Patent GB-783105-A (GB)
IPC: F02C9/16
Abstract: 783,105. Gas turbine plant. BENDIX AVIATION CORPORATION. Jan. 18, 1955 [Feb. 15, 1954], No. 1530/55. Class 110 (3). A gas turbine fuel control system comprising a main fuel control for delivering a quantity of fuel a predetermined percentage above the quantity required for optimum engine operation under pressure to the engine under all conditions of operation has a device for withdrawing a controlled percentage of fuel from the conduit which is a function of an engine operating condition and is settable manually. Fuel is supplied to a gas turbine engine by a fuel pump 36 which is connected to the burner manifold 38 by conduits 42, 44, a main fuel control 46 and a proportional by-pass control 48. A conduit 50 connects the controls 46, 48 with the lowpressure side of the pump 36. The by-pass control 48 withdraws fuel flowing from the main control 46 so as to maintain predetermined turbine inlet or outlet temperatures under various engine operating conditions. The control 48 is actuated by an electronic temperature control and amplifier unit 58 which may be of the type described in Specification 750,476 and which compares the actual engine operating temperature with a reference temperature which may vary with engine speed and pilot's control lever position. The difference between the actual and reference temperatures is measured as an error voltage in the amplifier and transmitted to the motor 60 regulating the control 48. A thermo-couple 66 located in the turbine inlet annulus is connected to the unit 58. A pilot's control lever 74, which is connected to the main fuel control 46 by a lever 76, is also connected to the unit 58 through leads 78, 80, 82, for controlling the reference temperature. Between 0 and 55 degrees settings of the pilot's lever, the bus-bars 88, 90 are connected through the lever so as to complete a circuit from a D.C. source (not shown) through a lead 94 to energize a relay 100. The relay may also be energized by a parallel circuit including a speedresponsive switch 104 which is closed when the engine speed is below a predetermined value. The relay 100 is therefore only de-energized when the lever 74 is above a 55 degree setting and the predetermined speed has been attained. The relay operates a double throw switch 106 so that when the lever 74 is between the 0 and 55 degrees and the switch 104 closed, the reference temperature is 1750‹ F. When the lever 74 is in the power range and switch 104 open, switch 106 contacts terminals 120, 130, to connect the unit 58 to the reference temperature of potentiometer 110 and to de-energize the solenoid 124. The by-pass control 48, Fig. 2, has a venturi 142 in the passage 42 connecting the inlet and outlet. A transverse passage 144 transmits the pressure at the throat of the venturi to a chamber 146 formed on one side of a diaphragm 148. The passage 42 is connected with the outlet conduit 44 through a pressurising valve 156 and to the by-pass conduit 50 through a branch passage 158, a restriction 160, a chamber 162, parallel passages 164, 165 and restrictions 166, 166<SP>1</SP> controlled by an hydraulically balanced by-pass valve 168. The area of the restriction 160 is varied by a valve 170 controlled by the unit 58. The pressurizing valve 156 ensures a minimum pressure in the passage 42 before fuel can flow to the burners and consists of a reciprocable valve 172 mounted in a sleeve 174 and urged in a closing direction by a spring 176. The preloading of the spring may be adjusted by a screw 194. The by-pass valve 168 is reciprocably mounted in a sleeve 200 and is fixed at one end to the diaphragm 148. A retainer plate 204 with the openings 206 and fixed by a locking-ring 205 holds the sleeve 200 in position. The openings 206 connect chamber 208 with chamber 162. Since the diaphragm 148 is not spring-loaded, the by-pass valve 168 will control the flow from the chamber 162 through the parallel passages 164, 165 to the bypass conduit 50 so that the pressure in the chambers 146, 208 are equal to one another and to the pressure at the throat of the venturi. Since the square root of the static pressure recovery in the venturi is proportional to the flow through it, the flow through the restriction 160 will also be a constant percentage of this flow for a given position of the valve 170. When the actual turbine inlet temperature is equal to the reference temperature, the valve 170 assumes its normal position as shown. The valve 170 includes an extension member 214 having rack 216 which is operated from the motor 60 through a gear 272, a torsion bar 266 and gearing 262 and 258. The torsion bar 266 absorbs the inertia of the motor 60 if the valve 170 abuts against either of the stops 238, 250. The extension member 214 also has a flange 218 and a nut 220. A threaded sleeve 224 which may be adjusted axially with respect to the housing is connected to the valve 170 by means of the spring retainers 234, 236, spring 232 and flange 218. An adjustable stop 238 limits the maximum opening of the valve 170. The normal position of the valve 170 may be adjusted by the sleeve 244 or by adjustment of the sleeve 240 carrying the restriction 160 by means of a screw 247 having at its end an eccentric 248. The solenoid 124 comprises a stop 250 which limits the closing of the valve 170 and which is spring-loaded against an adjustable stop 253 when the solenoid is not energized. When the solenoid is energized the stop 250 is urged downwards until the flange 251 abuts against the annular stop 254. When the solenoid 124 is energized, as during starting and acceleration of the engine, the stop 250 is brought into engagement with the valve 170 when the valve is in its normal position, thus preventing the possibility of by-passing less fuel but not affecting the maximum amount which may be by-passed. When the solenoid is de-energized, i.e. when the lever 74 is in the power range, the stop 250 abuts against the stop 253, and thus allows the valve 170 to move in either direction from the normal position. The shaft 256 of the motor 60 is rotatable in chamber 288 formed by a solenoid core 290 and an axially movable annular brake shoe 294. The brake shoe is urged leftwards by a spring 300 into engagement with a friction disc 302 fixed to the shaft 256. The solenoid 290 is normally maintained energized by a pilot-operated switch. When the pilot desires to fix the position of the valve 170 the solenoid is de-energized and the brake shoe 290 and friction disc 302 engaged to lock the shaft 256. The sub-assembly of motor 60, brake 308 and gear train 258 are held in the valve housing by a tapered alignment screw 318. Specification 753,305 also is referred to.