Patent GB-667787-A (GB)
Title: Improvements relating to electric toaster timing mechanism
IPC: A47J37/08
Filed: 1949-07-12
Abstract: 667,787. Thermal switches; electrically-released switches. HOOVER, Ltd. July 12, 1949. [July 13, 1948; July 13, 1948; July 13, 1948] Nos. 18392/49, 18393/49 and 18394/49. Class 38 (v). [Also in Group VI] In electric toaster timing apparatus comprising a temperature-responsive element arranged to be heated during each toasting period and to actuate release means for switching off the heaters at tne end of the toasting period, the temperature responsive element changes its shape progressively with varying temperature and has means dependent on its shape at the beginning of each toasting period, for-varying the mutual relationship between the element, the release means and their support so that the higher the temperature of the element at the beginning of the toasting period the greater must be the total change of shape of the element, and hence the higher its temperature, to actuate the release means. 'As shown in Fig. 1 a toaster comprises verticallyslidable toast carriers 4 having a bar 18 that is engaged by a pivoted latch 15 to hold them in toasting position where a lug on bar 18 engages a switch 41 and closes the heating circuit. A bimetallic strip 19 is attached to a brake drum 21 pivoted to a bracket 24 and urged in an anticlockwise direction by a spring 31 into contact with a stop 35 on a compensating bimetallic strip 36. The drum 21 is surrounded by a spring metal brake band 25 adapted to prevent rotation of the drum 21 and hence bracket 20 and the end of bimetallic strip 19 when the toast carriers are lowered. An auxiliary heater 29 is wound on and insulated from strip 19. A rheostat 32 is arranged so that as the drum rotates anticlockwise resistance in the auxiliary heater circuit diminishes and heating increases. To operate the apparatus the toast carriers are lowered, thereby closing switch 41, so that current is fed to the main and auxiliary heaters, and clamping the brake drum. As the strip 19 heats up it flexes and ultimately engages latch 15 which releases the carriers thus breaking the circuit and ending the initial toasting period. The carriers in turn release the brake band 25 so that the spring 31 turns the strip 19 until it engages stop 35 so that, if a new toasting period begins before the strip 19 has cooled, the end of the strip will move through the same distance as before to engage the latch except insofar as this distance is modified by bending of the second bimetallic strip 36. The position of stop 35 is adjustable by knob 40 according to the degree of toasting required. Fig. 4 shows a modification with a coiled bimetallic element 63 fixed to post 64 of a brake wheel 65 and carrying at its free end an insulated bridge contact 67 which engages contacts 68 when the element is heated and thereby energizes a solenoid 61 to release a latch 56 of rectangular toast carriers. When the carriers rise, brake 99 is released and wheel 65 rotates under the influence of spring 70 on the free end of the strip and cam 97 thereon is advanced to allow a vertically-movable auxiliary heater, from which the element draws its heat, to move closer to the element 63 at the next toasting operation. In two further modifications employing coiled bimetallic elements and cams, Figs. 7 and 10 (not shown), the free end of the element is adapted or funished with means to act on the releasing latch directly to release the carriers. The main .toaster heaters and auxiliary heater, Fig. 10 (not shown) are energized by a bridge contact on the carrier plate engaging two contacts on the platform. Specification 648,151 is referred to.