System and a method for determining a cause for impaired performance of a catalytic configuration

Abstract

A method that determines a cause for the impaired performance of a catalytic configuration of the exhaust gas of a combustion engine (231), the method including determining (s410) a course of a NOx-conversion ratio; determining (s420) a prevailing temperature of the catalytic configuration; increasing (s430) the temperature of the catalytic configuration from a prevailing temperature below a predetermined temperature value (Te) to a temperature (TSred) above the predetermined temperature value above which sulphur is removed from the catalytic configuration; and/or decreasing (s440) the temperature of the catalytic configuration from a prevailing temperature (TSred) above the predetermined temperature value (Te) to a temperature below the predetermined temperature value so as to impair the performance of the catalytic configuration in case sulphur is present; and determining (s450) one cause out of a set of causes on the basis of the course of the NOx-conversion ratio thus determined.

Claims

1. A method for determining a cause for impaired performance of a catalytic configuration for emission control of exhaust gas of a combustion engine, said catalytic configuration being arranged for NOx-conversion, the method comprising: continuously or intermittently determining a course of a NOx-conversion ratio; continuously or intermittently determining a prevailing temperature of said catalytic configuration; increasing the temperature of said catalytic configuration from a prevailing temperature below a predetermined temperature value to a temperature above said predetermined temperature value, said predetermined temperature value representing a temperature above which sulphur, poisoning said catalytic configuration, is removed from said catalytic configuration so as to improve the performance of said catalytic configuration in case sulphur, poisoning said catalytic configuration, is present; or alternately decreasing the temperature of said catalytic configuration from a prevailing temperature above said predetermined temperature value to a temperature below said predetermined temperature value so as to impair the performance of said catalytic configuration in case sulphur, poisoning said catalytic configuration, is present; determining one cause for impaired performance of said catalytic configuration out of a set of causes on the basis of said course of said NOx-conversion ratio obtained upon said increasing, or alternately, upon said decreasing, of the temperature of said catalytic configuration; and determining a change rate of said course of said NOx-conversion ratio and taking use of a low concentration of a reducing agent introduced for NOx-conversion in said exhaust gas as said one cause of said set of causes when said change rate exceeds a certain characteristic value.

2. The method according to claim 1, further comprising: taking the presence of poisoning sulphur in said catalytic configuration as one cause for said impaired performance of said catalytic configuration when said course of said NOx-conversion ratio reveals an increased performance of said catalytic configuration when the temperature is increased above said predetermined temperature value and exclude other causes of said set of causes.

3. The method according to claim 1, further comprising: taking the presence of poisoning sulphur in said catalytic configuration as one cause for said impaired performance of said catalytic configuration when said course of said NOX-conversion ratio reveals a decreased performance of said catalytic configuration when the temperature is decreased below said predetermined temperature value and exclude other causes of said set of causes.

4. The method according to claim 1, further comprising: taking use of a low concentration of a reducing agent introduced for NOx-conversion in said exhaust gas as one cause for said impaired performance of said catalytic configuration when a change of said reducing agent to a proper concentration reducing agent reveals an increased performance of said catalytic configuration or when a change of said reducing agent from said proper concentration to a low concentration reducing agent reveals an impaired performance of said catalytic configuration.

5. The method according to claim 1, wherein said set of causes comprises presence of poisoning sulphur, low concentration of a reducing agent introduced for NOx-conversion in said exhaust gas, aging of catalytic substances of said catalytic configuration and undesired defects related to said catalytic configuration.

6. A computer program product containing a program code stored on a computer-readable medium for performing method steps according to claim 1, when said computer program is run on an electronic control unit or a computer connected to the electronic control unit.

7. A system for determining a cause for impaired performance of a catalytic configuration for emission control of exhaust gas of a combustion engine, said catalytic configuration being arranged for NOx-conversion, the system comprising: first means being arranged to continuously or intermittently determine a course of a NOx-conversion ratio; second means being arranged to continuously or intermittently determine a prevailing temperature of said catalytic configuration; third means being arranged to increase the temperature of said catalytic configuration from a prevailing temperature below a predetermined temperature value to a temperature above said predetermined temperature value, said predetermined temperature value representing a temperature above which sulphur, poisoning said catalytic configuration, is removed from said catalytic configuration so as to improve the performance of said catalytic configuration in case sulphur, poisoning said catalytic configuration, is present; or alternately; fourth means being arranged to decrease the temperature of said catalytic configuration from a prevailing temperature above said predetermined temperature value to a temperature below said predetermined temperature value so as to impair the performance of said catalytic configuration in case sulphur, poisoning said catalytic configuration, is present; and fifth means being arranged to determine one cause for impaired performance of the catalytic configuration out of a set of causes on the basis of said course of said NOx-conversion ratio obtained upon said increasing, or alternately upon said decreasing, of the temperature of said catalytic configuration; and sixth means being arranged to determine a change rate of said course of said NOx-conversion ratio and taking use of a low concentration of a reducing agent introduced for NOx-conversion in said exhaust gas as said one cause of said set of causes when said change rate exceeds a certain characteristic value.

8. The system according to claim 7, further comprising: seventh means being arranged to take the presence of poisoning sulphur in said catalytic configuration as one cause for said impaired performance of said catalytic configuration when said course of said NOx-conversion ratio reveals an increased performance of the catalytic configuration when the temperature is increased above said predetermined temperature value and exclude other causes of said set of causes.

9. The system according to claim 7, further comprising: seventh means being arranged to take the presence of poisoning sulphur in said catalytic configuration as one cause for said impaired performance of said catalytic configuration when said course of said NOx-conversion ratio reveals a decreased performance of the catalytic configuration when the temperature is decreased below said predetermined temperature value and exclude other causes of said set of causes.

10. The system according to claim 7, further comprising: seventh means being arranged to take use of a low concentration of a reducing agent introduced for NOx-conversion in said exhaust gas as one cause for said impaired performance of said catalytic configuration when a change of said reducing agent to a proper concentration of reducing agent reveals an increased performance of said catalytic configuration or when a change of said reducing agent from said proper concentration to a low concentration reducing agent reveals an impaired performance of said catalytic configuration.

11. The system according to claim 7, wherein said set of causes comprises presence of poisoning sulphur, low concentration of a reducing agent introduced for NOx-conversion in said exhaust gas, aging of catalytic substances of said catalytic configuration and undesired defects related to said catalytic configuration.

12. A vehicle comprising a system according to claim 7.

13. The vehicle according to claim 12, wherein said vehicle is a truck, a bus, or a passenger car.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For fuller understanding of the present invention and its further objects and advantages, the detailed description set out below should be read in conjunction with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

(2) FIG. 1 schematically illustrates a vehicle according to an embodiment of the invention;

(3) FIG. 2a schematically illustrates a system according to an embodiment of the invention;

(4) FIG. 2b schematically illustrates a system according to an embodiment of the invention;

(5) FIG. 3a schematically illustrates a diagram according to an aspect of the invention;

(6) FIG. 3b schematically illustrates a diagram according to an aspect of the invention;

(7) FIG. 4a is a schematic flowchart of a method according to an embodiment of the invention;

(8) FIG. 4b is a schematic flowchart of a method according to an embodiment of the invention; and

(9) FIG. 5 schematically illustrates a computer according to an embodiment of the invention.

DETAILED DESCRIPTION

(10) FIG. 1 depicts a side view of a vehicle 100. The exemplified vehicle 100 comprises a tractor unit 110 and a trailer 112. The vehicle 100 may be a heavy vehicle, e.g. a truck or a bus. It may alternatively be a car.

(11) It should be noted that the inventive system is applicable to various vehicles, such as e.g. a mining machine, tractor, dumper, wheel-loader, platform comprising an industrial robot, forest machine, earth mover, road construction vehicle, road planner, emergency vehicle or a tracked vehicle.

(12) It should be noted that the invention is suitable for application in various systems comprising a combustion engine and an associated emission control system. The invention is suitable for application in various systems comprising a combustion engine and a catalytic configuration. Said catalytic configuration may comprise at least one SCR-unit. Said catalytic configuration may comprise one or more DOC-units, DPF-units (Diesel Particulate Filter) and SCR-units. It should be noted that the invention is suitable for application in any catalytic configuration and is therefore not confined to catalytic configurations for motor vehicles. The proposed method and the proposed system according to one aspect of the invention are well suited to other platforms which comprise a combustion engine and a catalytic configuration than motor vehicles, e.g. watercraft. The watercraft may be of any kind, e.g. motorboats, steamers, ferries or ships.

(13) The proposed method and the proposed system according to one aspect of the invention are also well suited to, for example, systems which comprise industrial combustion engines and/or combustion engine-powered industrial robots and an associated emission control system comprising a catalytic configuration.

(14) The proposed method and the proposed system according to one aspect of the invention are also well suited to various kinds of power plants, e.g. an electric power plant which comprises a combustion engine-powered generator and an associated emission control system comprising a catalytic configuration.

(15) The proposed method and the proposed system are also well suited to various combustion engine systems comprising a catalytic configuration.

(16) The proposed method and the proposed system are well suited to any engine system which comprises an engine, e.g. on a locomotive or some other platform, an associated emission control system comprising a catalytic configuration.

(17) The proposed method and the proposed system are well suited to any system which comprises a NO.sub.x-generator an associated emission control system comprising a catalytic configuration.

(18) The term “link” refers herein to a communication link which may be a physical connection such as an opto-electronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link.

(19) The term “line” refers herein to a passage for holding and conveying a fluid, e.g. a reducing agent in liquid form. The line may be a pipe of any size and be made of any suitable material, e.g. plastic, rubber or metal.

(20) The term “reductant” or “reducing agent” refers herein to an agent used for reacting with certain emissions in an SCR system. These emissions may for example be NO.sub.x gas. The terms “reductant” and “reducing agent” are herein used synonymously. In one version, said reductant is so-called AdBlue. Other kinds of reductants may of course be used. AdBlue is herein cited as an example of a reductant, but one skilled in the art will appreciate that the innovative method and the innovative system are feasible with other types of reductants.

(21) The term “fuel” refers herein to any fuel for powering an engine having an associated emission control system comprising a catalytic configuration. Fuel may also, where applicable, be supplied to the emission control system downstream of said engine so as to control a prevailing temperature of the exhaust gas and thus the catalytic configuration. Said fuel may comprise diesel, gasoline or ethanol, or any other suitable fuel.

(22) The term “set of causes” may according to one example herein refer to a set of causes comprising manual tampering of a reducing agent dosing system of the emission control system, such as providing a diluted reducing agent, and sulphur poisoning. The term “set of causes” may according to one example herein refer to a set of causes comprising manual tampering of a reducing agent dosing system of the emission control system, sulphur poisoning, natural aging of said catalytic configuration and accelerated aging of said catalytic configuration. The term “set of causes” may according to one example herein refer to a set of causes comprising manual tampering of a reducing agent dosing system of the emission control system, sulphur poisoning, natural aging of said catalytic configuration, accelerated aging of said catalytic configuration and mechanical failure of said catalytic configuration.

(23) In a case where it has been determined that sulphur poisoning is not the cause, a remaining set of causes may comprise any of: manual tampering of a reducing agent dosing system; natural aging of said catalytic configuration; accelerated aging of said catalytic configuration; and mechanical failure of said catalytic configuration.

(24) FIG. 2a schematically illustrates a system 299 according to an example embodiment of the invention. The system 299 is situated in the tractor unit 110 and may be part of a catalytic configuration, also denoted exhaust gas processing configuration. It comprises in this example a container 205 arranged to hold a reductant. The container 205 is adapted to holding a suitable amount of reductant and also to being replenishable as necessary. The container may be adapted to hold e.g. 75 or 50 litres of reductant.

(25) A first line 271 is provided to lead the reductant to a pump 230 from the container 205. The pump 230 may be any suitable pump. The pump 230 may be arranged to be driven by an electric motor (not depicted). The pump 230 may be adapted to drawing the reductant from the container 205 via the first line 271 and supplying it via a second line 272 to a dosing unit 237. The dosing unit 237 may also be referred to as a reducing agent dosing unit. The dosing unit 237 comprises an electrically controlled dosing valve by means of which a flow of reductant added to the exhaust system can be controlled. The pump 230 is adapted to pressurising the reductant in the second line 272. The dosing unit 237 is provided with a throttle unit, against which said pressure of the reductant may build up in the system 299.

(26) A first control unit 200 is arranged for communication with the pump 230 via a link L230. The first control unit 200 is arranged to send control signals S230 via said link L230. The first control unit 200 is arranged to control the operation of said pump 230 so as to for example adjust flows of the reducing agent within the system 299. The first control unit 200 is arranged to control an operation power of the pump 230 e.g. by controlling the electric motor.

(27) The dosing unit 237 is adapted to supplying said reductant to an exhaust system (see FIG. 2b) of the vehicle 100. More specifically, it is adapted to supplying a suitable amount of reductant in a controlled way to an exhaust system of the vehicle 100. In this version, one SCR catalyst (see FIG. 2b) is situated downstream of the location in the exhaust system where the supply of reductant takes place.

(28) A third line 273 running between the dosing unit 237 and the container 205 is adapted to leading back to the container 205 a certain amount of the reductant fed to the dosing unit 237. This configuration results in advantageous cooling of the dosing unit 237. The dosing unit 237 is thus cooled by a flow of the reductant when it is pumped through it from the pump 230 to the container 205.

(29) The first control unit 200 is arranged for communication with the dosing unit 237 via a link L237. The first control unit 200 is arranged to send control signals S237 via said link L237. The first control unit 200 is arranged to control the operation of said dosing unit 237 so as to for example control dosing of the reducing agent to the exhaust gas system of the vehicle 100. The control unit 200 is arranged to control the operation of the dosing unit 237 so as to for example adjust return flow of said reducing agent to the container 205.

(30) A second control unit 210 is arranged for communication with the first control unit 200 via a link L210. It may be releasably connected to the first control unit 200. It may be a control unit external to the vehicle 100. It may be adapted to performing the innovative steps according to the invention. It may be used to cross-load software to the first control unit 200, particularly software for applying the innovative method. It may alternatively be arranged for communication with the first control unit 200 via an internal network on board the vehicle. It may be adapted to performing functions corresponding to those of the first control unit 200, such as e.g. determining a cause for impaired performance of a catalytic configuration for the emission control of the exhaust gas of a combustion engine, said catalytic configuration being arranged for NO.sub.x-conversion.

(31) FIG. 2b schematically illustrates a system 289 of the vehicle shown in FIG. 1 according to an embodiment of the invention. The system 289 may constitute a part of the inventive system for determining a cause for the impaired performance of a catalytic configuration for the emission control of the exhaust gas of a combustion engine.

(32) A combustion engine 231 is during operation causing an exhaust gas flow which is lead via a first passage 235 to a DOC-unit 240. A second passage 245 is arranged to convey said exhaust gas flow from said DOC-unit 240 to a DPF-unit 250. A third passage 255 is arranged to convey said exhaust gas flow from said DPF-unit 250 to an SCR-unit 260. A fourth passage 265 is arranged to convey said exhaust gas flow from said SCR-unit 260 to an environment of the catalytic configuration. The catalytic configuration may comprise any of said components downstream said engine 231, including at least one member presenting catalytic features. The catalytic configuration may comprise any of said components downstream said engine 231, including at least one member presenting catalytic features being sensitive for sulphur poisoning.

(33) Said dosing unit 237 is arranged to provide said reductant to said third passage 255 upstream of said SCR-unit 260 and downstream of said DPF-unit 250. The first control unit 200 is arranged to control the operation of said dosing unit 237 so as to, where applicable, dose reducing agent into the third passage 255.

(34) Said SCR-unit 260 may comprise a vaporizing module (not shown) which is arranged to vaporize said dosed reducing agent so as to achieve a mixture of exhaust gas and reducing agent for treatment by means of an SCR-portion of the SCR-unit 260. Said vaporizing module may comprise a mixer (not shown) for mixing said vaporized reducing agent with the exhaust gas. Said vaporizing module may be formed in any suitable way. Said vaporizing module is configured to achieve a most effective vaporizing of the provided reducing agent as possible. Herein said vaporizing module has large surfaces where vaporizing of the provided reducing agent may be performed in an effective way. Said vaporizing module may consist of a metal or a metal alloy.

(35) Said SCR-unit 260 may according to one possible configuration comprise an ammonia slip catalyst ASC, not illustrated.

(36) A first NO.sub.x-sensor 233 is arranged upstream said DOC-unit 240 at said first passage 235. Said first NO.sub.x-sensor 233 is arranged for communication with the first control unit 200 via a link L233. The first NO.sub.x-sensor 233 is arranged to continuously determine a prevailing first content of NO.sub.x, denoted NOx1, in the first passage 235. The first NO.sub.x-sensor 233 is arranged to continuously send signals S233 comprising information about the prevailing first content of NO.sub.x to the first control unit 200 via the link L233.

(37) A second NO.sub.x-sensor 253 is arranged downstream said SCR-unit 260 at said fourth passage 265. Said second NO.sub.x-sensor 253 is arranged for communication with the first control unit 200 via a link L253. The second NO.sub.x-sensor 253 is arranged to continuously determine a prevailing second content of NO.sub.x, denoted NOx2, in the fourth passage 265. The second NO.sub.x-sensor 253 is arranged to continuously send signals S253 comprising information about the prevailing second content of NO.sub.x to the first control unit 200 via the link L253.

(38) Said first NO.sub.x-sensor 233 and said second NO.sub.x-sensor 253 may be used to provide information about prevailing contents of NO.sub.x in the first passage 235 and the fourth passage 265, respectively.

(39) According to an example said first control unit 200 is arranged to determine said first content of NO.sub.x, NOx1, according to a model stored in a memory thereof. Hereby said first control unit is arranged to continuously or intermittently determine/estimate/model/calculate a prevailing NO.sub.x content, NOx1, in said first passage 235. This model may be based on parameters such as engine speed RPM, engine load, dosed amount of fuel to said engine 231, etc.

(40) Said first control unit 200 is arranged to continuously or intermittently determining a course of a NO.sub.x-conversion ratio on the basis of said determined first NO.sub.x-content, NOx1, and said determined second NO.sub.x-content NOx2.

(41) A temperature sensor 243 is arranged at the third passage 255. Said temperature sensor 243 is arranged for communication with said first control unit 200 via a link L243. Said temperature sensor 243 is arranged to continuously measure a prevailing temperature Tmeas of the exhaust gas in said third passage 255 and send signals S243 comprising information about said measured temperature Tmeas to said first control unit 200 via said link L243. Hereby it is illustrated that said temperature sensor 243 is arranged upstream of said dosing unit 237 at the third passage 255. According to another example said temperature sensor 243 is arranged downstream of said dosing unit 237 at the third passage 255. According to another example two temperature sensors may be provided at said third passage 255, wherein one temperature sensor may be positioned upstream of said dosing unit 237 and one temperature sensor may be positioned downstream of said dosing unit 237. According to this example the first control unit 200 may use a mean value of temperature values detected by means of said two temperature sensors at the third passage 255.

(42) According to an example said first control unit 200 is arranged to determine a prevailing temperature Tmod of said exhaust gas according to a model stored in a memory thereof. Hereby said first control unit is arranged to continuously or intermittently determine/estimate/model/calculate a prevailing temperature Tmod of said exhaust gas in said third passage 255. This model may be based on parameters such as engine speed RPM, engine load, dosed amount of fuel to said engine 231, etc.

(43) Said first control unit 200 is arranged to continuously or intermittently determine a prevailing temperature of said catalytic configuration on the basis of said measured prevailing temperature Tmeas and/or said determined prevailing temperature Tmod. Hereby said first control unit 200 is arranged to determine a temperature of any relevant unit of the emission control system, such as the DOC-unit 240, DPF-unit 250 and SCR-unit 260.

(44) Said catalytic arrangement may comprise one or more SCR-units, a DOC-unit, a DPF-unit and an ASC-unit. Said catalytic arrangement may comprise any combination of one or more SCR-units, a DOC-unit, a DPF-unit and an ASC-unit. Hereby said first control unit 200 may be arranged to determine a means temperature of any combination of units of the emission control system, such as the DOC-unit 240, DPF-unit 250 and SCR-unit 260. This mean temperature may be controlled according to the inventive method. Hereby this mean temperature is controlled so as to increase from a prevailing temperature below a predetermined temperature value Te to a temperature above said predetermined temperature value and/or so as to decrease from a prevailing temperature above said predetermined temperature value Te to a temperature below said predetermined temperature value.

(45) Said first control unit 200 is arranged to control the temperature of the exhaust gas flow from said engine 231 by any suitable means. Hereby said first control unit 200 is arranged to increase the temperature of said catalytic configuration from a prevailing temperature below a to a predetermined temperature value Te to a temperature above said predetermined temperature value, said predetermined temperature value Te representing a temperature above which sulphur, poisoning said catalytic configuration, is removed from said catalytic configuration so as to improve the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present.

(46) Hereby said first control unit 200 is arranged to decrease the temperature of said catalytic configuration from a prevailing temperature above said predetermined temperature value Te to a temperature below said predetermined temperature value so as to impair the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present.

(47) Hereby said first control unit 200 is arranged to determine one cause out of a set of causes on the basis of said course of said NO.sub.x-conversion ratio thus determined.

(48) Hereby said first control unit 200 is arranged to take the presence of poisoning sulphur in said catalytic configuration as said one cause for impaired performance of said catalytic configuration when said course of said NO.sub.x-conversion ratio reveals an increased performance when the temperature is increased above said predetermined temperature value Te and exclude other causes of said set of causes.

(49) Hereby said first control unit 200 is arranged to take the presence of poisoning sulphur in said catalytic configuration as said one cause for impaired performance of said catalytic configuration when said course of said NO.sub.x-conversion ratio reveals a decreased performance when the temperature is decreased below said predetermined temperature value Te and exclude other causes of said set of causes.

(50) Hereby said first control unit 200 is arranged to take use of a low concentration of a reducing agent introduced for NO.sub.x-conversion in said exhaust gas as said one cause for impaired performance of said catalytic configuration when a change of said reducing agent to a proper concentration reducing agent reveals an increased performance of said catalytic configuration or when a change of said reducing agent from a proper concentration to a low concentration reducing agent reveals an impaired performance of said catalytic configuration. This change of said reducing agent may be indicated by means of a level sensor (not illustrated) being arranged at said tank 205. Said sensor is arranged for communication with said first control unit 200 via a suitable link (not illustrated).

(51) Hereby said first control unit 200 is arranged to determine a change rate of said course of NO.sub.x-conversion ratio and taking use of a low concentration of a reducing agent introduced for NO.sub.x-conversion in said exhaust gas as said one cause of said set of causes if said change rate exceeds a certain characteristic value.

(52) Hereby said first control unit 200 is arranged to determine said one cause out of a set of causes comprising the presence of poisoning sulphur, low concentration of a reducing agent introduced for NO.sub.x-conversion in said exhaust gas, aging of catalytic substances in said catalytic configuration, accelerated aging of catalytic substances in said catalytic configuration and undesired defects related to said catalytic configuration.

(53) Said first control unit 200 is arranged to perform the process steps depicted herein, comprising the process steps which are detailed with reference to FIG. 4b.

(54) FIG. 3a schematically illustrates a diagram wherein NO.sub.x-conversion CR is presented as a function of time t given in seconds s. The diagram comprises a number of graphs A-E, each representing a characteristic development of NO.sub.x-conversion relating to a specific situation. The FIG. 3a is to be analysed in conjunction with the FIG. 3b.

(55) A first graph A relates to a case where tampering of the emission control system is at hand. At a time point T0 a reducing agent having other than required and desired qualities is introduced and/or used. Hereby a level of NO.sub.x-conversion ratio is increased from an acceptable level to a non-acceptable level. The NO.sub.x-conversion rate is hereby staying at said level until an adequate reducing agent is used by the emission control system. When a proper reducing agent is used said NO.sub.x-conversion ratio will return to acceptable levels again. It is noted that the NO.sub.x-conversion ratio remains substantially unaffected by temperature variations in case tampering of the emission control system is at hand. It is characteristic that the NO.sub.x-conversion rate is shifted relatively quickly to a non-acceptable level after the reducing agent having other than the required and desired qualities has been introduced and/or used. The characteristic shape of the graph A may be identified by the first control unit 200 and may thus serve as a basis for deciding if the cause for the impaired performance of the catalytic configuration is said tampering.

(56) A second graph B relates to a case where fuel of said engine comprises too high levels of sulphur, and thus said exhaust gas also comprises sulphur. Said sulphur may hereby poison any catalytic element of the emission control system, such as the SCR-unit 260. Sulphur is hereby accumulated in said element and is gradually impairing performance of said element. It is illustrated that a NO.sub.x-conversion ratio is increased as long as a temperature of the catalytic configuration is below a certain predetermined temperature Te. Said predetermined temperature value Te is representing a temperature above which sulphur, poisoning said catalytic configuration, is removed from said catalytic configuration. If the temperature of said catalytic configuration is increased above said predetermined temperature value Te the degree of sulphur poisoning is decreased resulting in a decrease of said NO.sub.x-conversion ratio. By increasing said temperature from a first temperature Temp1, below said predetermined temperature Te, to a second temperature Temp2, it may be determined that sulphur poisoning is the probable cause of the impaired performance of the catalytic configuration. Also, by decreasing said temperature from the second temperature Temp2, above said predetermined temperature Te, to another temperature below said predetermined temperature Te, such as the first temperature Temp1, it may be determined that sulphur poisoning is the probable cause of the impaired performance of the catalytic configuration.

(57) It is noted that the NO.sub.x-conversion ratio is directly affected by temperature variations about said predetermined temperature Te. This is a characteristic behaviour of the determined NO.sub.x-conversion ratio. In case the NO.sub.x-conversion ratio is changing when shifting between temperatures below and above said predetermined temperature Te it may be determined that sulphur poisoning is the probable cause of the impaired performance of the catalytic configuration. This may be performed by means of the first control unit 200.

(58) A third graph C relates to a case where natural aging of said catalytic configuration is at hand. The graph C may be a reference line when determining the cause of an impaired performance of a catalytic configuration for the emission control of the exhaust gas of a combustion engine. Over time the catalytic configuration is slowly degrading and thus NO.sub.x-conversion capacities are impaired. It is noted that the NO.sub.x-conversion ratio remains substantially unaffected when shifting the temperature between temperatures below and above said predetermined temperature Te. The characteristic shape of the graph C may be identified by the first control unit 200 and may thus serve as a basis for deciding if the cause for impaired performance of the catalytic configuration is said natural aging. It may be decided that the relevant cause of impaired performance of the catalytic configuration is natural aging if the level of the NO.sub.x-conversion ratio is within a predetermined first NO.sub.x-conversion ratio interval.

(59) A fourth graph D relates to a case where accelerated aging of said catalytic configuration is at hand. Over time the catalytic configuration is degrading at a higher rate compared to natural ageing and thus NO.sub.x-conversion capacities are impaired. Accelerated aging may be caused by overheating of at least one member unit of the catalytic configuration. This means that one or more member units of the catalytic configuration are exposed to temperatures which will result in a negative impact of said member units. Various substrates of said member units may be associated with different critical temperature values, i.e. a temperature value above which member unit performance may be negatively affected (accelerated aging). It is noted that the NO.sub.x-conversion ratio remains substantially unaffected when shifting the temperature between temperatures below and above said predetermined temperature Te. The characteristic shape of the graph D may be identified by the first control unit 200 and may thus serve as a basis for deciding if the cause for impaired performance of the catalytic configuration is said accelerated aging. It may be decided that the relevant cause of impaired performance of the catalytic configuration is accelerated aging if the level of the NO.sub.x-conversion ratio is within a predetermined second NO.sub.x-conversion ratio interval. The second NO.sub.x-conversion ratio interval may be different from the first NO.sub.x-conversion ratio interval. NO.sub.x-conversion ratio values are to be within the respective first and second NO.sub.x-conversion ratio interval over time when deciding which form of aging of said catalytic configuration is at hand (natural aging, accelerated aging).

(60) A fifth graph E relates to a case where mechanical failure of a member of the catalytic configuration is at hand. This graph may present a number of different courses, depending upon the type of mechanical failure. However, this graph will present a different pattern than the other graphs (A-D) and it will thus be relatively easy to determine if the cause is mechanical failure.

(61) It is noted that the sign of NO.sub.x-conversion ratio is dependent on the temperature of the catalytic configuration in case there is sulphur poisoning said catalytic configuration.

(62) FIG. 3b schematically illustrates the temperature Tmeas, Tmod of the catalytic configuration given in degrees Celsius as a function of time t given in seconds s.

(63) Herein, initially, a prevailing temperature Temp1 of said catalytic configuration is below a predetermined temperature value Te. Thereafter said temperature is increased to a second temperature Temp2, which is higher than said predetermined temperature value Te. The increase is performed during the time period T1-T2. During a certain amount of time T2-T3 said prevailing temperature is controlled to stay at a level above said predetermined temperature Te. Thereafter said temperature is decreased to a temperature, such as Temp1, below said predetermined temperature value Te. The decrease is performed during the time period T3-T4.

(64) By analysing the behaviour of the NO.sub.x-conversion ratio when controlling said temperature of said catalytic configuration a cause of impaired performance of said catalytic configuration may be determined according to the inventive method.

(65) FIG. 4a schematically illustrates a flow chart of a method for determining a cause for the impaired performance of a catalytic configuration for the emission control of the exhaust gas of a combustion engine 231, said catalytic configuration being arranged for NO.sub.x-conversion.

(66) The method comprises a first method step s401. The method step s401 comprises the steps of: continuously or intermittently determining a course of a NO.sub.x-conversion ratio; continuously or intermittently determining a prevailing temperature of said catalytic configuration; increasing the temperature of said catalytic configuration from a prevailing temperature below a predetermined temperature value Te to a temperature above said predetermined temperature value, said predetermined temperature value Te representing a temperature above which sulphur, poisoning said catalytic configuration, is removed from said catalytic configuration so as to improve the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present; and/or decreasing the temperature of said catalytic configuration from a prevailing temperature above said predetermined temperature value Te to a temperature below said predetermined temperature value so as to impair the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present; and determining one cause out of a set of causes on the basis of said course of said NO.sub.x-conversion ratio thus determined.

(67) After the method step s401 the method ends/is returned.

(68) FIG. 4b schematically illustrates a method for determining a cause for impaired performance of a catalytic configuration for the emission control of the exhaust gas of a combustion engine, said catalytic configuration being arranged for NO.sub.x-conversion.

(69) The method comprises a first method step s410. The method step s410 comprises the step of continuously or intermittently determining a course of a NO.sub.x-conversion ratio. This may be performed by means of said first control unit 200. This may be performed on the basis of determined NO.sub.x values detected by the first NO.sub.x-sensor 233 and the second NO.sub.x-sensor 253. Alternatively said first NO.sub.x value may be calculated. Herein the term determining intermittently, regarding the NO.sub.x-conversion ratio, means that a NO.sub.x-conversion ratio may be determined on the basis of corresponding first and second NO.sub.x values, which pair of values is determined every 2, 5, 10, 30 or more seconds.

(70) The course of the NO.sub.x-conversion ratio may according to one example be determined before, during and after a temperature change, which temperature change is relating to a temperature change passing the predetermined temperature value Te.

(71) The course of the NO.sub.x-conversion ratio may according to one example be determined only before and after a temperature change, which temperature change is relating to a temperature change passing the predetermined temperature value Te.

(72) After the method step s410 a subsequent method step s420 is performed.

(73) The method step s420 comprises the step of continuously or intermittently determining a prevailing temperature of said catalytic configuration. This may be performed a number of different ways. The temperature of said catalytic configuration may relate to a measured or calculated/estimated/modelled/determined temperature value of the SCR-unit 260. The temperature of said catalytic configuration may relate to a measured or calculated/estimated/modelled/determined temperature value of a number of units of the catalytic configuration.

(74) Herein the term determining intermittently, regarding the temperature, means that a temperature of said catalytic configuration may be determined every 2, 5, 10, 30 or more seconds.

(75) The temperature may according to one example be determined before, during and after a temperature change, which temperature change is related to a temperature change passing the predetermined temperature value Te.

(76) The temperature may according to one example be determined before and after a temperature change, which temperature change is related to a temperature change passing the predetermined temperature value Te.

(77) After the method step s420 a subsequent method step s430 is performed.

(78) The method step s430 comprises the step of increasing the temperature of said catalytic configuration from a prevailing temperature below a to a predetermined temperature value Te to a temperature above said predetermined temperature value. Said predetermined temperature value Te is representing a temperature above which sulphur, poisoning said catalytic configuration, is removed from said catalytic configuration so as to improve the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present. The temperature below the predetermined temperature value Te may be the temperature Temp1. The temperature above said predetermined temperature value Te may be the temperature Temp2.

(79) By controlling said temperature of said catalytic configuration so as to increase said temperature according to the proposed method it is possible to identify sulphur poisoning, if any, as a cause of impaired performance of said catalytic configuration.

(80) According to one example the step of continuously or intermittently determining a course of a NO.sub.x-conversion ratio according to step s410 may be performed during temperature increase process according to the step s430. According to one example the step of continuously or intermittently determining a course of a NO.sub.x-conversion ratio according to step s410 is performed during temperature increase process according to the step s430.

(81) The method step s440 comprises the step of decreasing the temperature of said catalytic configuration from a prevailing temperature above said predetermined temperature value Te to a temperature below said predetermined temperature value so as to impair the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present. By controlling said temperature of said catalytic configuration so as to decrease said temperature according to the inventive method it is possible to identify sulphur poisoning, if any, as a cause of impaired performance of said catalytic configuration. The temperature below the predetermined temperature value Te may be the temperature Temp1. The temperature above said predetermined temperature value Te may be the temperature Temp2.

(82) According to one example, the step of continuously or intermittently determining a course of a NO.sub.x-conversion ratio according to step s410 may be performed during the temperature decrease process according to the step s440.

(83) According to one example, the step of continuously or intermittently determining a course of a NO.sub.x-conversion ratio according to step s410 is performed during the temperature decrease process according to the step s440.

(84) One of the method steps s430 and s440 may be omitted according to an example of the inventive method. According to one example the method step s440 is performed before the method step s430. According to one example the method comprises performing a number of steps s430 and/or a number of steps s440.

(85) After the method step s440 a subsequent step s450 is performed.

(86) The step s450 comprises the step of determining one cause out of a set of causes on the basis of said course of said NO.sub.x-conversion ratio thus determined. Said set of causes may comprise presence of poisoning sulphur, low concentration of a reducing agent introduced for NO.sub.x-conversion in said exhaust gas, aging of the catalytic substances in said catalytic configuration and the undesired defects related to said catalytic configuration.

(87) According to one example embodiment it is in a first action determined if the cause is poisoning sulphur. This may be performed on the basis of NO.sub.x-conversion ratio changes characteristically when increasing and/or lowering the temperature above and under the predetermined temperature Te. As a second action, if the cause is not determined to be poisoning sulphur, the cause may be determined on the basis of comparisons between the determined NO.sub.x-conversion ratio course and the predetermined NO.sub.x-conversion ratio courses, each representing a different cause among a set of courses. The set of courses may according to one example hereby be at least one among:

(88) a) manual tampering of a reducing agent dosing system;

(89) b) natural aging of said catalytic configuration;

(90) c) accelerated aging of said catalytic configuration; and

(91) d) mechanical failure of said catalytic configuration.

(92) Hereby one cause out of the set of causes may be determined.

(93) According to one embodiment it is in a first action determined if the cause is poisoning sulphur or manual tampering of a reducing agent dosing system. In this example it is determined that the cause is manual tampering if it is decided that the cause is not poisoning sulphur.

(94) The step s450 may comprise the step of taking a proper action depending upon which cause is determined. Said action may be engine torque limiting actions (in case of tampering of the catalytic configuration e.g. using inadequate reductant), generating error codes (in case of sulphur poisoning), generating and displaying information for an operator of the vehicle (in case of sulphur poisoning), etc.

(95) After the step s450 the method is ended/returned.

(96) FIG. 5 is a diagram of one version of a device 500. The control units 200 and 210 described with reference to FIG. 2 may in one version comprise the device 500. The device 500 comprises 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 element 530 in which a computer program, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

(97) The computer program P comprises routines for determining a cause for the impaired performance of a catalytic configuration for the emission control of the exhaust gas of a combustion engine 231, said catalytic configuration being arranged for NO.sub.x-conversion.

(98) The computer program P may comprise routines for continuously or intermittently determining a course of a NO.sub.x-conversion ratio (NOx1/NOx2).

(99) The computer program P may comprise routines for continuously or intermittently determining a prevailing temperature of said catalytic configuration.

(100) The computer program P may comprise routines for controlling an increase of the temperature of said catalytic configuration from a prevailing temperature below a predetermined temperature value Te to a temperature above said predetermined temperature value, said predetermined temperature value Te representing a temperature above which sulphur, poisoning said catalytic configuration, is removed from said catalytic configuration so as to improve the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present.

(101) The computer program P may comprise routines for controlling a decrease of the temperature of said catalytic configuration from a prevailing temperature above said predetermined temperature value Te to a temperature below said predetermined temperature value so as to impair the performance of said catalytic configuration in case of sulphur, poisoning said catalytic configuration, is present.

(102) The computer program P may comprise routines for determining one cause out of a set of causes on the basis of said course of said NO.sub.x-conversion ratio thus determined.

(103) The computer program P may comprise routines for taking the presence of poisoning sulphur in said catalytic configuration as said one cause for the impaired performance of said catalytic configuration when said course of said NO.sub.x-conversion ratio reveals an increased performance when the temperature is increased above said predetermined temperature value Te and exclude other causes of said set of causes.

(104) The computer program P may comprise routines for taking the presence of poisoning sulphur in said catalytic configuration as said one cause for the impaired performance of said catalytic configuration when said course of said NO.sub.x-conversion ratio reveals a decreased performance when the temperature is decreased below said predetermined temperature value and exclude other causes of said set of causes.

(105) The computer program P may comprise routines for taking use of a low concentration of a reducing agent introduced for NO.sub.x-conversion in said exhaust gas as said one cause for the impaired performance of said catalytic configuration when a change of said reducing agent to a proper concentration reducing agent reveals an increased performance of said catalytic configuration or when a change of said reducing agent from a proper concentration to a low concentration reducing agent reveals an impaired performance of said catalytic configuration.

(106) The computer program P may comprise routines for determining a change rate of said course of NO.sub.x-conversion ratio and taking use of a low concentration of a reducing agent introduced for NO.sub.x-conversion in said exhaust gas as said one cause of said set of causes if said change rate exceeds a certain characteristic value.

(107) The computer program P may comprise routines for determining said one cause out of a set of causes comprising the presence of poisoning sulphur, low concentration of a reducing agent introduced for NO.sub.x-conversion in said exhaust gas, aging of the catalytic substances in said catalytic configuration and the undesired defects related to said catalytic configuration.

(108) The computer program P may comprise routines for performing any of the process steps detailed with reference to FIG. 4b.

(109) The program P may be stored in an executable form or in compressed form in a memory 560 and/or in a read/write memory 550.

(110) Where it is stated that the data processing unit 510 performs a certain function, it means that it conducts 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 memory 550.

(111) The data processing device 510 can communicate with a data port 599 via a 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 via a data bus 511. The read/write memory 550 is arranged to communicate with the data processing unit 510 via a data bus 514. The links L210, L230, L231, L233, L237, L243 and L253, for example, may be connected to the data port 599 (see FIGS. 2a and 2b).

(112) When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 will be prepared to conduct code execution as described above.

(113) Parts of the methods herein described may be conducted by the device 500 by means of the data processing unit 510 which runs the program stored in the memory 560 or the read/write memory 550. When the device 500 runs the program, method steps and process steps herein described are executed.

(114) The foregoing description of the preferred embodiments of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive, nor to limit the invention to the variants described. Many modifications and variations will obviously suggest themselves to one skilled in the art. The embodiments have been chosen and described in order to best explain the principles of the invention and their practical applications and thereby make it possible for one skilled in the art to understand the invention for different embodiments and with the various modifications appropriate to the intended use.

(115) The components and features specified above may within the framework of the invention be combined between different embodiments specified.