Abstract:
The invention relates to a heating system for a liquid conveyor system, particularly for a urea supply system of a catalytic converter of an internal combustion engine, comprising at least one first heater ( 4 ) for defrosting a liquid, and at least one filter heater ( 14 ) for heating a filter ( 5 ) for liquid filtering, wherein the filter heater ( 14 ) is formed by a heating section—designed as a resistance heating element—of an electrical connecting line ( 12 ) of the first heater ( 4 ).

Description:
This invention relates to a heating system for a liquid conveyor system, particularly for a urea supply system of a catalytic converter of an internal combustion engine. 
     A catalytic converter requires urea as ammonia supplier. Motor vehicles accordingly have a urea tank as a standard in which urea solution is stored for the catalytic converter. In frosty weather, the urea solution can freeze up so that a heating system is required to defrost the urea solution as quickly as possible so that the urea required for catalytic converter operation can be made available. 
     It is the objective of the invention to show an economical way of how a catalytic converter of an internal combustion engine can be put faster into working condition at temperatures below freezing. 
     This problem is solved by a heating system for a liquid conveyor system, particularly for a urea supply system of a catalytic converter of an internal combustion engine, comprising at least one first heater for defrosting a liquid, and at least one filter heater for heating a filter for liquid filtering; the filter heater is formed by a heating section—designed as a resistance heating element—of an electrical connecting line of the first heater. 
     The first heater may be, for example, a tank heater for heating a liquid tank and/or a pump heater for heating a conveyor pump of the liquid conveyor system. It is preferred in any case that the heat output of the first heater is higher than the heat output of the filter heater. It is possible here that the liquid conveyor system comprises a plurality of first heaters—for example, one tank heater and one pump heater—and/or a plurality of filters with filter heaters. In that case, it is generally favorable that the heat output of the first heaters is selected respectively higher than the heat outputs of the filter heater or filter heaters. 
     It was found within the scope of the invention that, even when a pump and/or a tank heater is used, a fairly long time can frequently pass until liquid urea solution can be provided to a catalytic converter since the urea ice particularly contained in a urea filter defrosts only slowly. In this respect, a heating system according to the invention can provide an extremely economical remedy since the filter is heated with a filter heater formed by a connecting line—designed as a resistance heating element—of the first heater designed as a tank or pump heater. The costs of a separate heater insert for the filter can thus be saved, and no additional connecting lines for the filter heater are required. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional details and advantages of the invention are explained on the basis of exemplary embodiments with reference to the enclosed drawings. Identical and corresponding components are partly designated with matching reference symbols. The features described in the following can be used individually or in combination to create preferred embodiments of the invention. In the Figures: 
         FIG. 1  shows a schematic presentation of an exemplary embodiment of a heating system according to the invention; 
         FIG. 2  shows a schematic presentation of another exemplary embodiment of a heating system according to the invention; and 
         FIG. 3  shows a schematic presentation of a urea supply system with another exemplary embodiment of a heating system according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a section of a urea supply system for a catalytic converter of a motor vehicle. The system comprises a dual urea tank in which a first part comprises an only indirectly heated storage tank  1  and a second part a defrosting vessel  3  heated by the tank heater  4 . In the exemplary embodiment shown, the defrosting vessel  3  is provided within the storage tank  1 ; however, it can basically also be provided outside. A one-piece design is also possible in which the storage tank  1  is directly heated. 
     The heating system shown in  FIG. 1  concerns an insert  11  for a storage tank  1  of a motor vehicle. The insert  11  comprises a defrosting vessel  3  for fast defrosting of a part of the urea volume stored in the storage tank  1 ; also, a filter housing in the form of a filter cup  5 . 1  for the reception of a filter element  5 . 2 , a tank heater  4  for defrosting urea ice in the defrosting vessel  3 , and connecting lines  12 ,  13  by means of which a heating current can be conducted through a PTC heating element (not shown) included in the tank heater  4 . 
     The filter  5  is heatable by means of a filter heater  14  which is formed by a heating section of the connecting line  12 , the heating section being designed as a resistance heating element. The same heating current thus always flows through the filter heater  14  as well as through the tank heater  4 . Consequently, the PTC heating element of the tank heater  4  automatically limits the heat output of the tank heater  4  as well as of the filter heater  14 , and overheating is impossible since PTC heating elements (positive temperature coefficient) show a sudden increase in their electric resistance when a threshold temperature is exceeded. 
     The heating section  14  is formed by a resistance wire, preferably of a heating conductor alloy, for example an FeCrAl alloy. The use of a polymer resistance material is also possible—a PTC polymer, in particular. The resistance wire used has an electric resistance of at least 0.2 Ωmm 2 /m, preferably at least 0.6 Ωmm 2 /m, particularly preferable at least 1.2 Ωmm 2 /m, in the exemplary embodiment shown of 1.44 Ωmm 2 /m. The heating section  14  is embedded by extrusion in the filter cup  5 . 1  made of plastic by injection molding, preferably in its bottom, and it is arranged in a plurality of windings, preferably in a meandering or coil form. Also possible is a resistance heating element in the form of interlacing of a resistance material. 
     In the heating system  11  shown, the filter cup  5 . 1  is connected with a tank cover for the defrosting vessel  3 . A preferred one-piece design can do without a sealing point between tank cover and filter cup. It is here particularly advantageous when filter cup  5 . 1  and defrosting vessel  3  form a unit, according to  FIG. 1 , which is inserted in the storage tank  1  and thereby closes an opening of the storage tank  1 . 
     The insert  11  is part of a urea supply system which comprises, aside from the storage tank  1 , a pump  6  including pressure control and valve by means of which urea solution can be pumped via the intake lines  2  and  10  through the filter  5  via the connecting line  15  into the supply line  7  leading to the catalytic converter. In frosty weather, urea solution contained in the defrosting vessel  3  is first defrosted and then pumped via the intake line  10  into the filter  5  and from there to the connecting line  7 . The capacity of the defrosting vessel  3  is dimensioned such that the urea solution contained therein is sufficient to start up a catalytic converter. After the urea solution in the defrosting vessel  3  has been completely defrosted, the heat generated by the tank heater  4  is also automatically supplied to urea solution outside of the defrosting vessel  3  and thus the entire contents of the storage tank  1  is defrosted so that urea solution can be pumped through the intake line  2  into the filter  5 . 
     To support the defrosting process in the defrosting vessel  3 , the defrosted urea solution can be returned via the return line  8  into the defrosting vessel  3  so that the heat generated by the heater  4  is distributed better in the defrosting vessel  3 . Furthermore, the liquid passage opening  9  forms an overflow so that an excess of heated urea solution can escape from the defrosting vessel  3  and get into the surrounding interior space of the tank  1 . 
     The intake line  10  is a plastic tube which passes as an intake duct through the tank heater  4 . Preferably, the intake line  10  is also heatable so that the urea solution frozen therein can be quickly defrosted. In the exemplary embodiment shown in  FIG. 1 , intake line heating is realized such that, closely adjacent to the intake line  10 , the connecting line  12  is provided and, in the corresponding section, it is also designed as a resistance heating element, particularly as a resistance wire. The connecting line  12  thus has a thermoconducting connection with the intake line  10  so that heat generated by the connecting line  12  can be used for defrosting urea solution in the intake line  10 . The connecting line  12  may be adjacent to the intake line  10  or be coiled around it. A series connection is thus provided of tank heater  4 , filter heater  14  and intake line heating. Due to the self-regulating effect of the PTC heating element of the tank heater  4 , the filter heater  14  as well as the intake line heating are accordingly protected against overheating. 
     In the exemplary embodiment shown, only the connecting line  12  is designed as a resistance heating element. Yet, it is also possible to design the connecting line  13  as a resistance heating element as well to thus heat the intake line  10  and/or the filter  5  therewith. For example, one section of a connecting line can serve as filter heating and one section of the other connecting line as intake line heating. 
     The exemplary embodiment shown in  FIG. 2  essentially differs from the exemplary embodiment described on the basis of  FIG. 1  that the intake line  10 —through which urea solution from the defrosting vessel  3  can be drawn into the filter  5 —is designed as a thin stainless steel tube, preferably of V4A steel, and serves as a resistance heating element. The intake line  10  thus simultaneously presents the tank heater  4 . 
     The intake line  10  is arranged in the defrosting vessel  3  in a plurality of windings, preferably spiraling or meandering windings, and projects at its upper end with one also preferably coiled section into the filter  5 . The specific resistance of the metal tube forming the intake line  10  is preferably at least 0.2 Ωmm 2 /m, in particular, at least 0.6 Ωmm 2 /m, and 0.75 Ωmm 2 /m in the exemplary embodiment shown. 
     When a heating current is conducted through the metal tube forming the intake line  10 , this will result in its heating up and thus in the defrosting of the urea solution surrounding the intake line  10  in the defroster vessel  3  and the filter  5 . The section of the intake tube  10  projecting into the filter here serves not only as a filter heater  14  for heating the filter  5  but also as a connecting line of the tank heater  4 . The metal tube forming the intake line  10  may be designed in one piece or may have a plurality of sections connected by couplings, for example plug-in couplings; said sections may be different in design with regard to material and diameter. 
     To avoid overheating of the intake tube  10 , a temperature sensor  16  is provided in a thermoconducting connection to the intake tube, preferably fastened on the intake tube. It is particularly favorable to provide the temperature sensor  16  underneath the filter  5  since no urea solution generally surrounds the intake tube  10  there and the risk of overheating is therefore the highest. In case of overheating, the plastic of the filter cup  5 . 2  and the sealing point at the passage of the intake tube  10  might be damaged. 
     For both exemplary embodiments, it is favorable during operation when a heat output of approx. 10 to 30 watt is released by the filter heater, and a heat output of at least 50 watt, preferably 70 watt to 150 watt, by the tank heater. 
     To be able to supply liquid urea solution even faster to a catalytic converter, the heating system described can be integrated into a urea supply system in which the supply line  7  and/or the connecting line  15  are also heated. Such line heating can be particularly favorably effected such that corrosion-resistant metal tubes, preferably of stainless steel, are used for the corresponding lines through which a heating current is conducted for defrosting the urea solution so that the metal tubes heat up as resistance heating elements. 
       FIG. 3  is a schematic presentation of a urea supply system for a catalytic converter of a motor vehicle. The urea supply system comprises as a first part a urea tank  1  with a filter which are heated by a heating system essentially corresponding to the heating system described on the basis of  FIG. 1 . The heating system of the first part is the tank heater  4  as the first heater for defrosting liquid. 
     The urea supply system shown in  FIG. 3  comprises as a second part a conveyor module  20  by means of which urea solution can be pumped from the urea tank  1 ,  3  to a catalytic converter  30 . The conveyor module  20  includes a conveyor pump  21  and a heating system which comprises, as a first heater, a conveyor module heater  25  and additionally a filter heater  28  for heating a filter  24  belonging to the conveyor module. The conveyor module  20  furthermore comprises a dosing valve  22  which is preferably heated, same as the pump  21 , by the conveyor module heater  25 . By means of the dosing valve  22 , the urea solution supplied via the connecting line  7  is distributed to the supply line  32  leading from the filter  24  to the injection nozzle  29  of the catalyzer  30 , and to a return line  31  leading to the urea tank  1 ,  3 . 
     As another component, the conveyor module  20  comprises a control unit  23  which can control, for example, the pump  21 , the dosing valve  22 , as well as the heating system. 
     The most important function of the conveyor module heater  25  is the defrosting of liquid in the pump  21  in frost conditions so that the conveyor module heater  25  is a pump heater in the exemplary embodiment shown. The conveyor module heater  25  preferably contains a PTC heating element and can be provided, for example, in a housing of the pump  21  or of the conveyor module  20 . In the schematic presentation of  FIG. 3 , the conveyor module heater  25  seems to be provided at a considerable distance from the conveyor pump  21 . This schematic presentation has been chosen for better clarity; however, in this respect, it does not correspond with the actual conditions. The conveyor module heater  25  is preferably provided close to the conveyor pump  21  and has a good thermoconducting connection with the conveyor pump  21  via thermal bridges. Suitable thermal bridges can be particularly formed by housing parts. 
     The filter heater  28  is designed like the filter heaters  14  of the exemplary embodiments described on the basis of  FIGS. 1 and 2 . The filter heater  28  is thus formed by a heating section—designed as a resistance heating element—of the connecting line  26  of the conveyor module heater  25 . Reference is also made to the corresponding description of  FIG. 1  with regard to further details, for example in terms of the preferred materials or the arrangement of the heating section. Like the filter in the exemplary embodiment explained in the preceding part, the filter  24  preferably comprises a filter housing—for example, a filter cup—in which the filter heater  28  can be embedded. 
     It is particularly advantageous to design not only the heating section—forming the filter heater  28 —of the connecting line  26  of the conveyor module heater  25  from resistance wire but to use such resistance wire for the complete connecting line  26  of the conveyor module  20 . Accordingly, in the exemplary embodiments shown, the connecting line  12 ,  26  is formed by a resistance wire which extends up to the first heater  4 ,  25 . The heater section of the connecting line  12 ,  26  forming the filter heater  14 ,  28  comprises windings so that the major part of the connecting line  12 ,  26  is provided in the filter  5 ,  24  and, consequently, the heat output released by the connecting line is released for the major part in the filter  5 ,  24 . 
     The maximum power of the conveyor module heater  25  amounts to approx. 30 to 40 W in operation; the maximum power of the filter heater  28  to approx. 20 W to 40 W. At temperatures below freezing, the electric resistance of the first heater  4 , is preferably higher than the electric resistance of the filter heater  14 ,  28 .