Patent GB-892657-A (GB)
Title: Heating system comprising electric switching means
IPC: H01H89/04
Filed: 1960-04-29
Abstract: 892,657. Cam-operated switches; thermal  switches. PROCTOR-SILEX CORPORATION. April 29, 1960 [April 30, 1959], No. 15096/60. Class 38 (5). [Also in Group XXXV] A control unit for electric cooker hot-plates, for example, comprises three single-pole, singlethrow switches 14, 15 and 16, in a common casing 10 having an operating knob 12 which is turned to move switches 15 and 16 on and off and to operate a latch on switch 14, is depressed to release the latch of switch 14, and is angularly settable to predetermine the operating temperature of thermal switch 16. The casing 10 is moulded with various recesses and shoulders to carry the switch parts and has openings for ventilation purposes. Switch 16 comprises a bi-metal strip with heater 40 actuating one contact while the co-operating contact is carried on a spring blade (Fig. 6, not shown), the position of which is adjustable by a coupled spring blade 37 (Figs. 1 and 2) bearing on an outer cam track 22 on cam member 18 (Figs. 3 and 4). Switch 16 has an " off " position and preferably a snap-action. Switch 15 (the provision of which is preferred but not essential) comprises a fixed contact 51 co-operating with a contact 50 carried on a spring blade 95 movable between " on and "off" positions by a track 21 on the cam member 18. An auxiliary blade 48 engages blade 95 when switch 15 is " on " to energize a pilot lamp 46 (Fig. 8). Switch 14 comprises a fixed contact 52 and a movable contact 53 carried on a spring blade 57 biased to the open position shown in Fig. 4. A triangular latching member 56 is pivoted at 81 and has a nose 86 which is depressed by track 19 on cam 18 at least when the cam is in the " off " position of switches 15 and 16 so that a laterally extending member 84 on triangular member 56 depresses blade 57 to close contacts 52, 53. In this condition (Fig. 3) a resilient blade 54 (biased flat against the base of the casing 10) engages behind a part 87 of member 56 and latches switch 14 closed. The latch is releasable by depression of knob 12 which moves shaft 20 to compress a spring 63 and resilient " spider " 64, causing the end 55 to project through the base of casing 10 and lift blade 54 clear of the part 87 of member 56 which is then rotated by the resilience of blade 57 and switch 14 is opened. The cam 18 is loosely mounted on the shaft end 55 but rotates therewith by virtue of the " spider " 64 which has its centre and legs fixed respectively to shaft 20 and cam 18. Cam 18 is prevented from axial movement by three posts 70, 71 and 72 (Figs. 2 and 3), against which it is held by spider 64, spring 63 and a spring member 59 fixed to cover-plate 11. In use, the control unit works in conjunction with a cycling switch 27 which has snap contacts 41, as shown in Fig. 8, coupled to a bimetal member 42 heated partly by heater 44 and partly by conduction from the temperaturesensing element 43 which is physically located in proximity to the hot-plate heating elements 25 and 26. It is stated that instead of operating switch 16 by heater 40 it may be connected to the cycling switch 27 by hydraulic or mechanical means. In a modification (Figs. 11, 12 and 13, not shown), the switch 14 is biased to the closed condition and a different latch arrangement holds it open when the shaft 55 is depressed, the latch being released by cam track 19 to close switch 14 when switch 15 is " off,"