Patent GB-1374542-A (GB)
Title: Auto-synchronising drive assemblies
IPC: F41A9/30
Filed: 1972-12-01
Abstract: 1374542 Machine gun GENERAL ELECTRIC CO 1 Dec 1972 [10 Dec 1971] 55538/72 Heading F3C A machine gun comprising a barrel 12, Fig. 4, disposed for recoil and counter-recoil movement in a receiver 10 and an ammunition feed mechanism having first teeth spaced apart by a uniform tooth pitch, each for engaging and advancing a round of ammunition, and second teeth spaced apart by said uniform pitch, an ammunition feed driving means coupled to said barrel for transmitting a recoil stroke and a counter-recoil within each cycle, said driving means comprising a first element having a stroke for engaging and driving, during said recoil stroke, one of said teeth a first distance in the rounds feed direction, and a second element having a stroke for engaging and driving, during said counter-recoil stroke, another one of said second teeth a second distance in the rounds feed direction, the mid-point of said stroke of said first element being spaced from the midpoint of said stroke of said second element by a distance equal to an odd integer multiple of half tooth pitches of said feed mechanism, whereby said driving means drives said feed mechanism up to one tooth pitch during the initial cycle and one tooth pitch during each subsequent cycle. The ammunition feed driving means comprises a shaft 32 having two fourtooth sprockets 34 and having a longitudinally movable four-tooth ratchet wheel 40 splined thereto, a shaft 36 having two four-tooth sprockets 38 and having a longitudinally movable four-tooth ratchet wheel 42 splined thereto, a crank assembly 44 which can alternately axially move the wheels 40, 42 forwardly and rearwardly of the gun barrel, and feed cam plates 46, 48, each having a respective cam slot 50 to receive a respective drive roller (not shown) mounted on the barrel 12. Each cam plate 46 or 48 has a travel limiting slot which receives a limit pin, the latter being fixed to a respective side wall of a feed assembly 18 and each cam plate has a respective slot 52 for oscillating about an axis "A", Fig. 5, of a crank-shaft 54, the latter having pins 56 respectively mating with the slots 52. The crank-shaft 54 carries downwardly driving pawls 58 and upwardly driving pawls 60, the pawls alternately engaging the wheels 42, 40, Fig. 4. An autosynchronism feed drive can be provided by having an odd number of teeth on the feeder sprockets and on the ratchet wheels so that the driven pawls, the centres of whose driving strokes lie in a plane which includes the axis of the respective ratchet wheel, cannot reverse their roles, since when the feeder is in a synchronous position, only one drive pawl can enter a ratchet tooth. Alternatively the mechanism can be made autosynchronous by displacing the driving pawls so that the mid-points of their respective strokes with respect to the axis of the drive ratchet are separated by an angular distance equivalent to an odd number of half tooth spaces of the drive ratchet wheel. This is accomplished by raising or lowering the feed drive rocker shaft centre line so that it does not lie in a plane which includes the axis of the feeder shafts 32, 36. The driving pawls 58, 60 are shown at the upper extreme of the rocker shaft operating stroke in Figs. 1A, 1B and 1C, and at the lower extreme of the rocker shaft operating stroke in Figs. 2A, 2B and 2C. The mid-points of the operating strokes of the panels 58, 60, Figs. 3A and 3B, are separated by an angular distance equal to an odd number of half-tooth spaces. The ratchet wheel 42, Figs. 1A, 1B, 1C, 2A, 2B, and 2C, is supported by the shaft 36 which extends to drive the sprockets 38. The shaft 54 is caused to move upward during the counter-recoil motion of the gun mechanism and downward during the recoil stroke. The pawls 58, 60 are urged against the toothed face of the ratchet wheel 42 by springs 62 and 64 respectively in co-operation with retaining means 66, 68.