Patent GB-675483-A (GB)
Title: Improvements relating to thermo-responsive control switches
IPC: H01H37/36
Filed: 1949-02-01
Abstract: 675,483. Thermal switches. GENERAL MOTORS CORPORATION. Feb. 1, 1949. [Feb. 12, 1948] No. 2698/49. Class 38 (v). [Also in Groups XIII and XXXV] In a control switch for a cooker 160, Fig. 2, a thermal element (see Group XIII) comprises a capsule 20, Fig. 1, communicating with a pilot bulb and formed of two nickel-ironchrome discs 22, 24 welded together on circumferential flanges 36. A follower 26 welded to the upper disc 22 bears on a projection 42 of a primary lever 44 pivoted at 46 while, at the end of the long arm of the lever, a post 52 is riveted to one end of a tension leaf spring 54, in turn riveted to the contact end of a toggle lever 56. Also at this end of the lever 56 a U-shaped member 68 is riveted and its limbs project into a porcelain contact case 70 for connection by split pins to L-shaped contact members 72, 74, Fig. 2, which co-act at these ends with main terminals 76, 78. A pair of ears 58, Fig. 4 at the opposite end of the lever 56 ride in a pair of notches 60, Fig. 1, in a frame 50 and are connected to toggle springs 62 anchored to a curve-sectioned metal strip 64 at the opposite end of the frame 50. A control knob 94, Fig. 1, is clipped on to a sleeve 88 which not only, by rotation, raises or lowers an inner plug 84 bearing the capsule 20 but also carries both a cam 121 co-acting with a spring 127 and the hub 137 of a cam 139, Fig. 6. The spring 127 holds the knob frictionally in any set position and also forms a stop at the "off" and "broil" positions at the extreme ends of the temperature range. When the knob 94 is turned to the "broil" position a projection on the cam 121 moves the cam 139 round to raise a cross member 147 and, resting thereon, a U-shaped member 161, Fig. 6 pivoted by a pin 163 (Fig. 1) on the frame 50. Adjustably screwed to the yoke 165 (Fig. 1) of the member 161 is a member 167 with an aperture 169 which normally retains a tongue 171 on the end of the primary lever 44 to prevent rising thereof. Starting from cold, for normal heating the knob 94 is set to the legend indicating the desired temperature for the cooker and the capsule 20 is thus raised so that at the required temperature the primary lever 44 and the toggle 56 are moved to lower the member 68 and thus open the contacts between the L- shaped members 72, 74 and the main terminals 76, 78 (Fig. 2) connected to supply lines 80, 82. Before the thermal element operates, however, a circuit is made through contact members 72, 74 to terminals 155, 157 (Figs. 2, 6) so that a heating element 159 of a lower part of the cooker is connected across the supply lines 80, 82 while a circuit is made through the member 74 and a terminal 193 which is permanently connected thereto so that upper heating elements 187, 189 are connected in series to a half voltage supply across the line 82 and a line 191 from the neutral supply line N. In the position for broiling, with the cross member 147 raised by the cam 139, the lower element 159 is disconnected by the raising of pins 149 attached to the member 147 (Fig. 6), because of the raising of the transverse legs 151, 153 of the L-shaped members 74, 72. At the same time, however, the U-shaped member 161 raises a push bar 177 to which it is coupled and which in turn raises a blade 179 (Fig. 2) into contact with a stationary member 183 which is permanently connected to the junction of the L-shaped member 72 since the latter is urged upwardly by a spring 197, Fig. 6. In this way the supply line 80 is connected by way of the member 72, member 183, the blade 179 and a conductor 185 to the upper heating elements 187, 189, the former of which is thereby subject to full line voltage between the supply lines 80, 82, while the latter is subject to half voltage between line 80 and the neutral line 191. For quick pre-heating, the knob 94 is first turned to the "broil" position and then immediately returned to the desired baking temperature whereby the tongue 171 of the primary lever 44, Fig. 1, is. first released from the aperture 169 by the raising of the U-shaped member 161 which however is not allowed to drop, as are the pins 149, with the return of the knob, because a shoulder 173 on the adjustable member 167 rests on the tongue 171. Thus in the preheat position the upper heating elements 187, 189 are fully energized as for broiling but since the pins 149 are dropped the lower element 159 is also energized for quick preheating. However as the cooker compartment 160 approaches the set temperature, expansion of the capsule 20 trips the primary lever 44 and the tongue 171 is lowered into the aperture 169 to allow the U-shaped member 161 to be pushed down by a spring 230, Fig. 1, on the push bar 177 and thus for blade 179 to be lowered. This will give the circuits for normal heating, as previously described, controlled by the thermal element opening and closing the contacts between the members 72, 74 and the terminals 76, 78.