DE102005022209B4 - Process for the regeneration of an internal combustion engine, in particular a diesel internal combustion engine, downstream nitrogen oxide storage catalytic converter - Google Patents

Abstract

method for the regeneration of an internal combustion engine, in particular a Diesel internal combustion engine, downstream nitrogen oxide storage catalytic converter, at the for the duration of the regeneration phase by means of a motor control device a substoichiometric Lambda value is adjusted, characterized in that in the regeneration phase falls below a predetermined minimum reaction temperature in the nitrogen oxide storage catalyst from the engine control unit at least temporarily predetermined and adjusted a low temperature lambda value that gets bigger and bigger so less fat than the one for the regeneration phase at reaction temperatures equal to or greater than the minimum reaction temperature given substoichiometric Lambda target value.

Description

The The invention relates to a method for regenerating an internal combustion engine, in particular a diesel internal combustion engine, downstream nitrogen oxide storage catalytic converter, according to the preamble of claim 1.

Such methods for the regeneration of a diesel internal combustion engine downstream nitrogen oxide storage catalyst are well known, since it is necessary due to the limited storage capacity of the nitrogen oxide storage catalysts to provide a constant change between Einspeicherphasen and regeneration phases. In these regeneration phases, the exhaust gas contains the necessary reducing components, such as HC, H ₂ and CO, whereby the oxygen concentration drops to very low levels and may even be reduced to a minimum, possibly in conjunction with an upstream oxidation catalyst. This leads to a disintegration of the metal nitrate previously stored during the Einspeicherphasen in the nitrogen oxide storage catalyst, which, inter alia, to a release of NO, which is then reduced at the precious metal contacts with the reducing exhaust gas components HC, H ₂ and CO to N ₂ .

To a complete Implementation or reduction of the released nitrogen oxides is followed by a breakthrough of the reducing agent, which by means of a sensor for lambda detection is detected and falls below a predetermined lambda value used as a termination criterion to end the regeneration phase becomes. Below a certain reaction temperature, the reduction reaction takes place but not fast enough, which is also known as kinetic inhibition becomes. this leads to now that both the nitrogen oxides and the introduced reducing agent can only be partially implemented. The emission of nitrogen oxides and in particular of hydrocarbons during the Regeneration increased itself and there is a faster breakthrough of the reducing agent than this at higher Reaction temperatures are the case, which is an undesirable early Demolition of regeneration has the consequence. This early Abort the regeneration leads turn to an incomplete one Restoration of the nitrogen oxide adsorption capacity of the nitrogen oxide storage catalyst, which in turn means that the storage times decrease and the fuel consumption increases. This problem is especially true in diesel internal combustion engines, because there in contrast to the Otto internal combustion engines lower exhaust gas temperatures are present.

To tackle this problem of regeneration at low exhaust temperatures, is in the DE 196 14 540 A1 proposed a catalyst for the purification of the exhaust gases of diesel engines, which should be able to oxidize in particular the long-chain, hardly oxidizable paraffins in the exhaust gas at temperatures below 200 ° C and at the same time reduce the nitrogen oxides despite the high oxygen content of the diesel exhaust. For this purpose, a catalyst is specifically proposed which contains one or more zeolites and at least one platinum group metal. In addition, the catalyst comprises one or more metal oxides from the group consisting of aluminum silicate, aluminum oxide and titanium oxide, wherein the aluminum silicate should have a weight ratio of silicon dioxide to aluminum oxide of 0.05 to 1 and the platinum group metals are deposited only on these additional metal oxides.

Furthermore, from the DE 198 54 794 A1 a catalyst for the purification of the exhaust gases of a diesel engine is known which has two superimposed functional layers on an inert support body, wherein the first lying directly on the support body layer has a nitrogen oxide storage function and the second, directly in contact with the exhaust gas layer, a catalytic Owns function. This second functional layer additionally has a hydrocarbon storage function and its catalytic function is provided by catalytically active noble metals of the platinum group, which are deposited in highly dispersed form on finely divided, acidic support materials. This should enable a better utilization of the reductive components contained in the exhaust gas for the reduction of nitrogen oxides.

Next is also from the DE 199 30 494 A1 a catalyst for the reduction of nitrogen oxides in an oxidizing and reducing atmosphere is known which contains iridium on a support material. The support material used is silicon dioxide or a dealuminated zeolite in the acidic H form with a modulus of more than 20, preferably more than 100, or mixtures thereof. Iridium is deposited on the outer surface of these substrates with average particle sizes between 10 and 20 nm. Such a catalyst constructed to increase the conversion rates even at lower exhaust gas temperatures and have a good resistance to poisoning by the sulfur oxides contained in the exhaust gas.

all these solutions is common that they lower the regeneration efficiency Exhaust gas temperatures or reaction temperatures by change increase the catalyst build up to attempt.

Next is from the DE 102 40 977 A1 a method for heating a catalyst is known, with which the temperature in at least one of the Kataly can be determined. Specifically, this is achieved by first determining the oxygen storage capacity of each or a group of catalysts by means of a Lanbdasprung and the determined respective oxygen storage capacity of the catalyst or a heat input taking into account the lower heating value and an exhaust gas mass flow, the energy input and thus a temperature in at least one catalyst is determined, whereby a regulation and control of the heating of the catalyst or catalysts is made by adjusting the fat and lean phases.

Next is from the DE 102 37 382 A1 a method for operating an internal combustion engine is known, by means of which a sufficiently accurate and reliable diagnostic capability of an associated emission control system, which includes a pre-catalyst and a NO _x -Speicherichatysator should be possible. This will be at the DE 102 37 382 A1 Concretely, this is achieved by ascertaining values of an NO _x storage activity, various NO _x storage catalyst temperatures and various pre-catalyst temperatures. Subsequently, correlation patterns between the NO _x storage activity and the values of the NO _x storage catalyst temperature and the values of the pre-catalyst temperature are determined and compared with predetermined test patterns. After the comparison, a precatalyst status signal is generated as comparison result.

Finally, out of the DE 103 07 723 A1 a method is known with which a high emission stability of a runnable internal combustion engine can be achieved while reducing fuel consumption. This is achieved in that a lean-running internal combustion engine for maintaining predetermined emission limit values in dependence on predetermined operating parameters, which include at least one status signal of the NO _x storage catalytic converter, is temporarily operated with a lambda value equal to 1 or a lambda value greater than 1, wherein a target value of a nitrogen oxide Raw emission is selected as a function of a value of the state signal NO _x storage catalytic converter.

In contrast, is It is the object of the present invention to provide a method for regeneration one of an internal combustion engine, in particular a diesel internal combustion engine Downstream nitrogen oxide storage catalyst available with a simple way to almost complete regeneration a nitrogen oxide storage catalyst even at low reaction temperatures possible is.

These Task is solved with the features of claim 1.

According to claim 1 is in the regeneration phase when falling below a predetermined minimum reaction or regeneration temperature in the nitrogen oxide storage catalyst of the engine control device at least temporarily such a low temperature lambda value given and adjusted, the larger and therefore less fat is as the one for the High-temperature regeneration phases at reaction temperatures equal or greater than the minimum reaction temperature given substoichiometric Lambda value.

By this simple and targeted increase of the Lambda value during the Low temperature regeneration phase becomes the oxygen concentration increased in the exhaust and the concentration of the reducing agent is reduced accordingly. This results in a longer one Regeneration phase, the danger of a reductant breakthrough and an incomplete one Regeneration of the nitrogen oxide storage catalyst by premature termination However, the regeneration is significantly reduced, since the nitrogen oxide storage catalyst due to the changed Exhaust gas composition through the then taking place exotermen processes faster is heated. By doing so leaves Obviously increase the efficiency of nitric oxide reduction. One further associated advantage of this process is that by the then more moderate lowering of the oxygen concentration in the exhaust also a reduced release of nitrogen oxides at the beginning the regeneration phase is effected.

With such a method of the invention is thus a simple method for complete regeneration of a nitrogen oxide storage catalyst even at low temperatures, especially temperatures of less as 300 ° C to disposal put, without that Interventions on the catalyst structure itself are required or the nitrogen oxide storage catalyst upstream heating measures need to be provided for heating the exhaust gas.

Especially in this case, preference is given to a process control according to claim 2, according to the in the regeneration phase at lower minimum reaction temperature Low-temperature lambda value to be regulated as a function of the amount of the temperature deviation the currently detected reaction temperature of the predetermined minimum reaction temperature is given. Particularly advantageous here is a characteristic-defined Tightening of activities with decreasing temperature, which means that the lower the actual Reaction temperature is, the higher the low-temperature lambda value while the regeneration phase is adjusted. For example, here certainly low-temperature lambda values up to 0.99, preferably up to be adjusted to 0.98, assuming a lambda value of about 0.94 starts.

Next the targeted increase of the lambda value to the low temperature lambda value during the entire regeneration phase it is according to claim 3 according to a another particularly preferred variant of the present invention Particularly advantageous that by means of the engine control device in the regeneration phase at lower minimum reaction temperature a multi-stage lambda control of a predetermined low temperature lambda value starting at predetermined increments to the lambda target is made. Switching between the individual stages takes place depending on of predetermined parameters. These parameters can be time and / or temperature parameters so that the switching either purely time-controlled or even after Achieve defined reaction temperatures, such. For example, catalyst temperatures, can be done. With such a "lambda stage" can be also the regeneration time and thus the additional consumption in comparison achieve the described one-time increase of the lambda value.

In a particularly preferred concrete procedure is The multi-stage lambda control according to claim 4, a two-stage Lambda control, in which in a first stage, a low temperature lambda value between 0.95 and 1.00, d. H. possibly also a stoichiometric one or approximate stoichiometric Lambda value can be adjusted while in a second stage a lambda value of less than or equal to 0.95 as substoichiometric Lambda value is specified. With such a concrete procedure can be excellent regeneration efficiency at low reaction temperatures, how they can be present in particular in the operation of diesel internal combustion engines achieve.

To Claim 5 will be the actual Reaction temperature by detecting the exhaust gas temperature and / or the storage catalytic converter temperature specified. For example, can thus depending on the temperature before or after or in the (modeled) storage catalyst either merely an increase in the lambda value in the low-temperature regeneration phase to the low-temperature lambda value or even a multi-level lambda control be applied.

A preferred procedure, the principle also independent can be used by the process guides described above, is claimed with the features of claim 6, according to the term the regeneration phase by means of a motor control device a stoichiometric Lambda value is adjusted, one by means of a sensor device detected, a predetermined threshold underrunning Reduk means means breakthrough signaled as the termination criterion the end of the regeneration phase and from the engine controller for a predetermined storage period is switched to the Einspeicherphase. According to the invention is at a fall below a predetermined minimum reaction temperature by means of the motor control device at a predetermined switching time or at predetermined switching times after a sensor-controlled regeneration phase end initiated at least one further low-temperature regeneration phase, wherein the time interval between the individual low-temperature regeneration phases is greater than the predetermined time interval between the high-temperature regeneration phases at reaction temperatures equal to or greater than the predetermined minimum reaction temperature are.

In this multiple regeneration according to the invention thus further regeneration cycles are connected after the sensor-controlled termination of the regeneration in short intervals. With the increasing number of regeneration phases, the catalyst temperature increases successively, whereby the activity is significantly increased in terms of the reduction reaction. The number of additional low-temperature regeneration phases is specified according to claim 7 temperature-dependent, the regeneration phases follow each other in short intervals compared to the high-temperature regeneration phases. In this case, according to claim 8, the duration of the at least one further low-temperature regeneration phase is preferably shorter than that of the first low-temperature regeneration phase. Specifically, for this purpose, as claimed in claim 9, it is provided that the at least one further low-temperature regeneration phase is interrupted by the engine control unit when it falls below a lambda threshold value specified for these low-temperature regeneration phases. This Lambdaschwellwert is set lower according to claim 10 for their compared to the first low-temperature regeneration phase shorter duration than for just this first low-temperature regeneration phase bene first lambda threshold, said first lambda threshold preferably also corresponds to the lambda threshold of the high-temperature regeneration phases. It should be noted at this point that the low-temperature lambda values and the lambda target values always refer to the exhaust gas composition upstream of the nitrogen oxide storage catalytic converter, while the lambda threshold values mentioned in connection with the multiple regeneration relate to the exhaust gas composition according to the nitrogen oxide storage catalytic converter. With such measures, a procedurally simple to perform multiple regeneration without expensive aparativen effort with the already existing components and measures possible.

Around in this multiple regeneration breakthroughs during the first cycles or It is special to minimize low temperature reaction phases advantageous, this procedure at least for a part of the first regeneration phases with the previously described Procedures to combine according to which a lower temperature lambda value is given, which is larger and so less fat than the one for the regeneration phase at reaction temperatures equal to or greater than the minimum reaction temperature given substoichiometric Lambda target value.

With Claim 12 is also determined that the predetermined minimum reaction temperature less than 300 ° C should be, this minimum reaction temperature preferably in a temperature window of 250 ° C to 300 ° C.

The The invention is explained in more detail below with reference to a drawing:

It demonstrate:

1 schematically the exhaust gas composition in a standard regeneration in a high-temperature regeneration phase,

2 schematically the exhaust gas composition at a low-temperature regeneration phase with adjusted low-temperature lambda value,

3 schematically the exhaust gas composition in a multi-stage lambda control, and

4 schematically the exhaust gas composition in a multiple regeneration with two cycles.

In the 1 is schematically plotted on the left side the concentration of components NO _x , HC and CO in ppm and on the right side the lambda value of the exhaust gas composition above time.

The 1 shows schematically a so-called standard regeneration or high-temperature regeneration phase, in which the reaction temperature has not fallen below a predetermined minimum reaction temperature. Dashed and with the reference numeral 1 provided here is the lowering of the lambda value of a value of z. B. about 1.5 during the so-called Einspeicherphase drawn on the sub-stoichiometric lambda value of about 0.94 during the regeneration phase. This is the lambda value before the nitrogen oxide storage catalytic converter.

The curve 2 indicates the time course of the NOX concentration after the nitrogen oxide storage catalyst, while the curve 3 the course of the HC concentration and the curve 4 characterize the course of the CO concentration according to the nitrogen oxide storage catalyst in each case by way of example.

At the End of the regeneration phase, here by the breakthrough of reducing agents HC and CO is then shown by means of the engine control unit the regeneration phase ends and the lambda value before the nitrogen oxide storage catalyst again to the default value for the Einspeicherphase (here 1.5, for example) regulated.

In the event that the reaction temperature below the predetermined critical minimum reaction temperature of z. B. 300 ° C, will, as in the 2 is shown, set by the engine control unit in the regeneration phase, a low-temperature lambda value and adjusted (here in the figure of 2 of about 0.96) which is larger and therefore less fat than that in the high-temperature regeneration phase of 1 default sub-stoichiometric lambda target of 0.94. This course of the low-temperature lambda value before the storage catalyst in the 2 with the reference number 5 characterized. The curves 2 . 3 and 4 here once again mark the time courses of the concentration values of NOX, HC and CO, again in each case after the nitrogen oxide storage catalyst. Again, then a switch from the low-temperature regeneration phase in the Einspeicherphase at a detected Reduktionsmitteldurchbruch, where, as a comparison of the 1 and 2 shows that the concentrations of HC and CO are significantly lower than in the high-temperature regeneration phase according to 1 , so that the breakthrough criterion for this case of the low-temperature regeneration phase of the 2 must be adjusted accordingly. This measure according to the invention thus requires only one compared to the process management 1 negligible longer regeneration phase.

One opposite in the 2 process control shown again more advantageous process control with respect to the 1 shorter regeneration time and even lower excess consumption is in the 3 represented in which a two-stage lambda control is performed, which in the 3 with the reference number 6 is marked. In the case of this two-stage lambda control, when the predetermined minimum reaction temperature is undershot, a higher low-temperature lambda value is set at the beginning of the low-temperature regeneration phase than during the process 2 the case is. This Never The temperature of the lambda lambda is approximately 0.98. Subsequently, in a second stage during this low-temperature regeneration phase, the lambda value of here z. B. 0.94, resulting in the through the curves 2 . 3 and 4 shown exhaust gas composition, which has significantly lower values with respect to the individual components NO _x , HC and CO, as in the 1 and 2 the case is. Here as well, a correspondingly adapted reducing agent breakthrough is defined as the termination criterion.

In the 4 Finally, a process control according to the multiple regeneration variant is shown, in which, when a predetermined minimum reaction temperature falls below a standard regeneration of 1 corresponding first low-temperature regeneration phase is carried out with a standard lambda target value before the nitrogen oxide storage catalyst of 0.94 until the abort criterion is reached at a predefined reductant breakthrough. Unlike the standard regeneration of 1 However, here is the engine control unit at predetermined switching times after the first regeneration phase 8th at least one further low-temperature regeneration phase 9 initiated, wherein the time interval between the individual low-temperature regeneration phases is shorter than the predetermined time interval between the high-temperature regeneration phases. To achieve this, the termination criterion for the additional additional low-temperature regeneration phases is used 9 a Lambda threshold value is set or regulated, which is lower than that for the first low-temperature regeneration phase 8th predetermined lambda lambda value, these lambda thresholds do not refer to the state of the exhaust gas composition before the nitrogen oxide storage catalyst, but to the exhaust gas composition after the nitrogen oxide storage catalyst. reference numeral 10 indicates the course of the lambda value before the nitrogen oxide storage catalytic converter for the second low-temperature regeneration phase 9 and is compared to the first low-temperature regeneration phase 8th significantly shorter in time. For the low-temperature regeneration phase, the lambda target value of 0.94 is also retained as the default value in our example case. The number of additional low-temperature regeneration phases 9 Depending on the actual reaction temperature, it is preferably predetermined by the engine control unit as defined by the characteristic. These not shown here, possibly required further low-temperature regeneration phases 9 can then each have a course according to the in the 4 illustrated low-temperature regeneration phase 9 exhibit.

According to a particularly preferred process control, what in the 4 dash-dotted lines and with the reference numerals 7 ' and 10 ' is also a combination of this measure with the previously in connection with the 3 carried out multi-stage lambda control described. Of course, a combination with the process would be according to 2 possible, but this is not shown here for reasons of clarity.

Claims (12)

Method for the regeneration of an internal combustion engine, in particular a diesel internal combustion engine, downstream nitrogen oxide storage catalytic converter in which a stoichiometric lambda target value is adjusted for the duration of the regeneration phase by means of an engine control device, characterized in that in the regeneration phase falls below a predetermined minimum reaction temperature in the nitrogen oxide At least temporarily a low-temperature lambda value is set and adjusted by the engine control unit at least temporarily, which is greater and therefore less rich than the substoichiometric lambda target value specified for the regeneration phase at reaction temperatures equal to or greater than the minimum reaction temperature. Method according to claim 1, characterized in that that in the regeneration phase at below minimum reaction temperature Low-temperature lambda value to be regulated as a function of the amount of the temperature deviation the current reaction temperature of the predetermined minimum reaction temperature is specified, in particular characteristic defined over the Motor control device is specified. Method according to claim 1 or 2, characterized that by means of the engine control device in the regeneration phase when the minimum reaction temperature is below a multi-stage lambda control from a predetermined low-temperature lambda value starting in predetermined increments made to the lambda value is, whereby the switching between the individual stages in dependence of predetermined parameters, in particular time and / or temperature parameters becomes. Method according to claim 3, characterized that in a two-stage lambda control in a first stage a low-temperature lambda value between 0.95 and 1.00 and in a second Stage a lambda value of less than or equal to 0.95 given becomes. Method according to one of claims 1 to 4, characterized in that the actual Re action temperature is specified by detecting the exhaust gas temperature and / or the storage catalytic converter temperature. Method, in particular according to one of claims 1 to 5, where for the duration of the regeneration phase by means of a motor control device a substoichiometric Lambda value is adjusted, one by means of a sensor device detected, a predetermined threshold below reducing agent breakthrough signaled as the termination criterion the end of the regeneration phase and from the engine controller for a predetermined storage period is switched to the Einspeicherphase, characterized that falls below a predetermined minimum reaction temperature by means of the engine control device to (a) predetermined (s) switching time (s) after a sensor-controlled first low-temperature regeneration phase end initiated at least one further low-temperature regeneration phase is, with the time interval between the individual low-temperature regeneration phases shorter is the predetermined time interval between the high temperature regeneration phases at reaction temperatures equal to or greater than the predetermined minimum reaction temperature are. Method according to Claim 6, characterized that of the engine control unit, the number of additional Low-temperature regeneration phases dependent on from the actual reaction temperature, in particular characteristic defined, is specified. Method according to one of claims 6 to 8, characterized that the duration of the at least one further low-temperature regeneration phase shorter is than that of the first low temperature regeneration phase. Method according to one of claims 6 to 8, characterized that the at least one further low-temperature regeneration phase from the engine control unit falls below one for this Low-temperature regeneration phases predetermined lambda value is canceled. Method according to claims 8 and 9, characterized that for the at least one further low-temperature regeneration phase predetermined lambda threshold value as second lambda threshold lower is as the for the first low-temperature regeneration phase predetermined first lambda threshold. Method according to one of claims 6 to 10, characterized that a low-temperature lambda value only for a part of the low-temperature regeneration phases, beginning with the first low-temperature regeneration phase, predetermined becomes. Method according to one of claims 1 to 11, characterized that the predetermined minimum reaction temperature is less than 300 ° C, preferably in a temperature window of 250 ° C to 300 ° C.