Patent GB-861716-A (GB)
Title: Fuel regulating apparatus for a prime mover
IPC: F02C9/16
Filed: 1957-05-02
Abstract: 861,716. Fluid-pressure servomotor-control systems. WOODWARD GOVERNOR CO. May 2, 1957 [May 10, 1956], No. 14043/57. Class 135. Apparatus for regulating the fuel flow to a prime mover comprises a settable speed governor which controls a first pilot valve of a servo system which positions the main fuel supply valve, a detecting means for detecting changes in a variable condition which affects operation of the prime mover, differential mechanism for continuously comparing the actual fuel flow, as determined by the position of the main valve member, with the desired fuel flow as determined by the value of the said condition and operating a second control valve in accordance with the difference in such a way that it interrupts movement of said main valve when the difference reaches a predetermined amount. The speed governor 12 controls a pilot valve 52 of a servo-piston 6 connected to a rod 35 which is connected by a crank 34 to the stem 19 of the main fuel supply valve 10. The stem of the valve 52 has a piston 60 which receives a feedback fluid loading controlled by an accumulator piston 54 and an adjustable restriction 61 to provide primary and secondary compensation. The rod 35 is also acted on by a biasing piston 7 and two other servo-pistons 8 and 9 the purpose of which is described later. The pressure drop across the valve 10 is detected by a piston 28 which acts on a pilot valve 26 which controls a by-pass valve 22. The compressor outlet pressure is determined by a device comprising two bellows 72, 75 which control a pilot valve 79 which controls a piston 81 which acts through gearing on a cam 83. The compressor inlet temperature is determined by a device 85, 88 which controls a pilot valve 91 which controls a piston 87 which determines the axial position of the shaft 93 the angular position of which is determined by a servo-system including a speed senser 13, a pilot valve 100, a piston 103 and a rack and pinion 104, 105. A three-dimensional cam 120 on the shaft 93 positions a rod 118 attached to one end of a floating lever 114 the other end of which is positioned by the cam 83. A rod 112 interconnects a point 113 on the lever with a point 111 on a lever 123 one end of which is positioned by a cam 125 on the rod 35 i.e. is positioned in accordance with actual fuel flow. The point 111 moves in accordance with the theoretically correct rate of fuel flow called for by the detectors 14, 15 and 13. The end 126 of the lever 123 is therefore positioned in accordance with the difference between the actual and the desired fuel flows and controls a pilot valve 127 accordingly. Normally ports 133, 144 of the valve 127 are connected to low pressure so that the servo piston 6, controlled as above described, determines the position of the valve 10. If the difference between actual fuel flow and the theoretically desired flow reaches an amount predetermined by the spacing of the lands 130, 131 one or other of the ports 133, 134 is closed so locking the servo-piston 6. If the predetermined amount is exceeded, the valve 127 moves to allow high-pressure fluid to flow to either of servo-pistons 8 or 9 and the rod 35 is moved in the appropriate direction to reduce the difference i.e. the pilot valve 127 overrides the governor 12. If there is a reduction in the speed setting of the governor 12, the fuel flow is reduced ; if, however, the reduction falls below a predetermined minimum value the valve 127 allows fluid to flow to a motor 140, the rod 118 is withdrawn from the cam 120 so that the point 111 is only controlled by the cam 83 responsive to compressor outlet pressure. The stems of the pilot valves 26, 52, 100 are biased by bimetallic strips 150, 151, 152 respectively which compensate for changes in fuel temperature. If the sensing device 15 causes the shaft 93 to over-travel to the right, i.e. if the temperature falls below a minimum, the end of the shaft 93 moves a bell crank 155 which through levers 156, 64 alters the speeder spring setting accordingly. When the fuel supply is shut off by seating of valve member 162 a by-pass valve 167 is opened thereby preventing excessive pressure rise at the inlet of the main fuel valve 10 as the prime mover coasts to a stop.