DE102007016478A1 - Exhaust gas treatment device operating device for motor vehicle, involves influencing dosing signal with correction signal based on measure for operating duration of exhaust gas treatment device for increasing dosing of reagent unit - Google Patents

Abstract

The method involves requiring a reagent unit for catalytic supported conversion of nitrous oxide of an internal combustion engine (10). Dosing of the reagent unit with a dosing signal is defined based on a downstream nitrous oxide actual value that is measured by a nitrous oxide sensor (18) in an exhaust gas treatment device (14) according to a catalyzer (16) in the exhaust gas treatment device. The dosing signal is influenced with a correction signal based on a measure for operating duration of the exhaust gas treatment device for a purpose of increasing the dosing of the reagent unit. Independent claims are also included for the following: (1) a device for operating an exhaust gas treatment device that is arranged in an exhaust gas region of an internal combustion engine (2) a control device program for executing a method for operating an exhaust gas treatment device (3) a control device-program product with a program codes stored in a machine readable medium for executing a method for operating an exhaust gas treatment device.

Description

State of the art

The The invention is based on a method for operating an exhaust gas treatment device, which for catalytically assisted implementation at least of NOx requires a reagent, and from a device to carry out the method according to the category of independent Claims.

object The present invention also includes a controller program and a controller program product.

In the DE 199 03 439 A1 a method for operating an internal combustion engine is described in the exhaust gas region of an SCR catalyst (Selective Catalytic Reduction) is arranged, which reduces the nitrogen oxides contained in the exhaust gas of the internal combustion engine with a reagent to nitrogen. The dosage of the reagent or a precursor of the reagent is preferably carried out as a function of operating variables of the internal combustion engine, such as the speed and the injected amount of fuel, which can be used at least as a measure of the emitted nitrogen oxides of the internal combustion engine. Furthermore, the dosage is preferably carried out as a function of exhaust gas parameters, such as the exhaust gas temperature and / or the operating temperature of the SCR catalyst. As a reagent, for example, the reducing agent ammonia is provided, which can be obtained from a urea-water solution as a precursor of the reagent. The dosage of the reagent must be carefully determined. Too low a dosage has the consequence that nitrogen oxides can no longer be completely reduced. Too high a dosage leads to a reagent slip, which can lead to an unnecessarily high reagent consumption on the one hand and, on the other hand, depending on the nature of the reagent, to an unpleasant odor nuisance.

In the DE 10 2004 031 624 A1 a method is described for operating an SCR catalytic converter used for cleaning the exhaust gas of an internal combustion engine, in which a control or regulation of the reagent filling level in the SCR catalytic converter is provided to a predetermined memory nominal value. On the one hand, the specification of the desired memory value ensures that in the transient states of the internal combustion engine a sufficient amount of reagent is available for the most complete possible removal of the raw NOx emission of the internal combustion engine and that, on the other hand, reagent slippage is largely avoided. The reagent filling level in the SCR catalytic converter is determined on the basis of a catalyst model which takes into account the NOx mass flow flowing into the SCR catalytic converter, the NOx mass flow leaving the SCR catalytic converter, the catalyst temperature and, if appropriate, the reagent slip. The maximum possible reagent level of the SCR catalyst depends in particular on the operating temperature of the catalyst, which is highest at low operating temperatures and decreases with increasing operating temperature to smaller values. The efficiency of the SCR catalyst depends on the catalytic activity, which is lower at low operating temperatures, goes through a maximum with increasing operating temperature and decreases again with increasing operating temperature.

In the DE 10 2005 042 489 A1 (not prepublished) is described a method for operating an internal combustion engine, in whose exhaust gas region an SCR catalyst is arranged, which is acted upon by a reagent which contributes to the NOx conversion. The NOx concentration downstream of the catalyst is measured with a NOx sensor having cross-sensitivity to the reagent, such as ammonia. The measured NOx concentration is compared with a calculated NOx concentration. Depending on the difference, the dosage of the reagent is intervened. A plausibility check is provided, in which the amount of reagent metered in a predetermined period of time and the amount of reagent reacted in the SCR catalyst and / or the amount of NOx converted are compared with one another. Since due to the cross-sensitivity of the NOx sensor relative to the reagent at a detected difference can not be decided easily whether an overdose or underdose of the reagent is present, the plausibility is provided, which allows a statement about the correction made the dosage.

A similar approach is from the DE 10 2006 041 676 A1 (not prepublished), which also contemplates comparing the difference between a calculated and measured downstream NOx concentration after an SCR catalyst with a differential threshold. If a difference threshold is exceeded, a measure to reduce or completely stop the dosage is taken. Thereafter, the difference is checked for a measure of increase, and if the difference exceeds the measure of the increase, a measure to increase the dosage is taken.

In the DE 10 2005 042 490 A1 (not pre-published) is also a method of operation an internal combustion engine described in the exhaust gas region at least one SCR catalyst is arranged, which is acted upon by a reagent which contributes to the NOx conversion. A plausibility check is provided for the difference determined between a measured measure of the NOx concentration downstream of the catalyst and a calculated measure. It is assumed that the NOx sensor has a cross-sensitivity to the reagent. The determined differences are evaluated in each case. Depending on the evaluation results, the definition of the reagent signal is intervened. With the measures described a long-term adaptation of the reagent signal is achieved.

A similar approach is from the DE 10 2005 042 487 A1 (not prepublished), which also calculates a measure of the NOx downstream of the catalyst and measures it with a NOx sensor transverse to the reagent. The starting point is a regulation of the reagent fill level in the SCR catalytic converter to a desired value. A plausibility check of the sensor signal can be carried out by a slight overdose of the reagent, which is based on a maximum possible reagent level in the catalyst. In this operating state of the catalytic converter, it can be assumed that the NOx sensor detects the reagent slippage. By an intervention in the desired level of the reagent in the catalyst in dependence on the determined difference between the calculated and the measured NOx concentration, a short-term adjustment of the dosage can be achieved, which corresponds to a short-term adaptation.

The Currently available NOx sensors show in terms of Accuracy tolerances on, with the view of getting sharper expectant emissions regulations can affect the measurement result. In particular, it must be assumed that the NOx sensors have a long-term drift that affects the measurement result. Additionally or alternatively to the drift of a NOx sensor may be a drift of a reagent delivery device and / or an aging of a catalyst and / or a change cause the NOx emissions of an internal combustion engine, that a predetermined minimum NOx conversion rate of the exhaust treatment device no longer respected.

Of the Invention is based on the object, a method for operating an exhaust gas treatment device and a device for carrying out indicate the procedure over the entire operating period the exhaust treatment device ensure a predetermined minimum NOx conversion.

The The object is achieved by that in the independent claims specified features each solved.

Disclosure of the invention

According to the invention provided, a dosing signal indicating the dosage of a reagent determines, depending on a measure of the operating life of the exhaust treatment device in terms of Increasing the dosage of the reagent with progressive Operating duration of the exhaust treatment device with a correction signal to influence.

The According to the invention provided measure provides over the entire operating life of the exhaust treatment device the required minimum NOx conversion safe.

A possibly occurring drift, in particular long-term drift of NOx sensor and / or a reagent introduction device and / or a catalyst and / or a change in NOx emissions an internal combustion engine is provided with the invention Measure compensated. The correction signal is set to a value range determined on the one hand always a sufficient dosage of Reagent and on the other hand one overly high reagent slippage due to overdose avoids.

The procedure according to the invention is based on the finding that due to tolerances or drifts of individual components of the exhaust gas treatment device and / or due to changes in the NOx emissions of an internal combustion engine even with an NOx sensor operating within the specified accuracy, insufficient NOx conversion in the exhaust gas treatment device already exists can occur. When commissioning the exhaust treatment device tolerances can be considered in the context of the application. During later operation of the exhaust treatment device such an intervention to compensate for drifts is no longer readily possible. The procedure according to the invention tends to provide for a slight overdosage of the reagent in order to always be able to comply with the prescribed minimum NOx conversion rate. However, an unnecessary overdose of the reagent need not be accepted, since the NOx sensor provides a sensor signal in a possible overdose of the reagent due to a cross-sensitivity to the reagent, with which the overdose as part of a scheme or an adaptation can be counteracted. Short term reagent slip peaks are also registered by a tolerant NOx sensor.

advantageous Further developments and refinements of the invention Approach arise from dependent claims.

A Embodiment provides that the metering signal pre-controlled and is regulated. The feedforward takes place for example on the basis of a calculated reagent level in catalyst. Of the Agent level is conveniently determined by a catalyst model. The catalyst model considered before preferably at least the catalyst temperature and a measure of the NOx mass flow.

According to one Design is provided that on the difference between a Measure of the measured NOx concentration and a NOx setpoint is controlled. The determined difference is preferably used, the calculated reagent level in Catalyst to influence.

A Embodiment provides a short-term adaptation, which in the catalyst model when calculating the reagent level in the catalyst engaging. Alternatively or additionally, preferably one Provided long-term adaptation, which is preferably a manipulated variable corrected, from which the dosing signal is obtained.

A Design provides that as a measure of the Operating time of the NOx sensor the driven kilometers of a motor vehicle be used, in which the internal combustion engine as a drive is used.

The Correction signal is preferably set to a value range of 1.0 set to 1.2, so that the correction signal for a multiplicative linkage is suitable.

The inventive device for implementation of the method initially relates to a control unit, specially prepared for carrying out the method is.

The Control unit preferably contains at least one electrical memory, in which the process steps as a control unit program are stored.

The Control unit program according to the invention provides that all steps of the invention Procedure to be executed when it is in a control unit expires.

The Control unit program product according to the invention with a stored on a machine-readable carrier Program code carries the inventive Procedure when the program runs in a controller.

Further advantageous developments and refinements of the invention The procedure results from further dependent claims. Embodiments of the invention are in the drawing shown and in the following description in more detail explained.

It demonstrate:

1 a technical environment in which a method according to the invention runs and

2 a relationship between a dosing signal and a NOx concentration downstream of a catalyst or a relationship between the dosing signal and a reagent slippage.

1 shows an internal combustion engine 10 in the exhaust area 12 a reagent delivery device 14 and at least one catalyst 16 are ordered. In the exhaust area 12 occur a NOx emission NOx_vK the internal combustion engine 10 and a NOx concentration NOx_nK after the catalyst 16 on.

Downstream of the catalyst 16 is a NOx sensor 18 provided, which is a measure of the NOx concentration NOx_nK as the NOx actual value NOx_Mes a control unit 20 provides. The reagent delivery device 14 , the catalyst 16 as well as the NOx sensor 18 together form an exhaust treatment device 14 . 16 . 18 ,

The control unit 20 provides the reagent dosage 14 a dosing signal s_D available.

The internal combustion engine 10 emits an exhaust gas stream containing the NOx emissions NOx_vK. The NOx components in the exhaust gas should be in the catalyst 16 to be converted to less harmful exhaust gas components. This is the catalyst 16 preferably configured as SCR catalyst, which requires a reagent, such as ammonia, for conversion.

The reagent or a precursor of the reagent, such as a urea-water solution, is passed over the reagent delivery device 14 preferably directly into the exhaust gas area 12 upstream of the catalyst 16 brought in. The dosing quantity is determined by the dosing signal s_D from the control unit 20 depending on at least one measure of the NOx emissions of the Internal combustion engine 10 NOx_vK set.

Such a measure for the NOx emissions NOx_vK, instead of a direct measurement, is preferably based on, for example, at least one operating variable of the internal combustion engine 10 , For example, the speed and / or a fuel signal calculated.

In the exemplary embodiment shown, it is assumed that the dosing signal s_D is set in the context of a feedforward control, which in a control 30 is included. Furthermore, it is assumed that the pilot control or the regulation of the metering signal s_D based on the reagent fill level in the catalyst 16 takes place, which should be set to a reagent level setpoint Fül_Sol. Since the reagent-level actual value is not readily accessible by measurement, the reagent-level actual value should be provided as a calculated reagent-level actual value Fül_Sim.

The calculation is based on a catalyst model 32 , for example, the temperature of the catalyst 16 , the NOx emissions NOx_vK and the dosing signal s_D are provided. The catalyst model 32 and the calculation of the reagent level in the catalyst 16 can be taken from the above-mentioned prior art in detail.

The pilot control in the control 30 Defines a manipulated variable s as a function of the difference between the reagent fill level setpoint Fül_Sol and the calculated reagent fill level actual value Fül_Sim. The manipulated variable s becomes after passing through a signal correction 34 to the dosing signal s_D. Due to the fact that there is no actual feedback of a measured actual value - the reagent level actual value - a pilot control is assumed instead of a regulation to the reagent level setpoint Fül_Sol.

The precontrol is superimposed on a control which is able to compensate for component-related tolerances and drifts. In the embodiment shown, it is assumed that the control is based on the downstream of the catalyst 16 occurring NOx concentration NOx_nK, which is the NOx sensor 18 the control unit 20 as NOx actual value NOx_Mes available, the actual NOx value NOx_Mes at least a measure of the downstream of the catalyst 16 occurring NOx concentration NOx_nK reflects.

In the exemplary embodiment, it is assumed that the control is based on a change in the reagent fill level in the catalyst 16 based. Furthermore, it is assumed that the control takes into account the difference d, which occurs between the actual NOx value NOx_Mes and a NOx target value NOx_Sol.

One embodiment provides a short-term adaptation which, depending on, for example, the difference d, provides a short-time adaptation signal Adapt_K_ti. The short-time adaptation signal Adapt_K_ti is detected in a short-time adaptation signal determination 38 determined as a function of the difference d and as a short-time adaptation signal Adapt_K_ti example, the catalyst model 32 made available, so that by changing the calculated reagent-level actual value Fül_Sim can be used in the short term in the provision of the dosing signal s_D. This can be responded to in the short term both to an underdose and an overdose.

A further embodiment, which may be provided alternatively or additionally, provides for a long-term adaptation, which likewise provides a long-term adaption signal Adapt_L_ti as a function of the difference d, for example. The long-term adaptation signal Adapt_L_ti is determined in a long-term adaption signal determination 40 determined as a function of the difference d and as a long-term adaptation signal Adapt_L_ti, for example, in the signal correction 34 used to correct the manipulated variable s. The signal correction 34 then provides the dosing signal s_D.

It is assumed that the NOx sensor 18 has a cross-sensitivity to the reagent. This means that initially it can not be distinguished between too low a dosage of the reagent, with the result that the undesirable NOx concentration NOx_nK increases, and too high a reagent dosage with the consequence that a reagent slippage NH3 occurs.

In 2 qualitatively the relationship between the dosing signal s_D and the NOx concentration NOx_nK on the one hand and between the dosing signal s_D and the reagent slippage NH3 on the other hand is shown. The actual NOx value NOx_Mes is passed through during the transition from too low to too high a dosage.

The metering of the reagent is preferably carried out with the metering signal s_D such that at the same time the lowest possible NOx concentration NOx_nK and a minimal possible reagent slip NH3 occurs. In 2 is a Dosiersignal start value s_D_St registered, which is at the commissioning of the NOx sensor 18 he should give, when the reagent level has the reagent level setpoint Fül_Sol and at the same time the NOx actual value NOx_Mes and the NOx target value NOx_Sol match.

In the course of operation of the internal combustion engine 10 or the exhaust gas treatment device 14 . 16 . 18 can not be ruled out that the NOx sensor 18 is subject to a signal drift, which has the consequence that the measured actual NOx value NOx_Mes no longer coincides with the actual NOx concentration NOx_nK. Furthermore, with a drift of the other components 14 . 16 the exhaust treatment device 14 . 16 . 18 be counted. The reagent delivery device 14 , which is composed of numerous mechanical components, may be subject to a drift, which causes the metered amount of reagent deviates from the predetermined amount of dosing signal s_D. Furthermore, the catalyst is subject 16 aging, which means that, for example, with increasing age more reagents are needed. Furthermore, it must be expected that the NOx emissions of the internal combustion engine 10 are subjected to a long-term drift.

In order to ensure compliance with the lowest possible NOx concentration NOx_nK during the entire operating time of the exhaust gas treatment device 14 . 16 . 18 can be ensured is provided, the dosage of the reagent with increasing operating time of the exhaust treatment device 14 . 16 . 18 to increase. The service life of the exhaust treatment device 14 . 16 . 18 generally corresponds to the operating time of the entire system, including the service life of the internal combustion engine 10 , In the following, reference will only be made to the service life of the exhaust treatment device 14 . 16 . 18 , The dosing signal s_D becomes dependent on a measure of the operating time of the exhaust gas treatment device 14 . 16 . 18 influenced in the sense of increasing the dosage of the reagent with a correction signal k_Sol.

The correction signal k_Sol provides a correction signal detection 42 depending on the operating time of the exhaust treatment device 14 . 16 . 18 ready. When commissioning the exhaust treatment device 14 . 16 . 18 For example, the correction signal k_Sol is preferably set equal to 1 to a correction signal start value K_St. In this case, the dosing signal start value s_D_St will be set. The changes in the correction signal k_Sol occur, for example, as a function of the operating hours h of the exhaust gas treatment device 14 . 16 . 18 , Unless the internal combustion engine 10 is provided for driving a motor vehicle, can be used as a measure of the service life of the exhaust treatment device 14 . 16 . 18 in addition to the operating hours of the internal combustion engine 10 in particular, the distance traveled by the motor vehicle km are used.

The consideration of the correction signal k_Sol takes place in a setpoint correction 44 , which links the NOx target value NOx_Sol with the correction signal k_Sol and provides a corrected target value NOx_k_Sol. The linking is preferably carried out multiplicatively such that at the beginning of the operating period of the exhaust gas treatment device 14 . 16 . 18 no correction and with increasing operating time of the exhaust treatment device 14 . 16 . 18 an increasing correction takes place, which tends to increase the dosage of the reagent.

The corrected NOx target NOx_k_Sol becomes a summer 46 provided, which determines the difference between the corrected NOx target value NOx_k_Sol and the NOx actual value NOx_Mes and provides the difference d. The difference d intervenes in the regulation 30 or in the pilot control by, for example, an increase in the reagent level setpoint Fül_Sol and affects the manipulated variable s. An increase in the corrected NOx target value NOx_k_Sol leads to an increase in the manipulated variable s and thus to an increase in the metering signal s_D. The increase in the dosage of the reagent is in 2 with the arrow 50 symbolizes registered.

The influencing of the dosing signal s_D in the sense of increasing the dosage with increasing operating time of the exhaust gas treatment device 14 . 16 . 18 First, make sure that at a drift of the NOx sensor 18 , in which the measured NOx actual value NOx_Mes is less than the actual NOx concentration NOx_nK, nevertheless sufficient dosing of the reagent always takes place in order to be able to maintain a predetermined minimum NOx conversion rate. If a drift of the NOx sensor 18 has occurred, in which the measured actual NOx value NOx_Mes is higher than the actual NOx concentration NOx_nK, with increasing operating time of the exhaust gas treatment device 14 . 16 . 18 Nevertheless, no increased reagent NH3 be accepted because of the cross-sensitivity of the NOx sensor 18 Overdose can be compensated for the reagent.

However, the measure provided according to the invention also makes it possible to maintain a predetermined minimum NOx conversion rate, although the NOx sensor 18 within the allowable tolerance range but drifts within the remaining components 14 . 16 the exhaust treatment device 14 . 16 . 18 and or a change of the internal combustion engine 10 emitted NOx emissions occurs. Even in this case would be without the inventively provided measure even with a properly operating NOx sensor 18 not excluded that the specified minimum NOx conversion rate is not met.

Overall, with the inventively provided measure - a tendency with the operating time of the exhaust treatment device 14 . 16 . 18 Increasing overdose of the reagent - compensated for a weakness of the entire system in terms of underdosing of the reagent without due to the robustness of the entire system overdose of the reagent an unnecessary overdose must be accepted, because even a tolerant NOx sensor 18 registers short term reagent breakthrough peaks due to its cross-sensitivity to the reagents.

The range of values in which the correction signal k_Sol should lie can be determined on the basis of an estimate of the expected drifts. The range of values is, for example, between 1 and 1.2. The value 1 corresponds to the value at start-up of the exhaust treatment device 14 . 16 . 18 and the value of 1.2 the value of the highest expected service life of the exhaust treatment device 14 . 16 . 18 , It is assumed that the value 1 does not affect the NOx target value NOx_Sol and the value 1.2 increases the NOx target value NOx_Sol to the corrected NOx target value NOx_k_Sol, whereby the metering of the reagent increases with increasing operating time h, km of the exhaust gas treatment device 14 . 16 . 18 or the operating time of the entire system including the internal combustion engine 10 increases.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19903439 A1 [0003]
• DE 102004031624 A1 [0004]
• - DE 102005042489 A1 [0005]
• DE 102006041676 A1 [0006]
• - DE 10205042490 A1 [0007]
• DE 102005042487 A1 [0008]

Claims (15)

Method for operating an exhaust gas area ( 12 ) an internal combustion engine ( 10 ) arranged exhaust gas purification device ( 14 . 16 . 18 ), for the catalytically assisted conversion of the NOx emissions (NOx_vK) of the internal combustion engine ( 10 ) requires a reagent whose metering with a metering signal (s_D) in dependence on a downstream of a in the exhaust gas purification device ( 14 . 16 . 18 ) contained catalyst ( 16 ) of a in the exhaust gas purification device ( 14 . 16 . 18 ) contained NOx sensor ( 18 ) measured actual NOx value (NOx_Mes), characterized in that the dosing signal (s_D) as a function of a measure (h, km) for the operating time of the exhaust gas treatment device ( 14 . 16 . 18 ) is influenced in the sense of increasing the dosage of the reagent with a correction signal (k_Sol). Method according to claim 1, characterized in that that the dosing signal (s_D) is precontrolled and regulated. A method according to claim 2, characterized in that the dosing signal (s_D) based on a calculated reagent level actual value (Fül_Sim) in the catalyst ( 16 ) is piloted. A method according to claim 3, characterized in that the calculated reagent-level actual value (Fül_Sim) based on a catalyst model ( 32 ), which at least the catalyst temperature (te_Kat) and a measure of the NOx emissions (NOx_vK) of the internal combustion engine ( 10 ) considered. Method according to claim 2, characterized in that that on the difference (d) between the actual NOx value (NOx_Mes) and a NOx setpoint (NOx_Sol) is regulated. Method according to claim 5, characterized in that that difference (d) is the calculated reagent level feedback (Fül_Sim) influences. A method according to claim 2 or 5, characterized in that a short-term adaptation is provided, which in the catalyst model ( 32 ) in the calculation of the reagent-level actual value (Fül_Sim) in the catalyst ( 16 ) intervenes with a short-time adaptation signal (Adapt_K_ti). Method according to Claim 2 or 5, characterized that a long-term adaptation is provided, which is a manipulated variable (s) to the dosing signal (s_D) with a long-term adaptation signal (Adapt_L_ti) corrected. Method according to claim 5, characterized in that that the correction signal (k_Sol) corrects the NOx setpoint (NOx_Sol). Method according to claim 3, characterized that the correction signal (k_Sol) a reagent level setpoint (Ful_Sol) corrected. A method according to claim 1, characterized in that as a measure (h, km) for the operating time of the exhaust gas treatment device ( 14 . 16 . 18 ) the traveled distance (km) of a motor vehicle is used, in which the internal combustion engine ( 10 ) is used as a drive. Method according to claim 1, characterized in that that the correction signal (k_Sol) starts with the value 1 and until increases to the value of 1.2. Device for operating a in an exhaust area ( 12 ) an internal combustion engine ( 10 ) arranged exhaust treatment device ( 14 . 16 . 18 ), for the catalytically assisted conversion of the NOx emissions (NOx_vK) of the internal combustion engine ( 10 ) requires a reagent whose metering with a metering signal (s_D) in response to a downstream of a in the exhaust gas treatment device ( 14 . 16 . 18 ) contained catalyst ( 16 ) of a in the exhaust treatment device ( 14 . 16 . 18 ) contained NOx sensor ( 18 ) is determined, characterized in that at least one for carrying out the method according to one of claims 1 to 12 specially prepared control unit ( 20 ) is provided. Control unit program that performs all the steps of a method according to one of claims 1 to 12, when the program is stored in a control unit ( 20 ) expires. A control program product having a program code stored on a machine-readable carrier for carrying out the method according to one of claims 1 to 12, when the program is stored in a control device ( 20 ) is performed.