Patent GB-485617-A (GB)
Title: Improvements in or relating to jacks, more particularly for retractable undercarriages for aircraft
IPC: B64C25/22
Filed: 1936-11-14
Abstract: 485,617. Fluid-pressure jacks. ONIONS, J. H., and AUTOMOTIVE PRODUCTS CO., Ltd. Nov. 14, 1936, Nos. 31159 /36 and 27577/37. [Class 78 (iii)] [Also in Groups XXVIII, XXIX, and XXXIII] In fluid-pressure jacks of the kind comprising a cylinder and plunger constituting a pulling and pushing connection between a pair of relatively movable members, the movement of the plunger relative to the cylinder, produced in one direction by liquid or gaseous pressure from an external source, compresses gas contained in a closed chamber or chambers within the jack thereby storing up energy for moving the plunger in the opposite direction. Means may be provided for returning the plunger by externally supplied fluid pressure in the event of loss or leakage of the stored energy. The invention is particularly applicable to jacks for operating retractable undercarriages, landing flaps, bomb hoists, fairing doors, movable fairings for gun turrets &c. on aircraft. As shown in Fig. 1, the jack cylinder comprises a tubular part 10 with heads 11, 12 secured therein by screws 13. The plunger 16 is secured to a hollow stem 15 passing through the head 12, the inner end 15a of the stem forming a stop to limit the compression and the outer end being closed by a plug 22 which may be adjustable to vary the internal volume. A connection 20 provides for supply of fluid under pressure to contract the jack and a valve 21 enables the initial pressure in the closed chamber A to be regulated. Sealing washers are provided as shown and terminal fittings 23a, 24a provide for attachment to the members to be operated, the arrangement being that, when the jack is operated in one direction by fluid pressure in the chamber B, the gas in chamber A is compressed to provide the restoring means when the fluid pressure in chamber B is relieved. Several variations of the internal arrangement are described. In Fig. 2, the chamber A is connected to the external fluid supply, the chamber B containing gas and communicating by an opening 26 with the chamber C in the hollow plunger stem. In Fig. 4, a fixed piston 40, carried by a rod 41 attached to the cylinder head 42, operates in the plunger stem which slides thereon, the chamber E, so formed, communicating with the chamber D by a passage 45 and the gas being stored in the chambers F, G. Alternatively gas may be enclosed in the chambers D, E, fluid pressure being applied to the chambers F, G. To enable the return stroke to be performed by admission of external fluid pressure in the event of failure of the compressed gas, the two gas chambers D, E or F, G, as the case may be, are dissociated, one being retained as a closed chamber, the other being connected to an external source of pressure for use as required. For example, in Fig. 8, the jack is extended by fluid pressure supplied to the chambers D, E, gas compressed in the chamber F provides the restoring force, and the chamber G is connected to an outside source of supply by a passage 63, for use in emergency. Variations of this arrangement are described and illustrated. A form is also described in which the jack cylinder contains a pair of opposed plungers with oppositely projecting hollow stems connected to the two relatively movable members to be operated. Fig. 12 shows a liquid pressure operating system for controlling a jack in which the pressure fluid is admitted to the chambers F, G, gas is compressed in the chamber E to provide the restoring force and, in case this fails, the chamber D is connected to the external supply which is delivered thereto as required. A pump 82 draws liquid from a reservoir 83 and feeds it to a control valve 84 with outlets connected to the two ends of a locking valve 85 from which pipes 86, 87 lead to the respective chambers F and D. In the central position of the valve piston the openings 97, 100 to the pipes are sealed so that the jack is locked in position. If liquid from the valve 84 is admitted to the right-hand end of the valve casing 85, movement of the piston 90 firstly opens the pipe 87 to a space 94, allowing return of any liquid in the chamber D to the reservoir through an opening 101 in the piston, and subsequently uncovers the pipe 86 to admit pressure fluid to the chamber F, G. In the opposite process, the pipe 86 is first opened to the return space 94, allowing expansion of the gas in the chamber E, the pipe 87 being connected to the reservoir 83 by a lightly loaded one-way valve 103 to avoid production of a vacuum in the chamber D. If the air pressure in chamber E is insufficient to extend the jack, the pump will supply liquid through the port 100 to the chamber D. Specifications 425,207 and 481,449, [both in Group XXXIII], are referred to.