Patent GB-684581-A (GB)
Title: Fuel control apparatus for jet engines
IPC: F02C7/22
Filed: 1950-05-19
Abstract: 684,581. Gas turbine plant. GENERAL MOTORS CORPORATION. May 19, 1950 [May 27, 1949], No. 12544/50. Class 110(iii) [Also in Group XXIX] The fuel supply to the burners of a gas turbine jet propulsion engine is regulated by a by-pass valve between the fuel pump outlet and inlet which is controlled by a second valve comprising two independently movable parts one of which is connected to means responsive to ambient air temperature and the other to means responsive to altitude pressure. The fuel from the pump passes into the control apparatus, Fig. 15, through a port 41 into a passage 42 and then passes through a throttle valve 44 to the burners through an outlet passage 43. The passage 42 is connected to a passage 53 leading to the pump inlet by a by-pass passage 52 having a solenoid operated valve 50. A duct 54 having an automatically controlled valve 55 also connects the passage 42 to the passage 52. The arrangement is such that when the valve 50 is open, the fuel flows direct back to the pump and the valve 55 is not effective. The valve 50, Fig. 5, is connected by a link 93 with a solenoid armature 94 slidable in a non-magnetic tube 95 fixed to a magnetic base 96. A magnetic shell 97 surrounds the magnet coil 989. A core 99 attached to an end plate 100 supports a bushing 102 which houses a spring 103 used to force the armature 94 downwards and thus open the valve 50. As the coil 98 is normally de-energised, the valve 50 is normally open. The valve 55, Fig. 1, which slides in a guide 115 has flow-metering notches 119 in its flange 120 and, as shown, is in the closed position to which it is urged by a compression spring 121. The spring 121 is confined between a cap 124 and a piston 130 mounted in a cylinder 131. A lever 136, Fig. 9, carrying a pin 137 supporting a lever 138 is pivoted to the top of the piston 130, by pins 135. The lever 136 has a bifurcated portion 139 slidable in a cradle 140 which is pivoted by pins 141 in the arms 142 of a lever 143, Fig. 1, which is in turn pivoted on the housing of the control apparatus. A thumb screw 145 enables the distance between the axis of the pins 135 and 141 to be varied and a screw 148 enables the lever 136 to be fixed to the cradle 140. The left hand end of the lever 138 is connected by a link 151 with a valve 154, Fig. 1, having lands 155, 156, slidable in a valve guide 157 having grooves 158, 159, 160. As shown, in Fig. 15, groove 158 is connected to the passage 42 by a passage 162 in which is mounted a filter 161, groove 160 is connected to passage 52 through the recess 117 of the valve guide 115 and groove 159 is connected by passage 164, in the housing to the lower end of cylinder 131. The valve 154 is controlled by means responsive to altitude pressure acting on the right hand end of lever 138, through a bar 172. The altitude pressure sensitive means comprise spring loaded metal bellows 170 and evacuated bellows 180 connected together by the bar 172. The interior of the bellows 170 is connected through the coupling 166 to the intake of the compressor. The spring loading of the bellows 170 may be adjusted by a screw 175. A tube 185 is provided in the bellows 180 to limit the amount of their contraction. As the altitude increases, bellows 180 expand and cause lever 138 to rotate and lower valve 154. This connects groove 159 to groove 160 and allows fluid to escape from below the piston 130 into the passage 52. The piston 130 then moves downwards and releases the pressure on the spring 121 so that the pressure above the valve 55 opens it further and the amount of fuel by-passed is increased. As the piston 130 moves downwards it causes counterclockwise rotation of lever 136 about the pivots 141 thereby causing pivot 137 supporting the lever 138 to move up to cause 154 to shut off the groove 160. As the altitude decreases the bellows 180 collapse and cause lever 138 to raise valve 154. This connects grooves 158 and 159 and allows fluid to pass from chamber 42 to beneath the piston 130 and increase the compression in the spring 121. The valve 55 therefore closes and the amount of fuel by-passed is decreased Due to .leakage of fuel past the piston 130 and valve 154 the housing 132 becomes full of fuel. This fuel passes back into the fuel system through holes 190, in a baffle plate 191, Fig. 15, and the by-pass 52. As a sudden closing of the throttle valve 44 would cause a considerable pressure increase in the by-pass 52, a non-return valve 194 is provided to prevent this pressure reaching and damaging the bellows 170, 180. Leakage of fuel past the top of the valve 154 is drained away through the passages 200 and 53. The valve guide 157 is movable and is used to control the operation of valve 55 in response to changes in atmospheric temperature. The valve guide 157 is pivoted by means of a rod 248 and a pin 246 to an arm 245, Fig. 2, forming part of a lever 229. The lever 229 has at one end an arcuate slot 228, Fig. 1, which moves on a roller 227 journalled on a stud 226 attached to one arm of a bell-crank 220 and at the other end is attached to the inner race of a ball bearing the outer race of which is connected through a thumb screw 237 to temperature responsive bellows 242. A lever 232 pivoted to the housing is also attached to the inner race of the ball bearing. The other arm of the bell-crank 220 is attached to the rod 218 of a spring loaded piston 214 enclosed in a cylinder 211. The lower end of the cylinder 211 is closed by a plug 213 and is connected by a duct 210, Fig. 15, with the fuel outlet passage to the burners 43. The spring 215 is rated so that the piston 214 does not move until the pressure in the fuel manifold has reached a relatively high value. Below this value, the axis 226 of the roller 227 is in line with the axis of the pin 246 as shown in Figs. 1 and 2, so that the expansion and contraction of the capsule 242 will only cause the lever 229 to rotate about these axes. Above this value, the piston 214 will rise and move the roller 227 to the left hand end of the arcuate slot 228. Movement of the capsule 242 will cause the rod 229 to rotate about the axis 226 but as this is not now in line with the axis 246 the rod 248 will move and actuate the valve guide 157. The amount of movement of the valve guide will depend upon the amount by which the roller 227 is displaced to the left by the action of the piston 214. The initial setting of the valve 154 is adjusted by varying the position of the fulcrum pin 144, Fig. 1. This pin is eccentrically mounted on a screw threaded into the housing. As described the invention is intended to be used as an auxiliary control, the supply of fuel to the burners being controlled by another control, the arrangement being such that if this control fails the solenoid operated valve 50 is energised and the control described comes into operation. If desired the valve 50 may be dispensed with and the control described used as a main control. The throttle valve 44, Fig. 7, is operated by a lever 66 through a shaft 65 and crank arm 68. The crank arm 68 is urged against the bushing 61 by a spring 69 which lies between a plug 70 and a nut 71 threaded on the shaft 65. The sleeve 45 surrounding the valve 44 has diametrically opposite grooves 75 and 76 which communicate with passages 42 by holes 77, 78. Opposite these holes the valve has a long groove which communicates with shorter grooves so that as the valve opens the area of flow passage is increased. In a place at right angles to the place of the holes 77, 78, the sleeve 45 has holes 79, 80. The flow through the hole 80 is controlled by an adjustable needle valve 81. The holes 79, 80 allow the passage of the fuel for idling purposes.