Patent GB-691307-A (GB)
Title: Improvements in and relating to cushioning devices such as shock absorbers
IPC: F16F9/44
Filed: 1949-11-02
Abstract: 691,307. Hydraulic shock absorbers. CLOUDSLEY, J. L. Feb. 2, 1951 [Nov. 2, 1949; Nov. 15, 1949; Nov. 22, 1949], Nos. 28108/49, 29269/49 and 29887/49. Class 108 (iii). The natural rate of re-assertion of a spring to normal after compression or extension, is altered in a predesired manner by control of the rate of leakage of fluid through a dash-pot piston 15 movable in a dashpot 11 into which the fluid, when under pressure, enters by a passage 23 through the piston 15, and from which it escapes through a second passage 25, the flow capacities of the passages 23, 25 being varied in relation to one another. As shown, the dashpot 11 is mounted within the piston body 1 of a telescopic shock-absorber connected between the two ends of the spring, which may be a doorclosing spring, or a vehicle-suspension spring. The dashpot 11 and piston body 1 are secured in locked relation on the threaded end 7 of the shock-absorber piston-rod 3. A sleeve 17 having a flange 22, is slidably mounted in the end-face 29 of the piston body 1 and is inwardly urged by spring discs 32, 33, 34. A valve seat 21 on the flange 22, engages the under face of the dash-pot piston 15. The flange 24a of a bush 24 entered in the mouth of the passage 23 has the same depth as that of the valve seat 21. A stem 16 of the piston 15 is slidable at 19 in the bush 17, and is formed with openings 20. Inward movement of the piston 15 is limited by a boss 26 which engages the end face 11a of the dashpot, and defines an annular space 26<1> between the upper surface of the piston 15 and the face 11a. The passage 25 may be obturated by a metering pin of either uniform or axiallyvariable cross-section and which may also act as an oil filter. The pin may be threaded in the lower end of the piston-rod, Fig. 3 (not shown), and formed with a screw-driver adjustment slot at its lower end. Alternatively the metering pin may extend through the greater part of an axial bore formed in the piston-rod. The upper end of the rod is then in threaded engagement with the bore and is adjustable from the outside of the shockabsorber by the insertion of a screw-driver into the piston-rod bore. The metering-pin bore opens out into the attachment eye of the shock-absorber and the eye is formed with an aperture at a point diametrically opposite the bore to facilitate insertion of the screw-driver. The metering rod may extend wholly through the passage 25 or only into its upper end. In the latter arrangement, Fig. 4 (not shown), the passage 25 is no longer obturated by the metering rod after a predetermined degree of downward movement of the piston 15 in its dashpot. The metering pin may be a close fit in the piston-rod bore and a column of liquid may be disposed between the upper end of the rod and a plug threaded into the upper end of the bore. Rotation of the plug acting on the liquid brings about axial adjustment of the metering-rod. Instead of being adjusted by a screw-driver, the metering rod may be remotely controlled, e.g. by the driver of a vehicle by the action of a flexible shaft. In another construction, Fig. 5 (not shown), the passage 25 extends between the boss 26 and a large diameter bore formed horizontally in the waist 18 of the piston extension 19. A metering rod is disposed loosely in the passage and its lower end rests on the lower surface of the horizontal bore. In a further construction, Fig. 6 (not shown), the metering rod extends upwardly from, and is rigid with, the base of the shock-absorber main pressure cylinder. In another arrangement in which no metering-rod is used, the passage 25 is disposed as shown dotted at 25a in Fig. 2. Operation.-On downward movement of the piston (compression), liquid lifts the disc 32 and flows freely up through the piston. On upward movement (rebound), pressure developed in the space 121 within the main piston 1 acts on the disc 32 to close the ports 30. Pressure in the space 12<1>, in compressing the discs 33, 34 together and acting on the flange 22, causes depression of the sleeve 17 and thus permits restricted flow through the piston via the valve seat 22 and passages 20. Liquid is also able to pass upwardly through the passage 23 and acts upon the upper face of the piston 15 thus causing the piston 15 to move downwardly. The upper end of passage 25 then becomes open to the space 26<1> above the piston 15. Since the effective cross-section of the passage 25 is smaller than that of the passage 23, the piston 15 continues its downward travel until the flange 24a re-approaches the flange 25, thereby reducing the effective cross-section of the passage 23. In a modified construction in which the piston is double-acting, the depth of the flange 24<1> is made less than that of the valve seat 21 so that the passage 23 is not entirely closed in the static condition of the shock-absorber. The spring disc 32 is then arranged to provide a suitable degree of resistance to upward flow of liquid through the ports 30. The invention may also be applied to the base valve assembly of a piston and cylinder shock-absorber of the type having an outer concentric, or otherwise disposed, liquid reservoir, e.g. the base valve assembly described in Specification 670.567. Specifications 526,945 and 664,491 also are referred to. According to the first Provisional Specification the spring, the rate of which is to be controlled, may be a pneumatic spring, and the invention may thus be applied to oleopneumatic shock-absorbers.