Patent GB-554605-A (GB)
Title: Improvements in or relating to lever-operated electric switching devices
IPC: H01H23/02
Filed: 1941-12-18
Abstract: 554,605. Variable-pitch propellers. CHILMAN, J. A., and MORRIS, E. H. Dec. 18, 1941, Nos. 16363/41 and 455/42. [Class 114] [Also in Group XXXVII] A switch, of the type in which an actuating level 18 rocks a contact lever 10 into engagement with fixed contacts 17 and locks it in that position by means of a shaped cam part 22 at its limit of movement, is provided with interchangeable. means such as a cover 24 with a given length of slot 25, so that, by varying the cover, the movement can be restricted so that the contacts will engage but the lock will not operate, so that the switch will open on release of the lever, by action of a spring such as 20. Modifications are described in which two such contact levers are side by side on the same pivot but reversely mounted, operated by the same lever, and in which each contact lever has a contact member as 15 at both ends co-acting with further fixed contacts. In a further modification, Fig. 7, two such switches 58, 59 are mounted side by side so as to be selectively operated by a single handle 65 acting in a "gate" in a changeable cover-plate 72. The actuating levers 69, 68 extend from separate sleeves 67, 66 slotted axially at 71 to allow the handle to slide, with its mounting sleeve 62 from one to the other. Inadvertent actuation of a switch may be prevented by making one or more of the slots in the plate 72 narrow so as to prevent movement of the handle 65 into it until an outer sleeve of the handle is pulled out against a spring. A selective switch for controlling, for example, the variation in pitch of air-screws, comprises two double-pole double throw switches 100, 101 mounted side by side, and the contact levers oppositely arranged so that one can be locked in engagement, by the cam-action of the operating lever, when the handle 107 is moved to its limit in each direction. The operating levers 102, 103 are mounted on separate sleeves 104, 105 which are slotted at 106 so that the handle, when moved to the rightwill actuate switch 101 alone but when moved to the left will operate both switches, the movement being controlled by a "gate" in cover plate 116, Fig. 13. When the handle is to the left, movement into slot 118 operates switch 100 but switch 101 "idles." When to the right, movement into slot 119 moves lever 103 to operate switch 101 only but an extension 110 of sleeve 108 is rotated and a pawl 112 engages with sleeve 104 so that, on returning handle to mid position, sleeve 104 and lever 102 actuate switch 100 to an extent which does not lock, the contacts in engagement. An electromagnet 115 releases the pawl when desired and allows the switch 100 to reverse. As applied to controlling the pitch of airscrews, the switches 100, 101, Fig. 15, would be under the control of the pilot to over-ride the normal engineer's control switch 129, which gives, through contacts 137, a finer setting of the blades, and through contacts 138 a coarser setting, and through contacts 139 an automatic speed control, of the reversible motor 120 with forward and reverse field windings 121, 122. With the pilot's switch in normal position, the switches are as shown, with the engineer's switch operative. By moving switch 100 to position 100a, the pilot can "feather" the blades at a high rate by the addition of voltage from a "booster" 127, until the cutout 123 opens. To "unfeather," he may either move switch handle to mid position which restores engineer's control or operate the blades at high rate by using the reverse switch 101 which would move to 101a (Fig. 15). The "booster" then passes current to the field winding 122 through cut-out 125 and the blades may be moved to reverse at a high rate. When reverse is no longer desired, the movement of switch handle to mid-position actuates switch 100 as above explained to a position at which it "feathers" the blades until the cut out 124 closes and high voltage current passes through line 144 to electromagnet 145 to release switch 100 by lifting the pawl 112. Thus when the blades, in the course of their "unreversing" reach normal fine-pitch setting the operation stops and normal engineer's control is restored.