Safety device for ammunition

The invention is directed to the provision of a safety device to prevent premature detonation of ammunition, particularly low spin projectiles of the type in which a primer pellet is positioned in a rotor which rotates from an unarmed to an armed position upon firing. The safety device is biased under the action of the spring to project into a groove in the rotor so as to be engageable with an end face of the groove. If the projectile is fired with normal acceleration, the resulting force will cause the safety device to become disengaged from the groove in the rotor against the action of the spring. If acceleration is below normal, the safety device will engage the rotor and lock it in an unarmed position. An inertial mass lock is also provided as an additional measure against accidental or premature arming of the projectile. A retard mechanism delays rotation of the rotor to an armed position for a selected time period sufficient for the projectile to advance a safe distance from a gun or launcher before becoming armed.

BACKGROUND OF THE INVENTION 
The present invention relates to a safety device for securing the primer 
pellet in ammunition in a locked position during non-firing conditions, 
and for releasing the primer pellet to an armed position under expected 
firing conditions. 
The problem of securing ammunition such as projectiles, grenades, rockets, 
etc. is gaining in importance as new high performance explosives and 
weapon systems with increased ballistic efficiency are being developed. 
Also, the safety requirements have been increased. For example, the NATO 
MIL-STD (Military Standard) 1316B of Feb. 15, 1977 requires that at least 
two safety devices physically independent of each other must be provided 
in approved ammunition. This requirement has, until now, been difficult to 
fulfill, especially for projectiles with low spin. In practice, the second 
safety device has usually been omitted. 
A known form of safety device has the primer mounted in a rotatable body or 
rotor with radial bores which are engaged by radial projections having a 
wedging effect. This safety combination insures that minor impacts during 
transportation will not cause unintentional detonation, and the unlocking 
of the primer to an armed position will occur only after the projectile 
has traversed a distance of about seven to fifteen meters from the mouth 
of the gun barrel. This known configuration is not considered to meet 
present safety requirements, since the arming of the primer occurs at too 
short a distance from the gun for safety. 
It is therefore a principal object of the present invention to provide a 
secure, electrically ignited arming device for ammunition which insures a 
higher degree of safety than has been provided heretofore, and can be used 
particularly for projectiles with low spin when fired. It is a particular 
object to provide a safety device that will lock the primer in an unarmed 
position if the firing acceleration forces are below normal, and that will 
remain operative even under conditions of substantial transverse 
accelerations. 
It is a further object of the invention to provide a safety device for 
ammunition which prevents unlocking of the primer to an armed position 
under non-firing conditions such as accidental impacts during 
transportation or if the flight of the projectile is abnormally 
interrupted. A broad object of the invention to provide an ammunition 
safety device that is simple, economical, compact, and of great mechanical 
stability. 
SUMMARY OF THE INVENTION 
A safety device for a primer pellet holder installed in ammunition has 
means for guiding the movement of the primer pellet holder from a locked 
to an armed position, and means for securing the primer pellet holder in a 
locked or unarmed position except in response to normal acceleration 
forces during firing. The locking arrangement includes a bore in the 
ammunition housing arranged approximately in line with the direction of 
acceleration, a bolt movable in the bore in the longitudinal direction 
and, preferably, at least partially movable in the transverse direction, 
biasing means normally urging the bolt in the direction of acceleration so 
as to extend into a groove formed in the primer pellet holder defining the 
unarmed position thereof, projecting means, preferably a flange, on the 
end of the bolt adapted to extend into said groove, and locking means on 
the end of the groove defined in the primer pellet holder for engaging 
said projecting flange of said bolt in the unarmed position. 
The bolt is adapted to move against said biasing means out of said groove 
during conditions of normal firing acceleration, thereby permitting 
movement of said pellet holder to the armed position. Preferably, the bolt 
has a conical shape so as to be movable longitudinally and at least partly 
transversely in the corresponding, conical shaped bore, and the bore has a 
cylindrical zone forward of its conical zone for accomodating the movement 
of the projecting flange in the longitudinal direction during 
acceleration. 
In one preferred embodiment of the invention, the primer pellet holder is a 
rotor having the groove formed on at least a part of its circumference. 
The projecting flange extends into the groove and is adapted to engage the 
locking means defined at an end of the groove. In another embodiment, the 
primer pellet holder is a slide movable transversely in a channel, and the 
bolt is oriented in the direction of acceleration or at an angle thereto. 
Preferably, the safety device also includes an inertial mass release means 
for releasing the primer pellet holder for movement to the armed position 
upon firing, and a retard mechanism for delaying the movement of the 
primer pellet holder to the armed position for a predetermined safety 
period. The safety device of the invention permits reliable control of the 
movement of the primer pellet holder from the locked to the armed position 
in accordance with the conditions of normal acceleration upon firing, and 
therefore prevents unintended detonation of the round. Due to the bolt 
being movable transversely as well as longitudinally, transverse 
accelerations during firing of the round can be absorbed without the bolt 
becoming wedged and thereby having its functionality impaired.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIGS. 1 to 3, there is shown a preferred form of the safety 
device for use in an electrically primable projectile M to be fired at 
high acceleration in the direction b.sub.N. Although one embodiment of the 
operative elements of the safety device is shown, it is to be understood 
that other forms may be used which will accomplish the purposes of the 
invention described herein. 
Bore 1 in housing 7 of the projectile M is conically shaped over at least a 
portion of its length. Threaded ring 1a closes bore 1 and at the same time 
centers spring 8 which biases forward complementary conical bolt 2 having 
projecting flange 3 at its end face. Bore 1 has cylindrical part 4 to 
accomodate longitudinal movement (i.e. in the direction of main 
acceleration) of flange 3. 
In the center of housing 7 is primer pellet holder 6, illustrated in the 
preferred embodiment as a rotor with pivot point D. Over a part of its 
circumference, the primer pellet holder 6 has groove 5, with terminating 
portion 5a at one end and locking face 5b at the other end. Inside pellet 
holder 6 is primer pellet 9 and an insulated pole pin 10 protruding 
therefrom. Pellet 9 is connected to holder 6 by mounting 11, and pole pin 
10 is maintained in constricted bore 12 of holder 6. 
At the end of the pellet holder 6 in the direction of main acceleration 
b.sub.N, there is electrical charge generator 13, consisting of an 
ignition generator with a safety and storage circuit and a target sensor. 
Charge generator 13 has telescoping contact 14 which applies contact 
surface 15 to pellet holder 6. At the other end of pellet holder 6 is 
booster charge 16, initiation point 17 of which likewise projects into 
housing 7 toward holder 6. 
The rectangular coordinate system shown in FIG. 1a indicates, in the 
positive part of the abscissa, the direction of the main acceleration 
b.sub.N of projectile M. The projectile is in this acceleration zone when 
being fired. After leaving the gun barrel or launch path, projectile M 
experiences a flow resistance, such that, after a certain flight duration, 
the positive acceleration values which previously were continuously 
increasing become, relatively speaking, negative values in the zone marked 
-b.sub.N. Upon actual firing, the projectile experiences different angular 
positions on its ballistic trajectory, which result in components of 
transverse accelerations b.sub.Q (positive and negative). 
When projectile M is fired on a ballistic trajectory, pellet holder 6, 
initially locked by an inertial mass lock (described in detail further 
herein), is unlocked by the acceleration forces and undergoes, from the 
starting position shown in FIG. 1, a clockwise rotation about pivot point 
D. These forces act also on conical bolt 2, whereby the latter is pushed, 
due to its mass, in the direction of threaded ring 1a and is thus pulled 
with its projecting flange 3 out of the groove 5, as shown in FIG. 2. When 
firing at normal firing accelerations, the forces are high enough for a 
sufficiently long time, so that bolt 2 is kept in the position shown in 
FIG. 2. The spring tension and the design and mass of the bolt are 
selected such that the bolt is driven back far enough under the expected 
normal firing conditions. This enables pellet holder 6 to rotate 
270.degree. in the given time, and reach the armed condition illustrated. 
In the armed position, telescoping contact 14 of electrical charge 
generator 13 slides into bore 12 of pellet holder 6 and contacts pole pin 
10. When the target sensor closes the circuit, the detonating charge is 
electrically ignited. The shock wave produced in the primer pellet 9 
causes a detonation transmission at initiation point 17 of booster charge 
16. 
If the firing acceleration is below normal or expected conditions, or if 
the flight of the ammunition round is stopped prematurely, for example, by 
impinging on an obstacle, the acceleration forces acting on bolt 2 change, 
so that the bolt is pushed by spring 8 back into its end position in bore 
1. Flange 3 then projects into groove 5 and acts to stop pellet holder 6 
in its rotation by engagement of locking face 5b with projecting flange 3, 
as shown in FIG. 3. The projectile is thus inactivated and cannot be armed 
without re-acceleration. This safety device is also effective to prevent 
arming of the ammunition upon accidental movement of the rotor as, for 
example, during storage or handling, since the spring will maintain the 
bolt 2 in the safety position. 
Further embodiments and features of the invention are described with 
reference to FIGS. 4 to 12. For reasons of clarity, electrical charge 
generator 13 and booster charge 16 are symbolized by arrows in FIGS. 4 and 
5. In FIG. 4, a retarding mechanism for the safety device has balance 
wheel 18 surrounded by four balls 19, which are guided concentrically to 
wheel 18 by ball rim 20 and clamping ring 21. Retention pin 22 serves as a 
hold-down for this arrangement. Pellet holder 6 is shown with pellet 9 
fixed in opening 11 by means of threaded pin 23. 
As shown in FIGS. 4, 9 and 10, the safety device further comprises an 
initial release mechanism in the form of an inertial mass lock, having 
piston 24 slidably located in bore 27 in housing 7. Constricted bore 28 
provides an opening for exchange of air into bore 27 and limits the slide 
path of piston 24 to the release position shown in FIG. 10 upon normal 
acceleration. Piston 24 has detent recesses into which balls 42 of the 
inertial mass lock shown in FIGS. 9 and 10 engage. Journal end 32 of the 
pellet holder has slit 33 (see FIG. 6) for securing an end of arming 
spring 29 (shown in FIG. 8) which biases the holder for clockwise rotation 
when the inertial mass lock is released. 
In FIG. 5, a retard mechanism is provided for slowing rotation of the 
pellet holder for a selected safety delay period sufficient to allow the 
projectile to accelerate a safe distance beyond the gun barrel or launcher 
before it becomes armed. Stop pin 30 acts to limit the overall rotational 
path of the pellet holder by cam abutment 31. The pellet holder rotor, 
shown in detail in FIG. 6, is guided and centered in housing 7 by 
cylindrical portion 36 and has at one end cam abutment 31 and at its other 
end journal 32. 
The pellet holder has an opening on one side for the uptake of primer 
pellet 9, which is secured in place by threaded pin 23 screwed into 
threaded hole 34 leading into the interior of the rotor. Four detent 
recesses 35, arranged at angles of 90.degree., are adapted for the 
suspension and retention of balls 19. 
Referring in further detail to FIGS. 6-10, the inertial mass lock of the 
rotor has three parallel bores 27 and 27', slidably receiving piston 24 
and lock pins 38 and 39. Transversely to these bores is ball race bore 37. 
Lock pins 38 and 39 hold piston 24 in the locked state whereby rotation of 
the pellet holder is prevented and it is maintained in the inactivated 
position. Conical part 25 of piston 24 and tips 38' and 39' of lock pins 
38 and 39 engage in corresponding bores 27" of the housing 7 in the locked 
position. The lock pins 38 and 39 are biased into the locked position at 
their ends 38" and 39" by the springs 40 and 41. A secure mechanical 
contact is provided by the balls 42 held in position by lock pins 38 and 
39 in recessed portion 26 of piston 24. 
The mode of operation of the inertial mass lock will now be described. In 
the locked state, i.e. during storage and transportation of the 
ammunition, the condition shown in FIG. 9 is maintained so that pellet 
holder 6 cannot be rotated into the armed position. If the ammunition is 
fired with high acceleration, the acceleration acts immediately on piston 
24 and lock pins 38 and 39, so that they assume the position shown in FIG. 
10. The unlocked state is thereafter maintained by balls 42 blocking 
recess of piston 24, thereby preventing it from springing back into the 
locking position. 
The primer pellet holder 6, being rotatable while in the unlocked state 
shown in FIG. 10, receives a clockwise torque from spring 29. The rotation 
of the pellet holder is delayed by the retard mechanism, as balls 19 are 
successively pressed by balance wheel 18 into and out of recesses in ball 
rim 20, whereby the balance wheel executes an oscillating escapement 
movement. A predetermined delayed rotary movement of pellet holder 6 is 
thus provided in accordance with the desired time needed for fore-barrel 
safety. The delay time required may range from a few milliseconds to 
several seconds, depending on the projectile, the design of the retard 
mechanism, and the needs of the particular use. 
The safety device, shown in FIGS. 1 to 3, is physically independent of the 
initial unlocking and rotary movement of the pellet holder 6. It now 
controls the rotation of the pellet holder from the unlocked to the armed 
position in response to the acceleration behavior of the projectile in 
flight. In accordance with a principal feature of the invention, a conical 
shape is preferably provided for bore 1 and for the rotation-symmetrical 
bolt 2. By a selected cone angle in the range from 10.degree. to 
30.degree., preferably 15.degree., an undesired jamming of the bolt is 
prevented in the event of substantial transverse acceleration behavior in 
flight. 
By the selection of the material and size of bolt 2 and of spring 8, the 
arming operation of bolt 2 with respect to pellet holder 6 can be 
predetermined within wide limits. In FIG. 11, the rotation-symmetrical 
bolt 2 with its spring 8 is shown on a coordinate system with the angle 
formed between the direction of the main acceleration b.sub.N and the 
instantaneous direction of the projectile being designated by alpha 
(.alpha.). 
The diagram of FIG. 12 shows the relationship, for arming the projectile, 
between acceleration values as multiples n of the normal acceleration of 
gravity g and the angle .alpha. for certain materials. The materials shown 
are aluminum, designated Al (density=2.7 g/cc), steel, St (density=7.8 
g/cc) and Reconit, Re (trademark of Gueggi AG, Grenchen, Switzerland, for 
an alloy consisting of 92.5 per cent W, 7.5 per cent Ni/Cr/Cu, density=18 
g/cc). As indicated, a projectile can be safely armed by this invention 
even under extreme transverse acceleration conditions. Furthermore, the 
invention can be integrated almost universally into projectiles using 
existing electrical priming systems. For cylindrical housing 7, the 
outside dimensions can be of the order of 20 mm diameter and length. 
In FIG. 13 another embodiment of the invention is shown in simplified form. 
This employs a slide type primer pellet holder equipped with the described 
safety device. Axis of symmetry S indicates the direction of main 
acceleration b.sub.N. Slide type primer pellet holder 6' is arranged 
normal to axis S and has primer pellet 9 with pole pin 10 (shown in the 
unarmed position), V-track groove 5', and blind-hole bore 43. In bore 43, 
arming or extension spring 29' is fastened between the holder and housing 
7'. A safety device, identical with that of FIG. 1, projects into groove 
5' and is biased forwardly by spring 8 secured by threaded ring 1a. 
At the front of the projectile is electrical charge generator 13 with 
telescoping contact 14 applied to pellet holder 6'. On the opposite side 
is booster charge 16' at a small distance from pellet holder 6'. The 
retard mechanism is symbolized by arrow H and acts at one end of the 
pellet holder. 
The mode of operation of this device is analagous to that described 
previously. The acceleration forces acting on bolt 2 move projecting 
flange 3 out of groove 5'. Arming spring 29' pulls the slide toward the 
armed position, where pole pin 10 of primer pellet 9 is in electrical 
contact with telescoping contact 14. Upon target impact, primer pellet 9 
ignites and detonates booster charge 16' in a known manner. If the 
acceleration forces are interrupted or are abnormal, bolt 2 is moved 
forward to re-engage flange 3 in groove 5', so as to lock and prevent 
continued movement of the pellet holder toward the armed position. 
The embodiment shown in FIG. 14 is constructed analogously to that of FIG. 
13, except that, to reduce the space requirement, bolt 2 is arranged at an 
angle to axis of symmetry S of projectile M. To insure safe detonation of 
the booster charge, primer pellet 9 is installed in pellet holder 6" 
obliquely; i.e. oriented in the direction of the axis of symmetry S. 
Projecting flange 3' of bolt 2 is formed like a pawl so as to be 
engageable with locking face 5b" of groove 5" of pellet holder 6". The 
selection of the angle of the bolt 2 to the axis S can be optimized, for 
example, with the aid of the diagram of FIG. 12, for an expected range of 
dynamic flight behavior of the projectile when fired. 
The described embodiments of the invention provide a high degree of safety 
and reliability in cases in which, due to its trajectory and/or its firing 
behavior, the projectile has relatively high transverse accelerations. It 
excels moreover by its simplicity, small overall size, and ability to be 
integrated into existing as well as newly devised priming systems. The 
safety device is also effective to prevent accidental movement of the 
rotor, for example during storage or handling, since the spring will 
maintain the bolt in the unarmed position. 
As previously noted, the invention has been designed particularly for use 
with the rotary and slide type pellet holders. While only certain 
preferred forms of my invention have been described, it will be clear to 
those skilled in the art that various changes and modifications can be 
made, for example, by the use of the equivalent materials, components, or 
sequences of operation. All such modifications are intended to be included 
within the scope of my invention which is to be broadly construed and not 
to be limited except by the character of the claims appended hereto.