Abstract:
A vehicle has a fuel system operative to chemically reform a fuel gas, a supply unit for supplying the fuel system with the fuel gas, and a gas reservoir provided with a storage volume for an intermediate storage of the fuel gas, the storage volume having a size that is changeable.

Description:
BACKGROUND OF THE INVENTION 
   CROSS-REFERENCE 
   The invention described and claimed herein below is also described in DE 10 2004 063 071.2, filed Dec. 28, 2004. This German Patent Application. whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d). 
   The present invention relates to a vehicle with a supply unit for supplying a fuel system, in particular an internal-combustion engine, a fuel cell unit, a catalytic converter and/or the like, with a fuel gas. 
   Modern internal-combustion engines, in particular gasoline engines for vehicle propulsion, are equipped with catalytic exhaust-gas converters. Particularly during cold starts, however, even higher quantities of unburned hydrocarbons are emitted, e.g., due to incomplete fuel evaporation or fuel condensation on the still-cold cylinder walls, but also due to the fact that the temperature of the catalytic converter is still too low. 
   Adding hydrogen (H 2 ) or hydrogenous reformate gas to the internal-combustion engine results in improved combustion properties and lower emissions. For the starting phase, it is possible to add hydrogen or hydrogenous reformate gas to the fuel, or to burn this reformate gas exclusively in the internal-combustion engine. The hydrogen can be produced in a suitable quantity “on board” the vehicle, e.g., via the step of reformation from liquid hydrocarbons such as gasoline or diesel fuel, etc., atmospheric oxygen and water. In the case of steam reforming, for example, only water is used. In the case of autothermal reforming, water and air are used, and in the case of partial oxidation, only air is used. In the reforming process, hydrogen is produced, as is carbon monoxide (CO), which is also suitable for combustion in the internal-combustion engine. 
   While the reformer is starting up, however, only a very small amount of reformate gas or none at all is delivered for use in the engine combustion chamber. Hydrogen and reformate gas reservoirs are already known for use to bridge this phase; they are generally filled with combustible reformate gas after the start-up phase or the cold start. 
   It is disadvantageous, however, that the reservoir pressure is limited by the low reformer operating pressure (e.g., approx. 2 bar), since intermediate compression of the gas upstream of the reservoir is generally considered not to be particularly advantageous, for reasons of energy and system complexity. Higher reservoir pressures could be achieved using higher reformer pressures, but this generally fails because the air compression that takes place upstream of the reformer is technically more complex and requires greater energy expenditure. The storage volume of the gas reservoir must therefore be designed appropriately large in size for a given preheating time and engine power. Due to inert gas components in the reformate gas, such as carbon dioxide, nitrogen, water, etc., the storage volume actually required is approximately three-fold greater than is actually necessary. 
   In addition, it is a disadvantage that the compressed gas reservoir—which is generally common—cannot be emptied completely, and instead can only be emptied to the point of pressure equalization. As such, a comparably large dead volume in the reservoir is unusable. 
   Furthermore, vehicles with fuel cells are already in use, the fuel cells being used in particular to supply energy to the drive motor and/or to supply energy to electrical devices as “APUs”. When the fuel cell is used to supply energy to an electric drive motor, an internal-combustion engine is usually not provided. 
   Vehicles of this type that rely on fuel cells to supply electrical power also include reformers for reforming hydrocarbons into a fuel gas. With these vehicles, reservoirs for storing the reformate gas are already known. 
   In addition, metal-hydride reservoirs or the like—in addition to compressed gas reservoirs—are already used in fuel-cell vehicles. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to propose a vehicle a supply unit for supplying a fuel system with a fuel gas, the fuel system being designed to chemically reform the fuel gas, and a gas reservoir with a storage volume for the intermediate storage of the fuel gas being provided, and the storage of the fuel gas being improved during “low-pressure” applications in particular. 
   In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a vehicle, comprising a fuel system operative to chemically reform a fuel gas; a supply unit for supplying said fuel system with the fuel gas; and a gas reservoir provided with a storage volume for an intermediate storage of the fuel gas, said storage volume having a changeable size. 
   A vehicle according to the present invention is unique in that the size of the storage volume of the gas reservoir is changeable. This feature makes it possible, e.g., to evacuate the stored fuel gas completely. For example, when the gas reservoir is empty, the storage volume is nearly zero. This is a particular advantage with “low-pressure” systems in particular, since the efficiency of storage is markedly increased compared to the related art. With the related art, in the case of which compressed gas reservoirs or metal-hydride reservoirs having a constant storage volume are used, a considerable quantity of fuel gas still remains in the gas reservoir in the evacuated state, which markedly degrades the efficiency of storage. 
   In addition, with a storage volume that changes in terms of size, it is advantageous that a different amount of space is required depending on the quantity of fuel gas being stored. For example, when a gas reservoir has been largely evacuated, it is possible for it to take up only a very small amount of the space available in the vehicle. 
   For example, the gas reservoir is designed in the style of a bellows or the like, with the volume stored in the reservoir being changeable according to the present invention. Advantageously, a wall element can be provided, at least a portion of which can be folded or rolled. 
   The gas reservoir preferably includes at least one elastically expandable wall element. With an elastically expandable wall element of this type, the size of the storage volume of the gas reservoir is changeable in a particularly simple manner. For example, the elastically expandable wall element is designed in the manner of a bladder, a balloon, a diaphragm or the like. 
   As an alternative or in combination therewith, the gas reservoir can also include—in a hollow shape, in particular in a cylinder or the like—an adjustable and/or displaceable wall element, such as a piston or the like. In a corresponding embodiment of the present invention, the external or total volume of the gas reservoir that takes up space remains constant, for example, regardless of the extent to which the gas reservoir is filled. At the same time, however, according to the present invention, the size of the storage volume—which is limited at least partially by the displaceable pushing device or the like in particular—can be changed accordingly. 
   Mechanical filling and/or evacuation of the gas reservoir and/or the storage volume can also be provided, if necessary. For example, the displaceable piston in a cylinder can be adjusted mechanically with the aid of a drive device such as an electric motor, etc., such that the storage volume is enlarged and, as a result, fuel gas is suctioned into the gas reservoir. 
   A filling device for filling and/or evacuating the gas reservoir with fuel gas preferably has at least one compressed gas for applying external pressure to the storage volume of the gas reservoir. Pneumatic filling and/or evacuation of the gas reservoir is realizable as a result. This is an advantage in particular with the embodiment according to the present invention in which an elastically expandable wall element is provided. This elastically expandable wall element is acted upon in an advantageous manner by the pneumatic filling and/or evacuation. 
   Advantageously, the gas reservoir includes at least a second storage volume for the intermediate storage of the compressed gas. Preferably, at least one partition is provided in the gas reservoir, with the intermediately-stored fuel gas located on one side, and the intermediately-stored compressed gas located on the other side. 
   In a particular embodiment of the present invention, the size of the second storage volume is changeable. By changing the second storage volume, the filling and/or evacuation of the gas reservoir and/or the first storage volume for the fuel gas can be realized in an advantageous manner. 
   In a preferred embodiment of the present invention, at least one protection device is provided to safeguard the gas reservoir, the total storage volume of the gas reservoir being essentially determined by the protection device. For example, the protection device is designed as a mechanically-fixed screen, brace, fabric or the like; mechanical protection of at least the first storage volume for the fuel gas is realizable as a result. 
   The protection device preferably includes at least one substantially closed container wall. In particular, the protection device is realized as a nearly closed container, in particular as a pressure vessel, with at least one supply and discharge line. 
   In a preferred embodiment of the present invention, the filling device includes at least the protection device. For example, the filling device and/or protection device is designed as a nearly closed container as described above, so that storage of the compressed gas can be realized in an advantageous manner. 
   In a preferred embodiment of the present invention, the gas reservoir is designed—at least in an operating state—such that the stored fuel gas is located on one side of the wall and atmospheric air is located on the other side or outside of the wall. 
   In a particular further development of the present invention, the compressed gas is configured as intake air of the internal-combustion engine. In terms of the present invention, “intake air” is understood to be the air to be drawn into the internal-combustion engine with a small amount of vacuum; in modern vehicles, this air is located between the air filter and the internal-combustion engine. The intake air of the internal-combustion engine has a vacuum in the range of 0.3 to 0.7 bar, and is therefore less than the atmospheric air pressure of approximately 1 bar. 
   The use of intake air as the compressed gas in the filling device is of particular advantage in a filling phase of the gas reservoir. For example, the fuel gas presses—with a pressure of approximately 2 bar—against the relatively low pressure of the intake air entering the gas reservoir from the reformer, enabling the gas reservoir to be filled with fuel gas in an advantageous manner. 
   The compressed gas is preferably configured as the exhaust gas from the internal-combustion engine. With modern vehicles, the pressure of exhaust gas from the internal-combustion engine is greater than atmospheric pressure, thereby allowing this pressure to be used to evacuate the gas reservoir in an advantageous manner. For example, the exhaust gas presses—with approximately this amount of pressure—against the fuel gas stored in the first storage volume of the gas reservoir, the storage volume being connected with the intake region of the internal-combustion engine, e.g., in the evacuation phase, in which a pressure of approximately 0.3 to 0.7 bar exists. The pressure differential enables an advantageous evacuation of the first storage volume with fuel gas to be realized. The first storage volume of the fuel gas can therefore be reduced to nearly zero, so there is nearly no dead volume in the fuel gas reservoir. 
   Preferably, at least one reformer unit is provided for reforming a fuel into the fuel gas. For example, the reforming unit is designed as a reformer for reforming the fuel into the fuel gas. 
   In a particular further development of the present invention, at least one cooling device is provided to cool the fuel gas and/or the compressed gas, in particular the exhaust gas and/or the reformer gas. As a result, it is also possible to use materials with less temperature-resistant properties, such as plastics, rubber or the like, for the gas reservoir or, in particular, the elastically expandable wall element. On the other hand, the cooling of the fuel gas in particular results in an effective reduction in the storage volume required, i.e., in the first storage volume required, which increases the efficiency of storage even further. As a result, the energy density of the stored gas or the fuel gas is increased accordingly. This means the quantity of fuel gas stored in the first storage volume or the gas reservoir is increased. 
   Basically, the fuel gas can be used, preferably in a cold-start phase, to supply the internal-combustion engine or the gasoline engine, a fuel cell unit or fuel cell stack, a vehicle catalytic converter, in particular the catalytic exhaust-gas converter and/or catalytic converters in a fuel cell system with the fuel gas according to the present invention in an advantageous manner, with the components described above combusting or oxidizing the fuel gas in an advantageous manner. 
   With vehicles with internal-combustion engines, engine work is preferably used to fill and/or evacuate the first storage volume or the gas reservoir. As a result, in particular, no separate filling or evacuation drives or the like are required. 
   By using the different pressures of operating gases such as exhaust gas, intake air, atmospheric air, etc., available in a vehicle, a particularly effective filling and/or evacuation of the first storage volume for the fuel gas can be implemented in an advantageous manner. 
   The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1   a  and  1   b  show a schematic illustration of a gas reservoir according to the present invention in a filling phase a and in an evacuation phase b, 
       FIG. 2  shows a schematic block diagram of an internal-combustion system with a gas reservoir according to the present invention, in the filling phase, and 
       FIG. 3  shows a schematic block diagram of the internal-combustion system in a evacuation phase. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A gas reservoir  1  according to the present invention is shown schematically in  FIG. 1 . Gas reservoir  1  includes a housing  2 , which is configured, e.g., as a pressure vessel housing  2 . The storage volume  3  for storage of a fuel gas  4  is located in gas reservoir  1 . 
   A bladder  5 , essentially, for delineating storage volume  3  is provided between fuel gas  4  and housing  2  of gas reservoir  1 . In the exemplary embodiment of the present invention shown, bladder  5  is designed as an elastically expandable bladder. 
   In addition to storage volume  3  for fuel gas  4 , gas reservoir  1  also includes a second storage volume  6  for a compressed gas  7 . Compressed gas  7  is delineated by housing  2  and bladder  5 . 
   Gas reservoir  1  includes a first opening  8  for fuel gas  4  and a second opening  9  for compressed gas  7 . The two openings are provided for the inflow and outflow of corresponding gases  4 ,  7 . In principle, separate inflow and outflow openings can also be provided. 
   A filling state of gas reservoir  1  for fuel gas  4  is shown in  FIG. 1   a . This also means that this is an evacuation phase of gas reservoir  1  for compressed gas  7 . With the filling phase according to  FIG. 1   a , fuel gas  4  flows into storage volume  3  with a first pressure p 1  and produces a volume V 1 . Compressed gas  7  has a pressure p D , which is less than pressure p B  of fuel gas  4 . Three outflow lines, each with a valve  13 , are shown schematically in  FIG. 1  in the region of opening  9  for compressed gas  7 . For example, line  10  is designed for the inflow and outflow of atmospheric air, line  11  is designed for the inflow and outflow of exhaust gas, and line  12  is designed for the inflow and outflow of intake air in an internal-combustion engine of a vehicle. For example, in the filling phase, valve  13  in line  12  for intake air is opened with pressure p s =0.3 to 0.7 bar, so that an advantageous pressure gradient is realized between volume  3  and volume  6 , so that bladder  5  expands and storage volume  3  gradually increases, and fuel gas  4  therefore flows into gas reservoir  1 . 
   An evacuation phase of gas reservoir  1  for fuel gas  4  is shown in  FIG. 1   b . In the example shown, this means that fuel gas  4  flows out of gas reservoir  1  and, at the same time, compressed gas  7  flows into gas reservoir  1  through opening  9 , so that volume  6  gradually increases and volume  3  gradually becomes smaller. According to  FIG. 1   b , a storage pressure p 2  with a volume V 2  exists in storage volume  3  of fuel gas  4 ; storage pressure p 2  is less than pressure p D  of compressed gas  7 . In this case, for example, valve  13  in line  11  for the exhaust gas from the internal-combustion engine of the vehicle is opened, so that volume  6  is acted upon with an exhaust-gas pressure p A  that is greater than atmospheric pressure. In this phase, fuel gas  4  can be directed to an intake manifold—not shown in FIG.  1 —of the internal-combustion engine, which has a pressure p s  of 0.3 to 0.7 bar. As a result, an advantageous pressure gradient is realized that results in the gradual evacuation of storage volume  3 . 
   A bladder reservoir  1  is shown in  FIG. 1  as an example. According to the present invention, a diaphragm reservoir, piston reservoir, bellows or the like can also be used in particular. 
   The integration of gas reservoir  1  in a supply and/or drive system of a vehicle according to the present invention is shown in greater detail in particular in  FIGS. 2 and 3 , the filling of fuel gas  4  being shown in greater detail in  FIG. 2 , and the evacuation of fuel gas  4  from gas reservoir  1  being shown in greater detail in  FIG. 3 . In  FIGS. 2 and 3 , elements having the same reference numerals as those used in  FIG. 1  are designed as comparable components. 
   In these embodiments of the present invention, e.g., fuel  14  is pumped out of a tank  15  using a pump  16  to a valve  17 , in particular an injection valve with a nozzle, and to a reformer  18 . Fuel  14  can be gasoline, diesel fuel or the like. 
   To reform fuel  14 , reformer  18  also requires air  19 , which it receives via either a filter  20 , a fan  21  or a valve  22 , in particular a metering valve  22 . Reformer  18  generally functions at comparably high operating temperatures and has a catalytically active substance for reforming fuel  14  into a reformate containing hydrogen and/or carbon monoxide. 
   Cooling  23  is preferably located downstream of reformer  18 , so that the reformate has temperatures below approximately 100° C. A valve  24  and a branching  25  are located between cooling  23  and gas reservoir  1 . In  FIGS. 2 and 3 , valve  24  is designed als a non-return valve  24 . In special applications, this non-return valve can also be designed as a control or switching valve  24 , e.g., in accordance with valves  13 . A line  26  branches off from branching  25  to a valve  27 , which is designed, in particular, as a metering valve  27  with a nozzle. 
   Filter  20  is connected via a line  28  with an engine  29  or with a combustion chamber of engine  29 , so that atmospheric air  19  can be supplied to it. Fuel  14  is metered via valve  17  to engine  29  and, via valve  27 , reformate from reformer  18  can be supplied or metered directly and/or indirectly to engine  29  from gas reservoir  1 . The supply of reformate from reformer  18  or gas reservoir  1  takes place in a cold-start phase of engine  29  in particular, so that exhaust gas  30  from engine  29  contains relatively few harmful emissions. For exhaust treatment, a catalytic converter  31  and, in particular, one or more lambda probes, etc., which are not shown, are also provided. 
   A branching  32  is located downstream of engine  29  in particular, so that exhaust gas  30  can be directed to catalytic converter  31  and storage volume  6  of gas reservoir  1  via line  11  and valve  13 . 
   In addition, storage volume  6  for compressed gas  7  in gas reservoir  1  is advantageously connected via line  12  and valve  13  with intake line  28 , so that intake air  19  in engine  29  is usable as compressed gas  7  according to the present invention. 
   The filling as illustrated in  FIG. 2  and the evacuation as illustrated in  FIG. 3  takes place essentially as described in detail with reference to  FIG. 1 . In addition, line  10  for ambient air  19  is shown only schematically in  FIGS. 2 and 3 . Line  10  can also be eliminated. In this case, for example, exhaust gas  30  and—in special operating cases—atmospheric air could be supplied to gas reservoir  1  via line  11 . 
   In the filling process illustrated in  FIG. 2 , valve  13  in line  12  is opened, and valve  2  in line  11  is closed. Reformer  18  produces, e.g., a reformate with a pressure p R  of approximately  2  bar, so that this pressure p R =2 bar exists in storage volume  3  and intake manifold pressure p s  of approximately 0.3 to 0.7 bar exists in storage volume  6 . As a result, bladder expands as indicated by the arrow such that storage volume  3  increases and storage volume  6  decreases. 
   In the case of evacuation as illustrated in  FIG. 3 , valve  13  in line  12  is closed, and valve  13  in line  11  is open, so that an exhaust-gas pressure p A  in storage volume  6  is greater than atmospheric pressure. Valve  24  is closed, so that storage volume  3  with engine  29  is acted upon via line  26  with intake pressure p s  of approximately 0.3 to 0.7 bar. As a result, a pressure gradient exists in gas reservoir  1  that causes bladder  5  to contract as illustrated by the arrow, and stored fuel  4  or reformate is supplied to engine  29  via line  11  and open valve  27 . 
   In addition, an advantageous evacuation  40  can be provided, according to  FIGS. 2 and 3  in particular, with which fuel  4  is usable for further applications. For example, fuel  4  can be supplied to a fuel cell unit or a fuel cell stack. 
   Basically, an advantageous control unit can be provided for controlling the filling and evacuation procedure of gas reservoir  1 . For example, the control unit is integrated in the engine management or, in the case of fuel cells, in the fuel-cell regulating system of the vehicle and, in particular, is advantageously connected with the valves shown and the other active components and/or actuators, and with sensors to be provided as necessary. 
   In general—although this is not shown in greater detail—relatively hot exhaust gas  30  can also be cooled using a cooling device to temperatures less than 100° C., so that bladder  5  is exposed to relatively low thermal stress. 
   It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
   While the invention has been illustrated and described as embodied in a vehicle with a supply unit, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
   Without further analysis, the foregoing will reveal fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of the invention. 
   What is claimed as new and desired to be protected by Letters Patent is set fourth in the appended claims.