GB1092997A - Improvements relating to hydraulic servo systems - Google Patents

Abstract

1,092,997. Fluid-pressure servomotor systems. BRITISH AIRCRAFT CORPORATION (OPERATING) Ltd. March 15, 1966 [Feb. 24, 1965], No. 7905/65. Heading G3P. [Also in Division G1] A hydraulic servo control system comprises a control device of the jet and flapper type in which a gyroscope is directly connected to the flapper. The output signal of the gyroscope 1 moves a lever.2 about its pivot 3 to cause the lever to vary the back pressure of a jet or nozzle 7 supplied via a restriction 8, such pressure variation being communicated via line 10 to a relay valve as described below. The movable cylinder 5 of a dashpot is connected via spring 4 with arm 2" of lever 2 and serves to make the movement of the lever proportional to the time integral of the signal from the gyroscope. The movable cylinder 12 of a stabilizing dashpot is directly connected to arm 2", and a spring 14 adjustably loads arm 2'. Opposite sides of the fixed pistons 5', 12' of the dashpots are interconnected by restrictions 6, 13 which may be of any of the forms indicated in Figs. 2a-d, (not shown). The relay valve Fig. 3a (not shown) comprises a piston having spaced lands 53, 54, a high-pressure inlet 25, a drain port (26) and an outlet 27 connected to a power device (Fig. 4). The signal in line 10 acts on land 53 and the outlet 27 communicates with land 54 via restriction 56. In the alternative relay valve of Fig. 3b (not shown), land (53') has a central extension (31) acted on by the signal in line (10), and the annular area of land (53') is acted on by a further signal in line (30). Land (54') abuts a spring (32) carried by a piston (34) which latter is mechanically movable to introduce another input signal. The power device comprises a pilot valve 67, 37 and a piston 65, 42, the pilot valve controlling communication between larger annular chamber 40 above piston 65 and either exhaust 41 or input 127. If the input signal from the relay valve increases, valve head 37 moves downwardly against spring 36 and admits the new signal pressure to chamber 40 thereby moving the piston downwardly until valve 37 is reseated. In the practical embodiment of Figs. 5-7 (not shown), the gimbal shaft (3) itself co-operates with the nozzles (7), the shaft being provided with flats for this purpose. The end of shaft (3) carries two leaf springs (4') the free ends of which carry pistone (73) supported by diaphragms (74), opposite sides of the latter being connected via capillary tubing. Pistons (73) thus form the movable elements of a pair of integrating dashpots. A vane (2) carried by shaft (3) is movable between stops (11) in a chamber (12) to form the stabilizing dashpot, opposite sides of the vane being connected via a restriction of the type shown in Fig. 2d, which latter has an arrangement of four orifices forming a bridge network which gives a linear relationship between rate of displacement and applied force and a pressure drop independent of viscosity.