Patent GB-1462082-A (GB)
Title: Power turbine nozzle control system
IPC: F01D17/20
Filed: 1974-05-31
Abstract: 1462082 Fluid-pressure servomotor systems GARRETT CORP 31 May 1974 [4 June 1973] 24197/74 Heading G3P [Also in Division F1] A gas turbine engine, e.g. in a vehicle, having a gas generator (11), Fig. 2 (not shown) and a power turbine (23) with adjustable nozzle guide vanes (25) includes a fluid servosystem 26 for adjusting the latter to facilitate starting and running of the engine. Servosystem 26 comprises an actuator piston 31 having a rack 28 engaging pinion 30 connected to the power turbine guide vanes, a servovalve 34 and a positioning piston 36 connected to the latter via linkage 53. To start the engine manual throttle 35 is set at its idling position and an electric starter motor (43) is energized to rotate the gas generator (11). The latter drives a hydraulic pump (37) which feeds fluid to a pressure line 41 and thence through valves 67, 84 and line 65 to act above piston 36 causing it to move downwards against the bias of centering spring 62. Servovalve 34 thus also moves downwards causing piston 31 to move upwards and open the guide vanes towards a position offering minimum load on the gas generator. Downwards movement of piston 36 stops when a line 80 vents the pressure above the piston to drain line 70 via valve 82. When the gas generator reaches self sustaining speed, the gas generator governor 48 opens switch 50 to cut out the starter motor and simultaneously, via lever 73, change over interconnected valves 82, 67. Thus line 80 is no longer vented but line 65 and the space above piston 36 are vented so that the piston moves upwardly under the action of spring 62 causing the guide vanes to close to a position in which they drive the power turbine. Acceleration then continues up to idling speed, at which point the pressure signal generated by the power turbine governor (90) and acting via line 91 causes spring biased diaphragm 93 to move rightwards and switch valve 84 so as to admit pressure fluid from line 41 to above piston 36. The latter thus moves downwards to open the guide vanes so as to control the speed of the power turbine and prevent it exceeding the idling value. To produce driving power, throttle 35 is then opened causing a finger 100 to hold collar 101 to the left thus overriding the power turbine governor (90) and venting the space above piston 36 to drain 70 via valves 84, 67. Piston 36 thus moves upwards and tends to shift the guide vanes towards the normal maximum power closed position. Simultaneously the throttle cam 54 adjusts link 53 and moves servovalve 34 downwards so as to open the guide vanes towards the neutral position irrespective of the movement of piston 36. At the same time switch 103 is closed causing a solenoid 105 to dither, depending on the gas temperature and/or turbine speed sensed by device (102A) or monopole generator (102), thus pressurizing the underside of piston 36 via valve 68 to tend to close the guide vanes towards the maximum power position. Should throttle 35 now be closed, switch 103 is opened de-energizing solenoid 105 to vent the underside of piston 36. Simultaneously finger 100 releases collar 101 so that power turbine governor (90) moves valve 84 rightwards to pressurize the top of piston 36. The latter thus moves downwards past the closed vent line 80 so that the guide vanes are shifted through the fully open position to a braking position in which they retard the power turbine.