DE102006041676A1 - Reagent i.e. ammonia, and/or reagent precursor i.e. aqueous urea solution, dosing method for internal combustion engine, involves performing measure for increasing dosage, when difference exceeds quantity for raising dosage - Google Patents

Abstract

The method involves determining a difference between determined and measured nitrogen oxide concentrations downstream to a catalytic converter (16) e.g. selective catalytic reduction (SCR) catalytic converter. The difference between the concentrations is compared with a difference-threshold value. A measure of lowering or preventing dosage is performed during exceeding of the difference-threshold value. The difference is inspected on a quantity for raising the dosage. A measure for increasing the dosage is performed, when the difference exceeds the quantity for raising the dosage. Independent claims are also included for the following: (1) a device for dosing a reagent and/or reagent precursor into an exhaust gas region of an internal combustion engine (2) a computer program comprising instructions to perform a method for dosing a reagent and/or reagent precursor into an exhaust gas region of an internal combustion engine (3) a computer program product with a program code stored on a machine readable medium for performing a method for dosing a reagent and/or reagent precursor into an exhaust gas region of an internal combustion engine.

Description

State of the art

The The invention is based on a method for dosing a reagent in the exhaust region of an internal combustion engine and by a device to carry out the method according to the preamble of the independent claims.

object The present invention also relates to a computer program a computer 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 reagent precursor is preferably carried out as a function of operating parameters of the internal combustion engine, such as the speed and the injected fuel quantity. Furthermore, the dosage is preferably carried out as a function of at least one exhaust gas characteristic, such as the exhaust gas temperature or the operating temperature of the SCR catalyst. As a reagent, the reducing agent ammonia is provided, which is obtained from a reagent precursor (urea-water solution).

The Dosing of the reagent or the reagent precursor in the exhaust area must be carefully be determined. Too low a dosage has the consequence that the nitrogen oxides in the SCR catalyst are no longer completely reduced can be. Too high a dosage leads to a reagent slip, on the one hand to an unnecessarily high Reagent consumption and on the other hand, depending on the nature of the reagent, can lead to an unpleasant odor nuisance.

In the DE 10 2005 042 487 A1 (not prepublished) is a method for dosing a reagent or a reagent precursor in the exhaust region of an internal combustion engine is described, which also contains an SCR catalyst. The reagent level in the SCR catalyst is controlled or regulated to a predetermined desired reagent level that is set at least to a maximum value that corresponds to a full reagent-filled SCR catalyst. When sensor signal changes occur, it can always be assumed that the dosage is too high. The SCR catalyst is always operated at the maximum possible efficiency at which the highest possible NOx conversion occurs.

In the DE 10 2005 042 489 A1 (not prepublished) a method for operating an internal combustion engine is 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 in the SCR catalyst. A measure of the NOx concentration downstream of the SCR catalyst is both calculated and measured with a NOx sensor having cross-sensitivity to the reagent. A difference is determined between the calculated measure and the measured measure of the downstream NOx concentration after the SCR catalyst, which is taken into account in the determination of a metering signal which determines the metering of the reagent or of the reagent precursor. A plausibility check is provided in which the amount of reagent or precursor reagent metered in a predetermined period of time and the amount of reagent reacted in the SCR catalyst and / or the amount of NO x converted are compared with one another. In case of a deviation, a correction signal is provided which influences the dosing signal.

A further education in the DE 10 2005 042 489 A1 described procedure is in the DE 10 2005 042 490 A1 (not pre-published), which provides that the differences are determined and stored in chronological order. The dosing signal is determined as a function of a predetermined number and / or predetermined order of evaluation results of the differences. As a result, a long-term adaptation of the metering signal is achieved.

The described methods aim at a long-term adaptation of the dosing signal from. The long-term adaptation allows in the case of a feedforward control, a correction of the metering signal. simultaneously The long-term adaptation can be used to diagnose the dosing signal become.

Of the Invention is based on the object, a method for dosing a reagent or a reagent precursor in the exhaust gas region specify an internal combustion engine, which is a fast adaptation especially with an underdosing enabled.

The The object is achieved by those specified in the independent claims Features each solved.

Disclosure of the invention

The procedure according to the invention The features of the independent method claim has the advantage of a rapid reaction in particular to a present underdose of the reagent or under dosage of the reagent precursor.

advantageous Further developments and refinements of the procedure according to the invention arise from dependent Speeches.

A Embodiment provides that the reagent level provided in the catalyst as calculated reagent level becomes. This becomes a comparatively difficult immediate acquisition the reagent level avoided in the catalyst.

A Embodiment provides that the measure for lowering / suppression or increase the Dosage by an increase or lowering the calculated reagent fill level in the catalyst becomes. As a result, an already existing arrangement continues to be used and with the procedure according to the invention added, this means, be programmed. An influence on the dosage is with a Correction signal possible that For example, a pre-control of the dosage engages and there a metering valve characteristic shifts.

in principle can be an intervention in the dosage in any operating condition, in particular also a transient Operating state. Preferably, however, it is provided that an intervention in the dosage only in stationary or quasi-stationary operating states of Internal combustion engine is made. This will be a mistake Intervention avoided. The intervention can be done by a Evaluation of the difference only in stationary or quasi-stationary operating states of the Internal combustion engine performed or one already performed Evaluation is forwarded and recycled.

To the Recognition of a stationary or at least quasi-stationary Operating state of the internal combustion engine can be a measure of the load of the internal combustion engine and / or a fuel signal and / or the rotational speed of the internal combustion engine and / or the engine's outgoing NOx concentration upstream the catalyst and / or a travel speed of a motor vehicle, which contains the internal combustion engine as drive, are used.

A advantageous development provides for an adaptation in which For example, the number of measures to increase the Reagent or reagent precursor dosage is detected and after crossing a predetermined number of transgressions the calculation of the reagent level in the catalyst with a correction signal is influenced such that the calculated Reagent filling level as part of the adaptation in the longer term is reduced.

The inventive device to carry out of the procedure concerns first a control unit, that to carry out the process is specially prepared.

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

The sees computer program according to the invention that all steps of the method according to the invention are carried out, when it runs on a computer.

The Computer program product according to the invention with a program code stored on a machine-readable carrier performs the method according to the invention off if the program is run on a computer or in the controller.

Further advantageous developments and refinements of the procedure according to the invention arise from the description. An embodiment of the invention is shown in the drawing and in the following description explained in more detail.

It demonstrate:

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

2 a reagent level and a difference over time.

1 shows an internal combustion engine 10 , in their intake area 11 an air sensor 12 and in their exhaust area 13 , a reagent delivery device 14 with a metering valve 15 , a catalyst 16 and a NOx sensor 17 are arranged. In the exhaust area 13 an exhaust gas mass flow ms_Abg occurs. Upstream of the catalyst 16 occurs an upstream NOx concentration NOx_vK and downstream of the catalyst 16 a downstream NOx concentration NOx_nK.

The air sensor 12 represents a control unit 20 an air signal ms_L, the internal combustion engine 10 a speed n and the NOx sensor 17 one downstream to the catalyst 16 measured downstream NOx concentration NOx_nK_Mes available. The control unit 20 represents a fuel metering device 21 a fuel signal m_K and the metering valve 15 , which doses a reagent p under pressure p or reagent precursor under pressure p, a dosing signal s_DV available.

The control unit 20 preferably contains a size determination 25 which the air signal ms_L, the rotational speed n and a measure Md for the load of the internal combustion engine 10 which provides a calculated upstream NOx concentration NOx_vK_Sim, a calculated exhaust mass flow ms_Abg_Sim and a fuel signal m_K.

The control unit 20 further preferably contains a catalyst model 30 to which the catalyst temperature te_Kat, the upstream NOx concentration NOx_vK, the exhaust gas mass flow ms_Abg and the metered reagent amount or reagent precursor amount m_Rea are provided and which have a calculated reagent filling level NH3_FS_Sim, a conversion efficiency eta_NOx and a calculated downstream NOx concentration NOx_nK_Sim provides. The calculated reagent level NH3_FS_Sim is fed back and stands for the catalyst model 30 available as additional input.

The detected downstream NOx concentration NOx_nK_Sim and the measured downstream NOx concentration NOx_nK_Mes become a difference determination 40 which provides the difference d_Sens between the two signals.

The control unit 20 also preferably includes a difference score 50 to which the difference d_Sens is made available and which provides a first and second difference evaluation signal d_Sens_BW1, d_Sens_BW2.

The control unit 20 preferably further contains a reagent level correction device 60 in which the difference d_Sens, an enable signal FG, a difference threshold d_Sens_Lim, the first difference evaluation signal d_Sens_BW1 and the second difference evaluation signal d_Sens_BW2 are provided and which the reagent level increase signal + NH3_FS and the reagent level lowering signal -NH3_FS.

The reagent level lowering signal -NH3_FS becomes an adaptation arrangement 70 provided which provides a correction signal Korr.

The enable signal FG provides an enable signal detection 80 ready, which the measure Md for the load of the internal combustion engine 10 or the fuel signal m_K, the rotational speed n and the upstream NOx concentration NOx_vK be provided.

2a shows the reagent level NH3_FS in the catalyst 16 , Entered are a reagent level set point NH3_FS_Sol, the calculated reagent level NH3_FS_Sim, an effective reagent level NH3_FS_eff, the reagent level increase signal + NH3_FS and the reagent level decrease signal -NH3_FS.

2 B shows the difference d_Sens as a function of the time ti. Entered are 6 different times ti1-ti6. For the second and fifth times ti2, ti5, the difference d_Sens exceeds the difference threshold d_Sens_Lim.

The arrangement works as follows:
When operating the internal combustion engine 10 Depending on the operating state, a more or less high upstream NOx concentration NOx_vK arises upstream of the catalytic converter 16 which in the catalyst 16 to be converted. In the embodiment shown, the catalyst 16 realized as an SCR catalyst, which requires a reagent for NOx conversion. As a reagent, for example, ammonia is provided which acts as a reducing agent. The reagent can go directly into the exhaust area 13 be dosed. Alternatively it can be provided, a reagent precursor in the exhaust gas region 13 to dose. As a reagent precursor for the reagent ammonia is a urea-water solution in question.

The reagent or reagent precursor will be loaded with the reagent delivery device 14 directly into the exhaust area 13 brought in. In the embodiment shown, it is assumed that a urea-water solution is introduced as the reagent, which is at a predetermined operating pressure p and from the metering valve 15 is metered in dependence on the dosing signal s_DV. The dosing signal s_DV is pre-controlled in a feedforward control not shown in more detail with reference to a metering valve characteristic.

The further determination of the dosing signal s_DV takes place in the embodiment shown by a regulation of the reagent filling level NH3_FS in the catalytic converter 16 , Details of this can the above-mentioned prior art DE 10 2005 042 487 A1 are taken to the full content. There is regulated to a maximum possible reagent level NH3_FS. In the present case is of it assumed that is controlled to a reagent level setpoint NH3_FS_Sol, which allows a margin up and down.

To ensure proper metering of the reagent or reagent precursor, the downstream of the catalyst is downstream 16 arranged NOx sensor 17 vorgese hen, which detects the downstream NOx concentration NOx_nK and the control unit 20 as measured downstream NOx concentration provides NOx_nK_Mes.

A plausibility check of the dosing may be performed based on a comparison of the measured downstream NOx concentration NOx_nK_Mes with the determined downstream NOx concentration NOx_nK_Sim. A corresponding procedure is in the aforementioned prior art according to DE 10 2005 042 489 A1 described in full.

In principle, that could be used in difference determination 40 determined difference d_Sens be used directly to influence the dosing signal s_DV. In the exemplary embodiment shown-as in the related prior art-the dosing signal s_DV is indirectly influenced by either increasing the calculated reagent level NH3_FS_Sim with the reagent level increase signal + NH3_FS or by lowering it with the reagent level-lowering signal.

To determine the calculated reagent level NH3_FS_Sim in the catalyst model 30 For example, the catalyst temperature te_Kat and / or the upstream NOx concentration NOx_vK and / or the exhaust gas mass flow ms_Abg and / or the metered reagent amount or reagent precursor amount m_Rea are used.

The catalyst model 30 provides in addition to the calculated, fed back to the input reagent level NH3_FS_Sim the determined downstream NOx concentration NOx_nK_Sim ready. The catalyst model is determined based on the upstream NOx concentration NOx_vK and the calculated conversion efficiency eta_NOx 30 the downstream NOx concentration NOx_nk_Sim.

For example, the upstream NOx concentration NOx_vK could be measured with another NOx sensor upstream of the catalyst 16 is to be arranged. In the illustrated embodiment, the upstream NOx concentration becomes NOx_vK from the size calculation 25 for example, from the air signal 305 and the dimension Md for the load of the internal combustion engine 10 calculated. Optionally, the speed n of the internal combustion engine 10 considered.

The dimension Md for the load of the internal combustion engine 10 For example, at least approximately corresponds to the position of an accelerator pedal not shown in detail, if the internal combustion engine 10 is provided in a drive of a motor vehicle. From the described quantities, the size determination 25 continue to provide the calculated exhaust mass flow ms_Abg_Sim and the fuel signal m_K.

Both in the size determination 25 as well as the catalyst model 30 In addition to the mentioned input variables, further input variables can be taken into account.

In 2a is the reagent-level setpoint NH3_FS_Sol registered, which should be constant in the embodiment shown and neither the minimum nor the maximum possible reagent level NH3_FS should correspond, so that the calculated reagent level NH3_FS_Sim, if possible with the not readily measurable effective reagent Level NH3_FS_eff should match, increase or decrease.

In the reagent level correction device 60 the difference d_Sens is compared with the difference threshold d_Sens_Lim, which in 2 B is registered. Between the first and second times ti1, ti2, it is assumed that the calculated reagent level NH3_FS_Sim coincides with the specified reagent level setpoint NH3_FS_Sol without major deviations. The difference d_Sens is below the difference threshold d_Sens_Lim.

At the second time ti2, the difference d_Sens exceeds the difference threshold d_Sens_Lim. Thereafter, the reagent level increase signal + NH3_FS is immediately provided. As a result, the dosing signal s_DV is immediately reduced or completely switched off. At least from the second time ti2 evaluates the difference score 50 the difference d_Sens and provides either the first or the second difference evaluation signal d_Sens_BW1, d_Sens_BW2 depending on the result.

The difference rating 50 Checks a measure of the increase in the difference d_Sens. For example, a determination of the differential quotient could be provided at predetermined times. Particularly suitable is a determination of the difference quotient on the basis of a predetermined time, which may be, for example, in the range of seconds, for example four seconds. In the exemplary embodiment shown, it is assumed that the determination of the difference quotient takes place between the second and third times ti2, ti3.

If the default rate of increase is not reached, the difference score represents 50 the first difference evaluation signal d_Sens_BW1 ready. If, on the other hand, the predefined measure for the increase has been reached or overshadowed, the difference assessment represents 50 the second difference evaluation signal d_Sens_BW2 ready.

In the exemplary embodiment shown, it is assumed that the difference d_Sens increases only slightly after the second time ti2 and then decreases again, so that the predefined measure for the increase is not reached and the difference evaluation 50 provides the first difference evaluation signal d_Sens_BW1. Based on the assumptions described, it can be assumed that the effective, not readily detectable effective reagent level NH3_FS_eff increases between the first and second times ti1, ti2, so that the calculated reagent level NH3_FS_Sim is increasingly dependent on the effective reagent level until the second time ti2. Level NH3_FS_eff deviates.

To the second time ti2, the correction takes place at which the calculated Reagent filling level NH3_FS_Sim again at least approximately coincide with the effective reagent level NH3_FS_eff should.

Due to the described conditions it must be assumed that the increase of the NOx sensor 17 measured actual downstream NOx concentration NOx_nK_Mes in reality was not present and that the increase due to a cross-sensitivity of the NOx sensor 17 relative to the reagent, due to the increasing overdose as slip downstream to the catalyst 16 occured.

The Dosage break or at least reduce the dosage in the illustrated embodiment at least approximately be finished at the fourth time ti4. Thereafter, the dosage is again added.

Between the fourth and fifth If ti4, ti5, an increase in the difference d_Sens should again occur. wherein the difference d_Sens the difference threshold d_Sens_Lim to the fifth Time ti5 reached or exceeded. At the fifth time ti5, therefore, the reagent level increase signal + NH3_FS is immediately provided, that to an interruption or at least to a reduction the dosage leads.

Due to the evaluation of the difference d_Sens between the fifth and sixth time ti5, ti6 represents the difference score 50 at the latest at the sixth time ti6 that the difference d_Sens has exceeded the measure for the change in the difference d_Sens and then provides the second difference evaluation signal d_Sens_BW2, which the reagent-level correction device 60 at the sixth time ti6 for providing the reagent level lowering signal -NH3_FS. As a result, at the sixth point in time ti6, the metering is not only continued, but due to the lowering of the reagent-level-lowering signal -NH3_FS far below the reagent-level-target value NH3_FS_Sol, correspondingly greatly increased.

Based on the assumptions described, it can be assumed that the effective reagent filling level NH3_FS_eff drops to values below the reagent level setpoint NH3_FS_Sol between the fourth and fifth times ti4, ti5. The increase in the difference d_Sens between the fourth and fifth times ti4, ti5 is actually based on an increase in the downstream NOx concentration NOx_nk, which is the NOx sensor 17 with the measured downstream NOx concentration NOx_nK_Mes correctly reflected. The sharp increase in the difference d_Sens between the fifth and sixth times ti5, ti6 is an indication that there was actually an underdosing of the reagent or the reagent precursor, which occurs shortly after the fifth time ti5, in the illustrated embodiment, at the sixth time ti6 , is corrected upwards as soon as possible.

In the dosage of the reagent or the reagent precursor is intervened expediently when the internal combustion engine 10 is in a stationary or at least quasi-stationary operating state, in which it can be assumed that the upstream NOx concentration NOx_vK does not change or changes only slightly. This is not a requirement. In principle, an intervention is readily in transient operating conditions of the internal combustion engine 10 possible.

In the embodiment shown, the intervention in the dosage is only released when the release signal FG is present, which is the release arrangement 80 provides. The procedure generally provides that the difference d_Sens in the reagent level correction device 60 only under certain conditions or the be passed on or suppressed.

The release arrangement 80 For example, the upstream NOx concentration NOx_vK is provided, for example, from the size determination 25 is provided as the calculated upstream NOx concentration NOx_vK_Sim. The release signal FG is provided only when the upstream NOx concentration NOx_vK, NOx_vK_Sim does not exceed a predetermined maximum allowable change.

Alternatively or additionally, the release arrangement 80 the release signal FG in response to a predetermined maximum allowable change in the speed n, that of the release arrangement 80 is available.

Furthermore, alternatively or additionally, the release arrangement 80 the release signal FG in response to a predetermined maximum allowable change in the dimension Md for the load of the internal combustion engine 10 or the fuel signal m_K, that of the release arrangement 80 also be available.

The adaptation arrangement 70 , which is realized for example as a counter, determines the number of occurred reagent-level lowering signals - If, for example, a predetermined threshold for the number is exceeded, the adaptation arrangement provides 70 the correction signal Korr ready, which is used in particular in the feedforward not shown in detail of the dosing signal s_DV, for example, to move the metering valve characteristic. The adaptation counteracts a possibly more frequent underdosing of the reagent or of the reagent precursor. Details of the adaptation can according to the above-mentioned prior art according to DE 10 2005 042 490 A1 are taken, to which also incorporated by reference.

Claims (12)

Method for dosing a reagent / reagent precursor into the exhaust area ( 13 ) an internal combustion engine ( 10 ), which is used for the catalytic conversion of NOx in a catalyst ( 16 ), in which the difference (d_Sens) between a determined and measured NOx concentration (NOx_nK_Sim, NOx_nK_Mes) downstream of the catalytic converter ( 16 ), characterized in that the difference (d_Sens) is compared with a difference threshold value (d_Sens_Lim) that, when the difference threshold value (d_Sens_Lim) is exceeded, a measure for lowering or suppressing the dosage is taken so that the difference ( d_Sens) is then checked for a measure of a rise and that if the difference (d_Sens) exceeds the measure of the rise, a measure to increase the dosage is taken. A method according to claim 1, characterized in that the reagent level (NH3_FS) in the catalyst ( 16 ) is provided as calculated reagent level (NH3_FS_Sim). A method according to claim 2, characterized in that the measure for lowering / inhibiting or increasing the dosage by increasing or decreasing the calculated reagent filling level (NH3_FS_Sim) in the catalyst ( 16 ) is taken. A method according to claim 1, characterized in that an intervention in the dosage in stationary or quasi-stationary operating states of the internal combustion engine ( 10 ). A method according to claim 4, characterized in that an evaluation of the difference (d_Sens) in stationary or quasi-stationary operating states of the internal combustion engine ( 10 ) is carried out or taken into account. A method according to claim 4 or 5, characterized in that for detecting a stationary or quasi-stationary operating state of the internal combustion engine ( 10 ) a measure (Md) of the load of the internal combustion engine ( 10 ) or a fuel signal (m_K) are used. A method according to claim 4 or 5, characterized in that for detecting a stationary or quasi-stationary operating state of the internal combustion engine ( 10 ) the speed (n) of the internal combustion engine ( 10 ) is used. A method according to claim 4 or 5, characterized in that for detecting a stationary or quasi-stationary operating state of the internal combustion engine ( 10 ) the upstream NOx concentration (NOx_VK, NOx_vK_Sim) upstream of the catalyst ( 16 ) is used. Method according to claim 1, characterized in that that the number of measures to increase the dosage is detected and that after exceeding a predetermined Number of exceedances influences a metering valve characteristic with a correction signal (Korr) becomes. Device for dosing a reagent of a reagent precursor into the exhaust gas area ( 13 ) an internal combustion engine ( 10 ), characterized in that at least one prepared for carrying out the method according to one of claims 1 to 9 control device ( 20 ) is provided. Computer program that shows all the steps of a procedure according to one of the claims 1 to 9, when it runs on a computer. Computer program product with a program code stored on a machine-readable carrier for carrying out the method according to one of Claims 1 to 9, when the program is stored on a computer or in the control unit ( 20 ) is performed.