Patent GB-498780-A (GB)
Title: Improved safety mechanism for clockwork time fuzes for projectiles
IPC: B62H5/06
Filed: 1938-02-22
Abstract: 498,780. Projectile fuzes. MEFINA SOC. ANON. Feb. 22, 1938, No. 5576. Convention date, May 25, 1937. [Class 9 (i)] Relates to a safety mechanism for clockwork time-fuzes for projectiles adapted to be set over a period of at least a fraction of a revolution, of the kind in which the hammer, tensioned by a spring, is held in the unarmed position by a centrifugal trigger itself held inwards by a time regulating member driven by the clockwork until, at the end of a period corresponding to the previously adjusted setting, the time regulating member releases the trigger which in turn, under centrifugal force, releases the hammer, the fuze also including a centrifugally operated safety bolt. According to the invention, this safety bolt determines the zero position of the time regulating member and is itself locked in this position against accidental release by the time regulating member, the arrangement being such, however, that the safety bolt is positively released by the time regulating member to allow the setting of the fuze, but when the time regulating member is restored to zero it again automatically assumes the interlocked position except when it is subjected to centrifugal force exceeding a certain limit during flight, in which case it is maintained in the released position and thus permits the centrifugal trigger to release the hammer and effect the explosion of the projectile. As shown, the spring-pressed hammer 10 is held in the unarmed position by a centrifugally-operated pivoted trigger 13 which engages in a notch 15 therein. The tip 16 of the trigger bears against the inner face of an annular abutment 17 of a toothed crown 18 which constitutes the time regulating member and is in connection by means of a pinion 19 with the driving shaft 20 of the clockwork. A gap 21 in the abutment 17 is formed with oblique surfaces 22, 23, whilst in the crown 18 a space between two teeth is omitted at a place previously determined by the position of gap 21, so that an abutment 24 is formed whereby the maximum setting is fixed and the gap 21 cannot in any case, during the setting operation, i.e. turning the crown 18 in an anticlockwise direction from the zero position shown in Fig. 2 to the position of maximum setting shown in Fig. 3, come before the tip 16 of trigger 13 and thereby release the hammer. Slidably mounted beneath the trigger 13 is a safety bolt 27 normally drawn inwards by a spring 28. This bolt is formed with a head 29 having an inclined inner surface 30 and a curved outer surface 31 which cooperates with the surface 23 on the abutment 17 in the zero position to prevent a clockwise rotation of the crown 18, whilst the bolt itself is locked against outward movement. On anticlockwise rotation of the crown 18 to set the fuze, the surface 22 on the abutment 17 engages the oblique surface 30 on the head of the bolt 27 and moves the latter outwardly into the Fig. 3 position against the spring 28. Should the fuze be eventually set back to zero, the bolt 27, owing to the action of the spring 28, automatically moves back into its original interlocking position. After discharge of the projectile, however, the bolt 27 is held in its outward position by the action of centrifugal force against the spring 28 and, when the gap 21 in the abutment 17 comes opposite the trigger 13, the latter moves outwardly under centrifugal force and releases the hammer 10. According to a modification, the member 27 may be in the form of an eccentrically mounted swinging bolt.