Patent GB-625574-A (GB)
Title: Automatic heat control apparatus
IPC: A47J31/047
Filed: 1946-06-14
Abstract: 625,574. Timing apparatus for controlling cooking. HUENERGARDT, W. H. June 14, 1946, No. 17875. [Class 28(i)] [Also in Groups XXXV and XXXVII] A device for controlling the heating of a liquid such as coffee consists of an electric heater supported on a pivoted platform which is upheld by a spring. The vibration set up by the boiling liquid causes the sprung platform to oscillate, thereby releasing the escapement of a clock-type time delay which in turn moves a heater change-over switch to a central " off " position. When the liquid has cooled to a predetermined temperature, a bimetallic strip trips a catch to allow the change-over switch to complete its movement and close the circuit of a small heater coil that keeps the liquid warm. Pushbuttons are provided for re-setting and manual release. The heater 196, Fig. 9, has a small coil used by itself for warming, and in parallel with a. main coil for boiling the liquid. Secured to the heater is a platform 51, Figs. 9 and 17, pivoted at 53 to an underlying platform 20 which is itself pivoted 'to the base 15 by a pin 44. A third platform 19 pivoted at 24 has a slit extension finger 30, Fig. 17, which is pivotally linked with an extension 36 of platform 20 by means of a fulcrum plate 33. The free end of the upper platform 51 is hooked through a hole in platform 19 and is pivotally linked to it by a plate 58. The assemblage of pivoted platforms is supported by a compression spring 37, and upward movment is limited by a hooked stop plate. A counterweighted lever 63 is frictionally pivoted to platform 19 so that its pivot is stiff enough to transmit any small oscillations of the platform, but is free to swing to accommodate the initial downward deflection as the platform is loaded. A bell crank 75 transmits the oscillations of lever 63 to a lever 100, Fig. 11, secured to a pivoted double pawl 84 co-operating with an escapement wheel 87 which, through a train of gears and a friction clutch, controls the movement of a section 94 spring loaded by a tension spring 97. When the liquid boils, the vibrations of the platform assembly allow the escapement to release the sector 94, causing a trip arm extension 104 to move against a 'trip 106 forming part of a pivoted plate 107 journalled at its extremities 109, 110. As this plate rotates it raises an arm 115 on a cantilever 114, pivoted at 116, which in turn releases a switch controlling plate 121. This plate pivots about a spindle 124, and is normally urged in an anti-clockwise direction by a compression spring 126. When the mechanism is loaded however this plate 121 is held down by a catch 117 on the cantilever 114, so that a switch terminal plate 131, also pivoted on spindle 124, can be raised by a light compression spring 134. In this position contact studs 139 carried on a plate 136 secured to the plate 131, bridge three fixed upper contacts, thus joining the two heater coils in parallel to the supply. When the escapement gear releases the switch controlling plate 121 it bears down on the terminal plate 131, and, since spring 126 is made stronger 'than spring 134, the attached contact plate 136 is forced downwards, thus opening the heater contacts, until a projecting arm 147 is arrested by a notch 164, Fig. 13, cut in the lower arm of a crank 153 whose move ments are controlled by a bi-metallic strip 160 runnng below the heater element. As this strip cools it turns the crank 153 in an anti-clockwise direction and releases the arm 147 of the contact plate 136 which plate moves down to bridge lower fixed contacts and connect the warming coil in circuit. The contacts are 'then locked by a spring catch 149, which is tripped on resetting by an extension 129<SP>1</SP> on plate 121, Fig. 11. Re-setting is effected by depressing a button, 179, Figs. 9 and 11 which presses a disc 173 simultaneously on to the end of the switch controlling plate 121 and on a forked extension 169 of the pivotal plate 107. The switch controlling plate returns the switch contacts to their initial upper position and re-sets the trip 114. The pivotal plate 107 moves the arm 104 to reset the escapement gear spring 97. A button 180 trips the mechanism. In an alternative switch mechanism, Figs. 8, 18, 19 (not shown), the switch controlling plate 121 directly opens and closes contact studs mounted on spring plates, without the use of the. quick make and break springs 134, 126.