KR20180119496A - Method for operating an scr system with at least two metering valves - Google Patents

Abstract

The present invention relates to a method for operating an SCR system with at least two SCR catalyst converters and at least two metering valves. At least one metering valve is assigned to each SCR catalyst converter, and through the metering valve, a reducing agent solution is metered and supplied for the SCR catalyst converter. The metering and the supplying are separately performed in each time through different metering valves, and through the different metering valves, conversion (62) between the metering and supplying is controlled in accordance with the whole maximum efficiency (e_(gmax1), e_(gmax2)) of the SCR catalyst converter to reduce a nitrogen oxide.

Description

METHOD FOR OPERATING AN SCR SYSTEM WITH AT LEAST TWO METERING VALVES [0002]

 The present invention relates to a method of operation of an SCR system having two or more metering valves, wherein the switching between metering supplies via different metering valves is performed according to the overall efficiency. The present invention also relates to a computer program for executing each step of the method when executed in a computing device and to a machine-readable storage medium storing the computer program. Finally, the present invention relates to an electronic control device configured for carrying out a method according to the present invention.

Currently, SCR (Selective Catalytic Reduction) method is used to reduce nitrogen oxides (NOx) in the exhaust gas at the time of post-treatment of the exhaust gas of the internal combustion engine. DE 103 46 220 A1 describes the basic principle. Here, 32.5% urea aqueous solution (HWL), also known commercially as AdBlue ^® , is metered into the exhaust gas. Typically, a metering valve is provided in the metering module for metering the urea aqueous solution into the exhaust gas flow upstream of the SCR catalytic converter. In the SCR catalytic converter, the urea aqueous solution reacts with ammonia, which will subsequently be combined with nitrogen oxides, from which water and nitrogen are produced. The urea aqueous solution is supplied to the metering module through the pressure line from the reducing agent tank using a supply module having a supply pump.

There is also known an SCR system in which a plurality of SCR catalytic converters acting in combination with the exhaust gas are arranged in the exhaust gas line.

Typically, for example, engine proximity SCR catalytic converters and underfloor SCR catalytic converters are arranged in the form of coatings on particle filters in so-called combination systems. The metering feed of urea aqueous solution is carried out through a plurality of metering valves, and each SCR catalytic converter is assigned a metering valve mounted upstream. Thereby, the desired mass of the reducing agent solution can be precisely metered and supplied. Typically, the metering valve is connected to a common supply module and the metering valve can share at least a portion of the common pressure line.

Such SCR systems are often structurally designed such that the metering feed through the metering valves is not to be carried out simultaneously, but rather should be operated in a strategy that is performed in a time-separated manner. In this case, switching between metering supplies via different metering valves is performed. Strategies with each ammonia charge level of the SCR catalytic converter, a query for each temperature, and / or a fixed conversion time are common.

The method relates to an SCR system for an internal combustion engine having two or more SCR catalytic converters and two or more metering valves. One or more metering valves are assigned to each SCR catalytic converter such that the reducing agent solution for the assigned SCR catalytic converter is metered. On the one hand, since the metering feed is done separately via different metering valves, each SCR catalytic converter is fed individually with the mass of the reducing agent solution provided for it. On the other hand, they are dispensed temporally and metered in rather than being metered simultaneously through different metering valves. In this case, switching between metering supplies of different metering valves is performed. For example, it is metered first through one of the metering valves and then to the metering supply via the other metering valve, at which time the metering feed through the first metering valve is terminated so that the two metering supplies are run in sequence . It is necessary to control the switching between the metering supplies since they are metered in time.

The operating method of the SCR system is provided for controlling the switching between metering supplies via different metering valves according to the maximum overall efficiency of the SCR catalytic converter for the reduction of nitrogen oxides. The efficiency represents the ratio between the mass of reduced NOx in the SCR catalytic converter and the mass of nitrogen oxide entering the SCR catalytic converter. Likewise, the overall efficiency represents the above-mentioned rates corresponding to all the associated SCR catalytic converters. The maximum overall efficiency represents the maximum possible total efficiency for each metering feed.

The individual efficiencies can be calculated, for example, by a suitable model that reproduces the chemical reaction in the catalytic converter based on a reaction kinetics method. As a basic parameter of these calculations, the ambient conditions such as the NOx concentration and / or the NH3 concentration upstream of the catalytic converter, the temperature of the catalytic converter, the exhaust gas mass flow and / or the exhaust gas pressure are required. The NOx concentration and / or NH3 concentration upstream of each catalytic converter may be determined based on the sensor or on a model basis. Similarly, the NH3 concentration upstream of the catalytic converter can be calculated using information on the amount of metered and supplied regenerating means. In order to determine the (individual) efficiency, an inverse proportion of the efficiency may alternatively be used. That is, the efficiency is subtracted from 1. In other words, the efficiency and the inverse proportion are related to each other such that the efficiency and the inversely calculated sum are one. As a result, the inverse proportion of the efficiency can be determined, for example, by the mass of nitrogen oxide, which can be measured by the nitrogen oxide sensor downstream of the SCR catalytic converter and passing through the SCR catalytic converter, Quot; is the ratio between the aforementioned masses of nitrogen oxides that can be measured by the sensor and flow into the SCR catalytic converter.

Preferably, the overall efficiency described above can be calculated as the product of these individual efficiencies. Particularly preferably, an inverse proportion of the individual efficiency is used instead of the individual efficiency, and again, the product is inversely proportional to the product so that the product is subtracted from 1 to calculate the overall efficiency. As a result, the individual efficiencies of the SCR catalytic converters can be used for the calculation of the overall efficiency, and the individual efficiencies can be determined simply for the temporally separate metering feed as described above.

Preferably, instead of individual efficiencies, maximum individual efficiencies may be used in calculating the maximum overall efficiency. This also applies in relation to the inverse proportion of individual efficiencies when maximum individual efficiencies are used instead of individual efficiencies. The maximum individual efficiency reflects the maximum possible efficiency of the SCR catalytic converter when the SCR catalytic converter is operated at the optimal conditions and the desired target ammonia charge level. Preferably, the maximum individual efficiency for the SCR catalytic converter to which the metering valve is to be assigned is also inversely proportional to the individual efficiency, which can be used for the corresponding individual efficiencies. In particular, the maximum individual efficiency can be determined from the model for the SCR catalytic converter at the desired target ammonia charge level.

It can be envisaged that in the calculation of the individual efficiency or overall efficiency, so-called ammonia slip may occur, in which unreacted ammonia passes through one of the SCR catalytic converters, which ammonia charge of the subsequent SCR catalytic converter It can affect the level.

For each SCR catalytic converter placed between the internal combustion engine and the SCR catalytic converter for which the individual efficiencies are calculated, the mass to be reduced of the nitrogen oxides is reduced and the main load of the SCR is applied to the SCR catalytic converter directly connected to the internal combustion engine. From this, a different change of the individual efficiency is formed when the metering supply between the corresponding metering valves is switched. At this time, the individual efficiency of the SCR catalytic converter directly connected to the internal combustion engine is changed most weakly. Therefore, the overall efficiency also changes at the time of conversion.

According to one aspect, a configuration is provided in which, when the overall efficiency after switching is greater, the metering feed through one of the metering valves is switched to the metering feed via the other metering valve. As a result, the metering feed can be controlled such that the overall efficiency for SCR is maximized.

According to another aspect, a configuration may be provided in which, when the mass of the totally reduced nitrogen oxide after the conversion is larger, it is switched from the metering feed via one of the metering valves to the metering feed via the other metering valve. The mass of the totally reduced nitrogen oxide can be calculated directly from the total efficiency and the mass of nitrogen oxide entering the SCR catalytic converter.

In addition, another parameter may be provided that switches from a metering feed via one of the metering valves to a metering feed via another metering valve. These other parameters, when converted from a metering feed through one of the metering valves to a metering feed via another metering valve, directly or indirectly lead or contribute to an increase in the mass of the overall reduced nitrogen oxide, This increase in mass as a whole can be indicated or indicated directly or indirectly. As an example, the nitrogen oxide concentration depends on the mass of the nitrogen oxide.

In particular, a computer program, when executed in an arithmetic or control unit, is configured to perform each step of the method. This enables the implementation of the method in existing electronic control devices without the need for structural modifications to be performed. To this end, the computer program is stored in a machine-readable storage medium.

By executing a computer program in a conventional electronic control device, an electronic control device configured to operate the SCR system is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are shown in the drawings and are described in detail in the following description.
Figure 1 shows a schematic diagram of an SCR system with two metering valves for two SCR catalytic converters which can be operated using an embodiment of the method according to the invention.
Figure 2 shows a flow diagram of a first embodiment of a method according to the invention.
Figure 3 shows a flow diagram of a second embodiment of the method according to the invention.

1 schematically shows an SCR system 1 having two metering modules 11, 12 for two SCR catalytic converters 21, 22 in an exhaust line 30 of the cavity of an internal combustion engine 3 do. The first SCR catalytic converter 21 is arranged immediately downstream of the internal combustion engine and can be provided as a coating layer on, for example, a particle filter. Downstream of the first SCR catalytic converter 21, a second SCR catalytic converter 22 is connected. The first metering module 11 includes a first metering valve 110 through which a reducing agent solution is metered into the exhaust gas line 30 upstream of the first SCR catalytic converter 21. [ Similarly, the second metering module 12 includes a second metering valve 120 through which a reducing agent solution is introduced upstream of the second SCR catalytic converter 22, and in this embodiment, to the first SCR catalytic converter 21). The metering modules 11 and 12 are connected via a pressure line 13 to a supply module 14 comprising a supply pump 140 which supplies the reducing agent solution from the reducing agent tank 15 to the pressure line 13 Supply. The pressure line 13 has a first section 131 which leads to the first weighing module 11 and a second section 132 which leads to the second weighing module 12, . The reducing agent solution is supplied to the first metering valve 110 via the first section 131 of the pressure line 13 and to the first metering valve 110 via the metering supply line 13 to the second metering valve 120 through the second section 132 of the second metering valve 120.

An electronic control unit 4 is also provided which is connected to at least the supply module 14 or the feed pump 140 and the two weighing modules 11 and 12 or the two weighing valves 110 and 120, do. In this case, the metering valves 110, 120 are alternately opened alternately through switching, and thus controlled to be metered and supplied separately in time. To this end, a feed pump 140 provides a desired mass of reducing agent solution for each SCR catalytic converter 21,22, and the reducing agent solution is fed via a metering valve 110,120 to a corresponding SCR catalytic converter 21, 22).

A first nitrogen oxide sensor 41 is also arranged in the exhaust gas line 30 upstream of the SCR catalytic converters 21 and 22 (and of the first metering valve 110) Where it detects at least the incoming mass (m _i ) of nitrogen oxides flowing into the first SCR catalytic converter (21). A second nitrogen oxide sensor 42 is arranged downstream of the SCR catalytic converters 21, 22 for detecting the mass (m ₀ ) of the outgoing nitrogen oxides passing through the SCR catalytic converters 21, 22. A value for the mass m _i which is detected through the two nitrogen oxide sensors 41 and 42 and for the incoming nitrogen oxide and a value for the outgoing mass m _o are transmitted to the electronic control unit 4. In another embodiment, the nitrogen oxide sensors 41 and 42 detect the respective concentration values of the nitrogen oxides in the exhaust gas line 30, which are transferred to the electronic control device 4 and from which the respective amounts of nitrogen oxides The mass (m _i , m _o )

The first SCR catalytic converter 21 is assigned a first discrete efficiency e ₁ and the second SCR catalytic converter 22 is assigned a second discrete efficiency e ₂ . Separate efficiencies e ₁ and e ₂ are obtained for each SCR catalytic converter 21 and 22 by converting the converted mass m _c of nitrogen oxides reduced in each SCR catalytic converter 21 and 22 And the mass m _i introduced into each of the SCR catalytic converters 21, 22, respectively. In this case, it is applied that the first efficiency e ₁ increases and the second efficiency e ₂ decreases when metered and supplied through the first metering valve 110 on the one hand. On the other hand, when metered through the second metering valve 120, it is applied that the second efficiency e ₂ increases and the first efficiency e ₁ decreases. When metered via the second metering valve 120, an unshown ammonia slip through the first SCR catalytic converter 21 must be considered. Because the first SCR catalytic converter 21 is arranged immediately downstream of the internal combustion engine 3, it occupies the main load of the SCR. For this reason, the first efficiency e ₁ is varied to a lesser extent than the second efficiency e ₂ when metered in through each of the other metering valves 110, 120.

Figures 2 and 3 show a flow diagram of a first embodiment or a second embodiment of the method according to the invention. The same reference numerals denote the same steps, and will be described only once in connection with FIG. 2 below.

In the first embodiment shown in FIG. 2, the SCR system 1 is initially operated (50) with a metering feed via the first metering valve 110. However, as shown in FIG. 3 in connection with the second embodiment, the SCR system 1 may well be operated with metering feed through the second metering valve 120 initially in the first embodiment (70) . The measurement 51 of the incoming mass of nitrogen oxide m _i is performed through the first nitrogen oxide sensor 41 and the measurement 52 of the outflow mass m _o of the nitrogen oxide is measured by the second nitrogen oxide sensor 41. [ (42). From this, the total efficiency e _g is calculated (53) according to the following equation (1).

Between the overall efficiency (e _g) it is (not shown in Figure 2), the converted mass (m _c) of the nitrogen oxide and the whole mass that is commonly introduced into to all relevant SCR catalytic converter (21, 22) (m _i) . Equation 2 reflects the relationship between total efficiency e _g and individual efficiency e ₁ , e ₂ .

In another step, a first discrete efficiency e ₁ is determined 54 and a second discrete efficiency e ₂ is determined 55.

Concurrently, a model 56 having a target ammonia charge level (FNH3 _target ) is set for each SCR catalytic converter 21, 22, and ammonia slip by the first SCR catalytic converter 21 is considered. From this model 56 the maximum first efficiency _e1max for the first SCR catalytic converter 21 is determined 57 and on the other hand the maximum second efficiency _e1max for the second SCR catalytic converter 22 is determined, The efficiency ( _e2max ) is determined (58). Thus, the first in the case include the desired target charge level of ammonia SCR catalytic converter (21) (FNH3 _target), up to a first efficiency (e _1max) is the maximum possible efficiency of the first (e _1). Similarly, it also applies for a maximum second efficiency (e _2max ).

In order to calculate the maximum total efficiency (e _gmax1 ) for the metering supply through the first metering valve 110 according to the following equation (3) during the current metering via the first metering valve 110, the maximum efficiency of the first (e _1max) is used in conjunction with the determined second individual efficiency (e ₂₎ (59).

In the same manner, when the metering is supplied through the second metering valve 120, which may be switched at the time of metering, according to the following equation (4), the metering supply via the second metering valve 120 to calculate the maximum efficiency (e _gmax2), up to the second efficiency (e _2max) is used in conjunction with the determined first individual efficiency (e ₁₎ (60).

In the first embodiment, a comparison 61 of the two maximum total efficiencies e _gmax1 , e _gmax2 is performed. When the maximum total efficiency e _gmax2 for metering supply through the second metering valve 120 is greater than the maximum total efficiency e _gmax1 for metering via the first metering valve 110, A conversion (62) is performed for metering feed through the catalytic converter (120) because a larger mass of nitrogen oxides can be reduced thereby. Otherwise, the current metering supply through the first metering valve 110 is maintained (63).

The individual efficiencies can be determined basically, for example, using the corresponding models that reproduce the chemical reactions in the catalytic converter, based on a reaction kinetics method. As a basic parameter of these calculations, the ambient conditions such as the NOx concentration and / or the NH3 concentration upstream of the catalytic converter, the temperature of the catalytic converter, the exhaust gas mass flow and / or the exhaust gas pressure are required. The NOx concentration and / or NH3 concentration upstream of each catalytic converter can be determined based on the sensor and / or on the model. Similarly, the NH3 concentration upstream of the catalytic converter can be calculated using information on the amount of metered and supplied regenerating means.

3, there is shown a second embodiment in which the SCR system 1 is initially operated (70) with a metering feed through a second metering valve 120. Likewise, the SCR system 1 is operatively connected to the metering feed through the first metering valve 110, likewise preferably in the second embodiment, as already explained in Fig. 2 with respect to the first embodiment, . For the description of the second embodiment in Fig. 3, the description of Fig. 2 is referred to. Hereinafter, only the difference from the first embodiment, that is, Fig. 2, will be described. The calculation 71 of the converted mass (m _c ) of the nitrogen oxide, which has been reduced through the two SCR catalytic converters 21 and 22, is executed instead of the calculation 53 of the common efficiency e _g . The calculated mass (m _c ) is calculated (71) using the following equation (5), using the previously determined mass (m _i ) and outgoing mass (m _o ) of the nitrogen oxides.

(M _c ) and the individual efficiencies (e ₁ , e ₂ ) shown in the following equation (6) by using the equations ( ₁ ) and ( ₂ ) Is obtained.

As shown in the following equation (7), the converted mass (m _c ) can also be expressed according to the overall efficiency (e _g ): &_lt; EMI ID ₌

In the course of the addition of the method, in a similar manner, the maximum converted mass (m _cmax1 ) at the time of metering via the first metering valve 110, as shown in equation (8) Is calculated from the efficiency (e _gmax1 ) (72).

Similarly, as shown in equation (9), the maximum converted mass ( _mcmax2 ) at the time of metering via the second metering valve 120 is calculated from the maximum total efficiency (e _gmax2 ) at this metering supply (73).

Then, in the second embodiment, a comparison 74 of the two maximum converted masses of nitrogen oxides ( _mcmax1 , _mcmax2 ) is performed. When the maximum mass m _cmax1 for the metering supply through the first metering valve 110 is greater than the mass m _cmax2 maximally converted for metering through the second metering valve 120, A switching 75 for metering via the metering valve 110 is performed. Otherwise, the current metering feed through the second metering valve 120 is maintained (76).

In other embodiments, for example, the converted mass ( _mc ) of nitrogen oxides, such as nitrogen oxide concentration, or other parameters related to overall efficiency, can be considered. The switching can also be controlled using a corresponding comparison of the parameters for the metering feed via the first metering valve 110 and the metering feed via the second metering valve. The conversion takes place when the overall converted mass (m _c ) (which may be indirectly determined) of the nitrogen oxides after conversion is greater.

It is noted that in the embodiments enumerated herein, only SCR systems having two metering valves 110, 120 for two SCR catalytic converters 21, 22 have been described. This method is also applicable to SCR systems with a larger number of metering valves and / or SCR catalytic converters, unless metered simultaneously through all metering valves.

Claims (9)

A method of operating an SCR system (1) having two or more SCR catalytic converters (21,22) and two or more metering valves (110,120), wherein each SCR catalytic converter (21,22) 110 and 120 through which the reducing agent solution for the assigned SCR catalytic converters 21 and 22 is metered and the metering feed is supplied separately and in time via the different metering valves 110 and 120 A method of operating a separate SCR system,
The switching between metering supplies via different metering valves 110 and 120 is controlled according to the maximum overall efficiencies e _gmax1 and e _gmax2 of the SCR catalytic converters 21 and 22 for the reduction of nitrogen oxides ≪ / RTI > Method according to claim 1, characterized in that the total efficiency (e _g ) is calculated as the product of the individual efficiencies (e ₁ , e ₂ ) of the SCR catalytic converters (21, 22). The method according to claim 2, characterized in that for the calculation of the maximum overall efficiency (e _gmax1 , e _gmax2 ), the maximum individual efficiency (&_quot; e ") for the SCR catalytic converters (21, 22) e _1max, e _2max) is provided, the maximum efficiency of the individual (e _1max, e _2max) is the corresponding individual efficiency _{(e 1, e 2),} SCR systems oPERATING characterized in that is used for that. Of claim 3 wherein the maximum individual efficiency (e _1max, e _2max) is characterized in that the determination of the model 56 of the SCR catalytic converter (21, 22) in the desired target ammonia charge level (FNH3 _target), SCR How the system works. 5. A method according to any one of claims 1 to 4, characterized in that when the maximum total efficiency (e _gmax1 , e _gmax2 ) is greater after the diversion (62, 75) Is switched to a metering supply via the other metering valve (110, 120). 6. A method according to any one of claims 1 to 5, characterized in that when the maximum converted mass of nitrogen oxide ( _mcmax1 , _mcmax2 ) is greater after the conversion (62, 75), one of the metering valves To the metering feed through the other metering valve (110, 120). ≪ Desc / Clms Page number 13 > A computer program configured to execute each step of the method according to any one of claims 1-6. 9. A computer readable storage medium having stored thereon a computer program according to claim 7. An electronic control device (4) configured to operate an SCR system (1) using the method according to any one of claims 1 to 7.

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