Patent GB-1280737-A (GB)
Title: A combustion engine fuel-metering system
IPC: F02C9/00
Filed: 1970-09-03
Abstract: 1280737 Gas turbine engine fuel systems BENDIX CORP 3 Sept 1970 [22 Sept 1969] 42156/70 Heading F1G A fuel control comprises a metering valve 62 actuated by a piston 64 responsive via conduits 72, 70 and chamber 66 to a regulated fuel pressure P R  and responsive via conduits 72, 88 and chamber 68 to an opposing variable control pressure P X  derived from P R  by means of a potentiometer comprising a fixed restrictor 92 and a leak-off valve 94 operated by a lever 96. A restrictor in the conduit 70 generates a pressure differential P R  -P S  which is a function of the rate of displacement of the piston 64, the generation being delayed by a spring-loaded movable wall 82 subjected to the pressure differential. A lever 99 is jointly operated in acordance with requested engine speed by a manually operated cam 100 and in accordance with actual engine speed by a cam 106 which is rotated by a servo-mechanism 219 in response to engine speed, the lever acting upon the lever 96 via a spring 124, temperature-compensating discs 119 and a bracket 114. The force exerted by the lever 99 is opposed by a force proportional to the pressure differential P R  -P S  , the pressures P R , P S  being applied for this purpose to respective bellows 122, 120 acting on the bracket. 114. In addition to rotating in response to engine speed, the cam 106 also axially movable in response to e.g. an engine temperature, by means of a servomotor 196. A three-dimensional speed cam surface 104 acts on the lever 99, and a further three-dimensional acceleration cam surface 108 acts on a lever 132 to produce axial movement of a three-dimensional cam 140 which is also rotated in accordance with the compressor delivery pressure. When the cam 100 is moved to request an increase in engine speed, the resultant movement of lever 99 causes the bracket 114 to move to the left to allow the lever 96 to be moved by a spring 164, acting via a lever 159, to reduce the opening of valve 94, the movement of lever 96 being limited by engagement of the lever 159 with a rod 150. The resultant increase in the pressure P X  drives the piston 64 to the right to increase the opening of the metering valve 62, thereby accelerating the engine. The resultant increase in engine speed and temperature produce rotational and axial displacement of the cam 106 and a consequent axial displacement of the cam 140. In addition, the increase in compressor discharge pressure attendant upon the increase in engine speed causes rotational displacement of the cam 140. The resultant movement of a follower 144, the rod 150 and the lever 159 allows the lever 96 to further reduce the opening of valve 94. The subsequent acceleration is scheduled by the cam 140 in accordance with the engine variables. Negative feedback is provided by linkage 168, 160 connecting the metering valve 62 and the lever 159. The negative pressure differential P S  -P R  arising from the opening movement of the metering valve 62 during acceleration which is lagged by movement of the movable wall 82 for purposes of stability, acts via the bellows 120, 122 to oppose the action of the lever 99 upon the lever 96, thereby applying negative feedback in accordance with the rate of opening of the metering valve 62 and therefore effectively in accordance with acceleration. When the actual engine speed approaches the requested speed, the cam 106 moves the lever 99 in the reverse direction to reduce the opening of the metering valve 62. The pressure differential applied to the bellows 120, 122 is now reversed, P S  now being lower than P R  the change being lagged by the movable wall 82. A similar course of events occurs during deceleration, but in this case the movement of the lever 96 is controlled by the lever 159 engaging a multiarm lever 172 rather than the rod 150. The lever 172 is connected to the follower 144 by linkage 178, 184 which can lengthen against the action of a spring 186. Movement of the lever 172 is limited by a stop 176 which fixes the minimum allowable fuel-flow, subsequent counterclockwise pivoting of the follower 144 improved by the cam 140 being accommodated by the spring 186.