Patent GB-577910-A (GB)
Title: Improvements in servo motors
IPC: F15B9/08
Filed: 1943-12-28
Abstract: 577,910. Fluid-pressure servomotorcontrol systems. HOBSON (AIRCRAFT & MOTOR) COMPONENTS, Ltd., H. M., and MADDOX, S. V. Dec. 28, 1943, No. 21712. [Class 135] In a vane-type servomotor, the control valve is situated in the hub of the vane and comprises lands and grooves running longitudinally of the valve and varied in pitch angle at appropriate points so as to give a desired non-linear relationship, between the movements of the valve and the vane. The servomotor and its valve may be employed in the control system for an aero engine where movement of the pilot's lever 10, Fig. 1, actuates simultaneously the valves 16, 17 of servomotors 25, 54 controlling the speed and boost of the engine. Servomotor 54 is connected to a lever 57 which alters the setting of a centrifugal governor 58 driven by the engine, the governor being coupled to a control valve 59 of a further servomotor adjusting the pitch of the propeller blades. Servomotor 25 is coupled by a link 51 to toggle links 52 so that movement of the vane of the servomotor adjusts a throttle valve 50 in the induction pipe and may also control the delivery of a fuel injection pump. The links 51, 52 are also connected to a bellows and servomotor device 53, as described in Specification 566,323, [Group XXVII], which is actuated by boost pressure through a pipe 46 and which serves to adjust the throttle 50 and the metering valve 44 of the fuel injection system. Movement of lever 10 simultaneously alters a cam 77 for adjusting the datum of a bellows 71 actuating the control valve of a servomotor 74 for altering the supercharger driving gear. Atmospheric pressure acts on the bellows 71. Boost and exhaust pressures also act on a compound bellows 63 to actuate a servomotor 69 controlling the ignition timing. In a practical embodiment, the pilot's control lever 10 is connected to a lever 18, 20. Fig. 2, pivoted on a shaft 19 so that movement of lever 10 moves the control valves 16, 17 longitudinally. The latter are each provided with four grooves varied in pitch angle at appropriate points and spaced around the central spindle, the opposite pairs of grooves being closed at opposite ends so that one pair of grooves is open to pressure liquid and the other pair to exhaust. When the valve 16 is moved, one groove of each pair will coincide with ports 28, 29 in the hub of the servomotor vane 25 to connect one side of the latter to pressure and the other side to exhaust, and the vane will move until the ports 28, 29 are again in register with the lands. The vane is connected to a lever 42 to which the link 51 leading to the throttle &c. is pivoted. Should the engine be stopped with the lever 10 in the slow running position, the oil pressure will drop and a spring-pressed plunger 40 will push the vane to a position giving a throttle opening suitable for starting. This servomotor also controls the fuel metering valve or means to vary the stroke of the fuel injection pump. Valve 17 is connected to lever 20 by a ball joint 23 so that the valve can be rotated by a lever 61 as well as moved longitudinally by lever 10. Lever 61 is connected to a further overriding lever 62, Fig. 1, normally held by a spring detent in the middle (inoperative) position. When lever 62 is moved to either end position, valve 17 is rotated and pressure liquid applied to the vane so that the propeller blades can be adjusted for feathering &c. Actuation of lever 18 also rotates a cam plate 77, Fig. 3, and, through a shaft 78 and stirrup 79, adjusts the loading on a capsule stack 71. which is subject to atmospheric pressure. As the atmospheric pressure alters, a piston valve 73 is moved by the capsules to control a vane servomotor 74 which alters the gear ratio of the supercharger. A rapid actuation of the servomotor is ensured by a rotary shuttle valve 76 as described in Specification 577,912. The gear ratio can also be changed by a manual overriding control connected to a lever 80 on shaft 78. Specifications 419,113, [Group XXVII], 470,492, 567,106, 572,485, [Group XXII], and 577,911 also are referred to.