Patent GB-691544-A (GB)
Title: Shock absorbers
IPC: F16F9/18
Filed: 1950-11-02
Abstract: 691,544. Hydraulic shock - absorbers. McINTYRE, W. D., McINTYRE, B. D., and McINTYRE, C. S., [trading as PATENT DEVELOPMENT CO.]. Nov. 2, 1950 [Jan. 5, 1950; Aug. 21, 1950], No. 26776/50. Class 108 (iii). In an hydraulic shock-absorber of the kind comprising a pressure cylinder (21) connected by a base-valve assembly (45) to a reservoir (19), a piston-rod (17) extending through the end of the cylinder remote from the base-valve end and passage means extending between the base-valve and piston-rod ends of the cylinder, on the (inward) compression stroke of the pistonrod at high piston speeds, a substantial proportion of the total resistance to movement of the piston 51 is provided by the restriction to liquid flow provided by the passage means, also the base valve assembly 45 provides resistance to the flow of liquid which is greater than that provided by the passage means for all piston operating speeds. In the construction shown, the passage means is in the form of circumferentially-spaced recesses 109 in the piston 51. A rubber rim 113 is held in closing relation with the upper end of the recesses 109 by an apertured spring disc 119. On compression movement of the piston-rod, resistance to liquid flow is initially provided by the rim 113, the flow restriction through the recesses 109 being negligible. At higher piston speeds, however, the resistance is mainly provided by this flow restriction. The piston has a conventional laminated disc valve 79 controlling flow (on the rebound stroke) through only two ports 61. The ports 61 offer no restriction to flow at low piston speeds but their effect outweighs that of the valve 79 at high piston speeds. The base valve assembly 45 comprises a conventional replenishing valve 101 controlling flow from the reservoir 19 to the pressure cylinder through ports 89. Flow in the reverse direction on the compression stroke is provided by a single port 91 and a laminated disc valve 75. The valve 75 provides resistance to flow at low piston speeds while the restriction to flow through the passage 91 provides the major control at high piston speeds. The diameter and length of the passage 91 is so related to the cross-sectional area and length of the recesses 109 and the viscosity of the liquid, as to ensure that the ratio of the respective volumes dealt with by the recesses 109 and the passage 91, is equal to the ratio of the area of the cylinder 21 minus the area of the piston to the area of the piston. In a modified construction, Figs. 9 to 11 (not shown), a plurality of passages 91 is provided so that compression flow through the base-valve assembly 45 is controlled solely by the valve 97. In a further modification, Figs. 1 to 4 (not shown), the rubber rim 113 and recesses 109 are replaced by a conventional disc-valve and starshaped loading spring (like the valve 101 of Fig. 5) which controls flow through a circumferentially-spaced set of passages extending axially through the piston. The passages provide a restriction to liquid flow at high piston speeds. Diagrams showing resistance to piston-rod movement at various piston speeds are given. The Specification also includes a table setting forth suitable piston-passage dimensions for shock-absorbers of different respective pressure-cylinder diameters. As a general rule, when using a liquid of 85 to 90 Saybolt seconds viscosity at 100‹ F., the total area of the piston-passage means should be between 0.4 and 5.0 per cent of the difference of the cross-sectional area of the pressure cylinder and piston-rod, when the length of the passage means is <3>/16 inch. Specification 676,521 is referred to.