Patent GB-617439-A (GB)
Title: Improvements in or relating to hydraulic shock-absorbers
IPC: F16F9/26
Filed: 1946-09-18
Abstract: 617,439. Hydraulic shock absorbers. HARDY, F. J., and BASTOW, G. Sept. 18, 1946, No. 28035. [Class 108(iii)] The invention relates to a shock-absorber of the kind comprising a cylinder divided into two compression chambers 17, 18 by a piston 11, movement of which from a normal position, transfers liquid between the chambers 17, 18 in one direction or the other under the control of spring-loaded valve means, the spring loading being varied by relative displacements of the parts between which the shock-absorber is connected, in such a manner that movement of the piston away from the normal positions is undamped or slightly damped, while return movement of the piston to the normal position is damped. According to the invention the shock-absorber comprises a valve-box forming part of the cylinder and having a pair of valve chambers 19, 20, each communicating with the respective compression chambers 17, 18, spring- controlled valves in the valve chambers respectively permitting transfer of liquid between the compression chambers in respective directions, a control shaft mounted on the cylinder carrying a pair of cams, each in engagement with respective reaction abutments of each valve spring, and a linkage between the piston and the control shaft, the arrangement being such that displacements of the piston away from the normal position rock the control shaft to load that valve which will control liquid transfer on the return movement, by an amount dependent on the displacement of the piston, the other valve remaining unloaded. A piston 11 operable by a bell-crank 14, 15 divides the cylinder into the two chambers 17, 18. The valve chamber 20 communicates with the chamber 17 through a passage 26 and a port 25 (Fig. 4) controlled by a valve 22b loaded by a coiled spring 30. The second valve chamber 19 communicates with the chamber 18 through a port controlled by a valve 22a (Fig. 3, not shown), similarly spring-loaded. The chamber 19 is connected directly with the cylinder chamber 17 by a passage 27 leading into the passage 26, and the chamber 20 is connected directly with the cylinder chamber 18 by a passage 28. An abutment 29 of the spring 30 has a stem 31 which is engaged by a cam 32b carried by a shaft 33 which is rotated under movement of the arm 15 by a ball-jointed link 35. A second cam 32a on the shaft 33 engages an abutment stem of the spring which loads the valve 22a controlling the port of the chamber 19. The cams 32a, 32b are arranged so that on rotation in either direction of the shaft 33 from its position corresponding to the normal position of the cam 15, the loading one of the two valve springs is increased, whilst the compression of the abutment stem corresponding to the other is released, and vice versa. The loading of both springs may be zero in the normal position of the arm 15, or the cams may be arranged so that each spring has a small initial loading which on movement of the arm 15 decreases to zero in the case of the valve spring which does not have its loading increased. Alternatively, each valve spring may have a small initial loading developed by a washer placed between the spring and its abutment and is thus independent of the camsetting and causes a small fixed amount of damping on movement from the normal position. Each valve may be provided with a small leak to modify its damping action. Rotation of the shaft 33 under change in vehicle loading is avoided by means of dashpot connection, Fig. 10, between each end 54, 55 of the link 35. The end 54 is secured to a plate 52 carrying a spiral strip 50 of thin metal, which is interleaved with a second spiral 51 similarly secured to the end 55. A housing 56 secured to the end 55 and slidable relative to the end 54 is filled with a suitable synthetic grease which may be a silicone. The strips 50, 51 may be interleaved by wrapping them round with an interleaving strip of paper or other material which is subsequently burnt or dissolved. In an alternative construction of dashpot (Fig. 9, not shown), one of the ends of the link 35 is secured to a diaphragm which has a damping orifice and on either side of which is mounted a flexible bellows. The other end of each bellows is closed by an end plate. The other end of the link 35 passes through a bearing in the diaphragm and is secured to the two end plates. Each bellows, which is connected by the damping orifice, is filled with a light mineral oil.