Abstract:
Disclosed is a method for operating an emission control system that is located in an exhaust gas zone of an internal combustion engine and comprises a catalytic layer causing an oxidation reaction as well as a particle filter in which at least one exhaust gas component is deposited when the internal combustion engine is operated and which is regenerated from said exhaust gas component in predefined operating phases. According to the inventive method, the air throughput through at least one combustion chamber of the internal combustion engine is reduced in the predefined operating phases in which the particle filter is regenerated.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a method for operating an emission control system, which is located in the exhaust gas zone of an internal combustion engine and comprises a catalytic layer causing an oxidation reaction and a particle filter, according to the class of the independent claim  1 . 
         [0002]    The subject matter of the invention at hand is also a computer program according to claim  9  as well as a computer program product according to claim  10 . 
       BACKGROUND 
       [0003]    A method for the regeneration of a particle filter located in an exhaust gas zone of an internal combustion engine became known from the German patent DE 199 06 287 A1. Said method changes between different operating states as a function of the last prevailing operating state and as a function of the condition of the particle filter. According to the innovative method, the particle filter is regenerated from the deposited particles in one operating state. This regeneration takes place at an increased temperature, whereat the particles, mainly sooty particles and ash particles, are burned by means of an oxidation reaction. 
         [0004]    The German patent DE 103 23 561 A1 describes a method for operating a structural member, especially a particle filter, which is located in an exhaust gas zone of an internal combustion engine, and an apparatus for the implementation of this method, wherein the regeneration phase is started as a function of the operating state of the internal combustion engine and/or as a function of the operating state of the structural member, particularly of the degree of depletion of the particle filter. The regeneration phase is thereby arbitrarily started by means of an extreme start signal. The regenerated state of the structural member can in this way be produced by a service technician, for example, when the vehicle, wherein the internal combustion engine is disposed, is being serviced in a garage. In so doing, a diagnosis of the internal combustion engine and its components can be performed. 
         [0005]    The regeneration of the diesel particle filter thereby takes place intermittently, for example, as a function of the exhaust gas backpressure. The exhaust gas and filter temperature necessary for an oxidation process for regeneration of the filter presume a sufficient rate of oxidation as a rule above approximately 600° C. Because said temperature can only be expected in the upper average pressure/rotational speed characteristic diagram of the internal combustion engine, an exhaust gas temperature boost, which is required for the regeneration of the filter, is induced by means of an afterinjection of diesel fuel into the combustion chamber or into the exhaust gas tract, while utilizing the reaction heat released in the process. These interventions are coupled with a disadvantageous increase in fuel consumption. 
         [0006]    Besides by means of an afterinjection, the regeneration of diesel particle filters can also take place by means of auxiliary burners in the complete exhaust gas stream or a secondary exhaust gas stream, engine management interventions which increase temperature, supplementary electrical energy or fuel additives. Regeneration by means of fuel additives is problematic with respect to the long term stability of the diesel particle filter. This results in this case from an input of metal ash, which can lead to a reduction in the service life of the diesel particle filter. 
       SUMMARY 
       [0007]    The method according to the invention with the characteristics of the independent claim  1  in contrast allows for a regeneration of the filter without a significant increased consumption by the internal combustion engine. By means of reducing the air throughput through at least one combustion chamber of the internal combustion engine, a significant increase in the heating value of the mixture and thereby an increase in the exhaust gas temperature, which is required for the regeneration of the filter, is in fact achieved at practically the same fuel consumption. 
         [0008]    The reduction of the air throughput through at least one combustion chamber of the internal combustion engine preferably takes place continuously during the entire predefined operating phase. A continuous regeneration of the filter is possible to a certain extent within certain limits by means of this continuous reduction of the air throughput. Even if no complete regeneration of the filter can take place in the process, the intervals for an intermittent regeneration of the filter are lengthened, for example, through additional measures in the form of afterinjections of diesel fuel into the combustion chamber or into the exhaust gas tract or, for example, by means of fuel additives. 
         [0009]    The predefined operating phase, wherein the regeneration of the filter takes place, is preferably a partial load range of the internal combustion engine. 
         [0010]    The reduction of the air throughput through at least the one combustion chamber can fundamentally be implemented in different ways. Provision is made in an advantageous embodiment for the reduction of the air throughput through at least the one combustion chamber of the internal combustion engine to be implemented by advancing the closing of at least one intake valve of at least one combustion chamber analogous to the Miller cycle. What is understood in the invention at hand by the closing of at least one intake valve in internal combustion engines with in each case one intake valve per combustion chamber is the advanced closing of this intake valve. Said advanced closing can take place in one or a plurality of combustion chambers, depending on the number of cylinders and the power stroke of these cylinders of the internal combustion engine. In internal combustion engines with, for example, two intake valves per combustion chamber, the advanced closing of both intake valves in one or a plurality of combustion chambers analogous to the Miller cycle is understood. 
         [0011]    Provision can also alternatively or additionally be made to the advanced closing of the one or several intake valves for an advanced closing of the one or several exhaust valves, whereby the residual gas content is increased and the air throughput decreases through the combustion chamber of the internal combustion engine as well. Also in this instance in an internal combustion engine, which has one exhaust valve per combustion chamber, the closing of this exhaust valve is in turn advanced. In internal combustion engines, which have more than one exhaust valve per combustion chamber, particularly two exhaust valves per combustion chamber, the closing of both of these exhaust valves is advanced in at least one combustion chamber. 
         [0012]    These embodiments assume a variable valve drive. It is the basic idea behind these configurations that the so-called Miller cycle, which up until now is only employed in large diesel engines, for example ship engines, is employed in a diesel internal combustion engine with direct fuel injection of a motor vehicle in order then to bring about a significant increase in the heating value of the mixture and thereby in the exhaust gas temperature in partial load areas with as a matter of principle high excess air. The advantage of this method is first of all that only small increases in consumption arise due to advancing the closing of the one or several intake valves and/or the one or several exhaust valves. Furthermore, as a result of this method, an impairment of the untreated exhaust gas emissions is no longer a factor. 
         [0013]    Provision is made according to another configuration of the method for a reduction in the air throughput to be brought about by at least one throttle valve located in the engine air intake. 
         [0014]    In so doing, the emission control system can be configured in different ways. Provision is made in one configuration for the catalytic layer causing the oxidation reaction to be configured as an oxidation catalytic converter, to which a diesel particle filter is subsequently attached. 
         [0015]    In another embodiment, provision is made for a diesel particle filter with an integrated catalytic layering, a so-called catalytic soot filter. 
         [0016]    The combination of a catalytic layer, which causes an oxidation reaction, and a particle filter is absolutely necessary for the method described above. This is the case because an oxidation of the nitrogen oxide into nitrogen dioxide, which is required for the continuous regeneration of the particle filter, particularly the diesel particle filter, first takes place by means of the catalytic layer. Such a continuous regeneration can only take place if the ratio of nitrogen dioxide NO2 to carbon C is proportionally larger than or equal to 8. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Examples of embodiment of the invention are depicted in the drawings and are described in detail in the description below. 
           [0018]      FIG. 1  is a technical environment wherein a method according to the invention is operating; and 
           [0019]      FIG. 2  schematically shows the process of the method according to the invention using a flow diagram. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  schematically and exemplary shows a combustion chamber  100  of an internal combustion engine, wherein a piston  105  travels upwards and downwards in an inherently known manner. The combustion chamber  100  has an inlet port  110  as well as an outlet port  120 . The outlet port  120  opens out into an exhaust gas tract  122 , wherein an emission control system comprising an oxidation catalytic converter  130  as well as a particle filter  140  is disposed. Provision can also be made for an inherently known, so-called CSF (catalytic soot filter) instead of the arrangement of an oxidation catalytic converter  130 , which causes an oxidation reaction, and a particle filter  140 . Said CSF is therefore a layered particle filter, whose catalytic layer brings about an oxidation reaction, particularly an oxidation of nitrogen oxide NO to nitrogen dioxide NO2. 
         [0021]    The inlet port  110  can be connected to the combustion chamber  100  by an intake valve  112 . The outlet port  120  can be connected to the combustion chamber by an exhaust valve  122 . The intake valve  112  as well as the exhaust valve  122  can be actuated by a variable valve drive in order to change the intake and exhaust control times within predefined limits. The intake valve  112  and the exhaust valve  122  can, for example, be actuated by an electrohydraulic valve control or something similar. The actuation can thereby take place via an engine control unit  150 . 
         [0022]    The depletion of the particle filter  140  is acquired in an inherently known manner, for example, by a differential pressure sensor  145 , which acquires the differential pressure of the exhaust gas in the exhaust gas direction of flow before and behind the filter  140 . The output signal of the differential pressure sensor  145  is likewise provided to the control unit  150 . Different operating states of the internal combustion engine are acquired by suitable sensors, for example by a sensor for acquiring the engine rotational speed, a sensor for acquiring the combustion temperature and the like. A sensor  160 , which is representative of this plurality of sensors, is shown in  FIG. 1 , whose output signal is provided to the control unit  150 . 
         [0023]    A throttle valve  170 , whose position is determined in the control unit  150  and which can be electrically activated, can furthermore be disposed in the inlet port  110 . 
         [0024]    The method for the regeneration of the particle filter  140  is described below in connection with  FIG. 2 . 
         [0025]    It is the basic idea of the invention to reduce the air throughput through the combustion chamber  100  of the internal combustion engine in predefined operating phases, in fact especially in the partial load range of the internal combustion engine. The consideration underlying the basic idea with respect to said partial load range is that a significant increase in the heating value of the mixture and thereby the exhaust gas temperature can be brought about by a reduction in the air throughput through the combustion chamber  100  in partial load ranges. The exhaust gas temperature can thereby be increased in such a manner that a passive, continuous regeneration of the particle filter  140  is possible. For this purpose, a test is initially made in step  210  to determine whether the operating phase for the regeneration, i.e. the partial load range, is present. If this is the case, a test is made in step  220  to determine whether the boundary conditions for a regeneration prevail, which are subsequently described in more detail, particularly a desired ratio of nitrogen dioxide NO2 to carbon C. If this is the case, the air throughput through the combustion chamber is reduced in step  230 . This can, for example, thereby result, in that the closing of the intake valve  112  is advanced, i.e. a displacement of the closing time of the intake valve  112  toward an advanced engine crankshaft angle. 
         [0026]    The displacement of the closing time to an advanced position results analogous to the Miller cycle. However, in contrast to the Miller cycle, the reduced air throughput resulting from the advanced closing of the intake valve is not compensated for in this case by a higher pressure in the inlet port  110 , which is produced by means of an exhaust gas turbocharger, a compressor or the like. According to the invention, less ballast air is supposed to be allowed into the combustion chamber precisely as a result of the advanced closing of the intake valve  112  in the partial load range of concern here, wherein already a high air excess exists. This action is done in order to bring about such a significant increase in the heating value of the mixture and thereby in the exhaust gas temperature required for the regeneration. 
         [0027]    The reduction in the air throughput through the combustion chamber  100  can strictly as a matter of principle also be achieved by an advanced closing of the exhaust valve  122  analogous to the Miller cycle using residual gas compression. 
         [0028]    A reduction of the air throughput through the combustion chamber  100  can also furthermore alternatively or additionally take place by means of a corresponding activation of the throttle valve  170 . 
         [0029]    The advantage of the method previously described lies as a result of the thermodynamic boundary conditions therein, in that only slight increases in consumption arise when the mass of fresh mixture is curbed, and said slight increases in consumption are accompanied by a continuous, passive regeneration of the particle filter  140  resulting from the increase in exhaust gas temperature. Moreover, the quality of the untreated exhaust gas emissions in the exhaust gas tract  120  improves. For this reason, the possibility exists to achieve a complete regeneration of the particle filter  140  in the low temperature range. 
         [0030]    This regeneration advantageously takes place thereby continuously during the entire operating phase, i.e. in the entire partial load range. In so doing, the continuous regeneration takes place in the manner described below. The nitrogen monoxide NO, which is present in the exhaust gas, is oxidized to nitrogen dioxide NO2 in the oxidation catalytic converter because the oxidation of unburned carbon (soot), i.e. carbon C to carbon monoxide CO or to carbon dioxide CO2, now takes place with nitrogen dioxide NO2 at significantly lower temperatures, which can be implemented in the previously described manner, than with molecular oxygen O2. It is therefore necessary for the oxidation catalytic converter  130  to constantly produce so much nitrogen dioxide NO2, that the unburned carbon, which simultaneously accumulates, is oxidized and that preferably an undesirable accumulation of unburned carbon, which leads to pressure losses in the particle filter  140 , does not occur. The oxidation of unburned carbon is thereby significantly determined by the ratio of carbon (soot) to nitrogen dioxide NO2. A complete regeneration is only possible at a ratio of nitrogen dioxide NO2 to carbon C, which is greater than 8. 
         [0031]    The method previously described for the continuous regeneration of the particle filter  140  located in the exhaust gas zone requires only a slight increase in consumption during the regeneration phase because high pressure losses at the particle filter  140  cannot arise, respectively the time intervals up to a forced regeneration, which, for example, is performed with afterinjections, significantly lengthen and the increase in fuel consumption is thereby significantly reduced. It is also very advantageous, in that an improved homogenization of the mixture can be realized as a result of the advanced closing of the intake valve, while at the same time the charge temperature is reduced prior to the initiation of combustion. In this way, the sooty emissions in the untreated exhaust gas are significantly reduced. 
         [0032]    Furthermore, an improvement in the cold start emissions, particularly in the emission of hydrocarbons and carbon monoxide, is feasible. These are significantly reduced by the increase in the heating value of the mixture and thereby the average gas temperature. 
         [0033]    It must be mentioned that the method previously described can be used parallel to the methods for the regeneration of the particle filter, which are known from the technical field. In said methods, a forced regeneration takes place in certain operating phases. In the case of this parallel application, the additional time-lag considerably increases between the two regeneration intervals, in which a forced regeneration, for example, by means of afterinjections is performed.