Patent GB-724750-A (GB)
Title: Improvements in or relating to fluid pressure servo-motor systems
Inventor: HARRISS JOHN HENRY
IPC: B64C25/22
Filed: 1951-09-10
Abstract: 724,750. Hydraulic machines; fluid-pressure servomotor-control systems. AUTOMOTIVE PRODUCTS CO., Ltd. Sept. 26, 1952 [Sept. 10, 1951], No. 21299/51. Classes 69 (2) and 135. A system comprising a servomotor unit which consists of a single servomotor or two or more servomotors operating together as one has at least two independent pressure fluid supply systems either of which is capable of maintaining operation of the servomotor unit without the assistance of the other, the unit being normally operated by fluid from a primary system, and a secondary system being connected to the unit automatically by means actuated by a fall in pressure in the primary system. The invention is described applied to the power-assisted operation of aircraft flying controls and in one form comprises a single servomotor having a fixed piston 75 within a moving cylinder 76 and controlled by a valve 87 actuated through a lever 80, motive fluid being derived from the primary supply system 73, or, if that fails, from the secondary system 74. Normally, pressure from the primary system conveyed to a chamber 98 overcomes a spring- loading on plungers 95, 96 to place a chamber 97 in communication with the chamber 98 through a passage 103 thus enabling pressure fluid to pass through a passage 106 to the righthand end of a plunger 91 urging the latter and a plunger 89 to the left to connect a conduit 84 leading to the control valve with the primary system through a non-return valve 94 and conduits 93, 105, and an exhaust conduit 85 from the control valve with the exhaust conduit 107 of the primary system through a conduit 108 and chamber 99. Should the primary system fail the spring 101 urges the plungers 95, 96 to connect the right-hand end of the plunger 91 with the exhaust conduit 107 thereby enabling the secondary supply pressure in a conduit 109 to move the plungers 89, 91 to the right to connect the conduit 84 through a conduit 92 with the secondary system instead of with the conduit 105, and the conduit 85 with the exhaust conduit 111 of the secondary. system. In a modification, two control valves, one for each supply system and connected to the manual control by a pivoted yoke, are employed, one valve controlling the servomotor when its supply system is operative whilst the other valve is held inoperative by a fluidpressure lock energized by the operative system. The pivoted yoke permits operation of one control valve whilst the other is held stationary. In a further modification two servomotors mechanically interconnected to operate together as one are employed, each having a control valve actuated by a common input member. Normally only one servomotor is operative, being supplied from the primary system, whilst the other is vented. In the event of failure of the primary system, the other servomotor is connected to the secondary system and the servomotor associated with the primary system is vented. Each control valve is actuated through a collapsible link which is extended by fluid pressure from the corresponding supply system so that the valve of whichever system is inoperative remains stationary. In a modification of the last arrangement, a tertiary supply system is connected to the servomotor associated with the secondary system in the event of failure of the latter.