Patent GB-655136-A (GB)
Title: Improvements in hydraulic shock absorbers
IPC: F16F9/50
Filed: 1948-08-19
Abstract: 655,136. Hydraulic shock - absorbers. KATZ, M. Aug. 19, 1948, No. 21912. Convention date, Oct. 22, 1947. [Class 108(iii)] The piston of a shock absorber forces liquid from one side of the piston to the other through a duct (two ducts in the case of a double-acting shock absorber, corresponding to each direction of movement), which opens into a cavity formed in an extremity of the piston, by way of an orifice controlled by a slide valve having one or more lateral apertures and axially movable in the cavity against a spring, the slide valve being set on displacement of the piston by the varying force exerted on it by a suitable resistance acting in opposition to the spring so that the orifice is controlled during the return stroke the degree of opening thereof being automatically adjusted by the relative speed of the piston. In the construction shown in Fig. 2, slide valves 25, 34 in respective piston cavities 24, 33 are outwardly urged by springs 27, 36 into a position defined by an annular abutment 26 on the valves and a corresponding annular abutment 2a rigid with the piston body 2. Each valve has one or more orifices 31. Each cavity 24, 33 is connected to the cylinder space at the opposite end of the piston by a respective duct 32, 41. A concentrically disposed displacement chamber (not shown), is connected with the respective cylinder spaces 18, 19 above and below the piston by spring-loaded flap valves. The upper valve is opened against the action of its spring by frictional contact with the piston rod on downward movement thereof. In operation, on compression from a normally inoperative central position of the piston, pressure developed in the space 19 inwardly deflects the valve 25 as shown, and liquid passes freely to the space 18, through the duct 41 and a spring- loaded valve 39. On the return stroke the valve 39 closes and the valve 25 is maintained in its inward position due to pressure of liquid in the space 18 acting through the duct 32 and upon the abutment 26. Flow between the spaces 18, 19 takes place through the duct 32, the orifice or orifices 31. and a spring-loaded ball valve 30. The valve 34 operates in a similar manner in respect of initial upward deflection from, and downward return to, the inoperative position. The piston and valve 34, however, are provided with parts 2a, 34a which define a liquid chamber 42 connected with the space 18 by a capillary orifice 43. The damping action of the orifice 43 prevents a return of the valve 34 on equalization of pressures in the spaces 18, 19 at the deadcentre position of the piston prior to its downward return to the central position. The orifices 31 and the valves 30, 39 may be arranged so as to provide a greater resistance on the outward than the return movement. Also only one instead of two slide valves may be provided. In a similar construction shown in Fig. 3, the lower slide valve 58 is formed with a reduced-diameter end-portion 59 which is engaged by balls 60 located in recesses 61 in the piston body in order to lock the valve 58 at the deadcentre position of the piston. The balls are driven into operative position by the action of a ring 62 composed of resilient laminations. The upper slide valve 51 has a collar 52, and the piston rod 47 a collar 48. Disposed between these collars in the inoperative position of the shock absorber, and frictionally slidable on the cylinder wall, is an extensible ring 49 (preferably a circular split wire ring). An annular groove 50 is provided in the cylinder wall. In operation, on downward piston movement from the inoperative position the slide valve 58 is driven inwardly from the position shown on the right, to that shown on the left of Fig. 3, and is held in position by the action of the balls 60. During this movement the collar 48 engages the ring 49 and drives it into the groove 50 and is then able to pass through the ring. On the commencement of the return movement the ring 62 allows the balls 60 to release the valve 58 but the latter is held in the damping position by pressure acting through the duct 32. On this movement the valve 51 is inwardly deflected by engagement of its flange 52 with the ring 49. A ring 49 may be provided for each end of the piston and may be so arranged that there is a neutral zone of piston travel for which the shock absorber is ineffective. The locking ring 62 may be displaced by liquid pressure instead of frictional action and may also be employed at each end of the piston. In the construction shown in Fig. 4, slide valves 72, 73 are outwardly urged by springs 72a, 73a to the end of corresponding cavities in the piston. On displacement from an inoperative central position the valve corresponding to the decreasing cylinder space is driven inwards by a respective spring 75 so as to control on the return stroke, the flow through a duct 76 through the piston.