GB1487255A - Time switch device - Google Patents

Abstract

1487255 Time switches DIEHL 13 Dec 1974 [16 Jan 1974] 53915/74 Heading H1N A time switch for a heating element 27 the heating power of which is variable by an adjustable thermostat 29 has a first pair of timed contacts 23 in series with a second pair 18 together in parallel with a series circuit of a third pair of timed contacts 22 and contacts of the thermostat 29, and comprises a manually rotatable shaft 1 coupled to drive means via a gear 3 and first slipping clutch 2 and carrying operating means for said first and third pairs of contacts 23, 22, (preferably in the form of two cam tracks 8) fixedly mounted on the shaft 1, and operating means for the second pair of contacts 18 (preferably in the form of a cam track 7) fixed relative to a gear 5 which is restorable by said drive means when manually rotated away from its initial position by shaft 1 via a second slipping clutch 4, said gear 5 having means 16 co-operating with a fixed stop 17 to limit its angular setting rotation; the arrangement being such that manual rotation of shaft 1 in a setting direction (12, Fig. 2, not shown), which is opposite to the timing drive direction (30), causes the gear 5 and cam 7 to be turned until arcuate dog 16 abuts stop 17, clutch 4 allowing further rotation to set cam 8 to a greater angular extent while leaving cam 7 set. The drive means is a synchronous motor 25 coupled to gearing 9, 10, 11. Gear 5 has a toothless portion such that pinion 11 automatically ceases to drive it after restoring it to its initial (contacts 18 open) position. To enable gear 3 and segmental gear 5 to be set without reaction on the drive pinion 11, this pinion is mounted in slotted bearings to ride free of gears 5 and 3 during setting rotation of shaft 1, a spring 13 ensuring its return into mesh. Cam 8 carries two tracks for contacts 23 and 22 respectively, hence the angular displacement between them is fixed, while the displacement relative to cam 7 (and thus contacts 18) is selectably variable. This displacement can be reduced by reverse rotation of shaft 1 without moving cam 7 since the drive over gears 9, 10, 11 holds the gear 5 stationary. The three pairs of contacts 18, 22, and 23 are closed by setting rotation of shaft 1 and synchronous motor 25 is energized to drive shaft 1 back to its start position, the contacts 18 opening after a fixed time interval (t 1 , Fig. 4, not shown) due to the limit set by stop 17; the contacts 22 then open after the preselected interval (t 2 , t 3 or t 4 for example) and contacts 23 open after a further (fixed) time interval (t 5 ). As applied to an electric oven (for example) a fixed thermostat 28 ensures an initial period at high temperature (say 200‹ C.) until contacts 18 open, then the thermostat 29 allows a lower temperature (say 130‹ to 180‹ C.) for a period set by adjustment of cam 8 according to the volume of food being cooked, for example, and contacts 23 keep motor 25 running until a final fixed cooling period (t 5 ) expires whereupon contacts 23 open to switch off motor 25 and lamp 26, which latter indicates that the food is ready to eat.