Abstract:
A tank for a reducing agent includes at least one side wall and a bottom. At least one heating unit is provided at least in the side wall or in the bottom. A motor vehicle having a tank is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation, under 35 U.S.C. §120, of copending International Application No. PCT/EP2009/061542, filed Sep. 7, 2009, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2008 048 798.8, filed Sep. 24, 2008; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a tank for a reducing agent having at least one heating unit. The present invention also relates to a motor vehicle having a tank. 
         [0003]    As a result of more stringent requirements for the limitation of pollutant emissions of motor vehicles, in particular of passenger motor vehicles and utility vehicles, SCR systems are ever more frequently being installed in motor vehicles. The SCR systems effect a reduction of nitrogen oxides contained in exhaust gas. Such SCR systems use a reducing agent (also in the form of a reducing agent precursor) which is brought into contact with the exhaust gas. An aqueous urea solution (for example AdBlue) which has a freezing temperature of approximately −11° C. is used, in particular, as a reducing agent. 
         [0004]    A tank is generally provided in the motor vehicles for the liquid reducing agent. The tank firstly permits an adequate operating range of the motor vehicle and secondly is constructed in such a way that the liquid reducing agent can be used at all operating points of the motor vehicle. In that case, provision is made in particular for heating units which, at cold temperatures, firstly re-liquefy the liquid reducing agent after a relatively long period of standstill of the motor vehicle, and secondly keep the reducing agent in the liquid state during the operation of the motor vehicle. In that case, the heating units have heretofore been provided only in line regions of the SCR system or in extraction devices of the tank, for example in an extraction pipe. Furthermore, small-volume buffer storage devices are known which, independently of the main tank volume, have their own heating units and can therefore be adequately heated more quickly. In that case, however, it must be noted that either only small volumes can be liquefied through the use of the heating units, and/or special system components such as additional buffer storage tanks must be provided in order to provide an adequate amount of liquid reducing agent for exhaust-gas purification. A further important demand on such heating units is also that the heating units consume as little energy as possible, in such a way that power storage devices or power supplies of the vehicle are subjected to the least possible loading. 
       SUMMARY OF THE INVENTION 
       [0005]    It is accordingly an object of the invention to provide a tank for a reducing agent having heating units and a motor vehicle having a tank, which overcome the hereinafore-mentioned disadvantages and at least partially solve the highlighted problems of the heretofore-known devices and vehicles of this general type and which, in particular, specify a tank having a heating unit which can be operated in an energy-saving manner and which requires as few further components as possible in order to provide the reducing agent in a liquid, and therefore operationally ready, state. 
         [0006]    With the foregoing and other objects in view there is provided, in accordance with the invention, a tank for a reducing agent. The tank comprises at least one side wall, a base, and at least one heating unit provided in at least one of the at least one side wall or the base. 
         [0007]    The tank may have virtually any desired outer shape, in particular with at least partially round or polygonal regions which are adapted to the spatial conditions of the motor vehicle. In this case, the tank has, in particular in an upper region, an extraction device for the reducing agent contained in the tank, in particular an extraction pipe which extends into the tank. The extraction device is preferably disposed on an upper wall region of the tank, in such a way that the reducing agent can at least not permanently impinge on seals which are required for the extraction device. 
         [0008]    The at least one side wall of the tank is preferably disposed in an encircling manner between the upper wall region and the base of the tank. The base of the tank is the region which is in particular always covered by reducing agent or which, with progressive emptying of the tank, at least defines the last surface covered in the tank. 
         [0009]    The heating unit is disposed in the side wall and/or in the base, and in particular is integrally molded or laminated within the side wall. The heating unit is constructed preferably from heating wires which are disposed within the side wall. For this purpose, the side wall or the base have a wall which is in particular insulated from the outside and which has a good heat transfer coefficient toward the tank interior. “In” the side wall or “in” the base means that the heating unit is surrounded by the material of the side wall/of the base, that is to say is in particular fully enclosed by that material. 
         [0010]    As a result of the configuration of the heating unit in the tank for a reducing agent, it is achieved in particular that no additional storage tank need be provided between the tank for the reducing agent and a device for metering the reducing agent into the exhaust system. For this purpose, the heating unit is disposed in the side wall and/or in the base in such a way that, in particular over a large area, those regions of a frozen reducing agent which are close to the wall can be liquefied again and supplied to the extraction pipe. As a result in particular of the configuration of the heating unit in the base region, an adequately large surface which is permanently covered by reducing agent is heated, and therefore the required amount of reducing agent is provided. The configuration of the heating unit over a large area in the wall of the tank is of significance in particular with regard to often interrupted operation of a motor vehicle, as a result of which the liquid reducing agent freezes and must be thawed out again at short intervals. Conventional heating units which can quickly liquefy only extremely small amounts of reducing agent are not provided for such operational demands. In that situation, the main volume of the reducing agent in the tank initially remains frozen, and caverns with liquid reducing agent are formed around the locally disposed heating units, in particular around the extraction pipe. After the extraction of the liquefied reducing agent in the partial regions, the heat energy of the heating units is then only transmitted to the frozen other regions of the reducing agent in the tank to an inadequate extent through the cavities which are then present and which are filled only with air, in such a way that further liquid reducing agent cannot be supplied in adequate amounts. 
         [0011]    The configuration of a heating unit in the side wall is advantageous in particular in that it allows the frozen reducing agent to be detached from the wall, and correspondingly permits or promotes sliding of the frozen reducing agent down in the direction of the base. It is thus possible for the heating unit which is adjacent an extraction device, and which is disposed in particular in the base, to transmit adequate amounts of heat energy into the frozen reducing agent, in such a way that, on a permanent basis, no cavities are generated and generally good heat transfer is permitted from the wall to the frozen reducing agent or liquid reducing agent. 
         [0012]    In accordance with another feature of the invention, the tank at least partially has a cross section which increases in size in the direction of the base. In this case, the cross section is, in particular, the area disposed perpendicular to the force of gravity, enclosed by the side surfaces. That area increases in size in the direction of the base, in such a way that the frozen reducing agent sinks in the direction of the base solely due to the influence of gravity. That effect is preferably assisted by virtue of heating units being disposed in the side walls, which heating units permit and/or accelerate the dissolution of the frozen reducing agent. 
         [0013]    In accordance with a further feature of the invention, the base has at least one depression and/or at least one sump. In this case, a sump refers to a partial volume which is connected to the tank, which is disposed in the base and which is suitable for collecting the liquid reducing agent, wherein the extraction device extends into the sump. In connection with the present invention, a depression preferably refers to a region at a lower level than the remaining region of the base. The liquefied reducing agent or else a remainder of the reducing agent generally collects in the region of the depression or in a sump connected to the depression, and is extracted from there through the use of an extraction device. 
         [0014]    In accordance with an added feature of the invention, the base has, at least in partial regions, a progressive slope at least in the direction of the depression or of the sump. In special applications, however, a degressive slope may also be advantageous. In relation to a planar structure, a construction of the base with a slope is advantageous in particular in that the reducing agent in frozen or liquid form is directed in the direction of the depression or of the sump, and thereby in the direction of the extraction device, under the force of gravity. In this case, different structures of the base, in particular structures with a progressive or degressive slope, can accelerate or assist such direction of the reducing agent. The construction with a progressive slope in particular results in a tank volume cross section which quickly decreases in size in the direction of the depression or sump, in such a way that in this case, an even smaller volume of the reducing agent needs to be kept in liquid form or liquefied through the use of the heating unit. 
         [0015]    In accordance with an additional feature of the invention, at least one side wall or the base has at least one bar which extends into a tank interior, and the at least one bar has a heating unit. In this connection, a bar refers to a narrow planar element, which may preferably be produced from the same material as the tank. In particular, the bar has good heat-conducting characteristics, in such a way that the heating unit, which is preferably disposed in the bar, can be operated in as effective a manner as possible, preferably symmetrically on all sides. 
         [0016]    The bar may furthermore be formed as a folded-in portion, that is to say for example may be produced through the use of a bellows-like deformation of the tank. In this case, heating units present in the wall of the tank may be deformed jointly therewith, in such a way that the heating units are then disposed in the bar within the tank. In order to provide for such a bellows-like deformation of the tank, the tank should be formed with an enlarged surface, in such a way that the desired tank volume is provided even after the bar is produced out of the wall of the tank. 
         [0017]    The at least one bar is disposed in the tank interior in such a way that, firstly, the extraction device is supplied with adequate reducing agent as quickly as possible, and secondly, cavity formation within the frozen reducing agent in the tank, which adversely affects a further liquefaction of the reducing agent, is prevented. For this purpose, the bar may be disposed so as to be inclined relative to the base and/or relative to the side walls, in such a way that firstly, frozen reducing agent can slip down to heated wall regions and make contact with them, and is therefore liquefied more quickly. Furthermore, partial regions of the tank may be formed which are more intensely heated by the bars and within which an adequate amount of reducing agent is liquefied very quickly. 
         [0018]    In accordance with yet another feature of the invention, an extraction pipe is provided for extracting reducing agent from the tank, wherein the extraction pipe has at least one rib on an outer circumferential surface, and the extraction pipe and the at least one rib are heated through the use of at least one heating unit. The rib is produced in particular from the same material as the extraction pipe and/or tank material. 
         [0019]    As a result of the configuration of a rib on the extraction pipe, the heated zone within the tank is increased in size significantly, and it is possible in particular through the use of the interaction with bars and heating units in the base and/or side walls for the formation of cavities within the frozen reducing agent, which adversely affects the further liquefaction of reducing agent, to be prevented. 
         [0020]    In accordance with yet a further feature of the invention, the heating units, disposed in at least one element from the group including side wall, base, bar, extraction pipe and rib, can be controlled independently of one another. In particular, the heating power of the heating units can be controlled as a function of the filling level of reducing agent in the tank, of the tank inclination, and or of the coverage of the heating unit with reducing agent. The heating units can furthermore advantageously be controlled, independently of one another, as a function of reducing agent, reducing agent temperature and/or outside temperature. 
         [0021]    Through the use of such individual controlling of the heating units as a function of different parameters, it is possible in particular for energy-saving operation to be realized and also for cavity formation within the tank to be prevented under all circumstances. A provision of liquid reducing agent to the extraction pipe can generally be ensured in this way. 
         [0022]    In accordance with yet an added feature of the invention, the at least one heating unit has a PTC element, in such a way that self-controlling of the heating units is made possible. PTC (positive temperature coefficient) elements are components having an internal resistance which increases non-linearly toward higher temperature values. In this way, a self-controlling effect is obtained which results in self-deactivation when a limit temperature is reached. Through the use of PTC elements, it is thus possible for the heating units to be heated only up to a predefined limit temperature, which is predefined primarily by the side wall material, base material, rib material and/or bar material being used. 
         [0023]    In accordance with yet an additional feature of the invention, the heating unit at least partially uses engine cooling water as a heating medium, that is to say accordingly it is connected, or can be connected in a targeted manner, in particular to a cooling circuit of the engine. 
         [0024]    In accordance with again another feature of the invention, the at least one side wall, the base, the bar or the at least one rib have a surface, and channel structures are formed on at least part of the surface. The channel structures are formed in particular as groove-like recesses on the surface through which the liquefied reducing agent can flow. The channel structures are provided in particular in such a way that frozen reducing agent which is at least partially present cannot settle on the side wall, on the base, on the bar or on the rib in such a way as to prevent run-off of liquefied reducing agent in the direction of the depression or of the sump. As a result of channels formed as recesses or grooves, the frozen reducing agent is deposited on the surfaces, and a run-off can take place under the frozen reducing agent through the channel structures which are formed. 
         [0025]    In accordance with again a further feature of the invention, the channel structures run substantially in the direction of the depression or the sump. In this way, it is advantageously achieved that the reducing agent is conducted to the lowest point of the tank or to the extraction pipe, and that the tank always has liquid reducing agent in the region of the extraction pipe. 
         [0026]    With the objects of the invention in view, there is concomitantly provided a motor vehicle, including at least one tank according to the invention. 
         [0027]    Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that the features specified individually in the dependent claims may be combined with one another in any desired technologically meaningful way and define further embodiments of the invention. 
         [0028]    Although the invention is illustrated and described herein as embodied in a tank for a reducing agent having heating units and a motor vehicle having a tank, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0029]    The construction and method of operation of the invention, however, 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 SEVERAL VIEWS OF THE DRAWING 
         [0030]      FIG. 1  is a diagrammatic, side-elevational view of a motor vehicle having a tank according to the prior art; 
           [0031]      FIG. 2  is a side-elevational view of a tank according to the invention; and 
           [0032]      FIG. 3  is a side-elevational view of a further embodiment of a tank according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Referring now in detail to the figures of the drawing for explaining the invention and the technical field in more detail by showing particularly preferred structural variants to which the invention is not restricted, and first, particularly, to  FIG. 1  thereof, in which the same reference numerals are used for identical objects, there is seen a diagrammatic side view of a tank  1  according to the prior art for a reducing agent  2 , in which the tank has a side wall  3  and a base  4 . The reducing agent  2  is removed from an interior  10  of the tank  1 , in particular from a sump  8 , through an extraction pipe  11 . The tank  1  is disposed in a motor vehicle  15 . 
         [0034]      FIG. 2  diagrammatically shows a side view of a tank  1  according to the present invention. The tank  1  has side walls  3  and a base  4  and the side walls  3  widen conically in the direction of the base  4 . In this way, the cross section  6  of the tank  1  increases in size in the direction of the base  4 . The extraction pipe  11  is disposed in a sump  8  which forms the lowest point of the base  4 . Each of the base  4 , the sump  8  and at least one side wall  3  has a respective heating unit  5  formed in a wall  16 . The heating units, in particular, have heating circuits which can be controlled independently of one another. In this case, the walls  16  are formed with good heat-conducting properties on the side thereof facing toward the tank interior  10 , and with insulation  17  with respect to the tank surroundings  18 . 
         [0035]      FIG. 3  shows a further embodiment of the tank  1  according to the invention with the side wall  3  and the base  4 , wherein a partial region, in this case the left-hand side of the tank  1 , has a depression  7  in the base  4 . In this case, the base  4  has a progressive slope in the partial region directed toward the sump element  8 . Furthermore, in the tank  1 , at least one rib  12  is disposed on an outer circumferential surface  13  of the extraction pipe  11 , and a bar  9  is disposed on the base  4  with a channel structure  14  which extends in the direction of the sump  8 . The bar  9  is, in particular, also provided in part with an inclination with respect to the base  4 , in such a way that frozen reducing agent  2  is also supported on the bar  9  which has a small area in relation to the side wall  3 . The combination of the cross section  6  of the side walls  3 , which widens in the direction of the base  4 , and the use of heated bars  9 , ensures that an adequate amount of reducing agent  2  is liquefied and supplied to the extraction pipe  11  at all operating points, in such a way that a supply of reducing agent  2  to an SCR system is possible at all times.