Abstract:
A safety and arming unit for a fuze of a projectile has a rotor for interruption of a firing chain. The rotor can rotate from a safe position to an armed position. In order to allow the safety and arming unit to be designed to be physically compact and such that it can be assembled easily, it is proposed that it has a first and a second rotor safety device which each engage in the rotor in order to block rotor rotation to the armed position, wherein the first rotor safety device is designed to carry out a release movement by virtue of its inertia during a launch acceleration of the projectile, and the second rotor safety device has a pyrotechnic charge for producing a release movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German patent application DE 20 2009 008 861.8, filed Jun. 27, 2009; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0002]    The invention relates to a safety and arming unit for a fuze of a projectile. The unit has a rotor for the interruption of a firing chain. The rotor can rotate from a safe position to an armed position. 
         [0003]    Projectiles, such as artillery projectiles, mortar shells or direct projectiles, normally have a fuze with a firing chain which, in its armed position, has two or more firing charges that are arranged one behind the other. The last of these firing charges directs its firing energy at a main charge, which is arranged in the projectile body of the projectile, in order to transmit firing energy to fire the main charge. 
         [0004]    A safety and arming unit for a fuze is used to prevent inadvertent activation of the main charge, whereas, however, the activation of the main charge is intended to be possible after arming. For reliable interruption of the firing chain, safety and arming units are known having a rotor which, in its safe position, ensures that the firing chain charge is not aligned with a further charge, or the firing chain is blocked by a mechanical barrier, thus reliably preventing the firing process to proceed from one firing charge to the next. 
       SUMMARY OF THE INVENTION  
       [0005]    It is accordingly an object of the invention to provide a safety for a projectile which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a safety and arming unit for a fuze that can be produced to be compact and ensures a high level of safety against inadvertent firing of the main charge. 
         [0006]    With the foregoing and other objects in view there is provided, in accordance with the invention, a safety and arming unit for a fuze of a projectile having a firing chain, comprising: 
         [0007]    a rotor for interruption of the firing chain, said rotor being rotatably disposed for rotation from a safe position to an armed position; 
         [0008]    a first rotor safety device and a second rotor safety device each disposed to engage in said rotor in order to block a rotation of said rotor into the armed position; 
         [0009]    said first rotor safety device being configured to carry out a release movement by virtue of an inertia thereof during a launch acceleration of the projectile; and 
         [0010]    said second rotor safety device including a pyrotechnic charge for effecting a release movement. 
         [0011]    In other words, the objects of the invention are achieved by a safety and arming unit of the type mentioned initially which, further, has a first and a second rotor safety device which each engage in the rotor in order to block rotor rotation to the armed position, wherein the first rotor safety device is designed to carry out a release movement by virtue of its inertia during an acceleration, and the second rotor safety device has a charge for producing a release movement. Two separate safety parameters can be used to unlock the rotor, and are dependent on different physical characteristics. The use of a charge to produce the release movement for the second rotor safety device makes it possible to design the second rotor safety device to be compact. The charge can be fired electronically, for example with the aid of a sensor which measures a physical parameter, for example a spin, a wind speed, a pressure difference, a temperature or the like. 
         [0012]    In one advantageous embodiment to the invention, the two release movements take place in a first and a second release direction, wherein the release directions are parallel to one another. The parallelity allows channels, in which safety elements of the rotor safety devices are provided, which each carry out the release movement, to be installed in a parallel direction, thus allowing the elements of the safety and arming unit to be fitted in one direction. This allows the safety and arming unit to be assembled easily, counteracting the probability of assembly errors occurring. Furthermore, the safety and arming unit can be designed to be very compact, by the release movements and release channels being parallel. The parallelity of the release directions includes them being parallel but opposite. 
         [0013]    The two release directions are expediently in opposite directions to one another. This makes it possible to prevent the acceleration which produces the first release movement from leading to an undesirable release movement of the second rotor safety device as well. The acceleration therefore actually acts against the second release movement, thus allowing the safety and arming unit to be designed to be particularly reliable. 
         [0014]    One advantageous refinement of the invention provides that the first rotor safety device has at least three safety elements which each have a safe position and an armed position and are designed to move in a chain reaction from their safe position to their armed position. By way of example, a chain reaction occurs when the respective next safety element does not start its release movement until the respectively previous safety element has reached its release position. Cascaded arming such as this allows a long arming time to be achieved by purely mechanical elements and without a clock, as a result of which the rotor is held reliably in its safe position for a long time. This makes it possible to ensure a high degree of short-range safety. 
         [0015]    The first safety element expediently blocks the second safety element in its safe position, and the second safety element expediently blocks the third safety element in its safe position. This makes it possible to reliably avoid faulty initiation of the third and final safety element. 
         [0016]    It is also advantageous for all three safety elements to be armed by a movement in the first release direction. A release movement such as this in one direction allows the first rotor safety device to be designed to be particularly compact. 
         [0017]    A further advantageous variant of the invention provides that the second rotor safety device has a safety element which, when in its safe position, engages in a first opening in the rotor, blocking the rotor, and is moved further into the rotor for release. This means that there is no need for the safety element to be moved out of the rotor in a mechanically complex manner. Furthermore, it is possible to ensure that the rotor stays blocked still by the safety element if the charge is fired inadvertently. The first opening is expediently a depression or recess in the rotor. 
         [0018]    Advantageously, a second and a third opening open into the first opening, wherein the second opening is shorter than the third opening and is aligned with the safety element when the rotor is in the safe position, such that this safety element is inserted into the second opening in the event of inadvertent, premature ignition of the second rotor safety device and projects beyond the rotor through the shorter length of the second opening, and thus keeps the rotor blocked. This makes it possible to reliably prevent inadvertent premature unlocking of the rotor. 
         [0019]    The third opening is expediently intended to hold the safety element such that the rotor is released for movement to the armed position. For this purpose, the safety element can be completely surrounded by the rotor, such that it does not project out of the rotor in any direction. 
         [0020]    In order to keep the safety element reliably in the second or third opening after firing of the charge of the second rotor safety device, the safety element and the second and/or the third opening are designed such that the safety element is seated with an interference fit in the second and/or third opening respectively. This therefore reliably prevents the safety element from sliding out of the second or third opening inadvertently. An interference fit can be achieved particularly reliably by means of at least one conical section, which is incorporated on the safety element or at least in the third opening, such that the conical section creates the inference fit when the safety element is fired into the opening. 
         [0021]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0022]    Although the invention is illustrated and described herein as embodied in a safety and arming unit for a projectile, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0023]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
         [0024]      FIG. 1  is a perspective view, obliquely from above, of a safety and arming unit for a fuze of a projectile, having a rotor and a triple bolt system as the first rotor safety device, in the safe position; 
           [0025]      FIG. 2  is a similar perspective view showing the triple bolt system and the rotor in its armed position, 
           [0026]      FIG. 3  is a perspective view, obliquely from below, of the rotor and the triple bolt system; 
           [0027]      FIG. 4  is a schematic section through a second rotor safety device with a charge and a safety element in its safe position; 
           [0028]      FIG. 5  is a sectional view showing the safety element in its armed position in the rotor; and 
           [0029]      FIG. 6  is a section showing the initiated second rotor safety device with the safety element in a short opening in the rotor, thus blocking the rotation of the rotor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a safety and arming unit  2  for a fuze of a projectile, in the form of a schematic and perspective illustration obliquely from above. The term above is understood with reference to the direction of the fuze nose or projectile nose. The safety and arming unit  2  has a rotor  4 , which is illustrated in its blocking safe position in  FIG. 1 .  FIG. 3  likewise shows the rotor  4  in its safe position, but obliquely from below, while in contrast  FIG. 2  shows the rotor  4  in its armed position. The rotor  4  can rotate about a shaft  6 , which can be seen in  FIG. 3 , although its rotation is limited by two stop bolts  8 ,  10 . In its safe position, the rotor  4  rests on the stop bolt  8 , while in contrast the stop bolt  10  blocks the rotation of the rotor  4  beyond its armed position. 
         [0031]    A stemming charge  12  (i.e., transfer charge) is arranged in the rotor  4  and is moved by a movement of the rotor  4  from the safe position, as shown in  FIG. 3 , to the armed position, aligned with a firing charge  14 , which is fired electrically. In the armed position, the stemming charge  12  is fired by the firing charge  14 , and itself fires a booster charge (not illustrated) which, like the firing charge  14 , is arranged in a fixed position in the fuze, the stemming charge  12  likewise being arranged so as to be aligned with said booster charge when in the armed position. In the safe position, firing of the firing charge  14  is prevented from being passed to the booster charge by the mechanical block formed by the solid rotor  4 , thus interrupting firing of the entire firing chain. 
         [0032]    In its safe position, the rotor  4  is held mechanically blocked by two rotor safety devices  16 ,  18 , which engage in a respective recess  20 ,  22  in the rotor  4 . These two interlocks prevent rotation of the rotor  4  about its shaft  6 . In this case, the first rotor safety device  16  engages radially from the outside in the rotor  4  while, in contrast, the second rotor safety device  18  engages in the axial direction in the rotor  4 , and thus blocks it in its safe position. The axial direction is parallel to a launch direction  24  of the projectile. 
         [0033]    The first rotor safety device  16  is in the form of a triple bolt system with three safety elements  26 ,  28 ,  30 , which are each in the form of a bolt and are mounted such that they can move in the fuze, in the launch direction  24  of the projectile. In this case, a respective spring  32 ,  34 ,  36  pushes them to their safe position, as illustrated in  FIG. 1  and  FIG. 3 , and as indicated in  FIG. 2 , as well. 
         [0034]    While the projectile is being launched, the launch acceleration acts on the three safety elements  26 ,  28 ,  30  which, by virtue of their inertia, exert a force downwards, in the opposite direction to the launch direction  24 . Two balls  38 ,  40  in corresponding grooves in the safety elements  28 ,  30  prevent these safety elements  28 ,  30  from moving downwards, however, that is to say in the opposite direction to the launch direction  24 , since these balls  38 ,  40  cannot move out of the grooves. However, the first safety element  22  can be moved downwards against the force of the spring  32 , and is pulled downwards by its inertia in the opposite direction to the launch direction  24 , as a result of which the spring  32  is compressed. When a conical section  42  reaches the ball  38 , as illustrated in  FIG. 2 , then the tapered upper part of the safety element  26  creates a sufficient amount of space for the ball  38  so that it can be moved in the direction of the first safety element  26 . In this case, the groove in the second safety element  26  is provided at the top with an incline, for example in the form of a conical section, which pushes the ball  38  out of the groove by means of the force of the safety element  28  acting downwards, as a result of which the second safety element  28  is released to carry out its release movement. The second safety element  28  is now moved in the same first release direction as that previously of the safety element  26 , downwards against the spring force of the spring  34 . 
         [0035]    The second safety element  28  is likewise provided with a conical section  44  which, on reaching the ball  40 , releases it, as can be seen in  FIG. 2 . It is pushed out of its groove by the third safety element  30  and now releases the third safety element  30  to carry out its release movement in its release direction, in the opposite direction to the launch direction  24 . The third safety element  30 , which engages in the recess  20  in the rotor  4 , is pushed downwards against the force of the spring  36 , as a result of which the safety element  30  is moved out of the recess  20  in the rotor  4 , and therefore releases the rotor  4 . The rotor  4  can now—for example run by spring force, inertia if the projectile is spinning, or by some other driving element—rotate from its first safe position, which is shown in  FIGS. 1 and 3 , through about 30° to a second safe position, in order to be blocked there once again. 
         [0036]    The cascaded arming process of the three safety elements  26 ,  28 ,  30  from their safe position as illustrated in  FIG. 1  to the armed position as illustrated in  FIG. 2  means that the rotor  4  is not armed immediately after the launch acceleration occurs, but is still held for a while in its safe position, thus achieving a high degree of short-range safety. As a result of the third safety element  30 , virtually twice the arming time is required to arm the first rotor safety device  16 , as in the case of a known double bolt system. 
         [0037]    After the initial arming of the rotor  4  by the first rotor safety device  16 , one safety element  46  of the second rotor safety device  18  is still engaged in the recess  22  in the rotor  4 , as illustrated in  FIG. 4 , and blocks the rotor rotation of the rotor  4  in its armed position. For this purpose, the safety element  46  strikes a stop  48 , thus blocking further rotation of the rotor  4 . The rotor  4  is now held in its second safe position, in which the rotor  4  blocks the firing chain, and the stemming charge  12  has not yet been arranged aligned with the firing charge  14  and the booster charge. 
         [0038]    The safety element  46  is held secured by a sleeve  56 , which is mounted in a fixed position in the fuze, that is to say such that it cannot move with respect to an external skin of the fuze, thus stopping rotation of the rotor  4  by the safety element  46 . 
         [0039]    In addition to the safety element  46 , the rotor safety device  18  has a charge  50  which can be fired electrically and encloses the safety element  46  in the rotor  4 , to be precise in a first opening  52  or a second opening  54 , both of which open into the recess  22 . If the rotor  4  has already been released by the first rotor safety device  16 , and has been pivoted to its second safe position, as is illustrated in  FIG. 4 , then the safety element  46  is fired into the second opening  54 , and is held completely by the second opening  54  and the recess  22 , as is illustrated in  FIG. 5 , as a result of which the rotor  4  can now rotate to its armed position. 
         [0040]      FIG. 6  shows the rotor  4  in its first safe position, in which the safety element  46  is arranged aligned with the first opening  52 . In the event of inadvertent initiation of the charge  50  and the safety element  46  being fired into the rotor  4 , the safety element  46  is fired into the opening  52 , which is designed to be shorter than the opening  54 . The safety element  46  is still held in the sleeve  56 , which is mounted such that it cannot rotate, and is now also held in the opening  52 , thus blocking rotation of the rotor  4  from the first safe position. 
         [0041]    The safety element  46 , which has been fired into the first or second opening  52 ,  54 , is seated with an inference fit in the first or second opening  52 ,  54 , into which it is fired by the force of the explosion of the charge  50 . In consequence, the safety element  46  is held firmly in the respective opening  52 ,  54  and cannot fall out again. This prevents inadvertent renewed blocking of the rotor  4  when the safety element  46  is in the second opening  54 , and inadvertent release of the rotor  4  to its second safe position when the safety element  46  is in the first opening. 
         [0042]    The release movement of the safety element  46  in a second release direction runs parallel to the launch direction  24 , but in the opposite direction to it. The powerful acceleration forces during launch of the projectile therefore result, by virtue of the inertia of the safety element  46 , in the latter being pressed in the opposite direction to its release direction. This counteracts inadvertent release of the rotor  4  during launch of the projectile.