Patent GB-794102-A (GB)
Title: Hydraulic servomotor follow-up systems
IPC: B63H25/28
Filed: 1954-08-04
Abstract: 794,102. Fluid-pressure servomotor-control systems. MERCER, J. Aug. 4, 1954, No. 22596/54. Class 135. A correspondence control system applicable to the rudders &c. of aircraft or water-borne craft and having a hydraulic servomotor with follow-up disposed between the manuallyactuated steering-wheel and the rudder includes a main or L.P. source of liquid for effecting the normal relatively small angular displacements of the rudder needed to keep the craft on its course and an auxiliary or H.P. source for effecting the occasional large displacements thereof necessary when altering course. As shown in Fig. 1, the operating bar 7 of a rudder post 2 is actuated by a jack 4, the supply of pressure liquid to the ends of which from main and auxiliary pumps 22, 45 respectively is controlled by a valve 3 having a spring-loaded closure member 17a coacting with seats on the valve body and a member 17. The latter member is connected by a rod 16 to the free end of one of a pair of capsules 9 connected by pipes 10 to capsules 8, the positions of the free ends 11 of which are regulated by a spring-loaded pivoted lever 12 controlled by a screw 15 operated by the steering-wheel 1. The capsules and their connecting pipes are filled with liquid, and changes in the temperature of the liquid which would alter the position of the member 17 are compensated by a capsule 47 connected by a pipe 52 to a tank 48 of the same capacity as, and disposed close to, the capsules 9, the free end 49 of the capsule 47 adjusting the position of a spring-loaded wedge 50 coacting with a wedge 53 on the lever. In order to relieve the bearings of the rudder post 2 of the major part of the reaction forces applied thereto, the jack cylinder and the bar 7 are pivotally connected to a lever 28 itself pivoted to a fixed part of the craft. The L.P. pump 22 is connected directly to an accumulator 53 and through a non-return valve 55 and pipes 23a and 24 to the upper end of the jack and the valve 3 respectively, the valve being also connected through a pipe 24a with the lower end of the jack. The H.P. pump 45 communicates through a non-return valve 59 with an accumulator 54 and through a second non-return valve and a pipe 44b with a valve 41 having a spring-loaded closure member 40 adapted to be opened through a rod 39 by a cam surface 43 on one end of a lever 35, the opposite end of which is pivoted to the movable rods 16 of the capsules 9. The outlet from the valve 41 is connected by a pipe 44a to the valve 3 which is pivoted to the lever 28 to provide follow-up. To effect clockwise movement of the rudder post 2, the steering-wheel is rotated to move the lever 12 anti-clockwise and depress the free ends of the capsules 8 and thus effect downward movement of the valve member 17 and displacement of the lower end of the closure member 17a from its seat on the valve 3, to permit the flow of L.P. liquid from the pipe 24 through the pipe 24a to the lower end of the jack. The jack piston 5 is thus forced upwards and rotates the rudder-bar 7. At the same time, the lever 28 moves the valve 3 so that its seat closes on the lower end of the member 17a. Reverse movement of the steering-wheel results in the raising of the member 17 so that its seat moves away from the closure member 17a and opens the lower end of the jack to the exhaust port 26 which discharges into the tank 110. In this case, the jack piston moves downwards under the pressure of the liquid on its upper face and the upper end of the member 17a closes on the seat of the member 17. When a change of course is required, the consequent large movement of the steering-wheel results in a corresponding large displacement of the lever 35 and opening of the valve 41 and the flow of H.P. liquid through the pipe 44c and the valve 3 to the appropriate end of the jack to effect the necessary rotation of the rudder post 2. Fig. 2 shows a modification in which the rudder bar 7 is operated by a pure torque applied by jacks 4, 4<SP>1</SP> the opposite ends of which are interconnected by pipes 66, 67, and in which the L.P. pump is a radial cylindrical reciprocating pump 22 having means for reversing the flow therethrough and a stroke-adjusting yoke 22a operated by a piston 64 in a cylinder 61. One end 62 of the cylinder is permanently supplied with H.P. liquid from a pump 45 or a duplicate pump 45<SP>1</SP> and the opposite end 63 is open through pipes 68, 69 and the control valve 3 either to exhaust or H.P. liquid, according to the positions of the valve members 17, 17a. During small course-holding movements of the steering-wheel, L.P. liquid from the pump 22 is directed by a distribution valve 71 to the jacks. When, during large course-changing movements of the steering- wheel, a point is reached at which the L.P. liquid is unable to effect further displacement of the rudder, H.P. liquid is supplied to the jacks through the distribution valve 71, the normally spring-balanced piston of which is displaced to one end or the other of the valve by H.P. liquid admitted to either of the valve chambers 72 or 73. In addition to the steering-wheel control, the valve 3 may be regulated by a hand-lever 86. In the event of failure of the follow-up means, the operation of the jacks may be effected by H.P. liquid, the flow of which is regulated by a piston valve 96 under the control of a hand lever 98. Fig. 3 shows a stabilizer 94 controlled by a jack 4, the supply of pressure liquid to which is controlled by the valve 3 which is regulated by a pendulum 109 carrying mercury switches 112, 113 when the rate of oscillation is below a predetermined value and by a pendulum 1<SP>1</SP> when the rate exceeds this value. Thus, during oscillations of the pendulum 109 of small amplitude, the switch 113 controls solenoids 124, 127 determining the direction of movement of the rod 138 connected to the valve member 17 and the supply of L.P. liquid to the jack, while in the case of oscillations of greater amplitude the switch 112 controls a solenoid 119 which operates a valve 41 controlling the flow of H.P. liquid from the pump 45 to a follow-up regulator 146 and the jack. When the rate of oscillation exceeds the predetermined value, the valve member 17 and the follow-up regulator come under the control of the pendulum 1<SP>1</SP> which is connected by a rod 98 with a bellows 99 having a small aperture opening to the atmosphere and connected by a rod 100 to a link 103 connected to the pendulum 109 and a link 160. The diameter of the orifice is such that movement of the rod 100 occurs only when the rate of oscillation exceeds the predetermined value. In another arrangement, the rudder-bar 265, Fig. 4, is controlled by a pair of jacks 252 supplied with H.P. or L.P. liquid under the control of H.P. and L.P. distributer valves 226, 229 disposed one above the other and the piston rods of which are pivoted to a vertical lever 285 pivoted near its lower end to the piston-rod 282 of a jack 277 pivoted to a girder 281 and operated by pressure liquid supplied by a pump 272 controlled by the steering wheel 271. The extreme lower end of thelever has a short arm carrying a block in which is set a ball 288 through which freely passes a rod 291 connected by a ball joint 292 to the rudder bar. The lower end of the lever is normally held in position by two powerful springs 293, 294. The lever is part of a follow-up for returning the distributer valves to their neutral positions on completion of a steering movement. Modifications of this arrangement include the provision of a hand-actuated pump for use in the event of breakdown of the H.P. and L.P. pumps, and the substitution of a single distributing valve for the H.P. and L.P. valves.