GB536357A - Improvements in or relating to snap-action electric switches - Google Patents

Abstract

536,357. Snap-action switches; retraction switches ; switch contacts. KELSALL, A. J., and PYE, Ltd. March 14, 1940, No. 4821. [Class 38 (v)] A switch comprises a rigid pivoted arm 5 and a snap-over member formed by a bowed spring strip 9, one end of which is pivoted adjacent the pivot of the arm 5, the other end being carried by the free end of the arm so that pivotal movement of the latter causes the spring to snap over its dead-centre position. 'As shown, the pivoted end of the arm 5 is hooked and terminates in a knife-edge 8 engaged in a groove 4 in a post 2 secured to, or moulded into, the casing. The spring 9 is held in grooves 3, 7 respectively in the post 2 and the down-turned free end of the arm 5, the spring tending to force the arm to the right and so maintaining the end 8 in the groove 4 of the post. The spring carries a contact member 13 co-operating with upper and lower contacts 14, 15. Downward movement of the arm 5 causes the spring to snap over to the upwardly-curved form, the contact 13 then engaging the contact 14; on release of the arm 5, the parts return to the position shown. A plunger 17 may operate on the arm 5 directly or, as shown, through a spring 18 forming a cushioning member, which allows further depression of the plunger after the arm has. been moved to its full extent. By suitable choice of the positions of the fulcra of the arm 5 and spring 9 the switch may be caused to remain in either of its positions. Knife edge contacts may be employed. The switch may comprise two sets of switch mechanism supported side-by-side by the same pillar; or, one pivoted arm may be employed with a plurality of snap over springs. The switch, may be employed to control tell-tale lamps indicating the position of retractable landing-gear on aircraft, in which or in other applications where it may be exposed to low temperatures, it may be provided with a heater in the casing.