Patent GB-781346-A (GB)
Title: Improvements in or relating to pressure fluid-operated servo-systems
IPC: G05D1/00
Filed: 1955-07-25
Abstract: 781,346. Fluid-pressure servomotors. BENDIX AVIATION CORPORATION. July 25, 1955 [Aug. 10, 1954], No. 21469/55. Class 135. In a fluid-pressure servo-system including a servomotor 77 selectively operable through a first distributer valve 10 from a pilot's control lever 9 in a first condition of the system and through a second distributer valve 8 from an automatic pilot 7 in a second condition of the system, the first distributer 10 being lockable in an inoperative position and the second distributer being connectable with and disconnectable from the fluid supply, an arrangement normally acting in the first condition to unlock the first distributer 10 and connect the second distributer 8 to the supply, and in the second condition to lock the first distributer 10 and disconnect the second distributer 8 from the supply, a predetermined force developed by the lever 9 in the second condition of the system unlocks the first distributer 10 and disconnects the second distributer from the supply whereby the lever 9 overrides the automatic pilot 7. Automatic operation.-A solenoid 19 is energized upon closing a switch 17 and its plunger 23 lifts the spool 25 of a valve 12 and enables pressure fluid to flow from conduit 29 into a conduit 31 that opens into chambers 33, 34 of the first distributer valve 10; fluid also enters a conduit 35 and hence a chamber 37 at one end of a cut-off valve 39. The fluid in chambers 33, 34 presses pistons 43, 45 against shoulders 47, 49 to hold the spool 50 of distributer 10 in the central position; the fluid in chamber 37 moves the spool 52 of valve 39 from a stop 53 to abut another stop 54 to enable fluid from a conduit 57 to pass into a further conduit 59 and across the second distributer valve 8 into conduits 65, 67 and thence into chambers 68, 69 and through orifices 71, 72 to drain. When an armature 73 is moved from its central position the flow through one orifice 71 or 72 is decreased and that through the other is increased whereupon the resulting pressure difference in chambers 68, 69 urges the spool 75 of the distributer 8 in one direction or the other away from its central position and thus connects the conduit 59 to conduits 60, 62 or 61, 63 to cause the servomotor piston and therefore a control surface 6 to move in a corresponding direction. The armature 73 is moved in response to output from an amplifier 80 connected to a pair of coils 82, 83, the amount of movement being related to the phase and amplitude of the signal from an automatic pilot system 7 which for the surface 6 shown comprises inductive follow-up and pitch devices 85 and 87, the latter being controlled by a vertical gyroscope. The servomotor piston is also attached to the rotor of the device 85, the lever 9 and the spool 50 by linkage 11 which during automatic operation constrains the lever 9 to follow the action of the surface 6. Should the aircraft deviate from a given attitude generated in the device 87 causes movement of the servomotor piston and surface 6 until the signal from the device 85 is equal and opposite to that from the device 87 whereupon the input to the amplifier is zero and the armature 73 returns to the central position. Manual operation.-Upon moving the lever 9 the spool 50 is displaced in one direction or the other and releases the pressure in one of the chambers 33 or 34 to a drain conduit 40 by way of conduits 97 and 96 or 98 so releasing the pressure in conduits 31 and 35 and the spool 52 is urged by a spring 100 against an abutment 53 thereby preventing automatic operation of the distributer 8 and enabling fluid from a conduit 101 to be supplied to the servomotor 77 through one or other of conduits 103, 104. Change-over from manual to automatic operation.-A switch 110 is closed and consequent energization of a solenoid 112 over a time-delay switch 140 causes a plunger 118 to elevate the spool 120 of a valve 13 so that fluid from conduit 29 flows into a conduit 124 and brings about movement of the spool 126 of a transfer valve 14 to interconnect conduits 29 and 57 but the flow of pressure and drain fluid is retarded by orifices 128 and 130 as is the automatic control of the servomotor piston; when the delay switch 140 de-energizes the solenoid 112 the pressure in conduit 124 is released to the drain conduit 40 and the spools 120 and 126 are spring returned to the positions shown.