Patent GB-896018-A (GB)
Title: Thermostatically controlled electric switch
IPC: H01H35/26
Filed: 1958-10-31
Abstract: 896,018. Thermal switches; cam-operate switches. HART MANUFACTURING CO Oct. 31, 1958 [Oct. 31, 1957], No. 35049/58 Class 38 (5). [Also in Group XXXV] A switch assembly for thermostatically controlling a bake element A or a broil element B or for connecting both for preheating purposes, has auxiliary moving contacts 12, 13 co-operating with fixed contacts 10, 11 under the control of a slidable cam 32 having a short recess 32a and a long recess 32b. In the position shown in Fig. 2, the cam 32 holds both contacts open, but if moved to the central position wherein a lug 31 enters a locating recess 38 in a spring 39, both contacts are allowed to close. If the cam is then moved to the right-hand position, contacts 11, 13 remain closed due to the long recess 32b, but contacts 10, 12 are opened by the end of the recess 32a. The contacts 10-13 are connected to the elements A, B and to main contacts 16- 21, as shown in Fig. 7. The main contacts consist of bridging contacts 20, 21 arranged to bridge contact pairs 16, 17, and 18, 19, the former controlling the element B and the latter the element A. Contacts 20, 21 are loosely carried by an insulating member 40 itself loosely carried on a U-shaped member 50 which is pivoted to the lower end of a fixed frame 51 and is connected by a tension-spring 53 to a rocker 52 pivoted on a stud 49 fixed in frame 51. A thermal capsule 55 is biased by a spring 48 and has a rod 54 on which is adjustably threaded a sleeve 58 which bears on rollers 60 carried by the rocker 52. The sleeve 58 is adjustable by a knob 85 which also carries with some lost motion a ring 86 carrying a pin 88 which engages a notch 89 in the cam 32. For baking, the knob is rotated to adjust the capsule for the desired temperature, the cam 32 at the same time being moved to its middle position to allow contacts 12, 13 to close. The rocker 52 is also moved to snap the spring 53 across dead centre to close contacts 18, 19, 21. The other main contact 20 is, however, prevented from engaging its fixed contacts by a latch 70 pivoted at 73 which has a portion 76 which is below a step 77 on the right-hand end of member 40. The element A then cycles on and off under the control of the capsule. The knob has a spring ball 94 arranged to engage either of two recesses 97, 98 in the ring 86, it normally engaging the former. When the knob is rotated for baking, the ring rotates with the knob until the cam is held by spring 39, further movement of the knob forcing the ball 94 out of the recess 97. For broiling, the knob is further rotated until a shoulder 93 thereon engages a lip 91 on the ring 86 which is then moved positively to move the cam 32 to its right-hand position where the contact 12 is opened to de-energize the bake element. At the same time an arm 35 on the cam 36 moves the latch 70 to the right to free the right-hand end of member 40 so that contact 20 can close the broil circuit. If pre-heating is required followed by baking at a set temperature, the knob is then moved back to the required setting and owing to the engagement of ball 94 and the recess 98, the ring 86 is also moved to its centre position to allow contact 12 to close to re-energize the bake element, the broil element remaining energized until the required temperature is reached, when the contacts 20, 21 open, contact 20 subsequently being held again by latch 70. A modified knob is described with reference to Figs. 10-13 (not shown).