Patent GB-622352-A (GB)
Title: Improvements in and relating to time switches controlling electric and other heating appliances
IPC: G04C23/16
Filed: 1947-03-14
Abstract: 622,352. Clockwork actuated valves. BRITISH THOMSON-HOUSTON CO., Ltd. March 14, 1947, No. 7200. Convention date, March 15, 1946. [Class 135] [Also in Group XXXVII] A switch for controlling a cooking range comprises a synchronous electric clock, two time-setting dials 4, 5 on the clock-face, adjustable by a knob 12 to determine the time of stopping and starting a baking operation by means of a two-stage slotted-disc assembly geared to the dials and co-operating with a clock-driven rotary finger to operate the switch through a master cam set by a hand-control knob 50. The cam serves to cock the two-stage timing device, and select either automatically-timed baking or manually-controlled baking and broiling. The hand-control knob also serves to indicate the " automatic on " and " off " conditions during " timed baking." The clock comprises a synchronous motor 18 driving the hour and minute hands 1, 2 through suitable gearing 19, 24, and a friction clutch 20 which allows the hands to be set. The time-setting dials 4, 5 are mounted on hollow shafts 8, 11 surrounding the clock spindles, the outer dial 4 and being rotatable by the setting knob 12 through rod 13 and gears 14 ... 16. The baking time is preselected by rotating the dial 4 so that the part 7, or the corresponding other end of the sector engages the " stop " indicator on the dial 5 and rotates it to the finish-of-baking time. The dial 4 is then run back to the startof-baking time, uncovering the " hours-tocook " scale on the dial 5. The setting knob 12 also rotates the slotted disc 28 of the twostage timing device, through gears 37, 281 to a corresponding setting, and the slotted disc 29 is similarly connected through gears 291, 30 and 31 ... 33 to the dial 5. The discs 28, 29 when " cocked " as described below are spring- biassed towards a rotatable finger 25 driven by gears 26, 27 from the clock hour shaft so that the finger passes through the slots 42, 43 at the set times allowing the disc-assembly to snap forward. A spring-loaded, pivoted, bellcrank lever 39 having an arm 41 engaging between the gears 28<SP>1</SP>, 29<SP>1</SP> provides the forward bias, and also rotates the switch-operating master-cam 48 at each forward step by means of a cam-follower 56 on its other arm 391 engaging with a face cam surface 63, 64, Fig. 6, so that the switch is first closed and then opened. The knob 50 is rotated with the cam to the " automatic on " and " off positions. The master-cam also has two sets of radial cam surfaces 52, 52<SP>1</SP> and 53 which operate the main on/off switch 49 and bake/broil change-over switch 54. In the " timed-bake " position, the radial cam 52<SP>1</SP> holds the main switch 49 open, Fig. 3. When the finger 25 snaps through the disc 28 to the " automatic on " position, the cam-follower 56 moves down the surface 63, rotating the cam 48, thereby allowing the switch 49 to close (Figs. 4, 7, not shown). When the finger 25 snaps through disc 29 to the off position, the cam follower 56 moves down surfaces to position 66, rotating the cam 48 so that the lobe 52 opens the switch 49. To cock the disc assembly initially, the cam 48 is turned by hand, to the " automatic-bake " position, the cam-follower rides up the surfaces 64, 63 and turns the bell-crank lever 39, thereby pulling the slotted-disc assembly back, and the finger 25, which is resiliently mounted (Fig. 2a, not shown), rides over the dished edges of discs 28, 29 and springs down to hold them in the cocked position ready to be released. If the knob 50 is turned to the " bake " or " broil " position, respectively, the disc-assembly is cocked as above, and the cam follower 56 then moves on to snap into the locating detents 68, 70 in the periphery of the master-cam, whereby it is held in position even if the timing device operates. The cam may be manually turned to the off position at any time. If the discassembly is cocked, the cam follower rides up the surface 71 of an auxiliary cam, into the detent 73, locating the master-cam in the off position, and holding the discs 28, 29 away from the finger 25 to reduce wear. If the discassembly is half cocked, i.e. " automatic on " position, the cam-follower 56 will ride into the detent 75 carried by a resilient blade 74 on the auxiliary cam, thus locating the master-cam until the follower is released by the timing device to drop to the bottom of the face cam track 66. If the knob 50 is unintentionally left between " off " and " bake " so that the cam follower 56 is in the lower dotted position, Fig. 6, a friction brake 77 which presses against a portion of the cam lobe 52 (Figs. 5 and 9, not shown) prevents the switch being operated to the on position by the timing device. The Specification states that the term switch is used in its broadest sense to mean a device for switching on and off the flow of electricity, gas, oil, &c.