Patent GB-1264898-A (GB)
IPC: F02D25/02
Filed: 1969-11-06
Abstract: 1,264,898. Gas turbine power plant. BENDIX CORP. Nov.6, 1969 [Nov. 15, 1968], No.54466/69. Headings F1G and F1Q. Control apparatus is provided for co-ordinating the relative power output of two gas turbine engines each of which is connected to drive a power absorbing device and is provided with a fuel control device including a governor mechanism responsive to the position of a common engine control lever, to the speed of the associated engine and to a variable control fluid-pressure, which pressure when increased is adapted to reset the governor mechanism so as to increase fuel-flow to the associated engine and thus power output thereof, the control apparatus comprising two sensor means operatively connected to the two engines respectively and adapted to produce two output signals representative of the power output of the two engines respectively, a first control means responsive to the difference between the output signals and adapted to increase the variable control pressure resetting the governor mechanism of the engine having the lower power output so as to increase the fuel-flow thereto, and a second control means responsive to the difference between the sum of the output signals and a reference signal representing a maximum permissible total power output of both engines and adapted to decrease simultaneously both control pressures and thereby the fuel-flow to both engines to limit their total power output at the maximum permissible value. Two gas turbine engines 20, 22, Fig.1, each comprising a turbine 30 driving a compressor 26 and a turbine 34 driving a load, are controlled by respective fuel control units 46, 48, each unit 46, 48 being controlled by the compressor discharge pressure transmitted via a line 70, and by centrifugal governors 186, 254, Fig.2, driven by the turbines 34, 30 respectively. Pressure signals from torque-sensing devices 112, 118 are applied. to opposed bellows 98, 100, of a common control unit 72 whereby a flapper 96 is positioned relative to orifices 84, 86 in accordance with the difference between the torque outputs of the two engines. These pressure signals are also applied to bellows 134, 136 acting in unison to vary the position of a flapper 132 relative to a pair of orifices 124, 126, Fig. 3, in accordance with the sum of the torque outputs. A line 88 vented by the orifices 84, 124 and a line 90 vented by the orifices 86, 126 are connected to the units 46 and 48 respectively. To increase the speed of the output turbines 34, a lever 278 is moved to increase the tension of the spring 274 of each governor 254, thereby causing a flapper 270 to seat against an orifice 272 and thereby cause a decrease in the air pressure differential acting on a diaphragm 228. A rod 232 is thereby urged to the left to pivot levers 196, 198 counter-clockwise to block passages 190, 192. The resultant rise in air pressure in chambers 180, 184 reduces the pressure differential across a bellows 172 to zero and increases the pressure acting on an evacuated bellows 174, whereby the opening of fuel metering valve 168 is increased. The resultant increase of speed of the compressor 26 causes the governor weights 220 to overcome a spring 216 to pivot the lever 198 relative to the lever 196, thereby venting passage 192 and so reducing the pressure in the chamber 184. This increases the opening of the fuel metering valve 168 still further to provide increased acceleration. As the power turbine 34 approaches the selected speed, the governor weights 258 overcome the spring 274 to move the flapper 270 away from the orifice 272. The resultant increase in the pressure differential across the diaphragm 228 causes the lever 196 to be pivoted against the action of its spring 202 to vent the passage 190. The resultant drop in pressure in the chamber 180 causes the bellows 172 to reduce the opening of the fuel metering valve 168, whereby the power turbine 34 is stabilized at the selected speed. If, say, the torque output of turbine 34 of engine 22 is greater than that of engine 20, the resultant increase of pressure in bellows 98 relative to that in bellows 100 causes the flapper 96 to move towards orifice 84 and away from orifice 86. Since the orifices are choked when the flapper 96 is in its neutral position, this has no effect on the flow through orifice 86, but the flow through orifice 84 decreases. The resultant increase of pressure upstream of orifice 84 decreases the pressure differential across the diaphragm 228 of the fuel control unit 46 whereby the opening of the fuel metering valve 168 of engine 20 is increased to equalize the torque outputs of the two engines and thereby return the flapper 96 to approximately the neutral position. If the sum of the torque outputs of the two engines tends to exceed a predetermined maximum, the bellows 134, 136 move the flapper 132 away from orifices 124, 126 to increase the pressure differential across the diaphragms 228 of both fuel control units 46, 48 whereby the opening of both fuel metering valves 168 is reduced. In the event of malfunction of one engine, causing a drop in its torque output which cannot be eliminated by the consequent movement of the flapper 92, the action of the flapper 132 in limiting the sum of the torque outputs to the predetermined maximum causes the other engine to provide more than its normal maximum torque output during operation at maximum power so that the maximum power remains available on a temporary emergency basis.