Abstract:
A protection device for the floor of a land vehicle against mines, said device comprising at least one caisson with a convex external surface oriented towards the ground wherein said caisson incorporates a median part arranged between two lateral walls and extending over the full length of said caisson, the median part of said caisson being of a thickness (E) greater than that (e) of said lateral walls and being designed so as to transmit the stress, when a mine detonates, towards said lateral walls.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The technical scope of the invention is that of devices to ensure the protection of the floor of a land vehicle against mines. 
   2. Description of the Related Art 
   To protect the floor of a land vehicle it is known to position armor under the floor so as to absorb and/or deviate the blast produced by the mine. Know armor comprises one or several metallic or composite layers and possibly deflector means. 
   Patent DE10144208 thus describes armor incorporating a convex caisson covering the vehicle floor. The shape of the caisson ensures the deviation of part of the mine&#39;s blast. 
   These known types of armor or protection devices are usually of constant thickness over the full width to be protected and are defined according to the maximal constraints generated by the mine. This results in a considerable mass for the armor which prejudices the vehicle&#39;s mobility. It also results in reduced ground clearance. 
   A device to protect a vehicle floor is known by patent WO03/102489 which comprises different elements fixed by bolts (two longitudinal beams, transversal beams, oblique lateral beams, and armor plates). In such a device there are several armor plates fastened to the beams and covering specific zones of reduced dimension. The architecture is not optimized with regard to the transmission of stresses. 
   SUMMARY OF THE INVENTION 
   The aim of the, invention is to propose a protection device to ensure, with a relatively reduced overall mass, effective protection for the floors or lower parts of vehicles against the effects of mines, and namely blast-effect mines. 
   Thus, the invention relates to a protection device for the floor of a land vehicle against mines, such device comprising at least one caisson with a convex external surface oriented groundwards and wherein this caisson incorporates a median part arranged between two lateral walls and extending over the full length of the caisson, the median part being of a thickness greater than that of the lateral walls and being designed so as to transmit the stress, when a mine detonates, towards the lateral walls. 
   According to a particular embodiment, the median part may be formed by a separate median part which will be made integral with the lateral walls by fastening means. 
   The median part may be in contact with the lateral walls by bearing surfaces. 
   The median part may incorporate at least one internal cavity. 
   According to another embodiment, the median part and the lateral walls may constitute a single-piece assembly. 
   In all the embodiments, the caisson may have at least one internal partition. 
   The caisson may also enclose at least one block of shock-absorbing material. 
   According to one embodiment of the invention, the caisson may constitute an element added onto a vehicle. 
   According to another embodiment, the caisson may itself constitute part of the very structure of a lower part of a vehicle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will become more apparent from the following description of different embodiments, such description being made with reference to the appended drawings, in which: 
       FIG. 1   a  schematically shows a vehicle passing over a mine, such vehicle equipped with a floor protection device according to the invention, 
       FIG. 1   b  is a detailed view of an embodiment of the bearing surfaces, 
       FIG. 2  shows a top view (following arrow F marked in  FIG. 1 ) of a first embodiment of a protection device according to the invention, 
       FIGS. 3 and 4  also show a top view of two other embodiments of the device according to the invention, 
       FIGS. 5   a  and  5   b  show another embodiment of the invention,  FIG. 5   b  being a top view and  FIG. 5   a  being a cross section, such section being made along plane AA marked in  FIG. 5   a.    
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1   a  shows a vehicle  1  which incorporates a cab  2  carried by wheels  3  connected to the cab by axle arms  4 .  FIG. 1   a  shows a blast effect mine positioned on the ground  6 . When ignited, this mine generates high pressure (schematized by arrows P) in the direction of the floor  7  of a vehicle  1 . 
   In accordance with the invention, a device  8  is provided to ensure the protection of the floor  7  (or lower part) of the vehicle. 
   The device is shown here in the form of a separate caisson fastened to the lower part of the vehicle  1 . 
   It is naturally possible, without departing from the scope of the invention, to define a vehicle whose actual structure will incorporate the device  8  incorporated with the cab  2  from the onset. The caisson  8  may thus be incorporated with the floor itself. 
   The caisson  8 , within the meaning of the invention, is intended as a structure delimited by walls and which itself delimits an internal volume  9 . This structure may be added onto an existing vehicle to make an over-protection. It may also be designed, from the onset, into the vehicle as a constitutive part of a vehicle cab or floor. 
   In accordance with the invention, the caisson  8  has a convex external surface oriented groundwards  6 . 
   This caisson furthermore incorporates a median part  10  arranged between two lateral walls  11   a ,  11   b.    
   This median part has a thickness E which is greater than the thicknesses e of the lateral walls  11   a  and  11   b.    
   The lateral walls  11   a  and  11   b  are thus constituted by sheet metal (for example, sheet steel) whereas the median part is formed here by a part  10  (for example, of steel), obtained by machining or casting, and which is made integral with the lateral walls  11   a ,  11   b  by fastening means, for example, welding. 
   As may be more particularly seen in  FIG. 2 , which is a top view of the caisson following arrow F marked in  FIG. 1   a , the part  10  extends over the full length L of the caisson  8 . 
   Moreover, the caisson  8  is delimited at its front and rear faces by steel closing plates  12   a  and  12   b , welded to walls  11   a  and  11   b . To make the device lighter, it is naturally possible not to provide closing plates  12   a ,  12   b  (namely when the caisson is an add-on protection). 
   Part  10  will preferably be linked to walls  11   a ,  11   b  by bearing surfaces  13  which will be inclined with respect to the vertical (see  FIG. 1   a ). 
   The caisson  8  will be given a length L equal to that of the part of the vehicle which is to be protected first and foremost. It is possible for the caisson  8  to be of a total length equal to the length of the vehicle  1 . 
   By proposing to give the caisson  8  a thickness at its median part E which is greater than that of its lateral walls  11   a ,  11   b , the resistance of the caisson is improved and the caisson is made lighter. Indeed, the lateral walls are further from the ground than the median part and they are inclined. It is thus possible for them to be made lighter with respect to the median part. 
   The caisson according to the invention behaves in a totally different manner to that of known convex caissons during the detonation of a mine. 
   Known caissons deviate part of the mine&#39;s blast thanks to their convexity, but they must be sufficiently resistant mechanically to avoid the sheet metal making up the caisson tearing. This results in caissons which are thick and heavy. 
   The caisson according to the invention incorporates a solid median part  10  resistant to tearing which transmits part of the shock received to the lateral walls. This transmission is made via the bearing surfaces  13  linking the lateral parts to part  10 . 
   If part of the blast is deviated by the convex form, the main stress, received vertically at part  10 , is transmitted to walls  11   a ,  11   b  causing them to deform and causing the caisson  8  to gradually flatten towards the floor  7 . 
   This mechanical deformation has slower kinematics than that of caissons with even thickness. It enables the energy communicated by the mine to be consumed and thereby protects the floor. 
   The lateral walls  11   a  and  11   b  may thus be thinner since they are located at a distance from the median part which is the part most stressed by the mine&#39;s effects. 
   The bearing surfaces  13  shown in  FIG. 1   a  are plane surfaces substantially perpendicular to lateral walls  11   a  and  11   b.    
   It is naturally possible for the bearing surfaces to be given another shape or orientation to make it easier to attach part  10  by welding and to transmit the stresses. 
     FIG. 1   b  thus shows substantially horizontal bearing surfaces  13  which are formed by grooves  14  arranged on each side of part  10  onto which the beveled ends of the lateral walls  11   a ,  11   b  are applied. 
   Someone skilled in the art will dimension the lateral walls  11   a ,  11   b  and part  10  according to the characteristics of the mine threat against which protection is sought for the vehicle as well as to the characteristics of the vehicle itself. 
   It is thus possible to make caissons  8  whose height H is lower than that of known blast deviation caissons. The vehicle&#39;s ground clearance is thus improved. 
   For an equivalent protection capacity, the surface density of the caisson may thus be reduced with respect to that of known caissons of even thickness. This results in protection&#39;s reduced overall mass. 
   A caisson  8  has been described which associates steel lateral walls  11   a ,  11   b  which a median part  10  also made of steel. It is naturally possible to implement different materials. A caisson  8  may thus be made of a magnetic materials, such as aluminum for example, aluminum alloys or titanium. The caisson  8  may also be made partly of composite materials. These solutions enable the caisson to be further lightened and its magnetic signature reduced. 
   The internal volume  9  of the caisson  8  may house the mechanical organs of the vehicle, for example the drive shaft. 
   The external form of part  10  may also be different from a triangular shape. A part  10  may be adopted whose external profile is rounded, for example cylindrical or hyperbolic. 
   It is also possible for a caisson to be made as a single piece whose median part  10  is made in one piece with the lateral walls  11   a ,  11   b . The caisson  8  will in this case be a single piece obtained, for example, by casting or machining. 
     FIG. 3  shows another embodiment of the invention in which the caisson  8  incorporates internal partitions  15  enabling it to be made more rigid. These partitions have an analogous profile to that of the closing plates  12   a ,  12   b  and press both on the lateral walls  11   a ,  11   b  and on part  10 . 
   The partitions  15  will be made, for example, in the form of sheets of metal welded to walls  11   a ,  11   b . Such an embodiment enables different deformation zones for the caisson&#39;s structure to be delimited between each pair of partitions. 
   So as to further improve the level of protection, it is possible, as shown in  FIG. 4 , to place one or several blocks  16  of a compressible material between two partitions  15 . The blocks may be made, for example, of a cellular material (such as a honeycomb). The blocks may be of a metallic material, or else an organic or composite one. 
   It is naturally possible for one or several blocks  16  to be provided for a caisson which does not have any partitions  15  (such as the caisson shown in  FIG. 2 ). In this case, the block or blocks  16  will be fixed to the caisson  8 , for example by bonding onto the lateral walls  11   a ,  11   b.    
     FIG. 4  shows two blocks  16  arranged at a front part of the caisson  8 . The two housings delimited by the partitions  15  to the rear of the caisson  8  have no blocks. It is thus possible to provide shock-absorbing blocks  16  only for a zone of the caisson  8  which requires particular reinforcement. 
     FIGS. 5   a  and  5   b  show another embodiment of the invention in which the caisson  8  incorporates a lightened median part  10 . This part  10  thus incorporates cavities  17  evenly spaced over its length. 
   These cavities enable the mass of the part to be reduced without reducing its rigidity at the same time. 
   Someone skilled in the art will easily dimension the number, shape, dimensions and spacing of the cavities  17  in part  10  according to the rigidity properties required. 
   The cavities  17  may be made by machining or else obtained by casting during the manufacture of part  10 . 
   It is naturally possible to combine the different embodiment described previously according to operational requirements. 
   A caisson may be defined according to  FIGS. 5   a ,  5   b  which also incorporates partitions  15  and/or blocks  16 . 
   In this case, the shape of the bearing surfaces  13  may be chosen like those shown in  FIG. 1   b.    
   Finally, longitudinal partitions may be provided in the volume  9  of the caisson that are perpendicular to transversal partitions  15 . An internal mesh will thus be made inside which the blocks of shock-absorbing material may be arranged.