GB559361A - Improved pitch control mechanism for variable pitch propellers - Google Patents

Abstract

559,361. Fluid-pressure servomotor-control systems. HOOVER, W. S. Dec. 12, 1941, No. 16072. [Class 135] [Also in Group XXXIII] The fluid pressure motor for varying the pitch of the propeller blades is controlled by a speed responsive governor acting through a servomotor which comprises a cylinder, a piston therein movable in opposite directions from a neutral position to which it is resiliently urged, and provided with a restricted, normally open, passage from one side of the piston to the other, means being provided for closing said passage. The pitch adjusting mechanism is actuated by a fluidpressure vane motor 108, Fig. 7, driven in one direction or the other by the operation of one of a pair of plungers 110, 112 mounted on the propeller hub and selectively driven by engagement with adjustable stationary cams 120, 118. The selection of the cam is effected by the movement of an arm 20 connected to the piston rod 142 of a fluid pressure servomotor 138 the direction of flow of pressure fluid to which is controlled by a valve actuated by a centrifugal governor driven by the propeller driving engine. The cams 118, 120 are in the form of eccentric flanges on sleeves 124, 122, Fig. 9, mounted on a bearing 126 fixed to the engine casing and having the same eccentricity with the propeller shaft 12 as the eccentricity of the cams so that in one position of the sleeves 124, 122 on the bearing the cams are concentric with the shaft 12 and neither plunger 110, 112 is actuated. The arm 20 is formed with a collar 132 surrounding the sleeve 122 and carrying pins 134, 136 extending into slots in the sleeves. On movement of the arm 20 in either direction the pins turn one of the sleeves only, the other remaining stationary and the corresponding plunger is brought into operation. Pins 127, 131 limit the movements of the sleeves. The piston 140 of the servomotor 138 is urged to central neutral position by balanced springs 146, 148 and the ends of the cylinders are in communication by a passage 150 controlled by a doubleacting ball valve 152 urged to open position by balanced springs 154, 156. If the engine speed varies, the governor controlled valve is actuated to admit pressure fluid to one end of the cylinder 138 and open the other end to exhaust. The resulting adjustment of the propeller pitch restores the engine speed to normal, closing the governor controlled valve. The springs 146, 148 then return the arm 20 to neutral position, liquid flowing from one end of the cylinder 138 to the other through the passage 150. While the engine is being started and brought to speed, the governor valve is open and the piston 140 is at one end of the cylinder. The pressure in the cylinder actuates the ball valve 152 to close the passage 150 during this time to prevent unnecessary leakage of pressure fluid to the exhaust. The governor controlled valve is mounted in a housing 36, Fig. 2, secured by its base 26 to the engine casing. A shaft 24 driven by the engine rotates the governor weights 38 which act to move axially a plunger 42 connected by a cross-pin 44 with the sleeve valve 46 controlling ports 48, 50 in a fixed sleeve 52. The ports 48, 50 communicate with passages leading by pipes 98, 100, Fig. 7, with the ends of the servomotor cylinder 138 and the spaces at the ends of the valve 46 communicate with each other and, through passages 96 and the hollow shaft 24, with the crank casing of the engine. The engine lubricating oil is pumped through a suction passage 70 by a gear pump 30, 32 to a delivery chamber 76, and, when the valve 46 is closed, circulates back to the passage 70 through a byepass passage 85 controlled by a non-return valve 78. The pump 30, 32 can draw oil from the passage 70 through either of two ports according to the direction in which the shaft 24 is driven, the other port being closed by a plug. Similarly two delivery ports, one of which is also closed by a plug, lead from the pumps to the chamber 76. Specification 557,906, [Group XXXIII], is referred to.