Patent GB-211563-A (GB)
Title: Improvements in or relating to the damping of the reaction movements of running vehicles or the like
IPC: F16F9/48
Filed: 1922-11-20
Abstract: 211,563. Hofmann, J. Nov. 20, 1922. Vibration-dampers.-Shock absorbers of the type wherein the return movements only of the axle are damped are constructed so that the damping action or braking resistance to said return movements is the greater the larger the amplitude of the movement from the normal position, but is prevented from being excessive when such movement takes place at a high speed. In one form of shock absorber, the initial movement of the axle allows a cam 5, Fig. 1, to move freely in a clockwise or anticlockwise direction according as the axle rises or falls. A piston 8 divided into two chambers A, B by a partition 11 is forced up to follow the cam by a spring 15 allowing the liquid to flow from B to A through posts 12 which are uncovered by a valve 13 the opening movement of which is resisted by a weak spring 14. On the return movement of the cam the ports 12 are closed and no passage of liquid is permitted until the pressure in A overcomes the spring 20, forcing disc 19 to rise and carry with it sleeve 16, which movement uncovers apertures 23 and allows the liquid to pass from A to B. The effective leverage of the cam is greatest at its maximum deflection and decreases as it returns to its mean position. In a modification, Fig. 4, two cylinders and pistons are similar to that shown in Fig. 1, but have in addition axial grooves 34, annular groove 32, and apertures 33. Assuming that the cam lever 5 moves clockwise, the left-hand piston moves freely as liquid passes from A to B through the axial and annular grooves and apertures 33, while the right-hand piston follows the lever in the same manner as the piston in Fig. 1. On the return movement, the left-hand piston is free to follow the cam owing to the fact that ports 12 are uncovered, but the right-hand piston, in view of the fact that the axial and annular grooves are not now in communication. resists the return of the cam with a damping resistance and does not move until the pressure in A is sufficient to overcome the spring 20, as in Fig. 1. In a further modification, a fluid-containing hollow casing 45, Figs. 6 and 7, is mounted to oscillate on a pin 44 secured to the frame of the vehicle. A valve member 53 is loosely carried between springs 52 by the casing. Within the casing and held against rotation is a stationary port member having a hollow depending portion 58 dividing the casing into two chambers A, B. On movement of the hollow casing, say anticlockwise, the liquid passes unhindered from A through port 59 and space f, and into B through ports 62. On return, ports 62 are closed by the valve 64, and since port 60 is closed by valve 53 due to the displacement of the axle the pressure in B must rise sufficiently to force valve 53 from the port 60 against the springs 52. Instead of using coil springs a leaf spring may be used. In a shock absorber employing friction mechanism for the damping action, a plate 122, Fig. 10, is secured to the axle and an outer case 137, 141 to the vehicle chassis. The plate 122 is provided with a central boss in which, by means of grooves 124, slides a nut 130 which engages with a helical slot 133 on a central screw secured to the outer casing. Opposed springs 134, 135 are provided as shown. Friction washers 145, 146 carrying plates 147, 148 having ratchet teeth with which engage pawls 128 are interposed between the plate 122 and the outer casing. Assuming that under shock the axle approaches the chassis, the nut 130 moves to the right, compresing spring 135 and relieving spring 134. Friction washer 146 will be carried round freely by the pawls while casing 137 is pressed against friction washer 145, which, however, does not rotate relatively to the casing since the pawls ride over the teeth on plate 147. On return movement, the friction washer 145 is rotated by the pawl in frictional engagement with the casing, so introducing damping action while the friction washer 146 remains stationary. As the shock absorber approaches normal position, the movement of the nut 130 relieves the pressure of the spring 135 until the springs balance at the normal position.