Patent GB-573400-A (GB)
Title: Improvements in or relating to power plant control means
IPC: B64C11/30
Filed: 1943-01-06
Abstract: 573,400. Fluid-pressure servomotor-control systems. UNITED AIRCRAFT CORPORATION. Jan. 6, 1943, No. 283. Convention date, Feb. 9, 1942. [Class 135] An engine control has the setting of the speed controlling means adjusted by a torqueresponsive mechanism for preventing overspeeding of the engine upon a sudden increase in power. The Figure shows the invention applied to an aircraft power plant including a variable pitch propeller. The blades of the propeller 10 are adjusted by a single-acting power piston 74 loaded by a compression spring 78 and acting through rods 76, 82, 86 and slip ring 84. The power piston is controlled by a centrifugal governor 32 driven by the propeller shaft 14 through bevel gearing 22, 24 and toothed gears 26, 28, which gears also drive a motive fluid pump 34 regulated by a relief valve 58. The pump outlet is connected by a passage 60 with a port 64 in a fixed sleeve and a second port 68 in the sleeve is connected by a pipe 66 with the power cylinder 70. Connection between the port 68 and the pressure port 64 or a drain port is controlled by a tubular ported valve 36 moved by the governor 32. A follow-up valve 98 co-operating with the valve port associated with the port 68 is coupled by a lever 100 to a piston 94 loaded by a spring 106 and subject to fluid pressure produced by a piston 90 slidable in a cylinder 88 arranged in tandem with the cylinder 70. The pressure acting on the piston 94 is dissipated through a bleed orifice adjusted by a needle valve 108. The propeller shaft is connected to the driving shaft 16 by a two-speed epicyclic gear 18. This gear comprises a toothed annulus 120 supported by the engine casing 12 and having two sets of teeth 120, 120<1>, a driving pinion 110 on the shaft 16 and a pinion 112 on the propeller shaft. The planet pinions have three sets of teeth 116, 116<1>, 116<11>, the teeth 116<1> being in permanent gear with the pinion 112 and the teeth 116 in permanent gear with the pinion 110. In the low gear position shown, the teeth are in mesh with the teeth 120<1>, while in the high gear position the teeth 116<11> mesh with the teeth 120. The planet pinions are moved to change gear by a double-acting piston 124 controlled by a manually-actuated valve 132. The governor is loaded by a spring 40 bearing against a piston abutment 42 slidably mounted in a cylinder 44 provided with a rack 50 in engagement with a pinion 52 rotatable by pulley 54. A spring 56 between the closed end of the cylinder and a cap 46 takes part of the spring load and facilitates operation of the pulley. The cylinder 44 is connected by pipes 150 either to an exhaust port 154 or to a pressure line 152 by a valve 146 actuated by a spring-loaded piston 144. The cylinder housing the piston 144 is connected by a pipe 138 to the gear-changing cylinder 126. In the low gear and neutral positions, the pipe 138 is connected to drain by a passage 140 in the piston 124. When the piston is moved to change the gear into high gear, pressure is admitted to the pipe 138 which moves the valve 146 to admit pressure to the cylinder 44. This moves the spring- abutment piston into contact with a stop 156 so increasing the tension of the loading spring and raising the speed setting of the governor. The annulus of the change speed gear is pivoted at 166 to a piston 160 working in a cylinder connected by a pipe 170 full of liquid to a cylinder 172 housing the smaller diameter part of a spring-loaded differential piston. The larger diameter part works in a cylinder 171 connected by a pipe 178 with the conduit 104 so that when the torque transmitted is increased the volume of fluid between the pistons 90 and 94 is increased which has the effect of lowering the speed setting of the governor. In a modification, variations of pressure in the pipe 170 move a single-acting piston between stops to change the position of the fulcrum of the lever 100. This piston may also form part of a dashpot arranged to permit the piston to move upwards quickly and downwards slowly. In another arrangement, an additional piston and cylinder subject to the pressure in the conduit 170 is interposed between the cylinder 44 and the piston spring-abutment 42, the conduit 170 being provided with a suitable restriction. In a further modification, the volume of fluid between the pistons 90 and 94 is varied by a piston arranged in tandem with a differential piston actuated by fluid pressure from the line 60 under the control of a valve slidable in a bore in the piston and actuated by a bellows subject to the pressure in the engine manifold. Specifications 560,522 and 573,401 are referred to..