What we claim is
1. In a safety and arming device for a fuse in a launchable missile which includes a housing, a turbine wheel driven by ram air, a rotatable drive shaft coupled to said turbine wheel, a rotatable countershaft releasably coupled to said drive shaft at one end thereof and axially displaceable from said drive shaft as a result of rotation thereof, a shutter disposed within said housing and rotatable about the longitudinal axis of said countershaft, and a spring which rotatably urges said shutter from a safety position to an arming position, the improvement which comprises: first means for retaining said shutter in said safety position which is responsive to acceleration of said missile for releasing said shutter; second means for retaining said shutter in said safety position which is responsive to the axial displacement of said countershaft for releasing said shutter, said countershaft having the other end thereof threadably coupled to said housing; and means positioned between said first and second retaining means for preventing the axial displacement of said countershaft until after said first retaining means has released said shutter; said countershaft having a peripheral groove formed thereabout which is firstly engageable by said preventing means and then, after said axial displacement, by said second retaining means.
2. The device as set forth in claim 1, wherein said housing further comprises a stationary sleeve through which said countershaft extends, said sleeve having apertures formed therethrough in which are positioned said second retaining means, said shutter further having axial grooves formed therein for receivably engaging said second retaining means when in said safety position.
3. The device as set forth in claim 2, wherein said preventing means is moveable perpendicularly to the longitudinal axis of said countershaft, wherein said housing further includes a radial slot having two apertures into one of which extends said preventing means, and wherein said peripheral groove of said countershaft includes a cam surface of urging said preventing means radially outwardly within said slot upon the axial displacement thereof.
4. The device as set forth in claim 3, wherein said first retaining means extends into the other aperture of said radial slot prior to the release of said shutter thereby, the portion of said first retaining means extending through said second slot serving as an abutment to prevent outward radial movement of said preventing means.
BACKGROUND OF THE INVENTION
The present invention relates to a safety and arming device for fuses in launchable missiles, comprising a rotatable shutter actuated by a spring tending to rotate the shutter from a safety position to an arming position, said shutter being blocked against rotation by blocking means which are movable from their blocking position upon a rotating movement of a countershaft which is releasably coupled to the shaft of a turbine wheel driven by ram air, said shaft extending in the axial direction of the shutter.
There are known a number of various safety and arming devices for fuses in shells, bombs, rockets and other missiles or projectiles, which devices are intended to put the fuse at safety during storage, transportation, handling and firing and cause the fuse to be armed at an adequate distance from the firing or launching position. Thus, from U.S. Pat. No. 3,435,767 there is known a safety and arming device having a rotatable shutter which, when the fuse is at safety, is blocked in a position in which the explosive train is interrupted. The blocking is obtained by means of a wing-nut-shaped blocking element which is threadingly engaged with a countershaft driven by a turbine wheel positioned in the nose portion of the missile and driven by ram air. Because of the threaded engagement the wing nut will be axially displaced upon rotation of the countershaft, thereby bringing the wing nut out of engagement with the shutter, which may then rotate by the action of a spring.
However, this safety device is relatively complicated, and furthermore, the arming only depends on a rotation of the countershaft and a concomitant axial displacement. In other words, only one external force is required to cause an arming. This gives an unduly small security of the fuse staying at safety until it has been fired and has passed any obstructions which may give a priming or detonating signal. Furthermore, the arming forces which have to be overcome, are relatively great and also increase towards the end of the arming operation, which is highly undesirable when the power for carrying out the arming operation is provided by a turbine driven by ram air.
There are also known so-called shock safeties which are released due to the acceleration during firing, an axially displaceable weight being moved rearwardly in the device against a spring force when the projectile is fired or discharged. It is further known to combine such acceleration or shock safeties with a safety which is released due to the rotation of the projectile. By providing two safeties, a double security is of course achieved, since two independent forces are required to arm the fuse.
Finally, U.S. Pat. No. 2,805,623 discloses a safety in which the countershaft itself blocks the shutter, but is axially displaced upon rotation thereby to disengage the shutter, which may then be rotated about an axis perpendicular to the countershaft. The shaft is in turn blocked by an arming wire which is attached to a carrier plane, and which is consequently pulled away as the missile in which the fuse is mounted, falls away from the plane. Thus, the patent specification is not concerned with a missile that should be launched or fired.
SUMMARY OF THE INVENTION
An object of the present invention is to construct a safety device which provides further security. At the same time, the device shall be simple and thereby cheap in production, but above all reliable. It should further lend itself for use in rotating as well as non-rotating, launchable projectiles or missiles.
According to the invention, this is achieved in a device which is characterized in that the countershaft is displaced axially due to its rotation, that the shutter is blocked by blocking means which are permitted to leave their blocking position as a consequence of an axial displacement of the countershaft in the axial direction of the shutter, and that there is provided an acceleration or shock safety which in addition to directly securing the shutter also holds a blocking element in engagement with the countershaft in order to block said shaft against axial displacement.
This secures that for arming the fuse not only a shock releasing the shock safety of the shutter and a rotation of the countershaft releasing the rotational safety of the shutter are required. It is even required that such a shock and such a rotation occur in a certain sequence, since a release of the shock safety is a condition for the release of the rotational safety.
According to a preferred embodiment of the invention the blocking means are positioned in throughgoing apertures in a stationary sleeve between the shutter and the countershaft and extend into axial grooves in the shutter. The blocking element of the acceleration or shock safety in its blocking position may extend perpendicularly to the countershaft into a peripheral groove therein. If the blocking means are positioned rearwardly of the blocking element when viewed in the direction of displacement of the countershaft, this peripheral groove can also be used to permit displacement of the blocking means from their blocking position.
The device according to the invention satisfies all security requirements placed on fuses in projectiles which due to the firing or discharging are subjected to a certain acceleration and a certain aerodynamic pressure. Thus, it is also secure for non-rotating projectiles, e.g. fin-stabilized missiles. Because of its simplicity it simultaneously combines these advantages with a high reliability and functional ability, especially because the moment required at the countershaft for the arming operation is small as well as uniform. The arming operation requires both a shock and an aerodynamic pressure. Thus, it is not possible to arm the fuse by withdrawing an arming wire and subsequently rotating the countershaft. Furthermore, the device is exceptionally simple and cheap in production.
An embodiment of the invention will now be described, reference being had to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an axial section through the safety and arming device in safety position. The section is taken through the axis of an acceleration or shock safety.
FIG. 2 is a section along the same plane as that of FIG. 1, but illustrates the acceleration and shock safety after the occurrence of a shock which has ended the effect of this safety.
FIGS. 3 and 4 are axial sections through the device in secured and armed condition, respectively, but along another plane than the sections of FIGS. 1 and 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The shown device has a housing 1, which schematically is shown as composed by a base 2, a peripheral wall 3 and a cover 4. The base 2 is made with a central, sleevelike portion 5 protruding from the base through the cover 4. The lower portion of the sleeve 5 is provided with threads 6 in engagement with corresponding threads 7 on a shaft 8. The shaft 8 is a countershaft, the end of which is designed for being coupled to the shaft of a turbine which is operated by ram air (the air encountered by the missile in the trajectory). The coupling is capable of transmitting a torque, but permits free axial movement of the countershaft 8 relatively to the turbine shaft, so that the countershaft 8 will be rotated by the turbine and thereby displaced rearwardly in the housing (downwards in the Figures) due to the threaded engagement with the housing, whereby the coupling between the countershaft 8 and the turbine shaft will be released. The coupling, the turbine and the position of the safety device in a missile are not illustrated in the drawings, but as far as these aspects are concerned, reference is made to U.S. Pat. No. 3,435,767.
An annular body or so-called shutter 9 is rotatably mounted around the sleeve 5 in the housing 1. The shutter contains an electric detonator 10 and a so-called delayed detonator 11 (FIG. 4). The shutter 9 is biased by a torsional spring 12 seeking to rotate the shutter to the arming position shown in FIG. 4, in which the detonator 10 is armed by contact with a spring 13 and the detonator 11 is armed due to the fact that it is positioned immediately behind a percussion point 14. However, when the fuse is at safety, the shutter 9 is secured in another angular position by means of two safeties, an acceleration or shock safety shown in safety position in FIG. 1, and a further safety shown in FIG. 3, respectively.
The acceleration or shock safety in FIG. 1, operating in accordance with known principles, consists of a sleevelike housing 15 and a sleeve-shaped weight 16 displaceably mounted therein. In the safety position the weight 16 protrudes from the sleeve 15 and into a bore 17 in a member which is secured to the housing 1 of the device, so that the weight 16 itself will positively prevent the shutter 9 from rotating to the arming position. A compression spring 18 is arranged between the weight 16 and the bottom of the sleeve 15. The weight 16 is secured in the illustrated safety position by means of a ball 19 which engages an aperture 20 in the sleeve 15 and an aperture 21 in the weight 16. In the drawings only one ball 19 is shown, but it will be understood that two or more balls spaced around the periphery may advantageously be used. The ball 19 is kept in place in the illustrated position by a weight 22 which is positioned within the sleeve-shaped weight 16 and is normally kept in the upper end thereof by a spring 23 acting between the weight 22 and the bottom of the weight 16. The weight 22 has a portion of reduced diameter permitting the ball 19 (or balls) to disengage the aperture 20 in the safety housing 15, so that the weight 16 may move axially therein.
In the safety housing 15 immediately behind the aperture 20 there is also provided a further aperture 24, the object of which will appear later when the function of the device is described.
In addition to providing a direct blocking of the shutter 9 the weight 16 in its safety position also keeps a blocking element 25 in the form of a cylindrical locking pin having hemispherically rounded ends in the position shown in FIG. 1, in which it extends radially through a hole in the sleeve 5. Opposite the position at which the locking pin 25 extends through the sleeve 5, the countershaft 8 has a portion 26 of reduced diameter forming a peripheral groove. Thereby, a rearwardly facing shoulder 27 is provided on the countershaft 8, said shoulder cooperating with the locking pin 25, so that the countershaft cannot move rearwardly in the housing 1 so long as the locking pin 25 is blocked by the weight 16 against outward movement.
The abovementioned further or second safety or blocking of the shutter 9 is illustrated in FIG. 3 and consists of two diametrically opposed blocking means in the form of balls 28, each positioned in an aperture in the sleeve 5 and extending into axial grooves 29 in the shutter 9. The balls 28 cannot move out of the grooves 29 as long as the countershaft 8 is in the position illustrated in FIG. 3.
The operation of the safety and arming device is as follows:
Upon firing, the forces of inertia prevailing will try to force the weights 16 and 22 rearwardly against the force of the springs 18 and 23, respectively. At first, however, only the weight 22 is able to move rearwardly, the weight 16 being blocked by the ball 19. However, when the weight 22 moves rearwardly, the ball 19 may move into the space provided by the reduced diameter portion of the weight 22. The force on the weight 16 will force the ball 19 to move in this manner, whereupon the weight 16 can move rearwardly in the sleeve 15. The masses of the weights 16 and 22 and the spring characteristics of the springs 18 and 23 are so tuned that the weight 22 will start its forward return movement due to the force from the spring 23 before the weight 16 starts its return movement. Thus, when the weight 16 has been displaced so far that the aperture 21 lies directly opposite the aperture 24 in the safety housing 15, the ball 19 will be forced into the aperture 24 by the forwardly returning weight 22. The weight 16 is thus locked in a retracted position in which there is no blocking or safety effect.
When the projectile has left the discharge tube, the not shown turbine may start rotating the countershaft 8 and displace it rearwardly in the axial direction as a consequence of the engagement between the threads 6 and 7. During this operation the locking pin 25 will be radially displaced away from the shaft 8.
The peripheral groove formed by the portion 26 of reduced diameter into which the locking pin 25 extends, will thus be axially displaced and, as shown in FIG. 4, allow the balls 28 to move out of the grooves 29 in the shutter 9. Both the blockings of the shutter 9 have then become inoperative, and the spring 12 can rotate the shutter to the arming position shown in FIG. 4. When the shutter has been rotated to the arming position, it is locked relatively to the housing 1 by means of a spring biased locking pin (not shown) engaging a corresponding recess.