Patent GB-596737-A (GB)
Title: Improvements in or relating to quick-motion mechanisms normally operated by stored energy, for example for on-load tap changing of electric transformers and the like
IPC: H01H9/00
Filed: 1945-08-01
Abstract: 596,737. Snap-action switches. FOWLER, J., and METROPOLITAN - V I C KERS ELECTRICAL CO., Ltd. Aug. 11 1945, No. 19821. [Class 38(v)] In a latched, two-position, snap-action, mechanism with positive follow-up action, suitable for transformer tap-changing gear, Fig. 9, a driving shaft O carries two pinwheels G, H, engaging Maltese-cross wheels E, F, carrying cranks U, V, respectively. Crank V drives a spring-straining rod Z which is attached to a lever D freely pivoted on the switch-operating shaft A. For clockwise rotation of the shaft O, the sequence of operations during the first 180 degrees rotation of the wheels G, H, is as follows: -Pins K1, K2 engage wheel F turning crank V through 180 degrees so that rod Z rotates lever D to position B<1> straining the spring S, when pin N on the other end of lever D strikes the tail of trigger T1 releasing lever L; meanwhile from 45 to 135 degrees pin J1 has engaged wheel E turning crank U through 90 degrees, so that collar X on rod W moves clear of the trunnion R to allow the lever L to snap over from Position 1 to Position 2, under the action of spring S, after the contact throwoff spring has moved the lever L past the dead-centre. During further movement of the shaft O from 180 to 360 degrees no movement of the wheel F takes place, but from 225 to 315 degrees pin J2 engages wheel E moving the crank U through a further 90 degrees and collar Y on the rod W moves up against the trunnion R in Position 2, providing positive drive for the lever L if it has failed to complete its travel under spring action. During this operation, both cranks U, V move through 180 degrees, and continued clockwise rotation of the shaft O would act similarly to move lever L back to Position 1. In order to give the pin K2 a 45 degrees lead on pin J2 on reverse rotation of the shaft O, a sectorshaped key P, Fig. 9A, on the latter engages a sector Q on the wheel G to provide the necessary 180 degrees lost motion. In a modification, Fig. 10, the shaft O carries two discs respectively fast and loose thereon and with cam grooves C, B, engaged by rollers R1, R2, on bell-crank levers E1, E2, which oscillate toothed quadrants G1, G2. The quadrant G1 meshes with a pinion H1, pivoted freely on the driven shaft A, to which is attached the lever L. Pinion H1 and lever L carry pins J2, J1, respectively, which project between the ends of a torsion spring S. The quadrant G2 meshes with a pinion H2, also freely pivoted on the shaft A, and carrying a positive-drive quadrant Q with stops X, Y. A sequence of operations similar to that above occurs in half a revolution of the driving shaft, the cam tracks being so arranged that pin J2 strains the torsion spring S until a projection on the quadrant G1 strikes the trigger T1 releasing the lever L, the quadrant Q meanwhile moving so that the stop X is clear of the lever L, which snaps over as soon as it is released. The operation is completed by further rotation of quadrant Q, positive drive being provided by stop Y if necessary. Key K engaging the ends of a slot in the disc carrying the groove B, provides the 90 degrees lost motion necessary to obtain the correct sequence on reverse rotation of the driving shaft.