Patent GB-1344477-A (GB)
Title: Shock absorbers
IPC: F16F9/48
Filed: 1971-04-19
Abstract: 1344477 Hydropneumatic buffers ALFRED TEVES GmbH 19 April 1971 [4 March 1970] 20176/71 Heading F2S A shock absorber, e.g. for use between a railway vehicle body and a bumper-baulk carrying the buffers and couplers, comprises a cylinder 1 in which a piston 3 defines one end of a variable chamber 13 and is normally biased to rest at an end of its path as shown (due to the pressure of gas in a piston-rod chamber 11 transmitted by liquid in the chamber 13); during an inward (shock-absorbing) stroke of the piston 3 and its rod 2, flow of liquid from the chamber 13 is regulated (by holes 4, Fig. 1, or 20<SP>1</SP>, Fig. 2, in a metering tube 5 or 18 over which passes the annular piston 3) and at the beginning of the return stroke a valve 7 or 19 responsive to the liquid pressure augments the relative cylinder and piston movement (by opening to increase the return flow to the chamber 13 from a chamber 12 in the piston-rod 2 and defined in part by a free piston 10, and from an annular chamber 15 around the rod) while during the rest of the return stroke the flow regulation retards the movement. In Fig. 1, the apertures vary in size. During the shock-absorbing stroke, a valve 9 opens to the chamber 12, because of the liquid pressure in the tube 5, and liquid flows into the chamber 12 then through holes 14 into the chamber 15. With the gas pressure in piston-rod chamber 11  initiating the return stroke, the liquid from chambers 12 and 15 flows into the tube 5 through the holes 4, the valve 9 now being closed but the valve 7 opened by the pressure, to boost the return stroke at the beginning, before it is retarded and then finally softened by flow through the holes 14 from the chamber 15 and leakage around the tube 5. In Fig. 2, a tube 19 inside the tube 18 is normally biased by a spring 26 to rest against an end closure 18<SP>1</SP> of the outer tube, but, as shown, can be slid to rest against an end closure 6 of the cylinder 1, when urged by the liquid pressure built up in the tube 19 by a shock-absorbing stroke and a return stroke commences. The tubes 18, 19 not only each have two opposite rows of holes 20<SP>1</SP>, 21 and 20, 21<SP>1</SP> (the rows at one or other side of the tubes, e.g. 21 and 21<SP>1</SP>, coinciding according to the axial position of the inner tube 19) but also a ring of apertures 22, 23 and 22<SP>1</SP>, 23<SP>1</SP> at each end, the corresponding rings of the two tubes also coinciding or not according to the axial position of the tube 19. These rings of apertures constitute valves. In the position shown, the piston 3 has completed a return stroke (from adjacent the cap 6) during which the apertures 22, 22<SP>1</SP> have been in the open position indicated to accelerate the return, particularly as it began. The tube 19 is about to close the gap s to open the apertures 23, 23<SP>1</SP> ready to facilitate a shock-absorbing stroke and also to open the bottom rows of holes 20 and 20<SP>1</SP> whose size, number and spacing determine the characteristics of that stroke; the holes 21, 211, designed by the same features of the return stroke, are closed in this position of the tube 19. The hole arrangement is such that the shock absorber cannot be blocked by closure of all the holes at once. A thermostat in the tubes 18, 19 may control a by-pass between chambers 12 and 13 to compensate for viscosity change. The shock-absorbing force may be constant throughout or it may rise initially.