DE10318214A1 - Process to determine the age-condition of a nitrogen oxide storage catalytic converter by comparison of de-toxified unit with original value - Google Patents

Abstract

The The invention relates to a method for determining the state of aging a storage catalytic converter (3) of an internal combustion engine (1), with the following steps: Determine the decrease in the storage capacity of the Storage catalyst (3) and determination of the aging condition of the Storage catalyst (3) from the determined decrease in storage capacity. It it is proposed that the storage catalytic converter (3) be detoxified, before the decrease in storage capacity is determined and the state of aging of the storage catalyst (3) determined from the decrease in storage capacity becomes.

Description

The The invention relates to a method for determining the state of aging a storage catalytic converter of an internal combustion engine according to the preamble of claim 1.

Modern internal combustion engines have a regulated three-way catalytic converter and a NO _x storage catalytic converter for exhaust gas purification. The three-way catalytic converter is also known as a TWC (Three-Way Catalyst) and serves as a pre-catalyst for the reduction of carbon monoxide and hydrocarbons in the exhaust gas. The NO _x storage catalytic converter, on the other hand, is arranged downstream of the three-way catalytic converter and, in superstoichiometric operation, has the task of taking up nitrogen oxides from the exhaust gas and temporarily storing them.

Must be, however, the _NOx storage ability of the NO _x storage is limited, so that the NO _x storage time before the exhaustion of its storage capacity regenerated to prevent a breakdown of the NO _x storage as this to an increase in NO _x Emissions would result.

As is known, the regeneration of the NO _x storage catalytic converter can be carried out by temporarily enriching the mixture composition of the internal combustion engine, so that the stored nitrogen oxides are converted into less environmentally harmful compounds.

The problem with such exhaust gas cleaning systems with a NO _x storage catalytic converter is the fact that the NO _x storage catalytic converter is poisoned by the sulfur still present in commercially available fuels, as a result of which the NO _x storage capacity decreases with increasing operating time.

Thus, when sulfur-containing fuel is burned, especially in lean operation, sulfur oxides are formed, which are bound and stored in the NO _x storage catalytic converter like nitrogen oxides on the catalytically active surface. However, the sulfur compounds stored in this way in the NO _x storage catalytic converter are chemically much more stable than the NO _x compounds, so that the stored sulfur compounds are not removed from the NO _x storage catalytic converter during the normal regeneration of the NO _x storage catalytic converter. As a result of the increasing incorporation of sulfur compounds in the NO _x storage catalytic converter during the operating period, the absolute NO _x storage capacity of the NO _x storage catalytic converter is continuously reduced.

This sulfur-related poisoning of the NO _x storage catalytic converter and the associated decrease in the absolute storage capacity can, however, be reversed, as is known, by heating the NO _x storage catalytic converter to the so-called desulphation temperature and operating under stoichiometry, the desulphation temperature being above the normal operating temperature and for example at a NO _x storage catalyst in barium technology is approx. 650 ° Celsius to 750 ° Celsius. The increase in the exhaust gas temperature required for the desulfation of the NO _x storage catalytic converter can take place, for example, by retarding the ignition timing.

However, the storage capacity of the NO _x storage catalytic converter not only decreases during the operating period due to the sulfur poisoning described above, but also decreases due to irreversible thermal aging. It is therefore known to block the lean operation of the internal combustion engine from a certain aging state of the NO _x storage catalytic converter in order to comply with the specified exhaust gas standards despite the aging-related decrease in the storage capacity of the NO _x storage catalytic converter.

The aging state of the NO _x storage catalytic converter is usually determined by determining the storage capacity of the NO _x storage catalytic converter. It is important to distinguish between a poisoning-related decrease in storage capacity on the one hand and an aging-related decrease in storage capacity on the other hand, since the sulfur-related poisoning of the NO _x storage catalytic converter is reversible and can be reversed by desulfating, whereas the thermally induced aging is irreversible.

It is therefore known, when determining the aging state of a NO _x storage catalytic converter, to determine the poisoning-related decrease in the storage capacity, taking into account the predetermined sulfur content of the fuel, using a sulfurization model.

Farther is in the known method for determining the state of aging of the storage catalytic converter measured the decrease in storage capacity, for which various methods are known, the following briefly to be discribed.

A known method for determining the decrease in the storage capacity of the NO _x storage catalyst is based on the so-called regeneration agent integral, ie during the regeneration of the NO _x storage catalytic converter up to the fat jump the regeneration agent made available to the NO _x storage catalytic converter. It is assumed here that the regeneration agent is integral proportional to the amount of nitrogen oxide previously stored. If the regeneration agent integral is reduced, a corresponding decrease in the storage capacity of the NO _x storage catalytic converter is then concluded, this decrease being caused by poisoning or thermal aging.

In another known method for determining the decrease in the storage capacity of the NO _x storage catalytic converter, on the other hand, the NO _x concentration gradient across the NO _x storage catalytic converter is measured at the start of regeneration and compared with a model value in order to determine the difference between the measured value and the model value calculate the decrease in storage capacity.

In a known method for determining the aging state of the NO _x storage catalytic converter, the decrease in storage capacity caused by thermal aging is then calculated by forming the difference between the measured decrease in storage capacity and the poisoning-related decrease in storage capacity calculated on the basis of the sulfurization model. This advantageously enables a distinction to be made between the poisoning-related decrease in storage capacity on the one hand and the aging-related decrease in storage capacity on the other hand, so that poisoning of the NO _x storage catalytic converter does not lead to premature blocking of lean operation or even to premature replacement of the NO _x storage catalytic converter.

A disadvantage of this known method, however, is the inaccuracy when determining the decrease in storage capacity due to poisoning using the sulfurization model, since the sulfur content of the fuel must be specified. However, this sulfur content depends on the type of fuel and can even vary depending on the brand and batch depending on the type of fuel. In addition, the sulfur content of the fuel varies widely in different countries. For example, Super Plus fuel in Germany has a sulfur content of 10ppm, whereas the sulfur content in Spain is around 100ppm. If the sulfur content of the fuel is actually higher than assumed in the sulfurization model, this leads to an incorrect determination of the aging condition of the NO _x storage catalytic converter, since the poisoning-related decrease in the storage capacity is incorrectly attributed to thermal aging, so that a too large thermal one Age of the NO _x storage catalytic converter is assumed. As a result, this can lead to premature blocking of lean operation or even to premature replacement of the NO _x storage catalytic converter.

The invention is therefore based on the object in the known method described above for determining the aging state of a NO _x storage catalytic converter to avoid the errors which result from fluctuations in the sulfur content in the fuel used.

The object is achieved on the basis of the known method described above for determining the aging state of a NO _x storage catalytic converter according to the preamble of claim 1 by the characterizing features of claim 1.

The invention encompasses the general technical teaching of first performing a detoxification of the NO _x storage catalytic converter before determining the aging state of the NO _x storage catalytic converter in order to minimize the influence of the poisoning-related decrease in the storage capacity of the NO _x storage catalytic converter on the determination of the aging condition. So the poisoning-related decrease in the storage capacity of the NO _x storage catalytic converter immediately after detoxification is negligible, so that even assuming an incorrect sulfur content in the fuel hardly leads to errors in the determination of the aging condition.

Preferably the implementation takes place detoxification not always before every determination of the state of aging, but only if the determination of the aging condition without a previous detoxification of the storage catalytic converter is critical Aging state of the storage catalytic converter results, for example blocking lean operation or even replacing the storage catalytic converter would require. In such a case, detoxification of the storage catalytic converter is then preferably carried out first made to the aging state of the storage catalytic converter again to check where the poisoning-related decrease in the storage capacity of the storage catalytic converter then no longer plays a role because of the previous detoxification.

at the inventive method is therefore first the decrease in storage capacity the storage catalytic converter determines what can be done in a conventional manner, as already described at the beginning.

Then will then preferably taking into account a sulfurization model of a predetermined sulfur content of the fuel Decrease in storage capacity calculated.

Then the difference between the total decrease in the storage capacity of the Storage catalyst and the theoretically calculated sulfur-related Decrease in storage capacity calculated, this difference being the thermally related and therefore irreversible decrease in the storage capacity of the storage catalytic converter reproduces.

The value calculated for the thermally induced decrease in the storage capacity of the storage catalytic converter is then compared with a predetermined maximum value.

At the The storage capacity of the Storage catalytic converter in any case sufficient so that neither Blocking the lean operation or an exchange of the storage catalytic converter is required.

If the determined thermally induced decrease in the storage capacity on the other hand exceeds the specified maximum value, that would actually be blocking lean operation or even replacing the storage catalytic converter required so that in the following a more precise determination of the age-related decrease in storage capacity is required.

For this in this case the storage catalytic converter is detoxified, to the influence of the sulfur-related decrease in storage capacity minimize.

Then follows then again a determination of the age-related decrease in the storage capacity of the Storage catalyst, the poisoning-related decrease in storage capacity because of the previous detoxification of the storage catalytic converter negligible is.

If this new determination of the aging-related decrease in storage capacity the detoxification in turn leads to an excessive value, so compliance is required the emission regulations a block of lean operation or even a Storage catalytic converter replacement required.

If the redetermination of the age-related decrease in the storage capacity against it leads to a lower value, so was the inflated value before detoxification on an incorrect calculation of the sulfur-related Decrease in storage capacity attributed to what for example, by assuming that the sulfur content is too low can be caused in fuel.

In In one variant, the specified value for the sulfur content is optimized of fuel. For this, the difference between the before Detoxification determined decrease in storage capacity and after detoxification determined decrease in storage capacity calculated to the predetermined Sulfur content depending to adjust from this deviation.

Preferably the decrease in the storage capacity of the Storage catalyst after detoxification several times in succession, whereby an average value is calculated from the values determined becomes.

Other Advantageous developments of the invention are characterized in the subclaims or are given below along with the description of the preferred Embodiment of the Invention with reference to the figures explained. Show it:

1 a simplified representation of an internal combustion engine with an exhaust gas cleaning system

2a - 2 B the method according to the invention for determining the aging state of a storage catalytic converter in the form of a flow chart,

3 a process for detoxifying the storage catalyst in the context of the 2a - 2 B illustrated method according to the invention

such as 4 a method for determining the decrease in the storage capacity of the storage catalyst within the scope of 2a - 2 B illustrated method according to the invention.

The schematic representation in 1 shows an internal combustion engine in a highly simplified form 1 with an exhaust gas purification system, the exhaust gas purification system having a three-way catalyst (English TWC - Three-Way Catalyst) and a downstream of the three-way catalyst 2 arranged NO _x storage catalyst 3 includes.

The three-way catalyst 2 is used here to reduce the hydrocarbon and carbon monoxide concentration in the exhaust gas, while the NO _x storage catalytic converter 3 has the task in superstoichiometric operation of taking up nitrogen oxides from the exhaust gas and temporarily storing them.

In addition, the exhaust gas purification system has an exhaust gas probe 4, which is in an exhaust gas channel between the three-way catalyst 2 and the NO _x storage catalyst 3 is arranged and measures the oxygen concentration in the exhaust gas. The exhaust gas probe is on the outlet side 4 with an electronic motor control 5 (Engl. ECU - Electronic Control Unit) connected, which the internal combustion engine 1 controls or the mixture composition of the internal combustion engine 1 pretends.

The exhaust gas cleaning system also has a temperature sensor 6 on that on the NO _x storage catalyst 3 is attached and the temperature of the NO _x storage catalyst 3 detected with the temperature sensor 6 on the output side also with the electronic motor control 5 connected is. However, it is alternatively also possible for the temperature sensor 6 the exhaust gas temperature upstream of the NO _x storage catalytic converter 3 measures, the temperature of the NO _x storage catalyst 3 is derived from the measured exhaust gas temperature.

In a variant of the invention, the exhaust gas cleaning system has an exhaust gas probe 7 on that in an exhaust duct between the internal combustion engine 1 and the three-way catalyst 2 is arranged and which is the oxygen concentration in the exhaust gas of the internal combustion engine 1 upstream in front of the three-way catalytic converter 2 measures. The electronic engine control system can use the oxygen concentration measured in this way 5 then determine whether the oxygen storage capacity of the three-way catalyst 2 is exhausted.

In a further variant of the invention, the NO _x storage catalytic converter is additionally downstream 3 another exhaust gas probe 8th arranged which the nitrogen oxide and the oxygen concentration downstream after the NO _x storage catalyst 3 measures to breakdown the NO _x storage catalyst 3 to be able to recognize. Such a breakdown of the NO _x storage catalytic converter 3 occurs when the absolute NO _x or O ₂ storage capacity of the NO _x storage catalyst 3 is exceeded and that in the exhaust gas of the internal combustion engine 1 contained nitrogen oxides or the oxygen no longer in the NO _x storage catalyst 3 can be saved.

Finally, there is an air mass sensor in the intake area of the internal combustion engine 9 arranged, which measures the air mass flow Q.

The method according to the invention for determining the aging state of the NO _x storage catalytic converter is described below 3 based on the flowchart in 2a and 2 B explained.

At the beginning of the process, the decrease A _{TOTAL of} the storage capacity of the NO _x storage catalytic converter is first 3 certainly. The determination of the total decrease A _{TOTAL of} the storage capacity of the NO _x storage catalytic converter 3 can for example by the in 4 described method take place, which will be described later in detail. It should only be mentioned that the value A _TOTAL both the poisoning related decline A _SULFUR the age-related decrease in A _THERM includes the storage capacity as the storage capacity.

In a further step, the poisoning- _related decrease in _{SULFUR of} the storage capacity is then calculated using a sulfurization model, taking into account the sulfur content of the fuel used, the sulfur content of the fuel being predefined as an application value.

In a next step, the age-related decrease A _{THERM of} the storage capacity is the difference between the total decrease A _{TOTAL of} the storage capacity and the previously modeled decrease A _{SULFUR of} the storage capacity of the NO _x storage catalytic converter 3 calculated.

The decrease A _{THERM of} the storage capacity calculated in this way is then compared in a next step with a predetermined maximum value A _MAX , the maximum value A _MAX being determined in such a way that the emission regulations are complied with in any case if the thermal aging A _{THERM of} the NO _x storage catalyst 3 does not exceed this maximum value.

If the previously mediated decrease A _THERM does not exceed the predetermined maximum value A _MAX , the process is repeated in a loop since the aging state of the NO _x storage catalytic converter 3 does not require any measures yet.

Otherwise, in a next step, the stratified operation of the internal combustion engine will start 1 temporarily blocked to avoid exceeding the emission limit values.

Then the NO _x storage catalyst 3 then subjected to desulfation, the desulfation of the NO _x storage catalyst 3 for example according to the in 3 described method can be done, which will be described later in detail.

After the desulfation of the NO _x storage catalytic converter 3 the decrease A _{i of} the storage capacity is then determined in a loop several times in succession, an average value A _{THERM being} calculated from the values A _i determined in the process. For this purpose, shift operation is temporarily released if the boundary conditions for the aging determination are given.

This value A _THERM for the decrease of the storage capacity of the NO _x -Speichervermögens the NO _x storage 3 is due to the previous desulfation of the NO _x storage catalyst 3 due to the sulfur-related poisoning of the NO _x storage catalytic converter 3 not influenced and therefore does not depend on the sulfur content of the fuel used, which is only available as an estimate.

In a next step, the A _THERM value is therefore compared again with the predetermined maximum value A _MAX to determine the aging state of the NO _x storage catalytic converter 3 to determine.

If the maximum value A _MAX after detoxification of the NO _x storage catalytic converter 3 is no longer exceeded, this shows that the excessive determination of the thermally induced decrease A _{SULFUR of} the storage capacity before the detoxification of the NO _x storage catalytic converter 3 was caused by the incorrect assumption that the fuel content used was too low. In this case, shift operation is therefore released again and the process is ended.

If the decrease A _THERM, on the other hand, also after the detoxification of the NO _x storage catalytic converter 3 exceeds the predetermined maximum value A _MAX , it can be assumed that the aging state of the NO _x storage catalytic converter 3 Measures required.

In the loop for the repeated determination of the age-related decrease A _{i of} the storage capacity, the time period T _{MAGER of} the lean operation is continuously measured and compared with a predetermined limit value T _MIN . This makes sense, since in the case of very long, stoichiometric operation without an interim requirement for regeneration of the NO _x storage catalytic converter 3 It can be assumed that the storage capacity of the NO _x storage catalytic converter 3 is hardly reduced due to aging. In such a case, shift operation is also released again.

Otherwise, shift operation remains blocked in order to comply with the emission regulations despite the aging capacity of the NO _x storage catalytic converter 3 to be able to comply.

In addition, a warning signal is generated in a further step, which prompts the user to change the NO _x storage catalytic converter 3 prompts.

The following is now briefly in 3 illustrated method for desulfating the NO _x storage catalyst 3 described.

At the beginning of the process, the NO _x storage catalytic converter is first heated 3 down to the desulfating temperature T _DESULFAT , the desulfating temperature T _DESULFAT usually being between 650 ° Celsius and 750 ° Celsius.

Then the internal combustion engine 1 then operated with a substoichiometric mixture ratio, which is in NO _x storage catalyst 3 embedded sulfur oxides from the catalytically active surface of the NO _x storage catalytic converter 3 to solve.

Finally, that is now in 4 illustrated method for determining the decrease A in the storage capacity of the NO _x storage catalyst 3 described.

At the beginning of the method, there is first a complete NO _x regeneration of the NO _x storage catalytic converter 3 by the internal combustion engine 1 is operated with a substoichiometric (rich) mixture.

This is then followed by lean operation, with the nitrogen oxide _{concentration} K upstream of the NO _x storage catalytic converter 3 and the nitrogen oxide concentration K _after the NO _x storage catalytic converter 3 is determined at the time the regeneration is initiated.

These two measured values then become the load quantity m _{NOx of} the NO _x storage _{catalytic converter} 3 calculated.

Further, a model value m _x 'for the loading amount of the NO _x storage catalytic converter 3 calculated.

From the calculated loading quantity m _NOx and from the modeled loading quantity m _NOx ', the decrease A in the storage capacity of the NO _x storage _{catalytic converter} is then changed over the loading straight line 3 calculated.

The Invention is not based on the preferred embodiment described above limited. Rather, a variety of variations and modifications are possible also make use of the inventive idea and therefore in fall within the protection zone.

Claims (12)

Method for determining the aging condition of a storage catalytic converter ( 3 ) an internal combustion engine ( 1 ), with the following steps: - Determination of the decrease in the storage capacity of the storage catalytic converter ( 3 ), - Determination of the aging condition (A _THERM ) of the storage catalytic converter ( 3 ) from the determined decrease in storage capacity, characterized in that the storage catalytic converter ( 3 ) is detoxified before the decrease in storage capacity is determined and the aging condition (A _THERM ) of the storage catalytic converter ( 3 ) is determined from the decrease in storage capacity. Method according to Claim 1, characterized by the following steps: a) determining the decrease (A _TOTAL ) in the storage capacity of the storage catalytic converter ( 3 ), b) comparison of the determined decrease (A _TOTAL ) of the storage capacity with a predetermined maximum value (A _MAX ), c) detoxification of the storage catalytic converter ( 3 ) if the determined decrease (A _TOTAL ) in the storage capacity of the storage catalytic converter ( 3 ) exceeds the specified maximum value (A _MAX ), d) redetermining the decrease (A _i ) in the storage capacity of the storage catalytic converter ( 3 ) after detoxification of the storage catalytic converter ( 3 ), e) determination of the aging condition (A _THERM ) of the storage catalytic converter ( 3 ) from the determined decrease (A _i ) of the storage capacity after detoxification. A method according to claim 2, characterized in that before the detoxification, the age-related decrease (A _THERM ) of the storage capacity is determined and compared with the maximum value (A _MAX ). Method according to Claim 3, characterized by the following steps: - Determination of the decrease (A _SULFUR ) in the storage capacity of the storage catalytic converter ( 3 ) before the detoxification of the storage catalytic converter ( 3 ), - Determination of the total decrease (A _TOTAL ) of the storage capacity of the storage catalytic converter ( 3 ) before the detoxification of the storage catalytic converter ( 3 ), - Determination of the age-related decrease (A _THERM ) of the storage capacity from the total decrease (A _TOTAL ) and the poisoning- _related decrease (A _SULFUR ) before the detoxification. A method according to claim 4, characterized in that the poisoning- _related decrease (A _SULFUR ) of the storage capacity as a function of a predetermined sulfur content of the fuel and the fuel consumption of the internal combustion engine ( 1 ) is determined using a given physical model. Method according to Claim 5, characterized by the following steps: - Determination of the deviation between the decrease in the storage capacity determined before the detoxification and the decrease in the storage capacity of the storage catalytic converter determined after the detoxification ( 3 ), - Adjustment of the specified sulfur content of the fuel depending on the determined deviation. Method according to at least one of the preceding claims, characterized in that before the detoxification of the storage catalyst ( 3 ) the lean operation and / or the stratified operation of the internal combustion engine ( 1 ) is blocked if the before the detoxification of the storage catalyst ( 3 ) determined decrease in storage capacity exceeds the maximum value (A _MAX ). A method according to claim 7, characterized in that the lean operation and / or the stratified operation of the internal combustion engine ( 1 ) is released again after detoxification, if a predetermined aging condition of the storage catalytic converter ( 3 ) has not yet been reached. Method according to at least one of the preceding claims, characterized in that the lean operation and / or the stratified operation of the internal combustion engine ( 1 ) after detoxification of the storage catalytic converter ( 3 ) is blocked when a predetermined aging condition of the storage catalytic converter ( 3 ) is reached. Method according to at least one of the preceding claims, characterized in that when a predetermined aging state of the storage catalytic converter ( 3 ) a warning signal is generated to promptly replace the storage catalytic converter ( 3 ) to enable. Method according to at least one of the preceding claims, characterized in that the storage catalytic converter ( 3 ) for detoxification heated up to a predetermined detoxification temperature and / or that the internal combustion engine ( 1 ) to detoxify the storage catalytic converter ( 3 ) is operated with a substoichiometric mixture ratio. Method according to at least one of the preceding claims, characterized in that after the detoxification of the storage catalyst ( 3 ) multiple decreases in the storage capacity of the storage catalytic converter ( 3 ) is determined, an average value (A _THERM ) being calculated from the determined values (A _i ).