Patent GB-692086-A (GB)
Title: Improvements in hydraulic servo motors
IPC: F15B20/00
Filed: 1949-06-10
Abstract: 692,086. Fluid-pressure servomotor-control systems. HOBSON, Ltd., H. M., and MOTT, L. F. May 12, 1950 [June 10, 1949], No. 15500/49. Class 135 In a hydraulic servomotor employed to position an output member such as the control surface of an aircraft and having a normally operative control valve 10 linked to an input member 12, a normally inoperative emergency control valve such as the sleeve 9 is provided which on seizure of the valve 10 and as a result of manual effort exerted on the input member to correct any undesired movement of the servomotor due to valve seizure is movable by the input member to take over control of the servomotor. The servomotor shown comprises a piston 4 connected to a fixed part 7 and arranged in a movable cylinder 3 connected to an output member 8 and unitary with a valve housing 5. The housing 5 has a pressure inlet 17, an exhaust outlet 20, and ports 28 leading to opposite sides of the servomotor. The inlet 17 supplies a central inlet port 18 and two additional inlet ports 19. The exhaust outlet 20 is connected to two outlet ports 21. The valve 10 normally slides in the sleeve 9 which is normally maintained stationary in the position shown by centralising springs 11 forcing washers 13 against end covers 14 on the housing 5 and collars 16 on the sleeve 9. The sleeve 9 has a central inlet port 22 normally opposite the port 18 and masked by a land 26 on the valve 10. It also has two outlet ports 23 normally opposite the ports 21 and masked by end lands 32. In addition, the sleeve 9 has emergency ports 24 and slots 27. The ports 18, 19, 21, 22, 23 are all of width w, the ports 24 are of width 2w, and the slots 27 are of width 5w. The movement of the valve 10 is limited to 2w by collars 31 and that of the sleeve 9 by surfaces 30 also to 2w. In normal operation the valve 10 controls the ports 22, 23 which remain in alignment with the ports 18, 21 respectively. If the valve 10 seizes, the sleeve 9 is displaced against one of the springs 11 due to movement of the input member in a direction contrary to the original movement of the valve 10 and after a displacement w the ports 18, 21, 21 are cut off. Further displacement of the sleeve brings one of the emergency ports 24 into register with one of the ports 19 and the other into register with a port 21. The pressure and exhaust connections to the servomotor are thus reversed and the output member is moved in the opposite direction to its original movement until the emergency ports are again closed. In Fig. 2, the emergency control valve 40 is disposed parallel to the valve 10 and connected thereto and to the input member 12 by a lever 33. Movement of the valve 40 is normally prevented by springs 11 I as in Fig. 1. The valve 40 has a central groove 41 and two pairs of grooves 42, 43. The groove 41 and the grooves 43 normally allow alternative pressure and exhaust connections to opposite ends of the servomotor on displacement of the valve 10. If the valve 10 seizes and the movement of the input member is reversed the manual effort moves the valve 40 until the ports 18, 21, 21 are cut off and subsequent movement brings one of the grooves 42 into register with one set of ports 19, 37 and the other into register with the opposite set of ports 35, 38 so that pressure fluid is supplied to one side of the servomotor and exhausted from the other. The collars 31 limit the movement of the valve 10 to w whilst stops 50 engaging a cover plate 51 limit the movement of the input member to an amount proportioned to that of the valve 10 so that the valve 10 may travel the full amount w. Specifications 673,370 and 673,373 are referred to.