Patent GB-569715-A (GB)
Title: Improvements in or relating to mechanical time fuzes and other delay-action mechanisms
IPC: F42C9/04
Filed: 1940-05-04
Abstract: 569,715. Time switches. VENNER TIME SWITCHES, Ltd., and BROOK, W. E. May 4, 1940, No. 8043. [Class 38 (v)] [Also in Group XXI] Delay-action mechanism of the kind comprising a spring-energized or other driving- element and a control-device (e.g. an escapement) which regulates the speed of movement of the driving-element, is provided with means for initiating immediate operation, before the expiration of the time delay, on disturbance of the mechanism through external conditions; and with means for rendering the mechanism ineffective for a short period after setting it. The invention is applicable to control switches for electrical apparatus, and it is stated that any form of inertia-operated, magnetic, or light-sensitive device may be used to effect the premature operation of the mechanism according to the nature of the external conditions relied upon, such as changes in pressure, temperature, magnetic field, or light intensity. It is also stated that the mechanism may be electrically driven with an eddy-current brake-form of controldevice, and may be adapted to initiate a plurality of operations at different times. The mechanism is shown as applied to a projectile time-fuse comprising a casing 1, carrying the spring-loaded firing-pin 5, and its associated mechanism, and having the usual shell, &c., attachment-neck 2, which is internally threaded to receive the detonator. A driving spring 7 has one end secured to the barrel 6, and the other end to a sleeve 10, the lower end of which is fitted with a ratchet-wheel 11 co-operating with a spring- pressed pawl 12. A timing dial 18, fast on the upper end of the sleeve 10, is graduated from a zero-slot 20 with which a knife-edge 31 on a trigger-arm 30 is arranged to co-operate. The arm 30 is pivoted on a detent-plate 22, freely mounted on a fixed stem 23 and through which the firing-pin passes. The plate 22 carries a cranked timing-arm 27, the tip 28 of which is adapted for selective engagement with a series of notches 29 on the upper edge of the barrel. A detent-arm 34, pivoted on the plate 22, engages a groove 35 in the head of the firing-pin to hold the same retracted until the timer end of the arm has travelled down the slot 20 sufficiently to swing its outer end clear of a peg 33 on the detent 34. The latter is then pulled away from the firing-pin by a spring 32. A removable pin 37 may be fitted to hold the arm 30'against entry into the slot 20 during the winding-up of the spring 7. The speed of rotation of the barrel 6 is controlled by a clock-pattern escapement 38 through a two-part gear-train 39, 40, which is driven from a gear 41, mounted through a boss 42, under the barrel. The gears are mounted between a pair of plates 13, 14, each formed in two intermeshing parts 13a-13b, 14a-14b, leaving small clearances to permit slight rotational movement of the parts 13b, 14b relative to the fixed parts 13a, 14a. The main gear train 40, which meshes with the gear 41 on the barrel, is carried by the fixed parts 13a, 14a, the escapement driving-gear being mounted on the movable parts 13b, 14b, the latter being normally spring- urged to disengage the gears 39, 40. The latter are normally held in mesh by the engagement of a knifeedged stop 53 on the underside of the part 14b of the plate 14, with a detent .55 pivoted on the fixed part of 14a. The latter is held in its position, shown in Fig. 6, against the pull of a spring 67 by the abutment of a pin 56 on the detent with the tail of a pivoted lever 57. The other end of this lever has a pin- and-slot connection with a trip lever 60, the further end of which is normally held against outward movement by abutment with the curved surface of a D-section cam 62 on the pivot-spindle of an arm 64 carrying a pair of counterweights 65, 66. If the mechanism is disturbed, the arm 64 is rocked whereby the cam 62 is turned to free the trip-lever 60, the detent 55 is pulled clear of the stop 53, and the part 14b is shifted by its spring to disengage the gears 39, 40. The barrel 6 is thus freed from the restraint of the escapement 38 to effect a premature or sudden release of the firing-pin. Figs. 5 and 6 show check-means for preventing this premature operation until after a short safety-period, comprising a lever 68 which is pivoted on the main gear-carrying part 14a, and carries at one end a toothed segment 69, spring-loaded to mesh with a gear 40a of the main train. A pin 70 at the-other end of the lever engages a check-lever 71 fitted with a key 73, arranged to engage a stud 74 on the counterweight 65 of the rocker-arm 64, to hold the latter, and the detent 55, against displacement. When the segment 69 passes out of engagement with the gear 41a the pin 70 is allowed to clear the lever 71, which is then retracted by its spring 72 to disengage the key 73 and stud 74, thus freeing the rocker-arm 64. For maintaining the check-means operative up to setting or priming of the mechanism, the lever 68 is locked by abutment with the uper end 76b of a spring- loaded plunger 76, which is held in its operative position by a shiftable lever 77 having a hooked end adapted to engage a groove near the headed lower end of the plunger. When the lever 77 is swung clear of the plunger, the latter is moved by its spring 85 until its head abuts the main safety-pin 75, for the firing-pin 5. The lever 68, however, is still fouled by the upper end of the plunger until further movement of the latter is permitted by the removal of the safety-pin 75.