Patent GB-711218-A (GB)
Title: Thermostatically-operated electric switches
Inventor: GARNER RUSSELL F
IPC: H01H35/26
Filed: 1951-02-15
Abstract: 711,218. Thermal switches. ROBERTSHAWFULTON CONTROLS CO. Feb. 15, 1951 [Feb. 15, 1950], No. 3701/51. Class 38(5) [Also in Group XXXV] A switch (Figs. 1-4) for controlling the bake and broil elements of an electric oven and permitting. of pre-heating comprises flexible contact arms 56, 56a having on opposite sides contacts 58, 58a and 60, 60a, respectively, and connected to the bake and broil elements, the arms 56, 56a, being inherently biased so that the bake contacts 58, 58a are normally closed. The circuit to the heating elements is completed through main bridging contacts 48, 48a carried by an H-shaped control lever 38 which is pivoted on knife edges 44 and has its centre arm connected by a spring 36 to the lower extremity of a main actuating lever 28 pivoted on a knife edge 30. The arrangement forms a snapmechanism which tends to keep the main contacts 48, 48a 'closed. The contacts 48, 48a are opened by movement of a button 22 on an expansible diaphragm 20 mounted on a screw 16 having lefthand threads and adjustable by a handle 18, the diaphragm being connected by a tube 24 to a liquid-filled bulb 25 located in the oven, and the button 22 engaging a depression 26 in the actuating lever 28. The spring arms 56, 56a are movable by an insulating plate 70 having pairs of projections 72, 86 and freely mounted at its upper end on a pin 74, its lower end being received between lugs 84 on a rocker 80 pivoted at 82. The plate 70 is movable by a projection 104 on an operating lever 100 pivoted at 102 and itself operated by a plunger 106 urged outwardly of the switch cover 12 by a spring 110. The plunger 106 may be directly depressed by hand or, 'as shown, by a cam 114 on the handle 18 and situated at the broil position of the latter. When the handle 18 is in the " off " position, the parts are as shown in Fig. 3 with the control lever 38 in the dotted line position. Rotation of the handle to a baking position permits closure of the main contacts 48, 48a (shown in full lines in Fig. 3) and the baking element circuit is completed through the contacts 58, 58a. Expansion and contraction of the diaphragm 20 controls the contacts 48, 48a to maintain the desired oven temperature. For a broiling operation the handle 18 is rotated further to operate the plunger 106 by the cam 114 whereby plate 70 is initially pivoted clockwise and the rocker 80 is moved counter- .clockwise. The arms 56, 56a are thereby flexed by the projections 86 and the broil contacts 60, 60a engage fixed contacts 68, 68a to energize the broil element. Also, the rocker 80 is latched by a notch 87 thereon engaging pawl 88 pivoted at 96 and having an arm 92 biased by a spring 98. On completion of movement of plunger 106 the contacts 68, 68a act as a stop and the plate 70 is moved counter-clockwise to cause bowing of the arms 56, 56a by the projections 72 and the contacts 58. 58a of the bake element circuit are opened, Fig. 4. A trigger member 96 on the actuating lever 28 co-operates with a ramp 94 on the arm 92 to release the latch 87, 88 and thus the plate 70, to open the broil contacts 60, 60a upon opening of the main contacts 48, 48a but this release action is ineffective so long as the plunger 106 is depressed to retain the plate 70. For a pre-heating operation the handle 18 is turned to the broil position to latch the rocker 80 and plate 70 and is then returned to a baking position. This return causes the plate 70 to pivot clockwise about the rocker 80 under the bias of the contact arms 56, 56a and the contacts 58, 58a close, hence both the broil and bake elements are energized, Fig. 5 (not shown). The pre-heating is terminated by expansion of the diaphragm 20 which causes the trigger 96 to operate the pawl 88 and thus permit the plate 70 to move and the broil contacts 60, 60a to open. The switch then functions as described for the bake operation. Fig. 6 (not shown) illustrates the circuit arrangement. In a modified construction, Fig. 9, the flexible contact arm 126 has an insulating extension 128 which co-operates with a contact arm 130 biased so that a contact 132 thereon engages a contact 136, thereby normally connecting fixed contact supports 66, 134, the contact 136 being connected to a tap on the bake element. As in the previous embodiment contacts 58a. 60a on the arm 126 control the bake and broil elements respectively, but the other arm 140 is shortened. Fig. 7 (not shown), and carries only a bake contact 58. During a baking operation the bake element is energized through contacts 58, 58a, and also the broil element is energized through an auxiliary circuit including the contacts 132, 136 in series with part of the bake element, Fig. 12. The additional heat provided by the broil element which is thus operated at less than  full wattage ensures uniform baking conditions. In a broiling operation the rocker 80 is latched by the pawl 88; and a projection 138 on the plate 70 opens contacts 132, 136; also, the broil contact 60a is closed and the bake contacts 58, 58a are opened, Fig. 10 (not shown). Pre-heating is achieved as in the first described embodiment, both the bake and broil contacts 58, 58a and 60a being closed and the tap contacts 132, 136 being open; Fig. 11 (not shown), (see Group XXXV). Reference has been directed by the Comptroller to Specification 539,481.