Armor retension mechanism having anti-theft means
GOVERNMENT INTEREST 
     The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without payment to us of any royalty thereon. 
    
    
     SUMMARY OF THE INVENTION 
     This invention relates to add-on armor for military vehicles, especially improved means for attaching armor plates to outer surfaces of a military vehicle. A particular aim of the invention is to incorporate an anti-theft mechanism into the attachment means. 
     The need for the anti-theft mechanism arises primarily because of a desire on the part of military officials to deter (prevent) enemy forces from gaining an insight into the ballistic capabilities of the add-on armor plates, e.g., by surreptitious removal of one or more plates from a vehicle. 
     In the past it was sometimes considered necessary or desirable to post guards in the vicinity of vehicles equipped with add-on armor panels, as a deterrent to the unauthorized removal of an armor panel from a vehicle. THe present invention is directed to an anti-theft mechanism built into the devices that are used to attach the armor panels to military vehicles. The anti-theft mechanisms are designed so that they can be removed when necessary, e.g., to repair damaged panels and/or replace the existing panels with other panels having different ballistic performance. 
    
    
     THE DRAWINGS 
     FIG. 1 is a side elevational view of a military vehicle utilizing our invention. 
     FIG. 2 is an enlarged fragmentary sectional view taken on line 2--2 in FIG. 1. 
     FIG. 3 is a fragmentary plan view taken in the direction of line 3--3 in FIG. 2. 
    
    
     THE DRAWINGS IN GREATER DETAIL 
     FIG. 1 shows a conventional military vehicle comprising a hull 10, rotary turret 12, and main gun 14. The vehicle propulsion system comprises an engine-transmission mechanism located within the hull in operative driving relation to drive sprockets 16 at the rear end of the vehicle. Endless tracks 18 are trained around sprockets 16, front idler wheels 20, and road wheels 22. 
     Add-on armor plates (panels) 24 are detachably mounted on selected vehicle surfaces to enhance battlefield survivability of the vehicle. The panels may be constructed of various different armor materials; the plate material depends to a certain extent on such factors as location on the vehicle (vehicle upper surface may require different material than the undersurface), or weight-performance tradeoff factors, or technology advances in ballistic materials development. Some illustrative armor materials are disclosed in U.S. Pat. No. 4,398,446 to Pagano et al and U.S. Pat. No. 4,368,660 to M. Held. 
     FIG. 2 illustrates a preferred mechanism for mounting an individual armor plate on the vehicle. The mechanism comprises a plural number of pads 26 welded to outer surface 27 of a vehicle wall 28. In most cases individual plates 24 are square or rectangular in plan outline; Four mounting pads 26 are used for each plate; typically the pads are located near corner areas of the associated armor plate (when the plate is in its mounted position). 
     Each pad 26 has a threaded opening 30 extending therethrough. The associated armor plate 24 is formed with circular through holes 32 spaced apart in accordance with the spacing of the various threaded openings 30. 
     A bolt 34 is extended through each hole 32 such that a threaded section 33 on the bolt screws into threaded opening 30. A smooth-surfaced section 36 on the shank area of the bolt is mated to the surface of associated hole 32. By using templates to accurately locate holes 32 and pads 26 it is possible to have the diameter of each bolt section 36 closely approach the hole 32 diameter, thereby ensuring a firm vibration-resistant mounting of plate 24 on the vehicle. 
     Each mounting bolt 34 includes an enlarged head 38 that overlies the outer face 39 of plate 24 to exert a clamping force thereon. The enlarged head 38 of the bolt comprises a circular base section 40 engageable on the outer face 39 of armor plate 24. The bolt head also includes a non-circular (e.g., hexagonal) section 44 sized to receive a wrench for bolt-turn purposes. 
     Our invention is concerned largely with anti-theft collars 46 adhered to face 39 of armor plate 24 in surrounding relation to head areas 38 of the mounting bolts 34. Welding is the preferred method of adhering each collar 46 to plate 24. The various collars 46 are welded to plate 24 after the associated bolts 34 have been screwed down into pads 26 to a desired torque value suitable for retaining plate 24 in place on the pads. 
     Each collar 46 is formed with a relatively small diameter opening 47 having a diameter slightly greater than the major diameter across corner areas of bolt head 38. A relatively large diameter counterbore 48 is formed in end face 49 of collar 46 to encircle the base section 40 of the bolt head. 
     The juncture between opening 47 and counterbore 48 forms an annular shoulder surface 51 that overlies circular base section 40 of bolt head 38. This relationship prevents the bolt from being unscrewed from pad 26 except after removal of collar 46 from armor plate 24. Such removal requires the use of a cutting torch to sever the weld connections between the collar and armor plate. 
     The axial dimension of counterbore 48 is preferably selected so that shoulder surface 51 closely overlies the radial face of circular section 40 of the bolt head. With a very close tolerance fit of surface 51 on the face of section 40 the bolt head is prevented from turing or loosening, as might result in vibrational play of plate 24 relative to pads 26. 
     If the axial dimension of counterbore 48 is somewhat greater than the axial dimension of circular section 40 there is a possibility that the bolt could slightly loosen or unscrew from pad 26. However, eventually circular section 40 would abut shoulder surface 51 to thereafter prevent any further unloosening of the bolt. Collar 46 serves as an anti-theft device to prevent surreptitious (unauthorized) removal of armor plate 24 from the vehicle on which it is mounted. 
     Each collar 46 preferably has approximately the same aixal dimension as the associated bolt head 38. This relationship minimizes the axial projection of the bolt-collar assembly from the outer face 39 of armor plate 24. This is advantageous in slightly minimizing the size of the target presented to the enemy force (concealment and/or enemy projectile avoidance). In a typical situation collar 46 would have an axial dimension of about three eighth inch. 
     The annular side surface 53 of each collar 46 is a frusto-conical surface tapering from collar end surface 49 at an angle of about forty five degrees. The primary purpose of the frusto-conical surface is to prevent the collar from being gripped by a wrench, thereby preventing removal by application of sufficient torque to break the welds. The frusto-conical surface also somewhat minimizes the profile (size) of the collar, thereby somewhat reducing the possibility of a direct hit by an enemy projectile. 
     The primary function of each collar 46 is as an anti-theft device, i.e., prevention of the bolt from being unloosened by an unauthorized person. However, the collar may also offer some ballistic protection for the otherwise unprotected bolt head 38. Collar 46 surrounds the bolt head and acts as a shield against oblique attack of the bolt head by an enemy projectile or armor fragmentation spray. 
     As noted previously, our invention relates primarily to the relationship between the hold-down bolts and associated anti-theft collars. The use of bolts to affix armor panels to vehicle surfaces is not new, per se. U.S. Pat. No. 2,380,393 to Berg shows a bolt system in an armor fastener environment. U.S. Pat. No. 4,167,889 also shows the use of bolts to retain armor panels in place on military vehicles. 
     We wish it to be understood that we do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art, without departing from the spirit and scope of the appended claims.