GB925471A - Manual and automatic hydraulic servomechanism - Google Patents

Abstract

925,471. Automatic control of aircraft. W. W. TRIGGS (Bell Aircraft Corporation). Aug. 31, 1959, No. 29603/59. Class 38 (4). [Also in Group XXIX] A power control system for an aircraft having a movable aerodynamic control surface, comprises a fluid-pressure actuator 16, 18 connected to the surface, a differentiallyfulcrumed manual control means 20, 50, 51 operatively connected with a resilientlycentred spool valve 48 in a housing 45 to move the spool in opposite directions from neutral position to control the actuator 16, 18 when the fulcrumed manual control means is unrestrained, a differential pressure - control valve or flapper 64 responsive to automatic signals and arranged to apply differential fluid pressures to opposite ends of the spool valve 48, and an electromagnetically actuated selector valve 65 for selectively switching the output of the control valve 64 to the spool valve 48 and selectively switching a secondary fluid pressure supply to cause actuation or deactuation of a pressure-responsive device such as a pair of lock-out pistons 58, 59 which are adapted to restrain or restore normal fulcruming movements of the manual control means 20, 50, 51. As shown, the output of the flapper control valve 64 may also be applied to opposite ends of the pressure-responsive device 58, 59, so that the arrangement is operable in three modes, namely (a) manual or " power control," (b) automatic or " autopilot " control, and (c) a stability augmentation mode in which both the manual and automatic controls are effective simultaneously. On actuation of the lock-out pistons 58, 59, the fulcrumed levers 50, 51 engage abutments 62, 63 on the housing 45 to restrain their normal fulcruming movement. The flapper valve 64 may be responsive to electrical signals. A cross-connection valve 74 across the power actuator allows for emergency operation in the event of loss of hydraulic pressure. In an alternative embodiment, duplicate spool valves operating the actuator in a dual supply system are engaged by tappets yoked together by side yokes connected to a pair of lockout or decoupler pistons, one of these yokes being coupled to the fulcrumed manual input member 20. A solenoid valve in a supply line to the differential pressure control valve and to the space between the pistons provides for engagement or disengagement of the tappets with the valve spools to allow operation in the manual or autopilot modes. To provide for operation in the third mode, the pistons are mounted in a sliding spring-urged over-ride cylinder whereby the tappets can be brought manually into over-riding engagement with the spool valves, only one position of this solenoid valve being necessary to cover both the autopilot and stability augmentation modes. An overall system shown diagrammatically in Fig. 1 may be responsive to signals of the nature indicated and may include the devices named in this Figure.