Patent GB-625062-A (GB)
Title: Improvements in retractable shock absorber struts particularly for aircraft landing gear
IPC: B64C25/60
Filed: 1946-10-24
Abstract: 625,062. Hydro-pneumatic shock-absorbers. KATZ, M. Oct. 24, 1946, No. 31615. Convention date, Oct. 25, 1945. [Class 108 (iii)] [Also in Group XXXIII] In a telescopic hydro-pneumatic shockabsorber more particularly for aircraft landing gear which is to be retracted when not in use, having means permitting transfer of oil or air from a main chamber into an auxiliary transfer chamber under the control of a valve device, the transfer chamber forms an integral part of the shock absorber and is separated from the main chamber to which it is adjacent, by the valve device which comprises a movable closing member which is subject on one hand to the variable pressure of fluid in the latter chamber and on the other hand to a constant antagonistic force, e.g. a spring, in such a way that it allows the passage of the fluid between the chambers, only when the force exerted by the fluid in the main chamber is less than the antagonistic force. In the construction shown in Fig. 1, pneumatic chambers 29, 30 are defined by relatively slidable cylinders 1, 5 and a tubular member 3 rigidly secured to the cylinder 1. A head 12 slidable on the member 3 has limited sliding movement relative to the cylinder 5 defined by a stop 16 and the engagement of a sealing ring 14 with the cylinder end. Ports 13 in the head 12 provide communication between the spaces 29, 30 when the head 12 is raised out of engagement with the end of the cylinder 5 by a spring 15 acting against the difference of pressure between the chambers. A piston 9 on the lower end of the member 3 defines liquid spaces 25, 26 and a further liquid space 27 is defined by a piston 19 carried by a hollow rod 18 rigidly secured to the base of the cylinder 5. In normal operation when absorbing landing or suspension shocks, communication between the pneumatic chambers 29, 30 is closed due to pressure in chamber 29 acting on the member 12. Pneumatic pressure in the space 29 provides a resilient suspension, and relative movement of the cylinders 1, 5 on compression is damped by liquid flow through orifices 20 in the piston 19, orifices 10 in the piston 9 and orifices 24 between the space 25 and the interior of the rod 18 which communicates with the space 27. On extension, the orifices 10, 20 are closed by valves 11, 21 and increased damping occurs through an annular space 10<SP>1</SP> between the piston 9 and the rod 18, liquid returning from the space 27 through additional ports 24<SP>1</SP> in the rod 18 which are uncovered by a valve 22. When load is substantially removed from. the shock absorber, the spring 15 is able to raise the valve 12 and the cylinders 1, 5 can be retracted slowly without compression of the air in the space 29. In the construction shown in Fig. 2, a piston 40 has limited sliding movement relative to a plunger cylinder 36 slidable within a main cylinder 32. The piston 40 has ports 41 which provide communication between a main liquid space 58 in the cylinder 32 and an annular space 60 between the cylinders 32, 36, when the piston is raised under the action of a spring 44. The ports 41 are closed when the piston is in its lowermost position (shown) relative to the cylinder 36 under the action of normal pressure in the liquid space 58. Liquid flow between the space 58 and a space 59 beneath the piston 40 is controlled by grooves 50 in a rod 49 which is rigidly secured to a diaphragm 33 of the cylinder 32. This flow may be increased during partial compression of the shock-absorber as during taxiing of an aircraft, by the uncovering of ports 47 in the piston 40 by a spring-loaded slide-valve 48 under the action of a spring 48a. This slide valve is moved against its spring 48a into closed position by a stop 51 on complete extension of the shock-absorber. The ports 47 are then closed in order to provide increased damping during the landing impact. The valve is maintained in closed position against the spring 48a by pressure in the chamber 58 acting through the ports 47 of the valve. Once this pressure is overcome by the spring 48a the valve opens and cannot again close until complete extension of the shockabsorber occurs. Compressed air is contained in a chamber 57 formed by the diaphragm 33 which communicates with the space 59 by a passage within the rod 49, ports 56 and valvecontrolled ports 52 in a piston 53 rigid with the lower end of the rod 49 and slidable with respect to the cylinder 36. In the completely extended position of the shock-absorber, i.e. when the pressure in the chamber 59 is at a minimum, the piston 40 is raised by the spring 44, and the cylinders 32, 36 may be easily retracted by a slow compression movement. Under normal load conditions pressure in the space 58 maintains the piston 40 in the closed position and on compression, liquid passes with damping through grooves 50 and/or orifices 47 into space 59 and thence through orifices 52, 56 and rod 49 to compress air in the space 57. On extension a reverse flow takes place and additional damping is provided by the closing of the orifices 52 by a valve 54. In the construction shown in Fig. 3 a cylinder 61 carrying a piston head 61<SP>1</SP> is slidable relative to a cylinder 64 having fixed diaphragm 69. A valve 80 is held against a plastic seat 79. by pressure of liquid in a space 85 of the cylinder 64 against the action of a spring 81 bearing between a ring 82 on the valve 80 and a ring 83 rigid with the cylinder 61. A floating piston 71 defines a pneumatic chamber 70 in the cylinder 65 and is limited in upward expansion by the diaphragm 69. A stem 72 on the piston 71 passes through a central port in the diaphragm and has grooves 73 which cause damping of flow between either side of the diaphragm. Increased flow through the diaphragm can occur when the shock absorber is functioning as a suspension as distinct from absorbing landing shocks by means of ports 74 controlled by a slide-valve 75 similar to the slide-valve 48 of Fig. 2. Under no-load conditions, the valve 80 is maintained in open position by the spring 81, and liquid can pass from the space 85 to a space 86 within the cylinder 61 thereby permitting relatively free retraction of the cylinders 61, 64. Under normal load conditions, pressure applied to the cylinder 61 is applied to the air in the space 70 through the liquid in space 85 and the piston 71, damping occurring through grooves 73 and/or ports 74. On extension additional damping occurs due to flow from the space 85 into an annular space 87 through pssages 88 which are otherwise byepassed by ports 77 controlled by a valve 78.