Patent GB-670044-A (GB)
Title: Improvements in pneumatic suspension devices for vehicles
IPC: B60G17/044
Filed: 1949-06-28
Abstract: 670,044. Pneumatic shock absorbers. CLERK, R. C. Sept. 27, 1950 [June 28, 1949], No. 17118/49. Class 108(iii) In a pneumatic suspension device adapted to support a vehicle frame from an axle and of the kind comprising a piston co-operating with a cylinder to compress an enclosed mass of air or other gas which is contained within two compression chambers, communicating with each other by a passage controlled by a valve, one of the chambers being bounded at least in part by the piston and the cylinder so that its volume varies with rise and fall of the axle relative to the vehicle frame, the valve is so arranged as to be progressively closed in response to to relative displacement of the piston and cylinder corresponding to displacement of the axle under load beyond a predetermined limit. In one embodiment, Figs. 1A and 1B, in which a piston 16 and piston-rod 13 are slidable in the lower end of a tube 10, the upper part of the tube 10 houses a tubular reservoir casting 20 which is closed at its lower end by a disc 24 and includes a hydraulic damper cylinder 23. The pistonrod 13 which extends through the disc 24 and cylinder 23 into a shield 29 above the damper cylinder and carries a damper piston 26, is provided, above the piston 16, with a bore 32 which communicates with an air chamber 7 between the piston 16 and disc 24 and a chamber 9 within the casting 20. The chamber 9 is filled with liquid to a level above the damper cylinder 23. A top closure plug 33 carries a needle valve 34, the lower end of which is tapered and is adapted to enter the bore 32 in the piston-rod when the latter rises above a predetermined limit. A damper valve assembly comprises a tubular valve body 36 lying parallel to the damper cylinder 23 and is retained in a web 37 in the casting 20. The valve body communicates at its upper end, through a series of ports 40, with the damper cylinder and at its upper end, through a series of ports 43, an annular groove 44 and a lateral port (not shown) in the web 37, with the chamber 9. A spring-loaded and apertured piston 41 having a non-return ball valve 45 therein is adapted when depressed, successively to uncover the ports 43. An apertured partition 36<SP>1</SP> in the valve body is normally closed by a spring-loaded ball valve 38. The space above the valve piston communicates by a duct 46 with the top of the damper cylinder and the space below the valve piston communicates through ports 47 with the groove 44. The space below the piston 16 may act as a pneumatic rebound damper by the provision in a lower end-plug of valved inlet and outlet ducts 49 and 50 respectively. Fluid pressure is established in the chambers 7 and 9 such as to balance the static load in the device when the pistons are nearer to the lower limit of the stroke. In operation, resistance to flow of air through the duct 32 for moderate amplitudes of piston displacement, is relatively small. For relatively high amplitudes, transfer of air through the duct 32, on contraction of the device, is throttled by the valve 34 and in the limit is substantially interrupted. Normal relative inward displacements of the piston and cylinder are damped by the damper piston 26, excess of liquid in the upper end of the cylinder 23 depressing the piston 41 and escaping to the chamber 9. On the return stroke, liquid is returned to the upper end of the cylinder 23 through the non-return valve 45. For abnormal displacements, liquid is supplied to the lower end of cylinder 23 directly from the chamber 9, through valve 38. In another embodiment, Fig. 2, in which the lower part of the device is identical with that of Fig. 1A, the piston-rod 13A extends through the closed inner end of a reservoir casting 20A and carries a slideably-mounted and spring- loaded mass 56. The mass 56 comprises a cylinder 63, having ports 69, 70. for a damper piston 60 mounted on the rod 13A against a compression spring 58. A tapered needle 34A co-operates with the bore 32 in the rod 13A and in operation for relatively slow but large amplitudes of piston displacement inwardly of the tube 10, the mass 56 is forced downwardly of the rod 13 to close the bore 32, the piston 60 in the limit, overrunning the port 69. For relatively rapid but small amplitude displacements, the needle 34A restricts only partially the bore 32 and the space below the piston 63 and the port 70 co-operate to damp out periodic oscillations of mass 56.