Abstract:
A band track for a tracked vehicle having enhanced resistance to mines includes a plurality of track pad units disposed on the bearing surface of the track band. The track pad units have extended end walls of sufficient height to distance the vulnerable portion of the band track from the shearing force of an exploding mine. These end walls are sufficiently strong to support the vehicle as it traverses terrain, but are configured to collapse in controlled manner under the force of an exploding mine. Such explosion forces a specifically configured front end wall of a trailing track pad to engage the matingly configured end wall of the leading track pad. The resulting mating juxtaposition of the adjacent end walls forms a relatively continuous physical barrier protecting the vulnerable section of the band track from shrapnel and other entrained ejecta of the explosion.

Description:
STATEMENT OF GOVERNMENT INTEREST 
       [0001]    The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without the payment of any royalties therefore or thereon. This patent is expected to be assigned to the United States Government. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The instant invention relates to band tracks for tracked vehicles, and more particularly, the instant invention relates to a mine resistant band track for tracked military vehicles, such as tanks, armored personnel carriers and the like. 
         [0004]    2. Technical Considerations and Prior Art 
         [0005]    Historically, warfare scenarios and deployment techniques have limited the use of land mines to certain well defined situations to impede or channel opposing forces. Advance knowledge of mine field locations could permit effective countermeasures using mine-clearing equipment, such as mine-clearing rollers mounted on lead vehicles, projected explosive line charges or, depending on the tactical situation, sacrificing vehicles and uniformed personnel by simply charging over the mine field. 
         [0006]    Introduction of mechanically emplaced and air-delivered mines on the modern battlefield has compounded the problem of maintaining the mobility of armored vehicles. Air and artillery delivery capabilities have introduced offensive mining techniques wherein mines are laid at random along approach routes. 
         [0007]    Tracked vehicles, such as tanks, can be stopped with relatively small explosive charges which are easily delivered by airplanes and artillery. Charges of this type cause a mobility failure by breaking track sections and temporarily stalling armored vehicles, such as tanks, which can then be destroyed by artillery and anti-tank weapons generally placed to cover a mined area. 
         [0008]    Blast mines generally have two damaging mechanisms operative when exploded. The first is the shearing forces associated with the rapid expansion of the blast envelope. As this blast envelope is spherical, the force at the blast envelope front generally diminishes at a cubic rate as distance from the point of explosion increases, in volumetric relationship to the spheroidal expansion. The second damage mechanism is the impact of entrained ejecta, whether from intentionally included shrapnel or from ground debris ejected upon explosion. The damage effect of the ejecta diminishes at a squared rate as the distance from the point of explosion increases, in relationship to the area of the spheroidal expansion surface. 
         [0009]    Band type tracks employ flexible material and are generally more vulnerable to being rendered inoperable by mines than are conventional chain-like hinge pinned type tracks. In band tracks fitted with track pads, the band track typically fails along a transverse line at the front or rear of one or more of the track pads. For a given event, it is not clear whether the failure caused by a mine explosion is primarily attributable to the shearing forces generated by the movement of the band track when impacted by the spherical blast envelope of the explosion or the impact of blast entrained ejecta. In most cases, it is likely that the band track failure is caused by both damaging mechanisms. 
         [0010]    In view of this evolution in expected battlefield conditions, there continues to be a need for new and improved mine resistant track configurations, including band tracks, for tracked vehicles. Further, it is desirable that such improved band track configurations resist both types of damaging mechanisms, the shearing forces and the blast entrained ejecta. 
       SUMMARY OF THE INVENTION 
       [0011]    In view of the aforementioned considerations, it is a feature of the instant invention to provide a new and improved band track assembly able to withstand explosive charges which are sufficient to disable the tracks of current tracked vehicles. 
         [0012]    In view of this feature, the instant invention contemplates a band track which includes a plurality of track pad units disposed on the outside or bearing surface of a traditional track band. The track pad units have extended end walls giving the track pad a certain height which distances the vulnerable portion of the track band from the shearing force of an exploding mine. The end walls of the track pad are configured with sufficient thickness, given the strength characteristics of the specific material selected for the pad, to support the vehicle as it traverses terrain characteristics, but are narrow or thin enough that the pad will collapse in a controlled manner under the greater force of an exploding mine. The end walls of the subject track pad are provided with curved sides that help deflect, rather than transmit, the very large compressional forces of the blast, thus tending to prevent development of the large shearing forces contributing to band track failure. 
         [0013]    Moreover, the end walls are further configured such that they collapse in a relatively controlled manner, whereby the force of an exploding mine forces a curved front end wall of a trailing track pad to mate or engage with the matingly configured end wall of the leading track pad. The mating juxtaposition of the respective end walls of the adjacent pads forms a relatively continuous physical barrier protecting the vulnerable section of the band track from shrapnel and any other entrained ejecta of the explosion. 
         [0014]    In addition, the instant invention contemplates a wheel and track assembly employing the afore-described track pad and track assembly in combination. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a side view of an armored vehicle, in this case a tank, employing the track pad and band track assembly in accordance with the features of the instant invention. 
           [0016]      FIG. 2  is a side view of a portion of band track illustrating a number of the track pad units which form the track pad of the present invention. 
           [0017]      FIG. 3  is a cross-sectional view of a track pad unit of the present invention, taken along line A-A of  FIG. 2 . 
           [0018]      FIG. 4  is a side view of a portion of the band track demonstrating the operation of the track pad units of the subject invention under the compressional force of the explosion of a mine. 
           [0019]      FIG. 5  is a side view of a portion of an alternative embodiment of the subject track pad further comprising a support wall or septum and a studded bearing or road surface. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    As seen in  FIG. 1 , a tracked vehicle  10  may be of the type that includes a band track  12  which is driven by a drive wheel  14 . Band track  12  is further entrained about multiple road wheels  16  and typically about an idler wheel  18 . In a preferred embodiment shown in  FIG. 2  but seen better in the cross-sectional view of  FIG. 3 , the subject invention band track  12  comprises a band body  20  having an inner surface  22  and an outer surface  24 . A center guide  26  is disposed on inner surface  26  and typically is medially placed thereon. Further, side guides  28  are located at least one edge, and more typically at both edges, of the inner surface  22 . 
         [0021]    Those of ordinary skill in the art will appreciate that, as in conventional wheel and track assemblies for tracked vehicles, the powered motion of the drive wheel  14  in turn causes the orbital motion of the endless band track  12  around entrained road wheels  16  and idler wheel  18 . It is also to be appreciated that the same wheel and track assembly and operation is provided on the other side of the vehicle  10 . Also in conventional manner, the orbital motion of the band track  12  is driven and guided by the operation of center guide  26  and side guides  28  on the inner surface  22  of the band track  12 , in coordination with appropriate guide receiving elements on each of wheels  14 ,  16  and  18 . 
         [0022]    A track pad  30 , comprised of multiple track pad units  32 , is disposed along the entire circumferential length of outer surface  24  of band body  20 . Each track pad unit  32  has a bearing or road surface  34  which is in contact with the varying surfaces of the different terrain over which the vehicle  10  travels. Bearing or road surface  34  may be selectively textured or studded to increase traction of the road surface  34  over the prevalent terrain condition. Each track pad unit  32  also comprises a front end wall  36  and a back or rear end wall  38  respectively placed at each end of unit  32  and extending from outer surface  24  of band body  20  to road surface  34 . The front end wall  36  extends contiguously from the outer surface  24  of band body  20  to a front edge of the bearing surface  34  and the rear end wall  38  similarly extends contiguously from the outer surface  24  of the band body  20  to a rear edge of the bearing surface  34 . Thus, the outer surface  24  of band body  20 , rear end wall  38 , bearing surface  34  and front end wall  36  define a pad cavity  40 . 
         [0023]    In the preferred embodiment shown in  FIGS. 2 and 4 , track pad units  30  are open sided, i.e., have no side walls such that pad cavity  40  presents openings in the direction transverse to the length of band track  12 . One of skill in the art, however, will appreciate that the subject invention will also provide its intended benefits in another configuration where the track pad unit  32  is provided with side walls (not shown) such that pad cavity  40  is fully enclosed. Those skilled in the art will appreciate that the benefits of side walls, including the ability to avoid the extra weight of debris which might otherwise be picked up in the pad cavity  30 , may be counterbalanced by the weight of the side walls themselves. Alternative embodiments of track pad unit  32  may further comprise sealed side walls (not shown) which combine with a sealed interior face of band body  20 , a sealed interior face of bearing or road surface  34 , and sealed front and rear walls  36  and  38 , to form a track pad cavity  40  having an enclosed volume capable of being filled with a gas, such as air, which may further be pressurized, creating a pneumatic element. In yet another alternative embodiment, this enclosed volume of track pad cavity  40  could be filled with a fluid, pressurized or unpressurized, creating an hydraulic element. 
         [0024]    The track pad units  32 , and specifically the ends walls  36  and  38 , are to be configured of such a width and thickness, given the strength of its composition material, that they will support the weight of the tracked vehicle  10 , with its supplies and occupants, as it travels over all types of terrain. Yet the width, thickness and strength of the front end wall  36  and the rear end wall  38  are selected such that these walls will collapse in a controlled manner under the force of a mine explosion. Moreover, the front wall  36  of each trailing track pad unit  32  is configured to matingly engage with the appropriately configured juxtaposed rear end wall  38  of the other, leading track pad unit  32  in such controlled collapse resulting from the compressional force of a mine explosion. 
         [0025]    In the preferred embodiment depicted in  FIGS. 2 and 4 , the front wall  38  has a generally convex arcuate shape capable of matingly engaging with the generally concave arcuate shape of the adjacent rear end wall  38  of neighboring track pad unit  32 . It may be preferred, although it is not critical, that the curve of the front end wall  36  be oriented so that it is convex relative to the forward direction of movement of the track  12  and that the rear end wall  38  be oriented to matingly curve in an arc which is concave relative to the forward direction of movement of the track  12 . Other embodiments in which the juxtaposed end walls have other mating configurations which can be conjoined upon controlled collapse are also within the scope of the present invention, so long as the shape and strength of the end walls  36  and  38  of track pad unit  32  can support the vehicle  10  as it travels across multiple types of terrain and yet will controlledly collapse or buckle under the force of a mine explosion. 
         [0026]    In another embodiment shown in  FIG. 5 , the track pad unit  32  may further comprise one or more additional interior support walls or septa  39 , located between front end wall  36  and rear end wall  38 , and extending between an interior side of bearing surface  34  and an exterior side of band body  20 . As explained above in connection with the configuration of end walls  36  and  38 , interior support septum or septa  39  are configured of such width and thickness, given the strength of its compositional material, to assist in supporting the weight of the tracked vehicle  10  as it traverses different terrain conditions. It will be appreciated by those of skill in the art that as the number of supporting septa  39 , which work in combination with end walls  36  and  38  to support the vehicle  10 , is increased, each supporting wall  39 , and also end walls  36  and  38  if desired, may be made thinner. Further, interior support septum or septa will be formed in a shape designed to further cooperate in the controlled collapse of the track pad unit in general, when the latter undergoes exposure to the explosive force of a mine. For example, the shape of the support septa  39  may be, but is not limited to, the arcuate shape analogous to the arcuate shape of front wall  36  and rear wall  38  illustrated in  FIG. 5 . 
         [0027]    In all embodiments, under the compressional force of an exploding mine, the end walls  36  and  38  of multiple track pad units  32  will controllably buckle or collapse such that adjacent pairs of front end walls  36  and rear end walls  38  will be conjoined to provide an essentially continuous physical barrier to the entrained ejecta, minimizing the deleterious effect this ejecta will have on the band body  20 . Maintaining the integrity of the band body  20  will allow the band track  12  to continue functioning, thus maintaining vehicle mobility even after being subjected to a mine explosion. 
         [0028]    Another aspect of the subject invention&#39;s ability to resist mine explosion relates to the height of the end walls  36  and  38 . Since the rapid expansion of the blast envelope of an exploding mine is essentially spherical, the associated shearing forces of the blast envelope will diminish in a cubic relationship as a function of distance from the point of explosion, just as the volume of a sphere increases as a cubic function of the sphere radius. Accordingly, the height of the end walls  36  and  38  will serve to distance the vulnerable band body  20  from the mine thus minimizing the effect of the shearing forces on the band body  20  upon explosion. The height of the end walls  36  and  38  must also be selected with consideration of additional factors such as overall vehicle height, track band weight and related fuel consumption, physical characteristics of the material from which the track band of the subject invention is formed, and the like. In a preferred embodiment, the height of the end walls  36  and  38  may range from about 25 mm. to about 150 mm. 
         [0029]    In operation, a time delayed mine, or a mine supplied with an insensitive fuse, may explode at some time after initial passage of the leading track pad, when the band track  12  may be in a position such as that illustrated in  FIG. 4 . In such case, under the sudden pressure increase of the blast envelope of the exploding mine, a plurality of the track pads  30  will undergo collapse of their respective front end walls  36  and rear end walls  38 , such that adjacent front and rear end walls on adjacent track pads  30  will be conjoined. Thus, the ejecta from the explosion confront an essentially continuous physical barrier formed by the conjoined end wall pairs and the intermediate track pad bearing surfaces  34 . In this manner, the ejecta have reduced effect on the band body  20 . Moreover, the effect upon the band body  20  of the shearing force of the blast envelope is diminished by the greater distance the blast envelope must travel, as a result of the height of the end walls  36  and  38  of each track pad unit  32 . Therefore, the track body  20  has significantly greater chance of maintaining its continuous physical integrity, keeping the vehicle  10  mobile in its hostile environment. By this operation, the band track of the subject invention well satisfies its mine resistant function allowing the vehicle  10  and its occupants to maintain mobility. 
         [0030]    Various alterations and modifications which do not depart from the scope and spirit of the invention will become apparent to those skilled in the art upon review of the foregoing specification and it is to be understood that the subject invention is to be limited only by the following claims.