Patent GB-627775-A (GB)
Title: Temperature responsive control mechanism
IPC: H05B1/02
Filed: 1947-04-10
Abstract: 627,775. Timer for toaster. DEHN, S. G. (Sunbeam Corporation). April 10, 1947. No. 9581. [Class 28(i)] [Also in Group XIII] In a temperature responsive type of heat timing mechanism especially for bread toasting, a thermostat is moved in a succession of cycles into and out of heat influenced position, whereby the toasting elements are switched on and off to heat up and then cool down, automatically providing a total time period for the toasting or other operation. The bimetallic thermostat 73 has a low ratio of mass to its surface area, so that the time lag caused by waiting for it to attain its operating temperature is reduced, so that the device is relatively unaffected by small voltage variation. A lens 25 in the side of the toaster casing in front of an indicating coil 26 shows when toasting is proceeding. Bread holding racks are supported on a carrier 29 slidable on rods 27, 28 when side handle 24 is moved up or down. To set the time for termination of the toasting a handle 82 is turned to rotate a cam 83 so that more or less of the cam surface is brought into the path of movement of a pin 74 on a bimetallic thermostat 73 so that toasting is stopped as below. Bread slices are inserted in the racks 14 and 15, Fig. 3 (not shown), and handle 24 is moved down to position, Fig. 7, so that roller 47 engages cam face 46 rocking the arm 36 to close contacts 33 and 31, and lug 49, Fig. 10, seats in notch 53 to retain arm 36 as in Fig. 7 to maintain contacts closed. During this movement roller 85, Fig. 10, engages upper edge 86 of gear segment 78 to rotate segment to position, Fig. 9, and pinion 67 and spring 68 rotate on the pin 66 with respect to collar 71 like a ratchet. Friction may rotate the pin 66 and the multiply thermostat 73 to position in Fig. 9 in which pin 74 engages the lower surface of abutment 91 and is thereby stopped. As the handle 24 and carrier 29 reach their lowest position the roller 85 is forced off the top edge of gear segment 78 by the flange 87 whereupon spring 79, Fig. 6, returns the segment so that pinion 67 and spring 68 rotate on pin 66 until spring end 68 comes against abutment 69. Thus pinion 67, spring 68 and pin 66 rotate counterclockwise until pin 74 engages cam 83 to bring the parts into the Fig. 10 position. When contacts 31, 33 are closed as above, current flows to the primary heating elements 16, 17 and 18, Fig. 4, and also through the secondary heating coil 58. The heat of coil 58 causes the bimetallic element 73 to warp towards the coil to withdraw, after a time, the pin 74 from cam 83 so that spring 79, Fig. 6, acting through 78, 67, 68, 71 and 66 rotates bimetallic element 73 counterclockwise to position in Fig. 11, where it is stopped by its pin 75 striking an abutment 92, thus bringing bimetal element 73 away from its heating coil 58. When 73 cools off it warps in the opposite direction until its pin 75 moves endways off abutment 92 so that 73 rotates through another half turn to bring it again in position where heating coil 58 re-warps it. Thereupon it rotates until pin 75 strikes adjustable abutment 92 and stops until it cools down again and so repeats the motions until the part 93, Fig. 10, of gear segment 78 lifts latch 51 off lug 49 so that arm 36 is moved by the springiness of switch lever 34 to open the contact to stop the loading. Any number of heating and cooling cycles can be got by regulating the tension of spring 79, the length of the gear segment 78 and the gear ratio between 78 and pinion 67. The accuracy of operation increases with the number of cycles. Modified shapes of bimetallic thermostats are also described. By hand knob adjustment of the relative positions of the cam 83 and the stop 92 the ratio of the heating to the cooling-off time can be adjusted.