Patent GB-673373-A (GB)
Title: Improvements in or relating to hydraulic servo motors and the like
IPC: B64C13/24
Filed: 1949-06-02
Abstract: 673,373. Follow-up systems. HOBSON, Ltd., H. M., MOTT, L. F., and WESTBURY, R. June 1, 1950.' [June 2, 1949] No. 14842/49. Class 40 (i). [Also in Group XXIX] A normally inoperative emergency actuating gear is provided in connection with a normally operative hydraulic actuator and in the event of failure of the hydraulic actuator, means operative by the input member of the actuator disable the latter and render the emergency actuating gear operative to control an output member. As applied to the operation of an aircraft control surface, the hydraulic actuator comprises a cylinder 14 slidable over a piston 15 fixed to the aircraft structure at 12. The cylinder has an extension 16 connected through a differential lever 18 to the output member 22. The hydraulic actuator is controlled by a valve 25 connected through a differential link 27 with the pilot's input member 34. The valve casing 24 is attached to the cylinder 14 and therefore follows up the movements of the valve. The emergency actuating gear comprises a screw jack 21, the fixed and movable parts 32, 20 of which are connected to the aircraft structure and the differential lever 18 respectively. As shown in Fig. 1, the screw jack 21 is operated by,a hydraulic motor 31 under the control of a valve 30 linked to the input member 34 and supplied with hydraulic fluid by a stand-by pump driven by an electric motor on closure of the switch contacts 54. The hydraulic motor 31 may, however, be replaced by an electric motor, the terminals 85, 86 (Fig. 3) of which .are connected to electric supply terminals 83, 84 by a reversing switch comprising pairs of contacts 81, 82 closed by the movement of a member 80 on a rod 79 connected to the input member but normally maintained in the neutral position shown by a yieldable ball catch 48 such as is described in Specification 673,369, [Group XXIX]. The catch 48 yields to allow displacement of the member 80 only on seizure of the servo-control valve 25. To prevent the catch 48 being released when the input member 34 is moved more rapidly than the output member 22 is capable of responding, a pivoted catch 68 is maintained in engagement with a notch 67 in the rod 79 by a plunger 71 responsive to the flow in a conduit 74 connecting the liquid supply 38 to the valve 25. The valve 25 is connected to the differential lever 27 through a further differential lever 65 one end of which is connected to a spring centralised plunger 63 having two apertures 76. If now in the conduit 74 ceases due to seizure of the piston 15 or failure of the liquid supply, the' catch 68 is released to permit operation of the screw jack by the electric motor. The piston 71 simultaneously releases a trip member 44 which allows a valve 39 to cut off the fluid supply from the valve 25 and connect the ends of the cylinder 14. The switch housing 46 is unitary with the movable part of the screw jack so that the movement thereof ceases when the contacts 81 or 82 move away from the member 80. If the control valve 25 seizes in an open position, the pilot's effort to correct the uncontrolled motion of the cylinder 14 causes the plunger 63 to be displaced whereupon a plunger 75 enters one of the holes 76 and relieves the load on a ball valve 78 which destroys the pressure difference across the piston 71 so that the rod 79 can be freed from the catch 68. The invention is applicable to systems including two main actuators as well as the emergency actuating gear. These actuators may be in the form of hydraulic jacks or hydraulic motors of a rotary type. They may be arranged in tandem or in parallel and in the latter case they may be connected. directly to or differentially with the output member. Specifications 605,264, 673,371 and 673,372, [all in Group XXIX], also are referred to.