Patent GB-934124-A (GB)
Title: Improvements in afterburner fuel and nozzle area control
IPC: F02K1/17
Filed: 1961-10-20
Abstract: 934,124. Gas-turbine jet-propulsion engines. GENERAL ELECTRIC CO. Oct. 20, 1961 [Oct. 26, 1960 (3)], No. 37709/61. Class 110 (3). [Also in Group XXIX] In an after-burner fuel and nozzle area control for a gas-turbine jet-propulsion engine, the main fuel supply, the after-burner fuel supply and the nozzle area are selectively and concurrently controlled in accordance with the position of a throttle lever. The throttle lever control of the nozzle area is modified by means responsive to turbine temperature and is further modified by means responsive to changes in the main fuel control during transitional speed periods of the engine. Furthermore, the control of the after-burner fuel supply in accordance with the throttle lever setting during periods when the turbine temperature exceeds a predetermined limit is shifted to and controlled by the means responsive to the turbine temperature or means responsive to nozzle area opening or both. In the schematic arrangement shown in Fig. 1 the range of the throttle lever 31 is indicated during normal and afterburner operation, the latter being indicated by the range A/B. The engine main fuel control is indicated at 33 and the metering valve at 39. The after-burner fuel and nozzle area control unit is indicated at 35, this being shown in detail in Fig. 2 together with the associated part of the main fuel control unit 33. The afterburner fuel pump is indicated at 43 together with the associated shut-off valve 45, these parts also being shown in Fig. 2. The afterburner metering valve assembly is indicated at 47 and the after-burner fuel supply manifold at 25. The variable area nozzle is indicated at 19 and a nozzle actuator at 29. A temperature sensitive device is indicated at 51 to detect temperature of the turbine exhaust gases, the signal being communicated through amplifier 53 to the control unit 35. The after-burner fuel pump 43 comprises a centrifugal impeller 55 and the inlet to the pump is controlled by the shut-off valve 45 comprising a valve member 61, the assembly being shown in the normal operation position in which no fuel is being supplied to the after-burner. The throttle shaft 73 is provided with a pilot valve 75 which, when the throttle shaft is rotated to the after-burner range A/B establishes communication between the line 77 and line 81 whereby servo-fluid (which may be fuel from the main fuel pump) may flow from line 69 into the cylinder 89 of the lock-out valve assembly 71 whereby (assuming the acceleration valve 139 to be closed) the piston valve 87 moves to the right thereby establishing communication between lines 101 and 67 so that servo fluid from the line 69 passes to the space above the piston 63 and the shut-off valve 61 is opened. The after-burner fuel pump thereupon supplies fuel through the check and drain valve assembly 231 to the line 59 and so to the fuel metering unit 47 and the after-burner fuel manifold 25. This action is subjected to an override, however, so that if the engine speed is not in accordance with that called for by the engine throttle then the valve member 87 cannot be moved to the right as described above. This override is controlled by an acceleration signal valve assembly 136 which forms part of the main fuel control unit 33, the relevant parts of which are shown in Fig. 2, and comprises an engine speed sensor 111 which controls a cam member 113 which provides a pair of cam surfaces, one surface controlling a speed lever 121 and the other surface controlling the lever 115 which provides acceleration fuel flow limiting. The cam 113 moves to the left with increasing engine speed and to the right with decreasing engine speed. The levers 121 and 115 provide stops which co-operate with abutments on a rod 119 which connects to the engine main fuel metering valve 39 (Fig. 1), movement of the rod to the left, causing increased fuel flow to the main burners and movement of the rod to the right, causing decreased fuel flow to the main burners. The speed lever 121 is pivotally mounted on an axially slidable shaft 123 which is pivotally connected to one end of a speed reset lever 125, the other end of the lever bearing against a speed reset cam 129 mounted on the throttle shaft 131. The lever 125 pivots on an abutment 133 carried by a pivoted lever 135 which also carries a valve element 137 which co-operates with a valve seat 139, the arrangement being such that if the engine speed differs from that called for by the throttle setting the valve 137, 139 is open and servo fluid supplied through line 81 to the cylinder 89 passes through check valve 107 and line 109 through the valve 137, 139 to drain so that after-burner fuel cannot be supplied. Once the engine speed reaches the called-for value, the acceleration valve closes and the piston valve 87 can then translate to the right, covering as it does so, the port 105 so that even if the acceleration valve 139 should subsequently open, no change in the position of the piston valve can occur. The variable area nozzle actuators 29 are controlled by a link 151 connected to a lever 153 on a rotatably mounted shaft 155, the lever 153 moving clockwise as shown to cause opening of the nozzle. The angular position of the shaft 155 is controlled by the piston 161 of a bleedtype servo 159 to which servo fluid is supplied through lines 69, 165, there being a fixed orifice 167 and a variable orifice 169, the latter being controlled by a flapper valve 171 which is secured on a rotatably mounted shaft 173. The servo piston 161 will normally follow movement of the flapper element 171, being compelled to do so by variation of the differential pressure across the piston. The position of the flapper element 171 is controlled either by the angular position of the throttle shaft 73, a cam 179 on which engages against the upper end of the flapper or by the angular position of the shaft 173 as determined by the turbine temperatureresponsive means 51 which, acting through the electric servomotor 203, positions the cam 199 as a direct function of turbine temperature. The cam 199 acts on a lever 197 to control the angular position of the shaft 191 which, acting through the lost-motion device 189, controls the angular position of the shaft 173 and so of the flapper element 171. The throttle lever acting through cam 179 positions the nozzle actuators during normal operation of the engine, but control of the actuators is taken over by the temperature responsive means during after-burner operation. The temperature control may be locked out during normal operation and for this purpose the stem 207 of the piston valve 87 has pivoted thereto a lever 209 pivotally mounted at 211, the end of the lever 209 acting against the lever 187 so as to prevent clockwise movement thereof when the valve 87 is in the non-afterburning position shown. When the valve 87 is moved to the right when after-burning is initiated, the lever 209 is rotated to a position clear of the lever 187. The nozzle area servo piston 161 is also interconnected with the acceleration valve 139, a port 213 in the servo cylinder communicating with the valve 139 through line 109. If the servo piston is towards the right-hand limit of its travel, the space to the left of the piston communicates through port 213 with the line 109 and should the acceleration valve 136 open as the result of an off-speed signal, the space to the left of the servo piston will be connected to drain and the servo piston will accordingly move to the left to cause the nozzle to open. Leftward movement of the servo piston will cease when the piston reaches the position shown in which the port 213 is closed off, that is unless the position of the flapper element is such as to cause further movement thereof. The after-burner fuel metering device 47, Fig. 1, receives a control signal from the afterburner fuel and nozzle control by means of the control rod 217 to which are pivoted levers 219 and 225; the lever 219 engaging the throttle lever cam 179 whereby the control rod 217 is positioned directly in accordance with the throttle cam position. This control is subject, however, to two overrides, one of which is dependent on the turbine temperature limit mechanism acting on the flapper element 171 and the other of which is dependent on the nozzle area opening acting through the cam 229. The flapper element 171 carries a stop 223 which may engage the pivoted lever 225 when the flapper element is moved to such a position as the result of engine over-temperature. The rod 217 thus acts to reduce the afterburner fuel supply. The cam 229 which is set in accordance with the nozzle area opening acts to lift the follower 221 from the throttle lever cam 179 whenever the propulsion nozzle is not sufficiently open that the engine can withstand the after-burner fuel supply which would otherwise be called for by the throttle lever cam 179.