Patent GB-726326-A (GB)
Title: Resilient transmission mechanism
IPC: G05G25/00
Filed: 1952-04-23
Abstract: 726,326. Dashpots; helical springs. WARMOES, J. J., and CLOSKIN, L. A. A. J. April 23, 1952 [April 25, 1951 ; Oct. 25, 1951], No. 10257/52. Class 108 (3). The invention relates to mechanism for transmitting a force F (Fig. 4) from a first movable member 2, to a second movable member 19, only when the force exceeds a predetermined amount. According to the invention, the mechanism comprises a cylinder 4 containing compressible fluid, and a piston 6 to which the force is applied, via a resilient member 11, to compress the fluid until the piston moves beyond a predetermined point at which it allows the release of fluid from the cylinder, and continued movement of the piston beyond that point applies the force or allows the application of the force from the first member to the second member. The member 2 is outwardly urged by a spring 3 relative to a casing 1. The cylinder 4 is slidably mounted in the casing 1, but its downward movement under the action of the spring 3 is normally limited by engagement with the member 19. A groove 221 in the wall of a hollow portion of the member 19 is normally engaged by the inner end 22 of a spiral spring 21. A rod 5 of the piston 6 has a conical end 5<SP>1</SP>, adapted on engagement with the spring-end 22 to displace it from the groove 221. A groove 9 in the rod 5, extends over a length which is greater than the length of a bore 4<SP>11</SP> in the end wall 4<SP>1</SP> of the cylinder 4. In operation, when the force F is applied, the piston 6 compresses air in the cylinder 8, until the lower end of the groove 9 extends below the wall 41. The piston 6 then descends rapidly, the conical end 5<SP>1</SP> displaces the spring end 22 and the force F is thus transmitted to the plunger 19 which is free to move downwardly. In a modified construction (Figs. 1 and 2, not shown), the cylinder 4 is rigid with the casing 1, and the force is transmitted from the piston 6 to the plunger 19 by the end of the rod 5 (the end of which is not conical). The plunger 19 is retained in its normal initial position by a snap-action leaf spring which snaps downwardly on engagement between the rod 5 and plunger 19. The snap-action may be augmented by provision of a coiled spring. The groove 9 in the rod 5 is replaced by an internal duct having lateral openings near each end of the rod 5. A plug 12 to which the upper end of the spring 11 is secured, may be axially preset relative to the member 2 in order to vary the preload of the spring. In the construction shown in Fig. 5, the cylinder 4 is also rigid with the casing 1. The plunger 19 is normally retained by a spring 191 which may be retracted out of engagement with the casing 1 into a recess 19<SP>11</SP> in the plunger 19, by the action of downward movement of the rod 5. The force F is transmitted to the plunger 19 by means of a plunger 12<SP>1</SP> rigid with the member 2 and a spring 25 (which may alternatively comprise a fluid). In a modification of the Fig. 5 construction (Fig. 6, not shown), the retainer spring 19<SP>1</SP> is replaced by a ball which normally engages an annular channel in the plunger 19 and is also partly retained in an aperture in the wall of a sleeve surrounding the plunger. Radially-outward movement of the ball to release the plunger 19, is normally prevented by a projection carried by a further spring-loaded sleeve. The latter sleeve is displaced by movement of the rod 5, to release the ball, and thus the plunger 19, after a predetermined movement of the piston 6.