Patent GB-833404-A (GB)
Title: Improved clock-driven timer
IPC: G04C23/16
Filed: 1958-03-03
Abstract: 833,404. Time switches. GENERAL MOTORS CORPORATION. March 3, 1958 [March 20, 1957], No. 6697/58. Class 38 (5). A cooker timer comprises a synchronous electric motor 42 driving normal clock hands 34, 35 having a setting knob 36, cooking cessation time being set by knob 37, which moves an indicator 33 rectilinearly over scale 31, and cooking duration time being controlled by knob 38, which moves an indicator 32 rectilinearly over scale 29 and has " Off and " Manual " positions. The switch 70 (Figs. 2 and 4) comprises moving contacts 73 and 74 carried respectively by spring blades 75 and 76 secured on insulator 77 and biased to engage fixed contacts 71 and 72. An actuator yoke 68 is pivotally mounted on insulator 77 and carries an insulator member 61 shaped as shown in Fig. 4 to engage spring blades 75 and 76. The free end of yoke 68 is forked and located under a shoulder on spool 67 loosely carried on a sleeve 64 slidable on the clock spindle. A spring 66 urges sleeve 64 towards the front of the timer, and in the " off " condition of the timing mechanism (see below) the sleeve 64 is allowed to move and a shoulder thereon moves the spool 67 to depress yoke 68 and thereby open the switch contacts. When the timing mechanism forces sleeve 64 back against action of the spring 66 the yoke 68 is permitted to return under action of the blade springs 75 and 76 and thereby close the switch. The timing mechanism comprises two pulley assemblies 50 and 51 loosely journalled on the clock spindle and having toothed peripheries. A flange 56 is secured to pulley assembly 50 and is half the diameter thereof. A cable 120 is fixed around flange 56, idler pulleys 123 and 124 and carries indicator 33 such that the angular position of pulley assembly 50 is shown on cessation time scale 31. Another cable 125 passes around pulley assemblies 50 and 51 in opposite directions (Fig. 14, not shown) and operates a differential pulley unit carrying indicator 32 such that this indicates on the duration scale 29 the position of pulley assembly 51 with respect to pulley assembly 50. Arcuate slots 99, 100, 101 (Fig. 6) in pulley assembly 51 loosely accommodate lugs on the end of a bridge member 63 which is secured to the sleeve 64. Slots in pulley assembly 50 allow the lugs on bridge 63 to enter when the pulley assemblies are angularly aligned and sleeve 64 can then move under action of spring 66 to open the switch 70. This aligned position corresponds with the " off " indication on scale 29. When the pulley assemblies are relatively displaced the edges of the slots in assembly 50 exert a camming action on inclined edges of the lugs on bridge 63 (Figs. 17, 18 and 21, not shown) such that sleeve 64 is forced back against spring 66 and allows switch 70 to close, providing a latch 92 is not effective (see below). Thus the cessation time is determined by the position of pulley assembly 50 whilst cooking duration is determined by the relative displacement of assembly 51. Knob 37 sets the position of pulley assembly 50 but also rotates assembly 51 an equal amount so that their relative position, and therefore indicator 32, is unaffected, Initial movement of knob 37 causes a lock release member 159 (Fig. 2) to move a locking lever 153 (Fig. 6) out of engagement with the periphery of pulley assembly 50, and then hub 165 and pinion 171 thereon are rotated via friction clutch 147, 160. At the same time a twoway pawl 168 is caused to engage a pinion 170 which is loosely journalled on hub 165. Pinions 170 and 171 rotate pulley assemblies 51 and 50 respectively. On release of knob 37 lever 153 locks assembly 50, while pawl 168 disengages pinion 170, leaving assembly 51 free for relative rotation by pinion 141 which is friction driven by knob 38. Bridge 63 and sleeve 64 are thereby moved against spring 66 but latch 92 retains spool 67 in the switch-open position. In the " off " position shown in Fig. 6, a time arm 49 attached to the hour hand spindle can revolve without impediment as a cam 111 on pulley assembly 50 holds a time lever 80, pivoted on assembly 51, out of its path; but in the set position the relative displacement of assembly 50, and therefore cam 111, allows spring 83 to move lever 80 such that a flange 91 thereon is in the path of arm 49. At the same time the other end 87 of lever 80 engages latch 92 to lock it in the latched position shown. As time arm 49 rotates it engages flange 91 at the cessation time less the cooking duration time and pivots lever 80 to disengage the end 87 from latch 92. The assembly 51 is then driven by time arm 49 (through the lever 80) and an upstruck tang 95 on latch 92 is pressed against bridge 63 which remains stationary since the slots 99, 100 and 101 are somewhat longer than the lugs on bridge 63 and the friction between these lugs and assembly 50 is greater than the force exerted by spring 96 on latch 92; after about five minutes the latch 92 is thus forced clear of spool 67 which is then free to move and allows switch 70 to close. Arm 49 continues to rotate assembly 51 until at cessation time it is aligned wtih assembly 50 and the slots in the latter allow bridge 63 to move under spring 66 and open switch 70. When the timer is set to " manual " position the assembly 51 is rotated counterclockwise from the " off " position (Fig. 6) and an extended part of cam 111 maintains the lever 80 out of the path of time arm 49 and clear of latch 92; bridge 63 rides out of the slots in assembly 50 (Fig. 21, not shown), and switch 70 closes.