Abstract:
A mobile machine, in particular a counterweighted fork lift truck, has at least one pressurized tank, in particular to carry fuel that is in a gaseous state under normal conditions. The tank has an at least approximately rectangular external contour in at least one cross-sectional plane.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to German Application No. 10 2005 042 939.4, filed Sep. 9, 2005, which application is herein incorporated by reference in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a mobile machine, in particular a counterweighted fork lift truck, with at least one pressurized tank for carrying fuel which is in a gaseous state under normal conditions. The invention also relates to a pressurized tank for an industrial truck.  
         [0004]     2. Technical Considerations  
         [0005]     Mobile machines are frequently operated with fuels that are in a gaseous state under normal (e.g., ambient) conditions. In addition to hydrocarbon-based fuels, such as propane, butane and methane, increasing use is being made of hydrogen, which can be used to operate a fuel cell unit, for example. The mobile machine generally has one or more pressurized tanks for the storage of these fuels. To be able to store the largest possible quantity of fuel, the tanks are generally pressurized at relatively high pressures, conventionally more than 25 bar and typically on the order of magnitude of 200 bar, as high as 350 bar for hydrogen, and, in individual cases, as high as 700 bar.  
         [0006]     In mobile applications, an objective is generally to make the components as lightweight as possible to increase the cargo-carrying capacity of the vehicle. With fuel tanks of the known art, attempts have consequently been made to design the fuel tanks so that they are as lightweight and simultaneously as stable as possible, for which reason aluminum alloys or compound materials are used. An additional objective of tanks of the known art is to achieve maximum filling pressures and, therefore, maximum filling quantities while using the minimum quantities of material. As a result of which, the tanks are generally cylindrical or spherical in shape with an approximately uniform wall thickness. However, tanks of this type utilize the available space inefficiently, especially if two or more such tanks are located next to each other because unused space remains between the tanks or between the tanks and a housing wall, which is generally flat and straight. Locating the tank(s) at a location outside the chassis of the vehicle, as is frequently done on vehicles that are operated with liquefied natural gas, avoids this problem but has the disadvantage that the tank is exposed without protection to environmental factors, including but not limited to mechanical damage and solar radiation. Additionally, outboard installation restricts accessibility to the vehicle and/or the view of the vehicle operator. The installation of additional components in the vicinity of tanks of the known art is also made more difficult on account of the round geometry, and frequently requires complex and expensive supplemental brackets and mountings which are attached to the surrounding frame or housing components.  
         [0007]     An object of the invention is, therefore, to create a mobile machine, in particular a counterweighted fork lift truck, with at least one pressurized tank, in particular to carry fuel that is in a gaseous state under normal (i.e., ambient) conditions, which has a high level of operational safety and reliability and a long period of operation, has a simple construction, makes optimal utilization of space, and makes possible particularly economical operation.  
         [0008]     An additional object of the invention is to create a pressurized tank for a mobile machine that has a high level of operational safety and a long period of operation, has a simple construction, and makes possible particularly economical operation.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention provides a mobile machine having a tank that has an at least approximately rectangular external contour in at least one cross-sectional plane. The external contour is thereby free of major indentations, bulges or projections, e.g., of the type that are present on an approximately hourglass-shaped structure or as a result of the complex, time-consuming and expensive attachment of support feet or rings. Consequently, the tank can be located in a particularly space-saving manner on an at least likewise approximately flat molded housing wall and/or framed plate girder of the industrial truck. In particular, the tank can be located efficiently in corners of the housing and/or of the frame because it occupies these spaces optimally. The fastening of the tank is also facilitated because a uniform support of the tank on the housing and/or frame parts is achieved.  
         [0010]     It is particularly advantageous if the pressurized tank has an approximately rectangular external contour in three cross-sectional planes that are approximately perpendicular to one another. The tank thereby has an approximately cuboid shape and can be fitted particularly efficiently in empty spaces of the industrial truck that are likewise shaped. In particular, in industrial trucks in which a conventional battery is replaced by an energy supply unit with fuel cells and a fuel tank, the energy supply unit has an external contour that is approximately identical to the external contour of the cuboid battery tray. A cuboid tank can be installed in a particularly space-efficient manner in an energy supply unit of this type. The installation of additional components in the vicinity of the tank is also facilitated because there are flat support surfaces and contact surfaces on all sides of the tank.  
         [0011]     It is particularly advantageous if at least one pressure chamber of the pressurized tank has an approximately circular or arcuate cross section in at least one cross-sectional plane. Circular or curved cross sections are easy to manufacture and are particularly well suited for the pressure chamber because they eliminate the occurrence of dangerous stress peaks at high pressures. Defined maximum or minimum tapping or bleed points for the contents also become easy to realize.  
         [0012]     By providing the pressure chamber of the pressurized tank with a coating, the pressure tightness of the tank can be improved and the tank itself can be protected against damage, e.g., from corrosion.  
         [0013]     The pressurized tank can be made of a ferrous material, in particular steel. Ferrous materials are economically available and are easy to work. The properties can be effectively adapted to meet the requirements of the specific application by means of alloying and heat treatment. It is possible to fabricate an original molding close to the final shape by casting and/or forging with relatively little effort and at relatively low cost. Steels have, among other things, the toughness desired for the intended purpose. Ferrous materials also have a relatively high density so that the tank becomes relatively heavy. In particular, when the pressure chamber has a circular cross section and the external contour has a rectangular cross section, the ferrous material of the tank is present in the corner areas that remain unoccupied in tanks that have a circular external contour, which means that the tank is significantly heavier than a conventional tank of the same volume that effectively occupies a similar amount of space, which can have significant advantages on mobile machines.  
         [0014]     It is appropriate if the pressurized tank has a base body and at least one closing element. Because the tank is constructed from at least two parts, the fabrication process is facilitated. With a standard base body and the use of different closing elements, it thereby becomes possible to adapt the tank to the specific conditions in which it is used, in particular to the fuel used or the location in which it is installed.  
         [0015]     It is particularly advantageous if the closing element comprises at least one fitting and/or at least one connection device for at least one fitting and/or a pipe. The presence of these fittings and/or connection devices reduces the amount of effort required for installation because the connecting device or the fitting can be installed together with the closing element. For different connection requirements, the same base body of the tank can be adapted to other connection conditions by another closing element.  
         [0016]     In an additional configuration of the invention, it is advantageous if the base body of the pressurized tank comprises at least one connecting device for at least one fitting and/or at least one pipe. Devices to fill and/or empty the tank can thereby be connected easily.  
         [0017]     In one advantageous development of the invention, the pressurized tank has at least two separate pressure chambers, thereby making it possible to store different gases in the tank. The pressure chambers can also be pressurized at different pressures.  
         [0018]     It is particularly advantageous if the pressurized tank has devices for the fastening of the pressurized tank, in particular to the vehicle and/or to additional tanks. The time and effort required for the installation are thereby reduced, and fastening devices to the frame or to housing parts of the industrial truck are no longer necessary.  
         [0019]     In one advantageous configuration of the invention, the pressurized tank is provided for the storage of hydrogen. Hydrogen has a number of advantages as a power source for industrial trucks in particular, including the absence of harmful emissions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     Additional advantages and details of the invention are explained in greater detail below on the basis of the exemplary embodiment illustrated in the accompanying drawings. Identical parts are identified with the same reference numbers throughout.  
         [0021]      FIG. 1  shows a pressurized tank of a mobile machine of the invention;  
         [0022]      FIG. 2  shows a pressurized tank with two pressure chambers for a mobile machine of the invention; and  
         [0023]      FIG. 3  shows a counterweighted fork lift truck with a fuel cell system and a pressurized hydrogen tank of the prior art. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]      FIG. 3  shows a counterweighted fork lift truck  1  with a fuel cell unit  2  and a hydrogen tank  3  as one example of a mobile machine that can be used in the invention. Loads are held and transported on load-holding means  4  (such as forks) that are not shown in any further detail in the drawing. To compensate for the weight of the load, there is a counterweight  5  in the stem area of the fork lift truck  1 . Between a front axle  6  and a rear axle  7  of the fork lift truck  1  there is a battery compartment  8  which holds a lead battery (not shown here) or an energy supply unit  9 . The energy supply unit  9  comprises essentially a fuel cell unit  2 , a hydrogen tank  3 , and additional auxiliary units  10  that are not illustrated in detail. The hydrogen tank  3  has the basic cylindrical shape that is conventional for such applications in the known art, and for mobile applications is preferably made of a relatively lightweight material, such as an aluminum alloy or a fiber-reinforced composite material, for example. As a result of the basic cylindrical shape of the tank  3 , additional areas  11 ,  11   a  of the energy supply unit  9 , in particular between the tank  3  and a base plate  12 , and a wall  13  of a housing  14  of the energy supply unit  9  are not occupied. The tank  3  is fastened by means of retaining straps  15  to the base plate  12  of the energy supply unit  9 . The fuel cell unit  2  is supported by a retaining device  16  which is fastened to the wall  13  of the housing  14  of the energy supply unit  9 . If the energy supply unit  9  is used instead of a conventional battery tray, the useful load-carrying capacity of the vehicle  1  is less than when a lead battery is used because the latter is significantly heavier than the energy supply unit  9  and, thus, can counterweight heavier loads.  
         [0025]      FIG. 1  is a schematic illustration of a pressurized tank  20  of the invention for use in an industrial truck  1 . The tank  20 , which is fabricated from steel, includes a base body  21 , which has an approximately cuboid external contour, and a cylindrical interior pressure chamber  22 , as well as two closing elements  23 , only one of which is shown in the drawing for the sake of simplicity. The closing element  23  can be connected, e.g., screwed, to the base body  21 , for which purpose there can be suitable borings  24  in the closing element  23  and threaded borings  25  in the base body  21 , and a conventional seal system (not shown here). However, other types of fastenings of the known art can potentially also be used, such as welding, for example, or the introduction of a thread on the outside diameter of a cylindrical closing element  23  and a corresponding mating thread on the end surface of the compression chamber  22 . Already molded onto the closing element  23  is a pipe segment  26  to which a filling or emptying line can be connected.  
         [0026]     As a result of its cuboid basic shape, the tank  20  can be fitted with precision into the corner  11   a  of the energy supply unit  9 . The cavities  11 ,  11   a  are thereby filled and the weight of the energy supply unit  9  and, thus, of the fork lift truck  1  is significantly increased. The traction of the vehicle  1  is also improved if it is used for towing, as well as the cargo capacity, because the stability is favorably affected by the relatively heavy tank  20 , which is located far from the front axle  6  which acts as the center of motion. In side walls  27  of the base body  21  there are borings  28  that are provided with threads, by means of which the tank  20  can be fastened to the wall  13  and the base plate  12  of the housing  14  of the energy supply unit  9 . The borings  28  can also be used for the fastening of additional components so that the retaining device  16  for the fuel cell unit  2  can be omitted.  
         [0027]     As a result of the cuboid shape, a plurality of such tanks  20  can also be located next to one another or above one another. In this case, it is also conceivable to provide the base body  21  in its longitudinal direction with dovetail guides, for example, to connect the tanks  20  to one another or to a frame and/or housing of a mobile machine or of an energy supply unit  9 . On a construction of this type, it is possible by lining up a plurality of tanks  20  in a row to store even greater quantities of gas and thereby to equip different models of mobile machines with different levels of fuel requirements using only one basic shape of the tank  20  or of the base body  21 .  
         [0028]      FIG. 2  shows an additional embodiment of the invention in which two separate cylindrical pressure chambers  32  are located in a tank  30  with a cuboid base body  31 . It is thereby possible to store different gases, such as hydrogen and nitrogen, in one tank  30  and/or to store one gas at different pressures. However, a tank  30  of this type can also be used instead of two individual tanks  20 , each with one-half the volume, which makes a connection between the two pressure chambers  32  a good idea. This connection can be made, for example, via connecting ducts in the base body  31 , although external pipes are also conceivable, which can be connected to closing elements  23  of the type shown in  FIG. 1 , for example.  
         [0029]     It goes without saying that other embodiments of the invention are also conceivable. For example, the invention can be used advantageously not only on counterweighted fork lift trucks but on all mobile machines in which space is at a premium and frequently a specified minimum weight or a specified weight distribution must be achieved, i.e., for example, on other industrial trucks, especially in industrial tow trucks, the traction of which is directly related to their weight. The use of the invention has additional advantages in excavators or movable work platforms in which counterweights are used to counterbalance the loads that are carried during operation.  
         [0030]     Naturally, the storage of gases and gas mixtures other than hydrogen is also conceivable, as well as the storage of gases that are in a liquid state under elevated pressure at ambient temperature. The cross section of the compression chambers  22 ,  32  can, of course, have a shape that is different from the shape shown in the illustration. For example, with a sufficient wall thickness, the cross section of the compression chambers  22 ,  23  can also be approximately cuboid like the external contour of the tanks  20 ,  30 . Likewise, openings can also be provided in the base bodies  21 ,  31  of the tanks  20 ,  30 , for example for the connection of pipes and/or fittings and for the routing of sensor cables. The base bodies  21 ,  31  can also be manufactured in different ways, depending on the material used. Suitable materials are, in particular, those that have high strength and are heavy, are easy to fabricate and work, therefore including steels in particular, whereby in particular with regard to corrosion resistance, either an alloy which is sufficiently corrosion resistant can be selected, depending on the operating conditions, and/or the pressure chambers  22 ,  32  can be provided with a coating. Suitable fabrication methods for the base bodies  21 ,  31  also include a number of different methods, whereby the preferred methods are those that make it possible to obtain the desired profile in the form of “yard goods”, i.e., in approximately any desired length, such as, for example, extrusion and rolling. In this case, the extruded shape can easily be cut to length to fabricate a base body  21 ,  31  of the desired length. Cast base bodies  21 ,  31  are also conceivable.  
         [0031]     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.