Patent GB-753305-A (GB)
Title: Fuel feed control system for gas turbine engines
IPC: F02C9/16
Filed: 1952-09-09
Abstract: 753,305. Gas turbine plant. BENDIX AVIATION CORPORATION. Sept. 9, 1952 [Sept. 26, 1951], No. 22641/52. Class 110(3) [Also in Group XXIX] A fuel control system for a gas turbine engine having combustion equipment fed with air by a compressor comprises a metering valve positioned with respect to a metering restriction by means responsive to a plurality of engine operating condition and means for maintaining a constant metering head across the restriction irrespective of any variations in engine power selected by the operator. Fuel from a pump 32, Fig. 2 flows through a conduit 33 into an annular chamber 34 and thence through orifices 35 into the interior of a metering valve 36. An outlet orifice 38 formed in the wall of the valve 36 co-acts with an orifice 39 formed in bearing bushing 37 for the valve to provide a variable metering orifice 40 of rectangular or rectilinear contour so that its dimensions vary as the linear function of engine operating conditions as described below. Orifice 40 discharges into an annular chamber 41 which is connected to the burners by conduits 32, 42<SP>1</SP>. A valve 46 controls a passage 48 between the pump discharge conduit 33 and a return conduit 48<SP>1</SP> so as to maintain the pressure drop across the valve 36 constant. The valve 46 is urged to its closed position by a spring 49 against the pressure drop across a diaphragm 50. The chambers on either side of the diaphragm 50 are connected to the conduits leading to and from the valve 36. The valve 46 is mounted in bellows 53 in such a manner that the spring length is maintained constant irrespective of the position of the valve. Should the valve 46 open due to an increase in pressure drop across the diaphragm 50, the spring 49 will be compressed and the land 55 will move relative to the base 53<SP>1</SP>and open the ports 55<SP>1</SP>. Fuel will then flow through the ports 55<SP>1</SP> and the spring acting on the base 53' will cause the bellows 53 to extend and close again the ports 55<SP>1</SP>. Should the valve 46 close due to a decrease of the pressure drop across the diaphragm 50, the land 55 will move upwardly relative to the ports 55<SP>1</SP> and fuel at the pump discharge pressure will flow through the passages 51, 46' and ports 55<SP>1</SP> to the chamber 54 and cause the bellows 53 to collapse and close the ports 55<SP>1</SP>. The relief valve 56 limits the maximum pump discharge pressure. The passage 58 is used for connecting the metered fuel passage to the same passage of the control unit of another engine in a power plant comprising more than one engine. The metering valve 36 is rotated in response to changes in compressor discharge pressure and moved axially to some predetermined position for a given value of compressor inlet temperature and engine speed. The compressor discharge pressure acts on bellows 61, Fig. 3, which are connected to evacuated bellows 62 by a link 63 to balance out the effects of atmospheric pressure. The link 63 carries a pin 64 which engages a slot in a lever 65 adjustably pivoted at one end by a screw 66. The other end of the lever 65 has an adjustable contact member 67 which engages a pilot valve 68. The pilot valve allows fuel taken from the annular conduit 34 through a filter 75 to be supplied to one side or the other of a piston 78 which is connected through adjustable members 86 to an arm 84 secured to the valve 36. A spring loaded piston 88 which is vented to the cylinder of the piston 78 by a passage 89 is provided to engage the contact member 67 to balance the loads on the pivot valve 68. The fuel flow during acceleration and in the area where the compressor is liable to surge are limited by a cam 90 and during steady operation by a cam 91. The cams 90, 91 are rotatably positioned as a function of engine speed and axially positioned as a function of compressor inlet temperature. Variations of temperature sensed by the bulb 99 will cause the bellows 96 to expand and contract and move the shaft 92, to which the cams are attached. axially. The angular position of the cams is determined by a speed governor formed by weights 100 pivoted to a disc 102 attached to an engine driven shaft 103. The weights 100 act on a bush 105 against the action of a spring 106. The bush has a pin 107 which engages one end of a lever 108 to the other end of which is pivoted a floating lever 109, one end of the lever 109 is attached to the pilot valve 110 of 'a servomotor the other end of which is attached to the piston rod 111 of the servomotor piston 112. The piston 112 actuates a rack 113' which rotates a pinion 114 attached to the shaft 92. The cam follower 120, which is mounted on an arm 122 attached to a shaft 123 positions a pair of fingers 130, 130' with respect to a collar 132 attached to the shaft 133 and thus limits the opening movement of the valve 36. The cam follower 121 is mounted on an arm 126 attached to a hub 127 which is splined for longitudinal movement on a hollow shaft 128 journalled on the shaft 123. The hollow shaft 128 has a pair of fingers 131, 131<SP>1</SP> which also co-operate with the collar 132 to limit the opening movement of the valve 36. The collar 127 is positioned on the 'shaft 128 by a bell crank 148 which is set by the pilot through a lever 143, cam 139 and rod 147. Cam 140 also operated by the pilot through the lever 143 is used to vary the loading on a governor spring 135 which balances the load of the governor weights 137 pivotally mounted on the disc 102. A cam 141 is used to operate a shut off valve 157. The position of the cams 139, 140 and 141 on the shaft 142 can be adjusted by screws 145. The operation of the control its as follows. With the pilot's lever in the stop position and the valve 157 closed, the starter motor is engaged. Fuel will then be metered by the control but instead of passing to the engine will be passed through passages 159<SP>1</SP> and passages 57 and 48<SP>1</SP> back to the suction of the pump. When the pilot's lever is moved to; the start position the valve 157 is opened and the ignition energized. When the combustion chambers have been ignited the ignition is switched off and the pilot's lever moved to the ground idling position. This will cause (a) the cam follower 121 to be moved downwardly by the spring 129 along the surface of the cam 91 which will cause the shaft 128 to rotate clockwise and reset the fingers 131, 131<SP>1</SP> and (b) the cam 140 to be rotated to increase the loading of the governor spring 135 which will in turn cause the metering valve to move to the right and increase the area of the metering orifice 40. When the speed of the engine begins to increase the weights 100 acting through the servometer 112 will cause the cam 90 to be rotated and this cam acting through the follower 120 will cause the fingers 130, 130<SP>1</SP> to come into contact with the collar 132 and limit the opening movement of the valve 36. On further acceleration of the engine, the cam 91 acting through the follower 121 will move fingers 131, 131<SP>1</SP> against the collar 132 as shown in Fig. 4B and hold the fuel flow constant as the engine accelerates further until the point is reached where the force of the governor weights 137 balances the setting of the governor spring 135. Further movement of the pilot's control lever causes the above to be repeated. A stop 138 limits the closing travel of the valve during deceleration. To prevent a maximum temperature at the turbine inlet being exceeded, an orifice 161 controlled by a valve 162 carried by spring loaded bellows mounted in a chamber 164 is provided. The chamber 164 is connected through a passage 165 with the compressor discharge. The passage 165 is vented to atmosphere or the compressor inlet through a calibrated orifice 169 and is provided with a variable orifice 165' the area of which is controlled by a contoured needle 167 actuated by a stack of bimetallic discs 168 movement of which is responsive to the temperature at the compressor discharge, Since the pressure at the compressor discharge is, in a given engine, proportional to the air flow the pressure drop across the orifice 161 will be indicative of the turbine inlet temperature. The pressure drop across the orifice 161 acts on a diaphragm 174 controlling a valve 171. The. valve 171 is similar to the valve 46 already described and when the pressure drop across the orifice 161 exceeds a predetermined figure, the valve 171 opens and allows fuel to flow back to the suction side of the fuel pump through the passage 173. An emergency control arrangement is shown in Fig. 6. In this arrangement, the valve 46 is replaced by a valve 46<SP>11</SP> which is mounted on spring loaded bellows 200, the outside of which is connected to the pump discharge passage 33 and the inside to the metered fuel passage 42. A pressure relief valve 243 and pressurizing valve 245 which maintains a predetermined pressure drop across the control are also provided. A transfer valve 204 actuated by an electric motor 215 is also provided When a switch 219 is operated either manually or automatically by means responsive to an engine condition such as overspeed or fall off in engine torque or power at take off, the motor215 opens the valve 221. Fuel at pump discharge pressure then enters the chamber 220 and forces the transfer valve 204 to the left which opens the port 222 and closes the passage 42. At the same time passage 229 is connected to passage 229'. Pump discharge pressure now acts on both sides of the bellows 200 and springs 201 closes the valve 46<SP>11</SP>, so that fuel returning to the pump suction must pass through the passage 232 and across valve 231. The valve 231 then functions as a regulator valve controlling the pressure drop across the throttle valve 238. The valve 231 is controlled by spring loaded bellows 233 located in a chamber 235. The chamber 235 to open to pump d