GB557316A - Improvements in or relating to hydraulic control devices - Google Patents

Abstract

557,316. Fluid-pressure servomotor-control systems ; variable pitch propellers. UNITED AIRCRAFT CORPORATION. April 19, 1940, No. 7136. Convention date, May 25, 1939. [Class 135] [Also in Group XXXIII] A hydraulic control system for adjusting the pitch of screw propellers which is of the kind described in Specification 526,100 in which the propeller blades 18 are adjusted by bevel gears 20, 22 operated by a hydraulic motor 24 the piston 28 of which is subjected at one end to fluid pressure e.g. the pressure of the oil lubricating system and at its other end to a higher pressure is constructed with a booster pump 44 which delivers oil at a higher pressure than the pressure produced by the lubricating oil pump 30, the excess pressure being controlled and kept constant by a spring-controlled relief valve 48 which delivers oil to a chamber 46 from which it can pass to the motor 24 or to exhaust through a conduit 72, according to the setting of a valve 56 which is under the control of a speed-responsive governor 58. If the engine speed is too high the valve 56 directs the high pressure oil to passages 60, 62, 64, 66 to the motor, and the piston is moved to raise the pitch of the propeller and lower the speed of the engine. At low speeds the oil is byepassed to the sump and the pitch its reduced so as to increase the speed of the engine. The valve 48 is constructed as shown in Fig. 2 of a cylindrical valve chamber 84 connected by a pipe 52 back to the inlet of the booster pump. In the chamber 84 is a sliding member 80 with an apertured reduced part 86 sliding in the chamber 46 and arranged to slide over a hollow cylinder 94 attached to an adjustable closing screw 96. A spring 82 normally keeps the valve closed, but at a predetermined pressure the valve opens to permit excess oil to pass through an aperture 90 to the passage 52.