Abstract:
An exhaust-gas aftertreatment device for an internal combustion engine, for use in a motor vehicle, includes an exhaust tract with at least one exhaust pipe and at least one exhaust-gas aftertreatment element. The exhaust-pipe internal wall and/or the at least one exhaust-gas aftertreatment element have/has a vapor-sorbing material forming at least one exhaust-tract-side sorption element.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of DE 10 2013 018 920.9 filed Nov. 13, 2013, which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The invention relates to an exhaust-gas aftertreatment device for an internal combustion engine and to a method for heating an exhaust-gas aftertreatment device. 
     In modern exhaust-gas aftertreatment systems, it is conventional for multiple types of exhaust-gas aftertreatment elements, for example catalytic converters or particle filters, to be integrated into an exhaust tract and for a targeted reduction of individual pollutant types to be sought by the exhaust-gas aftertreatment elements. Some of the exhaust-gas aftertreatment elements however attain their full performance or their optimum working temperature only when the internal combustion engine has warmed up. For this reason, extensive measures are implemented which ensure rapid heating of the exhaust-gas aftertreatment elements in the cold-start phase of an internal combustion engine. 
     From DE 198 00 654 A1, for example, it is known for a first water trap, an electrically heatable honeycomb body, a honeycomb body with catalytically active coating and a second water trap to be arranged in series in the exhaust-gas flow direction in an exhaust tract for an internal combustion engine. The electrically heatable honeycomb body and the honeycomb body with catalytically active coating may in this case preferably form a structural unit, whereby the honeycomb body with catalytically active coating can be heated more quickly by the electrically heatable honeycomb body in the cold-start phase of the internal combustion engine. In this way, the reduction of the pollutants in the exhaust gas of the internal combustion engine is improved. The two water traps further ensure that the two honeycomb bodies are in a dry state and thus warm up particularly rapidly. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an exhaust-gas aftertreatment device for an internal combustion engine, in particular for use in a motor vehicle, and a method for heating an exhaust-gas aftertreatment device, by means of which exhaust-gas aftertreatment device and method it is possible for the reduction of the pollutant emissions, in particular in the cold-start phase of the internal combustion engine, to be achieved in a simple and functionally reliable manner with high effectiveness. 
     The invention relates to an exhaust-gas aftertreatment device for an internal combustion engine, in particular for use in a motor vehicle, having an exhaust tract with at least one exhaust pipe and at least one exhaust-gas aftertreatment element. According to the invention, the exhaust-pipe internal wall and/or the at least one exhaust-gas aftertreatment element have/has a vapour-sorbing material for the purpose of forming at least one exhaust-tract-side sorption element. 
     The adsorption and/or absorption of the vapour, in particular water vapour, originating for example from the exhaust gas of the internal combustion engine by the vapour-sorbing material lead(s) to condensation of the vapour, and thus to a release of heat energy. 
     The heat energy causes the sorption element formed by the exhaust-pipe internal wall and/or the at least one exhaust-gas aftertreatment element to be heated, such that, upon a start of the internal combustion engine, in particular upon a cold start of the internal combustion engine, the entire exhaust tract is heated more rapidly, and the at least one exhaust-gas aftertreatment element can attain its optimum operating temperature more quickly. In this way, the heating of the at least one exhaust-gas aftertreatment element is simplified considerably, because only the vapour-sorbing material has to be provided. Accordingly, it is for example possible to dispense with electrical lines and terminals for the supply of energy to an electric heating element. Since, furthermore, the exhaust-pipe internal wall and/or the at least one exhaust-gas aftertreatment element form(s) the at least one exhaust-tract-side sorption element, it is also not necessary for an additional heating element to be provided in the exhaust tract. In this way, the flow resistance and the exhaust-gas back pressure in the exhaust tract are not significantly increased, and the at least one exhaust-gas aftertreatment element is heated in a particularly effective manner taking into consideration the fuel consumption of the internal combustion engine. 
     In one specific embodiment, the exhaust-pipe internal wall and/or the at least one exhaust-gas aftertreatment element may be coated, at least in regions, with the vapour-sorbing material. In this way, the at least one sorption element can be of particularly simple form. Alternatively and/or in addition, the at least one exhaust-gas aftertreatment element may be produced at least in regions from the vapour-sorbing material. The effectiveness of the at least one sorption element can be further improved in this way. It would likewise also be conceivable for the exhaust-pipe internal wall to be produced at least in regions from the sorbing material. 
     In a further specific embodiment, the at least one exhaust-gas aftertreatment element may be formed by at least one catalytic converter and/or by at least one particle filter. The at least one catalytic converter and/or the at least one particle filter can be heated in a particularly simple manner by the vapour-sorbing material. 
     In one preferred embodiment, the content, in particular the mass content, of the vapour-sorbing material of the at least one sorption element arranged in particular in an inlet region of the exhaust tract may decrease in the exhaust-gas flow direction. In this way, it is possible for more vapour, in particular water vapour, to be sorbed from the exhaust-gas stream of the internal combustion engine with a defined amount of vapour-sorbing material in the at least one sorption element. It may preferably be provided that the content of the vapour-sorbing material of the at least one sorption element decreases in degressive fashion in the exhaust-gas flow direction. 
     Alternatively and/or in addition, the content, in particular the mass content, of the vapour-sorbing material of a sorption element arranged in an outlet region of the exhaust tract may increase in the exhaust-gas flow direction. It is ensured in this way that, when the internal combustion engine is at a standstill, no or only very little vapour, in particular water vapour, can pass into the exhaust tract as a result of a supply of air from the outside. The content of the vapour-sorbing material may preferably increase progressively in the exhaust-gas flow direction in order to increase the vapour absorption from the air in an effective manner. 
     In a further embodiment, the content, in particular the mass content, of the vapour-sorbing material in the exhaust tract, and thus considered across multiple sorption elements positioned in series in the exhaust-gas flow direction, in particular in an inlet region of the exhaust tract, may decrease in the exhaust-gas flow direction. In this way, a large amount of water vapour, for example, is sorbed close to the engine, and therefore, the exhaust-gas aftertreatment element positioned closest to the engine can be heated to the desired temperature very rapidly. As a result of the removal of a large amount of water vapour at the very beginning, it may then only be necessary to provide a relatively small amount of sorption material in the exhaust-gas aftertreatment elements situated downstream. The content of the vapour-sorbing material in the exhaust tract may preferably decrease, in this case for example degressively, in the exhaust-gas flow direction. 
     Alternatively and/or in addition, the content, in particular the mass content, of the vapour-sorbing material in an outlet region of the exhaust tract may increase in the exhaust-gas flow direction, such that when the internal combustion engine is at a standstill, no or only very little air moisture can pass into the exhaust tract as a result of a supply of air from the outside. Said content of the vapour-sorbing material may preferably increase progressively in the exhaust-gas flow direction. 
     In a further alternative embodiment, the content, in particular the mass content, of the vapour-sorbing material may be greater in an exhaust tract intermediate region arranged between an inlet and an outlet region of the exhaust tract than in an exhaust tract region situated upstream and/or downstream thereof. The exhaust tract intermediate region is preferably formed by an exhaust-gas aftertreatment element which has a greater content of sorption material than at least one exhaust-gas aftertreatment element situated upstream and/or at least one exhaust-gas aftertreatment element situated downstream. This may be expedient for example for applications in which a particularly temperature-critical region is not situated at the beginning or end of the exhaust tract. 
     In one preferred embodiment, the at least one sorption element may be arranged and/or formed in a main line, through which a main exhaust-gas stream passes, of the exhaust tract. In this way, a particularly large fraction of the vapour can be sorbed from the exhaust-gas stream by means of the at least one sorption element. 
     The sorbing material may specifically be a zeolite and/or a silica gel and/or an aluminophosphate and/or a silicoaluminophosphate and/or a metal hydride. These permit particularly effective sorption of the vapour. The zeolite may preferably be an A-, X- or Y-type zeolite. The zeolites that are used preferably furthermore do not exhibit an SCR action. In particular, the zeolites that are used are in the form of non-metal-exchanged zeolites, for example are in the form of iron or copper zeolites. 
     In a further embodiment, a blocking device may be provided that blocks or enables a supply of exhaust gas and/or air to a sorption region that accommodates and/or forms the at least one sorption element as a function of defined internal combustion engine operating conditions. The blocking device prevents a supply of exhaust gas and/or air, or of the vapour contained therein, to the at least one sorption element, preferably when the internal combustion engine is at a standstill. 
     The blocking device may preferably have at least one blocking element arranged downstream of the sorption region for the purpose of blocking or enabling the supply of air. In this way, the supply of air can be blocked and enabled in a simple manner. Alternatively and/or in addition, the blocking device may have at least one blocking element arranged upstream of the sorption region for the purpose of blocking or enabling the supply of exhaust gas. In this way, it is possible in turn for the supply of exhaust gas to the sorption region to be blocked and enabled in a simple manner. 
     The at least one blocking element arranged upstream may specifically be in the form of a shut-off valve by means of which an exhaust-gas stream through an inlet pipe that forms the inlet of the exhaust tract can be blocked or enabled. In this way, the blocking element is of particularly simple form. 
     Furthermore, the at least one blocking element arranged downstream may be in the form of a shut-off valve by means of which an air stream through an outlet pipe that forms the outlet of the exhaust tract can be blocked or enabled. Accordingly, the at least one blocking element arranged downstream is of particularly simple form. The at least one shut-off valve arranged downstream may preferably be in the form of an exhaust-gas recirculation flap or an engine braking flap, which then assist, by way of a dual function, in ensuring a reduction in the number of components. 
     The at least one blocking element arranged downstream may also be in the form of a sorption brick and arranged and/or accommodated in the exhaust tract. A supply of vapour into the sorption region by the air flowing into the exhaust tract is reliably prevented by means of said sorption brick. Here, the sorption brick may advantageously be produced from a vapour-sorbing material and/or may have a substrate body that is coated with a vapour-sorbing material. 
     In an inventive concept that is expressly also claimed independently of the above exhaust-gas aftertreatment device, there is also proposed a method for heating an exhaust-gas aftertreatment device for an internal combustion engine, having an exhaust tract with at least one exhaust pipe and at least one exhaust-gas aftertreatment element. According to the invention, an exhaust-pipe internal wall and/or the at least one exhaust-gas aftertreatment element have/has a vapour-sorbing material for the purpose of forming at least one exhaust-tract-side sorption element, wherein the supply of exhaust gas and/or air and thus the supply of vapour to the at least one sorption element is enabled upon a start of the internal combustion engine, in particular upon a cold start of the internal combustion engine, and wherein, upon a deactivation of the internal combustion engine, the supply of vapour to the at least one sorption element is blocked by a blocking device. 
     It is ensured in this way that the at least one sorption element is heated only upon a start of the internal combustion engine, in particular upon a cold start of the internal combustion engine. Upon a deactivation of the internal combustion engine, or when the latter is at a standstill, the supply of vapour to the at least one sorption element is blocked, because a continuous supply of vapour would lead to vapour saturation of the at least one sorption element. 
     The vapour that is sorbed by the at least one sorption element may preferably be expelled from the sorption element at a defined sorption element temperature. In this way, the at least one sorption element can be regenerated when the exhaust-gas aftertreatment device is heated. In this way, the sorption element exhibits its full functionality upon the next start of the internal combustion engine. Said defined sorption element temperature lies in a range from approximately 280° C. to 500° C. in the case of metal hydrides, in a range from approximately 40° C. to 100° C. in the case of silica gels, and in a range from approximately 130° C. to 300° C. in the case of zeolites. The vapour-sorbing material that is used preferably also has a theoretical heat capacity of approximately 250 kWh/K. 
     The advantageous embodiments and/or refinements of the invention explained above and/or rendered in the subclaims may—aside from in the cases, for example, of explicit dependencies or non-combinable alternatives—be used individually or in any desired combination with one another. 
     The invention and its advantageous embodiments and/or refinements and the advantages thereof will be explained in more detail below, merely by way of example, on the basis of drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a diagrammatic illustration of an exhaust-gas aftertreatment device according to the invention, according to a first exemplary embodiment; 
         FIG. 2  shows a diagram illustrating the mass distribution of a vapour-sorbing material in the exhaust-gas aftertreatment device as per  FIG. 1 ; 
         FIG. 3  shows a diagram illustrating the mass distribution of a vapour-sorbing material of exhaust-gas aftertreatment elements of the exhaust-gas aftertreatment device as per  FIG. 1 ; 
         FIG. 4  is a diagrammatic illustration of an exhaust-gas aftertreatment device according to the invention as per a second exemplary embodiment; 
         FIG. 5  shows a diagram illustrating the mass distribution of a vapour-sorbing material in the exhaust-gas aftertreatment device as per a third exemplary embodiment; 
         FIG. 6  shows a diagram illustrating the mass distribution of a vapour-sorbing material of exhaust-gas aftertreatment elements of the exhaust-gas aftertreatment device as per  FIG. 5 ; and 
         FIG. 7  is a sectional illustration along the section plane A-A from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows an exhaust tract  1  according to the invention in a first embodiment. Said exhaust tract  1  has an inlet pipe  3  which is connected by way of a first end region to an internal combustion engine  5  and by way of a second end region to a particle filter housing or can  9  that accommodates a particle filter  7 . The particle filter pipe  9  is adjoined, in the exhaust-gas flow direction S, by a connecting pipe  15  that is coupled to the particle filter pipe  9  and to a catalytic converter housing or can  13  that accommodates a catalytic converter  11 . The exhaust tract  1  also comprises an outlet pipe  17  which is connected by way of a first end region to the catalytic converter pipe  13  and which issues, by way of a second end region, into the environment. 
     The particle filter  7 , the catalytic converter  11  and internal walls of the particle filter housing  9 , of the catalytic converter housing  13  and of the connecting pipe  15  are coated with a vapour-sorbing material. This emerges for example from the section through the connecting pipe  15  shown in  FIG. 7 . Accordingly, a layer  26  of sorbing material is applied, with a defined layer thickness, to an internal wall  27  of the connecting pipe  15 . The vapour-sorbing material may for example be a type-A zeolite, to name just one of the possible embodiments of said material. By virtue of said material sorbing vapour from the exhaust gas of the internal combustion engine  5  or from the surrounding air, said vapour condenses, and heat energy is released. In this way, the entire exhaust tract  1  is warmed up more rapidly in the cold-start phase of the internal combustion engine  5 , whereby the particle filter  7  and the catalytic converter  11  can reach their optimum working temperature more quickly. 
       FIGS. 2 and 3  illustrate the mass distribution of the vapour-sorbing material in the exhaust tract  1 . To illustrate this, in  FIG. 2 , the catalytic converter  11 , the particle filter  7  and further exhaust-gas aftertreatment elements that can be integrated into the exhaust tract  1  are combined to form an exhaust-gas aftertreatment system  18 . Furthermore, the pipes arranged between the inlet pipe  5  and the outlet pipe  17  have also been combined into a single accommodating pipe  25  that accommodates the exhaust-gas aftertreatment system  18 . As per  FIG. 2 , a mass content m of the vapour-sorbing material in the exhaust-gas aftertreatment system  18  decreases degressively over the length l AS  of the latter in the exhaust-gas flow direction S. Said mass distribution permits faster heating of the particle filter  7  arranged in the region of the internal combustion engine  5 . 
     By contrast to  FIG. 2 , it is the case in  FIG. 3  that the exhaust-gas aftertreatment system  18  has again been broken down into individual exhaust-gas aftertreatment elements  19  in order to illustrate the mass distribution in the exhaust-gas aftertreatment elements  19 . As per  FIG. 3 , a mass content m of the vapour-sorbing material in the individual exhaust-gas aftertreatment elements  19  decreases degressively over the length l AE  of the respective exhaust-gas aftertreatment element in the exhaust-gas flow direction S. By means of said mass distribution, it is possible for more vapour to be sorbed from the exhaust-gas stream of the internal combustion engine  5  with a defined amount of vapour-sorbing material in each exhaust-gas aftertreatment element  19 , because the vapour quantity in the exhaust gas decreases owing to the fact that the exhaust-gas temperature decreases in the exhaust-gas flow direction S. 
     It also emerges from  FIG. 1  that the inlet pipe  3  has an inlet valve  20 . By means of said inlet valve, an exhaust-gas stream through the inlet pipe  3  can be blocked or enabled as a function of defined internal combustion engine operating conditions. Furthermore, the outlet pipe  17  has an outlet valve  21  by means of which an air flow into the exhaust tract  1  from the outside can likewise be blocked or enabled as a function of defined internal combustion engine operating conditions. 
     The individual method steps for fast heating of the exhaust tract  1  according to the invention will now be explained below: 
     Upon a cold start of the internal combustion engine  5 , or shortly before that, the inlet valve  20  and the outlet valve  21  are opened such that the exhaust gas of the internal combustion engine  5  can flow through the exhaust tract  1  into the environment. The vapour, for example water vapour, contained in the exhaust gas is taken in by the vapour-sorbing material, and, aside from the heat energy of the exhaust gas, additional heat energy is released. Said additional heat energy permits particularly rapid heating of the exhaust tract  1 . After the cold-start phase has taken place, the vapour-sorbing material is heated by means of the exhaust gas such that the vapour stored therein is expelled again and can flow out of the exhaust tract  1  into the environment. Upon a deactivation of the internal combustion engine  5 , or shortly thereafter, the inlet valve  20  and the outlet valve  21  are closed again in order to prevent a further supply of vapour to the vapour-sorbing material. In this way, saturation of the vapour-sorbing material before another cold start of the internal combustion engine  5  is reliably prevented. 
       FIG. 4  shows the exhaust tract  1  according to the invention as per a second exemplary embodiment. Here, the exhaust tract  1  does not have an outlet valve  21  for blocking and enabling the supply of air, and instead has a sorption brick  23  which is arranged in the accommodating pipe  25  and which follows the exhaust-gas aftertreatment system  18  as viewed in the exhaust-gas flow direction S. Said sorption brick  23  is a body which is produced from a vapour-sorbing material and which is of for example cylindrical or block-shaped form and which reliably prevents the supply of vapour into the exhaust-gas aftertreatment system  18  from the ambient air when the internal combustion engine  5  is at a standstill. 
       FIGS. 5 and 6  show the exhaust tract  1  according to the invention as per a third exemplary embodiment. Here, again, the exhaust tract  1  does not have an outlet valve  21  for blocking and enabling the supply of air. To nevertheless prevent the supply of vapour from the ambient air to at least some of the exhaust-gas aftertreatment elements  19 , it is provided here that the mass content m of the vapour-sorbing material increases progressively in the exhaust-gas flow direction S in that exhaust-gas aftertreatment element which directly adjoins the outlet pipe  17 . 
     LIST OF REFERENCE SIGNS 
     
         
           1  Exhaust tract 
           3  Inlet pipe 
           5  Internal combustion engine 
           7  Particle filter 
           9  Particle filter housing 
           11  Catalytic converter 
           13  Catalytic converter housing 
           15  Connecting pipe 
           17  Outlet pipe 
           18  Exhaust-gas aftertreatment system 
           19  Exhaust-gas aftertreatment element 
           20  Inlet valve 
           21  Outlet valve 
           23  Sorption brick 
           25  Accommodating pipe 
           26  Layer of vapour-sorbing material 
           27  Internal wall of connecting pipe 
         S Exhaust-gas flow direction