Patent GB-650601-A (GB)
Title: Improvements in or relating to control devices responsive to physical conditions andembodying conjointly operated electric switches
IPC: D06F34/08
Filed: 1948-10-11
Abstract: 650,601. Thermal switches; actuation of switches; switches held set and freed mechanically. ROBERTSHAW-FULTON CONTROLS CO. Oct. 11, 1948, No. 26476. [Class 38(v)] [Also in Group XIII]  A control device comprises first and second switching means respectively controlling first and second appliances, means responsive to a temperature, pressure, or other condition caused by the first appliance to simultaneously open both the switching means, and auxiliary switching means also operating simultaneously to keep the circuit of the second appliance closed until a further change of condition whereupon this circuit is also opened. The device is described applied to a clothes drier in which hot air is blown by a fan over clothes placed in a rotary drum and ensures that the clothes are not too hot to handle at the end of the drying period by switching off the heaters earlier than the motor driving the fan and drum. An L- shaped frame 10 has a channelshaped cover 14 supporting a spigot 24 on which rotates a bush 26 carrying a handle 28. A cam 38 formed on the bush 26 engages a recess 40 in the handle causing it to rotate therewith and co-operates with a switch operating bar 42 whereby the latter is urged inwardly against a leaf spring 46 and the supply circuit opened when the handle 28 is turned clockwise to the " off " position, in which it is arrested by a cam step 44, Fig. 5. A stud 48 threaded in the spigot 24 has a detent 50 engaging a slot 52 in the bush 26 so that a switch operating button 62, on a diaphragm 54 supported by the stud 48, is moved axially on rotation of the handle 28. The diaphragm 54 communicates by a tube 56 to a liquid-filled bulb 60 subjected to the drier temperature. The button 62 operates an apertured actuating lever 64 having a knife edge 66 engaging a bearing 68 in a bracket 70 fixed to the frame 10, the lever being connected by a tension spring 72 to the cross bar 74 of an R-shaped control lever 76 having its legs 78, 80 pivoted in knife-edge bearings 83 on the sides of a channel-shaped support 84. The support 84, Fig. 64, as projections 86 on vertical webs, whereby its rear edge is pivoted to the frame 10, and carries at the front a screw 88 by which the tension of the spring 72 is adjustable. The lever 76 carries an inverted U-shaped arm 92 having lugs 94 co-operating with shoulders 96 on the levers 76 and provided at the top with a hook 98 which engages beneath the upper bar of the lever 76 to limit its movement with respect thereto. An upward extension of the lever carries an insulating block 100 supporting a bridging contact 102 which co-operates with fixed contacts 104, 106. The arrangement is such that on expansion of the diaphragm, the spring 72 is moved overcentre and the contact 102 closed, the spring 72 opening the contact 102 on subsequent contraction of the diaphragm. Back contacts 118, 120 on the contacts 104, 106 and further fixed contacts 112, 114 respectively co-operate with bridging contacts 122, 124 mounted on insulating plates 126 carried by flexible members 128 on the opposite bifurcated ends of a lever 130. The lever 130 is pivoted by projections 132 in a bracket 90 and can be held in the closed position against the bias of a compression spring 134 by a rocker 136, Fig. 6, pivoted at 138 to an extension 140 of the bracket 90 and biassed by a spring 146 secured to the support 84. On depression of a button 152a stem 154 thereon engages the lever 130 beneath its pivot 132 whereupon a projection 148 on the lever 130 is caught by a notch 150 in the rocker 136. A lateral extension 144 on the actuating lever 64 engages an incline 142 on the rocker 136 whereby the lever 130 is unlatched on movement of the lever 64, due to expansion of the diaphragm 54. An insulating housing 158 secured behind the frame 10 carries a pair of contacts 162, 164 with which a contact bridge 166 carried by an insulating arm 172, co-operates. The arm 172 is pivoted at 171 in a mounting 173 and urged by a spring 178 to the closed position, and is controlled by a pin 180 engaging a plate 126 on the lever 130 so that the bridging contacts 122, 124, 166 act conjointly to engage their respective fixed contacts on depression of the button 152. A pair of spring contact arms 182, 184, also in the housing 158, are connected by terminals 192 to the supply lines 208 and can be conjointly disengaged from their respective fixed contacts 194, 196 by an underlying insulating plate 202 pivoted about a projection 200 and moved by the end 206 of theoperating bar 42, Fig. 7. A motor M drives the clothes drum and the fan which blows air heated by elements A, B. Counterclockwise movement of the handle 28 from the " off " position to the desired temperature setting determined by the dial 30 permits the bar 42 to withdraw and the supply contacts 182, 194 and 184, 196 to engage. Depression of button 152 then simultaneously closes the bridging contacts 122, 124 and 166 and completes the heater circuit from a line 208 through contacts 184, 196, contact 166, heaters A, B, contact 124, connection 198 and contacts 194, 182. The motor circuit is completed from a line 208, contacts 182, 194 and contact 122 to earth. The hot air blown through the drum expands the diaphragm 54 and at the desired temperature the actuating lever 64 closes the conact 102, the lever 130 being simultaneously unlatched by the extension 144 on the lever 64'and the contacts 122, 124 and 166 opened. The heater circuit is thereby interrupted but the motor circuit remains closed through the contact 102 whereby the clothes continue to be dried. On contraction of the diaphragm 54 to a temperature at which the clothes can be handled, the contact 102, snaps open and manual operation is necessary to initiate another drying cycle by pressing the button 152. In a modification the button 152 is dispensed with and its function performed by the handle 28 which is arranged to be also axially movable. The device may alternatively control fuel admission valves for burners and be controlled by the fuel pressure as well as by the heat produced by the fuel.