DE102018200572A1 - Method for checking an SCR system with at least two metering valves - Google Patents

Abstract

The invention relates to a method for checking an SCR system, which has a feed pump and at least two metering valves, wherein a metering valve is faulty and the other metering valves are faultless. The following steps are carried out: A metering ratio for one of the metering valves from a pressure difference (Δp _{E, k} , Δp _{E, k + 1} , Δp _{E, k + 2} ) between a pressure (p _{Ev, k} , p _{Ev, k + 1} , p _{Ev, k + 2} ) before metering (101, k, k + 1, k + 2) via this metering valve and a pressure (p _{En, k} , p _{En, k + 1} , p _{En, k + 2} ) After metering (k, k + 1, k + 2) and a metered volume (.DELTA.V _{E, k} , .DELTA.V _{E, k + 1} , .DELTA.V _{E, k + 2} ) of a reducing agent solution is determined. Thereupon, at least one additional metering ratio for another metering valve is determined from a pressure difference between a pressure before metering via this metering valve and a pressure after metering and a metered volume of the reducing agent solution. Subsequently, a comparison of the metering ratio of the one metering valve with at least one metering ratio of one of the other metering valves and detection of an error occur when the metering ratio of one metering valve deviates from the metering ratio of the other metering valve.

Description

The present invention relates to a method for checking an SCR system with at least two metering valves by means of comparison of metering ratios, which are determined during the metering via the respective metering valve. Furthermore, the invention relates to a computer program that performs each step of the method when it runs on a computing device, and a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method according to the invention.

State of the art

Today, SCR catalysts are used to reduce nitrogen oxides (NOx) in the exhaust of internal combustion engines in automobiles. The DE 103 46 220 A1 describes the basic principle of SCR (Selective Catalytic Reduction). Here are nitrogen oxide molecules, which are located on an SCR catalyst surface, in the presence of ammonia (NH3) as a reducing agent, reduced to elemental nitrogen. The reducing agent is provided in the form of a urea-water solution from which ammonia is split off, also known commercially as AdBlue®. A feed pump delivers the reducing agent solution from a reducing agent tank via a pressure line to at least one metering module. The metering module has a metering valve, via which the reducing agent solution is then metered into an exhaust gas line upstream of the SCR catalytic converter. The metering is controlled in an electronic control unit in which metering strategies for the operation of the SCR system are stored.

In a so-called "volumetric mode" of the SCR system, one makes the generally high accuracy of the feed pump and the property that in steady state the very well known, promoted by the feed pump mass of the reducing agent solution leaves the system as a metered mass again, advantage. In combination with the comparatively small tolerances of the delivered mass of the reducing agent solution by the feed pump, a high mass accuracy is established on average. If the mass balance is disturbed in volumetric mode, for example due to a defect in the feed pump or in the dosing module, the metered mass can no longer be checked directly. It is known in this case to monitor the pressure, for example by means of a pressure sensor.

Nowadays, multiple metering valves are often used in SCR systems, via which reducing agent solution is metered into the exhaust gas line, wherein the metering valves are usually assigned to different SCR catalysts. Typically, the plurality of metering valves are connected via at least a common portion of a pressure line to the same feed pump which provides the reductant solution for all metering valves. It is therefore not possible to assign the conveyed mass clearly only one metering valve.

The DE 10 2012 218 092 A1 describes a method for monitoring the function of at least one metering valve. The reducing agent solution is metered in a timed manner by means of the delivery pump and the at least one metering valve. The pressure during the activation of the metering valve is detected and evaluated by means of an adaptive filter. Thereupon, a comparison of these evaluated by means of the adaptive filter pressure values and expected comparison data is performed. Finally, based on this comparison, an error is detected in the metering valve and / or in the metered mass of the reducing agent solution.

Disclosure of the invention

The invention relates to a method for checking an SCR system, which has a delivery pump and at least two metering valves, in particular a plurality of metering valves. The feed pump delivers reducing agent solution via a pressure line to the at least two metering valves, which then meter the reducing agent solution into an exhaust gas line. Of the at least two metering valves, one metering valve is to be faulty and the other metering valves must be free from errors. A "faulty metering valve" means that the metering valve has a defect or metered in a defective volume or a defective mass of the reducing agent solution.

The method comprises the following steps:

A metering ratio for metering in via one of the metering valves is determined. For this purpose, a pressure difference between a pressure before metering via this metering valve and a pressure after metering is determined and this pressure difference is then set in relation to a metered volume of the reducing agent solution, as shown in formula 1: $$\alpha =\frac{\Delta p_e}{\Delta V_e}=\frac{p_{ev}-p_{en}}{\Delta {\text{V}}_{\text{e}}}$$

Here, α represents the metering ratio, Δp _E the pressure difference during dosing and ΔV _E the volume change during dosing. The pressure difference Δp _E when dosing can be used as a difference between p _Ev , the pressure before dosing, and p _En , the pressure after dosing, are calculated.

Furthermore, a further metering ratio for another metering valve is determined in the same way. Again, a pressure difference between a pressure before metering via this metering valve and a pressure after metering is determined and then set this pressure difference with the here metered volume of the reducing agent ratio. Formula 1 applies accordingly.

It should be noted here that at the same time only one metering of the reducing agent solution is carried out via only one metering valve, otherwise the respective volume change and the pressure difference can no longer be assigned to a metering valve, which would lead to the metering ratio being falsified. Dosing strategies are specified at a later point, in which the metering takes place one behind the other.

Subsequently, a comparison of the metering ratio of a metering valve with at least one metering ratio of one of the other metering valves. In other words, the comparison is a direct comparison of two metering ratios for two different metering valves.

If the metering ratio of one metering valve deviates from the metering ratio of the other metering valve, i. if the two dosing ratios differ, an error is detected. The detected error is a "quantity error" and first of all indicates that one of the two metering valves is faulty.

If the SCR system has more than two, hence three or more, metering valves, then such a direct comparison of the metering ratios for all metering valves of the SCR system can be carried out by repeating the above-mentioned steps of the method for the further metering valves. The direct comparisons preferably take place according to a scheme. In particular, metering valves which have already been compared in the current metering cycle by this method and in which no error was detected are omitted in the repetition. As a result, both time and resources - in particular reducing agent solution - saved. Optionally, it is possible to dispense with the determination of further metering ratios for further metering valves and their comparison if an error has already been detected previously.

In one aspect, a metering valve may be identified as defective if the associated metering ratio is above an upper threshold or below a lower threshold, i. outside a permitted range.

According to a further aspect, it can be provided that if the SCR system has three or more metering valves, a metering valve is recognized as defective if its metering ratio deviates from at least two metering ratios of other metering valves. Thus, the faulty metering valve can be detected with sufficient probability for further action.

In addition, additional metering ratios of other metering valves can be compared with each other, with the help of which the defective metering valve can be detected more reliably. In particular, the metering ratios of all metering valves of the SCR system can be determined, compared and included in this way.

In addition, it can be provided to determine a pressure ratio from the metering ratio and a delivery ratio for metering. The delivery ratio is determined by determining a pressure difference between a pressure before delivery of a reducing agent solution by the delivery pump and a pressure after delivery, and then comparing this pressure difference with a delivered volume of the reducing agent solution, as shown in formula 2: $$\gamma =\frac{\Delta p_F}{\Delta V_F}=\frac{p_{Fv}-p_{Fn}}{\Delta {\text{V}}_{\text{F}}}$$

Hereby poses γ the subsidy ratio, Δp _F the pressure difference in the promotion and ΔV _F the volume change in the promotion is. The pressure difference Δp _F in the promotion can be considered difference between p _Fv , the pressure before promoting, and p _Fn , the pressure after conveying, are calculated.

In Formula 3, the above-mentioned pressure ratio φ calculated from the metering ratio α and the delivery ratio y is further shown. In this case, use is made of the fact that the feed pump and the metering valves are connected to one another via at least part of a common pressure line, through which the reducing agent solution is conveyed. Consequently, the pressure after delivery corresponds to the pressure before metering (p _Fn = p _Ev ), and according to the volumetric principle, the delivered volume of the reducing agent solution corresponds to the metered volume (ΔV _F = ΔV _E ). $$\phi =\frac{\alpha }{\gamma }=\frac{\frac{\Delta p_e}{\Delta V_e}}{\frac{\Delta p_F}{\Delta V_F}}=\frac{\Delta p_e}{\Delta p_F}$$

The pressure ratio φ is defined in the manner shown here for metering via a metering valve. Since the metering valves share at least part of the common pressure line, through which the reducing agent solution is delivered and in which the pressure builds up, the pressure ratio φ can also be considered together for the metering via all metering valves of the SCR system.

The pressure ratio can be used as a precondition for the comparison of the metering ratios. The pressure ratio in a SCR system without error should be for each metering via one of the metering valves 1 his. It can be provided that the comparison of the metering ratios for the respective metering valve only takes place when the pressure ratio deviates from 1. In order to determine the deviation from 1, thresholds may be provided, wherein a deviation is detected when the pressure ratio exceeds or exceeds these thresholds. The pressure ratio or its deviation from 1 can be determined in a simple manner by measuring the pressure differences, for example by means of a pressure sensor. However, also errors of the feed pump can lead to changes in this pressure ratio.

If the pressure conditions for the metering valves have already been determined, the comparison of the metering ratios can be realized in an advantageous manner by comparing the pressure ratios for the respective metering valves. An error can then be detected for one of the metering valves if the pressure ratio of one metering valve deviates from the pressure ratio of the other metering valve. In addition, the metering valve, whose pressure ratio in this case deviates from 1, can be recognized as defective.

Special dosing strategies can be provided for the method, which are presented below. These dosing strategies can eliminate or at least reduce interference during metering, which can lead to incorrect metering ratios. The following dosing strategies can be partially or completely combined with each other.

In a dosing strategy, it may be provided to divide a simultaneous dosing request for a plurality of dosing valves into dosing requests for the dosing valves that are carried out alternately one after the other. This ensures that metering via different metering valves does not take place simultaneously.

In a further dosing strategy, a volume of the reducing agent solution to be metered in can be distributed over several doses. As a result, the number of dosing performed is increased and, consequently, also the evaluable Dosierverhältnisse.

In order to accurately determine the pressure difference during metering, it is necessary that the pressure before metering and the pressure after metering are sufficiently stationary. Therefore, it is preferable to wait for a waiting time between two consecutively executed metering units both via the same metering valve and via different metering valves in which the pressure settles. A preferred waiting time is preferably greater than 200 ms and particularly preferably greater than or equal to 250 ms. Similarly, when determining the pressure difference in the promotion that the pressure before delivery and the pressure after delivery are sufficiently stationary. It can therefore wait for a corresponding waiting time between promotion and metering.

If the feed pump feeds reducing agent during metering, the pressure within the pressure line is changed in such a way that the determined metering ratio is falsified. Consequently, it proves to be advantageous to reject the metering ratio determined during this metering.

In one aspect, for determining the metering ratio, a plurality of metered additions can be made via the same metering valve and the metering ratios can be averaged to a mean metering ratio. In this case, the sum of the pressure differences in the case of several metered additions can be set in relation to a summed metered volume in these metering units. Finally, this average metering ratio can be used instead of the metering ratio for the further process, in particular for the comparison of metering ratios. In this way measurement errors can be minimized.

The dosing ratio depends on the rigidity of the SCR system. Since the metering valves are hydraulically connected, the rigidity applies equally to all metering valves. In order to be able to compare the metering ratios for different metering valves, the metering strategy can be selected so that the rigidity remains constant. However, the stiffness may change with the amount of dissolved air in the reducing agent solution. Preferably, therefore, determining the metering ratios, in particular the average metering ratios, for the various metering valves in a close time interval from each other. Consequently, the waiting time between the consecutively executed dosing is not too large, for example about 250 ms. In addition, the stiffness depends on the prevailing pressure level. As a result, the dosages preferably occur within substantially the same Pressure level off. Equally, the determination of the delivery ratio can take place within a narrow time interval for determining the metering ratio and take place within the same pressure level.

The SCR system is not free of air, especially at the beginning of a dosing cycle, but usually contains air bubbles in the pressure line. If these air bubbles are also flushed out of the pressure line during dosing, the pressure difference and consequently also the dosing ratio change. Therefore, it can preferably be provided that the metering ratios are not determined at the beginning of the metering cycle.

The computer program is set up to perform each step of the method, in particular when it is performed on a computing device or controller. It allows the implementation of the method in a conventional electronic control unit without having to make any structural changes. For this purpose it is stored on the machine-readable storage medium.

By loading the computer program on a conventional electronic control unit, the electronic control unit is obtained, which is set up to check the SCR system with at least two metering valves.

list of figures

• 1 zeigt eine schematische Darstellung eines SCR-Systems mit mehreren Dosierventilen, das mittels eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens überprüft werden kann.
• 2 zeigt ein Diagramm einer Ansteuerung eines Dosierventils, einer Ansteuerung einer Förderpumpe und eines Drucks des SCR-Systems aus 1 über der Zeit.
• 3 zeigt ein Ablaufdiagramm eines ersten Ausführungsbeispiels des erfindungsgemäßen Verfahrens.
• 4 zeigt ein Ablaufdiagramm eines zweiten Ausführungsbeispiels des erfindungsgemäßen Verfahrens.
• 5 zeigt ein Ablaufdiagramm eines dritten Ausführungsbeispiels des erfindungsgemäßen Verfahrens.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

• 1 shows a schematic representation of an SCR system with a plurality of metering valves, which can be checked by means of an embodiment of the method according to the invention.
• 2 shows a diagram of a control of a metering valve, a control of a feed pump and a pressure of the SCR system 1 over time.
• 3 shows a flowchart of a first embodiment of the method according to the invention.
• 4 shows a flowchart of a second embodiment of the method according to the invention.
• 5 shows a flowchart of a third embodiment of the method according to the invention.

Embodiments of the invention

1 shows a schematic representation of an SCR system 1 for at least one SCR catalyst (not shown). The SCR system 1 includes three dosing modules 21 . 22 . 23 wherein a first dosing module 21 a first metering valve A comprising a second dosing module 22 a second metering valve B and a third dosing module 23 a third metering valve C having. The dosing modules 21 . 22 . 23 are via a pressure line 3 with a conveyor module 4 connected, which is a feed pump 41 comprising the reducing agent solution from a reducing agent tank 5 in the pressure line 3 promotes. The pressure line 3 splits downstream of a common section 30 in a first section 31 , the first dosing module 21 leads to a second section 32 , the second metering module 22 leads, and in a third section 33 , the third dosing module 23 leads, on. The SCR system 1 works in a volumetric mode in which the pump through which 4 delivered mass of the reducing agent solution completely through the metering valves A, B . C is metered. Furthermore, there is a pressure sensor 6 in the common section 30 the pressure line 3 arranged, there can measure the pressure p. The pressure sensor 6 , the conveyor module 4 , including the pump 41 and the dosing modules 21 . 22 . 23 , including the dosing valves A . B . C are with a common electronic control unit 7 connected and controlled by this.

In 2 is a diagram of a drive 100 one of the metering valves A . B or C , For example, the first metering valve A , with a variety of dosing 101 (For the sake of clarity only one metering provided with reference numerals) via this metering valve A and a drive 140 the feed pump 41 with several pump strokes 141 (Also provided only a pump stroke with reference numerals), by the reducing agent solution in the pressure line 3 is promoted over time t shown. In addition, the resulting pressure p that by means of the pressure sensor 6 in the pressure line 3 was measured. When a pump stroke 141 has been executed, the pressure p increases sharply and then decreases when dosages 101 to be executed gradually.

This diagram explains aspects of a dosing strategy used. The dosing strategy used here provides for a volume of the reducing agent solution to be metered in at several doses 101 to distribute. It is also intended, at the beginning of a dosing cycle some dosing 101 , for example, 100 doses with in total 3 Grams of reductant solution, of which three are shown in this diagram, wait where appropriate in the pressure line 3 existing bubbles were washed out.

In the diagram are three doses, which are used to determine a dosing ratio α _A . α _B . α _C (please refer 3 to 5 ), denoted by k, k + 1 and k + 2. For each of these dosages k, k + 1 and k + 2 are metered volumes ΔV _{E, k} ΔV _{E, k + 1} and ΔV _{E, k + 2} specified. Between two successive doses k, k + 1, a waiting time tw of 250 ms is waited for, in which the pressure p settles, and then the pressure p is measured. When choosing the waiting time tw care is taken not to make them too large, as otherwise the proportion of dissolved air in the reducing agent solution may change, which increases the rigidity of the SCR system 1 and consequently the metering ratio α _A . α _B . α _C changes. It is an example of the pressure p _{Ev, k} before dosing k and the pressure p _{En, k} after metering k (this corresponds to the pressure before the next metering k + 1) shown, from which a pressure difference Δp _{E, k} k is calculated for this metering.

When determining the dosing ratio α _A . α _B . α _C is about a lot of dosing 101 averaged to reduce possible measurement errors. This is the sum of all pressure differences Δp _E and the sum over all metered volumes ΔV _E educated. An averaged dosing ratio α is then determined from these two quantities according to the adjusted formula 1 *. $$\overline{\alpha }=\frac{{\displaystyle \Sigma \Delta p_e}}{{\displaystyle \Sigma \Delta V_e}}$$

relative feed α _A . α _B . α _C during dosing 102 which immediately before a pump stroke 141 done, and / or during dosing 103 in which the pressure p, after a pump stroke 141 is done, is not settled, were determined are discarded.

The in the description regarding 2 The explanations given apply equally to all metering valves A . B or. C , In particular, the same dosing strategy for all metering valves A . B and C used, but this can also be adjusted. Furthermore, the dosing strategy provides for simultaneous dosing requirements for several dosing valves A . B , and C in alternating succession dosing requirements for the metering valves A . B and C divide.

3 shows a flowchart of a first embodiment of the method according to the invention, which is suitable for the review of two metering valves. Here are two Dosierverhältnisse α _A , and α _B of two metering valves A and B of the SCR system 1 out 1 compared to each other. The third metering valve C is not considered here separately, with the three metering valves A . B and C are completely interchangeable in the process. Furthermore, in other embodiments, the third metering valve C be included by, in particular in a repetition of the method, in the following description, the first metering valve A or the second metering valve B through the third metering valve C is replaced.

At the beginning a measurement takes place 200 the pressure p _{Ev, A} before dosing 201 for the first metering valve A , The dosing 201 of the desired volume ΔV _{E, A} the reducing agent solution via the first metering valve A is carried out and then a measurement 202 the pressure p _{En, A} after dosing 201 carried out. From the pressure p _{Ev, A} before dosing 201 and the pressure p _{En, A} after dosing 201 becomes one in the dosing 201 via the first metering valve A occurring pressure difference Δp _{E, A} calculated 203 , From the calculated pressure difference Δp _{E, A} for dosing 201 via the first metering valve A and at this metering 201 metered volume ΔV _{E, A} the reducing agent solution according to formula 1 (see above), the metering ratio α _A for the first metering valve A determined 210 , As related to 2 already explained, the steps 200 to 203 be repeated, the sum over all pressure differences Δp _{E, A} as well as the sum over all metered volumes ΔV _{E, A} and an average metering ratio instead of the metering ratio α _A be determined.

After that, the waiting time t _W Waited before taking a measurement 220 the pressure p _{Ev, B} before dosing 221 via the second metering valve B he follows. Analog is the dosing 221 of the desired volume ΔV _{E, B} the reducing agent solution via the second metering valve B executed, then a measurement 222 the pressure p _{En, B} after dosing 221 performed and from these a pressure difference Δp _{E, B} for the second metering valve B calculated 223 , In the same way, the metering ratio α _B for the second metering valve B from the pressure difference Δp _{E, B} and the metered volume ΔV _{E, B} for its metering 221 determined 230 , Again, an already described averaging for the dosing ratio α _B be performed by following the steps 220 to 223 be repeated. In one embodiment, first, as described, the averaged dosing ratio for the first metering valve A and then the averaged dosing ratio for the second metering valve B determined. In a further embodiment, the steps become 200 to 203 and the steps 220 to 223 alternately carried out in succession or in a different order, before the averaged metering ratios are determined. It is important to note that the steps 200 to 203 and the steps 220 to 223 not run at the same time.

Finally, a comparison is made 240 the metering ratio α _A of the first metering valve A and the metering ratio α _B of the second metering valve B , The two dosing ratios will be different α _A and α _B from each other, will be on a mistake 250 , in particular to a quantity error, for one of the two metering valves A or B closed. The two dosing ratios are correct α _A and α _B match, no error is detected and the procedure is repeated. It is provided in further embodiments, that in the repetition, the third metering valve C (or optionally other existing metering valves) is included by the above steps for the third metering valve C (or the other (s) metering valves) are executed.

Is an error 250 recognized, the two metering ratios α _A and α _B the two metering valves A and B with a first, upper threshold S ₁ and a second, lower threshold S ₂ compared 260 , Is the dosing ratio α _A of the first metering valve A above the first threshold S ₁ or below the second threshold S ₂ This first metering valve A is detected as faulty 271 , Is the dosing ratio α _B of the second metering valve B above the first threshold S ₁ or below the second threshold S ₂ , this second metering valve B is detected as defective 272 , In further embodiments, for each of the metering valves A, B in the comparison 260 a separate pair of thresholds are used.

4 shows a flowchart of a second embodiment for checking three metering valves A . B and C of the SCR system 1 out 1 , The same steps are provided with the same reference numerals, so for their description on 3 is referenced. In addition to the two dosing ratios α _A and α _B for the first metering valve A and the second metering valve B whose investigations 210 and 230 have already been discussed in detail, is a dosing ratio in the same way α _C determined for the third metering valve C. 350 , For this a measurement takes place 340 the pressure p _{Ev, C} before dosing 341 via the third metering valve C , Analog is the dosing 341 of the desired volume ΔV _{E, C} the reducing agent solution via the third metering valve C executed, then a measurement 342 the pressure p _{En, C} after dosing 341 performed and from these a pressure difference Δp _{E, C} for the third metering valve C calculated 343 , The dosing ratio α _C for the third metering valve C then becomes the pressure difference Δp _{E, C} and the metered volume ΔV _{E, C} for its metering 342 determined 350 , Also for this dosing ratio α _C An averaging can be carried out in the manner already explained.

In a comparison 360 Now the three metering ratios α _A . α _B and α _C compared with each other. The three metering ratios are correct α _A . α _B and α _C no error is detected and the procedure is repeated. However, one of the dosing ratios deviates α _A . α _B or α _C From the other two, is the associated metering valve A . B or. C recognized as faulty. Specifically, when the dosing ratio α _A for the first metering valve A from the other two dosing ratios α _B and α _C deviates, the first metering valve A recognized as faulty 370 , Analog is when the dosing ratio α _B for the second metering valve B of the other two metering ratios α _B and α _C deviates, the first metering valve B detected as faulty 371 and, if the dosing ratio α _C for the third metering valve C from the other two dosing ratios α _A and α _B deviates, the third metering valve C recognized as faulty 372 ,

5 shows a flowchart of a third embodiment of the method according to the invention, which is a modification of the first embodiment. Like reference numerals indicate like steps for their description 3 is referenced. At the beginning of the process, a measurement takes place 400 the pressure p _Fv before a sponsoring 401 the feed pump 41 , It will be a pump stroke of 141 the feed pump 41 to promote 401 of a funded volume ΔV _F the reducing agent solution in the pressure line 3 executed. Following is a measurement 401 the pressure p _Fn after promoting 401 carried out. From the pressure p _Fv before the conveying 401 and the pressure p _Fn after promoting 401 is a pressure difference occurring during the promotion Δp _F calculated 403 , From the calculated pressure difference Δp _F for the promotion and the funded volume ΔV _F the reducing agent solution is a delivery ratio according to formula 2 γ determined 404 ,

Following in the manner already described, the metering ratio α _A of the first metering valve A determined 210 , The dosing ratio α _A of the first metering valve A is calculated with the previously calculated delivery ratio γ according to formula 3 in relation to a pressure ratio φ _A for the first metering valve A to calculate 410 , In the same way, the metering ratio α _B of the second metering valve B determined 230 and also a pressure ratio φ _B for the second metering valve B from this dosing ratio α _B and the funding ratio γ calculated 430 , In a comparison 440 it is determined whether one of the two pressure conditions φ _A and φ _B deviates from 1. Are both pressure conditions φ _A and φ _B Approximately 1, no error in the SCR system 1 detected and the procedure is (if necessary including additional dosing valves) repeated. Dodges at least one of the two pressure conditions φ _A or and φ _B from 1, will be a mass error in the SCR system 1 recognized. However, this quantity error can also be caused by a faulty delivery pump 41 originate. In the event that at least one of the two pressure conditions φ _A and or φ _B deviates from 1, therefore, a comparison is made 460 the two already calculated pressure conditions φ _A and φ _B together. Voices the two pressure conditions φ _A and φ _B Accordingly, both deviate equally from 1, becoming an error 470 the feed pump 41 recognized. The two pressure conditions soften φ _A and φ _B from each other, one of the two metering valves A or B be faulty, with the first metering valve A recognized as faulty 471 will if the first pressure ratio φ _A deviates from 1 and the second metering valve B recognized as faulty 472 will if the second pressure ratio φ _B deviates from 1.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10346220 A1 [0002]
• DE 102012218092 A1 [0005]

Claims (14)

Method for checking an SCR system (1), which has a delivery pump (41) and at least two metering valves (A, B, C), one metering valve being faulty and the other metering valves being faultless, comprising the following steps: - determining (210 ) of a metering ratio (α _A ) for one of the metering valves (A) from a pressure difference (Δp _{E, A} , Δp _{E, k} , Δp _{E, K + 1} , Δp _{E, k + 2} ) between a pressure (p _{Ev, A} , p _{Ev, k} , p _{Ev, k + 1} , P _{Ev, k + 2} ) before metering (201, 101, k, k + 1, k + 2) via this metering valve (A) and a pressure (p _{En , A} , p _{En, k} , p _{En, k + 1} , p _{En, k + 2} ) after metering (201, 101, k, k + 1, k + 2) and a metered volume (ΔV _{E, A} , ΔV _{E, k} , ΔV _{E, k + 1} , ΔV _{E, K + 2} ) of a reducing agent solution; Determining (220) at least one further metering ratio (α _B ) for another metering valve (B) from a pressure difference (Δp _{E, B} ) between a pressure (p _{Ev, B} ) before metering (221) via this metering valve (B) and a pressure (p _{En, B} ) after metering (221) and a metered volume (ΔV _{E, B} ) of the reducing agent solution; - comparing (240, 360) the metering ratio (α _A ) of the one metering valve (A) with at least one metering ratio (α _B ) of one of the other metering valves (B); and - detecting a fault (250) if the dosing ratio (α _A ) of one dosing valve (A) deviates from the dosing ratio (α _B ) of the other dosing valve (B). Method according to Claim 1 , characterized in that a metering valve (A, B, C) recognized as defective (370, 371, 372), when its metering ratio (α _A , α _B , a _C ) above a first threshold (S ₁ ) or below a second threshold (S ₂ ). Method according to Claim 1 , characterized in that when the SCR system comprises three or more metering valves (A, B, C), at least one further metering ratio (α _C ) for at least one further metering valve (C) is determined (350) and a metering valve (A , B, C) is recognized as defective (370, 371, 372) if its metering ratio (α _A , α _B , α _C ) of at least two metering ratios (α _A , α _B , α _C ) of other metering valves (A, B , C) deviates. Method according to one of Claims 1 to 3 , characterized in that a pressure ratio (φ _A , φ _B ) of the metering ratio (α _A , α _B ) and a delivery ratio (γ _A , γ _B ), which consists of a pressure difference (Δp _F ) between a pressure (p _Fv ) before a delivery (401) of a reducing agent solution by the feed pump (41) and a pressure (p _Fn ) after the conveying (401) and a delivered volume (.DELTA.V _F ) is determined (403), for a metering (201, 101, k , k + 1, k + 2) (410, 430) and comparing (240) the metering ratios (α _A , α _B ) is performed only when the pressure ratio (φ _A , φ _B ) deviates from 1. Method according to Claim 4 characterized in that the comparison (240) of the metering ratios (α _A , α _B ) is realized by a comparison (450) of the pressure ratios (φ _A , φ _B ) for the respective metering valves (A, B) and an error (461, 462) of the metering valve (A, B) is detected when the pressure ratio (φ _A ) of the one metering valve (A) deviates from the pressure ratio (φ _B ) of the other metering valve (B). Method according to one of the preceding claims, characterized in that in a metering a simultaneous metering request for a plurality of metering valves in alternately successively running metering requests for the metering valves (A, B) is divided. Method according to one of the preceding claims, characterized in that in a dosing a volume of the reducing agent solution to be dosed is distributed over several doses (k, k + 1, k + 2). Method according to one of the preceding claims, characterized in that, in the case of a dosing strategy, a waiting time (tw) is waited between two doses (k, k + 1, 201, 221) carried out in succession. Method according to one of the preceding claims, characterized in that, when the feed pump (41) during a metering (101, k, k + 1, k + 2) promotes reducing agent (141), in this metering (101, k, k +1, k + 2) determined dosing ratio (α _A ) is discarded. Method according to one of the preceding claims, characterized in that for determining (210, 230, 350) of the metering ratio (α _A , α _B , α _C ) a plurality of doses (k, k + 1, k + 2) on the same Metering valve (A, B, C) are executed and the metering ratio (α _A , α _B , α _C ) to a medium metering ratio ( α ) are averaged. Method according to one of the preceding claims, characterized in that a rigidity of the SCR system is taken into account in a dosing strategy. Computer program, which is set up, each step of the procedure according to one of Claims 1 to 11 perform. Machine-readable storage medium on which a computer program is based Claim 12 is stored. Electronic control unit (7), which is set up to operate by means of a method according to one of Claims 1 to 11 to check an SCR system (1) with at least two metering valves (A, B, C).

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