Patent GB-642322-A (GB)
Title: Temperature responsive control mechanism
IPC: H01H43/30
Filed: 1947-07-11
Abstract: 642,322. Thermal switches; snap-action switches. SUNBEAM CORPORATION. July 11, 1947, No. 18434. Convention date, Aug. 23, 1943. [Class 38(v)] [Also in Groups VI and XIII] A snap-action thermally-actuated timing switch in an electric toaster, (see Group VI), is arranged to control the operation of toasting slices of bread to a uniform colour, the switch being arranged to compensate for residual heat in the toaster when a series of toasting operations are carried out. Fig. 1 shows the switch at the commencement of an operation with the contacts 21, 22 open, these contacts being connected in series with the heating element 106 of the toaster and with the heating element 43 of the switch. In this position the switch contacts are held open against the tension of a spring 46 by a pawl 68 engaging a part 69 of a toggle lever 39 which is pivoted at 41 to the frame of the switch and at 38 to a vertical motion translating member 36. When a slice of bread is inserted into the toaster it depresses a lever (not shown) the extension 64 of which rises and lifts a pivoted bell-crank lever 79 which it abuts at 81. The pivot 76 of this lever rises causing a link 75 which carries the pivot 76 to turn clockwise about its fixed pivot 71, and an abutment 74 on the link 75 engages an abutment 73 carried by the pawl 68. Hence the pawl 68 is moved out of engagement with the part 69, which now moves clockwise as the member 36 snaps up to close the switch contacts 21, 22, Fig. 3. During this clockwise motion the part 69 strikes the end 78 of the lever 79 so disengaging it from the extension 64. The toaster elements and the heating element 43 are energized, the latter element heating the end of a bimetallic strip 25 by means of a comparatively heavy copper heat conducting member 26. When this end 33 of the strip 25 has been heated to a temperature determined by the setting of the spring 46 it snaps downwards to open the switch contacts. The switch is latched in the open position by the re-engagement of the pawl 68 with part 69. When the toast is removed, the extension 64 is lowered and the bell-crank lever 79 returns to its original position, Fig. 1, and the mechanism is now re-set for the next operation. The opening of the switch brings the heat-conducting member 26 into contact with a similar member 29 attached to the fixed end 27 of the thermal strip. This cools the member 26 and the end 33 of the strip 25 and causes a rise in temperature of the end 27 of the strip so causing a secondary thermostatic action which tends to bias the end 33 upwardly. If a new slice is inserted into the toaster before the end of this cooling period the parts 68, 69 unlatch but the switch does not re-close until the strip has been cooled sufficiently to be overcome by the spring bias. Should the toast be removed before the end of the timing period the extension 64 bears against the spring 46 and causes the switch to open. The compensation for residual heat in the toaster is obtained by means of the secondary thermostatic action which occurs due to the end 33 of the strip 25 being restrained from angular motion as described in Specification 564,991. The timing switch may be adjusted by means of a manually operated cam (not shown) against which the extension 55 of the pivoted spring retaining member 53 bears . The Specification sets out in some detail the manner in which the thermal characteristics of the timing switch may be arranged so as to compensate for voltage variations.