GB868419A - Hydraulic system for adjustable pitch aeronautical propeller - Google Patents

Abstract

868,419. Variable pitch propellers. UNITED AIRCRAFT CORPORATION. Dec. 16, 1957 [Dec. 18,1956], No. 39014/57. Class 114. Variable-pitch propellers are adjusted by an hydraulic motor fed with fluid under the action of a control valve, normally adjusted by a speed governor driven from the engine, and a feathering valve. The housing 14 contains the hydraulic motor which varies the pitch of the blades 12 through suitable cam and gear mechanism. The feathering valve 32 when in its " closed position (as shown) allows communication between the fluid supply source fed to conduit 28 and conduit 28a, which leads to control valve 34, and also connects conduits 26a, 26 and 30a, 30, conduit 26 feeding fluid to the hydraulic motor to decrease the pitch and conduit 30 supplying fluid to increase the pitch. The control valve 34 when in its " central " position (as shown) terminates the flow through conduit 28a from the supply source and this valve is moved by a governor 48, driven from gearing 42, against the action of spring 52 to connect conduits 28a, 30a to provide fluid to the hydraulic motor to increase the pitch, and when the spring loading is sufficient to overcome the governor action conduit 28a communicates with conduit 26a to decrease the pitch. The supply of hydraulic fluid is provided by a main pump 62 and a standby pump 64 which deliver fluid from a tank 56 supplied by pumps 58 from a tank 54. The main pump 62 delivers fluid past filter 66 and conduit 22 to the conduit 28 which is provided with a branch conduit 94 leading to a normally closed valve 92. The standby pump 64 delivers past filter 68 to a conduit 70 which communicates when valve 32 is " closed " with a conduit 70a leading to a spring loaded valve 72 having a small orifice 88, the main delivery flows through conduit 78 to a drain conduit 80 communicating with the tank 56 while part of the flow passes through the orifice 88 to conduit 82 which communicates through passage 84 of control valve 34, when in its " central " position, with conduit 86 which leads to the drain conduit 80. When control valve 34 is moved to vary the pitch it closes conduit 82 and the pressure in this conduit increases to the value existing in conduit 70a thus allowing valve 72 to close under the influence of its spring, thus the pressure in conduit 70 increases and opens a non-return valve 74 thus permitting the delivery from standby pump 64 to join the delivery from the main pump 62 whenever the pitch is changed. Similarly, when the feathering valve 32 is " opened " conduit 70 is closed and the two deliveries combine as above. Specifications 683,906, 724,284 and 824,078 are referred to.