Patent GB-597811-A (GB)
Title: A temperature-sensitive timing device
IPC: A47J37/08
Filed: 1944-03-15
Abstract: 597,811. Switches held set and freed mechanically. TURNER, C. R. March 15, 1944, No. 4873. [Class 38(v)] [Also in Group VI] The length of time taken to perform an operation, e.g. the toasting of bread, is automatically adjusted to the varying temperature conditions by means of a hydraulic circuit in which the viscosity of a liquid varies with the temperature so that its rate of flow through a restricted passage is varied and thereby delays or accelerates the automatic cut-off of the operation. The automatic timing apparatus comprises lower and upper metal bellows 70, 71, Fig. 8, separated by a disc 72 with a connecting valve passage 74 and also by a small bore bleeder circuit led up to a coil 107 located in a temperature-influenced chamber and back to the lower bellows. When the heating operation, for example, the toasting is started, the lower bellows is compressed to pump a charge of viscous liquid into the upper bellows 71, the resilience of which forces the liquid back through a tube 81. An insulated contact 63 depresses the switch arm 54 to close the switch 55, thus switching current to the heat elements 24 between the bread slices. The inner end of the lever 43 becomes engaged under the hook 58 of a rocking latch 57 to hold everything in toasting position but it can be unlatched if the knob 51 is raised to stop toasting and allow the bread holders to be rocked forwardly by the lever 43. The other end 94 of the lever 45 pushes up the lower bellows 70 to pump up a charge of the viscous liquid in the upper bellows 71. Automatic release at the end of a time interval takes place when the lower bellows 70 becomes fully extended downwards on the return of the viscous liquid of the top bellows 71 through the coil 107 and the pipes 80 and 81. The return of the lower bellows to expanding position is also assisted by curved spring 82, Fig. 7, acting through a lever 83. In case the temperature viscosity variation is not sufficient to determine toasting interval the bellows holding spring 82 may include a bi-metallic element 110 so that if the heat within the apparatus increases above a certain point, the bi-metallic element tends to expand and increase the force of spring 82 sc acting to cut short the toasting period. T h e time interval is begur when the knob 51 is lowered so that a lug 77 of back extension 67 of the lever 45 pushes the lower bellows up and drives the liquid into the top bellows. The time interval is ended by the bellows 71 acting to release the latch 57 so that the lever 45 is pivoted up by spring 49 and the lever 43 being raised by its spring 44 move the toasting racks 37, 35 out of the apparatus and at the same time opening the switch 55 to cut off the heating current. An adjustable cam 93 is interposed in the release mechanism operated by knob 97 at the front to delay or accelerate the release, a pointer 98 indicating the degree of adjustment as required for light-brown toast or otherwise. As an alternative the retarding bellows arrangement with small bore passage 130 and temperature coil may be used. In this case, Fig. 10, the upper chamber 133 is provided with a vent tube 143 which is also long enough to prevent the liquid or vapour from being forced out during its action.