Abstract:
The present invention relates to an exhaust system for a combustion engine, particularly of a vehicle, with an oxidation catalytic converter (oxicat), with an electrically heatable catalytic converter (E-cat) arranged upstream of the oxicat and with a fuel injector arranged upstream of the E-cat. 
     An energetically favourable mode of operation is achieved when a particle filter is arranged downstream of the oxicat, when a bypass path bypassing the E-cat commences downstream of the fuel injector and ends upstream of the oxicat and when the E-cat is designed for a smaller exhaust gas flow rate than the oxicat.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application claims priority to German Application No. 102010064020.4, filed Dec. 23, 2010, the entire teachings and disclosure of which are incorporated herein by reference thereto. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an exhaust system for a combustion engine, particularly of a vehicle, having the features of the preamble of Claim  1 . The invention additionally relates to a method for the heating-up of a particle filter in an exhaust system of a combustion engine, particularly a vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    From DE 196 26 837 A1 an exhaust system is known, which upstream of an oxidation catalytic converter, oxicat in brief, comprises an electrically heatable catalytic converter, so-called E-cat, wherein in addition a fuel injector is arranged upstream of the E-cat. With the known exhaust system, a NOX-storage catalytic converter, NOX-storage cat in brief, is additionally arranged between the E-cat and the oxicat. Furthermore, a bypass which bypasses the arrangement of fuel injector, E-cat ad NOX-storage cat and re-enters upstream of the oxicat is provided with the known exhaust system. With deactivated bypass, the entire exhaust gas flow flows through the E-cat and the oxicat. The E-cat can be heated electrically to the extent that reaches its minimum operating temperature or light-off temperature. With heated-up E-cat, fuel can be injected into the exhaust gas flow upstream of the E-cat with the fuel injector, which is converted in the E-cat. The highly exothermic reaction that occurs in the process generates hot exhaust gases, with the help of which the NOX-storage cat can be regenerated. 
         [0004]    From DE 196 26 836 A1 a further exhaust system of this type is known. 
         [0005]    From DE 10 2005 015 479 A1 an exhaust system is known, which downstream of an oxidation catalytic converter or oxicat includes a particle filter, wherein downstream of the particle filter an SCR-catalytic converter is additionally arranged. Upstream of the SCR-catalytic converter a reduction agent metering device is arranged, with the help of which a reduction agent can be injected into the exhaust gas flow between the particle filter and the SCR-catalytic converter. Furthermore, a bypass for bypassing the SCR-catalytic converter is provided. 
         [0006]    A further exhaust system with SCR-catalytic converter and reduction agent injection is known from DE 101 28 414 A1. 
         [0007]    Finally, from DE 100 36 401 B4 an exhaust system is known, wherein upstream of a particle filter a NOX-storage catalytic converter is arranged, wherein upstream of this NOX-storage catalytic converter an oxidation catalytic converter is arranged. 
         [0008]    In particular with diesel engines, particle filters are used in order to filter particles such as for example soot out of the exhaust flow of the diesel engine. Such particle filters have to be regenerated from time to time, which is regularly performed in that the particle charge is burnt off. To this end, the particle filter has to be heated until its particle charge self-ignites, the so-called light-off. In the case of modern combustion engines which operate with a comparatively high efficiency it can be that the exhaust temperature in many operating states of the combustion engine remains below the required light-off temperature, so that it is not easily possible to regenerate the particle filter at the desired point of time. 
         [0009]    In principle it is possible, upstream of the particle filter, to arrange an oxidation catalytic converter in the exhaust line and introduce fuel into the exhaust gas upstream of the oxidation catalytic converter. Insofar as the oxidation catalytic converter has its minimum operating temperature, it can convert the fuel carried along in the exhaust gas, which leads to a highly exothermic reaction that generates hot exhaust gas, with the help of which the particle filter can be heated up to the regeneration temperature. However, it is such that in many operating states of the combustion engine the exhaust temperature is not adequate to heat the oxidation catalytic converter up to its minimum operating temperature. In principle it is now conceivable to use an electrically heatable catalytic converter instead of a conventional oxidation catalytic converter which can be electrically heated up to its minimum operating temperature. The energy expenditure required for this purpose however is extremely high, which greatly impairs the ecological balance of the combustion engine. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention now deals with the problem of stating an improved embodiment for a method for the heating-up of a particle filter for an exhaust system of the type mentioned at the outset, which is more preferably characterized in that a reliable heating-up of the particle filter can be realised with comparatively low energy requirement. 
         [0011]    According to the invention, this problem is solved through the subjects of the independent claims. Advantageous embodiments are the subject of the dependent claims. 
         [0012]    The invention is based on the general idea of arranging an oxidation catalytic converter (oxicat) in an exhaust system having a particle filter upstream thereof and to additionally arrange an electrically heatable catalytic converter (E-cat) upstream of said oxicat and additionally provide a fuel injector (HCI) upstream of said E-cat. In addition, a bypass path bypassing the E-cat is proposed, which commences downstream of the HCI and ends upstream of the oxicat. It is now of particular importance that the E-cat is designed for a smaller exhaust gas flow rate that the oxicat. The proposed design results in that although the fuel is being fed to the entire exhaust flow, only a part of the exhaust-fuel mixture flows through the E-cat while the rest of this mixture flows through the bypass, thus bypassing the E-cat. The E-cat dimensioned for the small part-exhaust gas flow can be heated up to its minimum operating temperature with comparatively little electric energy, so that with comparatively little energy expenditure the fuel in the part exhaust gas flow can be exothermically converted. The hot exhaust gases of the E-cat which develop in the process intermix with the remaining gas flow upstream of the oxicat and lead to a heating-up of the oxicat. The oxicat can then exothermically convert the fuel carried along in the remaining exhaust gas flow, as a result of which the temperature in the exhaust gas is further increased, which results in the desired heating-up of the following particle filter. 
         [0013]    The fundamental idea of the present invention thus consists in heating up only a part flow of the exhaust gas-fuel mixture with the help of an E-cat, so that the E-cat can be dimensioned significantly smaller and thereby consumes significantly less energy than an E-cat that is designed for the entire exhaust gas flow. 
         [0014]    For example, the E-cat is designed for an exhaust gas flow rate that is between 30% and 70%, preferentially approximately at 50% of the exhaust gas flow rate for which the oxicat is designed. 
         [0015]    According to an advantageous embodiment, the E-cat and the oxicat can be arranged in a common exhaust pipe or in a common housing in which the bypass path is also formed. Because of this, a compact design is achieved which additionally makes a contribution that allows the heat to rapidly spread within the components. 
         [0016]    According to another embodiment, the bypass path can be throttled in order to make possible or control the flow through the E-cat. Furthermore, a flow mixing device can be arranged between E-cat and oxicat, which shortens the required mixing section and thus supports the achievement of a compact design. 
         [0017]    With an advantageous embodiment at least one additional oxidation catalytic converter (additional oxicat) can be arranged between E-cat and oxicat so that the bypass path bypasses the E-cat and the at least one additional oxicat. In this case, the at least one additional oxicat can be designed for a smaller exhaust gas flow rate than the previously mentioned oxicat, which in the following can also be called main oxicat. The E-cat in turn is designed for a smaller exhaust gas flow rate than the additional oxicat. With this design, only a very small exhaust gas flow rate is captured with the help of the E-cat in order to convert the fuel carried along therein. The hot exhaust gases resulting from this are mixed with a further part exhaust gas flow which only bypasses the E-cat via the additional bypass path in order to heat up the additional oxicat so far as to convert therein the fuel of this part flow. Only after the additional oxicat does the intermixing with the remaining exhaust gas flow, which via the (main) bypass path bypasses both the E-cat as well as the additional oxicat, take place. The conversion of the remaining fuel then takes place in the main oxicat in order to be subsequently able to heat up the particle filer with the hot exhaust gas of the main oxicat. 
         [0018]    For example, the additional oxicat can be designed for an exhaust gas flow rate which is at approximately 30% to 70%, preferentially at approximately 50% of the exhaust gas flow rate for which the main oxicat is designed. 
         [0019]    It is clear, furthermore, that more than one such additional oxicat can also be provided in order to realise at least one further stage with part conversion of the fuel. 
         [0020]    According to another advantageous embodiment, E-cat, main oxicat and the at least one additional oxicat can be arranged in a common exhaust pipe or housing, in which the main bypass path and the at least one additional bypass path are also formed. Here, too, a compact design with improved heat transfer is supported. 
         [0021]    With another embodiment, at least one separating wall can be provided which separates the main bypass path from the at least one additional bypass path. Additionally or alternatively, the main bypass path can be throttled. Additionally or alternatively the additional bypass path can be throttled. Additionally or alternatively a flow mixing device can be arranged between E-cat and additional oxicat. Additionally or alternatively a flow mixing device can be arranged between additional oxicat and main oxicat. 
         [0022]    The method for the heating-up of the particle filter proposed according to the invention thus works in such a manner that initially fuel is injected into a flow of engine exhaust gas transported in the exhaust system in order to form an engine exhaust gas-fuel mixture in this manner. Subsequently, a part flow of the engine exhaust gas-fuel mixture is converted in the E-cat in order to form a catalytic converter waste gas in this manner. This catalytic converter waste gas is then fed to the residual flow of the engine exhaust gas-fuel mixture in order to form a catalytic converter waste gas-engine exhaust gas-fuel mixture. This catalytic converter waste gas-engine exhaust gas-fuel mixture can then be converted in the oxidation catalytic converter in order to form a catalytic converter waste gas for heating-up the particle filter. 
         [0023]    Practically, the residual flow of the engine exhaust gas-fuel mixture can be conducted past the E-cat. It is particularly practical here to conduct the residual flow of the engine exhaust gas-fuel mixture past the E-cat in a heat transferring manner so that the heat from the E-cat is transferred to the residual flow of the engine exhaust gas-fuel mixture. 
         [0024]    With an embodiment additionally comprising at least one additional oxidation catalytic converter in addition to a main oxidation catalytic converter a further part flow of the exhaust gas-fuel mixture is admixed to the catalytic converter waste gas originating from the E-cat in order to form a catalytic converter waste gas-engine exhaust gas-fuel mixture. This catalytic converter waste gas-engine exhaust gas-fuel mixture is then converted in the mentioned additional oxidation catalytic converter in order to form a further catalytic converter waste gas. This further catalytic converter waste gas is then admixed to the residual flow of the engine exhaust gas-fuel mixture so as to form a further catalytic converter waste gas-engine exhaust gas-fuel mixture. Finally, this further catalytic converter waste gas-engine exhaust gas-fuel mixture is converted in the main oxidation catalytic converter in order to form a catalytic converter waste gas for heating-up the particle filter. 
         [0025]    With this embodiment it is also conceivable to conduct the further part flow of the engine exhaust gas-fuel mixture past the E-cat in a heat-transferring manner, so that the heat from the E-cat is transferred to the further part flow of the engine exhaust gas-fuel mixture. 
         [0026]    The residual flow of the engine exhaust gas-fuel mixture can also be conducted past the E-cat and/or the additional oxidation catalytic converter in a heat-transferring manner so that the heat from the E-cat and/or from the additional oxidation catalytic converter is transferred to the residual flow of the engine exhaust gas-fuel mixture. 
         [0027]    Of particular advantage is an embodiment, wherein the residual flow of the engine exhaust gas-fuel mixture flows onto a porous evaporation wall arranged upstream of the (only) oxidation catalytic converter or upstream of the main oxidation catalytic converter, while the catalytic converter waste gas-engine exhaust gas-fuel mixture coming from the E-cat or from the additional oxidation catalytic converter flows through the evaporation wall. In other words, an already heated-up part flow of the exhaust gas is used for heating the evaporation wall while another part of the exhaust gas flow conducts the fuel to be evaporated to the evaporation wall. The evaporated fuel is then discharged by the exhaust gas flows intermixing on the evaporation wall. 
         [0028]    Further important features and advantages of the invention are obtained from the subclaims, from the drawings and from the corresponding Figure description by means of the drawings. 
         [0029]    It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein same reference characters refer to same or similar or functionally same components. 
           [0031]    It shows, in each case schematically 
           [0032]      FIGS. 1 to 4  in each case a highly simplified schematic representation of an exhaust system in the form of a circuit diagram with different embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    According to  FIGS. 1 to 4  an exhaust system  1  comprises a particle filter  2  and upstream thereof an oxidation catalytic converter  3 , which in the following can also be called oxicat  3  or main oxidation catalytic converter  3  or main oxicat  3 . Upstream of the main oxicat  3  the exhaust system  1  additionally comprises an electrically heatable catalytic converter  4 , which in the following is also called E-cat  4 . In addition, the exhaust system  1  is equipped with a fuel injector  5 , which can also be called HC injector  5  or HCI  5 . With the help of the HC injector  5 , fuel  6  can be injected into the exhaust gas flow. The exhaust system  1  serves for discharging exhaust gases of a combustion engine  7 , which can be arranged in a vehicle. 
         [0034]    The exhaust system  1  introduced here additionally contains a bypass path  8 , which bypasses the E-cat  4  and in the following can also be called main bypass path  8 . The main bypass path  8  commences between the fuel injector  5  and the E-cat  4  and ends between the E-cat  4  and the main oxicat  3 . The E-cat  4  is designed for a smaller exhaust gas flow rate than the main oxicat  3 . In operation, the E-cat is only subjected to the throughflow of a part flow of the engine exhaust gas generated by the combustion engine  7 , while the residual engine exhaust gas flows through the main bypass path  8  and bypasses the E-cat  4 . 
         [0035]    The embodiments shown in  FIGS. 2 to 4  differ from the embodiment shown in  FIG. 1  in that additionally to the E-cat  4  and to the main oxicat  3  an additional oxidation catalytic converter  9  is provided, which in the following can also be called additional oxicat  9 . The additional oxicat  9  in this case is fluidically arranged between the E-cat  4  and the main oxicat  3 . In addition, the additional oxicat  9  is positioned so that the main bypass path also bypasses the additional oxicat  9  and thus ends between the additional oxicat  9  and the main oxicat  3 . Furthermore, an additional bypass path  10  is provided with these embodiments, which bypasses the E-cat  4  and to this end commences upstream of the E-cat  4  and ends between the E-cat  4  and the additional oxicat  9 . The additional oxicat  9  is designed for a smaller exhaust gas flow rate than the main oxicat  3 . In addition, the E-cat  4  with these embodiments is designed for a smaller exhaust gas flow rate than the additional oxicat  9 . The additional bypass path  10  with the embodiments of  FIGS. 2 to 4  is realised with the help of a separating wall  11 , which divides the main bypass path  8  so that the additional bypass path  10  ultimately represents a branch-off of the main bypass path  8 . 
         [0036]    To achieve a compact design, the E-cat  4  and the main oxicat  3  can also be arranged in a common exhaust pipe  12 . According to  FIGS. 2 and 3 , the additional oxicat  9  can also be accommodated in this common exhaust pipe  12 . Alternatively,  FIG. 4  shows an embodiment wherein the E-cat  4 , additional oxicat  9  and main oxicat  3  are accommodated in a common housing  13 . 
         [0037]    According to  FIG. 3 , the main bypass path  8  can be throttled. A corresponding throttling point  14  is formed in  FIG. 3  by a flow baffle. The additional bypass path  10  can also be practically throttled. A corresponding throttling point  15  is likewise indicated by a flow baffle in  FIG. 3 . Between the E-cat  4  and the main oxicat  3  a flow mixing device  16  can be arranged downstream of the end of the main bypass path  8  which in the example of  FIG. 3  is formed by a flow guiding element. In principle, a flow mixing device  17 , which is arranged downstream of the end of the additional bypass path  10  and which is represented in  FIG. 3  by a flow guiding element, can also be arranged between the E-cat  4  and the additional oxicat  9 . 
         [0038]    The throttling points  14 ,  15  and/or the flow mixing devices  16 ,  17  are only shown exemplarily in  FIG. 3 . It is clear that such throttling points and/or flow mixing devices can also be realised in corresponding manner with the other embodiments shown in  FIGS. 1 ,  2  and  4 . 
         [0039]    The exhaust systems  1  introduced here operate as follows: 
         [0040]    In order to be able to regenerate the particle filter  2  it has to be heated to a regeneration temperature or to its light-off temperature. With the embodiment shown in  FIG. 1 , this can be realised in that with the help of the fuel injector  5  fuel  6  is injected into a flow of engine exhaust gas  18  which is discharged in the exhaust system  1  by the combustion engine  7 . Through the injection of the fuel  6  an engine exhaust gas-fuel mixture  19  is formed. A part flow  20  of this engine exhaust gas-fuel mixture  19  is converted in the E-cat  4  in order to from a catalytic converter waste gas  21 . A residual flow  22  of the engine exhaust gas-fuel mixture  19  bypasses the E-cat  4  in the bypass path  8 . The mentioned catalytic converter waste gas  21  is admixed to the residual flow  22  of the engine exhaust gas-fuel mixture  19  so as to form a catalytic converter waste gas-engine exhaust gas-fuel mixture  23 . This catalytic converter waste gas-engine exhaust gas-fuel mixture  23  is converted in the oxicat  3  in order to form a catalytic converter waste gas  24  with which the particle filter  2  can be heated up. 
         [0041]    The bypass path  8  is practically coupled in a heat transferring manner to the E-cat so that the residual flow  22  of the engine exhaust gas-fuel mixture  19  is preheated while flowing through the bypass path  8 . 
         [0042]    The embodiment shown in  FIGS. 2 to 4  operates as follows for heating-up the particle filter  2 . 
         [0043]    Initially, fuel  6  is again injected into the engine exhaust gas  18  in order to obtain the engine exhaust gas-fuel mixture  19 . Then, a part flow  20  of the engine exhaust gas-fuel mixture  19  is again conducted through the E-cat  4  and converted therein in order to form the catalytic converter waste gas  21 . A further part flow  25  of the engine exhaust gas-fuel mixture  19  in the process bypasses only the E-cat  4  in the additional bypass path  10  while the residual flow  22  of the engine exhaust gas-fuel mixture  19  bypasses the E-cat  4  and the additional oxicat  9 . The catalytic converter waste gas  21  formed in the E-cat  4  is supplied with the further part flow  25  of the engine exhaust gas-fuel mixture  19  in order to form a catalytic converter waste gas-engine exhaust gas-fuel mixture  26 , which is subsequently converted in the additional oxicat  9 . Here, a further catalytic converter waste gas  27  is formed, which is mixed with the residual flow  22  of the engine exhaust gas-fuel mixture  19  so as to form a further catalytic converter waste gas-engine exhaust gas-fuel mixture  28 . This further catalytic converter waste gas-engine exhaust gas-fuel mixture  28  is converted in the main oxicat  3  in order to form the hot catalytic converter waste gas  24 , with the help of which the particle filter  2  can be heated up. 
         [0044]    Practically, the arrangement of E-cat  4  and additional oxicat  9  as well as of the bypass paths  8 ,  10  is made within the exhaust pipe  2  or within the housing  13  so that on the one hand the additional bypass path  10  is coupled to the E-cat  4  in a heat transferring manner so that the further part flow  25  of the engine exhaust gas-fuel mixture  19  can be preheated. On the other hand, the main bypass path  8  can also be coupled to the E-cat  4  and to the additional oxicat  9  in a heat-transferring manner so that the residual flow  22  of the engine exhaust gas-fuel mixture  19  can likewise be preheated. 
         [0045]    With the embodiment shown in  FIG. 4  a porous evaporation wall  29  is additionally arranged in the housing  13 , mainly upstream of the main oxicat  3  and downstream of the additional oxicat  9 . The porous evaporation wall  29  on the one hand, according to  FIG. 4  from the left, is subjected to an onflow by the residual flow  22  of the engine exhaust gas-fuel mixture  19  and on the other hand, according to  FIG. 4  from the right to left, subjected to a through-flow by catalytic converter waste gas  27  which comes from the additional oxicat  9 . On the evaporation wall  29 , the fuel carried along in the residual flow  22  of the engine exhaust gas-fuel mixture  19  can precipitate and re-evaporate. The evaporation heat required for this purpose then originates from the catalytic converter waste gas  27 , which flows through the evaporation wall  29 . Downstream of the evaporation wall  29  the mixture formation additionally takes place since the catalytic converter waste gas  27  flows through the evaporation wall  29  and intermixes with the residual flow  22  to the catalytic converter waste gas-engine exhaust gas-fuel mixture  28  on the outflow side. 
         [0046]    Insofar as such an evaporation wall  29  is to be realised with an embodiment according to  FIG. 1 , the evaporation wall  29  would have to be arranged between oxicat  3  and E-cat  4 . It would then be again subjected to an onflow of residual flow  22  of the engine exhaust gas-fuel mixture  19  on a first side and to a through-flow of catalytic converter waste gas  21  of the E-cat  4  coming from a second side. On the first side, the catalytic converter-engine exhaust gas-fuel mixture  23  would then form again which flows to the oxicat  3 .