Patent Publication Number: US-11650034-B1

Title: Internal captive collar joint for projectile

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC § 119(e) of U.S. provisional patent application 63/165,761 filed on Mar. 25, 2021. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The inventions described herein may be manufactured, used and licensed by or for the United States Government. 
    
    
     FIELD OF THE INVENTION 
     The invention relates in general to projectiles and in particular to multi-piece projectiles. 
     BACKGROUND OF THE INVENTION 
     Projectile bodies, such as artillery shells, are often assembled from multiple components. The assembled joints must be sufficient to withstand the high forces often experienced by projectiles. Spin-stabilized artillery projectiles, in particular, must survive immense torque loads that are imposed during cannon launch. 
     Current methods of assembling spin-stabilized artillery projectiles include using a threaded joint with a thread locking adhesive. The threaded joints have to be strong enough to withstand the forces from the release of stored energy during cannon launch. In some cases, a friction-based surface, such as a face knurling, is also used. 
     There are downsides to this approach. If not done properly, the threads or components fail under tensile load and the joined parts separate at muzzle exit. If the threaded locking adhesive or frictional surface fail, the components rotate which could lead to other issues. In addition, knurled interfaces are difficult to manufacture consistently and the friction is difficult to measure in a dynamic environment. The components tend to over-tighten or slip. 
     A need exists for a system and method for creating an artillery projectile with multiple components that are easily, yet robustly, joined together. 
     SUMMARY OF INVENTION 
     One aspect of the invention is a projectile having a first component, a second component and an internal captive collar. The first component has a castellated region and a stepped down region. The second component has a slotted region, an opening and a threaded region. The slotted region corresponds to the castellated region of the first component. The opening is sized to receive the stepped down region of the first component. The threaded region is along an internal circumference proximate to the opening. The internal captive collar is positioned between the first component and the second component. The internal captive collar is rotatably affixed about the stepped down region of the first component and further comprising a thread along an external circumferential surface. The thread is for interfacing with the threaded region of the second component such that a rotation of the internal captive collar draws the first component and the second component axially closer to each other until the castellated region of the first component interfaces with the slotted region of the second component and axially secures the first component to the second component. 
     Another aspect of the invention is an artillery projectile including a rocket motor assembly, a warhead component, an internal captive collar, a retaining nut and a gear key. The rocket motor assembly has a generally cylindrical body and further comprises a castellated region proximate an opening in the rocket motor assembly and a threaded region along an internal circumference proximate to the opening. The warhead component has a generally cylindrical body. The warhead component body further comprises a slotted region and a stepped down region. The slotted region corresponds to the castellated region of the first component. The stepped down region comprises a thread along its exterior surface. The stepped down region is sized and dimensioned for being received within the opening of the rocket motor assembly. The internal captive collar is positioned about the stepped down region of the warhead component. The internal captive collar further comprises a threaded region about an external circumferential surface and a crown gear about its face. The threaded region is for interfacing with the threaded region of the rocket motor assembly for drawing said rocket motor assembly axially closer to the warhead component. The rocket motor assembly is drawn closer to the warhead component until the stepped down region is inserted into the rocket motor assembly and the castellated region of the rocket motor assembly interfaces with the slotted region of the warhead. The internal captive collar secures the rocket motor assembly and the warhead component axially relative to each other. The retaining nut is axially aligned with and surrounded by the internal captive collar. The retaining nut is threaded around the stepped down region of the warhead component. The retaining nut captures the internal captive collar about the stepped down region and prevents axial translation of the captive collar. The gear key has a geared surface for interfacing with the crown gear such that a rotation of the gear key rotates the internal captive collar about the retaining nut. The gear key accesses the crown gear of the internal captive collar through an opening in between the rocket motor assembly and the warhead component. 
     Another aspect of the invention is a method for assembling a projectile. The method comprises the steps of: providing a first component and a second component to be joined, said first component further comprising a castellated region and a stepped down region and said second component further comprising a slotted region corresponding to said castellated region of the first component, an opening sized to receive the stepped down region of the first component and a threaded region along an internal circumference proximate to the opening; rotatably affixing an internal captive collar around the stepped down region of the first component, said internal captive collar further comprising a thread along an external circumferential surface for interfacing with the threaded region of the second component; axially aligning the first component and the second component such that the thread of the internal captive collar interfaces with the thread of the second component; drawing the stepped down region into the opening of the second component by rotating the internal captive collar about the stepped down region; and inserting the stepped down region into the second component until the castellated region interfaces with the slotted region. 
     The invention will be better understood, and further objects, features and advantages of the invention will become more apparent from the following description, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIG.  1    is an exploded section view of the artillery projectile, according to an illustrative embodiment. 
         FIG.  2    is an exploded perspective view of the artillery projectile, according to an illustrative embodiment. 
         FIG.  3    is a detailed view of the joint between the rocket motor assembly and the warhead component in an unassembled state, according to an illustrative embodiment. 
         FIG.  4    is a section view of the joint between the rocket motor assembly and the warhead component, according to an illustrative embodiment. 
         FIG.  5    is a detailed view of the internal captive collar and the gear key, according to an illustrative embodiment. 
         FIG.  6    is a section view of the assembled artillery projectile with the gear key, according to an illustrative embodiment. 
         FIG.  7    is detailed perspective view of the joint between the rocket motor assembly and the warhead component in an unassembled state, according to an illustrative embodiment. 
         FIG.  8    is a flowchart illustrating a method for assembling a projectile, according to an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A safe and reliable multi-component projectile enables cost effective manufacturing and assembly of the projectile. Artillery projectiles have to withstand large accelerations, both during launch, set-back, and during muzzle exit, set-forward, when the stored potential energy of the projectile is released. Locking the union from axial translation requires a means of the components butting up against each other. Major components of the projectile are joined by an internal captive collar which both draws the components together axially and then holds them together. When assembled, castellation features on one component mate with corresponding slots on the other component and serve to transmit torque. 
     The components are held together by a captive collar that is internal to the projectile. The internal captive collar is rotated about a central boss, allowing external threads on the collar to engage one of the mating components and pull that mating component into the other mating component in an axial only translation. The internal captive collar is rotated using a geared-key during assembly. This key engages a geared crown feature of the internal captive collar, allowing it to rotate. After assembly, the gear key is removed from the assembly. Castellated features nest within slots to transmit torque in the assembled projectile. 
     Throughout this specification, the projectile is illustrated in the context of an artillery projectile. More specifically, the specification describes a union between a warhead of an artillery projectile and a rocket motor of an artillery projectile. However, those skilled in the art will recognize that while the projectile and related methods of assembly are suited for an artillery projectile, the projectile and methods of assembly are not limited to artillery projectiles. Rather, the projectile may be any projectile in which two components, a fore portion and an aft portion, must be joined to create the body of the projectile. Further, while the invention is particularly suited to spin-stabilized projectiles, it is not limited to spin-stabilized projectiles. 
       FIG.  1    is an exploded section view of the artillery projectile, according to an illustrative embodiment.  FIG.  2    is an exploded perspective view of the artillery projectile, according to an illustrative embodiment. The artillery projectile is a spin stabilized artillery projectile. Spin stabilized, in this context, means the projectile leaves the muzzle spinning at a rate of 100 Hertz (Hz) to over 300 Hz. The artillery projectile is launched from ignited propellant producing sufficient pressure to propel the artillery projectile  1  through a cannon tube. The artillery projectile comprises a warhead component  10 , a rocket motor assembly  20 , an internal captive collar  30 , a retaining nut  40  and a geared key  50 . 
     The warhead component  10  and rocket motor assembly  20  both comprise generally cylindrical bodies. The warhead component  10  may taper toward the muzzle end of the component thereby forming a conical cylindrical body. A stepped down region  14  of the warhead component  10  is dimensioned to be received within an opening  208  at the front of the rocket motor assembly  20 . The rocket motor assembly  20  further comprises a castellated region  22  proximate the opening  208  with teeth  220  defined by a face of the rocket motor assembly  20 . 
       FIG.  3    is a detailed view of the joint between the rocket motor assembly and the warhead component in an unassembled state, according to an illustrative embodiment.  FIG.  4    is a section view of the joint between the rocket motor assembly and the warhead component, according to an illustrative embodiment. When inserted into the rocket motor assembly  20 , a castellated region  22  of the rocket motor assembly  20  mates with a slotted region  12  of the warhead component  10 . The exterior surfaces of the warhead component  10  and the rocket motor assembly  20  when assembled, form a relatively flush surface with each other. 
     The retaining comprises a thread  42  about an internal circumferential surface. The retaining nut  40  threads onto a threaded region  16  of the warhead component  10 , capturing the internal captive collar  30  about a cylindrical stepped down region  14  on the warhead component  10 . The retaining nut  40  eliminates any axial translation in the internal captive collar  30 , only allowing rotation about a cylindrical stepped down region  14  of the mating assembly. 
       FIG.  5    is a detailed view of the internal captive collar and the gear key, according to an illustrative embodiment. The internal captive collar  30  further comprises external threads  32  defined by an exterior circumferential surface. The internal captive collar  30  further comprises a crown gear  34  defined by a face of the internal captive collar  30 . 
     The rotation of the internal captive collar  30  allows external threads  32  to engage with the other mating assembly, thus translating it with respect to the projectile axis and nesting the castellation teeth  220  into the mating slots  120 . In the embodiment shown, the rocket motor assembly  20  further comprises internal threads  24  defined by an interior circumferential surface proximate the opening  208 . The external threads  32  of the internal captive collar  30  interface with the internal threads  24  of the rocket motor assembly  20  to assemble and retain the mating components  10 ,  20 . 
     Rotation of the internal captive collar  30  is accomplished by a geared key  50  that is used only at assembly. The geared key  50  comprises a geared region on an exterior circumferential surface which interfaces with the internal captive collar  30  via the crown gear  34 . This geared key  50  can apply the required torque for maintaining the joint during launch and flight of the projectile. 
     The geared key  50  is only used at assembly and removed after assembly. The geared key  50  is inserted and removed through an opening between the warhead component  10  and the rocket motor assembly  20 . A tool, such as an air tool, may be used to turn the geared key  50  and apply torque required to thread the internal captive collar  30  into the rocket motor assembly  20 . 
       FIG.  6    is a section view of the assembled artillery projectile with the geared key  50 , according to an illustrative embodiment.  FIG.  7    is detailed perspective view of the joint between the rocket motor assembly and the warhead component in an assembled state, according to an illustrative embodiment. As the geared key  50  is turned, the internal captive collar  30  turns due to the crown gear  34  and geared key  50  interface. As the internal captive collar  30  turns, it pulls the rocket motor assembly  20  up, allowing the teeth to mesh with the slots  120 . The body of the rocket motor assembly  20  never rotates, as it only translates axially. The projectile has a flat-on-flat interface between the warhead component  10  and the rocket motor assembly  20  which is required to withstand the acceleration forces from cannon launch. 
       FIG.  8    is a flowchart illustrating a method for assembling a projectile, according to an illustrative embodiment. At step  802 , a warhead component  10  and a rocket motor assembly  20  are provided. 
     At step  804 , the internal captive collar  30  is affixed to the stepped down region  14  of the warhead component  10  by the retaining nut  40  such that it is axially restrained but free to rotate about the stepped down region  14 . 
     At step  806 , the warhead component  10  and the rocket motor assembly  20  are axially aligned such that the exterior thread  32  of the internal captive collar  30  is aligned with the internal thread  24  of the rocket motor assembly  20 . 
     At step  808 , the internal captive collar  30  is rotated about the stepped down region  14  of the warhead component  10  by the geared key  50 . The rotation of the internal captive collar  30  draws the rocket motor assembly  20  toward the internal captive collar  30  and thereby the stepped down region  14  of the warhead component  10 . 
     At step  810 , the rocket motor assembly  20  and the warhead component  10  are drawn together axially until the castellated region  22  of the rocket motor assembly  20  mates with the slotted region  12  of the warhead component  10 . Teeth of the castellated region  22  insert into slots  120  of the slotted region  12 . 
     At step  812 , the geared key  50  is removed through an opening between and defined by the rocket motor assembly  20  and the warhead component  10 . 
     While the invention has been described with reference to certain embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.