Patent GB-537719-A (GB)
Title: Improvements in and relating to time switches
IPC: G04C23/16
Filed: 1940-02-23
Abstract: 537,719. Time switches. BRITISH THOMSONHOUSTON CO., Ltd. Feb. 23, 1940, No. 3412. Convention date, Feb. 24, 1939. [Class 38 (v)] Timing mechanism for automatically controlling the operation of a switch at predetermined times comprises a stationary clock dial 23 with hour and minute hands and solely supported by a central sleeve 110 surrounding the shafts of the hands so as to leave the edge of the dial free, a pair of independently-adjustable pointers 47, 48 indicating the times of automatic operation on the front marginal part of the dial, and hollow shafts 57, 57a carrying the pointers behind the dial and surrounding the sleeve 110 which supports it. The pointers may travel all round the dial, owing to the latter being supported only at the centre. As shown, a synchronous motor 12 drives through gears 14 and a friction clutch 15 the shaft 13 carrying the minute hand 16, the clutch facilitating setting of the hands. The hour hand 17 is carried by a hollow shaft 18 driven from the shaft 13 through gears 19 ... 22. The doublepole switch controlled by the clock comprises spring blades 24, 25 co-operating with fixed contacts 26, 27, the contacts being simultaneously operated by a post 28 which is moved by the flexure of a strip 29 brought about by the cam action of a lever 30. One end of this lever is. formed as a cam which, in the positions of the lever indicated by the chain lines I and III bends the strip 29 to the right and opens the switch contacts, and when the lever is in the positions indicated at II and IV, allows the contacts to close. The lever is held in positions I and II by contact with abutments 37, 38 on levers 40, 41, respectively pivoted on shafts 44, 45 and urged in a clockwise direction by a spring 46 connecting them. In order to close the switch at a preset time, the clock movement is caused at this time to rock the lever 40 clockwise, thus withdrawing the abutment 37 from the lever 30 which, urged by a spring 36 moves to position II, where it is held by the abutment 38. Lever 41 is subsequently rocked by the clock movement, the lever moving to position III and opening the switch. The movement of the lever 40 is produced by a toothed clutch 49 secured to the same sleeve 42 and. engaged at the appropriate time by fingers 52 carried by a spring 53 secured to a gear 50 driven from a gear 51 on the hour hand shaft 18. The spring 53 normally holds the fingers out of contact with the clutch 49, but when a cam portion 54 on it engages the end of a cam finger 55, as it is carried round on the gear 50, it moves the fingers 52 into engagement with the teeth of the clutch 49, rocking the lever 41 and so releasing the lever 30. The cam finger 55 is carried by a gear 56, which is rotated to set the time of operation of the switch by means of a gear 58 carried by the sleeve 57 concentric with the shaft 13 and having connected to it an arm extending round the edge of the dial and ending in a pointer 47 which co-operates with the normal time indications on it. A similar mechanism, set by a second pointer'48 operating similarly to the pointer 47, controls the release of the switch from position II to position III, that is, the time of opening of the switch contacts. The lever 30 may be set in any of the positions I-IV by a knob 68, positions III and IV corresponding respectively to closed and open positions of the switch contacts, uncontrolled by the timing mechanism. The lever is held in position III by a pivoted and counter-weighted stop 39 which moves to allow the end of the lever to pass it when the lever is rotated clockwise by the knob 68. The lever 30 in being set clockwise to positions I and II trips past the ends of the lugs 37, 38, but should these be locked owing to engagement of the clutches 49, 49a the knob is pushed inwardly against the action of the spring 36 to move the lever 30 to the rear and out of engagement with the lugs. A signal lamp 71 is illuminated to indicate that the timing mechanism is in operation through circuits completed by contact of the lever 30 with the lugs 37, 38. An alarm for timing short operations is set by pushing a shaft 79 inwardly against a spring 83 by a knob 85, which is turned to set the alarm for the desired period. The clock rotates the shaft 79 through gears 82, 81, and a clutch 80 until a finger 84 at the front of the shaft reaches a slot 87 in the plate 64, when the spring 83 pushes the shaft forward, demeshing the gears, and a clapper on the spring strikes a bell 78. The apparatus is shown connected to a fourposition switch with cam-operated contacts by which it may be caused to control the supply to any one of a cooker switch 91, a socket 92, and an oven switch 93, or to none of them. The switches 91, 93 supply current alternatively at 110 or 220 volts from a three-wire supply system. the time switch contacts 24, 26 and 25, 27 respectively controlling the 110 and 220 volt circuits.