DE10338181B4 - Method and device for influencing the temperature of a catalyst system - Google Patents

Abstract

A method for influencing the temperature of a catalyst system arranged in the exhaust system of a preferably direct-injecting stratified or lean-burn internal combustion engine, which comprises at least one primary catalyst and at least one main catalyst located downstream of the primary catalyst, a value of an oxygen storage capacity of the primary catalyst OSC_VK, the main catalyst OSC_HK and the catalyst system being determined and OSC_Katalyst Depending on these values, selective measures for influencing the temperature of at least one of the components of the exhaust system primary catalytic converter or main catalytic converter are carried out, characterized in that for the selective determination of the value of the oxygen storage capacity of the primary catalytic converter OSC_VK - within a time interval T_VK in which it is to be expected that OSC_VK greater than a stalyser OSC_HK is less than a threshold value OSC_HKS1, - from a temporal course of the oxygen c Concentration downstream of the main catalytic converter, the value of the OSC of the catalytic converter system OSC_K assigned to the time interval T_VK is determined and - OSC_VK is set approximately equal to OSC_K and - within a ...

Description

The invention relates to a method and a device for influencing the temperature of a catalyst system according to the preambles of the independent claims

Known catalyst systems used for exhaust gas purification of internal combustion engines frequently comprise at least one small volume precatalyst arranged close to the engine and at least one larger main catalytic converter arranged further downstream. The system components can be designed as oxidation catalysts for the conversion of unburned hydrocarbons (HC) and carbon monoxide (CO), as reduction catalysts for the reduction of nitrogen oxides NOx or as 3-way catalysts which simultaneously promote said oxidative and reductive conversions. In the case of lean-burn internal combustion engines, the main catalytic converter may additionally be equipped with a NOx storage component which, in lean operating phases in which the internal combustion engine is charged with an oxygen-rich air-fuel mixture with λ> 1, stores nitrogen oxides (NOx) in order to grease them Release operating intervals with λ <1 and reduce them again.

Vehicles with lean-running or direct-injection, stratified charge gasoline engines can be operated in the lower load range in various operating modes. In this case, the shift operation generally represents the most fuel-efficient operating mode. In order to exploit the maximum potential of this operating mode, the most frequent possible use of shift operation is sought.

The exhaust gas temperature of internal combustion engines usually decreases with decreasing load and to a lesser extent with decreasing speed. In longer lasting low load operation, z. As permanent idling, stop-and-go traffic, city driving, thus at least a first catalyst is partially cooled down so much that it no longer reaches its maximum possible conversion performance. In particular, the stratified operation with its relatively low exhaust gas temperatures compared to the stoichiometric engine operation at lambda = 1 particularly high demands on the exhaust aftertreatment. Especially with aged exhaust gas cleaning systems, the influence of aging leads to a shift in the light-off temperature in the direction of higher temperatures and thus to a correspondingly poorer light-off characteristic of the exhaust system.

In the prior art ( DE 197 29 087 C2 ) is known to fall below exhaust and / or catalyst temperature thresholds to take exhaust and / or catalyst temperature-increasing measures. Although a certain emission safety is ensured with these known methods, since a cooling of the catalysts is prevented by appropriate choice of the temperature thresholds. However, about the pure temperature threshold query no statement about the actual temperature of the catalyst catalyst is possible. Thus, when falling below a temperature threshold usually to ensure emission safety on the shift operation in favor of the "hotter" but also fuel consumption-increasing homogeneous operation must be waived, although usually the cooling of a small sub-zone of a catalyst can be tolerated below a temperature threshold.

Further, a main catalyst, which is at a temperature level above a predetermined light-off temperature, at least partially compensate for a loss of conversion at least one upstream cooled pre-catalyst and special temperature-increasing measures are not required.

Remedy can be taken here by measures to increase an exhaust gas and / or catalyst temperature depending on an energy drain from a catalyst. In this case, a heat flow necessary for the corresponding catalyst, based on the exhaust gas temperature, upstream of the precatalyst and a defined light-off temperature, is determined and cumulatively results in the energy discharge from the catalyst. When predefinable threshold values for the energy discharge are exceeded, exhaust gas and / or temperature-increasing measures can be taken. This determination is possible both for a pre-catalytic converter close to the engine and for a main catalytic converter arranged further downstream. The prerequisite here, however, is the determination of the corresponding conversion state of the primary catalyst or catalytic converter. In combination with the exhaust gas and / or catalyst temperature increasing intervention during engine operation is already a knowledge of the current conversion performance of pre- or main catalyst before the actual engine start of particular interest. This makes it possible to take into account the current light-off characteristic at the start of the engine by taking appropriate measures in the so-called "catalytic heating function", which is usually taken within the first 2 ... 120 seconds after engine start. As a result, different strategies for starting the engine can be realized, which result in dependence on the conversion performance of the catalysts, in particular the precatalyst and thus for faster achievement of the light-off temperature.

The prerequisite for the above measures is a selective determination of the current conversion performance of a catalytic converter. It is known that the oxygen storage capacity (OSC) of a catalyst correlates with the light-off temperature, in particular for the oxidation of unburned hydrocarbons HC.

From the DE 100 40 517 A1 A method is known for influencing the temperature of a catalytic converter system arranged in the exhaust system of a preferably direct-injection, stratified charge or lean-burn internal combustion engine, which comprises at least one primary catalytic converter and at least one main catalytic converter arranged downstream of the primary catalytic converter.

Known methods for determining the OSC, for example the document US 2003/0017603 A1 , take into account the waveforms of the exhaust gas purification system, usually a combination of close to the engine primary catalyst and downstream main catalyst, upstream or downstream of the main catalyst oxygen-sensitive measuring device. In this case, the OSC is determined either via the overall system, precatalyst and main catalyst or in the presence of an additional oxygen-sensitive measuring device between the catalysts selectively via the individual catalysts.

The object of the present invention is to provide a method and a device which enable optimized operation of a catalyst system as a function of a determined OSC of the precatalyst or main catalyst of the catalyst system in a simple and cost-effective manner.

According to the invention, this object is achieved by the features of the independent claims.

According to the invention, a generic method for the selective determination of the oxygen storage capacity of a precatalyst or main catalyst is further developed, in which the OSC of the individual catalysts for a system configuration with pre-catalyst arranged close to the engine and downstream main catalyst can be selectively determined between the catalysts without additional oxygen-sensitive measuring device.

For this purpose, first the OSC of the operating-temperature precatalyst is determined, at a time when the OSC of the main catalyst is not active or only slightly active. At a later time, in which both the pre-catalyst and the main catalyst reaches its operating temperature and thus the OSC of the entire system can be measured, the OSC of the main catalyst is determined. The OSC is determined from a corresponding signal curve of an oxygen-sensitive measuring device (lambda probe, NOx sensor) downstream of the main catalytic converter. Preferably, the determination of the OSC of the precatalyst with this method is carried out only after completion of any upstream heating measures, but before reaching / exceeding the light-off temperature of a downstream main catalyst.

In this case, the internal combustion engine is operated alternately between rich and lean air-fuel mixture and assessed the temporally different waveforms with respect to the stored oxygen mass. The larger the oxygen storage of a catalyst, the more time passes until the oxygen-sensitive measuring device recognizes the corresponding mixture jump after the catalyst or after the exhaust gas purification system.

When operating a catalyst system, it must be ruled out that any possible sulfur poisoning of the precatalyst, in particular of the NOx storage catalyst, which likewise leads to reduced OSC values, erroneously entails exhaust gas and / or catalyst temperature-increasing measures. A request for appropriate measures is only carried out as long as the sulfur loading of the catalyst is smaller than an applicable threshold. Preferably, sulfur poisoning of the NOx storage catalyst can be detected by at least one of the following measures. On the one hand, in the presence of an oxygen-sensitive measuring device (NOx sensor) downstream of the NOx storage catalytic converter, a NOx activity slump can be detected, and on the other hand, in an engine control unit, an arithmetic variable with an almost to be applied value for the fuel sulfur content, the sulfur input into the catalyst as a function of be enforced fuel mass. In combination with the selectively determined OSC values of the precatalyst or main catalyst, it is thus possible to differentiate between a sulfur-poisoned or aged catalyst.

• • In einem ersten Schritt wird die OSC des Vorkatalysators bestimmt, solange die Light-Off-Temperatur des Hauptkatalysators und somit seine Fähigkeit Sauerstoff ein- bzw. auszuspeichern nicht überschritten ist. Mit zunehmender Alterung der Katalysatoren im Fahrzeugbetrieb wird das Verfahren unempfindlicher hinsichtlich Streuungen, da die Light-Off-Temperatur des Hauptkatalysators mit zunehmender Alterung zu höheren Temperaturen verschoben wird. Hierdurch steigt auch die Temperatur, bei welcher ein alternierender Fett-Mager-Betrieb zu einer Sauerstoffeinspeicherung bzw. Sauerstoffausspeicherung führt. Bei Konzepten mit einer sauerstoffsensitiven Messeinrichtung (Lambda-Sonde) nach dem Vorkatalysator kann diese OSC-Bestimmung unabhängig von der Temperatur des Hauptkatalysators durchgeführt werden.
• • In einem zweiten Schritt, bei welchem sowohl der Vorkatalysator als auch der Hauptkatalysator ihre Betriebstemperatur erreicht haben und gleichmäßig durchwärmt sind, kann die Bestimmung der OSC des Gesamtsystems, wie bereits bekannt, über einen Sondensprung nach dem Hauptkatalysator erfolgen. Voraussetzung für eine reproduzierbare OSC-Bestimmung ist hierbei die homogene Durchwärmung des Gesamtsystems.
• • In einem dritten Schritt wird aus den ermittelten Werten die sich ergebene OSC für den Hauptkatalysator ermittelt: OSC-Hauptkat = OSC-System – OSC-Vorkat. Diese Werte werden dann mit frei in einem Steuergerät applizierbaren und für das entsprechende Katalysatorsystem gültigen Werte verglichen. Solange die Bestimmung der OSC des Gesamtsystems bzw. der einzelnen Katalysatoren die vorgegebenen Werte nicht unterschreitet, werden keine Maßnahmen hinsichtlich Entschwefelung getroffen. Sollte die OSC-Bestimmung einen Einbruch in der Gesamtsauerstoffspeicherkapazität zeigen, wird in nachfolgenden Schritten zunächst eine Differenzierung zwischen Vorkatalysator und Hauptkatalysator durchgeführt, analog zur Bestimmung der Sauerstoffspeicherfähigkeit des Gesamtsystems.
• • Wird durch Auswertung der selektiven OSC des Vor- bzw. Hauptkatalysators ein Einbruch der Sauerstoffspeicherfähigkeit unter einen vorgebbaren Wert ermittelt, wird zunächst zwischen einem Einbruch der OSC am Vorkatalysator bzw. am Hauptkatalysator differenziert.

The determination of the respective catalyst state is carried out by evaluating the previously determined OSC values. In a preferred embodiment of the method, this is done as follows:

• • In a first step, the precursor's OSC is determined as long as the light-off temperature of the main catalytic converter and thus its ability to inject and release oxygen is not exceeded. With increasing aging of the catalytic converters in vehicle operation, the method is less susceptible to scattering, since the light-off temperature of the main catalyst is shifted to higher temperatures with increasing aging. hereby Also increases the temperature at which an alternating fat-lean operation leads to an oxygen storage or oxygen storage. In concepts with an oxygen-sensitive measuring device (lambda probe) downstream of the precatalyst, this OSC determination can be carried out independently of the temperature of the main catalyst.
• In a second step, in which both the pre-catalyst and the main catalyst have reached their operating temperature and are heated uniformly, the determination of the OSC of the entire system, as already known, can take place via a probe jump after the main catalyst. The prerequisite for a reproducible OSC determination is homogeneous heating of the entire system.
• • In a third step, the determined values are used to determine the resulting OSC for the main catalyst: OSC main cat = OSC system - OSC precat. These values are then compared with values which can be applied freely in a control unit and are valid for the corresponding catalyst system. As long as the determination of the OSC of the total system or of the individual catalysts does not fall below the specified values, no measures are taken with regard to desulfurization. If the OSC determination shows a collapse in the total oxygen storage capacity, a differentiation between the precatalyst and the main catalyst is initially carried out in subsequent steps, analogous to the determination of the oxygen storage capacity of the entire system.
• If a collapse of the oxygen storage capacity below a predefinable value is determined by evaluating the selective OSC of the primary or main catalytic converter, a distinction is first made between a collapse of the OSC at the primary catalytic converter or at the main catalytic converter.

According to the invention, a value of the oxygen storage capacity of the primary catalytic converter OSC_VK and of the main catalytic converter OSC_HK is determined and, depending on this value, selective measures for influencing the temperature of at least one of the following components of the exhaust system catalyst system, precatalyst or main catalytic converter are carried out.

Preferably, the implementation of adjustments of Katalysatorheizmaßahmen immediately after engine start, or measures to increase the exhaust gas temperature levels while driving to maintain the conversion performance of the catalyst system.

The invention also includes an apparatus for carrying out the method according to the invention.

In the following, further advantages and aspects of the invention are also explained independently of their summary in the patent claims with reference to drawings.

Show it:

1 a schematic representation of an internal combustion engine of an exhaust system with a catalyst system,

2 the time profile of selected operating parameters of the internal combustion engine and an associated exhaust system in the implementation of a selective averaging of the OSC according to an embodiment of the method according to the invention,

3 a flowchart for the implementation of selective measures for influencing the temperature of a catalyst system according to the invention,

1 shows a schematic representation of a motor vehicle with an exhaust system. Exhaust gases of a preferably lean-running internal combustion engine 1 be over an exhaust pipe 3 . 3 ' a catalyst system which contains a precatalyst 2 and a series-connected main catalyst 11 comprises, supplied. The cleaned exhaust gases leave the catalyst system through the exhaust pipe 4 , Upstream of the precatalyst 2 between internal combustion engine 1 and precatalyst 2 can be an exhaust gas probe 5 be arranged, which detects a motorized lambda value Lambda_M of unpurified exhaust gas. The exhaust gas probe 5 is not mandatory, since Lambda_M can also be calculated from a model of engine operation. Downstream of the main catalyst is an oxygen sensor 6 arranged, which detects the oxygen content of the purified exhaust gas. The exhaust gas probe 5 or the sensor 6 are preferably lambda probes or other oxygen-sensitive sensors. Two-point lambda probes, broadband lambda probes and oxygen-sensitive NOx sensors with lambda probe function are particularly advantageous.

Signals from the sensor 6 become a controller 7 supplied, which among other things the internal combustion engine 1 depending on the operating conditions and / or a driver request request about an accelerator pedal supplied with fuel. The control unit 7 can signals from other sensors 9 . 10 . 12 . 13 , about engine speed, engine temperature, catalyst temperature, throttle position, load or power demand to the engine capture and a fuel supply 8th the internal combustion engine 1 To dose fuel accordingly. There is also a device 7a to determine a OSC from the waveform of the oxygen sensor 6 intended.

The precatalyst 2 is preferably a 3-way catalyst.

The catalyst 11 preferably has a storage capability for NOx and for oxygen (O2) and stores NOx contained in the exhaust gas during operation of the internal combustion engine 1 in lean operation. In an advantageous embodiment of the invention, the catalyst 11 preferably a NOx storage catalyst.

The combination of upstream in the exhaust stream 3-way catalyst 2 and downstream catalyst 11 proves to be particularly effective in the exhaust gas cleaning of lean-running engines. The precatalyst 2 can serve as a starting catalyst, which quickly reaches the required operating temperature after a cold start. At Lambda_M around a value of 1, this precatalyst works as a conventional 3-way catalyst. In lean operation with lambda> 1, carbon monoxide CO and hydrocarbons CH are converted in this precatalyst. Furthermore, the nitrate formation in a downstream NOx storage catalyst 11 get supported.

By way of another preferred embodiment of the invention, upstream of the primary catalytic converter, two primary catalytic converters are arranged in parallel with a junction point of an exhaust gas line upstream of the main catalytic converter. Another embodiment of the exhaust system includes two primary catalysts and two main catalysts each in an exhaust line with a arranged between the main catalyst and the primary catalyst connecting line between the two exhaust gas lines. Furthermore, it is also possible to arrange two series-arranged in the exhaust pipe precatalyst upstream of the main catalyst.

From the prior art, a method is known in which Lambda_M is increased and decreased, and the change in the signal of the oxygen probe arranged downstream of the catalyst system 6 is evaluated. In this case, the time delay between the exceeding of a predetermined first lambda lambda value upstream of the catalyst 2 and exceeding a predetermined second lean lambda value downstream of the catalyst 11 used to determine the storage capacity for oxygen.

A preferred embodiment of the invention enables a separate determination of the oxygen storage capacity of the components of the catalyst system. A decisive advantage is that according to the invention to one between the catalysts 2 and 11 arranged oxygen sensor can be dispensed with. The embodiment is based on the consideration that a separate determination of the OSC of one component of the catalyst system takes place when the measurable OSC of the other component 0 or with respect to the value of the OSC of the other component is negligibly small. In this case, by measuring the OSC of the entire system, the separate determination of the OSC of the active component of the catalyst system is possible.

It is known that the measurable OSC of a catalyst correlates with its temperature. Only when the light-off temperature, in particular carbon monoxide CO, is exceeded is an OSC determination possible with the method described above. For a NOx storage catalyst, it is known that the OSC is particularly suitable for diagnosing 3-way function and HC conversion of this type of catalyst.

The determination of the OSC is carried out according to the invention from the evaluation of the signal waveform of the oxygen sensor 6 downstream of the main catalyst 11 by means of the device 7a ,

For selectively determining the oxygen storage capability of the pre-catalyst, OSC_VK within a time interval T_VK in which OSC_VK is expected to be greater than a threshold OSC_VKS1 and where the measurable OSC of the main catalyst OSC_HK is less than a threshold OSC_HKS1 is the associated value of the overall OSC Catalyst system OSC_K determined. The threshold values OSC_VKS1 and OSC_HKS1 are catalyst type specific and may further differ due to series variations. The determination of the value of the OSC_K is preferably carried out by means of the evaluation of a time delay of the oxygen concentration downstream of the main catalytic converter. The value OSC_VK is set approximately equal to the value OSC_K in the time interval T_VK.

In 2 shows the time course of some relevant operating parameters of the internal combustion engine for a more detailed description of a preferred embodiment of the method according to the invention. In 2a shows the curve 100 in the course of time a temperature in the precatalyst. The starting point is a relatively lower temperature, as is the case, for example, after a cold start of an internal combustion engine. Some time after the start of the internal combustion engine reaches the temperature 100 the pre-catalyst a light-off temperature, it exceeds and approaches a substantially steady state value. The light-off temperature is usually defined as the temperature of a Catalyst, in which this has reached a conversion rate of 50%. However, in the method described here, the light-off temperature can be deliberately selected to be higher by a predefinable amount in order to ensure that the working range of the catalytic converter, if possible in the entire volume, is reached. In the present case, a light-off temperature for carbon monoxide CO is preferably used. As the precatalyst 2 is arranged closer to the internal combustion engine than the downstream arranged main catalyst 11 , There is a rise in temperature of the main catalyst 11 due to heating by the exhaust gases at a later time and with a lower gradient than the precatalyst 2 , In 2a is the course of the temperature in the main catalyst with 110 designated. It can be seen that the course of the temperature 110 of the main catalyst 11 only with a time delay compared to the temperature 100 of the precatalyst 2 increases.

In the 2 B respectively. 2c are the actual measurable oxygen loadings of pre-catalyst 2 OS_VK or main catalyst 11 OS_HK shown in their time course. The history of OS_VK is as 400 which by OS_HK as 410 designated. It can be seen that OS_VK assumes a significantly higher value at the latest at the time at which the temperature of the precatalyst Temp_VK is greater than the light-off temperature of the precatalyst Temp_LOVK. At this time, the temperature of the main catalyst Temp_H is well below its light-off temperature Temp_LOHK. Accordingly, the actual measurable oxygen loading is OS_HK, as from the course of the curve 410 is apparent, negligible or filled to the maximum value possible for the present main catalyst temperature, but significantly smaller than OSC_HKS1. This different behavior of OS_VK and OS_HK after the cold start is used to separately determine the precursor's OSC.

In the present case, therefore, the time interval T_VK in the OSC_VK is greater than a threshold value OSC_VKS1 and in which the value OSC_HK is less than a threshold value OSC_HKS1, given by the time interval in which Temp_VK is greater than the light-off temperature Temp_LOVK and Temp_HK less than the light-off temperature of the main catalyst is Temp_LOHK. The values of Temp_HK or Temp_VK can be determined by means of the sensors 12 respectively. 13 determined or calculated on the basis of a model. It is understood that the beginning T_VKS or the end T_VKE of the time interval T_VK can basically also be defined by a minimum or maximum time elapsed after a cold start of the internal combustion engine or a minimum or maximum heat input. As long as additional influencing factors such as outside temperature, vehicle speed, exhaust gas temperatures, exhaust gas mass flow or the like are not taken into account in the determination of the minimum or maximum time, a greater inaccuracy is to be expected in such a definition of the time interval T_VK. Preference is therefore given to a determination of T_VKS or T_VKE, in which influencing factors such as the outside temperature, the speed of the vehicle, exhaust gas temperatures, exhaust gas mass flow or the like are taken into account.

In 2a designated 300 the time course of the engine Lambda_M before the pre-catalyst 2 , The value of Lambda_M in 2a shows a mixture jump to determine the OSC_VK. Preferably, the exhaust system is initially charged with initially slightly rich exhaust gas with a lambda value between 0.70 and 0.99. From a point in time T_F, therefore, a rich lambda specification (lambda_fat) is given. Thus, the oxygen storage of the pre-catalyst and downstream arranged at cold start to date filled main catalyst 11 emptied. With a certain delay, a signal jump into the grease on the sensor 6 downstream of the main catalyst 11 observed. The signal jump can also be used to control to determine when subsequently the exhaust system with slightly lean exhaust gas (Lambda_mager) should be applied. Lambda is preferably in a range between 1.005 and 1.5.

As soon as the pre-catalyst 2 and the main catalyst 11 are filled with oxygen, there is a jump of the sensor signal to a lean value S _M 1. A time delay T ₁ between T_M and the time T_S is selected as a measure of the oxygen storage capacity of the precatalyst OSC_VK.

Since in this considered time interval T_VK the temperature of the main catalyst Temp_HK is below the light-off temperature Temp_LOHK, the determined OSC is approximately only on the pre-catalyst 2 attributed, which has a temperature in the considered time interval T_VK, which is above its light-off temperature Temp_LOVK.

It should be emphasized that the in 2 B drawn course 310 the lambda value after the pre-catalyst 2 is not used in this embodiment of the invention, since a corresponding sensor between the pre-catalyst 2 and the main catalyst 11 is not required. A temporal exhaust run length of precatalyst 2 to the oxygen sensor 6 downstream of the main catalyst 11 is incorporated as known per se in a correction of the time delay of T ₁ .

In a further particularly advantageous embodiment, the time T_F is before the time of release of the sensor signal. In particular, the time T_F before the start of heating the sensor 6 lie. In this case, before the actual reaching of the sensor release, the oxygen storage of the primary catalytic converter 2 completely cleared out. Upon reaching an evaluable waveform is then switched to lean conditions at the time T_M. As a result, additional time is gained, in which the main catalyst 11 is still in a warm-up phase and can store little oxygen according to its temperature. It is particularly advantageous if the oxygen storage of the precatalyst 2 emptied immediately before the actual sensor release.

The time T_M may be before a release of the sensor signal, as is done by the mentioned release procedure, if the predetermined release conditions are met. Appropriately, it is required that the sensor signal predetermined criteria of the evaluability such as absolute value, value of fluctuations or noise, jump characteristics or the like is sufficient. In particular, shows the waveform of the oxygen sensor 6 when using a lambda probe or a NOx sensor already shortly after the start of heating a dependency from which a lean or rich value of the exhaust gas or a fat-lean or lean-fat change can be closed. With regard to the change between rich and at least lean exhaust gas, therefore, this signal curve allows signal evaluation even before the actual sensor release. Preferably, a corresponding jump characteristic is evaluated here. It is particularly advantageous if OSC_VK is determined immediately after starting a sensor heating via a mixture jump. Furthermore, the time T_M, or T_F can be predicted on the basis of the self-adjusting time T ₁ .

Within a time interval T_K, in which it is to be expected that OSC_HK is greater than a threshold value OSC_HKS2 and OSC_VK greater than a threshold value OSC_VKS2, the value of the total catalyst system associated with the time interval T_K may be derived from the time course of the oxygen concentration downstream of the main catalytic converter 11 be determined. Conveniently, the time interval T_K is determined by the fact that there the temperature Temp_VK> as Temp_LOVK and the temperature of the main catalyst Temp_HK> Temp_LOHK, since at these temperatures, both the precatalyst 2 as well as the main catalyst 11 warm and active. The oxygen storage capacity of the entire catalyst system is preferably determined in the time interval T_K from a time delay T ₂ after a mixture jump, as in FIG 2a C is shown. The definition of the interval limits T_KS and T_KE can also be carried out in a different way than the temperature measurement, for example by setting minimum and maximum times after a cold start of the internal combustion engine or a minimum or maximum registered amount of heat.

The determination of the oxygen storage capacity OSC_HK is expediently carried out by forming the difference according to the equation OSC_HK = OSC_K-OSC_VK.

For reproducible values in determining the oxygen storage capacity of the entire catalyst system, a homogeneous heating of the entire system is required. Therefore, it is preferable in the presence of highly dynamic processes that lead to different temperature loads of precatalyst 2 and main catalyst 11 lead to a falsification of the results obtained, no evaluation of the OSC made. Highly dynamic processes are, for example, a strong acceleration with a subsequent constant driving or braking after a constant travel. The value of the time delay T ₂ is expediently as well as the time delay T ₁ by a temporal exhaust run length of the precatalyst 2 to the oxygen sensor 6 corrected.

For the diagnosis of the precatalyst 2 or the main catalyst 11 For example, following the determination of OSC_VK or OSC_HK, a comparison may be made with respective thresholds that are selected to be characteristic of proper operation of the catalyst. Depending on the result of the comparison and in combination with additional factors to be determined, measures are taken, such as regeneration or desulfurization of the main catalyst 11 or an error message that is stored in a motor control or displayed by means of a display instrument, if the threshold is exceeded. Otherwise, the diagnosis can be repeated at a later time.

• – Vorkatalysator in Ordnung VK i. O., Hauptkatalysator nicht in Ordnung HK n. i. O.
• – Vorkatalysator nicht in Ordnung VK n. i. O., Hauptkatalysator nicht in Ordnung HK n. i. O.
• – Vorkatalysator nicht in Ordnung VK n. i. O., Hauptkatalysator in Ordnung HK i. O. In Ordnung bezeichnet hier einen ausreichend hohen Wert der OSC.

For a catalyst system consisting of a precatalyst and a main catalyst, there are three possible error states:

• - Pre-catalyst in order VK i. O., main catalyst out of order HK ni O.
• - Pre-catalyst not OK VK ni O., main catalyst not OK HK ni O.
• - Pre-catalyst not OK VK ni O., main catalyst OK HK i. O. Okay here denotes a sufficiently high value of the OSC.

Depending on the determined values of the OSC, the sulfur loading of the Main catalyst S_HK and the NOx storage capacity SF_HK is inventively a flow for the implementation of temperature-influencing measures of the catalyst system, as in 3 is shown proposed.

In the flowchart of the 3 It is assumed that the main catalyst is a NOx storage catalyst. There is a limited NOx storage capacity SF_HK if SF_HK ≦ SW_SF. As an abbreviation for a sufficient NOx storage capacity is in 3 NOx i. O. used. Queries of catalyst states are labeled with a question mark. Steps S1 to S4 are followed by an OSC determination of the precatalyst, catalyst system, main catalyst and a diagnosis of the OSC of the overall system. In step S5, it is checked whether the precatalyst is in order.
VK i. O. - HK ni O.

If the main catalyst is out of order (S6), it is checked in step S7 whether the sulfur content in the NOx storage catalyst is greater than an applicable threshold SW1, since the sulfur loading of a catalyst also leads to a reduction in available OSC. Furthermore, it makes sense to check whether the NOx storage capacity of the NOx storage catalytic converter is already limited. In this case, depending on a threshold SW2 associated with the desulfurization, it is decided to desulfurize the main catalyst (S11), or measures are taken to keep the pollutant conversion of the exhaust system at a sufficiently high level (S13). SW2 can express a dependency of the distance traveled so far or the mass of fuel passed through. A suitable measure to increase the pollutant conversion can, for. As a restriction of lean operation or a substitution of the shift operation by other modes such. B. Homogeneous lean operation or homogeneous stoichiometric operation. This additionally leads to an increase in the temperature level in the entire exhaust system and thus to an increase in the total activity of the primary catalyst and catalyst.

• – gedrosselter Schichtbetrieb,
• – optimiertes Katheizen nach Motorstart,
• – Verzicht auf Schichtbetrieb zugunsten Homogen-Magerbetrieb.

VK n. i. O. – HK n. i. O.As long as the NOx storage capacity is above an applicable threshold, regardless of the current sulfur loading of the catalyst only temperature-increasing measures are taken when the temperature of the NOx storage catalyst is below a threshold SW3, SW4, in which a necessary conversion of pollutants in the exhaust gas is no longer guaranteed (S9, S15). These may be, in particular, measures which, although leading to an increase in the temperature level in the exhaust system, limit the consumption-optimized operation of the engine as little as possible during stratified operation. This can be achieved, for example, through steps such as:

• - throttled shift operation,
• - optimized catalyzing after engine start,
• - Waiver of shift operation in favor of homogeneous lean operation.

VK ni O. - HK ni O.

In this case, analogously to the method described above for an i. O. recognized pre-catalyst initially a determination of sulfur loading (S21) and a NOx storage capacity (S29) performed and appropriate measures to maintain the necessary pollutant conversion or temperature increase made, such as limitation, shift operation, substitution shift operation by homogeneous lean operation or homogeneous stoichiometric operation. In addition, however, basically temperature-increasing measures for the precatalyst S24, S31 are made to ensure maximum conversion of pollutants, especially after engine start. In this case, a heating measure is preferably varied by retarding the ignition angle to within the first 2 ... 120 seconds after "engine start".
VK ni O - HK i. O

In this case, analogously to the method described above for an n. I. O recognized pre-catalyst initially carried out a review of the NOx storage capacity. Should despite i. O. recognized main catalyst to be below the threshold for NOx storage capacity, after checking the sulfur loading either appropriate measures to maintain the necessary pollutant conversion or temperature increase are made, such as limitation shift operation, substitution shift operation by homogeneous lean operation or homogeneous stoichiometric operation or desulfurization of the catalyst requested. In the case of sufficient NOx storage capacity of the main catalyst only temperature-increasing measures for the precatalyst (S20) are made to a maximum conversion of pollutants, especially after engine start, at a time when the temperature of the main catalyst has not yet exceeded the light-off temperature , to ensure. Temperature-increasing measures are useful for both HC_CO and NOx. In this case, a heating measure is additionally varied within the first 2 ... 120 seconds after starting the engine.

According to a particularly advantageous embodiment of the method, a determination of the selective oxygen storage capacity should be made as far as possible in each vehicle trip. If this can not be achieved for various reasons, the values determined during the last OSC measurement are frozen, and the calculation of the cumulative mileage since the last desulphurisation or the fuel mass applied has been determined under super-stoichiometric conditions. As a result, desulphurisation of the catalyst is still ensured, at least for a state of emergency. Furthermore, the corresponding measures for increasing the temperature or pollutant conversion continue to be carried out.

The inventive method is achieved in particular in aged exhaust gas purification systems by selectively determining the oxygen storage capacity and thus the conversion capacity of the individual catalysts that can be addressed specifically to the different requirements of pre-catalyst or main catalyst and thus with maximum emission safety of low-consumption shift operation in a possible large operating range of the engine can be maintained.

LIST OF REFERENCE NUMBERS

1

Internal combustion engine

2

precatalyzer

3

exhaust pipe

3 '

exhaust pipe

4

exhaust pipe

5

lambda probe

6

oxygen sensor

7

control unit

7a

Establishment to identify an OSC

8th

fuel supply

9

sensors

10

throttle

11

main catalyst

12

temperature sensor

13

temperature sensor

100

Temperature in the precatalyst

110

Temperature in the main catalyst

200

Enable sensor heating

300

Exhaust lambda before the pre-catalyst

310

Exhaust lambda after the pre-catalyst

320

Exhaust lambda after the main catalyst

400

Oxygen loading precatalyst

410

Oxygen loading main catalyst

Claims (11)

A catalyst system comprising at least one precatalyst and at least one main catalytic converter arranged downstream of the primary catalytic converter, wherein a value of an oxygen storage capability of the primary catalytic converter OSC_VK, the main catalytic converter OSC_HK and the catalytic converter system OSC_K is determined and in dependence on these values, selective measures for influencing the temperature of at least one of the components of the exhaust gas system primary catalytic converter or main catalytic converter are carried out, characterized in that for the selective determination of the value of the oxygen storage capability of the primary catalytic converter OSC_VK - within a time interval T_VK in which it is to be expected that OSC_VK greater than a threshold OSC_VKS1 and in which the OSC of the main catalyst OSC_HK is less than a threshold t OSC_HKS1 is, - determined from a time course of the oxygen concentration downstream of the main catalyst of the time interval T_VK associated value of the OSC of the catalyst system OSC_K and - OSC_VK is set approximately equal to OSC_K and - within a time interval T_K, in which it is expected that OSC_HK larger as a threshold OSC_HKS2 and OSC_VK is greater than a threshold OSC_VKS2, - from a time course of the oxygen concentration downstream of the main catalyst, the time interval T_K associated value of the OSC_K of the catalyst system is determined and - for selectively determining the OSC of the main catalyst OSC_HK a difference of the values OSC_K and OSC_VK. A method according to claim 1, characterized in that T_VK is determined by the fact that within T_VK the temperature of the pre-catalyst Temp_VK is greater than a light-off temperature of the pre-catalyst Temp_LOVK and the temperature of the main catalyst Temp_HK is less than a light-off temperature of the main catalyst Temp_LOHK is. Method according to at least one of the preceding claims, characterized in that a value of at least one catalyst parameter sulfur loading S_HK or NOx storage capacity SF_HK determined and depending on this value or these values, at least desulfurization or an improvement of NOx conversion of the main catalyst is performed. A method according to claim 3, characterized in that at a sulfur loading S_HK greater than a threshold value SW1 and a limited storage capacity SF_HK smaller than a threshold value SW_SF preferably in dependence on a desulfurization parameter DeS, desulfurization is performed. A method according to claim 4, characterized in that, if DeS is greater than a threshold value SW2, desulfurization is carried out, and if DeS is smaller than a threshold value SW2, at least one measure for increasing NOx conversion is performed. Method according to at least one of claims 3 to 5, characterized in that, if SF_HK <SW_SF and a temperature of the main catalyst Temp_HK is less than a threshold value SW3 or SW4, at least one measure increasing the temperature Temp_K of the entire catalyst system is performed, where SW3 is a value S_HK> SW1 and SW4 is assigned a value S_HK <SW1. Method according to at least one of the preceding claims, characterized in that for determining an OSC the time profile of the oxygen concentration after at least one change of a lambda Lambda_M from a lean Lambda lambda lambda_mager to a rich lambda lambda_fett and / or lambda_fett from a rich Lambda_fett Lambda_mager is evaluated a lean lambda input. A method according to claim 7, characterized in that a time delay T ₁ , T ₂ after the change of the engine lambda value Lambda_M to a change associated with the reaction of the lambda value downstream of the main catalyst ( 11 ) is evaluated. A method according to claim 8, characterized in that the time delay T ₁ , T ₂ is corrected by a temporal Abgaslauflänge from the precatalyst to the oxygen sensor downstream of the main catalyst. Method according to at least one of the preceding claims, characterized in that depending on the values OSC_VK, OSC_HK and / or OSC_K at least one of the following measures is provided throttled shift operation, optimized catalyst heating after an engine start, waiving a shift operation in favor of a homogeneous lean operation or ignition angle shift to late. Apparatus for influencing the temperature of a catalyst system arranged in the exhaust system of a preferably direct-injection layered or lean-burn internal combustion engine, comprising at least one primary catalytic converter and at least one main catalytic converter downstream of the primary catalytic converter, wherein a device is provided, by means of which a value of an oxygen storage capability of the primary catalytic converter OSC_VK, the main catalytic converter OSC_HK and the catalyst system OSC_HK is determined and in dependence on these values selective measures for influencing the temperature of at least one of the components of the exhaust system primary catalytic converter or catalyst are performed, characterized in that by means of a device for selectively determining the value of the oxygen storage capacity of the primary catalytic converter OSC_VK Within a time interval T_VK in which it is to be expected that OSC_V is greater than a threshold value OSC_VKS1 and in which the OSC of the main catalytic converter OSC_HK is less than a threshold value OSC_HKS1, - From a time course of the oxygen concentration downstream of the main catalyst of the time interval T_VK associated value of the OSC of the catalyst system OSC_K can be determined and - OSC_VK is set approximately equal to OSC_K and Within a time interval T_K, in which it is to be expected that OSC_HK is greater than a threshold value OSC_HKS2 and OSC_VK is greater than a threshold value OSC_VKS2, From a time profile of the oxygen concentration downstream of the main catalytic converter, the value of the OSC_K of the catalyst system assigned to the time interval T_K can be determined, and - For the selective determination of the OSC of the main catalyst OSC_HK a difference of the values OSC_K and OSC_VK can take place.

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