Patent GB-645496-A (GB)
Title: Pneumatic spring
IPC: F16F9/084
Filed: 1947-10-15
Abstract: 645,496. Pneumatic springs. ANDREWS, E. S. (Coleman, S. L. C.). Oct. 15, 1947, No. 27658. [Class 108(iii)] A pneumatic spring comprises a pneumatic bellows in communication with a reservoir through valves which allow the passage of air from the bellows to the reservoir during compression of the bellows and through valves which allow passage of air from the reservoir to the bellows during expansion of the bellows and in which when the bellows expand after compression, these latter valves are kept closed by locking means carried by the bellows to trap air within the reservoir, until the bellows have expanded a predetermined distance. In the arrangement shown. a pneumatic spring comprises two flexible bags 68 and 69 which surround outer and inner tubes 1 and 2 of a hydraulic shock absorber. A piston tube 46 which is carried non-rigidly by a plate 3 screwed into the upper end of tube 1, projects into tube 2, and carries a piston 44. The piston tube 46 is provided with spaced ports A-K. A spherical ended member 6 by which the spring may be secured to the spring mass is supported by a bearing block 4, and a ring 11 secured by a locking device 13. The lower end of tube 2 is closed by a screwed plug 19 and is secured by means of a screwed stud 24 to a base member 23, which may comprise the central portion of the equalizing bar described in Specification 520,002. The stud 24 carries a small diameter tube 29. The tube 29 communicates at its lower end with a duct in a plug 30 screwed into the bottom of stud 24 whereby fluid, such as dewaxed oil, may be pumped into the tubes 1, 2. A cylindrical member 32 is screwed into the upper end of tube 2 and carries a piston ring 33a which is located in a square-section circumferential groove 33b and which bears against the bore of tube 1. A circumferential groove 34 formed round the piston ring 33a is provided with radial ports 35 whereby oil scraped from the inside of tube 1 by the piston ring may be returned through ports 36 in the member 32 to the tube 2. The bottom of member 32 is provided with a circular spring-loaded plate valve 38 adapted to open on the compression stroke of the shock absorber. A tubular reinforcement member 41 is screwed on to the lower end of tube 1 and is spaced from the tube 2 by a tube of anti-friction metal 42. The member 41 is held against rotation by set screws 43. A port 84 near the top of tube 1 leads into a metal box 85, secured to the tube 1, having ports 86 near its top and provided with a perforated partition 87, the space above the partition being filled with metal wool. A tube 88 surrounds the tubular member 41 and is provided with a flange which slidably engages tube 2. An inner tube 89 is secured to the top of tube 88 and slidably engages tube 1. A circular wall 49 in the hollow base member 23 is provided with inlet ports 52 and 64 controlled by spring-loaded valves 54, 65 and outlet ports 57 and 66 controlled by flap valves 58 and 67 respectively. The inlet and outlet ports communicate with air reservoirs 51, 51a on opposite sides of the shock absorber. The flexible fabric bags 68 and 69 which are impregnated with rubber or the like, are clamped together by means of plates 74, 75. The top of the bag 68 is clamped between a plate 78 and flange 77 integral with a flanged member 16 welded to the top of tube 1. The bottom of bag 69 is clamped to the top of the base member 23 by means of a plate 80. The plates 74, 75, 78 and 80 each comprise equal half sections to facilitate assembly to the bags 68 and 69 and are flared to permit flexure of the bags, to which air is admitted through a valve 83. In operation, compression of the spring forces air into the reservoirs 51 and 51a through the ports 52 and 64 and causes tube 88 to wedge the flap valves 57 and 58 tightly shut due to the telescoping action of tubes 1 and 2. Air pressure within the flexible bags and the tube 1 is equalized by the port 84. The metal wool in the box 85 prevents oil being carried over by the air flow. In rebound, the flow of air from the reservoirs 51 and 51a to the bags 68 and 69 is prevented by the closure of valves 54 and 65 until the tubes 1 and 2 extend far enough for the tube 41 to retract the tube 88 and release the flap valves 58 and 67. In addition, rebound is progressively damped by the flow of fluid from below to above the bottom of the cylindrical member 32 via the tube 46 and the ports A-K. The area of ports A-K may be varied to suit requirements. Also, the rubber bags, which may comprise more than two in number, may be made integral or they may be vulcanized together. They may also be cemented together and to the top and bottom of the shock absorber. The insides of the bags are preferably coated with Neoprene or the like to resist the action of oil. Gas other than air may be used and any suitable liquid may be substituted for oil. The spring may be used in combination with other springs. A multiplicity of springs may be employed where the sprung loads are heavy.