Abstract:
A method for treating exhaust gas of an internal combustion engine involves introducing less fuel into at least one first cylinder of the internal combustion engine than into at least one second cylinder of the internal combustion engine. Exhaust gas emerging from the at least one first cylinder is at least partially recycled into a supply air section of the internal combustion engine. At least the exhaust gas of the at least one second cylinder is supplied to an exhaust gas after-treatment unit. An exhaust gas line, by means of which exhaust gas of the at least one first cylinder of the exhaust gas after treatment unit can be supplied, is at least partially blocked.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
       [0001]    Exemplary embodiments of the invention are directed to a method for treating exhaust gas, and arrangement of an exhaust gas system on an internal combustion engine. Specifically, exemplary embodiments of the invention relate to a method for treating exhaust gas of an internal combustion engine, in which less fuel is introduced into at least one first cylinder of the internal combustion engine than into at least one second cylinder of the internal combustion engine. Exhaust gas exiting from the at least one first cylinder is at least partially recycled into an intake air tract of the internal combustion engine. At least the exhaust gas of the at least one second cylinder is supplied to an exhaust gas aftertreatment unit. Exemplary embodiments of the invention further relate to an arrangement of an exhaust gas system on an internal combustion engine of a vehicle. 
         [0002]    European patent document EP 2 206 898 A1 describes a method for aftertreatment of the exhaust gas of a multi-cylinder internal combustion engine of a vehicle, in which during low-load operation of the internal combustion engine a first group of cylinders is acted on by fuel, while a second group of cylinders is acted on by less fuel or no fuel at all. An exhaust gas line leads from each of the two cylinder groups to a respective duct of a two-duct turbine of an exhaust gas turbocharger. An exhaust gas recirculation line branches off from each of these two exhaust gas lines, the quantity of exhaust gas flowing through each of these exhaust gas recirculation lines being separately adjustable. The intake air for the internal combustion engine, which is compressed by a compressor of the exhaust gas turbocharger, is supplied to the respective cylinder groups via a separate intake air line, a throttle valve being situated in each of the two intake air lines. During hot operation, the cylinder group, into whose cylinders less fuel, or no fuel at all, is injected, is now acted on by a throttled supply air flow, and an exhaust gas recirculation valve of the exhaust gas recirculation line associated with this cylinder group is opened. In contrast, the exhaust gas of the cylinders of the other cylinder group is not recycled, but instead is returned to the turbine of the exhaust gas turbocharger. As a result, comparatively hot exhaust gas flows through the turbine, and flows further to a catalytic converter. 
         [0003]    In this arrangement, a plurality of lines with respective throttle elements is necessary to achieve the desired increase in the temperature of the exhaust gas, which is very complicated. 
         [0004]    Exemplary embodiments of the present invention, therefore, are directed to a method and an arrangement of the type mentioned at the outset that allow an increase in the exhaust gas temperature in a particularly simple manner. 
         [0005]    In the method according to the invention, an exhaust gas line via which exhaust gas of the at least one first cylinder is suppliable to the exhaust gas aftertreatment unit is at least partially blocked. This ensures that at best, a small portion of exhaust gas originating from the at least one first cylinder, which is operated with a low quantity of fuel or a quantity of fuel that is reduced to zero, reaches the exhaust gas aftertreatment unit. In contrast, the exhaust gas originating from the at least one second cylinder contributes to a greater extent to the temperature of the exhaust gas supplied to the exhaust gas aftertreatment unit. This is achieved in a particularly simple manner, namely, by blocking the exhaust gas line associated with the at least one first cylinder. Thus, separate intake air lines and throttle units for throttling are not necessary for the at least one first cylinder and the at least one second cylinder. Nevertheless, the at least one first cylinder having the injection quantity that is reduced, in particular to zero, makes practically no contribution to the temperature of the exhaust gas. 
         [0006]    The effective exhaust gas recirculation rate drops due to the reduction in the quantity of fuel introduced into the at least one first cylinder of the internal combustion engine. This is because for the intake air that is supplied to the at least one first cylinder, less fuel is available that may be converted into exhaust gas. Due to the reduction in the exhaust gas recirculation rate, the soot emissions of the internal combustion engine are also greatly lowered. In addition, a comparatively large quantity of nitrogen oxides is formed which, after oxidation of NO to NO 2 , is available for oxidizing, for example, soot particles retained in a particle filter. Passive regeneration of the particle filter may thus be achieved in a simple manner. Thus, for the regeneration of the particle filter it is not necessary to additionally provide the internal combustion engine with a metering device for introducing fuel into the exhaust gas. 
         [0007]    The temperature of the exhaust gas supplied to the exhaust gas aftertreatment unit may thus be increased in a particularly effective manner. Post-injection into the cylinders of the internal combustion engine may therefore be dispensed with. This is advantageous, since due to the late point in time of such a post-injection, the cylinder walls may be wetted with fuel, which in turn may result in mechanical problems due to the accompanying dilution of the motor oil. In addition, a throttle valve in the intake air tract of the internal combustion engine may be dispensed with, so that the costs associated with such a throttle valve and possible problems with the reliability of such a throttle valve are avoided. The method is thus characterized by particularly high reliability and cost advantages. 
         [0008]    However, due to the asymmetrical injection, in which less fuel is introduced into the at least one first cylinder of the internal combustion engine than into the at least one second cylinder of the internal combustion engine, not only it is possible to achieve an increase in the temperature of the exhaust gas in a particularly simple manner, but there is also the option to attain a comparatively high exhaust gas recirculation rate when this is desired. For this purpose, more fuel is then injected into the at least one cylinder, whose exhaust gas is recirculated, than into the at least one cylinder whose exhaust gas is not recirculated. 
         [0009]    A particularly simple design of the exhaust gas system may be achieved when, according to one advantageous embodiment of the invention, the quantity of exhaust gas that is recycled into the intake air tract of the internal combustion engine is adjusted by means of an adjusting device that is designed for at least partially blocking or opening up the exhaust gas line. In other words, the adjusting device is used not only for blocking the exhaust gas line, but at the same time is also used as an exhaust gas recirculation valve. A defined distribution of the exhaust gas flow of the at least one first cylinder, which is operated with a particularly small quantity of fuel or no fuel at all, over an exhaust gas recirculation line and the exhaust gas line leading to the exhaust gas aftertreatment unit may be achieved in a particularly simple manner. This makes the method particularly easy to carry out. 
         [0010]    It has also been shown to be advantageous when the internal combustion engine is operated in a low to medium load range, so that the exhaust gas line is completely blocked, and the exhaust gas exiting from the at least one first cylinder is completely recycled into the intake air tract of the internal combustion engine. The exhaust gas exiting from the at least one first cylinder then has no influence on the temperature of the exhaust gas which is present upstream from the exhaust gas aftertreatment unit. 
         [0011]    This complete recycling of the exhaust gas into the intake air tract may be carried out in particular up to a medium load range of up to 800 Nm, for example, since the exhaust gas recirculation rate is reduced due to the decreased quantity of exhaust gas leaving the at least one first cylinder. In contrast, for an internal combustion engine in which all cylinders are acted on by the same quantity of fuel, complete recycling of the exhaust gas may take place only in a comparatively low load range, for example in a load range of up to approximately 400 Nm, without impairing the operation of the internal combustion engine. 
         [0012]    Furthermore, it has been shown to be advantageous when the amount of fuel that is introduced into the at least one second cylinder is greater by the amount of lesser fuel that is introduced into the at least one first cylinder. A torque of the internal combustion engine is thus at least essentially maintained, which is achievable when the quantity of fuel to be provided for this torque is uniformly distributed over the cylinders of the internal combustion engine. Thus, despite the asymmetrical injection, the torque of the internal combustion engine does not decrease. 
         [0013]    It is also advantageous when the at least one first cylinder and the at least one second cylinder are each supplied with intake air via the same intake air tract. It is therefore not necessary to provide complicated, separate intake air lines, so that a particularly simple design of the intake air tract is achieved. 
         [0014]    In another advantageous embodiment of the invention, the cylinders of the internal combustion engine are supplied with the intake air unthrottled. Namely, providing a throttling device in the intake tract may thus be dispensed with, and controlling the air supply to the internal combustion engine is simplified. 
         [0015]    A particle filter as the exhaust gas aftertreatment unit is preferably regenerated when the exhaust gas line is at least partially blocked. It is thus possible to provide an active regeneration of the particle filter, i.e., a regeneration by fuel that is additionally introduced into the exhaust gas but not already combusted in the internal combustion engine, or also a passive regeneration, in which the soot retained in the particle filter is oxidized by nitrogen dioxide. 
         [0016]    Lastly, it has been shown to be advantageous when exhaust gas is suppliable to a first duct of a turbine of an exhaust gas turbocharger via the blockable exhaust gas line, while exhaust gas of the at least one second cylinder is supplied to a second duct of the turbine via a second exhaust gas line. It is thus ensured that in any event, exhaust gas from the at least one first cylinder mixes with exhaust gas from the at least one second cylinder, downstream from the turbine. At this location the exhaust gas may be supplied to the two ducts of an asymmetrical turbine in order to provide the internal combustion engine with this compressed intake air over a particularly large operating range. 
         [0017]    In the arrangement according to the invention of an exhaust gas system on an internal combustion engine of a vehicle, the internal combustion engine has at least one first cylinder and at least one second cylinder. By means of a control device, the first and second cylinders may be acted on by quantities of fuel that are different from one another. Exhaust gas exiting from the at least one first cylinder is at least partially recyclable into an intake air tract of the internal combustion engine via an exhaust gas recirculation line. The exhaust gas recirculation line branches off from a first exhaust gas line, via which exhaust gas of the at least one first cylinder is suppliable to an exhaust gas aftertreatment unit. The exhaust gas of the at least one second cylinder is suppliable to the exhaust gas aftertreatment unit via a second exhaust gas line. An adjusting device by means of which the first exhaust gas line may be at least partially blocked or opened up is situated in the first exhaust gas line. By means of the control device, asymmetrical injection into the first cylinder and the second cylinder is achievable, and by blocking the first exhaust gas line, primarily the exhaust gas from the at least one second cylinder is supplied to the exhaust gas aftertreatment unit. In this way, comparatively hot exhaust gas may be supplied, even under low load, to the exhaust gas aftertreatment unit using particularly simple means, namely, by utilizing the adjusting device. Thus, even under low load of the internal combustion engine, the exhaust gas aftertreatment unit may be brought to its light-off temperature, at which in particular it substantially converts or treats pollutants contained in the exhaust gas. When the exhaust gas aftertreatment unit is a particle filter, the particle filter may be regenerated by increasing the exhaust gas temperature. 
         [0018]    The quantity of exhaust gas that is recyclable into the intake air tract of the internal combustion engine via the first exhaust gas line is preferably adjustable by means of the adjusting device. It is then necessary to provide only one such adjusting device for blocking the first exhaust gas line, and at the same time, for adjusting the exhaust gas recirculation rate. 
         [0019]    The advantages and preferred embodiments described for the method according to the invention also apply to the arrangement according to the invention, and vice versa. 
         [0020]    The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and/or only shown in the figures may be used not only in the particular stated combination, but also in other combinations or alone without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0021]    Further advantages, features, and particulars of the invention result from the claims, the following description of preferred embodiments, and with reference to the drawings, which show the following: 
           [0022]      FIG. 1  schematically shows an internal combustion engine of a motor vehicle in which the exhaust gas from two cylinder groups is supplied via respective exhaust gas lines to a turbine of an exhaust gas turbocharger, whereby one of the two exhaust gas lines through which exhaust gas from a cylinder group flows may be blocked by means of an exhaust gas recirculation valve, and reduced quantities of fuel act on the cylinder groups; 
           [0023]      FIG. 2  shows a portion of a sectional detailed view of the two exhaust gas lines together with the exhaust gas recirculation valve situated in one of the two exhaust gas lines; and 
           [0024]      FIG. 3  shows curves depicting the increase in the exhaust gas temperature and the nitrogen oxide content, as well as the decrease in soot emissions of the internal combustion engine, as a function of the asymmetrical injection into the two cylinder groups. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  schematically shows an arrangement  10  of an exhaust gas system  12  on an internal combustion engine  14  of a motor vehicle, which may in particular be a utility vehicle. The internal combustion engine  14  includes a first cylinder group  16 , which in the present case has three first cylinders  18 ,  20 ,  22 . 
         [0026]    The exhaust gas from these three first cylinders  18 ,  20 ,  22  is supplied via a first exhaust gas line  24  to a first, small duct  26  of an asymmetrical turbine  28  of an exhaust gas turbocharger. An exhaust gas recirculation line  30  via which recycled exhaust gas is introduced into an intake air tract  32  of the internal combustion engine  14  branches off from the first exhaust gas line  24 . 
         [0027]    The three cylinders  18 ,  20 ,  22  of the first cylinder group  16 , under low load of the internal combustion engine  14 , are acted on by a smaller quantity of fuel than three further cylinders  34 ,  36 ,  38  of a second cylinder group  40  of the internal combustion engine  14 . The exhaust gas flowing from this cylinder group  40  having the second cylinders  34 ,  36 ,  38  is supplied via a second exhaust gas line  42  to a second, larger duct  44  of the turbine  28 . No exhaust gas recirculation line branches off from this second exhaust gas line  42  to the intake air tract  32 . 
         [0028]    The intake air, which has an air to fuel ratio λ&gt;1 and is unthrottled, and which is compressed by a compressor  46  of the exhaust gas turbocharger, is supplied to the first cylinders  18 ,  20 ,  22  and to the second cylinders  34 ,  36 ,  38 . 
         [0029]    The asymmetrical injection into the cylinders of the two cylinder groups  16 ,  40  takes place in such a way that the amount of fuel that is introduced into the first cylinders  18 ,  20 ,  22  is greater by the amount of lesser fuel that is introduced into the second cylinders  34 ,  36 ,  38 , in order to maintain a torque of the internal combustion engine  14  that is achievable with this overall injected quantity of fuel. 
         [0030]    The asymmetrical injection is used to increase the temperature of the exhaust gas exiting from the turbine  28 . To achieve this, even under low load of the internal combustion engine  14 , the first exhaust gas line  24  is completely blocked by means of an adjusting device in the form of an exhaust gas recirculation valve  48 , and the exhaust gas flowing from the first cylinders  18 ,  20 ,  22  is thus completely recycled into the intake air tract  32 . The temperature of the exhaust gas exiting from the turbine  28  is therefore influenced solely by the quantity of fuel that is injected into the second cylinders  34 ,  36 ,  38 , i.e., the cylinders of the second cylinder group  40 . As the result of the exhaust gas that exits from the cylinders  18 ,  20 ,  22  of the first cylinder group  16  not contributing to the temperature of the exhaust gas downstream from the turbine  28 , a particularly efficient and pronounced increase in temperature of the exhaust gas may be achieved due to the asymmetrical injection. 
         [0031]    Due to decreasing the quantity of fuel injected into the first cylinders  18 ,  20 ,  22 , in particular due to decreasing this quantity of fuel to zero, in addition the exhaust gas recirculation rate is lowered. This results in a marked decrease in the soot emissions of the internal combustion engine  14 , and at the same time results in an increase in the nitrogen oxides content in the exhaust gas. 
         [0032]    As the result of completely opening the exhaust gas recirculation valve  48 , which at the same time causes complete blocking of the first exhaust gas line  24  in the direction of the smaller duct  26  of the turbine  28 , no exhaust gas is introduced into this smaller, first duct  26  of the turbine  28 . This causes an increase in the temperature of the exhaust gas exiting from the turbine  28 , since the turbine  28  is supplied only with the exhaust gas from the second cylinder group  40 , which is acted on by an increased quantity of fuel. The temperature of the exhaust gas exiting from the first cylinders  18 ,  20 ,  22  thus has no influence on the exhaust gas temperature downstream from the turbine  28 , as illustrated by a curve  50  in  FIG. 3 . 
         [0033]    The decrease in the quantity of fuel introduced into the first cylinders  18 ,  20 ,  22  is equal to the increase in the quantity of fuel introduced into the second cylinders  34 ,  36 ,  38 , and thus results in the desired temperature increase. The hot exhaust gas then flows to an exhaust gas aftertreatment unit in the form of a particle filter  52 . The particle filter  52  may thus be actively regenerated in that the soot particles retained in the particle filter are burned off in a controlled manner at the increased temperature of the exhaust gas. Passive regeneration of the particle filter  52  by NO 2  which is formed by an oxidation catalytic converter (not shown) is also possible. Such an oxidation catalytic converter is customarily situated upstream from the particle filter  52 . 
         [0034]    As the result of achieving a reduced exhaust gas recirculation rate by decreasing the quantity of fuel injected into the first cylinders  18 ,  20 ,  22 , the exhaust gas may be recycled by completely opening the exhaust gas recirculation valve  48 , even up to medium load ranges of the internal combustion engine  14 , for example up to a load of 800 Nm. 
         [0035]    The control of the exhaust gas recirculation valve  48  and of injectors that inject the fuel into the cylinders  18 ,  20 ,  22 ,  34 ,  36 ,  38  is carried out by means of a control device  54  of the arrangement  10 . 
         [0036]    The manner in which an exhaust gas flow originating from the first cylinders  18 ,  20 ,  22  may be completely recycled by blocking the first exhaust gas line  24  by means of the exhaust gas recirculation valve  48  is particularly apparent from  FIG. 2 , this recycled exhaust gas flow being depicted by a flow arrow  56 . Similarly, a flow arrow  58  depicts the flow of the exhaust gas originating from the second cylinders  34 ,  36 ,  38 , via the second exhaust gas line  42 , to the turbine  28  of the exhaust gas turbocharger. 
         [0037]    The exhaust gas recirculation valve  48 , which acts as a 3/2-way control valve, allows the defined distribution of the exhaust gas flow from the cylinder group  16 , which is operated with a smaller quantity of fuel, to the exhaust gas recirculation line  30  on the one hand, and supplying to the first duct  26  of the turbine  48  on the other hand. As is apparent from  FIG. 2 , this control valve is preferably situated in the exhaust manifold. During hot operation, thus, when particularly hot exhaust gas is to be supplied to the particle filter  52  under low load of the internal combustion engine  14 , preferably the complete exhaust gas flow from the cylinder group  16 , into which the smaller quantity of fuel or no fuel at all is introduced, is led into the exhaust gas recirculation line  30 , and the supply line to the smaller duct  26  of the turbine  28  is blocked. 
         [0038]    The effects of the asymmetrical injection into the cylinders groups  16 ,  40  as described above are depicted in a graph shown in  FIG. 3 . The asymmetry of the injected quantity of fuel is indicated in % on the abscissa  60 , the total quantity of fuel injected into the first cylinders  18 ,  20 ,  22  relating to the total quantity of fuel injected into the second cylinders  34 ,  36 ,  38 . Temperature in ° C. is indicated on a first ordinate  62 , the curve  50  depicting the temperature at the outlet of the turbine  28  as a function of the asymmetrical injection. Accordingly, the temperature increases sharply and essentially linearly with increasing asymmetry. 
         [0039]    The nitrogen oxides content of the exhaust gas is indicated on a second ordinate  64 , in the present case expressed in g/kWh of delivered power of the internal combustion engine  14 . A curve  66  depicts the disproportionately strongly increasing quantity of nitrogen oxides in the exhaust gas with increasing asymmetry of the injection. Another curve  68  indicates the soot emissions of the internal combustion engine  14 . Based on this curve  68 , which, like the curve  50 , is essentially linear, it is apparent that the soot content of the exhaust gas decreases with increasing asymmetry of the injection. 
         [0040]    The curves  50 ,  66 ,  68  shown in the graph in  FIG. 3  are based on operation of the internal combustion engine  14  at 460 Nm and 1300 rpm. 
         [0041]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           10  Arrangement 
           12  Exhaust gas system 
           14  Internal combustion engine 
           16  Cylinder group 
           18  Cylinder 
           20  Cylinder 
           22  Cylinder 
           24  Exhaust gas line 
           26  Duct 
           28  Turbine 
           30  Exhaust gas recirculation line 
           32  Intake air tract 
           34  Cylinder 
           36  Cylinder 
           38  Cylinder 
           40  Cylinder group 
           42  Exhaust gas line 
           44  Duct 
           46  Compressor 
           48  Exhaust gas recirculation valve 
           50  Curve 
           52  Particle filter 
           54  Control device 
           56  Flow arrow 
           58  Flow arrow 
           60  Abscissa 
           62  Ordinate 
           64  Ordinate 
           66  Curve 
           68  Curve