Abstract:
The invention relates to a tank heating system, in particular for a urea tank of an internal combustion engine, comprising: a housing ( 2 ) in which is provided at least one PTC element, an electric connection line ( 3, 4 ) that is connected to the PTC element in order to carry a heating current via the PTC element, an intake pipe ( 5 ) for the conveyance of fluid, wherein at least a section of the electric connection line ( 5 ) is configured as a resistance heating element, that is in heat-conducting conduction with the inside of the intake pipe ( 5 ).

Description:
[0001]    The invention relates to a tank heating system, in particular for a urea tank of an internal combustion engine. 
         [0002]    A waste gas cleaning catalyst requires urea as alkaline air provider. Thus, a urea tank is a standard feature of motor vehicles for the storing of urea solution for the waste gas cleaning catalyst. Since it is possible for the urea solution to freeze in the case of frost, a tank heating system is required in order to defrost the urea solution as rapidly as possible so that the required urea is available for the catalyst. 
       SUMMARY OF THE INVENTION 
       [0003]    The object of the invention is to present a cost-effective manner in which a waste gas cleaning catalyst of an internal combustion engine can be rapidly brought into an operative condition in the case of temperatures below the freezing point. 
         [0004]    This problem is solved by means of a tank heating system with the characteristics set forth in claim  1 . 
         [0005]    In the case of temperatures below freezing point, with a tank heating system according to the invention it is possible to pump considerably faster a liquid urea solution through the intake pipe to a waste gas cleaning catalyst. Namely, in the case of a customary tank heater, the frozen urea in the intake pipe is defrosted at a moment at which a considerable portion of the urea solution in the urea tank has already been thawed out, so that only relatively late the urea solution can be pumped to the waste gas cleaning catalyst. In the case of a tank heating system according to the invention, the intake pipe is also heated so that the therein contained urea solution defrosts early on and, accordingly, it is possible to rapidly pump urea solution to the waste gas cleaning catalyst. In the case of a tank heating system according to the invention, this advantage is obtained in an extraordinarily cost-effective manner because at least one section of the required electrical connection line is configured as a resistance heating element for the defrosting of the frozen urea in the intake pipe. 
         [0006]    By way of example, the intake pipe can be arranged next to the housing and the connection line can be lead along the housing or the intake pipe, or it can be wound around it. Another possibility is to configure the intake pipe as a channel in the housing of the tank heating system. In particular, the section of the connection line configured as a resistance heating element can be formed by the intake pipe itself, insofar as the latter is made out of a metal with a sufficiently high resistance, in particular high-grade steel such as, e.g., V4A steel. 
         [0007]    Insofar as for the connection line is used a material that with respect to the urea solution is insufficiently corrosion resistant, it can be protected by an appropriate protective layer out of a corrosion-resistant synthetic material. 
         [0008]    In the case of the mentioned connection line it deals with the connection line of the PTC (Positive Temperature Coefficient) element provided according to the invention. By using the connection line of the PTC element for the heating of the intake pipe, the controlling property of the PTC element is advantageously used for the regulating of the heat for the intake pipe. 
         [0009]    The PTC element of a tank heating system according to the invention is preferably a PTC heating element. In principle, however, it is also possible to configure the PTC element as a control element and to connect it in series with an appropriate heating element. It is advantageous if ahead of or behind the heating elements of the tank heating system a heating output is emitted that amounts to at least double of the calorific output emitted by the connector lines. In particular, a calorific output of the PTC heating element(s) of at least 50 W is particularly favorable for the heating of an internal combustion engine&#39;s urea tank. 
         [0010]    Further details and advantages of the invention are explained by way of an embodiment with reference to the hereto attached illustrations. The therein described characteristics can be used either individually or combined in order to create preferred embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows an embodiment of a tank heating system according to the invention 
           [0012]      FIG. 2  shows the embodiment represented in  FIG. 1  without its housing 
           [0013]      FIG. 3  shows a detail drawing of  FIG. 2   
           [0014]      FIG. 4  shows another embodiment of a tank heating system according to the invention and 
           [0015]      FIG. 5  shows an internal housing of the embodiments represented in  FIGS. 1 to 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  shows the embodiment of a urea tank heating system  1  in an oblique view. The tank heating system  1  is provided with a plastic housing  2  in which are embedded  2  connection lines  3 ,  4 , by means of which a PTC heating element, described in more details in  FIG. 2 , inside the tank heating system  1  is supplied with electric power. Accordingly, the connection line  3  is connected to a power source, e.g., 13 V of a car battery, and the connector line  4  is shunted to earth. At threshold temperature, the PTC (positive temperature coefficient) heating elements present a rapid increase of their electric resistance which would preclude an overheating. 
         [0017]    In the illustrated embodiment, the connection lines  3 ,  4  run parallel to an intake pipe  5  that is configured as a channel in the plastic housing  2 . According to the invention, the intake pipe  5  is connected to a urea supply line so that urea solution can be pumped through the intake pipe  5  out of a urea tank and be carried to a waste gas catalyst of a motor vehicle. 
         [0018]    The connection line  3  consists of a resistance wire made out of a heat conducting alloy such, e.g., a FeCrAl alloy. It is also feasible to use a PTC alloy. The specific resistance of the utilized resistance wire should be preferably at least 0.2 Ωmm 2 /m, especially at least 
         [0019]    1.0 Ωmm 2 /m, especially preferred at least 1.2 Ωmm 2 /m, and 1.44 Ωmm 2 /m in the illustrated embodiment. Therefore, in the case of the illustrated tank heating system, the connection line  3  produces sufficient heat during operation in order to thaw out the frozen urea in the intake pipe  5 , so that the urea solution, defrosted by the PTC elements, can be conveyed at the earliest possible moment from the urea tank by the intake pipe  5 . 
         [0020]    In order to take advantage of a rapid defrosting of the frozen urea in the intake pipe  5 , it is possible to manufacture both connection lines  3 ,  4  out of resistance wire and to attach both in the immediate proximity of the intake pipe  5 . As a rule, it suffices to use resistance wire for one of the two connection lines  3 ,  4 . To obtain the best possible heat coupling to the intake pipe  5 , it is advantageous to arrange the connection line  3  or connection lines  3 ,  4 , out of resistance wire, as close as possible to the intake pipe  5 . 
         [0021]      FIGS. 2 and 3  show the tank heating system  1 , illustrated in  FIG. 1 , without the plastic housing  2 . This illustrated part of the tank heating system is hereinafter designated as internal heater part  6 . The connection lines  3 ,  4  are supported by a plastic support element  7  that is attached to an internal housing  8 , in which housing are provided several plate-shaped PTC heating elements. The internal housing  8  is a metal housing, preferably out of an aluminum alloy such as, e.g., an AlMgSi alloy, in particular an AlMgSi 0.5 . . . 1  alloy. 
         [0022]    The heating elements are supported on the internal housing  8  by a (not illustrated) assembly frame. The assembly can be considerably simplified by means of an assembly frame because an easily manageable unit is inserted into the internal housing  8 . The assembly frame is provided with joint plates  10  that protrude from the internal housing  8  and to which are affixed, preferably welded on, the connection lines  3 ,  4 . The assembly of an appropriate assembly frame with the therein supported components is described in patent DE 102 58 275 A1, the disclosure of which is the object of the application by reference. 
         [0023]    So that the heat produced by the PTC heating elements can be conveyed as well as possible to the urea solution in the urea tank, the tank heating system  1  has a central opening  20  for an enlargement of its surface, whereby on each of the two sides of the opening  20  an assembly frame with PTC heating elements is disposed inside the internal housing  8 . The joint plates  10  of the first assembly frame are connected to the joint plates  10 ′ of the second assembly frame by means of injection-molded junction lines  21 . 
         [0024]    After the insertion of the assembly frame with the therein supported PTC heating elements into the internal housing  8 , this metal housing  8  is compressed in order to obtain the best possible heat coupling of the heating elements to the internal housing  8 . The heat, emitted from the PTC elements, is absorbed by the internal housing  8  and conveyed to the heat exchanger elements  11 . 
         [0025]    The heat exchanger elements  11  consist of pipe sections out of high-grade steel, preferably V4A steel, that are pressed into brackets  12  of the metal housing  8 . The shape of the brackets  12  is adapted to the shape of the heat exchanger elements  11  in order to obtain the largest possible contact surface over which the heat from the brackets  12  can be conveyed to the heat exchanger elements  11 . The brackets  12  have an essentially cylindrical shaped interior space for the receiving of the tubular heat exchanger elements  11 . 
         [0026]    By using high-grade steel pipes as heat exchanger elements  11  it is possible to obtain an improved heat coupling to the urea solution to be heated. This is due to that the caloric conductivity of high-grade steel is higher than that of the plastic housing  2  used as protection of the internal housing  8 . Furthermore, by using several heat exchanger elements  11 , the produced calorific output can be concentrated on a lower portion of the urea tank so that, even in the case of an only partially full tank, the heat produced by the PTC heating elements can be fully used for the defrosting of the urea solution. 
         [0027]    For the pressing process, the brackets  12  have a protrusion  13 , open towards the interior space, which is compressed after the insertion of the heat exchange elements  11 , so that a compression fold is formed and the inside space is narrowed. The protrusion  13  has preferably a U-shaped cross-section. 
         [0028]    As protection against the corrosive urea solution, a synthetic material is sprayed unto the internal heater part  6  of the tank heating system  1 , illustrated in  FIGS. 2 and 3 , thus forming the plastic housing  2 . In order to obtain the best possible heat coupling of the heat exchanger elements  11  to the urea solution, the inside surfaces of the pipe sections constituting the heat exchanger elements  11  remain free. The pipe sections are encircled by O-rings  14  at their upper and lower ends, which are inserted into a groove of the plastic housing  2  to prevent the penetrating of urea solution into the plastic housing  2 . 
         [0029]      FIG. 4  shows another embodiment of a tank heating system  1 . The embodiment shown in  FIG. 4  differs from the embodiment described in  FIGS. 1 to 3  merely by the fact that the intake pipe  5  is configured as a metal pipe, preferably as a high-grade steel pipe, that is embedded into the plastic housing  2  of the tank heating system  1 . The intake pipe  5  is used as a connection line  3  to supply heating current to the PTC elements. The metal pipe  5  has such a high electric resistance that it is sufficiently heated by the heating current in order to defrost the frozen urea in the intake pipe  5 . The specific resistance of the metal pipe is preferably at least 0.2 Ωmm 2 /m, especially at least 0.6 Ωmm 2 /m and 0.75 Ωmm 2 /m in the illustrated embodiment. The connection pipe  5  is provided with a connection lug  15  for the contacting. 
         [0030]    In order to obtain a rapid defrosting of frozen urea in the intake pipe and a rapid operational readiness of a urea supply system for a waste gas cleaning catalyst it is favorable if at least one of the connection lines  3 ,  4  emits a calorific output of about 10 W to 20 W, and if the PTC heating elements of the tank heating system  1  emits a calorific output of at least 50 W but preferably 70 W to 150 W. 
         [0031]      FIG. 5  shows the internal housing  8  of above described embodiments. In the case of the internal housing  8  it deals with a metal housing that is configured as a hollow section, rather as an elastic aluminum alloy extruded section. As it can be seen, the internal housing  8  is provided with two passages  30  in each of which is arranged at least one heating element with a section of an assembly frame. 
         [0032]    The internal housing  8  presents further passages in the brackets  12  for the incorporation of the high-grade steel pipes  11 . The brackets  12  are connected to a central body  32  by means of arms  31 , in which body are placed the PTC heating elements. In such a manner, the produced heat is conveyed over a large surface to the urea solution to be defrosted. 
         [0033]    The produced heat can be conveyed in a particularly efficient manner via the tubular brackets  12  because a convectional current is formed therein. This effect can be used also without the utilization of the high-grade steel pipes  11 , whereby also the inside surfaces of the brackets  12  will be coated with a synthetic material as anti-corrosive protection. 
         [0034]    In  FIG. 5  can be seen in particular the protrusions  13  of the brackets  12  which, after the high-grade steel pipes  11  were put into place, are compressed to compression folds. 
         [0035]    The central body  32  presents a central channel  20  between the heating channels  30 . This central channel  20  causes first and foremost that the central body can be easier compressed in order to create an optimum heat coupling between the PTC heating elements and the metal housing  8 . Also in the central channel  20  can be placed a high-grade steel pipe. In order not to encumber the compressing, the central channel  20  remains preferably free, so that its inside surface will also be protected by a sprayed on synthetic material coating, that constitutes the plastic housing  2 , against the effects of the urea solution. 
       REFERENCE NUMBERS LIST 
       [0000]    
       
           1  Tank heating system 
           2  Plastic housing 
           3 ,  4  Connection lines 
           5  Intake pipe 
           6  Internal heater part 
           7  Supporting body 
           8  Internal housing 
           10 ,  10 ′ Joint plates 
           11  Heat exchanger elements 
           12  Brackets 
           13  Protrusion 
           14  O-ring 
           15  Connection lug 
           20  Central opening 
           21  Junction lines 
           30  Passage 
           31  Arms 
           32  Central body