TECHNICAL FIELD OF THE INVENTION

The present invention concerns a method for troubleshooting an SCR system. The invention also concerns a computer program product containing program code for a computer to implement a method according to the invention. The invention also concerns a device for troubleshooting an SCR system and a motor vehicle that is equipped with the device.

BACKGROUND

In vehicles today, e.g. urea is used as a reductant in SCR (Selective Catalytic Reduction) systems comprising an SCR catalytic converter, in which catalytic converter said reductant and NO _x gas can react and be converted into nitrogen and water. Different types of reductants can be used in SCR systems. For example, AdBlue is one commonly occurring reductant. One type of SCR system includes a container that contains a reductant. The SCR system also has a pump that is arranged so as to pump said reductant from the container via a suction tube and supply it via a pressurized tube to a dosing unit that is arranged in an exhaust system in the vehicle, such as in an exhaust pipe of the exhaust system. The dosing unit is arranged so as to inject a required amount of reductant into an exhaust system upstream of the SCR catalytic converter according to operating routines stored in a control unit in the vehicle.

There is a constant need to reduce the amount of emissions from engines in motor vehicles. This applies not least to heavy motor vehicles such as trucks and buses, as legal requirements demanding ever-lower emissions are continuously being made stricter. An error code is generated in SCR systems in vehicles today in connection with certain errors or operational deviations. This error code can, however, be far too unspecific, with the result that service personnel can have major problems identifying an error source in the SCR system. In certain cases where an error code pertaining to said SCR system is generated, it may be some other system that is not functioning in the intended manner, which can in turn negatively affect the SCR system, whereupon an error code is mistakenly generated for the SCR system. Even though it can be difficult to identify precisely which component in the SCR system is faulty, it is desirable to at least be able to rule out one or more of the components that are included in an SCR system. This is especially relevant for, for example, the SCR catalytic converter, as it is expensive and time-consuming to remove this component from the vehicle for, for example, visual inspection or other troubleshooting methods.

US 201 1296905, DE102010028846 and US201032605 described different methods for troubleshooting an SCR system. SUMMARY OF THE INVENTION

One object of the present invention is to provide a new and advantageous method for troubleshooting an SCR system. Another object of the invention is to provide a new and advantageous device and a new and advantageous computer program for troubleshooting an SCR system.

Yet another object of the invention is to provide a method, a device and a computer program for achieving reliable and user-friendly troubleshooting of an SCR system. These objects are achieved by means of a method for troubleshooting an SCR system according to claim 1 .

According to one aspect of the invention, a method is provided for troubleshooting an SCR system that contains a dosing unit for dosing reducing agent into an engine exhaust duct upstream of an SCR catalytic converter for reducing the NO _x level in an exhaust flow from said engine. The method comprises the steps of:

- determining the NO _x level in the exhaust flow downstream of said SCR catalytic converter;

- gradually changing the dosing of said reducing agent under predetermined operating conditions for said SCR catalytic converter;

- determining whether the SCR catalytic converter is able to reduce said NO _x level in the exhaust gas flow downstream of said SCR catalytic converter to a predetermined extent during said gradually changed dosing; and

- deciding, based on the result of said determination, whether said SCR catalytic converter is defective or not from the standpoint of NO _x level reduction. The method can comprise the step of:

- achieving said predetermined operating conditions in the form of a predetermined lowest temperature level for said SCR catalytic converter and a predetermined exhaust mass flow. The method can comprise the step of achieving said predetermined operating conditions in the form of a predetermined lowest temperature level for said SCR catalytic converter and an essentially constant and/or predetermined exhaust mass flow. The method can comprise the step of achieving said predetermined operating conditions in the form of a predetermined lowest temperature level for an exhaust duct from the engine and an essentially constant and/or predetermined exhaust mass flow. The method can comprise the step of achieving said predetermined operating conditions in the form of a predetermined lowest temperature level for exhaust in an exhaust duct that is arranged so as to conduct said exhaust from an engine to the surroundings and an essentially constant and/or predetermined exhaust mass flow. Said predetermined lowest temperature level can be, for example, 300 degrees Celsius. Said predetermined lowest temperature can be, for example, 350 degrees Celsius. Said predetermined lowest temperature level can be within a range of, for example, 300-400 degrees Celsius.

The method according to the invention can be implemented as a repair shop test. The method according to the invention can be carried out during operation when the vehicle is standing still, for example at a repair shop or service facility.

The method according to the invention can be carried out during operation, for example when the vehicle is being driven on a suitable stretch of road. The method according to the invention can be carried out when the vehicle is being driven under circumstances when favorable operating cases can be achieved, which operating cases can include that a lowest temperature for the SCR catalytic converter of the vehicle is achieved, and when an exhaust flow favorable to the method is achieved.

According to one aspect of the invention, the method according to the invention can be carried out by means of data detected by a NO _x sensor downstream of said SCR catalytic converter, whereupon other necessary data can be modeled or calculated in a suitable manner. A cost-effective implementation of the method according to the invention is thereby achieved.

The method can comprise the step of:

- achieving said predetermined operating conditions by controlling the operation of said engine. Said predetermined operating conditions can pertain to a specific rpm for said engine. Said predetermined operating conditions can pertain to a predetermined engine load. Said predetermined operating conditions can pertain to a specific fuel dosing for said engine. Said predetermined operating conditions can thus be achieved in an automatic and controlled manner, which advantageously entails that a desired operating state of the vehicle is achieved. Said operating conditions can comprise a state in which an exhaust flow from an engine of the vehicle is essentially constant.

The step of gradually changing said dosing can comprise continuously increasing or continuously decreasing the dosing. A precise method for troubleshooting can be achieved thereby.

The step of gradually changing said dosing can comprise incrementally increasing or incrementally decreasing the dosing. A relatively fast method for troubleshooting an SCR system can be advantageously achieved thereby.

The method can comprise the step of:

- waiting for a steady state in the reduction of the NO _x level downstream of said SCR catalytic converter. More accurate measurements of the NO _x level downstream of said SCR catalytic converter can thereby be obtained, which can advantageously result in it being possible to make a very probably accurate determination as to whether said SCR catalytic converter is defective or not from the standpoint of NO _x level reduction. Measurements by means of a NO _x sensor downstream of said SCR catalytic converter are advantageously achieved by waiting for a steady state at a suitable time, such as when the SCR system is in a stable state. In connection with changes in the dosing of the reducing agent, a certain amount of time may be needed for said NO _x sensor for stabilization.

The step of determining whether the SCR catalytic converter is able to reduce said NO _x level in the exhaust flow downstream of said SCR catalytic converter to a predetermined extent can comprise the step of: - determining the absolute values for said NO _x level in the exhaust flow downstream of said SCR catalytic converter, and/or the steps of:

- determining the absolute values for said NO _x level in the exhaust flow upstream of said SCR catalytic converter;

- determining the absolute values for said NO _x level in the exhaust flow downstream of said SCR catalytic converter; and

- determining a NOx conversion rate for the SCR catalytic converter on the basis of said NO _x level in the exhaust flow upstream of said SCR catalytic converter and said NO _x level in the exhaust flow downstream of said SCR catalytic converter.

Two different ways of determining the performance of said SCR catalytic converter are advantageously provided hereby. A versatile method is hereby provided for partly detecting whether an SCR system in which both only said NO _x level [in the] exhaust flow downstream of said SCR catalytic converter and said NO _x conversion rate for the SCR catalytic converter can be used.

The method can comprise the step of:

- representing the reduction of the NO _x level downstream of said SCR catalytic converter by said SCR catalytic converter during said gradually changed dosing as the absolute values of said NO _x level downstream of said SCR catalytic converter as a function of reducing agent dosing or NO _x conversion rate as a function of reducing agent dosing. According to one embodiment, a relatively inexpensive implementation of the method according to the invention is hereby achieved, as an extremely limited number of sensors (one NO _x sensor downstream of said SCR catalytic converter) are necessary. According to one embodiment, a well-defined basis for calculations according to the method according to the invention is hereby achieved, as a NO _x conversion rate reflects a prevailing performance of the SCR catalytic converter very well. Said ΝΟχ level downstream of said SCR catalytic converter as a function of reducing agent dosing can include a minimum. A method with a relatively limited need for calculating capacity can be achieved hereby. Said ΝΟχ conversion rate as a function of reducing agent dosing can include a maximum. A method with a relatively limited need for calculating capacity can be achieved hereby.

The method can comprise the step of:

- presenting said result of said determination of the reduction in said NO _x level in the exhaust flow downstream of said SCR catalytic converter (270) to a predetermined extent in the form of an error code. Said error code can be presented to an operator of the vehicle by means of suitable means. According to one embodiment, said error code can be stored in a memory of a control unit in the vehicle, which error code can be presented in a later stage to service personnel at, for example, a repair shop by means of suitable means. According to one embodiment, said error code can be sent automatically via a suitable network to a so-called fleet manager system or haulage contractor.

The method can comprise the step of:

- perform a check of the function of SCR system above and beyond said SCR catalytic converter. The efficient elimination of error sources in the SCR system or the vehicle can be achieved hereby, which can advantageously result in a reliable method for troubleshooting an SCR system. For example, any leakage of exhaust or reducing agent can be detected hereby. A check of the functions of various relevant sensors in the vehicle can be performed hereby. Said sensors can be, for example, NO _x sensors, exhaust mass sensors or temperature sensors. This can advantageously result in a reliable method for troubleshooting an SCR system. The method is easy to implement in existing vehicles. Software for troubleshooting an SCR system according to the invention can be installed in a control unit in the vehicle during its manufacture. A purchaser of the vehicle can then have opportunity to choose the function of the method as an option. Software containing program code for performing the innovative method for troubleshooting an SCR system can alternatively be installed in a control unit in the vehicle during an upgrade at a service station. In this case the software can be loaded into a memory in the control unit. Software that contains program code for troubleshooting an SCR system can easily be updated or replaced. Further more, different parts of the software that contain program code for troubleshooting an SCR system can be replaced independently of one another. This modular configuration is advantageous from a maintenance perspective.

According to one aspect of the invention, a device is provided for troubleshooting an SCR system comprising a dosing unit for dosing reducing agent into the exhaust duct of a engine upstream of an SCR catalytic converter to reduce the NO _x level in an exhaust flow from said engine. The device comprises:

- means adapted so as to determine the NO _x level in the exhaust flow downstream of said SCR catalytic converter;

- means adapted so as to gradually change the dosing of said reductant under predetermined operating conditions for said SCR catalytic converter; - means adapted so as to determine whether the SCR catalytic converter is able to reduce said NO _x level in the exhaust flow downstream of said SCR catalytic converter to a predetermined extent during said gradually changed dosing ; and

- means adapted so as to decide, based on the result of said determination, whether said SCR catalytic converter is defective or not from the standpoint of ΝΟχ level reduction. The device can comprise:

- means adapted so as to achieve said predetermined operating conditions in the form of a predetermined lowest temperature for said SCR catalytic converter and a predetermined exhaust mass flow. Said exhaust mass flow can be an essentially constant exhaust mass flow. Said exhaust mass flow can be an exhaust mass flow that is defined by a value that falls within a predetermined interval. Said exhaust mass flow can be a well defined exhaust mass flow. Said exhaust mass flow can be of a magnitude that is defined by a predetermined value.

The device can comprise:

- means adapted so as to achieve said predetermined operating conditions by controlling the operation of said engine. The device can comprise:

- means adapted so as to change said dosing by continuously increasing or decreasing the dosing.

The device can comprise:

- means adapted so as to gradually change said dosing by incrementally increasing or decreasing the dosing.

The device can comprise:

- means adapted so as to wait for a steady state in the reduction of the NO _x level downstream of said SCR catalytic converter.

Said means in the device adapted so as to determine whether said SCR catalytic converter is able to reduce said NO _x level in the exhaust flow downstream of said SCR catalytic converter to a predetermined extent can comprise:

- means adapted so as to determine the absolute values for said NO _x level in the exhaust flow downstream of said SCR catalytic converter; and/or:

- means adapted so as to determine the absolute values for said NO _x level in the exhaust flow upstream of said SCR catalytic converter;

- means adapted so as to determine the absolute values for said NO _x level in the exhaust flow downstream of said SCR catalytic converter; and

- means adapted so as to determine a NO _x conversion rate for the SCR catalytic converter on the basis of said NO _x level in the exhaust flow upstream of said SCR catalytic converter and said NO _x level in the exhaust flow downstream of said SCR catalytic converter.

The device can comprise:

- means adapted so as to represent the reduction in the NO _x level downstream of said SCR catalytic converter by said SCR catalytic converter during said gradually changed dosing as the absolute values of said NO _x level downstream of said SCR catalytic converter as a function of reducing agent dosing or the NO _x conversion rate as a function of reducing agent dosing.

In the device, said NO _x level downstream of said SCR catalytic converter as a function of reducing agent dosing can include a minimum.

In the device, said NO _x conversion rate as a function of reducing agent dosing can include a maximum. The device can comprise:

- means adapted so as to present said result of said determination regarding the reduction of said NO _x level in the exhaust flow downstream of said SCR catalytic converter (270) to a predetermined extent in the form of an error code.

The device can comprise: - means adapted so as to perform a check of the function of the SCR system above and beyond said SCR catalytic converter.

The foregoing objects are also achieved by means of a motor vehicle that contains the device for troubleshooting an SCR system. The motor vehicle can be a truck, bus or car.

According to one aspect of the invention, a computer program is provided for troubleshooting an SCR system, wherein said computer program contains program code for causing an electronic control unit or another computer connected to the electronic control unit to perform the steps according to any of claims 1 -12.

According to one aspect of the invention, a computer program is provided for troubleshooting an SCR system, wherein said computer program contains program code stored on a computer-readable medium for causing an electronic control unit or another computer connected to the electronic control unit to perform the steps according to any of claims 1 -12. According to one aspect of the invention, a computer program product is provided containing a program code stored on a computer-readable medium for performing the method steps according to any of claims 1 -12 when said program code is run on an electronic control unit or another computer connected to the electronic control unit.

Additional objects, advantages and new features of the present invention will be apparent to one skilled in the art from the following details, and through the exercise of the invention. While the invention is described below, it should be evident that the invention is not limited to the specifically described details. One skilled in the art who has access to the teaching herein will recognize additional applications, modifications and incorporations in other areas, which are within the scope of the invention. OVERVIEW DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and additional objects and advantages thereof, reference will now be made to the following detailed description, which is to read along with the accompanying drawings, in which the same reference designations refer to the same parts in the various figures, and in which: Figure 1 schematically illustrates a vehicle according to one embodiment of the invention;

Figure 2 schematically illustrates a device for troubleshooting an SCR system according to one embodiment of the invention;

Figure 3a schematically illustrates a flow diagram of a method according to one embodiment of the invention;

Figure 3b schematically illustrates, in greater detail, a flow diagram of a method according to one embodiment of the invention;

Figure 4a schematically illustrates a diagram according to one aspect of the invention;

Figure 4b schematically illustrates a diagram according to one aspect of the invention; and

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 show with reference to Figure 1 . The exemplified vehicle 100 consists of a tractor 1 10 and a trailer 1 12. The vehicle can be a heavy vehicle, such as a truck or a bus. The vehicle can alternatively be a car. It should be noted that the invention is suited for application in any arbitrary suitable SCR system, and thus is not limited to SCR systems in motor vehicles. According to one aspect of the invention, the innovative method and the innovative SCR system are well suited for platforms other than motor vehicles that contain an SCR system, such as watercraft. The watercraft can be of any arbitrary suitable type, such as motorboats, vessels, ferries or ships.

According to one aspect of the invention, the innovative method and the innovative SCR system are also well suited to, for example, systems containing a stone crusher or the like.

According to one aspect of the invention, the innovative method and the innovative SCR system are also suitable for, for example, systems that contain industrial motors and/or motorized industrial robots.

According to one aspect of the invention, the innovative method and the innovative SCR system are also well suited for various types of power plants, such as electrical power plants that contain a diesel generator.

The innovative method and the innovative SCR system are well suited for any arbitrary suitable engine system that contains an engine and an SCR system, such as a locomotive or other platform. The innovative method and the innovative SCR system are well suited for any arbitrary system that contains a NO _x generator and an SCR system.

The term "link" refers herein to a communications link, which can be a physical line, such as an opto-electronic communication line, or a non- physical line, such as a wireless connection, for example a radio or microwave link. The term "line" refers herein to a passage for containing and transporting a fluid, such as a reductant in liquid form. The line can be a tube of any arbitrary dimension. The line can consist of any arbitrary suitable material, such as plastic, rubber or metal..

The terms "reductant "and "reducing agent" refer herein to an agent that is used to react with certain emissions in an SCR system. These emissions can, for example, be NO _x gas. The terms "reductant" and "reducing agent" are used synonymously herein. According to one embodiment, said reductant is so-called AdBlue. Other types of reductants can naturally be used. AdBlue is cited herein as an example of a reductant, but one skilled in the art will perceive that the innovative method and the innovative device can be realized for other types of reductants. A device 299 in the vehicle 100 is shown with reference to Figure 2. The device 299 can be disposed in a tractor 1 10. The device 299 can be a part of an SCR system or contain an SCR system. The device 299 according to this example comprises a container 205 that is arranged so as to hold a reductant. The container 205 is arranged so as to contain a suitable amount of reductant, and is further arranged so as to be able to be filled as needed.

A first line 271 is arranged to conduct the reductant to a pump 230 from the container 205. The pump 230 can be any arbitrary suitable pump. The pump 230 can be a membrane pump comprising at least one filter. The pump 230 can be arranged so as to be driven by means of an electric motor (not shown). The pump 230 can be arranged so as to pump the reductant from the container 205 via the first line 271 , and to supply said reductant to a dosing unit 250 via a second line 272. The dosing unit 250 can comprise an electrically controlled dosing device by means of which a flow of reductant added to the exhaust system can be controlled. The pump 230 is arranged so as to pressurize the reductant in the second line 272. The dosing unit 250 is arranged with a throttle unit, which can also be referred to as a throttle valve, against which said pressure of the reductant can be built up in the device 299.

The dosing unit 250 is arranged so as to supply said reductant to an exhaust duct 290 in the vehicle 100. More specifically, the dosing unit 250 is arranged so as to supply, in a controlled manner, a suitable amount of reductant to an exhaust duct 290 in the vehicle 100, according to one aspect of the method according to the invention. According to this embodiment, an SCR catalytic converter 270 is arranged downstream of a location in the exhaust system where the addition of the reductant occurs. The amount of reductant that is supplied to the exhaust system is intended to be used in the SCR catalytic converter to reduce the amount of undesirable emissions.

The dosing unit 250 can be disposed in said exhaust duct 290, which is arranged so as to lead exhaust from a combustion engine (not shown) of the vehicle 100 to the SCR catalytic converter and on to the surroundings of the vehicle. A third line 273 is pre-existingly arranged between the dosing unit 250 and the container 205. The third line 273 is arranged so as to lead a certain amount of the reductant that is fed to the dosing valve 250 back to the container 205.

The first control unit 200 is arranged for communication with the pump 230 via a link L230. The first control unit 200 is arranged so as to control the operation of the pump 230. According to one example, the first control unit 200 is arranged so as to control the pump 230 by means of an electric motor (not shown). The first control unit 200 is arranged so as to influence a working pressure in the second line 272. This can occur in various suitable ways. According to one example, the first control unit 200 is arranged so as to change a prevailing rpm of the pump 230. The pressure can be changed thereby in a desirable manner. The working pressure can be increased by increasing the rpm of the pump 230. The working pressure can be decreased by decreased the rpm of the pump 230. The first control unit 200 is arranged for communication with a first temperature sensor 240 via a link L240. The temperature sensor 240 is arranged so as to detect a prevailing temperature T1 of an exhaust flow from the vehicle engine. According to one example, the first temperature sensor 240 is arranged in said exhaust duct 290 directly downstream of the vehicle engine and upstream of a dosing unit 250. The temperature sensor 240 can be pre-existingly arranged in a suitable location in said exhaust duct 290. The first temperature sensor 240 is arranged so as to continuously detect a prevailing temperature T1 of the exhaust flow and send signals containing information about said prevailing temperature T1 via the link L240 to the first control unit 200.

The first control unit 200 is arranged for communication with a second temperature sensor 260 via a link L260. The second temperature sensor 260 can be arranged so as to detect a prevailing temperature T2 of a surface in the exhaust system where the reductant is being vaporized. The second temperature sensor 260 can be arranged so as to detect a prevailing temperature T2 in the exhaust duct 290 at a suitable location. The second temperature sensor 260 can be arranged so as to detect a prevailing temperature T2 of a suitable surface or component of the exhaust duct 290. According to one example, the second temperature sensor 260 is arranged in the exhaust duct 290 upstream of the dosing unit 250. According to one example, the second temperature sensor 260 is arranged in the exhaust duct 290 upstream of the dosing unit 250. According to another example, the second temperature sensor 260 is arranged in a vaporizing unit (not shown) or the SCR catalytic converter 270 downstream of the dosing unit 250. The second temperature sensor 260 is arranged so as to continuously detect a prevailing temperature T2 of a surface or a component of the exhaust duct 290 and send signals containing information about said prevailing temperature T2 via the link L260 to the first control unit 200. According to one embodiment, the first control unit 200 and/or the second control unit 210 are arranged so as to calculate said first temperature T1 . This can occur by means of a stored calculation model. The first control unit 200 and/or the second control unit 210 can be arranged so as to calculate said first temperature T1 on the basis of, for example, a prevailing exhaust mass flow, prevailing engine rpm and prevailing engine load.

According to one embodiment, the first control unit 200 and/or the second control unit 210 are arranged so as to calculate said second temperature T2. This can occur by means of a stored calculation model. The first control unit 200 and/or the second control unit 210 can be arranged so as to calculate said second temperature T2 on the basis of, for example, a prevailing exhaust mass flow, prevailing engine rpm and prevailing engine load. A first ΝΟχ sensor 255 is arranged for communication with the first control unit 200 via a link L255. The first NO _x sensor 255 is arranged so as to continuously determine a prevailing NO _x level for said exhaust flow upstream of said SCR catalytic converter 270. According to one example, the first NO _x sensor 255 is arranged in the exhaust duct 290 upstream of said dosing unit 250. The first NO _x sensor 255 is arranged so as to continuously send signals containing information about a prevailing NO _x level upstream of said SCR catalytic converter 270 to the first control unit 200.

A second NO _x sensor 265 is arranged for communication with the first control unit 200 via a link L265. The second NO _x sensor 265 is arranged so as to continuously determine a prevailing NO _x level for the exhaust flow downstream of said SCR catalytic converter 270. The second NO _x sensor 265 is arranged so as to continuously send signals containing information about a prevailing NO _x level downstream of said SCR catalytic converter 270 to the first control unit 200. According to one embodiment, the first control unit 200 and/or the second control unit 210 are arranged so as to calculate said first NO _x level upstream of said SCR catalytic converter 270. This can occur by means of a stored calculation model. The first control unit 200 and/or the second control unit 210 can be arranged so as to calculate said first NO _x level on the basis of, for example, a prevailing exhaust mass flow, prevailing engine rpm and prevailing engine load.

The first control unit 200 is arranged so as to determine a prevailing NO conversion rate on the basis of said calculated or measured NO _x level upstream of said SCR catalytic converter and said measured NO _x level downstream of said SCR catalytic converter 270.

The first control unit 200 is arranged so as to determine the NO _x level in the exhaust flow downstream of said SCR catalytic converter 270. The first control unit 200 is arranged so as to determine the NO _x level in the exhaust flow upstream of said SCR catalytic converter 270. The first control unit 200 is arranged so as to achieve operating conditions suitable for the purpose for said SCR catalytic converter. The first control unit 200 is arranged so as, under predetermined operating conditions for said SCR catalytic converter 270, to gradually change the dosing of said reducing agent. The first control unit 200 is arranged so as to determine whether the SCR catalytic converter 270 is able to reduce said NO _x level in the exhaust flow downstream of said SCR catalytic converter to a predetermined extent during said gradually changed dosing. The first control unit 200 is arranged so as to decide, based on the result of said determination, whether said SCR catalytic converter is defective or not from the standpoint of NO _x level reduction.

The first control unit 200 is arranged so as to communicate with presentation means 280 via a link L280. Said presentation means 280 can be preexisting^ arranged in a cab of the vehicle 100. Said presentation means 280 can be fixedly mounted in the vehicle 100. Said presentation means 280 can be a mobile electronic unit. Said presentation means 280 can comprise, for example, a display screen. The first control unit 200 is arranged so as to present an error code or other relevant information pertaining to the innovative method for troubleshooting an SCR system. The first control unit 200 can be arranged so as to present, by means of said presentation means 280, a result as to whether said SCR catalytic converter 270 is defective or not from the standpoint of NO _x level reduction.

The first control unit 200 is arranged so as to communicate with a communication unit 285 via a link L285. Said communication unit 285 can be present in, for example, a service station, repair shop, haulage contractor or a so-called fleet management system.

Said communication unit 285 can be pre-existingly arranged in a cab of the vehicle 100. Said communication unit 285 can be fixedly mounted in the vehicle 100. Said communication unit 285 can be a mobile electronic unit. Said communication unit 285 can comprise, for example, a display screen. The first control unit 200 is arranged so as, automatically or upon request, to present an error code or other relevant information pertaining to the innovative method for troubleshooting an SCR system. The first control unit 200 can be arranged so as to present, by means of said communication terminal 285, a result as to whether said SCR catalytic converter 270 is defective or not from the standpoint of NO _x level reduction. The first control unit 200 is arranged so as to communicate with the dosing unit 250 via a link L250. The first control unit 200 is arranged so as to control the operation of the dosing unit 250 in order to, for example, adjust the supply of reductant to the exhaust system of the vehicle 100. The first control unit 200 is arranged so as to calculate an exhaust mass flow MF for the exhaust from the vehicle engine. The first control unit 200 is arranged so as to continuously determine an exhaust mass flow MF for the exhaust from the vehicle engine. This can occur in any arbitrary suitable manner.

According to one embodiment, the subsystem comprises a mass flow sensor (not shown) that is arranged so as to continuously measure a prevailing exhaust mass flow from the engine of the vehicle 100 in the exhaust duct 290 upstream of said SCR catalytic converter 270. Said mass flow sensor is arranged so as to continuously send signals containing information about a prevailing exhaust mass flow to the first control unit via a link arranged for that purpose.

A second control unit 21 0 is arranged so as to communicate with the first control unit 200 via a link L21 0. The second control unit 21 0 can be removably connected to the first control unit 200. The second control unit 21 0 can be a control unit that is external to the vehicle 100. The second control unit 21 0 can be arranged so as to perform the innovative method steps according to the invention. The second control unit 21 0 can be used to load software over to the first control unit 200, particularly software for performing the innovative method. The second control unit 21 0 can alternatively be arranged so as to communicate with the first control unit 200 via an internal network in the vehicle. The second control unit 21 0 can be arranged so as to perform essentially the same functions as the first control unit 200, such as gradually changing the dosing of said reducing agent under predetermined conditions for the SCR catalytic converter 270;

- determining whether the SCR catalytic converter 270 is able to reduce the ΝΟχ level in the exhaust flow downstream of the SCR catalytic converter 270 to a predetermined extent during said gradually changed dosing; and

- deciding, based on the result of said determination, whether said SCR catalytic converter 270 is defective or not from the standpoint of NO _x level reduction. Figure 3a schematically illustrates a flow diagram of a method, according to one embodiment, for troubleshooting an SCR system comprising a dosing unit for dosing reducing agent into the exhaust duct of an engine upstream of a SCR catalytic converter to reduce the NO _x level in an exhaust flow from said engine. The method comprises a first method step s301 . The step s301 comprises the steps of:

- determining the NO _x level in the exhaust flow downstream of said SCR catalytic converter;

- gradually changing the dosing of said reducing agent under predetermined conditions for said SCR catalytic converter;

- determining whether the SCR catalytic converter is able to reduce said NO _x level in the exhaust flow downstream of said SCR catalytic converter to a predetermined extent during said gradually changed dosing; and

- deciding, based on the result of said determination, whether said SCR catalytic converter is defective or not from the standpoint of NO _x level reduction. The method is concluded after the step s301 .

Figure 3b schematically illustrates a flow diagram of a method, according to one embodiment of the invention, for troubleshooting an SCR system comprising a dosing unit 250 for dosing reducing agent into an exhaust duct 290 of an engine upstream of an SCR catalytic converter 270 to reduce the NO _x level in an exhaust flow from said engine.

The method comprises a first method step s310. The method step s310 can comprise the step of activating the method according to the invention. Said activation can be performed by an operator of the vehicle 100. Said activation can be performed by repair shop personnel or service personnel at a repair shop or service facility. Said activation can occur by means of said presentation means 280 and/or said communication unit 285.

The method step s310 can comprise the step of achieving an operating state suitable for the method according to the invention. The method step s310 can comprise the step of achieving predetermined operating conditions in the form of a predetermined lowest temperature of said SCR catalytic converter 270 and a predetermined exhaust mass flow. Said exhaust mass flow can be determined by means of means intended for same, such as a mass flow sensor or suitable calculating means, such as the first control unit 200. The method step s310 can comprise the step of achieving predetermined operating conditions in the form of a predetermined lowest temperature with regard to said first temperature T1 and/or said second temperature T2. The method step s310 can comprise the step of achieving said predetermined operating conditions by controlling the operation of said engine.

The method step s310 comprises the step of determining the NO _x level in the exhaust flow downstream of said SCR catalytic converter. This can occur by measuring by means of said NO _x sensor 265.

A subsequent method step s320 is performed after the method step s310.

The method step s320 comprises the step of gradually change the dosing of said reducing agent under predetermined operating conditions for said SCR catalytic converter. The step s320 can comprise gradually changing said dosing by continuously increasing or continuously decreasing the dosing. The step s320 can comprise gradually changing said dosing by incrementally increasing or incrementally decreasing the dosing. The first control unit 200 and/or the second control unit 210 can thus continuously or intermittently determine the performance of the SCR catalytic converter 270 by determining a NO _x level downstream of said SCR catalytic converter and/or a NO _x conversion rate for the SCR catalytic converter 270. It should be noted that the NO _x level downstream of said SCR catalytic converter and/or a NO _x conversion rate for the SCR catalytic converter 270 can be determined for both gradually increasing dosing of the reducing agent and gradually decreasing dosing of the reducing agent. According to one embodiment, the dosing can be controlled continuously toward both increased dosing and decreased dosing during the determination of said NO _x level downstream of said SCR catalytic converter and/or a NO _x conversion rate for the SCR catalytic converter 270.

According to one embodiment, the dosing can be controlled toward increased dosing from relatively low dosing during the determination of said NO _x level downstream of said SCR catalytic converter and/or a NO _x conversion rate for the SCR catalytic converter 270.

According to one embodiment, the dosing can be controlled continuously toward decreased dosing from relatively high dosing during the determination of said NO _x level downstream of said SCR catalytic converter and/or a NO _x conversion rate for the SCR catalytic converter 270.

According to one embodiment, the dosing can first be controlled continuously toward decreased dosing from relatively high dosing, and subsequently controlled continuously toward increased dosing from relatively low dosing during the determination of said NO _x level downstream of said SCR catalytic converter and/or a NO _x conversion rate for the SCR catalytic converter 270.

According to one embodiment, the dosing can first be controlled continuously toward increased dosing from relatively low dosing, and subsequently controlled continuously toward decreased dosing from relatively high dosing during the determination of said NO _x level downstream of said SCR catalytic converter and/or a NO _x conversion rate for the SCR catalytic converter 270.

According to one example, said dosing can sweep toward increased dosing and decreased dosing within a suitable dosing range. A more interesting subrange with respect to the dosing of reducing agent can be observed thereby. Said subrange can advantageously be a suitable subrange that includes a maximum NO _x conversion rate for the SCR catalytic converter 270.

A subsequent method step s330 is performed after the method step s320.

The method step s330 comprises the step of determining whether the SCR catalytic converter is able to reduce said NO _x level in the exhaust flow downstream of said SCR catalytic converter to a predetermined extent during said gradually changed dosing.

The step s330 can comprise the step of determining the reducing agent dosing at which peak performance of the SCR catalytic converter 270 is presented under the given operating conditions. According to one embodiment, a maximum NO _x conversion rate is determined that reflects a peak performance of the SCR catalytic converter 270 under the given operating conditions. According to one embodiment, a minimal NO _x level downstream of said SCR catalytic converter is determined that reflects a peak performance of the SCR catalytic converter 270 under the given operating conditions.

A subsequent method step s340 is performed after the method step s330.

The method step s340 comprises the step of deciding, on the basis of said determination, whether said SCR catalytic converter is defective or not from the standpoint of NO _x level reduction.

This can be performed by comparing said determined maximum NO _x conversion rate to a predetermined value TH1 . If said determined maximum NO _x conversion rate exceeds said value TH1 , the SCR catalytic converter 270 is considered not to be defective. If said determined maximum NO _x conversion rate is below said value TH1 , the SCR catalytic converter 270 is considered to be defective. This can alternatively or complementarily be performed by comparing said determined minimum NO _x level to a predetermined value TH2. If said determined minimum value NO _x level exceeds said value TH2, the SCR catalytic converter 270 is considered not to be defective. If said determined minimum NO _x level exceeds said value TH2, the SCR catalytic converter 270 is considered to be defective.

The method step s340 can comprise the step of presenting said result of said determination in the form of an error code. The method step s340 can include presenting said result for an operator of the vehicle 1 00 by means of, for example, said presentation means 280. The method step s340 can include presenting said result for service personnel at a repair shop or service facility by means of, for example, said communication unit 280.

The method is concluded after the method step s340.

With reference to Figure 4a, a diagram is shown in which the NO _x conversion rate R for the SCR catalytic converter 270 is given as a function of the amount of reducing agent D dosed by the dosing unit 250. Said dosed amount of reducing agent can be a prevailing dosed amount of reducing agent. Said dosed amount of reducing agent can be an average value for the dosed amount of reducing agent as determined in a suitable way. The NO _x conversion rate R is expressed in terms of percentage [%]. Dosing of reducing agent D is expressed in terms of [g/minute].

The NO _x conversion rate R can be determined using equation 1 below: (1 ) ΝΟχ conversion rate = 1 - (NO _x level downstream/NO _x level upstream) It can be seen here that the SCR catalytic converter 270 exhibits a highest conversion rate R1 at a dosing D1 . The value R1 thus indicates a maximum value for the NO _x conversion rate in said curve R(D). According to one aspect of the invention, it can be determined that the SCR catalytic converter 270 is not defective from the standpoint of NO _x level reduction if said value R1 exceeds a predetermined threshold value TH1 . Said predetermined threshold value TH1 can be an appropriate value. Said predetermined threshold value TH1 can, for example, be 90%, 95% or 98%. Said predetermined value TH1 can be within a range of 95-99%.

According to one aspect of the invention, it can be determined that the SCR catalytic converter 270 is defective from the standpoint of NO _x level reduction if said value R1 is below said predetermined threshold value TH1 .

It should be noted that the dosing of said reducing agent occurs under predetermined operating conditions for said SCR catalytic converter. According to one example, said curve is generated only when a temperature T2 in the catalytic converter 270 exceeds a predetermined temperature Tth and a relatively high and/or stationary exhaust mass flow prevails. According to one example, said curve is generated only when a temperature T1 of the exhaust exceeds a predetermined temperature Tth and a relatively high and/or stationary exhaust mass flow prevails. Said operating conditions can be achieved by controlling the vehicle engine by means of said first control unit 200 and/or said second control unit 210.

With reference to Figure 4b, a diagram is shown wherein the NO _x level C downstream of said SCR catalytic converter 270 is given as a function of the amount of reducing agent D dosed by the dosing unit 250. The NO _x level C is expressed in terms of ppm (parts per million). The dosing of reducing agent D is expressed in terms of [g/minute]. It can be seen here that the SCR catalytic converter 270 achieves a lowest ΝΟχ level C2 downstream of said SCR catalytic converter 270 at a dosing D2. The value C2 thus indicates a minimum value for the NO _x level downstream of said SCR catalytic converter for a function C(D).

According to one aspect of the invention, it can be determined that the SCR catalytic converter 270 is not defective from the standpoint of NO _x level reduction if said value C2 exceeds a predetermined threshold value TH2. Said predetermined threshold value TH2 can be a suitable value. Said predetermined threshold value TH2 can, for example, be 40, 50 or 60 ppm. Said predetermined threshold value TH2 can be within the range of 70-100 ppm.

According to one aspect of the invention, it can be determined that the SCR catalytic converter 270 is defective from the standpoint of NO _x level reduction if said value C2 exceeds said predetermined threshold value TH2.

It should be noted that the dosing of said reducing agent occurs under predetermined operating conditions for said SCR catalytic converter 270. According to one example, said curve C(D) is generated only when a temperature T2 in the catalytic converter 270 exceeds a predetermined temperature Tth and a relatively high and/or stationary exhaust mass flow prevails. According to one example, said curve C(D) is generated only when a temperature T1 of the exhaust exceeds a predetermined temperature Tth and a relatively high and/or stationary exhaust mass flow prevails. Said operating conditions can be achieved by controlling the vehicle engine by means of said first control unit 200 and/or said second control unit 210.

A diagram an embodiment of a device 500 is shown with reference to Figure 5. In one embodiment, the control units 200 and 210 described with reference to Figure 2 can contain the device 500. The device 500 contains 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 section 530 in which a computer program, such as an operating system, is stored in order to control the function of apparatus 500. The apparatus 500 further contains a bus controller, a serial communication port, I/O devices, an A/D converter, a time and date input and transfer unit, an event counter and a termination controller (not shown). The non-volatile memory 520 also has a second memory section 540.

A computer program P is provided that can contain routines for troubleshooting an SCR system comprising a dosing unit for dosing reducing agent into an engine exhaust duct upstream of an SCR catalytic converter to reduce the NO _x level in an exhaust flow form said engine.

The computer program P can contain routines for determining the NO _x level in the exhaust flow downstream of said SCR catalytic converter. The computer program P can contain routines for gradually changing the dosing of said reducing agent under predetermined operating conditions for said SCR catalytic converter. The computer program P can contain routines for determining whether the SCR catalytic converter is able to reduce said NO _x level in the exhaust flow downstream of said SCR catalytic converter to a predetermined extent during said gradually changed dosing. The computer program P can contain routines for deciding, based on the result of said determination, whether said SCR catalytic converter is defective or not from the standpoint of NO _x level reduction. The computer program P can contain routines for achieving said predetermined operating conditions in the form of a predetermined lowest temperature level for said SCR catalytic converter and a predetermined exhaust mass flow. The computer program P can contain routines for achieving said predetermined operating conditions by controlling the operation of said engine. The computer program P can contain routines for waiting for a steady state in the reduction of the NO _x level downstream of said SCR catalytic converter. The computer program P can contain routines for:

- determining the absolute values of said NO _x level in the exhaust flow downstream of said SCR catalytic converter, and/or routines for:

- determining the absolute values of said NO _x level in the exhaust flow upstream of said SCR catalytic converter;

- determining the absolute values of said NO _x level in the exhaust flow downstream of said SCR catalytic converter; and

- determining a NO _x conversion rate for the SCR catalytic converter on the basis of said NO _x level in the exhaust flow upstream of said SCR catalytic converter and said NO _x level in the exhaust flow downstream of said SCR catalytic converter.

The computer program P can contain routines for representing the reduction of the said NO _x level downstream of said SCR catalytic converter by said SCR catalytic converter during said gradually changed dosing as the absolute values of said NO _x level downstream of said SCR catalytic converter as a function of reducing agent dosing or the NO _x conversion rate as a function of reducing agent dosing.

The computer program P can contain routines for identifying a function for a function regarding said NO _x level downstream of said SCR catalytic converter as a function of reducing agent dosing. The computer program P can contain routines for identifying a maximum for a function regarding the NO _x conversion rate for the SCR catalytic converter as a function of reducing agent dosing.

The computer program P can contain routines for presenting said result of said determination in the form of an error code. The computer program P can contain routines for performing a check of the function of SCR system above and beyond said SCR catalytic converter. The program P can be stored in executable form or in compressed form in a memory 560 and/or in a read/write memory 550.

When it is stated that the data-processing unit 510 performs a given function, it is to be understood that the data-processing unit 510 executes a certain part of the program that is stored in the memory 560, or a certain part of the program that is stored in the read/write memory 550.

The data-processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended to communicate with the data-processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data-processing unit 510 via a data bus 51 1 . The read/write memory 550 is arranged to communicate with the data- processing unit 510 via a data bus 514. For example, the links L210, L230, L240, L250, L255, L260, L265, L280 and L285 can be connected to the data port 599 (see Figure 2).

When data are received at the data port 599, they are stored temporarily in the second memory section 540. Once received input data have been stored temporarily, the data-processing unit 510 is arranged so as to execute code in a manner as described above.

According to one embodiment, signals received at the data port 599 contain information about the NO _x level upstream of the SCR catalytic converter 270. According to one embodiment, signals received at the data port 599 contain information about the NO _x level downstream of the SCR catalytic converter 270. According to one embodiment, signals received at the data port 599 contain information about a prevailing temperature of the exhaust upstream of the SCR catalytic converter 270. According to one embodiment, signals received at the data port 599 contain information about a prevailing temperature of an appropriate surface of or component in the exhaust duct 290, for example a temperature of the SCR catalytic converter 270. The signals received at the data port 599 can be used by the device 500 to decide whether said SCR catalytic converter is defective or not from the standpoint of NO _x level reduction.

Parts of the methods described herein can be performed by the device 500 with the help of the data processing unit 510, which runs the program stored in the memory 560 and/or the read/write memory 550. The method described herein is executed when the device 500 runs the program.

The foregoing description of the preferred embodiments of the present invention has been provided 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.