system

TECHNICAL FIELD

The present invention relates to a method for diagnosis of a sensor in an exhaust treatment system. In particular, the present invention relates to a method for diagnosis of an NO _x - sensor in an exhaust treatment system. The invention also relates to a computer program product, comprising program code for a computer, to implement a method according to the invention. The invention also relates to a system for diagnosis of a sensor in an exhaust treatment system and a motor vehicle, which is equipped with the system.

BACKGROUND

Exhaust treatment systems in motor vehicles today comprise a number of different components. For example, an exhaust treatment system may comprise a DOC-unit (Diesel Oxidation Catalyst) arranged in a passage downstream of a combustion engine in the vehicle. Other components that may be arranged downstream of said engine are a DPF-unit (Diesel Particulate Filter) and an SCR-catalyst (Selective Catalytic Reduction).

For many reasons, it is desirable to be able to diagnose individual components in an exhaust treatment system of motor vehicles, such as for example trucks and buses. Diagnosis of components in exhaust treatment systems of motor vehicles may, for example, be desirable to be able to determine the prevailing performance and/or function of the different components. Diagnosis of individual components in exhaust treatment systems may in certain countries be subject to laws, regulations or directives, which vehicle manufacturers must obviously comply with, not at least from an environmental and a competition point of view. Diagnosis of SCR-systems may today be problematic, since it is not possible, in a reliable manner, to demonstrate impaired performance of an NO _x -sensor. An incorrect determination that, for example, an NO _x -sensor is defective is associated with high costs of unnecessary service or replacement of the NO _x -sensor. One problematic aspect of said diagnosis is that said NO _x -sensor is cross-sensitive to ammonia, NH ₃ , entailing one way of determining an off-set error is to switch off the feeding of reductant to the SCR-system and to wait for a state of so-called dragging of the engine and carry out an NO _x -measurement when no NO _x -gas is generated. This method is, however, difficult to carry out with the arrival of so-called Eco-roll, hybrid drive and various

procedures to throttle the air flow in the exhaust after treatment system.

US20120255277 provides an overview of the diagnosis of an NO _x -sensor, wherein the fuel supply to an engine is throttled.

US20120303206 shows a method to diagnose one or several NO _x -sensors, which are placed upstream or downstream of an SCT-catalyst. The diagnosis is carried out with a least squares estimation.

SUMMARY OF THE INVENTION

Accordingly, there is a need, in a reliable and user-friendly manner, to diagnose an NO _x - sensor in an exhaust treatment system of a motor vehicle.

There is a need, in an efficient and reliable manner, to diagnose an NO _x -sensor in an exhaust treatment system in terms of performance.

One objective of the present invention is to provide a new and advantageous method for diagnosis of an NO _x -sensor in an exhaust treatment system. Another objective with the invention is to provide a new and advantageous system for diagnosis of an NO _x -sensor in an exhaust treatment system, and a new and advantageous computer program for diagnosis of an NO _x -sensor in an exhaust treatment system.

Another objective of the invention is to provide an alternative method for diagnosis of an NO _x -sensor in an exhaust treatment system, an alternative system for diagnosis of an NO _x - sensor in an exhaust treatment system and an alternative computer program to control the diagnosis of an NO _x -sensor in an exhaust treatment system. Another objective of the invention is to provide a method regarding an exhaust treatment system, a system regarding an exhaust treatment system, and a computer program to achieve a reliable diagnosis of an NO _x -sensor in a motor vehicle.

One objective of the invention is to achieve a reliable method to determine an off-set value for an NO _x -sensor for adapted control of an exhaust treatment system.

Some of said objectives are achieved with a method for diagnosis of an NO _x -sensor in a catalytic exhaust treatment system according to claim 1. Other objectives are achieved with a system for diagnosis of an NO _x -sensor in a catalytic exhaust treatment system according to claim 5. Advantageous embodiments are specified in the dependent claims. According to one aspect of the present invention, a method is provided to diagnose an NOx- sensor, arranged downstream of an arrangement comprising an SCR-catalyst in a catalytic exhaust treatment system to purify exhausts from an exhaust-generating system, comprising a combustion engine. The method may comprise the steps to:

- continuously determine an NO _x -level with said NO _x -sensor; - perform at least one action with the objective of increasing the SCR-catalyst arrangement's conversion degree with respect to NO _x and/or to reduce said NO _x -content downstream of said SCR-catalyst in order to determine an off-set indication for said NO _x -sensor, wherein said off-set indication is treated as a minimum NO _x -level value, which is the result of actions performed wherein said at least one action consists of at least one of the actions: - controlling the operation of said combustion engine with the objective of reducing the NOx- level in said exhausts;

- controlling the exhaust generating system with the objective of increasing said SCR- catalyst's temperature;

- increasing the supply of reductant to said SCR-catalyst arrangement; and - reducing a mass flow of said exhausts to said SCR-catalyst arrangement.

Said control of operation of said combustion engine, with the objective of reducing the NOx- level in said exhausts, may comprise increasing an EGR-level or controlling injection angles at fuel supply to said combustion engine. Here, said control may take place in a reliable and automatic manner.

Said control of the exhaust generating system, with the objective of increasing said SCR- catalyst's temperature, may advantageously be controlled in an accurate and reliable manner.

Said increase of the supply of reductant to said SCR-catalyst arrangement may

advantageously take place with high accuracy with the use of a dosage device, which device is an existing device in the exhaust treatment system. Herewith, a cost effective method is provided according to one aspect of the present invention. Said reduction of said mass flow in said exhausts to said SCR-catalyst arrangement may occur in a controlled manner, via a control device in the exhaust treatment system. Herewith, an automatic embodiment of said action is achieved, which advantageously provides a reliable and cost effective method according to one aspect of the present invention.

By determining said off-set indication, a basis for use in control algorithms of various functions in the exhaust treatment system may be provided, for example the function dosage of reductant. Said off-set indication may advantageously be used for correction of the detected NO _x -levels downstream of said SCR-catalyst arrangement. This may

advantageously contribute to lower emissions from said combustion engine, and herewith advantageously a more environmentally friendly operation of said combustion engine with the associated exhaust treatment system is advantageously provided.

The method may comprise the step to:

- perform at least two of said actions sequentially or at least partly simultaneously.

Herewith, a multifaceted and flexible method is achieved for diagnosis of said NO _x -sensor. Depending on the operating state of the exhaust purification system, one or several of said measures may be activated when suitable, and continue as long as this is deemed to be relevant to reduce said NO _x -level in the exhausts downstream of said SCR-catalyst arrangement. Application of said at least one action may be evaluated continuously and controlled in a suitable manner. The method may comprise the step to:

- as an introductory diagnosis for said NO _x -sensor, to determine whether the NO _x -level during a predetermined time period of exhaust purification does not fall below a

predetermined threshold value relating to said NO _x -level, whereafter continued diagnosis with the help of at least one of said actions is carried out. Herewith, a pre-diagnosis may advantageously be provided. Said products may, in an effective, simple and reliable manner, provide a preliminary indication of whether it is probable that said NO _x -sensor is defective, or at least has a substantial off-set error.

The method may comprise the step to: - carry out said at least one action in the form of incremental changes with subsequent result checks relating to said NO _x -level after each incremental change. Herewith, a determination of said off-set indication may advantageously occur in a relatively short time period after the initiation of said at least one action. Herewith, a cost effective and reliable method is provided according to one aspect of the present invention. According to one embodiment, said increase of said SCR-catalyst's temperature may occur in a number of steps of for example 10 degrees Celsius, wherein a result check is carried out after each such increase.

According to one embodiment, said reductant supply may be increased intermittently in a number of sequential steps, wherein each step entails a suitable increase of reductant supply per time unit, wherein a result check is carried out after each such increase.

According to one embodiment, said reduction of said mass flow of said exhausts may be carried out in a number of sequential steps, wherein a result check is carried out after each such reduction.

According to one embodiment, a method is provided to diagnose an NO _x -sensor, arranged downstream of an arrangement comprising an SCR-catalyst in a catalytic exhaust treatment system to purify exhausts from an exhaust generating system, comprising a combustion engine, comprising the steps of:

- continuously determining an NO _x -level with said NO _x -sensor; - taking at least one action with the objective of increasing the SCR-catalyst arrangement's conversion degree with respect to NO _x and/or to reduce said NO _x -level downstream of said SCR-catalyst in order to determine an off-set indication for said NO _x -sensor, wherein said offset indication is taken as a lowest NO _x -level value, which is the result of actions performed; - diagnosing the NO _x -sensor by way of the determined off-set indication for said NO _x -sensor, wherein said at least one action consists of at least one of the actions:

- controlling the operation of said combustion engine by way of increasing the EGR-level in said combustion engine and/or by controlling injection angles with respect to fuel supply in the combustion engine, with the objective of reducing the NO _x -level in said exhausts; - controlling the exhaust generating system, with the objective of increasing said SCR- catalyst's temperature;

- increasing the supply of reductant to said SCR-catalyst arrangement; and

- reducing a mass flow of said exhausts to said SCR-catalyst arrangement.

According to one aspect of the present invention, a system is provided to diagnose an NO _x - sensor, arranged downstream of an arrangement comprising an SCR-catalyst in a catalytic exhaust treatment system to purify exhausts from an exhaust generating system, comprising a combustion engine, comprising:

- elements adapted to continuously determine an NO _x -level with said NO _x -sensor;

- elements adapted to perform at least one action with the objective of increasing the SCR- catalyst arrangement's conversion degree with respect to NO _x and/or to reduce said NOx- level downstream of said SCR-catalyst;

- elements adapted to determine an off-set indication for said NO _x -sensor and to take said off-set indication as a minimum NO _x -level value, which is the result of actions performed, whereat said at least one action consists of at least one of the actions: - controlling the operation of said combustion engine with the objective of reducing the NOx- level in said exhausts; - controlling the exhaust generating system with the objective of increasing said SCR- catalyst's temperature;

- increasing the supply of reductant to said SCR-catalyst arrangement; and

- reducing a mass flow of said exhausts to said SCR-catalyst arrangement. The system may comprise:

- elements adapted to perform at least two of said actions sequentially or at least partly simultaneously.

The system may comprise:

- elements adapted, as an initial diagnosis for said NO _x -sensor, to determine whether the NO _x -level, during a predetermined time period of exhaust purification, does not fall below a predetermined threshold value relating to said NO _x -level, and to continue the diagnosis with the help of carrying out at least one of said actions.

The system may comprise:

- elements adapted to carry out said at least one action in the form of incremental changes with subsequent result checks with respect to said NO _x -level after each incremental change.

According to one embodiment, a system is provided for diagnosis of an NO _x -sensor, arranged downstream of an arrangement comprising an SCR-catalyst in a catalytic exhaust treatment system to purify exhausts from an exhaust generating system, comprising a combustion engine, comprising: - elements adapted to continuously determine an NO _x -level with said NO _x -sensor;

- elements adapted to perform at least one action with the objective of increasing the SCR- catalyst arrangement's conversion degree with respect to NO _x and/or to reduce said NOx- level downstream of said SCR-catalyst;

- elements adapted to determine an off-set indication for said NO _x -sensor and to treat said off-set indication as a minimum NO _x -level value, which is the result of actions performed, and to diagnose the NO _x -sensor via the determined off-set indication for said NO _x -sensor, wherein said at least one action consists of one of the following measures:

- controlling the operation of said combustion engine by way of increasing the EGR-level in said combustion engine and/or by controlling injection angles with respect to fuel supply in the combustion engine, with the objective of reducing the NO _x -level in said exhausts; - controlling the exhaust generating system, with the objective of increasing said SCR- catalyst's temperature;

- increasing the supply of reductant to said SCR-cata lyst arrangement; and

- reducing a mass flow of said exhausts to said SCR-catalyst arrangement.

According to one aspect of the present invention, a motor vehicle is provided, comprising a device in an exhaust treatment system according to any of the claims 5-8. Said motor vehicle may be a truck, a bus or a car.

According to one aspect of the present invention, a computer program is provided in a n exhaust treatment system, wherein said computer program comprises program code to cause an electronic control device or a computer, connected to the electronic control device, to perform the steps according to any of the claims 1-4.

According to one aspect of the present invention, a computer program is provided in a n exhaust treatment system, wherein said computer program comprises program code to cause an electronic control device or a computer, connected to the electronic control device, to perform the steps according to any of the patent claims 1-4, when said program code is executed in said control device or said computer.

According to one aspect of the present invention, a computer program is provided in a n exhaust treatment system, wherein said computer program comprises program code stored on a computer readable medium, to cause an electronic control device or a computer, connected to the electronic control device, to perform the steps according to any of the claims 1-4.

According to one aspect of the present invention, a computer program is provided in a n exhaust treatment system, wherein said computer program comprises program code stored on a computer readable medium, to cause an electronic control device or a computer, connected to the electronic control device, to perform the steps according to any of claims 1-4, when said program code is executed in said control device or said computer.

According to one aspect of the present invention, a computer program product, comprising program code stored in a computer readable medium, is provided to perform the method steps according to any of the claims 1-4, wherein said computer program is executed in a n electronic control device or in a computer connected to the electronic control device.

According to one aspect of the present invention, a computer program product comprising program code stored, in a non-volatile manner, in a computer readable medium is provided to perform the method steps according to any of the claims 1-4, when said program code is executed in an electronic control device or in a computer connected to the electronic control device.

Additional objectives, advantages and novel features of the present invention will be apparent to one skilled in the art from the following details, and through exercising the invention. While the invention is described below, it should be apparent that the invention is not limited to the specifically described details. One skilled in the art, having access to the teachings herein, will recognise additional applications, modifications and incorporations in other areas, which are within the scope of the invention.

GENERAL DESCRI PTION OF THE DRAWI NGS For a more complete understanding of the present invention and the additional objectives and advantages thereof, reference is now made to the following detailed description, which is to be read together with the accompanying drawings, in which the same reference designations relate to identical parts in the various figures, and in which:

Figure 1 schematically illustrates a vehicle, according to one embodiment of the invention; Figure 2a schematically illustrates a sub-system of the vehicle displayed in Figure 1, according to one embodiment of the invention;

Figure 2b schematically illustrates a sub-system of the vehicle displayed in Figure 1, according to one embodiment of the invention; Figure 3 schematically illustrates a diagram according to one 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 more detail a flow chart of a method, according to one embodiment of the invention;

Figure 5 schematically illustrates a computer, according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE FIGURES A side view of a vehicle 100 is shown with reference to Figure 1. The exemplified vehicle 100 consists of a towing vehicle 110 and a trailer 112, for example a bogie. The vehicle 100 may be a heavy goods vehicle, such as a truck or a bus. The vehicle 100 may, alternatively, be a car.

The term "link" as used herein refers to a communications link, which may be a physical line, such as an opto-electronic communication line, or a non-physical line, such as a wireless connection, e.g. a radio or microwave link.

The terms "reducing agent", or "reductant" as used herein, refer to a substance used to react with certain emissions in an SCR system. The terms "reductant" and "reducing agent" are used synonymously herein. These emissions may be e.g. NO _x gas. The said reductant is, according to one embodiment, also known as AdBlue. Obviously other types of reductants may be used. Herein, AdBlue is provided as an example of a reducing agent, but a person skilled in the art will realise that the innovative method and the innovative SCR-system may be realised for other types of reducing agent, in accordance with the innovative method.

It should be pointed out that the invention is suitable for application in a suitable exhaust treatment system comprising an SCR-catalyst, and is therefore not limited to an exhaust treatment system comprising an SCR-system in a motor vehicle. The innovative method and the innovative system are well suited to other platforms than land-based motor vehicles, and comprising an exhaust treatment system, such as e.g. watercraft. The watercraft may be of any suitable type, such as motor boats, ships, ferries or vessels.

The innovative method and the system according to the invention for an exhaust treatment system according to one aspect of the invention, are also suitable for e.g. systems comprising tractors, dump trucks, machinery, industrial engines and/or engine powered industrial robots.

The innovative method and the innovative system at an exhaust treatment system according to one aspect of the invention are also suitable for different types of power plants, e.g. electric power plants comprising a diesel-operated electric generator. The innovative method and the innovative system at an exhaust treatment system are well suited for any suitable engine system, comprising an engine and a n SCR system, e.g. in a locomotive or another platform.

The innovative method and the innovative system at an exhaust treatment system are well suited for a system comprising an NO _x -generator, for example a diesel engine whose exhausts must be purified.

The innovative method and the innovative system at an exhaust treatment system are well suited for a system comprising an NO _x -generator, for example a diesel engine, and an SCR- catalyst.

The term "conduit" as used herein means a passage to hold and transport a fluid, such as a reducing agent in liquid form. The conduit may be a conduit of any dimension. The conduit may consist of any suitable material, such as plastic, rubber or metal.

The term "diagnosis" as used herein refers to a diagnosis, which is not primarily treated as an error diagnosis. The term diagnosis refers to a diagnosis of an NO _x -sensor, wherein a n offset indication is determined. Said off-set indication may consist of a small value, such as 0 or near zero. Said determined off-set indication may be acceptable to the extent that said NOx- sensor is not deemed to be defective, and thus does not need to be replaced, even in a case where a relatively large off-set value is determined to be associated with said NO _x -sensor. Advantageously, said determined off-set indication associated with said NO _x -sensor may be used to correct measured NO _x -levels, wherein the corrected measured NO _x -levels may be used as a basis for control of a number of relevant

functions/components/aggregates/systems in the vehicle, such as, for example, an engine and/or an exhaust treatment system connected therewith. In this respect, an adapted control of the relevant functions/components/aggregates/systems may be advantageously achieved.

Figure 2a shows a system 299 in the vehicle 100. The system 299 may be arranged in the tractor 110. The system 299 may constitute a part of an SCR-system, which is comprised in the exhaust treatment system according to one aspect of the present invention, which exhaust treatment system is described in further details with reference to Figure 2b. The system 299 comprises, according to this example, a container 205 that is arranged to hold a reducing agent. A first conduit 271 is arranged to lead the reducing agent to a pump 230 from the container 205. Said pump 230 is arranged to pump the reducing agent from the container 205, via the first conduit 271 and to add said reducing agent to a dosage device 250, via a second conduit 272. The pump 230 is arranged to pressurise the reducing agent in the second conduit 272.

The dosage device 250 is arranged to add said reducing agent to an exhaust treatment system (see Fig. 2b) in the vehicle 100. More precisely, the dosage device 250 is arranged to, in a controlled manner, add a suitable amount of reducing agent to an exhaust treatment system in the vehicle 100. According to this embodiment, an SCR catalyst (not displayed) is arranged downstream of a position where the reducing agent is added. The amount of reducing agent that is added in the exhaust system is intended to be used in the SCR catalyst, in order to reduce the amount of undesired emissions.

A third conduit 273 is arranged between the dosage device 250 and the container 205. The third conduit 273 is arranged to lead back to the container 205 a certain amount of the reducing agent, which has been fed to the dosage device 250.

The first control device 200 is arranged for communication with the pump 230 via a link 292. The first control device 200 is arranged to control the operation of the pump 230, in order to e.g. control the flow of the reducing agent within the sub-system 299. The first control device 200 is arranged for communication with the dosage device 250 via a link L250. The first control device 200 is arranged to control the operation of the dosage device 250, in order to e.g. control the supply of reducing agent to the exhaust treatment system of the vehicle 100. The first control device 200 is arranged to activate circulation of said reducing agent via said pump 230, when this is deemed to be suitable. The first control device 200 is arranged to activate the supply of said reducing agent, when this is deemed to be suitable.

A second control device 210 is arranged for communication with the first control unit 200 via a link L210. The second control device 210 may be detachably connected to the first control device 200. The second control device 210 may be a control unit external to the vehicle 100. The second control device 210 may be arranged to carry out the method steps according to the invention. The second control device 210 may be used to transfer program code to the first control device 200, in particular program code to perform the method according to the invention. Alternatively, the second control device 210 may be arranged for communication with the first control device 200, via an internal network in the vehicle. The second control device 210 may be arranged to carry out substantially similar functions as the first control device 200.

Figure 2b schematically illustrates a system 289 in the vehicle 100 displayed in Figure 1, according to one embodiment of the invention. Said system 289 constitutes a part of an exhaust treatment system in the vehicle 100. Said system 299, which is described with reference to Figure 2a, may also constitute a part of said exhaust treatment system.

Herewith, a combustion engine 231 is provided, which, when operating, causes an exhaust flow that is led via a first passage 235 to a DOC-device 260. A second passage 245 is arranged to lead exhausts from said DOC-device 260 to a DPF-device 265. Said DPF-device 265 comprises a diesel particulate filter. A third passage 255 is arranged to lead exhausts from said DPF-device 265 to an SCR-catalyst arrangement 270. Said SCR-catalyst arrangement 270 may alternatively be referred to as an SCR-catalyst. Said SCR-catalyst arrangement may according to one example embodiment comprise a so-called slip-catalyst. Said slip-catalyst is arranged to convert ammonia into other substances than precisely ammonia and NO _x -gas. A fourth passage 256 is arranged to lead exhausts from said SCR-catalyst arrangement 270 to the environment surrounding the vehicle 100.

Said dosage device 250, which is described with reference to Figure 2a, is arranged to supply doses of reducing agent into said third passage 255, via control through the first control device 200. Figure 2b omits certain components in the SCR-system that are described with reference to Figure 2a, in order to clarify Figure 2b. It should be pointed out that said exhaust treatment system does not necessarily need to comprise said DOC-device 260 and/or said DPF-device 265. According to one alternative embodiment of said system 289, said first passage 235 is directly connected to said SCR-catalyst arrangement 270, wherein exhausts purified therein are arranged to be led to the environment surrounding the vehicle 100 via the fourth passage 256.

The first control device 200 is arranged for communication with the combustion engine 231 via a link L231. The first control device 200 is arranged to control the operation of said combustion engine 231. The first control device 200 is arranged to e.g. control the dosage of fuel to the combustion chamber in said combustion engine 231. The first control device 200 is, according to one example, arranged to control the operation of said combustion engine 231, in order to achieve certain conditions relating to exhaust temperature, exhaust mass flow and NO _x -level in the exhausts from said combustion engine 231.

A first NO _x -sensor 221 is arranged upstream of said DOC-device 260 at said first passage 235. Said first NO _x -sensor 221 is arranged for communication with the first control device 200 via a link L221. Said first NO _x -sensor 221 is arranged to continuously determine a prevailing first NO _x -level NO _x l in the first passage 235. Said first NO _x -sensor 221 is arranged to continuously send signals S221 comprising information about said prevailing first NO _x -level NO _x l in said first passage 235 to the first control device 200 via the link L221. Said first NO _x -sensor 221 is independent of whether or not said system 289 comprises said DOC-device 260 and DPF- device 265, and is arranged upstream of said SCR-catalyst arrangement 270. Said first NOx- sensor 221 is arranged upstream of said SCR-catalyst arrangement 270 and downstream of said combustion engine 231.

According to an alternative embodiment, said first control device 200 may be arranged to continuously model/calculate/estimate/determine a prevailing first NO _x -level NO _x lmod in the first passage 235. Said continuously modelled/calculated/estimated/determined prevailing first NO _x -level NO _x lmod may be used as an alternative to the prevailing first NO _x - level NO _x l, determined/measured with the first sensor 221 according to one aspect of the innovative method. A second NO _x -sensor 222 is arranged downstream of said SCR-catalyst arrangement 270 at said fourth passage 256. Said second NO _x -sensor 222 is arranged for communication with the first control device 200 via a link L222. Said second NO _x -sensor 222 is arranged to continuously determine a prevailing second NO _x -level NO _x 2 in the fourth passage 256. Said second NO _x -sensor 222 is arranged to continuously send signals S222 comprising information about said prevailing second NO _x -level NO _x 2 in said fourth passage 256, to the first control device 200 via the link L222.

Said first NO _x -sensor 221 and said second NO _x -sensor 222 may be used to provide information about the prevailing NO _x -levels in the first passage 235 and the fourth passage 245, respectively. Herewith, the first control device 200 may be arranged to continuously determine a prevailing conversion degree O with respect to NO _x -gas, based on said first NO _x - level NO _x l, NO _x lmod and said second NO _x -level NO _x 2. Said conversion degree O may alternatively be referred to as NO _x -conversion.

Said conversion degree O is herewith defined as:

NO _x 2

0 = 1 -

NO _x l

According to one alternative embodiment, said conversion degree O may be defined as:

NO _x 2

0 = 1 -

NO _x lmod According to one example embodiment, said first NO _x -sensor 221 is arranged in the first passage 235, upstream of said SCR-catalyst arrangement 270 and downstream of said combustion engine 231, in order to continuously measure/detect/determine a first NO _x -level NO _x l in the exhausts therein, and said second NO _x -sensor 222 is arranged downstream of said SCR-catalyst arrangement 270 at the fourth passage 256, in order to continuously measure/detect/determine a second NO _x -level NO _x 2 in the exhausts from the combustion engine 231. The first control device 200 is, according to one embodiment, arranged to continuously determine said conversion degree O as per above. Herewith, a continuous evaluation of said actions performed may be carried out. If it is determined that said conversion degree O is continuously increased, already initiated actions may continue. If it is determined that said conversion degree O is continuously increased, new, not yet initiated actions may be activated. Herewith, an evaluation function is achieved according to one aspect of the innovative method.

A temperature sensor 223 is arranged in said SCR-catalyst 270. Said temperature sensor 223 is arranged for communication with the first control device 200 via a link L223. Said temperature sensor 223 is arranged to continuously determine a prevailing temperature in said SCR-catalyst 270. Said temperature sensor 223 is arranged to continuously send signals S223 comprising information about said prevailing temperature Tmeas of the SCR-catalyst 270 to the first control device 200 via the link L223. According to an alternative embodiment, said temperature sensor 223 is arranged to continuously measure an exhaust temperature in the first passage 235, or in another suitable place in the exhaust treatment system.

According to one embodiment, a prevailing exhaust temperature Tmod may be determined/calculated/modelled in a suitable manner. This may be carried out with procedures stored in a memory of the first control device 200.

The first control device 200 is, according to one embodiment, arranged to control the exhaust generating system with the objective of increasing said SCR-catalyst's 270 temperature, based on said detected temperature Tmeas and/or said calculated temperature Tmod. Herewith, an advantageous feedback of the prevailing temperature in the exhaust treatment system takes place. In the event it is considered that said prevailing temperatures are too low, said first control device 200 may activate/continue with temperature increasing actions, in order to achieve said increase of said SCR-catalyst's 270 temperature.

A mass flow sensor 224 is arranged in the first passage 235. Said mass flow sensor 224 is arranged for communication with the first control device 200 via a link L224. Said mass flow sensor 224 is arranged to continuously determine a prevailing mass flow MFmeas in exhausts from said combustion engine 231. Said mass flow sensor 224 is arranged to continuously send signals S224 comprising information about said prevailing mass flow MFmeas of the exhausts to the first control device 200 via the link L224. According to one alternative embodiment, said mass flow sensor 224 is arranged to continuously measure a prevailing mass flow MFmeas in the second passage 245 or the third passage 255.

According to one embodiment, a prevailing exhaust mass flow MFmod may be determined/calculated/modelled in a suitable manner. This may be carried out with procedures stored in a memory of the first control device 200.

The first control device 200 is, according to one embodiment, arranged to control said reduction of the mass flow of said exhausts to said SCR-catalyst 270 with the objective of increasing the conversion degree of the SCR-catalyst arrangement with respect to NO _x , based on said detected exhaust mass flow MFmeas and/or said calculated exhaust mass flow MFmod. Herewith, an advantageous feedback of the prevailing exhaust mass flow in the exhaust treatment system takes place. In the event it is considered that said prevailing exhaust mass flow is deemed to be too low, said first control device 200 may activate relevant actions, in order to achieve said reduction of said exhaust mass flow to said SCR- catalyst 270. The first control device 200 is, according to one example embodiment, arranged to perform at least one action with the objective of increasing said conversion degree O with respect to NO _x in the SCR-catalyst 270, in order to determine an off-set indication for said NO _x -sensor, wherein said off-set indication is treated as a minimum NO _x -level value, which is the result of actions performed. Examples of actions that said first control device 200 is arranged to carry out are described below.

The first control device 200 is, according to one example embodiment, arranged to control the operation of said combustion engine 231 with the objective of reducing the NO _x -level in said exhausts upstream of said SCR-catalyst 231. The first control device 200 is arranged to e.g. control the EGR-level in an EGR-device in said combustion engine 231. The first control device 200 is arranged to e.g. control the injection angles for dosage of fuel to said combustion engine 231.

The first control device 200 is, according to one example embodiment, arranged to control the exhaust generating system with the objective of increasing said SCR-catalyst's temperature. This may take place in a number of various ways, for example via control of an exhaust brake in the combustion engine 231. Said control may be carried out with drivers stored in a memory of the first control device 200.

The first control device 200 is, according to one example embodiment, arranged to reduce a mass flow of said exhausts to said SCR-catalyst 270. Said mass flow reduction may occur in a suitable manner via control of said combustion engine 231. Said reduction in mass flow MF may occur intermittently in stages or continuously. Said reduction in mass flow may occur via drivers stored in a memory of the first control device 200.

The first control device 200 is, according to one example embodiment, arranged to control the reduction of a mass flow in said exhausts to said SCR-catalyst 270. This may occur in any suitable manner.

The first control device 200 is, according to one example embodiment, arranged to perform at least two of said actions sequentially or at least partly simultaneously. According to one embodiment, only one of said actions is carried out, in order to improve a conversion degree O relating to NO _x in the SCR-catalyst 270. According to one embodiment, at least two of said actions are carried out sequentially. According to one embodiment, all four of said actions are carried out substantially sequentially, i.e. a certain overlap of actions may occur.

According to one embodiment, all four said actions are carried out sequentially, with an interval for a suitably time period between the respective activation of a subsequent action, i.e. a certain overlap of the implementation of actions may occur. According to one example embodiment, the control device 200 is arranged to perform at least two of said actions simultaneously. The first control device 200 is, according to one example embodiment, arranged to perform all four said actions simultaneously. The first control device 200 is, according to one example embodiment, arranged as an initial diagnosis for said second NO _x -sensor 222, in order to determine whether the second NO _x - level NO _x 2, during a predetermined time period of exhaust purification, does not fall below a predetermined threshold value TH with respect to said second NO _x -level NO _x 2, in which case the continued diagnosis with the help of at least one of said measures is performed. In the event the second NO _x -level NO _x 2, during said predetermined time period of exhaust purification, does not fall below a predetermined threshold value TH, it may be determined that said second NO _x -sensor 222 may be defective, and that further diagnosis according to the innovative method may be initiated.

The first control device 200 is arranged to carry out said at least one action in the form of incremental changes with subsequent result checks with respect to said second NO _x -level NO _x 2 after each incremental change. Herewith, the first control device 200 may be arranged to control whether said action(s) performed have the intended effect, i.e. control that said conversion degree O of the SCR-catalyst 270 increases to a maximum conversion degree O. In the event a prevailing second NO _x -level NO _x 2 in the exhausts downstream of said SCR- catalyst 270 falls below a predetermined threshold value during a certain time period, and does not continue to decrease, the determination of said off-set indication may be carried out. Herewith, a lowest possible value with respect to said second NO _x -level NO _x 2 downstream of said SCR-catalyst 270 is determined. Herewith, said second NO _x -sensor 222 may thus be diagnosed according to one aspect of the innovative method. Said off-set indication may, where applicable, be determined after/during said actions performed. Said off-set indication is preferably the lowest possible value NO _x 2, which said second NO _x -sensor 222 measures after said actions performed.

Presentation elements 220 are arranged for communication with said first control device 200 via a link L220. The first control device 200 is arranged to present a result of said diagnosis of said second NO _x -sensor 222 to an operator of the vehicle 100 with said presentation elements 220. Said operator may be a driver of the vehicle 100. Said operator may be a service technician in a workshop of a vehicle service station.

Said result may, for example, indicate "proper function" or "defective". Said result may, for example, comprise information about said determined off-set indication, for example expressed in ppm (parts per million). For example, a degree of functional impairment in said second NO _x -sensor 222 may be presented, and such degree of functional impairment may be specified as a percentage. Said degree of functional impairment may be determined based on said determined off-set indication. Said presentation elements 220 may comprise speakers to render a synthesized voice or other audio feedback. Said presentation elements 220 may comprise a display screen, for example a so-called touch screen for visual feedback of said result.

Figure 3 illustrates a diagram that describes, schematically, the principles according to one aspect of the present invention.

In the diagram, said second NO _x -level NO _x 2 is determined with said second NO _x -sensor 222 as a function of time T, specified in seconds s, while various actions described herein are performed with the objective of increasing the SCR-catalyst's 270 conversion degree O with respect to NO _x , in order to determine an off-set indication for said second NO _x -sensor 222. As illustrated in said diagram, said off-set indication is treated as a minimum NO _x -level value NO _x min, which is a result of actions performed. Said minimum NO _x -level value NO _x min is designated with N6 in the diagram.

Initially, said exhaust treatment system has an NO _x -level Nl downstream of said SCR-catalyst 270. At a point in time Tl, a first action is activated, namely to control the operation of said combustion engine 231, with the objective of reducing said first NO _x -level NO _x l in said exhausts from said combustion engine 231. This may take place in different suitable ways. Herewith, said second NO _x -level NO _x 2 drops to a level N2.

At a point in time T2, a second action is activated, namely to control the exhaust generating system, comprising said combustion engine 231, with the objective of increasing the temperature of said SCR-catalyst 270. This may take place in different suitable ways.

Herewith, said second NO _x -level NO _x 2 drops to a level N3. At a point in time T3 a third action is activated, namely to increase the supply of reducing agent to said SCR-catalyst arrangement. This may take place in different suitable ways.

Herein, it is clear that the dosage of reducing agent first increases continuously in the dosage device 250. Herewith, said second NO _x -level NO _x 2 drops to a level N4. At a point in time T4, an incremental increase of the dosage of reducing agent occurs, wherein said second NOx- level NO _x 2 shows a response in the form of a step. Herewith, said second NO _x -level NO _x 2 drops to a level N5.

At a point in time T5, a fourth action is activated, namely to reduce a mass flow in said exhausts to said SCR-catalyst arrangement 270. This may take place in different suitable ways. Herewith, said second NO _x -level NO _x 2 drops to a minimum level N6, also referred to as NO _x min. This minimum value NO _x min occurs at a point in time T6. The value at said minimum level N6 is treated as said off-set indication. Herewith, said second NO _x -sensor 222 is diagnosed.

According to this example embodiment, said actions performed overlap with each other in time. Herewith, during the time period T5-T6 all four indicated actions are performed.

Herewith, during the time period T3-T4 said first, second and third action is performed. Herewith, during the time period T2-T3 said first and second action is performed. It should be pointed out that said various actions may have periods of intermission and subsequently be activated again before said minimum NO _x -level NO _x min is determined. Figure 4a illustrates schematically a flow chart of a method to diagnose an NO _x -sensor 222, arranged downstream of an arrangement comprising an SCR-catalyst 270 of a catalytic exhaust treatment system to purify exhausts from an exhaust generating system, comprising a combustion engine 231. The method step s401 may comprise the steps:

- to continuously determine an NO _x -level NO _x 2 with said NO _x -sensor 222; - to perform at least one action with the objective of increasing the SCR-catalyst

arrangement's conversion degree O with respect to NO _x and/or to reduce said NO _x -level NO _x 2 downstream of said SCR-catalyst 270, in order to determine an off-set indication for said NO _x -sensor 222, wherein said off-set indication is treated as a minimum NO _x -level value NO _x min, which is the result of actions performed, wherein said at least one action consists of at least one of the actions: - controlling the operation of said combustion engine 231 with the objective of reducing the NO _x -level NO _x l in said exhausts;

- controlling the exhaust generating system with the objective of increasing said SCR- catalyst's 270 temperature; - increasing the supply of reductant to said SCR-catalyst arrangement 270; and

- reducing a mass flow of said exhausts to said SCR-catalyst arrangement 270. Following the method step s401 the method is completed.

Figure 4b illustrates schematically a flow chart of a method to diagnose an NO _x -sensor 222, arranged downstream of an arrangement comprising an SCR-catalyst 270 in a catalytic exhaust treatment system to purify exhausts from an exhaust generating system, comprising a combustion engine 231.

The method comprises a first method step s405. The method step s405 may comprise the step of activating the diagnosis of said second NO _x -sensor 222. The method step s405 may comprise the step of activating diagnosis of said second NO _x -sensor 222, comprising the step of determining an off-set value associated therewith, also referred to as an off-set indication. According to the innovative method, at least one action is performed with the objective of increasing the SCR-catalyst arrangement's 270 conversion degree O with respect to NO _x , on order to determine an off-set indication for said second NO _x -sensor 222, wherein said off-set indication is treated as a minimum NO _x -level value, which is the result of actions performed. Said actions are carried out in the subsequent method steps s410, s420, s430 and s440, respectively. According to the method, at least one of the steps S410-440 is carried out. It should be pointed out that said method steps s410, s420, s430 and s440 may be carried out in a different order than the one exemplified herewith. At least two of these actions may, according to one example embodiment, be carried out simultaneously or at least partly simultaneously. An evaluation of the determination with respect to the point in time for detection of said minimum NO _x -level NO _x min takes place continuously, and where applicable a method step s450 is carried out. Following the method step s405, a subsequent method step s410 is completed. The method step s410 may comprise the step of controlling the operation of said combustion engine 231 with the objective of reducing said first NO _x -level NO _x l in said exhausts. Herewith, for example an EGR-level in said combustion engine 231 may be increased in a suitable manner. Alternatively, or as a complement, injection angles with respect to fuel dosage in the combustion engine 231 may be controlled in a suitable manner, in order to achieve the desired effect. Following the method step s410, a subsequent method step s420 is completed.

The method step s420 may comprise the step of controlling the exhaust generating system with the objective of increasing said SCR-catalyst's 270 temperature. This may for example occur by activating power consuming units operated by said combustion engine 231, for example an AC-unit in the vehicle 100. Said temperature increase may be achieved with the application of different throttles in the combustion engine 231, or application of an exhaust brake associated therewith. According to one alternative, a prevailing Lambda value for operation of said combustion engine 231 may be adjusted in a suitable manner. According to one alternative, said temperature increase may be achieved by way of impact of injection angles with respect to fuel dosage in said combustion engine 231. Following the method step s420, a subsequent method step s430 is completed.

The method step s430 may comprise the step of increasing the supply of reducing agent to said SCR-catalyst arrangement 270. This may occur via control of the dosage unit 250 with said first control device 200. Said increase of the supply of reducing agent to said SCR- catalyst arrangement 270 may occur continuously or intermittently in a suitable manner. Following the method step s430, a subsequent method step s440 is completed.

The method step s440 may comprise the step of reducing a mass flow of said exhausts to said SCR-catalyst arrangement 270. This may occur in a controlled manner via a control device in the exhaust treatment system. Following the method step s440, a subsequent method step s450 is completed.

The method step s450 may comprise the step, after the undertaking of at least one action specified in any of the method steps s410-s440 with the objective of increasing the SCR- catalyst arrangement's 270 conversion degree O with respect to NO _x , to determine an off- set indication for said second NO _x -sensor 222, wherein said off-set indication is treated as a minimum NO _x -level value NO _x min, which is the result of actions performed. This off-set indication is illustrated in the diagram with reference to Figure 3 at the point in time T6. Herewith, said second NO _x -sensor 222 is diagnosed according to one aspect of the innovative method. Following the method step s450, a subsequent method step s460 is completed.

The method step s460 comprises the step of presenting a result of said diagnosis of said second NO _x -sensor 222. Herewith, for example said detected minimum NO _x -level NO _x min may be presented. Herewith, said result may be presented in the form of an assessment such as "proper performance" or "defective", or in another suitable manner. This may occur via said presentation elements 220 and said first control device 200. Herewith, a result with respect to said diagnosis may be presented to, for example, an operator of the vehicle 100, a driver or service staff. Following the method step s460, the method is completed.

With reference to Figure 5, a diagram of an embodiment of a system 500 is shown. The control devices 200 and 210, which are described with reference to Figure 2a and Figure 2b, may in one embodiment 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 part 530, wherein a computer program, such as an operating system, is stored to control the function of the unit 500. Further, the unit 500 comprises a bus controller, a serial communications port, an I/O device, an A/D converter, a date-time input and transmission unit, an event counter and an interrupt controller (not shown). The non-volatile memory 520 also has a second memory part 540.

A computer program P is provided to control the diagnosis of an NO _x -sensor 222, arranged downstream of an arrangement comprising an SCR-catalyst 270 in a catalytic exhaust treatment system to purify exhausts from an exhaust generating system, comprising a combustion engine 231.

The computer program P may comprise procedures to continuously determine an NO _x -level with said second NO _x -sensor 222.

The computer program P may comprise procedures to perform at least one action with the objective of increasing the SCR-catalyst arrangement's 270 conversion degree O with respect to NO _x and/or to reduce said NO _x -level NO _x 2 downstream of said SCR-catalyst 270, in order to determine an off-set indication for said NO _x -sensor 222, wherein said off-set indication is treated as a minimum NO _x -level value, which is the result of actions performed, wherein said at least one action consists of at least one of the actions described herein. The computer program P may comprise procedures to diagnose the NO _x -sensor 222 with the determined off-set indication for said NO _x -sensor 222.

The computer program P may comprise procedures to control the operation of said combustion engine with the objective of reducing said first NO _x -level NO _x l in said exhausts. Herewith, accordingly said second NO _x -level NO _x 2 is also reduced. The computer program P may comprise procedures to control the operation of said combustion engine by increasing the EGR-level of said combustion engine and/or by controlling injection angles with respect to fuel dosage in the combustion engine, with the objective of reducing the NO _x -level in said exhausts.

The computer program P may comprise procedures to control the exhaust generating system with the objective of increasing said SCR-catalyst's 270 temperature.

The computer program P may comprise procedures to increase the supply of reducing agent to said SCR-catalyst arrangement 270.

The computer program P may comprise procedures to reduce a mass flow of said exhausts to said SCR-catalyst arrangement 270. The computer program P may comprise procedures to perform at least two of said actions sequentially or at least partly simultaneously.

The computer program P may comprise procedures to determine, as an initial diagnosis for said NO _x -sensor 222, whether the NO _x -level NO _x 2, during a predetermined time period of exhaust purification, does not fall below a predetermined threshold value with respect to said NO _x -level NO _x 2, in which case continued diagnosis is undertaken with the help of at least one of said actions. The computer program P may comprise procedures to carry out said at least one action in the form of incremental changes with subsequent result checks with respect to said NO _x - level NO _x 2 after each incremental change.

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

A statement that the data processing unit 510 performs a certain function means that the data processing unit 510 performs a certain part of the program stored in the memory 560, or a certain part of the program stored in the read/write memory 550.

The data processing unit 510 may 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 for communication with the data processing unit 510 via a data bus 511. The read/write memory 550 is arranged for communication with the data processing unit 510 via a data bus 514. The links L210, L220, L221, L222, L223, L224, L231, L250 and L292, for example, may be connected to the data port 599 (see Figure 2a and Figure 2b).

When data is received in the data port 599, it is temporarily stored in the second memory part 540. When input data received is temporarily stored, the data processing unit 510 is ready to carry out execution of code in the manner described above. According to one embodiment, signals received in the data port 599 comprise information about said first prevailing NO _x -level NO _x l, said second prevailing NO _x -level NO _x 2, a prevailing temperature Tmeas of said SCR-catalyst, a calculated temperature Tmod of exhausts or of said SCR- catalyst 270, a calculated exhaust mass flow MFmod and/or a measured exhaust mass flow MFmeas.

Parts of the methods described herein may be carried out by the unit 500 with the help of the data processing unit 510, which runs the program stored in the memory 560 or the read/write memory 550. When the unit 500 runs the program, the procedures described herein are executed.

The foregoing description of the preferred embodiments of the present invention has been furnished for illustrative and descriptive purposes. It is not intended to be exhaustive, or to limit the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order to best explicate the principles of the invention and its practical applications, and to thereby enable one skilled in the art to understand the invention in terms of its various embodiments and with the various modifications that are applicable to its intended use.