GB992433A - Temperature-responsive programme switches - Google Patents

Abstract

992,433. Tumbler driers. ROBERTSHAW CONTROLS CO. Oct. 19, 1962 [Nov. 2, 1961], No. 39729/62. Heading F4G. [Also in Division H2] Clothes within a perforate drum 22, Fig. 1, of a tumbler drier are heated by a current of air heated by a gas burner 30 which is drawn through the drum by a blower 38, the drum and blower being operated by a single motor 44. The flow of burner fuel is controlled by a pressure-regulating valve 54, a solenoid-operated shut-off valve 58 and a fuel control valve 56 which is automatically adjusted by a temperature control bulb 60 adjacent the air outlet of the drum to maintain the temperature of the exhaust air substantially constant. A further temperature control bulb 68 is located adjacent an auxiliary electric heater 66 to be responsive to the temperature of the air adjacent the drum inlet and is connected to a programme switch assembly 64 in step-by-step movement to electrically energize one or more of the drier control elements, viz. motor 44, valve 58 and heater 66 at selected points within the drying cycle. The programme switch assembly 64.-Fig. 2 comprises a switch-operating cam-plate 72 pivotally mounted on a shaft 74 which is biased by a torsion spring 104 about the shaft 74 and has spaced ratchet teeth 80, 82 projecting therefrom. Co-operating with the plate 72 is a pawl arrangement comprising pawl levers 138, 140 which are pivoted at one end by a knife edge 148, Fig. 4, bearing downwardly against a fulcrum member 150 and movable stud 176, and a fulcrum projection 174, respectively. The levers 138, 140 have teeth 142, 164, respectively, which are engageable with the ratchet teeth 80, 82 and the two levers are also pivotally movable relative to each other, about an axis defined by projections 152 on the lever 138 received in a depression 154 in the lever 140. The levers are biased by springs 160, 168 respectively to urge the teeth 142, 164, respectively, into and out of the path of movement of the ratchet teeth. The movable stud 176 forms part of an expansible wafer assembly 178 which is connected by a conduit 70 to the temperature control bulb 68 so as to control the position of the lever 140 and a cam 188 on a manually-operated dial shaft 130 co-operates with a temperature calibration screw 198 to adjust the normal rest position of the fulcrum member 150 and so predetermine the temperature of the drying cycle. Operation is initiated by inwardly pushing the dial shaft 130 to rotate an actuating lever assembly 112 to transmit the motion via the torsion spring 104 to the cam-plate 72 which thereby pivots in clockwise direction about the shaft 74 until the ratchet tooth 82 abuts pawl tooth 142. Continued rotation of the lever 112, however, under the spring bias forces tang 136 thereon into contact with a projection 252 on a reset lever 240 to pivot it in counter-clockwise direction about its pivot 242 to cause a projection 246 thereon, which forms a seat for the pawl teeth, to move upwardly and carry the teeth 164 and 142 clear of the teeth 80, 82 and hence the cam plate 72 to rotate under the bias of spring 104 until the tooth 80 is rotated beyond the tooth 142. Dial shaft 130 is then released and driven outwardly by a spring 122 and pawl tooth 142 drops in front of tooth 80 as the actuating lever 112 returns to its initial position and the cam-plate 72 is in the furthest position to the right (Fig. 6, not shown), to initiate the drying sequence. In this position, plungers 92, 94, 96, Fig. 3, which respectively open and close switch contacts 92a, 92b to control the auxiliary heater 66, contacts 94a, 94b to control the heater on-off valve 58 and contacts 96a, 96b to control operation of the motor 44 are not contacted by projecting cams 86, 88, 90 on the cam plate 72 so that the full heat is generated for tumbler drying. The effect of heat on the bulb 68 causes the wafer assembly 178 and the stud 176 to move upwardly to cause the pawl levers 138, 140 to pivot, allowing the cam-plate 72 step-by-step movement under the urging of the spring 104 due to the engagement of the teeth in the several positions shown in Figs. 6 to 9, release of the teeth being effected by the reset lever 240. The different positions of the camplate 72 ensures the plungers 92, 94, 96 are sequentially engaged by the cams 86, 88, 90, respectively, so as to open the circuits between the auxiliary heater 66, valve 58 and motor 44 according to the desired drying programme. Specification 926,061 is referred to.