Patent GB-558985-A (GB)
Title: Improvements in or relating to shock absorbers
IPC: F16F9/06
Filed: 1942-05-11
Abstract: 558,985. Shock-absorbers. RIBBESFORD, CO., Ltd., and THORNHILL, P. W. May 11, 1942, No. 6354. [Class 108 (iii)] A shock-absorber, particularly for vehicle wheel suspensions, in which increased damping is obtained when the movement of the parts exceeds a predetermined value, compresses telescopic members 10 and 13, 18 Fig. 2, defining a liquid-filled working space 43 of variable volume containing damping means, resilient means such as compressed air in spaces 39, 41 for supporting a normal load on the device, and an auxiliary working space 44 which decreases in volume as the end of the recoil or extension stroke is approached, the liquid then ejected from the space 44 being forced into another closed working space 42 against the pressure created by the resilient means in the space 41. In the device shown in normal position in Fig. 2, the hollow plunger 18 is fitted with a head 19 having radial passages 21 and a central bore 20 with the upper part 20a of which spring- separated, saucer-shaped, damping valve-members 22, 23, independently slidable on an axial rod 24, are adapted to co-operate. At its upper end the rod 24 carries a control piston 30 freely slidable in the plunger tube 18 and containing a packing-ring 31 which can allow slight leakage of air between the spaces 39, 41. A spring-pressed, annular valve-member 32 slidable in the operating cylinder 10 and of greater internal diameter than the plunger 18 normally engages a circumferential series of stops 35 formed by bulges in the cylinder 10, the spaces between the stops permitting the passage of guides 36 on the plunger head 19. In operation, slight shocks cause continual surging of liquid between the spaces 42, 43 and tend to maintain the valve-members 22, 23 respectively just above and below the upper part 20a of the bore 20. On compression of the shock-abosrber, the liquid in the space 43 forces the valve-member 23 to a position above the bore 20a and the liquid flows freely into the space 42 increasing the compression of the air in the space 41. In consequence, the piston 30 is moved upwardly and in the final position of the parts, the valve-member 23 blocks the bore 20a thus preventing the air-pressure in the space 41 from accentuating the recoil stroke, since the control rod 24 remains in an elevated position until the pressure in the space 43 drops to a low value. If, however, the shock-absorber is severely shortened and the air in the space 41 is considerably compressed, the valve device 22, 23 may not be capable by itself of checking the violent recoil. In this case, as the plunger 18 approaches the end of its recoil movement, a frustoconical seating 37 on the piston head 19 engages a similar surface 38 on the valve-member 32 and seals the space 44 from the space 43, the valve-member 23 then being below the passage 21 thus blocking the bore 20 and liquid is forced out of the space 44 into the space 42 against the considerable pressure of the air in space 41. In a modification, the lower end of the plunger is formed as a piston head in slidable engagement with the cylinder 10 and a space in the plunger above the piston-head communicates through radial passages with an annular space surrounding the plunger. The recoil valve member 32 is housed in an enlarged upper part of the cylinder 10 and on excessive recoil is adapted to be engaged by the upper surfaces of the piston-head. In a further modification, Fig. 5, the plunger is also formed with a piston-head 19a having a bore 20c through which the valve-members 22, 23 are slidable, and a recoil valve-member 32a, centralised by arms 51, is fixed to the control rod 24. During recoil, liquid in the annular space 44 flows through the radial passages 52 and valve device 22, 23 to the space 43 until reduction in pressure in the space 41 allows the compressed air in space 39 to force down the control piston 30 until the member 32a blocks the upper end of the bore 20c when the liquid is forced into the space 42 thus raising the air-pressure in the space 41. Specification 550,896 is referred to