GB681348A - Improvements in or relating to control valves more particularly for hydraulically controlled variable pitch propellers - Google Patents

Abstract

681,348. Fluid-pressure servomotor-control systems. UNITED AIRCRAFT CORPORATION. Jan. 12, 1949 [Jan. 23, 1948], No. 839/49. Class 135. In a control valve 82 of the spool type having lands 78, 80 co-operating with ports in a hollow shaft 52 to control the flow of fluid to the opposite sides of a double acting fluid servomotor which is continuously urged in one direction by an external force, the lands are the same width as the ports but are differently spaced so that when one port is closed by its land the other port is open to drain as shown in Fig. 2. The lands are nearer together than the ports so that when one land covers its co-operating port it maintains a fluid pressure in one side of the servomotor which opposes and preferably balances the external force. The reduction in pressure which occurs at the controlling edges of the lands and ports due to the flowing fluid is less at the drain controlling edges than at the pressure controlling edges since the former are always open further and thus the force tending to return the valve to its neutral position is diminished. In Fig. 1, the valve is applied to the control of a hydraulically-controlled variable pitch propeller the blades 18 of which are rotated through gearing 26, 28 and cam mechanism 32, 34 by a doubleacting hydraulic motor comprising a cylinder 38 carried by the hub 12 and an annular piston 36 opposite sides of which are fed through channels 48, 50 and conduits 44, 46 under the control of the spool valve 82. The latter is regulated by a centrifugal governor 56 driven from the engine by the hollow shaft 52 carrying a gear 42. The shaft 52 also drives a booster pump 58, 60, supplied from the engine lubricating pump 64. The pump 58, 60 supplies the space 76 between the lands 78, 80 through a passage 74 fitted with a relief valve 92. Fluid returns to a sump via one of the annular spaces 102, 91 and an axial passage in the valve. Specifications 526,100 and 607,856 are referred to.