Patent GB-544367-A (GB)
Title: Improvements in temperature regulators for electrical appliances
IPC: H01H35/26
Filed: 1940-08-28
Abstract: 544,367. Automatic control systems for electric heating appliances. WILCOLATOR CO. Aug. 28, 1940, No. 13579. Convention date, Sept. 2, 1939. [Class 38 (iv)] [Also in Group XXXVII] Temperature in an electrically heated oven &c. is thermostatically controlled by a regulator having a temperature adjustment handle which may place either of two independent heating circuits under control by the thermostat to the exclusion of the other or place both under such control for pre-heating after which one circuit is automatically made inoperative while the other remains under thermostatic control. The thermally responsive element, which is removable as a unit from the switch casing, comprises a fluid filled hollow chamber 60 connected with a bulb in the oven through a capillary tube 61 and secured to a plate 43. A pin 62 is pressed against the end of the bellow by a spring 64, a rod 63 is screwed into the pin by a detachable knob 72 and a shoulder on the rod thereby applies a variable pressure to a plate 52 through a bimetallic element 54 adapted to compensate for ambient temperature variations. Small projections on the plate 52 flex a dished rectangular snap element 47 into a position wherein its ends release pins 46, 42 whereby pairs of resilient switch blades 31, 29 respectively are free to complete the circuits of the " bake " and " broil " elements 34, 35 respectively. These circuits are opened again when the pressure within the bellows due to oven temperature has reached that corresponding to the setting of a knob 72 in relation to an index 76, whereupon the pressure of the spring 64 is sufficiently relieved to permit reversed flexure of the plate 47 and depression of the pins 42, 46. The actuation of the switch member by these pins is however controlled by a disc 78 carrying a cam 79 under its periphery and an arm 83 adapted to operate a stop 90 on a spring mounting or tumbler. The arrangement is such that in all adjustments of the knob below a given temperature the stop 90 and the cam 79 overlap the pin 46 so that the " broil element is maintained out of circuit. In settings above this the cam releases the pin 46 and the stop is positively removed from its path by a finger on the arm 83. The switch member 31 can then operate in addition to the switch member 24 and the circuits of both heaters are closed for rapid heating of the oven. The stop 90 then remains pressing against the side of the pin and when the set temperature is reached and both switches open the pin 46 a pin overlies the stop 90 so that the " bake " element only is effective in the automatic control of temperature. The knob 72 can be moved to a " broil " position corresponding to a maximum temperature setting) in which the cam 79 overlies the pin 42 and a finger on the cam disc pushes aside the stop 90 to permit the " broil element alone to function. In a modification, Fig. 21, the switch arms 31 are adapted to co-operate also with back contacts 92 whereby on a three-wire supply system the " broil " element 35 is connected in series with a resistance 99 to " balance " the heating in the oven ; this additional circuit is controlled by the thermostat through "bake" element switch 24. In this modification the heating elements 34, 35 may be interchanged so that a small heat is applied to the top of the oven when the baking element is de-energized so reducing temperature variation.