GB608879A - Improvements in thermostatic electric control devices - Google Patents

Abstract

608,879. Control systems for heating resistances; automatic temperature control systems. WILCOLATOR CO. Jan. 17, 1946, No. 1666. Convention date, March 15, 1944. [Class 38 (iv)] [Also in Groups XIII and XXXVII] A thermal regulator unit for use in ovens having high and low heat elements comprises a snap action thermostat normally controlling the low-heat element; a press-button preheating switch which connects the high-heat element in parallel with the low-heat element and is tripped by the thermostat to de-energize the high-heat element and a change-over switch to connect the thermostat in the high-heatelement circuit for high temperatures. The thermostat comprises a liquid-filled bellows 15, with internal stops 80, 81 to limit its contraction with fall of temperature below 150‹ F., the bellows being connected by a coiled capiliarytube 16 to a bulb in the oven (not shown). From opposite ends of the bellows project, respectively, a stud 8 bearing against a calibrating screw 18 in the temperature-setting dial 32 and a stud 59 bearing on the upper end of a pivoted operating lever 42 which is connected by an eccentrically-mounted stud 50 at its lower end to the middle leg 49 of a trifurcate blade snap-spring 46. The lever 42, Fig. 14, is pivoted by knife-edges 45 in notches 41 in the upper arms 39, 40 of a frame 35, Fig. 3, and the outer legs 47, 48 of the spring are mounted in grooves 38 in the lower arms 37 of the frame 35, so that the outer legs are held bowed as shown in Fig. 1. The counterclockwise pull of the central tongue 49 keeps the lever 42 bearing against the bellows stud 59. As the central tongue is moved by the bellows and lever from one side to the other of the grooves 38, the top of the spring follows it with a snap. An arm 61 on the upper end of the snap-spring carries an insulating saddle 65 with two contact bridges substantially as described in Specification 521,556, [Group XXXVII], to engage fixed contacts 72, 73 and 72, 74. The change-over switch, Fig. 2, comprises a contact blade 128 movable between two fixed contacts 115, 131, by a tappet 135 engageable by the inturned part 30 of a finger on the dial, when set to top-heat. The preheating switch comprises a spring-returned push-button 143 carrying a spring-biassed plate contact 150 which when the button is depressed bridges the depending contact surfaces 120, 125 and two plates 116, 124 connected to the terminal studs of the change-over switch. The button 143 is retained in the depressed position by the extended part 140 of the stem girding in a hole 162 in a lever 155 which is pivoted in a bracket 154, and held inclined by an adjusting screw 159 at the upper end of the lever 155, bearing on the thermostat stud 50. To heat the oven for baking, the dial is set to the desired temperature, and the preheat switchbutton 143 depressed to close the contactbridge 152 and connect the high-heat element in parallel with the low-heat element, Fig. 10, and the change-over switch blade 128 is normal. About 20‹ F. below the selected temperature, the bottom of the lever 42 carrying stud 50 moves sufficiently to allow the lever 155 to become less inclined, and the push-button is released with an audible click and visible movement, opening the contact bridge 152. Thereafter the thermostat controls the lowheat element over the contacts 70, Fig. 9, When the dial is set to top-heat, for " broiling," the change-over switch blade 128 is operated to connect the high-heat element to the thermostate contacts 70, Fig. 11.