Patent GB-607856-A (GB)
Title: Improvements in or relating to propeller control
IPC: B64C11/42
Filed: 1944-01-13
Abstract: 607,856. Fluid-pressure servomotorcontrol systems. UNITED AIRCRAFT CORPORATION. Jan. 13, 1944, No. 691. Convention date, Nov. 5, 1942. [Class 135] [Also in Group XXXIII] In a hydraulic control apparatus for variable-pitch propellers in which hydraulic fluid is supplied to a pitch-changing motor 30, 32 under the control of a governor-operated valve 106 from a first fluid pressure source such as a booster pump 78, 80, fluid pressure from a second source such as a motor-driven pump 172 is led to the first source and to the governoroperated valve to render the governor operation ineffective and to move the valve to a position in which fluid from both sources is directed to one side of the pitch-changing motor. Means are provided to limit the movement of the movable element 30 of the motor in each direction under normal governor operation, which means are rendered inoperative when fluid at the higher pressure is supplied by the motor-driven pump 172 for feathering, unfeathering and reversing the propeller for which operations three separate manual control elements 134, 216, 226 are provided. The unfeathering operation can only be effected when the pilot's hand control 126 of the governor valve 106 is in the lowest speed position, and the reversing operation is only possible when the aircraft is grounded and the rotational speed of the propeller is below the speed setting of the governor. The pitch-changing movement of the blades 18, Fig. 1, is effected by gears 21, 22 through a cam mechanism comprising similar but oppositely slopping cam slots 33 in a fixed sleeve 31 and a rotatable sleeve 24. The cam slots 33 have steep-pitched parts 33b, 33c at their ends for effecting the feathering and reverse operations respectively and these act as stops to prevent the movement of the annular piston 30 mounted on an extension 44 of the propeller shaft 14 in a cylinder 32, beyond the governor range. A further stop means when the propeller is moving towards a low pitch position is provided by ports 58 in a flange 56 on the piston, which ports are eventually obscured by a sealing ring 50 as the piston moves inwardly so that fluid cannot escape from the inner end of the cylinder 32 to passages 46 except through high-pressure check valves 62 which only open at a pressure above that for which.the booster pump 78, 80 is set. When the ports 58 are not obscured, fluid can pass through ports 47 or 49 and also into'the cylinder 32 through lightly-loaded check valves 60. The booster pump 78, 80 is driven by a hollow twoport shaft 66 splined at 78 and connected to the shaft 14 by gears 68, 70. The booster pump suction chamber 90 is supplied with oil from a pump 84 having a relief valve 86. The booster pump outlet is through a passage 96 to an annular channel 97 which can communicate with either of two further annular channels 98, 102 leading through passages 100, 104 to the respective sides of the piston 30, under the control of lands 108, 110 on the piston valve 106. The latter is normally controlled by the fly-balls 74 of the governor, the speeder spring 114 of which has an abutment 116 adjusted through a rack and pinion operated i by the pilot's lever 126 through sheaves 120, 122 and a cable 124. The channel 97 has a relief valve 128 which when open communicates with the pump suction 90. The high-pressure pump 172 feeds through a pipe 176 past a check valve 178 to the channel 97 and is driven by a motor 170 from a battery 146 when the solenoid-operated switch 168 is closed on operation of any of the control elements 134, 216, 226. When the feathering button 134 is depressed, a solenoid 150 controlling a piston valve 152 and a holding solenoid 158 are energized as well as the solenoid 166 actuating the switch 168. High-pressure fluid passes through channels 154, 184 to the base of the valve 106 which is thereby raised to its uppermost position in which high-pressure fluid passes through the passage 100 to the inner end of the cylinder 32 and moves the piston 30 to its extreme outer position in which the cam rollers 28, Fig. 1, mount the feathering part 33b of slots 33. On completion of the operation, a pressure surge acting through channels 100, 98, 181 opens a spring-closed switch 162 de-energizing the holding solenoid 158 so that the contactor 136 is opened by a spring 192, the valve 152 moves inwardly and the motor 170 stops. The propeller is now completely feathered and the governor valve 106 left under the control of the governor. For unfeathering, the manual control button 216 is depressed, but before the solenoid 166 can be energized the pilot's lever 126 must be in the low-speed position in which it closes a switch 214. Since the propeller is now stationary, the valve 106 will be in its lowest position and high-pressure fluid passes through channels 97, 102, 104 to the forward end of the piston 30, the pressure on which is sufficient to cause the check valves 62 to vent fluid to the rear of the piston. The button 216 may be released when the rotation of the propeller is firmly established. For reversing the propeller, the third manual control button 226 is depressed and the lever 126 is moved to the high-speed position. The circuit to the solenoid 166 is not complete until the landing gear is both extended and loaded, in which position it closes a switch 240. In the case of a seaplane, some form of hydrostatic switch may be used. The valve 106 will be in its lowest position with the lever 126 in the high-speed position and the engine throttled back so that high-pressure fluid passes to the front end of the cylinder 32 and moves the piston 30 to the extreme position passed that in which ports 58 are obscured. The limit of the reversing movement is set by the ports 58 again becoming obscured this time by a sealing ring 54. The resulting pressure surge opens the switch 162 and de-energizes a holding solenoid so that the button 226 is raised, and the contactor 228 leaves its contacts. If desired, the engine throttle may operate a switch in series with the switch 240. In order to prevent the relief valve 128 opening under the pressure from the pump 172, a fluid-pressure load is exerted on its rear face through a channel 180 past a piston valve 182 also connected to the channel 100. A further safety valve 243 opens when the pressure from either pump exceeds a safe limit. A check valve 92 prevents oil being forced back to the pump 84 by the pump 172. A supply of warm oil to the pumps is ensured by an inner auxiliary tank 196 in the reservoir 174 to which returning oil is fed over a saucer 204. The pump 84 is fed from an inner hopper 200 communicating with the tank 196 by a check valve 212.