SE538317C2 - System and method for performance control of a DOC unit exhaust gas purification system - Google Patents

Abstract

SUMMARY The invention relates to a process in a process for controlling the performance of a DOC unit (260) having an exhaust gas purification system comprising a first NOR sensor 5 (237) upstream of said DOC unit (260) and an SCR catalyst (270) downstream. said DOC unit (260). The process may comprise the steps of: - substantially emptying (s410) said SCR catalyst (270) on reducing agent; - determining (s420) a first NO2 content (NO2mod) has the exhaust gases on the basis of a determined NOR content upstream of said DOC unit (260) and a determined conversion rate (X) concerning conversion to NO2 has the exhaust gas purification system upstream of said SCR catalyst ( 270); - determining (s430) a second NO2 content (NO2measured) has the exhaust gases on the basis of a NH3 content (NH3measured) determined by means of a cross-sensitive NH3 sensor (278) and a NO2-measured cross-function function (F) for said NH3 sensor (278 ); and - assessing performance (s440) has said DOC unit (260) on the basis of said determined first NO2 content (NO2mod) and said determined second NO2 content (NO2measured). The invention also relates to a computer program product comprising program code (P) for a computer (200; 210) for implementing a method according to the invention. The invention also relates to a system for performance control of a DOC unit (260) and a motor vehicle (100) equipped with the system.

Description

TECHNICAL FIELD The present invention relates to a method for performance control of a DOC unit of an exhaust gas purification system. The invention also relates to a computer program product including program code for a computer for implementing a method according to the invention. The invention also relates to a system for performance control of a DOC unit of an exhaust gas purification system and a motor vehicle equipped with the system.

BACKGROUND Exhaust gas cleaning systems of today's motor vehicles include a number of different components. For example, an exhaust gas cleaning system may include a DOC unit (Diesel OxidationCatalyst) arranged in a passage downstream of an internal combustion engine of the vehicle. Other components which may be arranged downstream of said engine are a DP DieselReduction).

Particulate Filter) and a Selective Catalytic SCR Catalyst For many reasons it is desirable to be able to perform performance checks on individual components of exhaust gas cleaning systems in motor vehicles, such as trucks and buses.Performance control of components in exhaust gas cleaning systems in motor vehicles may be desirable and able to perform Performance control of individual components in exhaust gas cleaning systems may in some states be subject to laws, regulations or directives, which of course vehicle manufacturers must adhere to, not least from a competition perspective.

Said DOC unit is arranged to oxidize NO gas from an engine to NO gas. Said DOC unit can in some way convert a smaller amount of NO gas than is required and desirable into NOg gas. In some applications it may be desirable for said DOC unit to have a degree of conversion which is in a range between 40-60 ° />. If the DOC unit exhibits a degraded performance and, for example, only has a conversion rate of 30% or less, it may need to be cleaned, repaired, or replaced. This is of course associated with various costs, not least in terms of materials and working hours for service personnel.

A degradation of performance of said DOC unit can occur for several different reasons.

In cases where the said motor vehicle is equipped with a turbocharger, for example metal parts, such as chips or chips, can become detached and be carried with an exhaust current from the engine to the DOC unit and thereby damage it, which causes a degradation of performance of the DOC unit.

Furthermore, fuel from engine and / or lubricant for the engine and / or lubricant for a turbocharger can be supplied to said DOC unit and thereby cause degradation of its performance.

In cases where said engine is powered by ethanol, this fuel may be mixed with soto and added to said DOC unit, whereby degradation of performance thereof may be caused.

Performance control of the said DOC unit can today only be performed under certain specific conditions and operating conditions of the vehicle. In most cases when diagnosis or function check is to be performed, it must be performed when the DOC unit exceeds a certain temperature. To obtain this temperature, a method involving fuel dosing is used. The DOC unit thereby oxidizes supplied fuel and causes an increase in temperature of exhaust gases which can be measured downstream of said DOC unit, whereby diagnosis of the DOC unit can be performed in this case. For several reasons, it is not always desirable to diagnose a DOC device in this way. Furthermore, it is not even always possible to perform such a diagnosis.

US20120186226 describes a method for diagnosing a DOC unit by means of temperature measurement on an upstream side and a downstream side thereof, respectively.

SUMMARY OF THE INVENTION Thus, there is a need to reliably perform a performance check of a DOC unit of an exhaust purification system of an exhaust purification system of a motor vehicle.

There is a need to efficiently, reliably and user-friendlyly assess a DOC unit of various exhaust gas cleaning systems in terms of performance.

An object of the present invention is to provide a new and advantageous method for performance control of a DOC unit of an exhaust gas purification system.

Another object of the invention is to provide a new and advantageous performance control system of a DOC unit of an exhaust gas purification system and a new and advantageous computer program for performing a performance control of a DOC unit of an exhaust gas purification system.

A further object of the invention is to provide an alternative method of pre-performance control of a DOC unit of an exhaust gas purification system, an alternative system of performance control of a DOC unit of an exhaust purification system and an alternative computer program of controlling a performance control of a DOC unit of an exhaust purification system.

A further object of the invention is to provide a method of an exhaust gas purification system, an apparatus of an exhaust gas purification system and a computer program for achieving a reliable performance control of a DOC unit of a motor vehicle.

A further object of the invention is to provide a method of an exhaust gas purification system, a system of an exhaust gas purification system and a computer program for providing a reliable performance control of a DOC unit of an SCR system, which SCR system may be installed in a motor vehicle.

Some of said objects are achieved with a method for performance control of a DOC unit of an exhaust gas purification system according to claim 1. Other objects are achieved with a performance control system of a DOC unit of an exhaust gas purification system according to claim 8. Advantageous embodiments are stated in the dependent claims.

According to one aspect of the present invention, there is provided a method of pre-performance monitoring of a DOC unit of an exhaust gas purification system comprising a first NOX sensor upstream of said DOC unit and an SCR catalyst downstream of said DOC unit. The process comprises the steps of: - substantially emptying said SCR catalyst of reducing agent; - determining a first NOg content of the exhaust gases on the basis of an determined NOX content upstream of said DOC unit and a determined degree of conversion relating to conversion to NO2 of the exhaust gas purification system upstream of said SCR catalyst, - determining a second NOg content of the exhaust gases on the basis of an a cross-sensitive NHs sensor determined NHs content and a cross-sensitivity function relating to NO 2 said NHs sensor; and - evaluating the performance of said DOC unit on the basis of said determined first NO 2 content and said determined second NO 2 content.

This provides a reliable method for assessing the performance of a DOC unit. Advantageously, no temperature increase in the exhaust system is required to perform said performance control, which provides a fuel efficient process according to an aspect of the invention. The process may comprise the step of: In this case, an accurate method of calculating said first NOg content is provided.

The method may comprise the step of: - determining said cross-sensitivity function concerning NO 2 for said NH3 sensor based on a current operating point indication regarding an engine generating said exhaust gases and / or exhaust gas composition and / or exhaust gas temperature. In this regard, an accurate way of calculating said first NOg content is provided. The cross-sensitivity function indicates a measure of the cross-sensitivity of NO 2 of said ammonia sensor 278. The method may comprise the step of: - determining that the intended emptying of reducing agent of said SCR catalyst has been achieved by measuring said first NOX content upstream of said DOC unit and second DOC unit. content downstream of said SCR catalyst; and - take substantially consistent values of both NOX levels as a criterion for achieving the intended emptying. In this case, a reliable way of determining that emptying has taken place is provided. Furthermore, a reliable and user-friendly procedure for performance checking of a DOC unit is provided.

The method may comprise the steps of: - determining that the intended emptying of reducing agent of said SCR catalyst has been achieved by modeling / calculating said first NOX content upstream of said DOC unit and measuring a second NOX content downstream of said SCR catalyst; and - take substantially consistent values of both NOX levels as a criterion for achieving the intended emptying.

This provides a reliable way of determining that emptying has taken place. Furthermore, a reliable and user-friendly DOC unit performance control procedure is provided.

The method may comprise the step of: - assessing the performance of said DOC unit on the basis of said determined first NOg content and said determined second NOg content, wherein a ratio between said first NOg content and said second NOg content shall be outside a predetermined range to indicate that there is a lack of performance of said DOC unit.

A reliable and user-friendly method for performance control of a DOC unit is provided. The method may comprise the step of: - assessing the performance of said DOC unit on the basis of said determined first NOg content and said determined second NOg content, an absolute difference between said first NOg content and said second NOg content exceeding a predetermined threshold value indicate poor performance of said DOC unit. This provides a reliable and user-friendly DOC unit performance check procedure.

According to one aspect of the present invention, there is provided a pre-performance control system of a DOC unit of an exhaust gas purification system comprising a first NOX sensor arranged upstream of said DOC unit and an SCR catalyst arranged downstream of said DOC unit. The system comprises: means adapted to substantially empty said SCR catalyst reducing agent; means adapted to determine a first NOg content of the exhaust gases on the basis of a single determined NOX content upstream of said DOC unit and an determined conversion rate moving conversion to NO2 of the exhaust gas purification system upstream of said SCR catalyst; means adapted to determine a second NO 2 content of the exhaust gases on the basis of an NH 3 content determined by means of a cross-sensitive NH 3 sensor and a single-cross sensitivity function relating to NO 2 for said NH 3 sensor; and - means adapted to assess the performance of said DOC unit on the basis of said determined first NOg content and said determined second NOg content.

The system may comprise: - means adapted to determine said degree of conversion of the exhaust gas purification system upstream of said SCR catalyst by calculating the parameters exhaust temperature and exhaust mass flow.

The system may comprise: - means adapted to determine said cross-sensitivity function concerning NO 2 said NH 3 sensor based on a current operating point indication regarding an engine generating said exhaust gases and / or exhaust gas composition and / or exhaust gas temperature. The system may comprise: - means adapted to determine the intended discharge of redox of said SCCR catalyst achieved by measuring said first NOX content upstream of said DOC unit and measuring a second NOX content downstream of said SCR catalyst; and - means adapted to take substantially corresponding values of the two NOX levels as a criterion for achieving the intended emptying. The system may comprise: - means adapted to determine that the intended emptying of reducing agent of said SCR catalyst has been achieved by modeling / calculating said first NOX content upstream of said DOC unit; means adapted to measure a second NOX level downstream of said SCR catalyst, and - means adapted to take substantially consistent values of the two NOX levels as a criterion for achieving the intended discharge. The system may include: - means adapted to assess performance of said DOC unit on the basis of said determined first NOg content and said determined second NOg content, wherein the ratio between said first NOg content and said second NOg content shall be outside a predetermined interval to indicate that poor performance of said DOC content unit is available.

The system may comprise: - means adapted to assess the performance of said DOC unit on the basis of said determined first NOg content and said determined second NOg content, an absolute difference between said first NOg content and said second NOg content exceeding a predetermined threshold value. lack of performance of said DOC unit. A motor vehicle DOC is provided. According to an aspect of the present invention, there is provided a performance control system for an exhaust gas purification system according to any one of claims 8-14.

Said motor vehicle may be any of a truck, bus or passenger car.

According to one aspect of the present invention, computer programs are provided in one exhaust gas purification system, said computer program comprising program code for causing an electronic control unit or a computer connected to the electronic control unit to perform the steps according to any one of claims 1-7.

According to one aspect of the present invention, computer programs are provided in an exhaust gas purification system, said computer program comprising program code for causing an electronic control unit or a computer connected to the electronic control unit to perform the steps according to any one of claims 1-7, when said program code runs on said control unit or computer.

According to one aspect of the present invention, there is provided computer programs in one exhaust gas purification system, said computer program comprising program code stored on a computer readable medium for causing an electronic control unit or a computer connected to the electronic control unit to perform the steps of any of claims 1-7.

According to one aspect of the present invention, there is provided computer programs in one exhaust gas purification system, said computer program comprising program code stored on a computer readable medium for causing an electronic control unit or a computer connected to the electronic control unit to perform the steps of any of claims 1-7. when said program code is executed at said control unit or said computer.

According to one aspect of the present invention, there is provided a computer program product comprising a program code stored on a computer readable medium for performing the method steps of any of claims 1-7, when said computer program runs on an electronic control unit or a computer connected to the electronic control unit.

According to one aspect of the present invention, there is provided a computer program product comprising a program code non-volatile stored on a computer readable medium for performing the method steps of any of claims 1-7, when said program code is executed on an electronic controller or computer connected to the electronic controller.

Additional objects, advantages and novel features of the present invention will become apparent to those skilled in the art from the following details, as well as through the practice of the invention. Since the invention is described below, it should be understood that the invention is not limited to the specific details described. Those skilled in the art having access to the teachings herein will recognize additional applications, modifications, and incorporations within other fields which are within the scope of the invention. SUMMARY DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and further objects and advantages thereof, reference is now made to the following detailed description which is to be read in conjunction with the following drawings in which like reference numerals refer to like parts throughout the several figures, and in which: illustrates a vehicle, according to an embodiment of the invention; Figure 2 schematically illustrates a subsystem of the vehicle shown in Figure 1, according to one embodiment of the invention; Figure 3 schematically illustrates a subsystem of the vehicle shown in Figure 1, according to an embodiment of the invention; Figure 4a schematically illustrates a flow chart of a method, according to one embodiment of the invention; Figure 4b schematically illustrates in further detail a flow chart of a method, according to an embodiment of the invention; and Figure 5 schematically illustrates a computer, according to an embodiment of the invention.

DETAILED DESCRIPTION OF FIGURES Referring to Figure 1, a side view of a vehicle 100 is shown. The exemplary vehicle 100 consists of a tractor 110 and a trailer 112. The vehicle may be a heavy vehicle, such as a truck or a bus. The vehicle can alternatively be a car or a tracked vehicle.

Here, the term "link" refers to a communication link which may be a physical line, such as an optoelectronic communication line, or a non-physical line, such as a wireless connection, for example a radio or microwave link.

Here, the term "reductant" refers to an agent used to react to certain emissions in an SCR system. These emissions can e.g. be NOX gas. Said reductant is according to an embodiment so-called AdBlue. Of course, other types of deductants can be used. Here, AdBlue is mentioned as an example of a reductant, but one skilled in the art will recognize that the inventive method and the inventive SCR system can be realized for other types of reductants.

It should be noted that the invention is suitable for application to a suitable exhaust gas purification system comprising a DOC unit, and is thus not limited to a DOC unit of the inventive process and the inventive system is well suited for exhaust gas purification systems comprising a motor vehicle. For other platforms that include an exhaust gas cleaning system than motor vehicles, such as. watercraft. The watercraft can be of any kind, such as e.g. motorboats, ships, ferries or ships.

The inventive method and the inventive system in an exhaust gas purification system according to an aspect of the invention are also well suited for e.g. 11 systems including tractors, dumpers, power tools, industrial engines and / or powered industrial robots.

The inventive method and the inventive system in an exhaust gas purification system according to an aspect of the invention are also well suited for different types of power plants, such as e.g. an electric power plant comprising a diesel generator.

The inventive method and the inventive system of a single exhaust gas purification system are well suited for any engine system which includes a single engine, DOC unit and an SCR system, such as e.g. at a locomotive or other platform.

The inventive method and the inventive system of a single exhaust gas purification system are well suited for a system which includes a NOX generator, for example a diesel engine, the exhaust gases of which are to be purified.

The inventive method and the inventive system of a single exhaust gas purification system are well suited for a system comprising a NOX generator, for example a diesel engine, and a DOC unit.

Here, the term "conduit" refers to a passage for pouring and transporting a fluid, such as e.g. a reductant in liquid form. The pipe can be a pipe of any dimension. The conduit may consist of any suitable material, such as e.g. plastic, rubber or metal. Referring to Figure 2, there is shown a subsystem 299 of the vehicle 100. The subsystem 299 may be located in the tractor 110. The subsystem 299 may form part of an SCR system included in the exhaust purification system according to an aspect of the present invention, which exhaust purification system is described in further detail. with reference to Figure 3.

The subsystem 299 according to this example consists of a container 205 which is arranged to pour a reductant. A first line 271 is arranged to direct the reductant to a single pump 230 from the container 205. Said pump is 230 arranged to pump the up-reductant from the container 205 via the first line 271 and via a second line 272 supply said reductant to a dosing unit 250. The pump 230 is arranged. pressurizing the reductant in the second line 272.

The dosing unit 250 is arranged to supply said reductant to one (see Fig. 3) of 100. the dosing unit 250 is arranged to supply in a controlled manner a suitable amount of exhaust gas purification system to the vehicle More specifically, the scar reductant to an exhaust purification system of the vehicle 100. According to this embodiment, an SCR catalyst (see Fig. 3) arranged downstream of a position where supply of reductant is effected. The amount of reductant added to the exhaust system is intended to be used in the SCR catalyst to reduce the amount of unwanted emissions.

A third conduit 273 is provided between the metering device 250 and the container 205. The third conduit 273 is arranged to return a certain amount of the reductant fed to the metering unit 250 to the container 205.

The first control unit 200 is arranged for communication with the pump 230 via a single link 292. The first control unit 200 is arranged to control operation of the pump 230 for e.g. regulate flows of the reductant within the subsystem 299.

The first control unit 200 is arranged for communication with the dosing unit 250 via a link L250. The first control unit 200 is arranged to control the operation of 250 for the exhaust gas purification system of the vehicle 100. The first control unit 200 is arranged that the dosing unit e.g. regulating the supply of the reductant activating circulation of said reducing agent by means of said pump 230 when deemed appropriate. The first control unit 200 is arranged to activate dosing of said reducing agent when it is judged to be suitable. According to an aspect of the present invention, the first control unit 200 is arranged to shut off the supply of reducing agent to the SCR catalyst in order to substantially empty said SCR catalyst of stored / supplied reducing agent. According to an aspect of the present invention, the first control unit 200 is arranged to shut off the supply of reducing agent to the SCR catalyst in order to substantially completely empty said SCR catalyst of stored / supplied reducing agent. According to one aspect of the present invention, said first control unit 200250 is temporarily arranged to control said dosing unit in such a way that the supply of reducing agent to said exhaust gases ceases. Thus, in performing performance control of said DOC unit of the exhaust gas purification system, an aspect of the present invention no or substantially no reducing agent is added to said SCR catalyst of the exhaust gas purification system. This enables an efficient and accurate performance control of a DOC unit of said exhaust gas purification system.

A second control unit 210 is arranged for communication with the first control unit 200 via a link L210. The second control unit 210 may be releasably connected to the first control unit 200. The second control unit 210 may be a control unit external to the vehicle 100. The second control unit 210 may be arranged to perform the inventive method steps. The second control unit 210 can be used to upload program code to the first control unit 200, in particular program code to perform the inventive method. The second control unit 210 may alternatively be arranged for communication with the first control unit 200 via an internal network in the vehicle. The second control unit 210 may be arranged to perform substantially the same functions as the first control unit 200.

Figure 3 schematically illustrates a subsystem 289 of the vehicle 100 shown in Figure 1, according to an embodiment of the invention. Said subsystem 289 forms part of one exhaust gas purification system of the vehicle 100. Said subsystem 299 described with reference to Figure 2 may also form part of said exhaust gas purification system.

An engine 231 is provided, which in operation causes an exhaust gas flow which is directed via a first passage 235 to a DOC unit 260. A second passage 245 is arranged to direct exhaust gases from said DOC unit 260 to a DPF unit 265. Said DPF unit 265 includes a Diesel Particulate Filter. A third passage 255 is arranged to direct exhaust gases from said DPF unit 265 to an SCR catalyst arrangement 270. Said SCR catalyst arrangement 270 is alternatively referred to as SCR catalyst. A fourth passage 256 is arranged to conduct exhaust gases from said SCF1 catalyst arrangement 270 to an environment of the vehicle 100. Said dosing unit 250 described with reference to Figure 2 is arranged to dose reducing agents into said third passage 255.

It should be noted that said exhaust gas purification system need not necessarily include said DPF unit 265.

The first control unit 200 is arranged for communication with the motor 231 via a single link L231. The first control unit 200 is arranged to control operation of said motor 231. The first control unit 200 is for instance arranged to control fuel metering to the combustion chamber of said engine 231.

Fuel metering means (not shown) may be arranged upstream of said DOC unit 260 and downstream of said engine 231. The first control unit 200 is arranged for communication with said fuel metering means via a dedicated link (not shown). The first control unit 200 is arranged to control dosing fuel, for example diesel, into said first passage 235 by means of said fuel metering means to effect a so-called active regeneration of said DPF unit 265. According to an aspect of the present invention, inactive regeneration needs to be performed according to the inventive method , which provides a relatively inexpensive performance control method of the DOC unit 260.

A first NOX sensor 237 is arranged upstream of said DOC unit 260, said first passage 235. Said first NOX sensor 237 is arranged pre-communication with the first control unit 200 via a link L237. Said first NOX sensor 237 is arranged to continuously determine a saving NOX content NOX1 in the first passage 235. Said first NOX sensor 237 is arranged to continuously send signals S237 including information about a saving NOX content NOX1 in said first passage 235 to the first control unit. 200 via link L237.

A second NOX sensor 277 is arranged downstream of said SCR catalyst 270, said fourth passage 256. Said second NOX sensor 277 is arranged pre-communication with the first control unit 200 via a link L277. Said second NOX sensor 277 is arranged to continuously determine a current NOX content NOX2 in the fourth passage 256. Said second NOX sensor 277 is arranged to continuously send signals S277 including information about a current NOX content NOX2 in said fourth passage 256 to the first fourth passage 256. the control unit 200 via the link L277.

Said first NOX sensor 237 and said second NOX sensor 277 may be used to provide information on prevailing NOX content in the first passage 235 and the fourth passage 277, respectively. In this case, the first control unit 200 may be arranged to determine that intended emptying of reducing agent of said SCR catalyst 270 is achieved by measuring said first NOX content NOX1 upstream of said DOC unit 260 and measuring said second NOX content NOX2 downstream of said SCR catalyst 270, and taking substantially corresponding values of the two NOX levels as a criterion to be emptying is achieved.

According to one embodiment, said first NOX sensor 237 is arranged in the first passage 235, upstream of said DOC unit 260 and downstream of said engine 231 to continuously measure / detect / determine a first NOX content of the NOX1 exhaust gases there and said second NOX sensor 277 is arranged downstream of said SCR catalyst 270 to continuously measure / detect / determine a second NOX content NOX2 of the exhaust gases from the engine 231.

A temperature sensor 233 is arranged upstream of said DOC unit 260, said first passage 235. Said temperature sensor 233 is arranged pre-communication with the first control unit 200 via a link L233. The said temperature sensor 233 is arranged to continuously measure / detect / determine a single temperature T1meas of the exhaust gases in the first passage 235. The said temperature sensor 233 is arranged to continuously send signals S233 including information about a current temperature T1meas of the first exhaust gases in the first exhaust gases 200 in the first passage 23. link L233.

According to one embodiment, the first control unit 200 is arranged to determine by means of a calculation model stored therein a prevailing temperature T1cal of the exhaust gases in the first passage 235. Said prevailing temperature T1cal of the exhaust gases in the first passage 235 can be determined on the basis of e.g. a determined exhaust mass flow and a measured amount of fuel metered to the engine 230. Thus, the said rescue temperature T1cal can be calculated / modeled / estimated in a suitable manner by the said first control unit 200. According to an aspect of the present invention, at least some of said temperatures T1meas and T1cal can be used to model, for example, a degree of conversion X and cross-sensitivity function F.

A sensor (not shown) for measuring a saving exhaust mass flow l / IF may be provided in the first passage 235. Said exhaust mass flow sensor is arranged to continuously determine a saving exhaust mass flow l / IF in the first passage 235 and send signals including the information including first control unit 200 via a dedicated link (not shown).

According to one embodiment, the first control unit 200 is arranged to determine by means of a calculation model stored therein a rescuing exhaust gas mass l / / IF in the first passage 235. Said rescuing exhaust gas mass l \ / IF in the first passage 235 can be determined on the basis of e.g. a determined operating condition of the motor 231.

The first control unit 200 is according to one embodiment arranged to determine a first control unit 200 is according to one embodiment arranged to determine a second NOX content of exhaust gases upstream of said DOC unit 260. The first exhaust gases downstream of said SCR catalyst 270.

According to one embodiment, the first 200 is arranged to calculate / model / estimate said first NOX content NOX1 with a model stored therein.

An ammonia sensor 278 is provided with said SCR catalyst 270. According to an alternative embodiment, said ammonia sensor 278 is arranged downstream of said SCR catalyst 270 in the fourth passage 256. Said ammonia sensor 278 is arranged for communication with the first control unit 200 via a link L 278. arranged to continuously determine a rescue ammonia content in the NHsmeasured SCR catalyst 270 or in the fourth passage 256. Said ammonia sensor 278 is arranged to continuously send signals S278 17 the SCR catalyst 270 or a prevailing ammonia content NHsmeasured in said quarter link L27. The ammonia sensor 278 is cross-sensitive to NO2. This is an important aspect of the comprehensive information on a salvaging ammonia content NHsmeasured in passage 256 to the first control unit 200 via the inventive method.

The first control unit 200 is arranged to continuously or intermittently determine the first NOg content NO2 mode with respect to NOg gas of the exhaust gases on the basis of a determined first NOX content NOX1 upstream of said DOC unit 260 and a determined degree of conversion X relating to conversion to NO2 of the exhaust gas purification system SC catalyst 270. Said degree of conversion X can be determined on the basis of said determined exhaust gas temperature T1meas and / or T1cal and said determined exhaust gas mass flow l1 / IF. Said degree of conversion X can be determined continuously or intermittently based on relevant determined values, said determined exhaust gas temperature T1meas and / or T1cal and said determined exhaust gas mass flow l1 / IF. Said degree of conversion X can be determined continuously or intermittently based on a thermal inertia of the exhaust gas purification system. Said conversion degree X can be determined continuously or intermittently based on the relevant determined values of said determined exhaust gas temperature T1meas and / or T1cal and said determined exhaust gas mass flow l1 / IF and a thermal inertia of the exhaust gas purification system. A measure of said thermal inertia can be modeled / calculated / estimated by means of the first control unit 200. Said degree of conversion X indicates the degree to which NO gas is converted to NOg gas of said DOC unit 260.

The first control unit 200 may be arranged to model / calculate / determine said degree of conversion X on the basis of said determined exhaust gas temperature T1meas and / or T1 cal, said determined exhaust gas mass flow l1 / IF and a thermal inertia of the exhaust gas purification system.

Said degree of conversion X can be stated in percent (° / -. ~).

The first comparative content NO2mod is stated here, the product of said determined first NOX content NOX1 and said degree of conversion X. 18 NOX1 * X = NO2mod The first control unit 200 is arranged to continuously or intermittently determine another NO2 content NO2measured of the exhaust gases on the basis of a fixed content of NH at said SCR unit 270, or in said fourth passage 256, and a cross-sensitivity function F relating to NO 2 for said NH 3 sensor 278.

A cross-sensitivity related to NO 2 for said NH 3 sensor 278 can alternatively be determined on the basis of said determined exhaust gas temperature T1meas and / or T1cal, said determined exhaust gas mass flow MF and a measured thermal inertia in the exhaust gas purification system. Said cross-sensitivity can according to another alternative be determined on the basis of a prevailing operating point / operating condition of said engine 231. Said cross-sensitivity can be determined continuously or intermittently based on relevant determined values of said determined exhaust gas temperature T1mea and / or T1cal and said determined exhaust / gas / operating operating point of said engine 231 and / or and a measured thermal inertia in the exhaust gas purification system. Said cross-sensitivity indicates a measure of the cross-sensitivity to NO 2 of said ammonia sensor 278. Said cross-sensitivity function F can be determined in a suitable manner on the basis of said cross-sensitivity. Board cross-sensitivity function F can be a predetermined cross-sensitivity function.

The first control unit 200 is arranged to model / calculate / determine said cross-sensitivity on the basis of said determined exhaust gas temperature T1meas and / or T1cal and said determined exhaust mass flow l1 / IF and / or said rotational operating state of said engine 231 and / or a measured thermal fatigue the exhaust gas purification system.

Said cross-sensitivity function F can be specified in a suitable manner.

In this case, said second NO 2 content NO 2 measured is the product of said determined NH 3 content NHsmeasured and said cross-sensitivity function F.

NHsmeasured * F = NO 2measured 19 According to one aspect of the present invention, said first NOg content NOgmod and said second NOg content NOgmeasured are used to assess the performance of said DOC unit 260. In that case, said first NOg content NOgmod and said second NOg content NOgmeasured differs from too much, it can be determined that the said DOC unit 260 is defective to a certain extent. The magnitude of an absolute difference between said first NOg content NOgmod and said second NOg content NOgmeasured may indicate a measure of the degree to which said DOC unit 260 is defective.

According to one embodiment, the first control unit 200 is arranged to stop supplying a reducing agent to said exhaust gases in order to enable correct performance control of said DOC unit 260 according to an aspect of the method according to the invention.

The first control unit 200 may be arranged to control the emptying of said SCR catalyst 270 on reducing agent by interrupting / preventing dosing by means of said dosing unit 250.

The first control unit 200 may be arranged to determine a first NO 2 content NO 3 mode of the exhaust gases on the basis of a determined NOX content NOX 1 upstream of said DOC unit 260 and a determined degree of conversion X relating to conversion to NO 2 of the exhaust gas purification system upstream of said SCR catalyst 270.

The first control unit 200 may be arranged to determine a second NOg content NOgmeasured of the exhaust gases on the basis of a NHs content NHsmeasured determined by said cross-sensitive NH3 sensor 278 and a cross-sensitivity function NO2 for said NHs sensor 278. The first control unit 200 may be arranged to assess the performance of the DOC unit 260 on the basis of the said first NOg content NOgmod and the said second NOg content NOgmeasured.

The first control unit 200 may be arranged to determine said degree of conversion X of the exhaust gas purification system SCR catalyst 270 by calculation including the parameters exhaust temperature T1meas and / or T1cal, exhaust mass flow l1 / IF and a measured thermal inertia in the exhaust gas purification system.

The first control unit 200 may be arranged to determine said cross-sensitivity moving NO 2 of said NH 3 sensor 278 based on a current operating point indication with respect to said engine 231 generating said exhaust gases and / or exhaust gas composition and / or exhaust gas temperature. The first control unit 200 can be arranged to determine said exhaust composition in a suitable manner, for example by modeling / calculation / estimation on the basis of suitable parameters.

The first control unit 200 may be arranged to determine that the intended emptying of reducing agent of said SCR catalyst 270 has been achieved by measuring said first NOX content NOX1 upstream of said DOC unit 260 and measuring said second NOX content NOX2 downstream of said SCR catalyst 270. the first control unit 200 may be arranged to take substantially corresponding values at the two NOX levels as a criterion for achieving the intended emptying.

According to one embodiment, the first control unit 200 is arranged to calculate / model / estimate / determine that the intended emptying of reducing agent of the SCR catalyst 270 has been achieved. This can be done by means of a calculation model stored in a memory. The first control unit 200 may be arranged to calculate / model / estimate / determine that emptying of reducing agent of said SCR catalyst 270 has been achieved on the basis of at least some of the parameters exhaust gas temperature (Tfcal, T1meas) exhaust gas flow I / IF and thermal exhaust purification of the NOX1 content upstream of said DOC unit 260. Said calculation is based according to an embodiment on at least one of the mentioned parameters where the supply of reducing agent has been interrupted and the essential reduction agent is stored in the SCR catalyst. The first control unit 200 can be arranged to determine / model / calculate / estimate a measured thermal inertia in the exhaust gas purification system. A measure of thermal inertia may be predetermined and stored in a memory in the first control unit 200.

The first control unit 200 may be arranged to judge the performance of said DOC unit 260 on the basis of said determined first NO 2 content NO 2 mode and said determined second NO 2 content NOgmeasured, a ratio between said first NO 2 21 content NO 2 mode and said second NO 2 NO2measured content shall be outside a predetermined interval I to indicate that there is a lack of performance of the DOC unit 260.

The first control unit 200 may be arranged to assess the performance of said DOC unit 260 on the basis of said determined first NO2 content NO2mod and said determined NOg content NO2measured, an absolute difference, | NO2 mod- NOzmeasuredL between said first NO2 content NO2mod and said second NO2 content NO2measured exceeding a predetermined threshold TH1 indicates poor performance of said DOC unit 260.

Presentation means 220 are arranged for communication with said first control unit 200 via a link L220. The first control unit 200 is arranged to present a result of said performance control of said DOC unit 260. Said result may, for example, indicate "satisfactory function" or "defective". The example whisper a degree of disability of said DOC unit is presented, the degree of disability can be stated in percent. Said presentation means 220 may include speakers for reproducing synthesized voice or other audio letter coupling. Said display means 220 may comprise a display screen, for example a so-called touch screen for visual feedback of said results.

According to an embodiment of the inventive method and the system for pre-performance control of said DOC unit 260, said ammonia sensor 278 may include a NOX sensor for measuring a prevailing NOX content in the exhaust gas stream from said engine. Said built-in NOX sensor can in this case be arranged to determine a prevailing NO2 content where said ammonia sensor 278 is present. In this case, an alternative embodiment of the present invention would involve determining said second NO2 content and using this measured instead of said cross-sensitivity function determining second NO2 content NO2 as a basis for assessing the performance of said DOC unit 260. According to one variant, this alternative embodiment may constitute a complement to using said cross-sensitivity function F to determine said NOz content NOzmeasured. Figure 4a schematically illustrates a flow chart of a pre-performance control process of a DOC unit 260 of an exhaust gas purification system comprising a first NOX sensor 221 upstream of said DOC unit 260 and an SCR catalyst 27 downstream of said DOC unit 260. The process comprises a first process. Step s401 includes the steps of: - substantially emptying said SCR catalyst 270 on reducing agent; determining a first NO 2 content NO 2 mode of the exhaust gases on the basis of a determined NOX content upstream of said DOC unit 260 and a determined degree of conversion X-related conversion to NO 2 of the exhaust gas purification system upstream of said SCR catalyst 270; - determining a second NO2 content NO2measured of the exhaust gases on the basis of an NH3 content determined by a cross-sensitive NH3 sensor 278 and a cross-sensitivity function Touching NO2 for said NH3 sensor 278; and - judging the performance of said DOC unit 260 on the basis of said determined first NO2 content NO2 NO2mod and said determined second NO2 content NO2measured.After the process step s401, the process is terminated. method of Figure 4b flow chart of a performance check of a DOC unit 260 of an exhaust gas purification system comprising one schematically illustrates a first NOX sensor 221 upstream of said DOC unit 260 and an SCR catalyst270 downstream of said DOC unit 260.

The method includes a first method step s410. Process step s410 rabbit comprises the step of substantially emptying said SCR catalyst 270 of reducing agent.

Method step s410 may include the step of shutting down reducing agent dosing by said dosing unit 250 and waiting a predetermined time before the method proceeds.

Process step s410 may include the step of determining that the intended emptying of reducing agent of said SCR catalyst 270 is achieved by measuring said first NOX content upstream of said DOC unit 260 and measuring a second NOX content downstream of said SCR catalyst. If the values of the two NOX levels are substantially equal, this can be taken as a criterion that the intended emptying has been achieved.

Process step s410 may include the step of calculating / modeling / estimating / determining that the intended emptying of reducing agent of said SCR catalyst 270 has been achieved. This can be done by means of a calculation model stored in a memory of the first control unit 200. The first control unit 200 can be arranged to calculate / model / estimate / determine that emptying of reducing agent of said SCR catalyst 270 has been achieved on the basis of at least some of the parameters T1meas), exhaust mass flow l / IF, thermal inertia of the exhaust gas purification system and said first NOX content NOX1 upstream of said DOC unit 260. Said calculation is based according to one embodiment on at least one of said parameters when the supply of reducing agent has been interrupted in the scrubber. catalyst.

After the process step s410, a subsequent process step s420 is performed.

Process step s420 comprises the step of determining s420 a first NO 2 content NO mode of the exhaust gases based on a determined NOX content upstream of said DOC unit 260 and a determined degree of conversion X relating to conversion to NO 2 of the exhaust gas purification system upstream of said SCR catalyst 270.

The process step s420 may comprise determining said degree of conversion X on the basis of information on a salvage exhaust gas flow l \ / IF and a salvage temperature of exhaust gases upstream of said DOC unit 260. Said degree of conversion X may be modeled / calculated / estimated / determined appropriately.

After the process step s420, a subsequent process step s430 is performed. second NOg content NOgmeasured of the exhaust gases on the basis of a by means of a cross-sensitive NH 3 sensor 275 The process step s430 comprises the step of determining a 24 determined NH 3 content and a cross-sensitivity function F relating to NO 2 for said NH 3 sensor 275.

Process step s430 may comprise determining said NO 2 cross-sensitivity of said NH 3 sensor 278 on the basis of information of a prevailing exhaust gas mass MF and a prevailing exhaust gas temperature upstream of said DOC unit 260. Process step s430 may comprise said NH 2 sensitivity. 278 on the basis of at least one of: information on a prevailing exhaust gas mass flow l \ / IF, a prevailing temperature of exhaust gases upstream of the DOC unit 260, exhaust gas composition. The process step s430 may include determining said thermal inertia of the exhaust gas purification system and cross-sensitivity related to NO 2 for said NH 3 sensor 278 on the basis of information about an existing operating condition of the vehicle 100 and / or operating condition of the engine 231. The said NO / 2 may be determined for 27 appropriate way. cross-sensitivity regarding said NHs sensor After the process step s430, a subsequent process step s440 is performed.

Step s440 may include the step of judging the performance of said DOC unit 260 on the basis of said determined first NO 2 content NO 2 mode and said determined second NO 2 content NO 2 measured. This can be done in a number of different ways.

According to an example, the performance of said DOC unit can be judged on the basis of said determined first NO2 content NO2 mode and said determined second NO2 content NO2measured, wherein a ratio between said first NO2 content NO2 mode and said second NO2 content NO2measured shall be outside a predetermined range. to indicate that there is a lack of performance of the DOC unit 260.

According to an example, the performance of said DOC unit can be judged on the basis of said determined first NO 2 content NO 2 mode and said determined second NO 2 content, an absolute difference between said first NO 2 content and said second NO 2 content NO 2 measured exceeding a predetermined threshold value indicating poor performance of the DOC unit 260.

After the process step s440, a subsequent process step s450 is performed.

The method step s450 comprises the step of presenting a result of said performance control of said DOC unit 260. This may be done by said presentation means 220 and said first control unit 200. In this case a result relating to a saving performance of said DOC unit 260 may be presented to, for example, an operator of the vehicle 100 or service personnel. Said result may, for example, include information on whether said DOC unit 260 exhibits satisfactory function, limited function or non-existent function, with respect to degree of conversion or other performance. After the process step s450, a subsequent process step 460 is performed.

The method step s460 comprises the step of taking at least one eating action of the vehicle 100 and / or the exhaust system and / or the subsystem 299 and / or the subsystem 289 and / or another system as associated with the vehicle 100.

Said measure may be determined on the basis of said assessment of the performance of said DOC unit 260. Said measure may be determined on the basis of information on the size of the final degradation regarding the assessed performance of said DOC unit 260. For a case where said degradation size exceeds a predetermined value / saturation said DOC unit 260 is diagnosed as "defective". To diagnose said DOC unit 260 being defective is in this case to determine an eating measure.

Another example of action may be to control SCR control on the basis of the size of said downgrade with respect to said DOC unit 260. In case said DOC unit 260 is to some extent functionally impaired, for example overdosing of reducing agent by means of said dosing unit 250 may be performed. Another example of action may be to actively control the operation of the vehicle engine 231 based on the magnitude of said degradation with respect to said DOC unit 260 to avoid operation of the engine 231 at certain undesired operating points.

After the procedure step s460, the procedure is terminated. Referring to Figure 5, there is shown a diagram of an embodiment of a device 500. The controllers 200 and 210 described with reference to Figure 2 and Figure 3 may in one embodiment include the device 500. The device 500 includes a non-volatile memory 520, a data processing unit 510 and a read / write memory 550. The non-volatile memory 520 has a first memory portion 530 in which a computer program, such as an operating system, is stored to control the operation of the device 500. The device 500 further includes a bus controller, a serial communication port , I / O means, an A / D converter, a time and date input and transfer unit, a single event counter and an interrupt controller (not shown). The non-volatile memory 520 also has a second memory portion 540.

A computer program P is provided for controlling the performance control of a DOC unit 260 of an exhaust gas purification system comprising a first NOX sensor 237 upstream of said DOC unit 260 and an SCR catalyst 270 downstream of said DOC unit 260.

The computer program P may include routines for controlling an emptying process of said SCR catalyst 270 to substantially empty the SCR catalyst 270 reducing agent.

The computer program P may comprise routines for determining a first NO 2 content NO 2 modhos the exhaust gases on the basis of a fixed NOX content NOX1 upstream of said DOC unit 260 and a determined degree of conversion X relating to conversion to NO 2 hos exhaust gas purification system upstream of said SCR catalyst 270.

The computer program P may comprise routines for determining a second NO 2 content NOgmeasured of the exhaust gases on the basis of an NHs content NHseasured by means of a cross-sensitive NH 3 sensor 278 and a cross-sensitivity function F relating to the said NH 3 sensor 278.

The computer program P may comprise routines for assessing the performance of said DOC unit 260 on the basis of said determined first NOg content NOgmod and said determined NOg content NOgmeasured. The computer program P may comprise routines for determining said degree of conversion Xhos the exhaust gas purification system upstream of the SCR catalyst 270 through calculation including the parameters exhaust temperature T1meas, T1 cal, exhaust gas mass flow l \ / IF and a measured thermal inertia of the exhaust gas purification system.

The computer program P may include routines for determining said cross-sensitivity moving NO 2 of said NH 3 sensor 278 based on a current operating point indication regarding an engine 231 generating said exhaust gases.

The computer program P may include routines for determining said cross-sensitivity function F regarding NO 2 for said NH 3 sensor 278 based on a current operating point indication regarding an engine 231 generating said exhaust gases.

The computer program P may include routines for determining that the intended emptying of reducing agent of said SCR catalyst 270 is achieved by measuring said first NOX content NOX1 upstream of said DOC unit 260 and measuring second NOX content NOX2 downstream of said SCR catalyst P0. include procedures for taking substantially consistent values of the two NOX levels as a criterion for achieving the intended emptying.

The computer program P may comprise routines for: - determining that the intended emptying of reducing agent of said SCR catalyst 270 is achieved by modeling / calculating said first NOX content NOX1 upstream of said DOC unit 260 and measuring a second NOX content of NOX2 downstream of said SCR catalyst. 270; and - take substantially consistent values of the two NOX levels as a criterion for achieving the intended emptying.

The computer program P may comprise routines for calculating / modeling / estimating / determining that the intended emptying of reducing agent in said SCR catalyst 270 is achieved. The computer program P may comprise routines for evaluating the performance of said DOC unit 260 on the basis of said determined first NOg content NO2mod and said determined NOg content NOgmeasured, wherein a ratio between said first NO2 content NO2mod and said second NO2 content NO2measured shall be outside a predetermined interval I to indicate that there is a lack of performance of the DOC unit 260.

The computer program P may comprise routines for evaluating the performance of said DOC unit 260 on the basis of said determined first NO 2 content NO2mod and said determined second NO 2 content NOzmeasured, an absolute difference between said first NO 2 content NO 2 mod and said second NO 2 content NO2measured exceeding a predetermined threshold value TH1 indicates poor performance of the DOC unit 260.

The program P can be stored in an executable manner or in a compressed manner in a memory 560 and / or in a read / write memory 550.

When it is described that the data processing unit 510 performs a certain function, it should be understood that the data processing unit 510 performs a certain part of the program which is stored in the memory 560, or a certain part of the program which is stored in the read / write memory550.

The data processing device 510 can communicate with a data port 599 via data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read / write memory 550 is assigned to communicate with the data processing unit 510 via a data bus 514. To the data port 599, e.g. links L210, L220, L233, L237, L250, L277, L278, and L292 are connected (see Figure 2 and Figure 3).

When data is received on the data port 599, it is temporarily stored in the second memory part540. When the received input data has been temporarily stored, the data processing unit 510 is arranged to perform code execution in a manner described above. According to one embodiment, signals received at the data port 599 include information on 29 Parts of the methods described herein may be performed by the device 500 using the data processing unit 510 running the program stored in the memory 560 or read / write memory 550. When the device 500 runs the program, the methods described herein are executed.

The foregoing description of the preferred embodiments of the present invention has been provided for the purpose of illustrating and describing the invention. It is not intended to be exhaustive or to limit the invention to the variations described. Obviously, many modifications and variations will occur to those skilled in the art. The embodiments were selected and described in order to best explain the principles of the invention and its practical applications, thereby enabling those skilled in the art to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims (18)

PATE NTKRAV A method of performance checking a DOC unit (260) of an exhaust gas purification system comprising a first NOR sensor (237) upstream of said DOC unit (260) and an SCR catalyst (270) downstream of said DOC unit (260), characterized by the steps of: - substantially empty (s410) said SCR catalyst (270) on reducing agent; - determining (s420) an initial NO2 content (NO2mod) of the exhaust gases on the basis of a fixed NON content (N0,1) upstream of said DOC unit (260) and a fixed degree of conversion (X) of the NO2 of the exhaust gas purification system upstream named SCR catalyst (270); - determining (s430) a second NO2 content (NO2measured) has the exhaust gases on the basis of a NH3 content (NH3measured) determined by means of a cross-sensitive NH3 sensor (278) and a NO2-measured cross-function function (F) for said NH3 sensor (278 ); and - assessing performance (s440) has said DOC unit (260) on the basis of said determined first NO2 content (NO2nriod) and said determined second NO2 content (NO2measured). The process of claim 1, comprising the step of: - determining (s420) said degree of conversion (X) of the exhaust gas purification system 20 upstream of said SCR catalyst (270) by calculating the parameters exhaust temperature (Tlmeas; Ti cal), exhaust mass flow (MF) and thermal fidelity of said exhaust gas purification system. A method according to claim 1 or 2, comprising the step of: - determining (s430) said cross-probability function (F) concerning NO2 for said NH3 sensor (278) based on a current operating point indication regarding an engine (231) generating said exhaust gases, exhaust composition and exhaust temperature. A process according to any one of the preceding claims, comprising the steps of: - determining (s410) that the intended emptying of reducing agent of said SCR catalyst (270) has been achieved by all feeding said first NOR content (NO1) upstream of said DOC unit (260). ) and feeding a second NO 2 content (NO 2) downstream of said SCR catalyst (270); and - take (s410) essentially the corresponding value of the two NOx levels as a criterion that the intended emptying has been achieved. A method according to any one of claims 1-3, comprising the steps of: - determining (s410) that the intended emptying of reducing agent of said SCR catalyst (270) has been achieved by modeling / calculating said first NO content (NO1) tightening said DOC unit (260) and feeding a second NOx content (NO2) downstream of said SCR catalyst (270); and - take (s410) essentially the corresponding value of the two NOx levels as a criterion that the intended emptying has been achieved. A method according to any one of the preceding claims, comprising the step of: - judging the performance (s440) of said DOC unit (s260) on the basis of said determined first NO2 content (NO2mod) and said determined second NO2 content (NO2measured), wherein a ratio between said first NO2 content (NO2mod) and said second NO2 content (NO2measured) shall be outside a predetermined interval (I) may indicate that there is a lack of performance of said DOC unit (260). A method according to any one of claims 1-5, comprising the step of: - performing (s440) the performance of said DOC unit (260) on the basis of said determined first NO2 content (NO2mod) and said determined second NO2 content (NO2measured). ), wherein an absolute difference (NO2 mod— NO2measured) between said first NO2 content (NO2mod) and said second NO2 content (NO2measured) exceeding a predetermined threshold value (TH1) indicates poor performance of said DOC unit (260). A system for controlling the performance of a DOC unit (260) of an exhaust gas purification system comprising a first NOR sensor (237) arranged upstream of said DOC unit (260) and an SCR catalyst (270) arranged downstream of said DOC unit (260). ), characterized by: - means (200; 210; 500; 250) adapted to substantially empty said SCR catalyst (270) on reducing agent; means (200; 210; 500) adapted to determine a first NO2 content (NO2 mode) of the exhaust gases on the basis of a fixed NOx content (NO1), said DOC unit (260) and a fixed degree of conversion (X) are converted. to the NO 2 of the 31 exhaust gas purification system upstream said SCR catalyst (270); means (200; 210; 500) adapted to determine a second NO2 content (NO2measured) of the exhaust gases on the basis of a NH3 content (NH3measured) determined by means of a crucible NH3 sensor (278) and a crucifixion function (F) concerning NO2 for said NH3 sensor (278); and - means (200; 210; 500) adapted to assess the performance of said DOC unit (260) on the basis of said determined first NO2 content (NO2mod) and said determined second NO2 content (NO2measured). A system according to claim 8, comprising: - means (200; 210; 500) adapted to determine said degree of conversion (X) of the exhaust gas purification system upstream of said SCR catalyst (270) by calculating including the parameters exhaust temperature (Tlmeas; TI cal), exhaust mass flow ( MF) and thermal inertia of said exhaust gas purification system. A system according to claim 8 or 9, comprising: - means (200; 210; 500) adapted to determine said cranial function (F) concerning NO2 for said NH3 sensor (278) based on a current operating point indication relating to an engine (231) generating named exhaust gases, exhaust gas composition and exhaust gas temperature. A system according to any one of claims 8-10, comprising: - means (200; 210; 500; 237, 277) adapted to determine that the intended emptying of reducing agent of said SCR catalyst (270) has been achieved by feeding said first NON content (NO0.1) upstream of said DOC unit (260) and feed a second NOR content (NO2) downstream of said SCR catalyst (270); and - means (200; 210; 500) adapted to take substantially the corresponding value 25 of the two NO 1 levels as a criterion for the intended emptying has been reached. A system according to any one of claims 8-10, comprising: - means (200; 210; 500) adapted to determine that the intended emptying of reducing agent of said SCR catalyst (270) has been achieved by modeling / calculating said first NO, content. (N0.1) upstream of said DOC unit 30 (260); means (277) adapted to feed a second NO 1 content (NO 2) downstream of said 32 SCR catalyst (270); and - means (200; 210; 500) adapted to take the substantially consistent value of the Dada NO 'levels as a criterion for achieving the intended emptying. A system according to any one of claims 8 to 12, comprising: - means (200; 210; 500) adapted to assess the performance of said DOC unit (260) on the basis of said determined first NO2 content (NO2mod) and said determined second NO2 content (NO2measured), whereby a ratio between said first NO2 content (NO2mod) and said second NO2 content (NO2measured) shall be outside a predetermined range! (I) to indicate that there is a lack of performance of said DOC unit (260). A system according to any one of claims 8 to 12, comprising: - means (200; 210; 500) adapted to assess the performance of said DOC unit (260) on the basis of said determined first NO2 content (NO2mod) and said determined second NO2 content (NO2measured), whereby an absolute difference (NO2mod — NO2measured) between said first NO2 content (NO2mod) and said second NO2 content (NO2measured) exceeding a predetermined threshold value (TH1) indicates poor performance of said DOC unit ( 260). Motor vehicle (100; 110) comprising a system according to any of claims 8-14. A motor vehicle (100; 110) according to claim 15, wherein the motor vehicle is any of a truck, bus, passenger car, watercraft and tracked vehicle. Computer program (P) in an exhaust gas purification system, wherein said computer program (P) comprises program code for causing an electronic control unit (200; 500) or a computer (210; 500) connected to the electronic control unit (200; 500) to perform the steps according to any one of claims 1-7. A computer program product comprising a program code stored on a computer readable medium for performing the method steps of any of claims 1-7, when said program code is crossed on an electronic control unit (200; 500) or a computer (210; 500) connected to the electronic control unit (200; 500). 33 1/4 or 100 112