Patent GB-1091358-A (GB)
Title: Isochronous governor systems for gas turbine engines
IPC: F02C9/32
Filed: 1966-06-02
Abstract: 1,091,358. Fluid-pressure servomotor systems. GENERAL MOTORS CORPORATION. June 2, 1966 [July 1, 1965], No. 24562/66. Heading G3P. [Also in Division F1] A speed governing system for a gas turbine engine includes a first governor controlling the fuel supply to the engine and a second governor which modifies the action of the first governor to produce isochronous speed control of the engine. The gas turbine has a compressor 5, gas generator turbine 7 and power turbine 9 and is supplied with fuel from a pump 15 via a metering valve 18, the latter being controlled by a bellows device 27 which responds to variations in compressor discharge pressure in line 38 to meter fuel during acceleration. Device 27 is also controlled by governor devices 29, 30 responsive to the speed of turbines 7 and 9 respectively. Governor 29 has flyweights 31 which co-operate with flappers 54, 59 pivoted at 55 and interconnected by spring 65, spring 73 serving as a speeder spring. Flappers 54, 59 control the back pressure in nozzles 58, 62, the respective back pressures acting in device 27 on small, evacuated, bellows 49 and large, open, bellows 47. When the speed of turbine 7 reaches a predetermined value, lever 54 is first rocked a small amount relative to lever 59, and then the two levers are rocked together. When governor 29 is operative, the power output of turbine 9 is controlled, but when governor 30 is operative it acts on levers 54, 59 via diaphragm 86 and rod 87 to control the fuel flow in such a way as to produce isochronous governing of the power turbine. The governor 30 shown in Fig. 1 has an inherent droop characteristic and, according to the invention, is replaced by governor 30' (Fig. 2). In Fig. 2, a regulated pressure acts on the righthand side of diaphragm 86 (see Fig. 1) via conduit 38, regulating valve 112, 113 and line 82, and a control pressure acts on the left-hand side of the diaphragm, the control pressure being the back pressure of a nozzle 78 supplied from line 82 via restriction 83. If the power turbine speed increases, flapper 105 moves away from the nozzle to lower the control pressure. To provide isochronous governing, the flapper raises a spool 119 to admit more air to a chamber 118 to cause diaphragm 109 to open valve 112, 113 further to increase the regulated pressure. In the alternative embodiment of Fig.3 (not shown), the control pressure acting on diaphragm (86) is the back pressure from governor 30 (Fig. 1) and the regulated pressure is varied to achieve isochronous governing by means of a spool valve (143) controlled by a diaphragm (147) responsive to the difference between the control and regulated pressures. A throttle valve 41 (Fig. 1) responds to ambient temperature to control the bleed of air from line 40, and the regulators 106 (Fig.2) and (81, Fig. 3) respond to ambient pressure to maintain the regulated pressure a predetermined amount above ambient pressure. Turbine 9 may drive a lifting or propelling rotor of an aircraft. If the engine has only a single turbine, then the shafts of this turbine drives both governors 29, 30 at the same speed.