Abstract:
A heat exchanger ( 10 ) for arrangement inside a service-liquid tank ( 12 ), in particular inside a motor-vehicle service-liquid tank ( 12 ), comprising:
       a heat-exchanger liquid reservoir ( 14 ) for receiving a supply of liquid ( 22 ),   an electric heating device ( 20 ) which is constructed and arranged for the transfer of heat into the heat-exchanger liquid reservoir ( 14 ), and   a heat-exchanger line ( 24 ) which originates at least from the heat-exchanger liquid reservoir ( 14 ) and which is designed for the transfer of heat from the liquid flowing in the heat-exchanger line ( 24 ) to an area ( 26 ) outside the heat-exchanger line ( 24 ),
           characterized in that the heat-exchanger line ( 24 ), as a circulation line, discharges into the heat-exchanger liquid reservoir ( 14 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority to German Application No. 10 2016 203 558.4, filed Mar. 3, 2016. The entirety of the disclosure of the above-referenced application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to a heat exchanger for arrangement in a service liquid tank, in particular in a motor vehicle tank, comprising:
       a heat-exchanger liquid reservoir for accepting a supply of liquid,   an electric heating device that is constructed and disposed to transfer heat into the heat-exchanger liquid reservoir, and   a heat-exchanger line that originates at least from the heat-exchanger liquid reservoir, and which is constructed for the transfer of heat from the liquid flowing in the heat-exchanger line to an area outside the heat-exchanger line.       
 
         [0007]    Description of the Related Art 
         [0008]    A heat exchanger of the above-described type is known from DE 10 2009 028 113 A1. 
         [0009]    It is known from this publication to heat liquid with an electric heating device inside a heat-exchanger liquid reservoir separate from the reservoir volume of the motor vehicle service tank, and pump it away from the heat-exchanger liquid reservoir via a line. More specifically, in the case of the known heat exchanger the liquid is pumped from the heat-exchanger liquid reservoir out of the motor vehicle service-liquid tank for its intended use. Here the line of the known heat exchanger extends through the reservoir volume of the motor-vehicle service-liquid tank and then exits the motor-vehicle service-liquid tank, wherein when flowing through the line, which is actually not a primary heat-exchanger line but rather a pumping line, whose pumped material unavoidably gives off some heat during the pumping; due to the short length of time the heat-exchanger liquid remains in the line, only a small amount of heat from said liquid can be transferred to the reservoir volume of the service-liquid tank. 
         [0010]    A similar service-liquid tank with heat exchanger is also known from DE 10 2009 029 313 A1. 
         [0011]    The service-liquid tank in the last-mentioned publication has an additional heat-exchanger line. The heat-exchanger line, through which either cooling liquid or exhaust gas from the internal combustion engine of a motor vehicle flows, passes through the reservoir volume of the service-liquid tank in order to emit heat from the heat-exchanger fluid: exhaust gas or coolant liquid, to the reservoir volume of the service-liquid tank. The exhaust gas or the coolant liquid is not heated by an electric heating device, because the internal combustion engine serves as the heat source. 
         [0012]    The electric heating device is additionally present in the service-liquid tank, so that it can, as in the publication covering the device of the above-described type, also itself melt service liquid locally in the tank, when the internal combustion engine is still cold, and the coolant liquid is therefore not temperate enough to heat the service liquid, or an exhaust gas might not yet be flowing, because the internal combustion engine has not yet been put into operation. 
         [0013]    In the case of the heat exchanger of the above-described type, the service liquid stored in the actual service-liquid tank is used as the heat-exchanger liquid. 
         [0014]    In DE 10 2009 029 313 A two different heat-exchanger liquids are used, in one instance, as in the publication covering the device of the above-described type, it is the actual service liquid stored in the tank, and in the second instance, it is the fluid explained above, in the form of either exhaust gas or of coolant liquid of the internal combustion engine. 
       SUMMARY OF THE INVENTION 
       [0015]    The object of the present invention is to specify a heat exchanger of the above-described type, i.e. a heat exchanger with an electric heating device, which can transfer heat more effectively to the inside of a service-liquid tank than the heat exchangers in the prior art are able to. 
         [0016]    This object is inventively achieved by a heat exchanger of the type mentioned at the beginning, wherein the heat-exchanger line, as a circulation line, discharges into the heat-exchanger liquid reservoir. 
         [0017]    The heat-exchanger line is thus configured as a circulation line, which allows the liquid received by the heat-exchanger liquid reservoir to circulate between the electric heating device and a heat-emission area, so that—in contrast to the prior art—heated liquid is not simply conveyed through the service-liquid tank and out of it, but rather said heated liquid can flow repeatedly through the service-liquid tank and can thus ensure continuous heating of the service liquid received in the tank. 
         [0018]    Then the electric heating device only has to replace the heat quantity emitted in the heat-emission region of the heat-exchanger line, which also reduces the energy consumption of the inventive heat exchanger compared to the heat exchanger of the above-described type. 
         [0019]    Because the heated liquid is not simply conveyed out of the service-liquid tank, as is the case in the prior art, it is not suddenly lost as a heat reservoir, which, in the prior art, is particularly disadvantageous when there is an emptying of a liquid bubble surrounding the heating device in the otherwise frozen service liquid. 
         [0020]    The heat exchanger can comprise at least two components which, joined together, form between them at least one section of the heat-exchanger line. In this way, the two components can for example be partial or half-shells, each with recesses formed in them, wherein the half-shells can be fitted together to make a heat-exchanger component in which the recesses complement each other, forming a section of the heat-exchanger line. A recess can also be formed in only one of the two shell components, said recess being covered during joining by the other shell component, forming a section of a heat-exchanger line. In order to increase the amount of heat that can be conveyed per unit of time through the heat-exchanger line, it can be additionally provided that the heat exchanger, at least in sections, preferably at least in a section contributing to the construction of the heat-exchanger line, is manufactured from a filled plastic with a plastic matrix and filler particles embedded therein, wherein the filler-particle material has a higher thermal conductivity than the plastic material of the matrix. In this way a material is provided for constructing the heat exchanger which has a greater thermal conductivity and a lower thermal-conductivity resistance than unfilled plastic material. The plastic material of the plastic matrix is preferably thermoplastically deformable, so that the filled plastic can be given a desired shape by injection molding or a comparable forming process. However an unfilled plastic should not be ruled out for constructing the heat-exchanger line. 
         [0021]    The heat exchanger can have additional functions, in particular in the region of the heat-exchanger line-section formed as explained above by the at least two components that are to be joined; these are additional functions for which a special functional component would otherwise have to be provided. It can for example be provided that the heat exchanger has a filter carrier, in or on which a filter material is or can be arranged, preferably interchangeably arranged, outside the heat-exchanger line. The filter carrier is preferably designed as an integral part of the heat exchanger. 
         [0022]    In this way the heat exchanger can also serve the purpose of filtering the service liquid in the service-liquid tank before the liquid is extracted from the tank. In order to ensure that liquid service-liquid can, if necessary, also flow through the filter material that can be arranged in the filter carrier, a section of the heat-exchanger line can run inside the filter carrier. In this way, the heat-exchanger can transfer heat to the service liquid, or generally to its external surroundings in the immediate proximity of the filter carrier, so that sufficient heat, and thus service liquid in liquid form, can be guaranteed precisely in the region of the filter carrier. 
         [0023]    Furthermore, a pumping line that is separate from the heat-exchanger line can be provided inside the heat exchanger. With this pumping line, service liquid can be pumped out of the service-liquid tank for the intended use of the service liquid. 
         [0024]    For the pumping of service liquid that is as clean as possible, the pumping line preferably extends originating from an outlet in the region of the filter carrier. The filter carrier can have a wall enclosing a volume area. The outlet of the pumping line can then preferably lie in the volume area surrounded by the wall. One section of the heat-exchanger line preferably extends, for the above-mentioned reasons, inside the surrounding wall. In order to prevent the service liquid in the pumping line from solidifying, or as the case may be freezing, at least in sections, the pumping line preferably extends, at least in sections, parallel to a section of the heat-exchanger line, to be precise, if possible in the immediate proximity of the heat-exchanger line section, separated for example from the pumping line only by a common dividing wall that separates the heat-exchanger line from the pumping line. The outlet of the pumping line is also preferably surrounded by a section of the heat-exchanger line, the outlet and the wall section particularly preferably being separated from one another only by a common separating wall, in order to have the most direct heat transmission possible. 
         [0025]    A particularly functionally reliable pumping line can be obtained by the pumping line extending at least in sections between two heat-exchanger line sections, again preferably separated from each heat-exchanger line section only by a dividing wall, through which the heat from the heat-exchanger line can be transferred to the pumping line. Particularly preferably the two heat-exchanger line sections are parallel to one another. They can extend curvilinearly or rectilinearly. Preferably, both the pumping line and the at least one heat-exchanger line section are rectilinearly constructed in order to provide flow paths in the filter carrier, said paths originating from the preferred outlet of the conveyor line, that are as short as possible. 
         [0026]    In order to provide one or more of the functions named above, the heat exchanger can preferably have a heat-exchanger body wherein a section of the heat-exchanger line is constructed. The heat-exchanger body can particularly preferably be constructed of the components mentioned above, in particular template components, which, joined together, form a section of the heat-exchanger line. 
         [0027]    In addition to the section of the heat-exchanger line, the filter carrier and/or the pumping line can be formed within the heat-exchanger body, in particular integrally therewith. Thus a functionally integrated heat-exchanger body can be constructed from a few components, particularly preferably from only two shell components. 
         [0028]    In order to facilitate the assembly of the heat-exchanger body, it can have a connection-body end on which line-connection formations are provided for a supply line to the section of the heat-exchanger line formed inside the heat-exchanger body, and for a discharge line from the same. Then, even though the pumping line, at least in sections, is constructed inside the heat-exchanger body, a line connection formation is made for connecting a line to the section of the pumping line formed within the heat-exchanger body. Furthermore, a bypass line can be provided inside the heat-exchanger body in order to pump service liquid via this bypass line to a consumer, for example an injection assembly. For this bypass line as well, at least one line-connection formation, preferably two line-connection formations—a supply line and a discharge line—can be provided. Configuring all line-connection formations at the connection body end concentrates access to them in one place, and they can be correspondingly connected during assembly. For example, the line-connection formations can be configured for the connection of hose lines in order to connect the heat-exchanger body with flexible lines, for example with the heat-exchanger liquid reservoir and the like. 
         [0029]    The heat-exchanger body is preferably a hard-shell body, i.e. a dimensionally-stable body that can be produced for example by injection molding of thermoplastic synthetic material. 
         [0030]    The heat-exchanger body is particularly preferably constructed of the filled thermoplastic synthetic material with heightened heat conductivity described above. However this does not have to be the case. Unfilled thermoplastic synthetic material can also be used. 
         [0031]    The filter carrier can also be formed inside the heat-exchanger body, in which case between the connection-body end and the filter carrier at least the heat-exchanger line advantageously has flow sections that are parallel to one another, in order to enable the most efficient use, with a large surface area, of the part of the body located between the filter carrier and the connection-body end for heat transfer from the heat-exchanger line to the surroundings of the heat-exchanger body. 
         [0032]    The pumping line between the connection-body end and the filter carrier also preferably extends, at least in sections, completely parallel to the heat exchanger line. 
         [0033]    The present invention also relates to the heat-exchanger body, configured as described above, as an object in its own right. 
         [0034]    The heat-exchanger liquid reservoir can also be constructed as separate from the heat-exchanger body and connectable or connectable, preferably detachably connected or connectable to it in a flow-conveying manner, via conduit means. This permits attachment, independently of the attachment site, of the heat-exchanger liquid reservoir in a site that is particularly well-suited for attachment, for example near an additional heat source such as the internal combustion engine, an exhaust gas manifold, and the like. 
         [0035]    Alternatively, the heat-exchanger liquid reservoir can be designed as integral to the heat-exchanger body and constructed, for example, of the components named above, in particular shell components. 
         [0036]    The present invention also relates to a service-liquid tank, in particular a motor-vehicle service-liquid tank with a heat exchanger as it is described and further developed above. The present invention also relates to a service-liquid tank, in particular a motor-vehicle service-liquid tank with a heat-exchanger body that is at least partially accommodated therein, as it is described and further developed above. 
         [0037]    The heat-exchanger service-liquid reservoir can be situated in the service-liquid tank, wherein it, inside the service-liquid tank, provides a completely sealed-off volume that is only accessible through a supply and a discharge-line. This volume is preferably substantially smaller than the tank volume of the service-liquid tank, approximately 5% or less of that volume. Then, when as preferred, the service-fluid is the actual heat-exchanger liquid, the heat-exchanger liquid reservoir can be open to the tank receiving-volume of the service-liquid tank. Then the heat-exchanger liquid reservoir, can for example, be sealed off in sections, by one or more walls, from the rest of the tank receiving-volume, without being hermetically and completely sealed against the tank reception volume of the service-fluid tank. In this way, it can be ensured that the heat-exchanger liquid reservoir is always filled, as long as the service-liquid tank is filled. In the case of a heat-exchanger liquid reservoir inside the tank that is open to the tank volume, the heat-exchanger liquid reservoir is, in the installation position where it is ready for operation, advantageously open toward the top, however closed toward the side and toward the bottom, when the opening to the tank volume lies clearly under the maximum filling level, preferably under the minimal filling level. In this way, the liquid can flow, even in a filled or only partially filled service-liquid tank, into the heat-exchanger liquid reservoir, whereas the liquid, even when there is an emptied tank, can no longer flow out of the heat-exchanger liquid reservoir. The electric heating device for heating the supply of liquid in the liquid reservoir is preferably located inside the heat-exchanger liquid reservoir. 
         [0038]    Alternatively or additionally, the heating device can also be located outside the liquid reservoir, on a dividing wall of the same. 
         [0039]    The heat-exchanger liquid reservoir can also be located outside the service-liquid tank and be connected by means of lines, in particular flexible hose lines, to a heat-exchanger line section arranged in the service-liquid tank, connected for example to the heat-exchanger body. 
         [0040]    Spillage-protection plates can be formed on the heat-exchanger body in order to limit a movement of liquid in the immediate vicinity of the heat-exchanger body outside of said heat-exchanger body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0041]    The invention will be explained in more detail below on the basis of the accompanying drawings. 
           [0042]      FIG. 1  shows a highly schematic view of an inventive heat exchanger, 
           [0043]      FIG. 2  shows a top view of the joint plane of a partial shell (lower shell) of a heat exchanger body of the heat exchanger shown in  FIG. 1 , 
           [0044]      FIG. 3  shows the additional partial shell (upper shell) complementing the partial shell in  FIG. 2  to form a heat-exchanger body, and 
           [0045]      FIG. 4  shows a cross-sectional view through a line section of the heat-exchanger body in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0046]    In  FIG. 1 , a highly schematic representation of an inventive embodiment of a heat exchanger according to the present application is designated with  10 . The heat exchanger  10  serves to transmit heat to a service liquid, not depicted here, inside a motor-vehicle service-liquid tank  12 , which in  FIG. 1  is indicated only by a dotted line in a partial sketch. 
         [0047]    Aqueous urea solution, for example, is added to the service-liquid tank  12 , in order to feed said solution to a selective catalytic reduction of the exhaust gas in the exhaust-gas system of the motor vehicle that carries the tank  12  with the heat exchanger  10 . 
         [0048]    The heat exchanger  10  comprises a heat-exchanger liquid reservoir  14  that can be arranged in the tank  12  or outside the same. The heat-exchanger liquid reservoir is shown in  FIG. 1  as a container that is open at the top, as it is preferably configured with an arrangement of the liquid reservoir  14  inside the service-liquid tank  12 , so that service liquid  16  received in the service-liquid tank  12  can flow from above through the opening  18  in the heat-exchanger liquid reservoir  14  into the reservoir, and a sufficient filling of the heat-exchanger liquid reservoir  14  is ensured, i.e. with timely refilling, during the entire proper operation of the tank  12 . 
         [0049]    The heat exchanger  10  further comprises an electric heating device  20 , which in  FIG. 1  is only shown in highly schematic form. The electric heating device can, in the known manner, comprise an electric resistance heating trace, which is arranged between two films, or on a substrate, and can be covered with a foil or over-molded with plastic. However only simple and inexpensive heating resistors or other standard heating elements can also be used as an electric heating device. 
         [0050]    The electric heating device  20  is preferably arranged in the heat-exchanger liquid reservoir  14 , in order to heat the supply of liquid  22 , of the service liquid  16  received therein, there directly and keep it in a liquid state. 
         [0051]    Furthermore the heat exchanger  10  has a heat-exchanger line  24  that originates from the liquid reservoir  14  and extends at least partially inside the tank  12  in order to give off heat from the liquid flowing in it to an area  26  outside the heat-exchanger line  24 . In order to convey liquid from the heat-exchanger liquid reservoir  14  for the purpose of heat emission to the area  26 , a pump  28  is preferably provided, which, at a suitable extraction point, conveys liquid from the supply of liquid  22  in the liquid reservoir  14  to a heat-exchange body  30 . 
         [0052]    The heat-exchanger body  30  is formed of two injection-molding shells, to be specific an upper shell  30   a  and a lower shell  30   b  which are joined together in their joint plane to form the heat-exchanger body  30 . 
         [0053]    The components  30   a  and  30   b  of the heat-exchanger body, preferably produced by the injection molding process, are preferably produced using a filled synthetic material that is particularly suitable for heat transmission, wherein a matrix of thermoplastic synthetic material is filled with filler particles that have a greater thermal conductivity than the matrix material. 
         [0054]    On a body end region  30 , the heat-exchanger body  30  has a connection-body end  32  on which the line-connection formations  34 ,  36 ,  38 ,  40 , and  42  are formed, which are intended for the connection of line components. 
         [0055]    The heat-exchanger line  24  has a line section  24   a  (supply line) leading to the heat-exchanger body  30  that can for example be formed by a flexible hose or by a rigid tube. It also has a line section  24   b  formed inside the heat-exchanger body  30  which, due to the injection-molding technology construction of the heat-exchanger body  30 , is formed as a hard-shell line. 
         [0056]    The heat-exchanger line  24  also has a return line  24   c,  in which the return transport of the liquid  16  circulating in the heat-exchanger line  24  to the heat-exchanger liquid reservoir takes place. The return line  24   c  can also be configured as a flexible hose. 
         [0057]    The pump  28  pumps service liquid from the liquid supply  22  received in the liquid reservoir  14  via the supply line  24   a  to the line connection formation  34 , through which the service liquid enters the heat-exchanger body  30 . 
         [0058]    After passing through the heat-exchanger line section  24   b  in the heat-exchanger body  30 , the liquid, which has been cooled by emitting heat to the surroundings  26  through the line connection formations  36 , once again exits the heat-exchanger body  30  and is pumped via the return line  24   c  back to the supply of liquid  16  in the heat-exchanger liquid reservoir  14 . 
         [0059]    The heat-exchanger line section  24   b  has a meandering line-section with parallel rectilinear line branches, said line section lying between the connection-body end  32  and a filter-carrier body end  48 , on which a filter carrier  50  is formed. At least one part of the filter carrier  50  is formed as integral to the heat-exchanger body  30 . 
         [0060]    Arranged on the filter carrier  50  is a filter  52  sketched out by six struts, one filter  52  being provided on either side of the heat-exchanger body  30 , said filters enclosing between them, together with the filter carrier  48 , a spatial volume  54 . 
         [0061]    Centrally, arranged preferably approximately in both the direction of thickness of the filter carrier  48  and also in the diameter-direction of the same, there is an outlet  56  (see  FIG. 3 ) of a pumping line  58 , said outlet being assigned to the line-connection formation  42  that extends preferably rectilinearly between parallel line branches of the heat-exchanger line section  24   b.    
         [0062]    With the pumping line  58 , a service liquid can be conveyed out of the volume area  54 , during which pumping, due to the filter  52 , only filtered service liquid, and thus liquid that is sufficiently pure for the further handling process, can get into the volume area  54 . 
         [0063]    The pumping of service liquid through the pumping line  58  can take place by an additional pump  59  that is connected to the line formation  42 . With the pump  59 , the service liquid that is removed via the pumping line  58  can be discharged into the bypass line-connection formation  38  and at a suitable point, fed out of the bypass line-connection formation  40  by means of a rigid or flexible service-liquid line  61  to a consumer, for example an injection device in the exhaust-gas system, if the service liquid is an aqueous urea solution for a selective catalytic reduction. 
         [0064]    Alternatively the pump  28  can be used to pump service liquid out of the service-liquid tank  12  through the pumping line  58 , in particular if the service liquid stored in the tank  12  is identical to the liquid for the heat-exchange contained in heat-exchanger liquid reservoir  14 . 
         [0065]    In order to ensure as well that the service liquid in the volume area  54  inside the filter carrier  48 , said liquid being sucked in through the outlet  56  of the pumping line  58 , is actually present in liquid form, a section of the heat-exchanger line  24   b  formed in the heat-exchanger body  30  is preferably formed in the wall of the filter carrier  48 . This line section is indicated with  60 . The outlet  56  of the pumping line  58  can be surrounded by a line branch  62  of the heat-exchanger line  24   b  formed in the heat-exchanger body  30  in order to keep the outlet  56  from icing up. 
         [0066]    The heat-exchanger line  24 , as shown especially in  FIG. 1 , is a circulation line, from which liquid for a heat exchange is taken from the heat-exchanger liquid reservoir  14  and conveyed via a heat-exchanger line  24 , in particular via the section  24   b  of the heat-exchanger line  24  formed inside the heat-exchanger body  30 , and back again through the return line  24   c  into the heat-exchanger liquid reservoir  14 . In that way, the electric heating device  20  in the heat-exchanger liquid reservoir  14  needs only to convey the amount of heat to the liquid supply  22  that is emitted on the heat-exchanger body  30  to the external environment  26 . In that way, the service liquid in the service-liquid tank  12  can be convectively heated via heat exchange across large areas of the heat-exchanger body  30 , and the heat required for the heat exchange can be simply and efficiently fed to the service liquid  16  in the heat-exchanger liquid reservoir  14 . 
         [0067]      FIG. 4  shows a cross section through the region of the heat-exchanger body  30  in which the parallel line branches of the section  24   b  of the heat-exchanger line  24  formed in the heat-exchanger body  30  are located. Only the cross-sectional view is shown, without the line regions situated behind the cross-sectional plane. It can be seen that in the shell components  30   a  and  30   b,  originating from their respective joint planes  64 , or as the case may be  66 , recesses of different depths are formed, said recesses forming, when the two shell components  30   a  and  30   b  are joined to the heat-exchanger body  30 , the previously described liquid-conveying lines in the heat-exchanger body  30 . Advantageously, the pumping line  58  is formed between two line branches of the heat-exchanger line section  24   b  formed in the heat-exchanger body  30 , so that heat can be transferred along the common extent of the pumping line  58  and the heat-exchanger line section  24   b  directly through the common dividing wall of said lines between the liquid-conveying cavities, so that the service liquid present in the pumping line  58  can also be kept in liquid state.