Patent GB-1189149-A (GB)
Title: Improvements in and relating to Buffers and Draw Gear for Rail Vehicles
Inventor: THORNHILL PETER WARBORN
IPC: B61G11/12
Filed: 1967-08-08
Abstract: 1,189,149. Buffers and draw gear shock absorbers. OLEO INTERNATIONAL HOLDINGS Ltd. 16 July, 1968 [8 Aug., 1967], No. 36376/67. Heading B7T. An hydraulic buffer or draw gear shock absorber for rail vehicles comprises a cylinder 12, a plunger 10, a compression chamber 33 and a reservoir chamber 23, resilient means to provide a recoil force, and flow restricting means to control the flow of fluid from the compression chamber 33 to the reservoir chamber 23, comprising a first member 26 co-operating with a second profiled member 32 and with a seat during slow movement of the plunger relative to the cylinder to prevent liquid flow, the first member, during rapid movement of the plunger, moving out of co-operation with the seat and into co-operation with the profiled member 32 to provide an increasing liquid flow resistance as the plunger moves inwardly of the cylinder. The resilient means comprises an air filled chamber 22 separated from the reservoir chamber 23 by a piston 21. The cylindrical tubular member 26 is slidable in the end wall 24 of the plunger, its movement being limited by flanges 28 and 35. During slow compression, fluid is displaced from the compression chamber 33 to the reservoir chamber 23 through the space between the mouth of the member 26 and the tapered pin 32, until the lip 34 of the member 26 seats against the end wall 13 of the cylinder, preventing any further liquid flow. Further compression forces the flange 28 of member 26 away from the end wall 24 of the plunger producing a partial vacuum between the end wall 24 the member 26 and the guide tube 27. During rapid compression, the restricted liquid flow is insufficient to equalize the pressures in the two fluid chambers, and the pressure in chamber 33 acting on the sleeve member 26 forces it into the position shown in Fig. 3, the flange 35 engaging the recess 36, the liquid trapped between the two acting to cushion the final movement. As the plunger moves to the right an increasing flow resistance will be encountered due to the tapering of the pin 32. At the termination of the inward stroke of the plunger, the pressure drop in chamber 33 causes the lip 34 of member 26 to engage its seat on the end wall 13 preventing return flow of the liquid by this path. The return flow thus takes place through a passage or passages 37 having non-return valves 38. A passage 39 and non-return valve 41 provide an escape passage for any liquid which may leak into the space between the sleeve 26 and tube 27. A leak passage for the flow of liquid from the chamber 33 to the chamber 23 during slow compression may be provided in the rim 34. In a modification (Fig. 5), movement of the sleeve 25a into the tube 27a is limited by an internal flange 43 on the end of the tube 27a, cushioning being provided by liquid trapped between the flange 43 and flange 28a by the extension 44. The other end of the sleeve 26a has an internal flange 45 co-operating with the pin 32a which has a reduced neck 46 to provide sufficient orifice area during initial slow inward movement. The end of the sleeve 26a cooperates with a cylindrical rim 47 on a disc 48, the impact being cushioned by a number of spring washers 51. Steel or rubber springs may be used instead of the compressed air spring 22.