CN102817684B - The diagnostic method of filter and diagnostic module for gas extraction system NOx sensor - Google Patents

Abstract

The open one of the present invention is used for the diagnostic method with the filter (5) of the NOx sensor (4) of the gas extraction system (1) of SCR catalyst (3), the method includes the steps of: the working method (11) of this filter (5) is taken into account, calculates a NOx estimated value in (12) catalyst converter (3) downstream；Based on this NOx estimated value, set up a LINEAR N Ox model (13)；This NOx estimated value and this LINEAR N Ox model are compared (15)；When this difference comparing (15) is under a threshold value, disable (18,19) filter (5).

Description

The diagnostic method of filter and diagnostic module for gas extraction system NOx sensor

Technical field

The present invention relates to the filter for gas extraction system NOx sensor a kind of diagnostic method and A kind of diagnostic module, has SCR in particular for the one of the explosive motor of motor vehicles and urges Change the gas extraction system of device.

Background technology

There is SCR(SCR) system of catalyst converter is highly suitable for removing NOx Emission, especially when diesel engine exhaust.To SCR catalyst in activity SCR system In feed intake ammonia (NH₃), this ammonia absorption on a catalyst and with come self-purging NO and NO₂ React.NH₃The most directly feed intake, but in most of the cases molten with a kind of urea The form of liquid feeds intake, and this solution is partially converted into NH after injection it₃.Passive/passive In SCR system, not in the upstream of this catalyst converter actively/actively inject NH₃Or urea.Take and Instead of, NH is produced from another upstream component of this catalyst converter₃, such as, it is at engine The dilute NOx trap of LNT(during fuel-rich duty).

As NH that is that feed intake or that store in catalyst converter₃Time inadequate, or when temperature is not suitable for When the conversion completely of NOx, it is impossible to convert whole Nox and cause Nox to let out by catalyst converter Dew.If but the NH fed intake₃Too much and it is stored in catalyst converter, then may go out Now it is desorbed.Generally after being rapidly heated, (such as after engine loading raises), NH occurs₃ Desorption.But at NH₃During the excess that feeds intake, this is likely to occur at a constant temperature.

In order to accurately control the process in SCR catalyst, about downstream or catalyst converter after NOx and NH₃The information of concentration is meaningful.For this purpose, there is two kinds of biography Sensor, NH₃Sensor and NOx sensor.NH₃Sensor is only used for measuring NH₃Concentration or Amount, and NOx sensor is to NOx and NH₃It is all sensitive.This causes difficulty in the measurements, I.e. cannot determine simply, that this sensor has just detected is NOx value or NH₃Value.

A kind of filter described in parallel application DE 10 2,011 077 246.4 and filtration It is NOx measured value or NH that method determines the signal detected by NOx sensor₃Measured value. To this end, set up two different models or modeling method and/or it mated.One model is retouched State NOx conversion ratio in catalyst converter, and second model has described NH₃By catalyst converter Leakage behavior.

The degree of accuracy of this filter or efficiency depend on the NOx of catalyst converter upstream or the spy of signal Property.In order to make a distinction between NH3 value in NOx value and downstream NOx signal, should The NOx signal of the upstream of catalyst converter must have dynamic characteristic known to one.

In the case of occurring Nox to reveal in catalyst converter, NOx signal will dynamically follow the tracks of input NOx signal, and NH₃Value does not typically do that.Therefore, it is impossible in the upstream (example of catalyst converter As in constant driving mode) successfully determine a more constant NOx signal, and institute's mistake The NOx/NH of filter₃Signal should not be taken to a kind of feedback and controls.

Summary of the invention

General object of the present invention is, improves the working method of the gas extraction system with catalyst converter.

This purpose is to be realized by the feature of claim 1 and 10.Each dependent claims In define that the present invention is advantageously improved scheme.

According to the first aspect of the invention, a kind of for the gas extraction system with SCR catalyst The diagnostic method of the filter of NOx sensor comprises the following steps:

-run this filter, including the NOx estimated value calculating catalyst converter downstream；

-based on this NOx estimated value, set up a LINEAR N Ox model；

-NOx estimated value is compared with LINEAR N Ox model；

-when this difference compared is under a threshold value, disable this filter.

This method makes the filter for NOx sensor be stabilized, and determines this mistake The decision-making of filter is the most credible.One implementation of this filter is, continuously by two not Same model carries out mating and its accuracy being compared.One model represents conversion rate of NOx One simplification kinetic model.Another model is a kind of simple linear time algorithm, should Algorithm can describe NH in the time window limited well₃Slip behavior.In some situation Under, this filter can not be at NOx and NH₃Between make a distinction.This typically occurs at the most quiet In the case of state work, when NOx signal does not have enough dynamic characteristics.In this case, The NOx in catalyst converter downstream is described again by a linear time algorithm.By described condition Determination, can avoid this filter carry out mistake suppose or cause mistake decision-making.Such as, If the absolute difference between the two comparison signal less than a threshold value, can disable this filter, Or abandon or do not use its decision-making.

In order to compare, can be at a line of this NOx estimated value Yu this LINEAR N Ox model Error calculation is carried out between property NOx estimated value.The execution of this error calculation is simple, and carries Supply result quickly and reliably.

When the difference compared is more than a threshold value, this filter can be opened.This threshold value is permissible Corresponding with that threshold value for disabling, or two different threshold values may be used.Open or Enable and refer to, use the decision-making of this filter.When disabling, this filter still on backstage with Know that mode is run simultaneously, but its result will not be used.It is alternatively possible to filter is disconnected Connect, and reclose when opening.

When comparing with threshold value, this filter can keep starting a time-domain limited State.This mode of operation can be referred to as transient state and start.Transient state start in institute it is assumed that: If being made that a decision-making and NOx sensor signal have not moved to limit not long ago Boundary outside, then " old " filter decision-making, say, that start time or restriction time Between before territory, be the most effective.Generally, NOx and NH in catalyst converter downstream₃Will not constantly change Becoming, accordingly even when cannot make a policy according to current data, the decision-making made not long ago still may be used Can be effective.Transient state start institute it is assumed that, not yet do the decision-making that makes new advances, filter is still out That open and use its result to carry out feeding back or processing further.Transient state starts and makes a reservation at one Time period after or when the NOx sensor signal boundary predetermined above or below will It is deactivated.

In the case of filter disables, the change of the NOx value in catalyst converter downstream can be introduced.In It is in this case, when filter can not make reliable decision-making, can be for (coming spontaneous Motivation) NOx disturbance sets a mark (Flag) or an information, in order to reactivate The basic algorithm of this filter or make it reliably start.When filter disables, it does not provides Any signal, either NOx or NH₃.In this case, catalyst converter fed intake or note Enter and carry out, namely at the regulating loop of an opening in the case of not feedback (Regelkreis) carry out in.As long as NOx sensor signal is still within known, permission In boundary, here it is acceptable.But, when crossing this boundary, it thus may be desirable to Determine forcibly or calculate NOx sensor signal.This can reach by disturbance pointedly or change NOx ratio example in exhaust, that leave from engine and realize, such as by completely or partially Connect and/or disconnect exhaust-gas-recirculation valve (EGR).This situation can be such as in long-term static state Working method occurs, such as by a speed adjusting device (speed regulator).Once obtain A kind of known dynamic characteristic of this working method therefore this NOx signal acquisition, then this filtration Device just automatically begins to normally work.

In order to conversion rate of NOx is modeled, a dynamics of conversion rate of NOx can be used Model, can be preferably a kinetic model simplified, in order to reduce to calculate consuming and it After data process.

These steps or calculating can be implemented for point of multiple sampling times, and it has preferably one The sampling time of second.The quantity of sampling time point is too small will can not obtain consistent model, and mistake Big quantity will unnecessarily improve calculating and consume.

In order to calculate, these steps can use the sampled point recalled in time extraly Value, preferably within the time range of 20 seconds.This improves this calculating and the reliability determined, Its measured value directly records.In order to compare, can be later by between two signals Mean absolute difference is used as criterion.

According to the second aspect of the invention, a kind of for the gas extraction system with SCR catalyst The diagnostic module of the filter of NOx sensor, it includes a signal for filter signal Input, a computing unit being used for performing above-mentioned diagnostic method and one are for exporting The signal output part of this diagnostic method result.Advantages described above and amendment are same effectively.

Accompanying drawing explanation

By accompanying drawing, the present invention will be explained in more detail below, wherein:

Fig. 1 shows the schematic block diagram of a gas extraction system, and with good grounds of this gas extraction system band is sent out Bright diagnostic module.

Fig. 2 shows according to the present invention for the block diagram of the diagnostic method of a kind of filter.

Fig. 3 and 4 is respectively the chart of the application of the diagnostic method according to the present invention.

These diagrams are only used for explaining the present invention rather than are limited.These diagrams and each point Vertical part needs not be pro rata.Same reference marker represents same or similar part.

Detailed description of the invention

Fig. 1 shows the Diesel engine for internal combustion engine 2(such as motor vehicles) a row A part for gas after-treatment system 1.This exhaust after treatment system or gas extraction system 1 include a peace Put the catalyst converter 3 in engine 2 downstream, such as one SCR(SCR) catalysis Device.

The arranged downstream of catalyst converter 3 has a NOx sensor 4, is used for measuring NOx in exhaust Concentration or the amount of NOx.After NOx sensor 4 need not be directly positioned on catalyst converter 3, It is also in further downstream place.

The measured value of NOx sensor 4 is sent to a filter or the NH of this NOx sensor 4₃ Filter 5.Filter 5 processes this measured value can recognizing and is surveyed by NOx sensor 4 The value of amount is NOx value or NH₃Value.Filter 5 exports the signal of correspondence, such as to one Engine controller or exhaust aftertreatment controller export.

In the downstream of catalyst converter 3, in addition to the measured value provided by NOx sensor 4, filter Device 5 also needs to the amount of NOx concentration or NOx, described concentration or amount and is produced also by engine 2 Upward out in the side of catalyst converter 3.An extra NOx is there is in the downstream of catalyst converter 3 Sensor 6, or the NOx concentration in catalyst converter 3 downstream, this mould is determined by a model 6 Type determines NOx amount and/or concentration produced by engine 2.

Between catalyst converter 3 downstream, optional NOx sensor 6 and catalyst converter 3, it is configured with The most optional, for urea liquid or NH₃A decanting point 7.NOx sensor 6 or should Modeling effect is routed in the downstream of decanting point 7, to avoid the cross-sensitivity of NH3 (Querempfindlichkeit).

The output 5b of filter 5 and a diagnostic module 8 are connected.Diagnostic module 8 can be One independent unit, this unit with one for filter 5 signal signal input part 8a, One for performing the computing unit of diagnostic method and one for exporting the letter of the method result Number output 8b.Diagnostic module 8 can also be the part of a controller, sends out for such as one Motivation controller or an exhaust aftertreatment controller or the controller of filter 5.It is permissible Realize with the form of software program or software module.Signal output part 8b is the most in software Realize.The result exported by signal output part 8b can be filter 5 result in one solely Vertical value or checking, and/or be (freigegebene) that filter 5 is discharged or the knot not discharged Really.

By Fig. 2, the working method of diagnostic module 8 and this diagnostic method is described now.Should Diagnostic method is from the beginning of the NOx sensor 4 after catalyst converter 3.

The process being schematically shown in Fig. 2 have set up a LINEAR N Ox model first stage or Step 10.In first step or sub-step 11, run this filter 5, wherein at second step In rapid 11, estimation NOx value NOxPostEstV in catalyst converter 3 downstream is defined as filter 5 A result.

In order to carry out NOx modeling, have employed a 0D with dynamics the first progression at this CSTR(continuously stirred tank reactor (CSTR)) model.

$\mathrm{NOxPostEstV}=\frac{\mathrm{NOxPreV}}{1+\frac{k_R}{\mathrm{ExhFlowV}}}$

These signals can be scalar (detect or sample) or vector (has intelligent operation The time window of element).For time window, it is assumed that reaction velocity coefficient (k_R) it is normal Number.Optimum reaction velocity coefficient can reduce method by analysis method according to least square (Least-Squares-Abstiegsverfahren) determine:

$\mathrm{\ϵ}=(\left[\begin{array}{c}\frac{1}{\mathrm{ExhFlo}{w}_1}\\ \frac{1}{\mathrm{ExhFlo}{w}_2}\\ ...\\ \frac{1}{\mathrm{ExhFlo}{w}_N}\end{array}\right]k_R-\left[\begin{array}{c}\frac{\mathrm{NOxPr}{e}_1}{\mathrm{NOxPos}{t}_1}\\ \frac{\mathrm{NOxPr}{e}_2}{\mathrm{NOxPos}{t}_2}\\ ....\\ \frac{\mathrm{NOxPr}{e}_N}{\mathrm{NOxPos}{t}_N}\end{array}\right]+1)=({\mathrm{\θk}}_R-y)$

Wherein

$\mathrm{\θ}=\left[\begin{array}{c}\frac{1}{\mathrm{ExhFlo}{w}_1}\\ \frac{1}{\mathrm{ExhFlo}{w}_2}\\ ...\\ \frac{1}{\mathrm{ExhFol}{w}_N}\end{array}\right],$ $y=1-\left[\begin{array}{c}\frac{\mathrm{NOxPr}{e}_1}{\mathrm{NOxPos}{t}_1}\\ \frac{\mathrm{NOxPr}{e}_2}{\mathrm{NOxPos}{t}_2}\\ ...\\ \frac{\mathrm{NOxPr}{e}_N}{\mathrm{NOxPos}{t}_N}\end{array}\right]$

Optimal condition min (ε^Tε)

Make:

k_R=(θ^Tθ)^-1θ^Ty

In following step 13, build based on this NOx estimated value NoxPostEstV LINEAR N Ox model.One result of this LINEAR N Ox model is, catalyst converter 3 at step 14 One LINEAR N Ox estimated value NoxLinPostEstV in downstream is available.

Linear time algorithm for LINEAR N Ox model based on NOx model signals (NoxPostEstV-N vector (such as 20 sampled values)) carries out calculated as below:

NO_xLinPostEstV=an+b

Wherein a and b is suitable constant, and n is to (time horizon line (Zeithorizont) from 0 -1) number of samples between.

Minimized by least square method criterion and calculate a and b:

$\mathrm{\ϵ}=(\left[\begin{array}{cc}0& 1\\ 1& 1\\ 2& 1\\ ...& \\ N-1& 1\end{array}\right]\left[\begin{array}{c}a\\ b\end{array}\right]-\left[\begin{array}{c}\mathrm{NOxPostEs}{t}_1\\ \mathrm{NOxPostEs}{t}_2\\ \mathrm{NOxPostEs}{t}_3\\ ....\\ \mathrm{NOxPostEs}{t}_N\end{array}\right])=(\mathrm{\θ}\left[\begin{array}{c}a\\ b\end{array}\right]-y)$

Wherein

$\mathrm{\θ}=\left[\begin{array}{cc}0& 1\\ 1& 1\\ 2& 1\\ ...& \\ N-1& 1\end{array}\right],$ $y=\left[\begin{array}{c}\mathrm{NOxPostEs}{t}_1\\ \mathrm{NOxPostEs}{t}_2\\ \mathrm{NOxPostEs}{t}_3\\ ...\\ \mathrm{NOxPostEs}{t}_N\end{array}\right]$

Optimal condition min (ε^Tε)

Make:

$\left[\begin{array}{c}a\\ b\end{array}\right]={\left({\mathrm{\θ}}^T\mathrm{\θ}\right)}^{-1}{\mathrm{\θ}}^{T}y$

In second stage 15, by NOx estimated value and LINEAR N Ox model or LINEAR N Ox Estimated value compares mutually.

This is by root between NoxLinPostEstV and NoxPostEstV in step 16 Error calculation ε is carried out according to below equation_NOxLinObtained:

${\mathrm{\ϵ}}_{\mathrm{NOxLin}}=\frac{1}{N}\sqrt{{(\mathrm{NOxLinPostV}-\mathrm{NOxPostEstV})}^T(\mathrm{NOxLinPostV}-\mathrm{NOxPostEstV})}$

Error is the least, and it is linear the best that NOx estimates, is the most more difficult to determine this sensor 4 That measure is NOx or NH₃。

In fourth stage 17, confirm or determine the NOx signal of sensor 4 be NOx or NH₃Value.To this end, in step 18 by error signal_NOxLinWith a predefined boundary Or a threshold epsilon_MinCompare.Work as error signal_NOxLinLess than this boundary, then set one In other words mark or signal, so that the decision-making of filter 5 can not be carried out or consider, or will Filter 5 disables.Because point of each sampling time is calculated a new error signal, so right Error signal may be additionally contemplates that in this decision-making_NOxLinPrevious or front several values.

If error signal_NOxLinMore than this boundary, then run according to step 19 or started Filter 5.If non-this situation, then can be according to step 20, at so-called transient state starting state Under, make this filter 5 start still keeping known to one, in the time-domain that limits in advance.? Transient state open in institute it is assumed that: if being made that a decision-making and NOx the most at short notice Sensor signal has not moved to outside the boundary limited, then " old " filter decision-making, also That is when starting or before the time-domain of restriction, be still effective.

Work as long as transient state starts, just start filter 5 according to step 19, say, that Consider its result.After a predetermined time period or when a NOx sensor signal During above or below the predetermined limit, transient state is started and releases and jump to step 21.

In step 21, filter 5 is disabled, say, that disconnected or do not examine Consider its result.

When filter 5 disables, it does not provide any signal, either NOx or NH₃。 In this case, feeding intake or injecting and do not carrying out in the case of not feedback catalyst converter 3, Namely carry out in the regulating loop of an opening.As long as NOx sensor signal is still within In known, the limit that allows, here it is acceptable.

If determining NOx sensor signal to be in step 22 in the limit known, that allow Outside (this can be deviation positively or negatively), then can determine forcibly in step 23 Or calculating NOx sensor signal.This can by disturbance pointedly or change exhaust in, from NOx ratio example that engine leaves and realize, such as by completely or partially connecting and/or disconnected Open exhaust-gas-recirculation valve (EGR).

This method completes in diagnostic module 8.By this method, or outputing one has NOx or NH of effect₃Value, or output a signal, this signal provides filter 5 Reliability.Diagnostic module 8 is connected to NOx sensor 4, filter 5 in signal chains and enters one Between the controller (not shown) that step processes.Correspondingly, diagnostic module 8 also may be used To be integrated in controller or NOx sensor 4 and filter 5.

Fig. 3 and 4 shows multiple chart, and these charts show the method or diagnostic module 8 Working method.Wherein shown, by this diagnostic method or this diagnostic module 8, exhaust system System 1 or the working method of filter 5 become sane.

Fig. 3 shows a dynamic driving pattern, wherein can be well to NOx and NH₃ Value separates.The ε of LINEAR N Ox model_NOxLinError is the highest.Table Show the signal " number filter _ enable " (filter_enabled) that filter 5 starts, at great majority Time be start.In two charts of the lower section of Fig. 3, show obtained catalyst converter NOx and NH in 3 downstreams₃Value and the reality obtained by discrete measuring instrument or sensor Value, and it can be seen that these values meet the most each other.It is to say, enter by this method Row work is reliable.

Fig. 4 shows a kind of more static working method, and wherein this diagnostic method determines: nothing Method is made reliable decision-making and is disabled by filter 5.Therefore, in second time of this chart On section, signal " filter _ enable " is that do not open or relatively low.Then as it has been described above, Disable feedback, until filter 5 is again started up.

It can be determined that, although the error ε of LINEAR N Ox model_NOxLinRelatively low, but filter 5 are to maintain startup in about 260 seconds of beginning.Which results in following facts, i.e. NOx senses In any case device measures low-down value and the most all calibrates the result of filter 5.

The method or diagnostic module 8 can each with catalyst converter, especially (passive/passive Or active/active) SCR catalyst gas extraction system in be applied.

Claims (12)

1. the NOx sensor being used for there is the gas extraction system (1) of SCR catalyst (3) (4) diagnostic method of filter (5), the method has steps of:

Run (11) described filter (5), including calculating (12) described catalyst converter (3) The NOx estimated value in downstream；

LINEAR N Ox model (13) is set up based on described NOx estimated value；

Described NOx estimated value and described LINEAR N Ox model are compared (15)；

When the difference of described comparison (15) is under threshold value, disable (18,19) described Filter (5).

Diagnostic method the most according to claim 1, wherein in order to carry out described comparison (15), Enter between described NOx estimated value and a LINEAR N Ox estimated value of described LINEAR N Ox model Row error calculation (16).

Diagnostic method the most according to claim 1 and 2, wherein when described comparison (15) Difference starts described filter (5) when exceeding threshold value.

Diagnostic method the most according to claim 3, wherein exceedes described threshold value at comparative result In the case of, make described filter (5) keep within a predetermined period of time starting.

Diagnostic method the most according to claim 1, is wherein disabling described filter (5) In the case of, the NOx value to described catalyst converter downstream introduces a change (23).

Diagnostic method the most according to claim 1, wherein in order to calculate (12) described NOx Estimated value, have employed a kinetic model of conversion rate of NOx.

Diagnostic method the most according to claim 1, wherein in order to described LINEAR N Ox mould Type is modeled (13), have employed a kind of linear time algorithm.

Diagnostic method the most according to claim 1, wherein these steps are real at sampling time point Execute.

Diagnostic method the most according to claim 8, wherein these steps are real at sampling time point Executing, the sampling time is one second.

Diagnostic method the most according to claim 8, wherein for these steps, have employed The value of the multiple sampled points recalled in time.

11. diagnostic methods according to claim 8, wherein for these steps, have employed The value of the multiple sampled points recalled in time, is within the time range of 20 seconds.

12. 1 kinds of NOx being used for having the gas extraction system (1) of SCR catalyst (3) pass The diagnostic module of the filter (5) of sensor (4), described diagnostic module has one for filtering The signal input part (8a) of device (5) signal, one for perform according to claim 1 to 11 The computing unit of described diagnostic method and a letter being used for exporting described diagnostic method result Number output (8b).