which is positioned by the output lever 124 of the computer, the space 182 also being connected to a drain line 198 containing a restriction 200. When the valve 202 is moved by the computer, the pressure in space 182 varies to cause movement of the piston 178 and the metering valve 176. The rate of movement of the piston 178 is dependent on the rate at which fluid can flow into or out of the chamber 180 due to the restriction 188 and such movement varies the pressure in a bellows 204 to cause movement of the valve 202 to oppose its signal movement thus the movement of valve 202 is also proportional to the speed of piston movement to provide an integrating control. Surge override and fluid gate. In the event of the manual throttle being moved to provide a pulse signal which would cause surge, the surge sensor acts to reduce the demand signal by the use of a fluid gate. This gate comprises a fluid supply 224, Fig. 12 (not shown) to a nozzle 228 which normally directs fluid to a vent 232. The demand pulse signal is fed through a passage 238 leading to a nozzle 240 and, under normal conditions, the gate acts as an amplifier providing an output signal in passage 234 of equal frequency to the demand signal. If surge is imminent, a pulse signal is fed to a passage 242 leading to a nozzle 244 which acts in opposition to the demand signal thus providing a reduced frequency signal to the output passage 234. Pulse shaper. The Specification also describes a pulse shaper which comprises a supply source, 250, Fig. 14, leading to a nozzle 254 opposite a vent 258. A trigger pulse input is supplied through passage 260 and nozzle 262 to direct the jet to an output passage 264 which is shaped at 268 to provide a low pressure region which holds the jet deflected into passage 264 after the trigger pulse has ceased. The jet is again deflected into the vent by flow from the passage 264 through a restriction 272 to a variable volume chamber 274 and then through a restriction 280 to nozzle 282. The duration of the output pulse is determined by the volume of chamber 274 which is adjustable by a piston 276. This pulse shaper is used between the surge sensor and the fluid gate and may also be used as a simple amplifier in the other signal lines.