GB703619A - Improvements in or relating to engine control systems - Google Patents

Abstract

703,619. Gas turbine plant. ROLLS-ROYCE, Ltd. July 9, 1951 [July 10, 1950], No. 17265/50. Class 110 (3). [Also in Group XXIX] A system for controlling the supply of " additional fluid such as water to a gas turbine engine to augment the power thereof comprises engine-torque-responsive means adapted to control the delivery of additional fluid to the engine in dependence on the engine torque. Normally the supply of additional fluid is increased as the torque decreases so that a substantially constant value of the torque is maintained. The enginetorque-responsive means are arranged to become operative on the attainment or selection of a predetermined engine speed, and may be influenced by other operating conditions such as atmospheric pressure, or actual or selected engine speed. In Fig. 1, the supply of additional fluid through a metering orifice 10b is controlled by a valve 10a operated by a spring-loaded servo piston 11 in a cylinder 12 supplied through a pipe 36 with servo liquid. The piston 11 opposite sides of which are connected through a restriction 13 is controlled by a bleed valve 16 carried on an arm 18 projecting from a pillar 19 connecting two diaphragms 20, 21. The diaphragms 20, 21 separate a chamber 23 connected to a sump from an evacuated chamber 25 and a chamber 24 open to the atmosphere. Axial pressure is also applied to the pillar 19 by an inclined strut 28 abutting a piston 29 loaded by springs 32. The piston 29 is open through a pipe 33 to a pressure delivered by a torque meter in such manner that the pressure increases as the torque increases. Thus an increase in atmopheric pressure or a decrease in torque opens the metering valve 10a. The spring abutment 34 may be adjusted in accordance with the engine speed so that the torque meter pressure necessary to balance the spring load increases as the engine speed increases. Alternatively the spring abutment 34 may be adjusted by the engine speed selecting lever to increase the selected value of the torque as the selected engine speed is increased. In a modification, the bleed valve 16 is replaced by a shuttle lift valve which controls both the inlet and exhaust of the servo liquid to the cylinder 12. The shuttle lift valve is operated by a lever pivoted at one end and loaded in one direction by a spring and in the other by a piston exposed to the torquemeter pressure and by opposed capsules one of which is exhausted and the other of which is open to atmospheric pressure. In a further modification, the servo piston 11 is controlled by a bleed valve carried at one end of a spring-loaded lever loaded by opposed capsules 'and a torquemeterpressure-responsive piston as described above. In this form, the bleed valve is provided with a byepass valve which is closed to render the torque control operative on the selection or attainment of a predetermined engine speed. Figs. 4 and 5 show the application of the invention to an aircraft gas turbine engine driving an airscrew 83. An extension 82h of the eneine shaft 82a drives the sun wheel 79b of a planetary gear 79 of which the planet carrier 79c drives the airscrew shaft 83a, the annular gear 79a being connected to a casing 93 having a leak-off piston valve which controls the pressure in a conduit 117 leading to a spring loaded piston 115 in the torque control mechanism 104. The casing 93 is supplied by a pump 93c. The "additional fluid ", which may be fuel, metering valve 10 has a valve member t0a actuated by a servo piston 11 under the control of a shuttle valve 41 actuated by diaphragms 108, 109 and a pillar 111 similar to those in Fig. 1. The piston 115 which is loaded by a light adjustable spring 118 acts on the pillar 111 through a push rod 113 inclined thereto and its load is opposed by a similar push rod 114 loaded by a main spring 122 and an opposed trimmer spring 123., The latter is adjusted from the pilot's speed control lever 85 through a linkage 87, 88, 129, 128, 127 and a shaft 126 bearing a cam 125 operative on a lever 124. The shaft 126 also adjusts a valve 130 in the supply condit 102 to the shuttle valve. The valve is opened and the torque control rendered operative when an engine speed above a given value has been selected. The lever 85 operates a fuel control through a link 92 and the speed setting lever 84 of a constant speed unit (not shown) through a further linkage 89, 90, 91. The selected value of the torque may in some cases be arranged to decrease as the engine speed increases so that a constant power output is maintained.