Abstract:
Disclosed is a folding floatation device that is folded at the time when an amphibious vehicle is driven on the water, thereby providing improved safety and increased driving speed to the amphibious vehicle and a method for providing additional buoyance to the amphibious vehicle at the time of driving on the water by using the folding floatation device. According to the present invention, there are provided a folding floatation device with the lower portion opened, a folding flotation device with the upper portion opened and a closed folding flotation device, each of which is disposed at an appropriate location of the vehicle body, such that each floatation device is folded during driving on land and unfolded only during driving on the water, thereby providing additional buoyance to the amphibious vehicle. Therefore, the floatation device of the present invention can provide improved performance to existing amphibious vehicles and overcome design limitations on the driving on the water in case where a novel model is developed, thereby providing a high performance vehicle. With a method for embodying the folding floatation device with the lower portion opened in a space of a suspension device, more particularly, a water driving speed in a track driving manner can be enhanced over that in a water jet driving manner.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method for providing additional buoyance to an amphibious vehicle and a novel floatation device used according to the method, and more particularly, to a method for providing improved additional buoyance and water speed to an amphibious vehicle, by using a folding floatation device that is folded when the amphibious vehicle is driven on land and unfolded when it is driven on the water to provide the additional buoyance to the amphibious vehicle, thereby ensuring the safety of the amphibious vehicle at the time of driving on the water and the increment at the driving speed, which results in the improvement in the driving performance of the amphibious vehicle on the water.  
           [0003]    2. Background of the Related Art  
           [0004]    A conventionally proposed amphibious vehicle is designed in such a manner that a substantially large space is provided in the interior of a vehicle body and the total weight of the vehicle is lighter than weight (that is, an amount of displacement) allowing the vehicle to be fully submerged in the water, such that it can float on the water by the buoyance of water. If the amphibious vehicle receives persons or equipment at maximum load weight, it is submerged in the water approximately over 80%.  
           [0005]    However, if the amphibious vehicle is provided with an thick armor plate for the purpose of enhancing its protection capability, or since the amphibious vehicle is provided with some heavy mounting equipment such as heavy firearms, if the weight of the vehicle exceeds the buoyance, there is no expectation for good water driving capability of the amphibious vehicle even at its developing step. If this kind of amphibious vehicle goes across a river, a floating bridge should be disposed, which makes its combat strength undesirably low.  
           [0006]    On the other hand, the amphibious vehicle can obtain its driving force on the water by using a track rotation method and a water jet driving method.  
           [0007]    According to the track rotation method, an endless track of a suspension device rotates to push water such that the amphibious vehicle obtains its driving force. This does not need any separate driving device, so it is convenient and economical, but there is a disadvantage that the amphibious vehicle moves very slow.  
           [0008]    [0008]FIG. 1 illustrates a conventional amphibious vehicle  1 , where, as well known, a hanging  4  mounted on the outside of a suspension device  2  is adapted to make the flow of water good when the amphibious vehicle  1  is driven on the water, thereby improving the driving speed of the amphibious vehicle  1 . And, an endless track  3  is exposed on its front and rear portions in order for the amphibious vehicle  1  to be driven on land in a convenient manner. A reference numeral  6  denotes a water blocking plate that is adapted to be unfolded toward its front direction when the amphibious vehicle  1  is driven on the water, thereby preventing the upper portion of the amphibious vehicle  1  from overflowing with the water.  
           [0009]    An explanation of the generation of the driving force of the amphibious vehicle  1  according to the track rotation method will be in more detail described. If the track rotates in the water, the lower track pushes water back to generate the driving force, but at this time, the upper track moves in a reverse direction, which results in the generation of a reverse driving force. However, the direction of the flow of water is turned under the configuration of the amphibious vehicle surrounding the upper track, such that the reverse driving force is considerably decreased, and a difference of water pressure between the upper and lower track positions enables the driving force to be stronger than the reverse driving force. But the driving force obtained by the track rotation method is not enough and the power efficiency thereby is very bad.  
           [0010]    According to the water jet driving method, on the other hand, a flow tube is disposed in the interior of the vehicle body and a pump is installed within the flow tube. If the pump operates, water flows in the flow tube and then, the water within the flow tube is discharged to the outside, thereby obtaining the driving force of the amphibious vehicle. This method ensures a relatively fast water driving speed, but the water jet equipment is very expensive and additionally disposed in the interior of the vehicle body specially, such that there occur some disadvantages that the internal space of the vehicle body is decreased and the weight of the vehicle body is increased.  
           [0011]    In addition, the amphibious vehicle  1  does not take a streamline shape unlike a general ship, such that it has considerable water resistance in view of the characteristic of its structure. Therefore, the amphibious vehicle adopting the track rotation method is driven on the water at a velocity of 6 km to 7 km an hour and even though the water jet driving method is adopted, it is driven on the water at a velocity of 10 km to 12 km an hour.  
         SUMMARY OF THE INVENTION  
         [0012]    Accordingly, the present invention is directed to method and device for providing improved additional buoyance and water speed to an amphibious vehicle that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
           [0013]    An object of the present invention is to provide method and device for providing improved additional buoyance and an increased water driving speed to an amphibious vehicle when the amphibious vehicle is driven on the water, thereby ensuring a high combat strength of the amphibious vehicle.  
           [0014]    Another object of the present invention is to provide method and device for rendering buoyance of an amphibious vehicle desirably optimized to thereby reduce the volume of the amphibious vehicle submerged in the water, whereby the amphibious vehicle has relatively low resistance against water when driven on the water.  
           [0015]    Still another object of the present invention is to provide method and device for providing improved additional buoyance to an amphibious vehicle when the amphibious vehicle is driven on the water, thereby making it possible to mount additional combat equipment on the amphibious vehicle, which will result in a high combat strength of the amphibious vehicle.  
           [0016]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0017]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there are provided a folding floatation device with the lower portion opened, a folding floatation device with the upper portion opened, a closed folding floatation device, and a method for providing improved additional buoyance to an amphibious vehicle by using such floatation devices.  
           [0018]    With the floatation device configured in a relatively simple manner according to the present invention, the buoyance of the amphibious vehicle at the time of water driving can be remarkably increased.  
           [0019]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0021]    [0021]FIG. 1 is a perspective view illustrating a conventional amphibious vehicle;  
         [0022]    [0022]FIG. 2 is a perspective view illustrating a folding floatation device with the lower portion opened that is attached on an amphibious vehicle and thus folded according to a first embodiment of the present invention;  
         [0023]    [0023]FIG. 3 is a perspective view illustrating the folding floatation device with the lower portion opened that is attached on the amphibious vehicle and thus unfolded according to the first embodiment of the present invention;  
         [0024]    [0024]FIG. 4 is a perspective view illustrating a folding floatation device with the lower portion opened that is attached on an amphibious vehicle and thus folded according to a second embodiment of the present invention;  
         [0025]    [0025]FIG. 5 is a perspective view illustrating the folding floatation device with the lower portion opened that is attached on the amphibious vehicle and thus unfolded according to the second embodiment of the present invention;  
         [0026]    [0026]FIG. 6 is a graph illustrating the variation of the driving speed according to the variation of the driving force and water resistant force of the amphibious vehicle;  
         [0027]    [0027]FIG. 7 is a rear view illustrating a folding Floatation device with the upper portion opened that is attached on the rear side of an amphibious vehicle and thus folded according to a third embodiment of the present invention;  
         [0028]    [0028]FIG. 8 is a rear view illustrating the folding floatation device with the upper portion opened that is attached on the rear side of the amphibious vehicle and thus unfolded according to the third embodiment of the present invention;  
         [0029]    [0029]FIG. 9 is a perspective view illustrating a closed folding floatation device that is attached on the side of an amphibious vehicle and thus folded according to a fourth embodiment of the present invention;  
         [0030]    [0030]FIG. 10 is a perspective view illustrating the closed folding floatation device that is attached on the water blocking plate of the amphibious vehicle and thus folded according to the fourth embodiment of the present invention;  
         [0031]    [0031]FIG. 11 is an exemplary view illustrating an internal configuration of the closed folding floatation device according to the fourth embodiment of the present invention; and  
         [0032]    [0032]FIG. 12 is a plan view illustrating a partitioned internal configuration of the closed folding floatation device according to the fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0034]    [0034]FIG. 2 is a perspective view illustrating a folding floatation device  10  with the lower portion opened that is attached on an amphibious vehicle and thus folded according to a first embodiment of the present invention and FIG. 3 is a perspective view illustrating the folding floatation device with the lower portion opened that is attached on the amphibious vehicle and thus unfolded according to the first embodiment of the present invention.  
         [0035]    As shown in FIGS. 2 and 3, the amphibious vehicle  1  with a folding floatation device  10  opened at the lower portion thereof (hereinafter, referred to as “floatation device  10 ”) according to the present invention is provided with a hanging  11  extended downward in a relatively long length than the hanging  4  (see FIG. 1) attached on the conventional amphibious vehicle but disposed in such a manner as to be somewhat higher than a bottom surface  8  of the vehicle body of the amphibious vehicle.  
         [0036]    On the other hand, on the respective front and rear sides where a track  3  of the amphibious vehicle runs there is provided a track exposing part (that is, an opening)  5  for making the activity of the amphibious vehicle  1  smooth, and in this case, the floatation device  10  according to the present invention is installed on the above-mentioned track exposing part  5 . The flotation device  10  of the present invention is in a folded state as shown in FIG. 2, when the amphibious vehicle  10  is driven on land and in an unfolded state as shown in FIG. 3, when the amphibious vehicle  10  is driven on the water. At this time, when the amphibious vehicle  10  is in the folded state as shown in FIG. 2, the floatation device  10  allows the track  3  to be sufficiently exposed, such that the amphibious vehicle  1  can be smoothly driven on land, without any interruption.  
         [0037]    The floatation device  10  of the present invention is configured in such a manner that two or more folded plate frames  13  are coupled by a coupling member  14  with a hinge function and thus unfolded or folded, if necessary. The unfolding or folding of the floatation device  10  is carried out by means of an oil cylinder or other means.  
         [0038]    Between the plate frames  13  there is provided a waterproof fabric that is not shown in the drawing, such that the unfolding and folding of the plate frames  13  can be freely carried out and tightness against water can be obtained. At this time, if the waterproof fabric is adapted to connect the bottom end of the upper plate frame with the intermediate portion of the lower plate frame, the plate frames  13  can have the limited movement range when folded or unfolded and the waterproof fabric can be reduced to a minimum size. In order to obtain the tightness against water, there is provided a stop structure that is not further unfolded like an antenna drawn at the time when the plate frames  13  are unfolded to the maximum length thereof, in which a seal pad is provided.  
         [0039]    The back side opened of the floatation device  10  is rigidly attached on the track exposing part  5  on the front and rear sides of the amphibious vehicle  1 , respectively by using a welding method, and the frontmost plate frame  13 ′ is coupled with an appropriate operating device such as an oil cylinder. In this case, the operating device may be located at an arbitrary position where the floatation device  10  can be convenient to operate. The function of the operating device can be replaced in a manually operating manner, and at this time, there is a need for installation of a fixing device for maintaining the folded or unfolded state.  
         [0040]    If the floatation device  10  attached is unfolded (see FIG. 3), a closed space (hereinafter, referred to as “buoyance space”), which is closed by the other sides except the bottom side, is formed between the lower portion of the body of the amphibious vehicle  1  and the upper portion of the upper portion of the track  3 . At this time, the side hanging  11  is disposed in such a manner as to be somewhat higher than the bottom side of the unfolded floatation device  10 . This is to improve the safety in a rolling direction as will be in detail discussed later.  
         [0041]    The amphibious vehicle  1  with the floatation device  10  attached is provided with an air pumping device (or a plurality of air pumping devices) (which is omitted in the drawing) for supplying air absorbed from the atmosphere to the buoyance space. The air pumping device(s) is comprised of an air absorbing hole, an air exhausting hole, a switch valve, a pump and a control system. The air pumping device(s) is well known, and therefore, an explanation of it will be excluded in this detailed description for the sake of brevity.  
         [0042]    As shown in FIG. 2, while the amphibious vehicle  1  is driven on land in the state where the floatation device  10  is folded if it is to be driven on the water to go across a rivers the floatation device  10  is unfolded such that the buoyance space is formed. And, air is supplied by using the air pumping device to the buoyance space, with a consequence that the buoyance space is filled with the air.  
         [0043]    The amphibious vehicle is designed in such a manner as to be floated on a predetermined portion thereof even if it does not have any floatation device according to the present invention, but if it is provided with the floatation device  10  of the present invention, it can additionally obtain the buoyance corresponding to the water weight having the same volume as the air volume by virtue of the air in the interior of the buoyance space. During the amphibious vehicle  1  is driven on the water if an appropriate amount of air is continuously supplied to the interior of the buoyance space by means of the air pumping device, the air that is exhausted due to the movement of the vehicle body or the surface of water can be immediately filled up, with a result that the air layer in the buoyance space is constant and stable.  
         [0044]    As discussed above, with the floatation device of the present invention configured in a relatively simple manner, the buoyance of the amphibious vehicle upon driving on the water can be greatly increased. In addition, the height of the hanging  11  is designed to be somewhat higher than the bottom end of the floatation device at the time when the floatation device is unfolded, and the buoyance space is inclinedly formed by connecting the edge at the vehicle body side to the end of the hanging, such that when the amphibious vehicle is inclined left or right during driving on the water, the volume of the buoyance space at the inclined side is expanded by the surface of water insisting on having a horizontal surface and also the buoyance space expanded is immediately filled with air or gas supplied continuously, thereby resulting in the increment of the buoyance by the space really expanded. To the contrary, the buoyance space lifted upward is decreased by the same principle as mentioned above, such that surplus air is exhausted to the outside of the buoyance space and thus, the volume of buoyance is more decreased than that in the horizontal state. Therefore, a force for lifting the buoyance space upward acts on the buoyance space inclined and a force for pushing the buoyance space downward relative to the horizontal state of the surface of water, that is, a force for restoring the surface of water to its original horizontal state, acts on the buoyance space lifted upward, thereby ensuring safety on driving all the time.  
         [0045]    However, in case where the safety in the rolling direction is sufficient thereby making the additional buoyance not important or in case where the additional buoyance is more important, there is no need to render the buoyance space configured inclinedly, and if the folding floatation device at the front and rear portions of the amphibious vehicle with the side hanging is unfolded to the bottom surface of the vehicle body, the additional buoyance can be optimized.  
         [0046]    If the air is maintained in the buoyance space formed on the position of the suspension device of the amphibious vehicle, the upper track of the amphibious vehicle is exposed in the air, with a consequence that the reverse driving force produced on the upper portion of the track  3  disappears. That is to say, if the upper portion of the track  3  of the amphibious vehicle is located in the air of the buoyance space, the reverse driving force caused during the rotation of the upper portion of the track  3  in the water completely disappears, such that a forward driving force of the amphibious vehicle (i.e., a difference between the driving force caused from the lower portion of the track  3  and the reverse driving force caused from the upper portion of the track  3 ) is greatly increased. In addition, the power consumed in order for the upper portion of the track  3  to push the water is saved, thereby creating a high power efficiency, and if the increased power efficiency is used for the purpose of increasing the rotation speed of the track, the driving force of the amphibious vehicle is considerably improved, which results in a remarkably high driving speed on the water of the amphibious vehicle.  
         [0047]    If only the improvement at the driving speed according to the track driving method is desired, all devices and methods for rendering the upper track move in the air during the water driving, in addition to the folding floatation device with the lower portion opened and the method using the same, can be employed By way of example, the upper portion of the track is surrounded with a predetermined housing, in which the buoyance space is formed, and if the air is supplied in the buoyance space, the upper track moves in the air, thereby accomplishing the improvement at the driving speed.  
         [0048]    In case where the suspension device is closed with a predetermined housing to form the air buoyance space, it is desirable that the housing is not descended under the center height of a driving tooth wheel (sprocket) for the purpose of obtaining mobility on land such as capability for overcoming vertical obstacles.  
         [0049]    [0049]FIGS. 4 and 5 show a folding floatation device  20  with the lower portion opened according to a second embodiment of the present invention adopting such the housing. The height of the housing  21  on the front portion of the track is relatively high by the reason as discussed in the above, but the side hanging  24  is disposed somewhat low. And, there is provided a tight plate structure  22  with a double rotary arm  23  on the front portion of the front housing  21 , which is ascended upward during driving on land and descended downward during driving on the water, such that it is tightly contacted with the front housing  21  and the side hanging  24 , thereby resulting in the formation of the buoyance space. The tight plate structure  22  can be moved and fixed to the upper position and the lower position by means of an appropriate operating device or manually in the same manner as in the first embodiment of the present invention. When the tight plate structure  22  is descended downward to thereby form the buoyance space expanded, the tightness against water can be obtained if a seal pad made of a substantially elastic material is attached on the portion thereof contacted with the housing. FIG. 4 illustrates only the front housing  21 , but of course, the rear housing has the same structure as the front housing  21 .  
         [0050]    [0050]FIG. 6 is a graph illustrating the variation of the driving speed according to the variation of the driving force and water resistant force between the conventional amphibious vehicle and the amphibious vehicle with the floatation device attached according to the present invention, wherein a graph F 1  shows the driving force of the conventional amphibious vehicle and a graph R 1  shows the resistant force against water of the conventional amphibious vehicle. An intersection V 1  between the two graphs F 1  and R 1  represents the resulting driving speed of the conventional amphibious vehicle.  
         [0051]    The amphibious vehicle with the floatation device attached according to the present invention exhibits characteristics that the forward driving force is greatly increased and the resistance force against water is reduced in correspondence with the rate of the buoyance increased, such that the forward driving force is obtained as illustrated in a graph F 2  and the resistance force against water is obtained as illustrated in a graph R 2 . Therefore, the driving speed obtained as an intersection V 2  between the two graphs F 2  and R 2  is greatly increased when compared with the driving speed V 1  of the conventional amphibious vehicle.  
         [0052]    When the buoyance space is formed in the lower portion of the vehicle body, there occur some advantages such as the buoyance increase, the driving speed improvement and the safety in the rolling direction, whereas there occurs a disadvantage that the restoring force in a direction of pitch is somewhat reduced due to a free surface of water effect of the buoyance space. However, since the restoring force in the direction of pitch is greatly stronger than that in the rolling direction by the rectangular form of the amphibious vehicle, the reduction in the restoring force in the direction of pitch is not really important. The reduction in the restoring force can be offset by the increase of a freeboard according to the buoyance increment, which doesn&#39;t give any influence to the safety. Furthermore, in case where various kinds of floatation devices according to the present invention as will be discussed later are at the same time employed, the restoring forces in the directions of pitch and rolling are greatly increased, thereby improving the safety.  
         [0053]    In case where the folding floatation device with the lower portion opened that is employed in the space of the suspension device is changed to have the size and shape corresponding to the position where it is employed, that is, to have a similar structure to the folding floatation device with the upper portion opened as will be discussed hereinafter and applied on the side or rear portion of the vehicle body, the additional buoyance can be obtained and in this case, the basic principle of the folding floatation device with the lower portion opened is the same as the folding floatation device with the upper portion opened, an explanation of which will be excluded.  
         [0054]    [0054]FIGS. 7 and 8 show the folding floatation device  30  with the upper portion opened according to a third embodiment of the present invention.  
         [0055]    The folding floatation device  10  with the lower portion opened according to the first embodiment of the present invention is opened at the lower portion thereof, and to the contrary, the folding floatation device  30  with the upper portion opened according to the third embodiment of the present invention is opened at the upper portion thereof and applied on the rear portion of the amphibious vehicle  1 . Under the above configuration, the volume of the amphibious vehicle  1  to which the buoyance of water is applied is increased and contrarily, the weight thereof is not almost increased, such that a substantially high buoyance is applied to the amphibious vehicle  1 .  
         [0056]    Now, an explanation of the configuration of the folding floatation device  30  with the upper portion opened according to the third embodiment of the present invention will be in detail described.  
         [0057]    The folding floatation device  30  with the upper portion opened is configured in such a manner that a plurality of frames  33  is hinge-coupled between a fixing frame  32  fixed on the vehicle body and an outermost frame  31  by means of a coupling member  35 , each of the plurality of frames being provided with an outer cover  36  thereon. In addition, an elastic member  34  is attached between the fixed frame  32  and the frame  33 , between the plurality of frames  33  and between the frame  33  and the outermost frame  31  on the outer cover  36 , for the purpose of providing tension to them, such that when the floatation device  30  is folded, it can be folded regularly in a predetermined form. The unfolding and folding operations of the floatation device are carried out in a rotation-developing manner as the coupling member  35  has a hinge function, that is, by virtue of an oil cylinder  39  that is attached on the vehicle body at one end thereof and attached on the outermost frame  31  at the other end thereof or appropriate means.  
         [0058]    When the folding floatation device  30  with the upper portion opened is folded, the plurality of frames  33 , the elastic members  34  and the outer cover  36  are in orderly form folded and disposed in a space between the fixed frame  32  and the outermost frame  31 . In order to form the space, the fixed frame  32  and the outermost frame  31  exactly match with each other and have a section of “         ” to form the space therebetween. Specifically, a door is installed on the rear side of the amphibious vehicle, but in the state where the folding floatation device  30  with the upper portion opened is folded, the door can be freely used without any inconvenience.  
         [0059]    Since the buoyance space formed by the floatation device  30  according to the third embodiment of the present invention is exposed in the air, there is an advantage that pouring air to the buoyance space by using an air pumping device is not needed, whereas there is a disadvantage that the buoyance space is overflown with water during the amphibious vehicle is driven on the water, thereby somewhat reducing the buoyance the amphibious vehicle has.  
         [0060]    To remove the above-mentioned disadvantage, however, the flotation device  30  is provided with a fabric cover  37  that is attached on the top portion of the rear portion of the vehicle body at the one end thereof and is attached on a bar at the other end thereof. The fabric cover  37  is rolled and when unrolled, it can cover the opened part of the floatation device. That is, the fabric cover  37 , which is attached on the vehicle body at the one end thereof and rolled in normal case on the bar at the other end thereof, is unrolled to be fixed on a Velcro band  38  attached on the outermost frame  32  of the floatation device  30  to thus cover the opened part, thereby preventing flowing of water in the buoyance space.  
         [0061]    [0061]FIG. 9 shows the external appearance of the closed folding floatation device  40  according to a fourth embodiment of the present invention and FIG. 11 shows the internal configuration of the closed folding floatation device  40 .  
         [0062]    The closed folding floatation device  40  according to the fourth embodiment of the present invention is configured in such a manner that it is similar to the folding floatation device  30  with the upper portion opened, but it is provided with an outer plate  41  replacing the outermost frame  31 , it is relatively extended in length because attached on the side of the vehicle body and it forms a closed space when the floatation device  40  is unfolded by 90°, whereby it is completely closed in order not to flow water to the interior of the buoyance space when the amphibious vehicle  1  is driven on the water. The frame  42 , the outer cover  44 , the elastic member  43  and the coupling member  45  of the closed folding flotation device  40  are almost same as in the third embodiment of the present invention. Since the flotation device  40  can be unfolded or folded by means of an oil cylinder or other appropriate means, the amphibious vehicle is driven on land in the state where the floatation device  40  is folded and driven on the water in the state where the floatation device  40  is unfolded. The angle at which the floatation device  40  is unfolded or the direction upward and downward to which the floatation device  40  is unfolded is differently determined upon the structure the portion of the amphibious vehicle on which the flotation device  40  is attached has.  
         [0063]    The closed folding floatation device  40  exhibits a considerably poor function as the floatation device in case where the outer cover is broken by shots fired from an enemy force during combat. To avoid such the problem, the present invention adopts such an internal configuration as shown in FIG. 11  
         [0064]    As shown, the floatation device  40  according to the fourth embodiment of the present invention is provided with a plurality of balloons  47   a  and  47   b.  And, gas is poured to each of the plurality of balloons  47   a  and  47   b  by means of an air pouring hole  46  and a control valve  48 . Further, a pressure sensor  49  is attached on each balloon, for checking the expansion state of the corresponding balloon. The control valve  48  and the pressure sensor  49  are connected to the main control chamber of the amphibious vehicle and automatically controlled by a computer or controlled automatically.  
         [0065]    The plurality of balloons  47   a  and  47   b  are divided into the balloons  47   a  actually used at the time of driving on the water and the balloons  47   b  used at an emergency state. An allowable expansion volume of each balloon is greatly larger than the expansion volume of the outer cover of the floatation device  40  (for example, two times or more), and each balloon is made of a special rubber material having very strong elasticity and high tension strength unlike a general balloon.  
         [0066]    If the amphibious vehicle  1  with the closed folding floatation device  40  is to be driven on the water, the floatation device  40  is first unfolded by using the oil cylinder and the gas is poured to the balloons  47   a  by means of the respective air pouring holes  46 , thereby making the balloons  47   a  expanded. At this time, the floatation device  40  can be unfolded to its maximum expansion volume as the balloons  47   a  are expanded, thereby providing additional buoyance to the amphibious vehicle  1 . At this time, of course, the gas is not poured to the spare balloons  47   b.    
         [0067]    If some balloons  47   a  are broken due to the shots from the enemy force or other causes while the amphibious vehicle  1  is being driven on the water, the remaining balloons  47   a  are continuously expanded, thereby providing the same buoyance as in an initial state. As discussed above, since the total allowable expansion volume of the plurality of balloons  47   a  is over the maximum expansion volume of the floatation device  40  (for example, two times or more), the remaining balloons  47   a  are expanded large in case where one of the balloons  47   a  is broken to reduce the total volume of the balloons  47   a,  whereby the whole volume of the floatation device can be kept similarly to its initial volume.  
         [0068]    The balloons  47   a  are always expanded by the whole volume of the floatation device  40 , and therefore, even though the outer cover of the floatation device  40  is broken by the shots fired by the enemy force, pouring of water to the interior of the floatation device  40  through the broken holes can be minimized.  
         [0069]    If half or more the balloons  47   a  are broken to thereby cause the total expansion volume of the balloons  47   a  to be smaller than the maximum expansion volume of the floatation device  40 , the computer connected to the pressure sensor immediately recognizes the contents and commands the spare balloons  47   b  to carry out gas pouring, such that the spare balloons  47   b  are expanded to restore the buoyance of the amphibious vehicle to its original state.  
         [0070]    According to the fourth embodiment of the present invention, the number of balloons  47   a  and the number of spare balloons  47   b  to be provided with the floatation device  40  may be determined arbitrarily upon the kind and size of the amphibious vehicle. In some cases, the use balloons  47   a  and the spare balloons  47   b  are adjacent to each other in relation with 1:1 and whenever one is broken, the gas may be poured into the spare balloon adjacent thereto.  
         [0071]    Another structure of the closed folding floatation device  40  capable of providing safety against the shots fired is made by partitioning the buoyance space of the floatation device  40 . FIG. 12 shows a plan view of the amphibious vehicle, where a simply partitioned closed flotation device  50  as illustrated left may cause a problem that a plurality of bulkheads  51  are simultaneously broken by a shot fired toward the front side of the amphibious vehicle by the enemy force. Contrarily, a functionally partitioned closed floatation device  60  according to the present invention is provided with a plurality of inclined folding bulkheads  61  that have the angle slant to the front surface of the amphibious vehicle, thereby reducing the number of bulkheads  61  that may be broken at the same time. In order to make up for the buoyance lost at the time when one partitioned chamber is broken, each of the plurality of bulkheads  61  has a folding structure. Each of the plurality of bulkheads  61  having the folding structure is unfolded and greatly expanded, if the adjacent bulkhead that is in pressure equilibrium relation therewith is broken thus to reduce the pressure, such that the amount of buoyance lost can be restored considerably. In addition, when the floatation device is folded the inclined folding bulkheads  61  are folded and evenly distributed within the floatation device, such that the unbalance of the folded bulkheads  51  in a locally folded state of the simply partitioned floatation device  50  can be prevented. Each of the plurality of partitioned chambers of the functionally partitioned closed flotation device  60  is provided with an air pouring hole and a switch valve, to which an air supplying device is coupled, but an explanation of it will be excluded in the present description for the sake of brevity.  
         [0072]    Another application example of the closed floatation device is shown in FIG. 10. As shown, there is provided a folding floatation device  70  with the front portion closed between a water blocking plate  6  on the front surface of the amphibious vehicle and an upper portion  7  (see FIG. 1) of the front surface of the amphibious vehicle, thereby providing additional buoyance to the front side of the amphibious vehicle and achieving improved safety.  
         [0073]    By the way, since the upper portion  7  of the front surface of the amphibious vehicle is configured in such a manner as to be opened in order to check the state of a power apparatus installed in the amphibious vehicle, the folding floatation device  70  with the front portion closed is installed between the water blocking plate  6  with a double plate inside and outside on the front surface of the amphibious vehicle. Upon driving on the water, thereby, the inside water blocking plate  72  is fixed on the upper portion  7  of the front surface of the amphibious vehicle by means of fixing means (which is not shown) and only the outside water blocking plate  71  is unfolded, such that the floatation device  70  between the inside and outside water blocking plates  72  and  71  is unfolded. Upon checking the state of the amphibious vehicle on land, on the other hand, the floatation device  70  is not unfolded and the inside and outside water blocking plates  72  and  71  are fixed as a unitary body and then unfolded, thereby making the door on the upper portion of the front surface of the amphibious vehicle opened for the convenient checking.  
         [0074]    The folding floatation device  70  with the front portion closed may be provided with the frames and elastic member like the above-mentioned floatation device  60  or may be comprised of only the inside and outside water blocking plates  72  and  71  and the outer cover. Of course, in this case, there is a need for installation of an air supplying and adjusting system, but an explanation of it will be excluded.  
         [0075]    The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of devices. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.  
         [0076]    In other words, since the floatation devices  10  to  70  according to the preferred embodiments of the present invention are folded when the amphibious vehicle is driven on land, thereby not giving any influence in driving and unfolded when it is driven on the water, thereby forming buoyance space therein, they are not limited to the above-described types of devices, and only if they exhibit the above-mentioned characteristics, they are contained in the technical contents of the present invention.  
         [0077]    For example, the floatation device  10  according to the first embodiment of the present invention is not limited to the type of device with the buoyance space inclined according to the above-described structure in the first embodiment, but other kind of device where the sizes of left and right buoyance spaces are different when the amphibious vehicle is tilted to one side during driving on the water, thus to make the buoyance at the tilted side increased is contained in the scope of the present invention. To embody the above-mentioned other kind of device, a plurality of air holes are continuously formed on the lower portion of the hanging of the amphibious vehicle, or the hanging is cut partially and the sizes of buoyance are differently varied as the vehicle body is tilted.  
         [0078]    As clearly discussed above, the floatation device according to the preferred embodiments of the present invention, which is configured in relatively simple manner, can provide improved additional buoyance to an amphibious vehicle when the amphibious vehicle is driven on the water, ensure an increased water driving speed of the amphibious vehicle and improve safety during driving on the water, thereby ensuring a high combat strength of the amphibious vehicle.  
         [0079]    Additionally, the conventional amphibious vehicles are designed in such a manner that the weight thereof is under a predetermined level for the purpose of obtaining the buoyance enough to ensure the safety during driving on the water, thereby making it impossible to freely mount combat equipment on the amphibious vehicle, but the amphibious vehicle with the floatation device according to the present invention can mount the combat equipment corresponding to the additional buoyance, thereby resulting in the improvement of the combat strength.