Patent GB-629970-A (GB)
Title: Improvements in or relating to aircraft and like shock-absorbers
IPC: B64C25/60
Filed: 1947-06-12
Abstract: 629,970. Hydro-pneumatic shock absorbers. BRITISH MESSIER, Ltd., and ORLOFF, G. June 12, 1947, No. 15567. [Class 108 (iii)] In a hydraulic piston-andcylinder-type shock absorber in which liquid is compressed by a piston connected to the load, in a compression chamber, and in which the load is sustained by pressure in pressure chambers which receive liquid by restricted passages from the compression chamber during movement under load, the pressure chambers are in free communication with the compression chamber in recoil, and a recoil chamber is provided containing a piston member connected to the load so as to contract the chamber on recoil, the recoil chamber being in communication with the compression chamber to receive liquid freely therefrom but having a restricted return passage thereto. An upper cylinder 12 carries a piston 13 slidable in a lower cylinder 11, a liquid compression chamber 24 being formed between the piston 13 and a fixed diaphragm 15. An air pressure chamber 21 formed by the upper part of the cylinder 12 is in communication with the compression chamber 24 by a passage formed by a hollow pistonrod 17 which is rigid with the diaphragm 15 and carries a piston 18 slidable in the cylinder 12. The space 34 between the pistons 13, 18 constitutes the recoil chamber and communicates with the compression chamber 24 through restricted apertures 41 provided between the piston 13 and the piston-rod 17. The recoil chamber 34 is connected with the pressure chamber 21 by ports 36 controlled by a valve 35 which permits flow into the chamber 34 but prevents flow therefrom. Flow into the chamber 21 is baffled by a deflector plate 19 formed with apertures 20. Flow from the piston-rod 17 to the compression chamber 24 takes place through ports 23, some of which are controlled by valves 25 which permit flow from the hollow piston-rod to the chamber 24 but restrict flow in the opposite direction. A second air pressure chamber 26 is constituted by the lowermost part of the cylinder 11 beneath a floating piston 27. The piston 27 is acted on by fluid from the chamber 24 which is admitted through the diaphragm by a spring-loaded ball valve 31. Liquid may pass freely back through the diaphragm 15 by means of a ball valve 32. Under normal conditions the pressure in the chamber 21 is lower than that in chamber 26 but the compression ratio of chamber 21 is higher than that of chamber 26. Pressure in chambers 21, 26 may be replenished by inflation valves 33, 28. Alternatively, a single inflation valve 28 may be provided and the chambers 26, 21 are connected by a pipe which embodies a reducing valve 40, so that the pressure in chamber 21 is a predetermined amount lower than that in chamber 26. A series of flutes 37 in the piston-rod 17 have the effect of increasing the effective area of the apertures 41 about the central portion of the travel of the shock absorber. Each ball-valve 31, 32 may be replaced by two or more ball-valves of different sizes or operating at different pressures. Also the ball-valves may be replaced by restricted passages. The air pressure in the pressure chambers 21, 26 may be replaced by spring pressure, or by a fluid other than air. Moreover, the pressure in the chamber 26 may be equal to, instead of greater than, that of chamber 21. In operation, on compression, liquid passes from the chamber 24 with limited damping due to the valves 25, to the chambers 21 and 34. At a predetermined pressure in the chamber 21 the valve 31 opens and air is further compressed in chamber 26. On rebound, liquid passes freely from both chambers 21, 26 to the pressure chamber 24. Liquid in the recoil chamber, however, is forced with damping action through the apertures 41. The invention may also be applied to a tension shock absorber.