WO2015002591A1

WO2015002591A1 - DEVICE AND METHOD FOR DETECTION OF DEFECTIVE NOx SENSOR

Info

Publication number: WO2015002591A1
Application number: PCT/SE2014/050695
Authority: WO
Inventors: Mikael LUNDSTRÖM
Original assignee: Scania Cv Ab
Priority date: 2013-07-02
Filing date: 2014-06-10
Publication date: 2015-01-08
Also published as: DE112014002540T5; SE537270C2; SE1300461A1; DE112014002540B4

Abstract

The invention pertains to a method to detect at least one defective NOx sensor (255; 265) arranged in an exhaust pipe (290) from an engine (206), comprising the steps: - to continuously determine an NOx level in the exhausts from said engine (206) in said exhaust pipe (290) with said NOx sensor (255; 265); - to determine a rate of change (Η') in said continuously determined NOx level; - to compare a size of said rate of change (Η') with a predetermined value (H'max); and - in cases where said size of said rate of change (H') exceeds said predetermined value (H'max), to treat it as an indication that said NOx sensor (255; 265) is defective. The invention also pertains to a device for detecting at least one defective NOx sensor (255; 265) arranged in an exhaust pipe (290) from an engine (206), and a motor vehicle (100) comprising said device.

Description

Device and method for detection of defective NOx sensor TECHNICAL FIELD OF THE INVENTION

The present invention pertains to a method for detection of defective NOx sensors. 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 pertains to a device for detection of defective NOx sensors and a motor vehicle equipped with such a device. BACKGROUND

There are currently strict regulations in many countries relating to emissions of unwanted gases and particles from vehicles. Vehicle manufacturers constantly work on improving after treatment systems to make it possible further to reduce the amount of unwanted emissions in exhausts. Unwanted gases forming in the vehicle engines, for which there are restrictions, are e.g. nitrogen oxides (NOx, also called NOx).

One way of reducing the amount of NOx in exhausts is to use a so-called after treatment system, e.g. an SCR (Selective Catalytic Reduction) system. Said after treatment system may also be called an exhaust treatment system. This system comprises an SCR catalyst and a reductant, e.g. urea, in the SCR catalyst, said reductant and NOx gas may react and be converted into nitrogen and water.

The amount of NOx in exhausts is measured with at least one NOx sensor, which is placed in the exhaust system, e.g. downstream of the SCR catalyst. The sensor is used to detect the amount of NOx in exhausts released from the vehicle. The signal from the NOx sensor may be used to control e.g. the amount of reductant used in the SCR system, or to generate error codes when the amount of NOx is higher than a certain predetermined value. An error code generated when the amount of NOx in the exhausts is higher than a certain predetermined value is then registered in a control system of the vehicle. In certain cases such an error code may entail that a warning lamp starts to blink in the vehicle and the driver is recommended to drive to a service station within a certain predetermined period of time. In certain cases an error code generated based on an NOx sensor signal means that the vehicle's maximum speed is limited, until the cause of the error code has been corrected. In certain cases, an error code may be generated based on an incorrect NOx sensor signal, the error code of which may indicate that urea of a quality which does not meet certain predetermined requirements has been used.

A defective NOx sensor detects an incorrect amount of NOx in exhausts. A defective NOx sensor may cause incorrect error codes associated with an increased amount of NOx being generated. When servicing the vehicle, when an error code associated with an increased NOx level has been generated, a first service task may be to replace the NOx sensor. An NOx sensor is a component which is relatively easy to replace, and the service staff may want to ensure that the NOx sensor does not cause an incorrectly detected amount of NOx in the exhausts before they start more complex troubleshooting of the vehicle. In the cases where the NOx sensor is not defective, the NOx sensor is then replaced unnecessarily.

SU MARY OF THE INVENTION

One objective of the present invention is to provide a novel and advantageous method for detecting at least one defective NOx sensor.

Another objective of the invention is to provide a novel and advantageous device and a novel and advantageous computer program for detecting at least one defective NOx sensor. Another objective of the invention is to provide a method, a device and a computer program for achieving a reliable and user-friendly detection of at least one defective Ox sensor. These objectives are achieved with a method for detecting at least one defective NOx sensor according to claim 1, and a device according to claim 9.

The preferred embodiments are specified in the independent claims. According to one aspect of the present invention, a method is provided for detecting at least one defective NOx sensor arranged in an exhaust pipe from an engine, comprising the steps:

^■■ to continuously determine an NOx level in the exhausts from said engine in said exhaust pipe with said NOx sensor;

- to determine a rate of change in said continuously determined NOx level;

- to compare a size of said rate of change with a predetermined value; and

- in cases where said size of said rate of change exceeds said predetermined value, to treat it as an indication of said NOx sensor being defective. The inventors have realised that NOx sensors may have in-built defects. Said in-built defects in said NOx sensors may cause said NOx sensors to show incorrect measuring values during a limited time period. After such time period, the NOx sensor may revert to showing correct values. The inventors have realised that one indication of said defect in said NOx sensor may be determined by, with the help of the continuously determined NOx level of exhausts from an engine, determining a rate of change in said continuously determined NOx level. The size of said rate of change is compared with a predetermined value, and where said size of said rate of change exceeds said predetermined value, it is treated as an indication that said NOx sensor is defective. Said predetermined value is a suitable value, which may be determined in advance with the help of empirical data.

Said rate of change may be determined by calculating a time derivative of a curve, which is established based on the continuously determined NOx levels in said exhausts.

The size of said rate of change may be an absolute value of said size. Said rate of change may be specified with a positive or a negative sign.

The method may comprise the step:

- to compare said rate of change in said continuously determined NOx level with an expected rate of change in said NOx level, where said expected rate of change in said NOx level is determined with a corresponding NOx sensor arranged in said exhaust pipe, and/or a calculation model.

The inventors have realised that an exceeding of a predetermined value in a detected rate of change in said continuously determined NOx level in exhausts from the engine is an indicator of an inaccurate first NOx sensor, in some cases, however, a rate of change in the NOx level may be expected, where said rate of change exceeds a predetermined value, e.g. due to different operating modes in the engine. In such cases the determined rate of change in the NOx level, where said rate of change exceeds a predetermined value, does not indicate a defective first NOx sensor. In cases where said determined rate of change exceeds a predetermined value, and where said rate of change is not expected, said rate of change in said determined NOx levei is an indication of an inaccurate first NOx sensor.

Where a rate of change in the NOx level has been determined, where said rate of change exceeds a predetermined value, a comparison of the determined rate of change in the NOx leve! is made with an expected rate of change in the NOx level. Said expected rate of change in the NOx level may be determined with a corresponding second NOx sensor, arranged in an exhaust pipe from an engine. Said corresponding second NOx sensor may, according to one embodiment, be arranged on the same in- or outflow side of the SCR catalyst in said exhaust pipe as said first NOx sensor, e.g. an upstream side or a downstream side. According to one alternative, said corresponding second NOx sensor is arranged on the other in- or outflow side of the SCR catalyst in said exhaust pipe, in cases where said corresponding second NOx sensor is arranged on the other in- or outflow side of the SCR catalyst in said exhaust pipe, regard must be had to the movement of the exhausts in said exhaust pipe, in cases where said corresponding second NOx sensor is placed upstream of said SCR catalyst, and where said first NOx sensor which is detected as defective is placed downstream of said SCR catalyst, the exhausts will first reach said corresponding second NOx sensor, and subsequently, after a time period which is determined by how quickly the exhausts are transported in the exhaust pipe, said exhausts, on which a measurement has been carried out, will reach said first NOx sensor, in order to be able to compare the respective rates of change in the NOx Ievei, a suitable time synchronisation is therefore advantageously used.

The method may comprise the step:

^■■ to compare said rate of change in said continuously determined NOx level with an expected rate of change in said NOx level, where said expected rate of change in said NOx level is determined with a calculation model, wherein said calculation model comprises operating conditions in said engine.

An expected rate of change in said NOx level determined with a first NOx sensor may, according to one example embodiment, be determined with a corresponding second NOx sensor and/or a calculation model. Said corresponding second NOx sensor may be arranged upstream of said first NOx sensor in said exhaust pipe, e.g. upstream of an SCR catalyst in the exhaust pipe. Said corresponding second NOx sensor may be arranged downstream of said first NOx sensor in said exhaust pipe, e.g. downstream of an SCR catalyst in the exhaust pipe. in cases where said second NOx sensor is arranged upstream or downstream of said first NOx sensor, said comparison may be adapted according to parameters that impact the respective measured NOx level. Said parameters may relate to where said NOx sensor is placed in relation to the SCR catalyst, or a potential time delay in order to ensure that the respective NOx sensor determines the NOx level in substantially the same volume of exhausts.

An expected rate of change in the NOx level of said exhausts may, according to one example embodiment, be generated with a calculation model. Said calculation model may be based on different operating parameters, such as the amount of fuel injected in the engine, operating conditions in the engine, accumulated amount of administered reductant in the exhaust pipe, etc., and external parameters such as the gradient of the surface, prevailing air resistance for the vehicle, etc.

The method may comprise the step:

^■■ to determine, based on said comparison of said rate of change in said continuously determined NOx level with said expected rate of change in said NOx level, whether said rate of change is expected.

Said comparison of said rate of change in said continuously determined NOx level, with an expected rate of change in said NOx level, is carried out to determine whether the determined rate of change in the NOx level is expected. According to one example, a rate of change in the NOx level, where said rate of change exceeds a predetermined value, may occur where an accelerator pedal in the vehicle is quickly fully released. According to another example, a rate of change in the NOx level, where said rate of change exceeds a predetermined value, may occur where the accelerator pedal is qusckiy depressed to the floor. There are also other examples of operating modes where the rate of change in the NOx level, where said rate of change exceeds a predetermined value, may occur, such as during an upstart process of an NOx sensor. !n the above said cases said rate of change in the NOx level, where said rate of change exceeds a predetermined value, is expected.

The method may also comprise the step, where said rate of change in said continuously determined NOx level differs from said expected rate of change in said NOx level, to treat this as a confirmed defect in said NOx sensor.

Where a detected rate of change in said continuously determined NOx level in exhausts from an engine exceeds a predetermined value, and where said continuously determined NOx level differs from said expected rate of change in said NOx level, it is treated as a confirmed defect in said first NOx sensor.

The method may comprise the step:

- in cases where a defect is confirmed in said NOx sensor and where a time period, during which said size of said determined rate of change exceeds said predetermined value, is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change exceeds said predetermined value, to generate an error code associated with a defective NOx sensor. The inventors have realised that, where a defect is confirmed in said first NOx sensor, and where a time period, during which said size of said determined rate of change exceeds said predetermined value, is followed by a time period with a high determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change exceeds said predetermined value, this is, as a rule, associated with an intermittently faulty function in said first NOx sensor. In these cases, an error code associated with a defective first NOx sensor is generated. The inventors have realised that, where a defect is confirmed in said first NOx sensor, and where a time period, during which said size of said determined rate of change exceeds said predetermined value, is foiiowed b a time period with a lower determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change exceeds said predetermined value, this is, as a rule, associated with intermittently faulty function in said first NOx sensor. In these cases, an error code associated with a defective first NOx sensor is generated.

Since the NOx level varies over time depending on a number of factors, such as the engine's prevailing operating mode, a mean value of the NOx level during a time period before, and a mean value of the NOx level during a time period after said time period, during which said size of said determined rate of change exceeds said predetermined value, may be used, in case of a confirmed increase or decrease after the time period, during which the size of said determined rate of change exceeds said predetermined value, an error code associated with a defective NOx sensor is generated,

According to one example, said increase of said NOx level is confirmed only where the difference between the mean value of the NOx level during a time period before, and a time period after said time period, respectively, during which said size of said determined rate of change exceeds said predetermined value, exceeds a predetermined value.

According to one example, said decrease of the NOx level is confirmed only where the difference between the mean value of the NOx level during a time period before and a time period after said time period, respectively, during which said size of said determined rate of change exceeds a predetermined value.

According to one example embodiment, said error code associated with said NOx sensor is generated only where the increase is not expected. This may be verified by comparing the NOx level determined with a first NOx sensor with an NOx level determined by a corresponding second NOx sensor, or by comparing with an NOx level determined by a calculation model. According to one example embodiment, said error code associated with said NOx sensor is generated only where the reduction is not expected. This may be verified by comparing the NOx level determined with a first NOx sensor with an NOx level determined by a corresponding second NOx sensor, or by comparing with an NOx level determined by a calculation model.

According to one exampie embodiment, said increase of the NOx level is confirmed to be prevailing where the increase is expected, but where said increase exceeds said expected increase by a certain predetermined value. According to one example embodiment, said reduction of the NOx level is confirmed to be prevailing where the reduction is expected, but where said reduction is below said expected reduction by a certain predetermined value. The method may comprise the step:

- in case a defect has been confirmed in said NOx sensor and where a time period, during which said size of said determined rate of change exceeds said predetermined value, is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change exceeds said predetermined value, to replace a generated error code associated with an increased NOx level with said generated error code associated with a defective NOx sensor. in cases where said first NOx sensor, which has been confirmed to be defective, has been determining incorrect, measuring values of said NOx level, increased as well as decreased, and where said determined measuring values have reverted to expected measuring values in said NOx level, an operator may, e.g. at a service station, confirm that the incorrectly detected measuring values were probably due to the fact that said first NOx sensor only temporarily detected incorrect NOx levels.

The method may comprise the step:

- during a certain predetermined time period, to register the number of cases where the size of said rate of change exceeds said predetermined value;

- to compare the number of cases, where said size of the rate of change exceeds said predetermined value, with a predetermined number; and

- in case said number of cases exceeds said predetermined number, to treat it is a reliable indication that said NOx sensor is defective,

The inventors have realised that a first NOx sensor, which during a certain time period detects a number of cases where the size of said rate of change exceeds said predetermined value, and where said number of cases exceeds a predetermined number, indicates with a high probability that said first NOx sensor is defective. Said time period may be a certain predetermined time period, e.g. with a duration of between 5 minutes and 5 hours of operating time. Said time period may be a suitable time period, e.g. 20 or 100 operating hours for the vehicle. The method according to the invention may be carried out during operation, e.g. when the vehicle is driven on a suitable road section.

The method according to the invention may be carried out during operation when the vehicle is at a standstill, e.g. in a garage or service facility.

The method may be implemented in existing motor vehicles. Program code to detect at least, one defective NOx sensor arranged in an exhaust pipe from an engine may, according to the invention, be installed in a control device of the vehicle at manufacture of the same. A purchaser of the vehicle may thus be provided the opportunity to select the performance function as an extra option. Alternatively, program code to carry out the method according to the invention, to detect at least one defective NOx sensor arranged in an exhaust pipe from an engine, may be installed in a control device of the vehicle in connection with upgrading at a service station. In this case, the program code may be uploaded into a memory in the control device.

Program code for troubleshooting may, in connection with detection of at least one defective NOx sensor arranged in an exhaust pipe from an engine, be updated or replaced. Further, different parts of the program code for detection and handling of at least one defective NOx sensor, arranged in an exhaust pipe from an engine, may be replaced independently of each other. This modular configuration is advantageous from a maintenance perspective. According to one aspect of the present invention, a device is provided to detect at least one defective NOx sensor arranged in an exhaust pipe from an engine, comprising:

^■■ elements adapted to continuously determine an NOx level in exhausts from said engine in said exhaust pipe,

- elements adapted to determine a rate of change in said continuously determined NOx level;

- elements adapted to compare a size of said rate of change with a predetermined value; and

- elements adapted, in cases where said size of said rate of change exceeds said predetermined value, to treat it as an indication of said NOx sensor being defective.

According to one aspect of the invention, a device is provided to detect at least one defective NOx sensor arranged in an exhaust pipe from an engine, comprising:

- elements adapted to compare said rate of change in said continuously determined NOx level with an expected rate of change in said !MOx level;

The device may comprise:

- elements adapted to determine, based on said comparison of said rate of change of said continuously determined NOx level with said expected rate of change in said NOx level, whether said rate of change is expected.

The device may comprise:

- elements adapted, where said rate of change in said continuously determined NOx level differs from said expected rate of change in said NOx level, to treat this as a confirmed defect in said NOx sensor.

According to one aspect, the step of treating it as a confirmed defect in said NOx sensor comprises the step to determine that said NOx sensor is defective. The device may also comprise:

- elements adapted, in cases where a defect is confirmed in said NOx sensor, and where a time period, during which said size of said determined rate of change exceeds said predetermined vaiue, is foi lowed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change exceeds said predetermined value, to generate an error code associated with a defective NOx sensor. The device may also comprise:

- elements adapted, in case a defect, has been confirmed in said NOx sensor and where a time period, during which said size of said determined rate of change exceeds said predetermined vaiue, is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change exceeds said predetermined value, to replace a generated error code associated with an increased NOx level with said generated error code associated with a defective NOx sensor. The device may comprise:

- elements adapted, during a certain predetermined time period, to register the number of cases where said size of said rate of change exceeds said predetermined value;

- elements adapted to compare the number of cases, where said size of the rate of change exceeds said predetermined vaiue, with a predetermined number; and

- elements adapted, in case said number of cases exceeds said predetermined number, to treat it is a reliable indication that said NOx sensor is defective. According to one aspect of the present invention, a motor vehicle is provided, comprising the device to detect at least one defective NOx sensor arranged in an exhaust pipe from an engine. The motor vehicle may be a truck, a bus or a car. According to one aspect of the invention, a computer program is provided to detect at least one defective NOx sensor arranged in an exhaust pipe from an engine, wherein said computer program comprises program code to cause an electronic control device or another computer connected to the electronic control device to perform the steps according to any of the claims 1-8.

According to one aspect, of the invention, a computer program is provided to detect and handle at least one defective NOx sensor arranged in an exhaust pipe from an engine, wherein said computer program comprises program code stored on a computer-readable medium to cause an electronic control device or another computer connected to the electronic control device to perform the steps according to any of the claims 1-8.

According to one aspect of the 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 1-8, when said program code is executed in an electronic control device or in another 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 DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the additiona! objects 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 pertain to identical 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 to detect at least one defective NOx sensor arranged in an exhaust pipe from an engine, according to one embodiment of the invention;

Figure 3a schematically illustrates a diagram, according to one aspect of the invention; Figure 3b schematically illustrates a diagram, according to one aspect of the invention;

Figure 3c schematically illustrates a diagram, according to one aspect of the invention;

Figure 3d schematically illustrates a diagram, according to one aspect of the invention;

Figure 3e schematically illustrates a diagram, according to one aspect of the invention;

Figure 3f schematically illustrates a diagram, according to one aspect of the invention; Figure 3g schematically illustrates a diagram, according to one aspect 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 aspect of the invention; and

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

DETAI LED DESCRI PTION OF THE FIGURES

A side view of a vehicle 100 is shown with reference to Figure 1. The exemplary vehicle 100 consists of a tractor 110 and a trailer 112. The vehicle may be a heavy goods vehicle, such as a truck or a bus. The vehicle may, alternatively, be a car. It should he pointed out that the invention is suitable for application in any suitable combustion engine and is thus not limited to an engine in a motor vehicle. The method according to the invention and the device according to one aspect of the invention are well suited to platforms other than motor vehicles that comprise an engine, such as watercraft. The watercraft may be of any suitable type, such as motor boats, ships, ferries or vessels.

The method according to the invention and the device according to one aspect of the invention are also suitable for e.g. systems comprising a stone crusher or similar.

The method according to the invention and the device according to one aspect of the invention are also suitable for e.g. systems comprising industrial engines and/or engine driven industrial robots.

The method according to the invention and the device according to one aspect of the invention are also suitable for different types of power plants, e.g. a power plant comprising a diesei-operated electric generator.

The method according to the invention and the device according to the invention are also well suited for any suitable engine system comprising an engine, e.g. in a locomotive or another platform. The method according to the invention and the device according to the invention are also well suited for any suitable system comprising an NOx generator.

The term "link" 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 term "conduit" 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 terms "reducing agent" or "reductant" as used herein mean a substance used to react with certain emissions in an SCR system. These emissions may be e.g. NOx gas. The terms "reductant" and "reducing agent" are used synonymously herein. The said reductant is, according to one embodiment, so-called AdBiue, Obviously other types of reductants may be used. AdBiue is given as an example of a reducing agent; however, one skilled in the art will realise that the method according to the invention and the device according to the invention may be realised for other types of reducing agents. With reference to Figure 2, a device 299 in the vehicle 100 is shown. The device 299 may be arranged in the tractor 110. The device 299 may consist of a part of, or comprise, a device to detect at least one defective NOx sensor. The device 299 comprises, according to this example, a container 205 which is arranged to hold a reductant. The container 205 is arranged to comprise a suitable amount of reductant and is also arranged to be filled as needed. The device comprises, according to this example, a combustion engine 206 and an exhaust pipe 290,

A first conduit 271 is arranged to lead the reducing agent to a pump 230 from the container 205. The pump 230 may be arranged to pump the reducing agent from the container 205 via the first conduit 271 and via a second conduit 272, to add said reducing agent to a dosage device 250, The dosage device 250 may comprise an electrically controlled dosage device, through which a flow of reductant added to the exhaust pipe 290 may be controlled. The dosage device 250 is arranged to add said reductant to said exhaust pipe 290 in the vehicle 100. According to this embodiment, an SCR catalyst 270 is arranged downstream of a location in the exhaust system where the reducing agent is added. The amount of reductant which is added in the exhaust system is intended to be used in the SCR catalyst 270 in order to reduce the amount of undesired emissions.

A diesel oxidation catalyst 259 is arranged in the exhaust pipe 290 downstream of said engine 206. Said diesel oxidation catalyst 259 is arranged in the exhaust pipe 290 upstream of said SCR catalyst 270. Said diesel oxidation catalyst 259 may be referred to as a DOC device.

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

The first control device 200 is arranged for communication with the pump 230 via a link L230. The first control device 200 is arranged to control the operation of the pump 230. A first Ox sensor 255 is arranged in the exhaust pipe 290. The first NOx sensor 255 is arranged for communication with the first control device 200 via a link L255. The first NOx sensor 255 is arranged to continuously determine a prevailing NOx level in the exhaust flow in the exhaust pipe 290, upstream of said SCR catalyst 270. According to one example, the first NOx sensor 255 is arranged in the exhaust pipe 290, upstream of said dosage device 250. The first NOx sensor 255 is arranged to continuously send signals, comprising information about a prevailing NOx level upstream of said SCR catalyst 270, to the first control device 200. According to one embodiment, a rate of change H' in said continuously determined NOx level is determined with said first NOx sensor 255, with the help of the first control device 200. The control device 200 is arranged to compare a size of said rate of change H' with a predetermined value H'max, and where said size of said rate of change H' exceeds said predetermined value H'max, it is treated as an indication that said first NOx sensor 255 is defective. According to one example embodiment, the first NOx sensor 255 is arranged to continuously determine a prevailing NOx level in the exhaust flow in the exhaust pipe 290, downstream of said SCR catalyst 270.

A second NOx sensor 265 is arranged in the exhaust pipe 290. The second NOx sensor 265 is arranged for communication with the first control device 200 via a link L265. The second NOx sensor 265 is arranged to continuously determine a prevailing NOx level in the exhaust flow in the exhaust pipe 290, downstream of said SCR catalyst 270. The second NOx sensor 265 is arranged to continuously send signals, comprising information about a prevailing NO_x level downstream of said SCR catalyst 270, to the first control device 200. According to one embodiment, a rate of change H' in said continuously determined NOx level is determined with said second NOx sensor 265, with the help of the first control device 200. The control device 200 is arranged to compare a size of said rate of change H' with a predetermined value H'max and, in case said size of said rate of change H' exceeds said predetermined value H'max, to treat it as an indication that said second NOx sensor 265 is defective.

According to one example embodiment, the second NOx sensor 265 is arranged to continuously determine a prevailing NOx level in the exhaust flow in the exhaust pipe 290, upstream of said SCR catalyst 270.

According to one example embodiment, the first control device 200 is arranged to determine an expected rate of change H'exp in said NOx level with the help of a continuousl determined NOx level, where said continuously determined NOx level is determined with said first, or second NOx sensor 255, 265. According to one example embodiment, an expected rate of change H'exp in said NOx level is determined with the help of a continuously determined NOx level, where said continuously determined NOx level is determined with a third (not displayed) NOx sensor arranged in said exhaust pipe 290. According to one embodiment, at least a third NOx sensor (not displayed) may be arranged for communication with the first control device 200 via a link intended for this purpose. Said third NOx sensor may be arranged to continuously determine a prevailing NOx level in the exhaust flow, upstream or downstream of said SCR catalyst 270. Said third NOx sensor is arranged to continuously send signals, comprising information about said prevailing NOx level, to the first control device 200.

The first control device 200 is arranged to compare said determined expected rate of change H'exp with said determined rate of change H' in order to conclude whether said first or second NOx sensor 255, 265 is defective.

The first control device 200 is arranged to compare said rate of change H^! in said continuously determined NOx level, where said rate of change H' is determined with the help of measuring values from said first NOx sensor 255, with an expected rate of change H'exp in said NOx level, where said expected rate of change H'exp in said NOx level is determined with said corresponding second NOx sensor 265 or said corresponding third NOx sensor. According to one embodiment, the first control device 200 is arranged to compare said rate of change H' in said continuously determined NOx level, where said rate of change H' is determined with the help of measuring values from said first NOx sensor 255, with an expected rate of change H'exp in said NOx level, where said expected rate of change H'exp is determined with the help of measuring values from said second NOx sensor 265 or third NOx sensor.

The first control device 200 is arranged to compare said rate of change H' in said continuously determined NOx level, where said rate of change H' is determined with the help of measuring values from said second NOx sensor 265 with an expected rate of change H'exp in said NOx level, where said expected rate of change H'exp in said NOx level is determined with said corresponding first NOx sensor 255 or said corresponding third NOx sensor. According to one embodiment, the first control device 200 is arranged to compare said rate of change H' in said continuously determined NOx level, where said rate of change H' is determined with the help of measuring values from said second NOx sensor 265, with an expected rate of change H'exp in said NOx level, where said expected rate of change H'exp is determined with the help of measuring values from said first NOx sensor 255 or said third NOx sensor.

According to one example embodiment, the first control device 200 is arranged to calculate said expected rate of change H'exp in said NOx level upstream of said SCR catalyst 270. This may be done with a calculation model which is stored in a memory in the first control device 200. The first control device 200 may be arranged to calculate said expected rate of change H'exp in said NOx level upstream of said SCR catalyst 270 based on operating conditions in said engine, such as the amount of injected fuel in the engine, the prevailing engine speed of the engine, power output and the prevailing load of the engine, etc.

According to one embodiment, the first control device 200 is arranged to calculate said expected rate of change H'exp in said NOx ievei downstream of said SCR catalyst 270. This may be done with a calculation model. The first control device 200 may be arranged to calculate said expected rate of change H'exp in said NOx level downstream of said SCR catalyst 270 based on operating conditions in said engine, such as the amount of injected fuel, the prevailing engine speed of the engine, power output and the prevailing load of the engine, etc. The first control device 200 is arranged to detect at least one defective NOx sensor 255, 265 arranged in an exhaust pipe 290 from an engine 206. The first control device 200 is arranged:

^■■ to continuously determine an NOx level in the exhausts from said engine 206 in said exhaust pipe 290 with said MOx sensor 255, 265;

- to determine a rate of change H^! in said continuously determined NOx level;

- to compare a size of said rate of change H' with a predetermined value H'max; and

- in cases where said size of said rate of change H^! exceeds said predetermined value H'max, to treat it as an indication that said NOx sensor 255, 265 is defective.

The first control device 200 may he arranged to compare said rate of change H^! in said continuously determined NOx level with an expected rate of change H'exp in said NOx level, where said expected rate of change H'exp in said NOx level is determined with a corresponding NOx sensor 255; 265 arranged in said exhaust pipe 290 and/or a calculation model.

The first control device 200 may be arranged to determine said expected rate of change H'exp with a calculation model, wherein said calculation model comprises operating conditions of said engine.

The first control device 200 is arranged to determine, based on said comparison of said rate of change H' in said continuously determined NOx level with said expected rate of change H'exp in said NOx level, whether said rate of change H' is expected. The first control device is arranged, where said rate of change H' in said continuously determined NOx level differs from said expected rate of change H'exp in said IMOx level, to treat this as a confirmed defect in said NOx sensor 255; 265.

The first control device is arranged 2!

- in cases where a defect is confirmed in said Ox sensor 255; 265 and where a time period, during which said size of said determined rate of change H^' exceeds said predetermined value H'max, is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change H' exceeds said predetermined value H'max, to generate an error code associated with a defective NOx sensor 255; 265.

The first control device 200 is arranged, in cases where a defect is confirmed in said NOx sensor 255, 265 and where a time period, during which said size of said determined rate of change H' exceeds said predetermined value H'max, is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change H' exceeds said predetermined value H', to replace a generated error code associated with an increased NOx level with said generated error code associated with a defective IMOx sensor 255; 265.

The first control device 200 is arranged to

- during a certain predetermined time period, to register a number of cases X where the size of said rate of change H' exceeds said predetermined value H'max;

- compare the number of cases X, where the size of said rate of change H' exceeds said predetermined value H'max, with a predetermined number Xmax; and

- in case said number of cases X exceeds said predetermined number Xmax, to treat it as a reliable indication that said IMOx sensor 255, 265 is defective. Xmax may be a suitable number, e.g. 1, 3, 5 or 10. Xmax may be a suitable number exceeding 10.

The first control device 200 is arranged for communication with the presentation means 280 via a link L280. Said presentation means 280 may be arranged in a driver's cabin in the vehicle 100. Said presentation element 280 may be fixed in the vehicle 100. Said presentation element 280 may be a mobile electronic device. Said presentation element 280 may comprise e.g. a display screen. The first control device 200 is arranged to present an error code and/or other relevant, information, relating to the innovative method of detecting at least one defective NOx sensor arranged in an exhaust pipe 290 from an engine 206. The first control device 200 may be arranged to present a result, via said presentation element 280, as to whether or not said NOx sensor 255, 265 is defective. The first control device 200 may be arranged to present a result, via said presentation element 280, as to whether or not said NOx sensor 255, 265 is fully functional. The first control device 200 is arranged for communication with a communication device 285 via a link L285. Said communication device 285 may be located in for example a service station, garage, hauler or a so-called fleet management system.

Said communication device 285 may be arranged in a driver's cabin in the vehicle 100. Said communication device 285 may be fixed in the vehicle 100. Said communication device 285 may be a mobile or an electronic device. Said communication device 285 may comprise for example a display screen. The first control device 200 is arranged to automatically or on request present an error code and/or other relevant information relating to the innovative method of detecting a defective NOx sensor 255, 265 arranged in an exhaust pipe 290 from an engine 206. The first control device 200 may be arranged to present a result, via said communication terminal 285, as to whether or not said first 255 and/or second 265 NOx sensor is defective. 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 software to the first control device 200, in particular software 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, e.g. to detect at ieast one defective NOx sensor 255, 265 arranged in an exhaust pipe 290 from an engine 206. The second control device 210 may be arranged:

- to continuously determine an NOx level in the exhausts from said engine 206 in said exhaust pipe 290 with said NOx sensor 255, 265;

- to determine a rate of change H' in said continuously determined NOx level;

- in cases where said size of said rate of change H' exceeds said predetermined value H'max, to treat it as an indication that said NOx sensor 255, 265 is defective. With reference to Figure 3a, a diagram is displayed where the NOx level in the exhausts from an engine 206 is specified as a function of time T. The NOx level is specified in terms of ppm (parts per million). The time T is specified in terms of seconds (s). According to one aspect of the invention, the NOx level in the exhausts from an engine 206 in an exhaust pipe 290 is determined continuously with at. ieast one NOx sensor 255, 265. In Figure 3a, a curve 1 is displayed, which is generated with continuous measuring values detected with said NOx sensor 255, 265, where said NOx sensor 255, 265 determines the NOx level in an exhaust pipe 290 leading exhausts from an engine 206. A control device 200, 210 determines a rate of change H' in said continuously determined NOx level. The size of said rate of change H' is compared with a predetermined value H'max, and in case said size of said rate of change H' exceeds said predetermined value H'max, it is treated as an indication that said NOx sensor 255, 265 is defective. In Figure 3a, a size of said rate of change H', where said size exceeds said predetermined value H'max, has been detected at the point in time T2.

Said rate of change H' may be determined by deriving said curve 1 in relation to time. The size of said rate of change may alternatively be obtained by analysing a determined size of a measuring value of the NOx level in said exhausts at a number of points in time. When the NOx level differs by more than a predetermined value between two consecutive points in time, e.g. the point in time Tl and the point in time T2 in Figure 3a, it may be determined that the size of said rate of change H' exceeds said predetermined value H'max, and hence said rate of change H' indicates at the point in time T2 that, said NOx sensor 255, 265 is defective.

According to one aspect of the present invention, the determination of whether said NOx sensor 255, 265 is defective may comprise the step of considering whether said NOx level, in connection with said rate of change HP exceeding said predetermined value H'max, exceeds a predetermined threshold value Tvl, if said NOx level exceeds said predetermined threshold value Tvl, in connection with said rate of change H' exceeding said predetermined value H'max, it may be determined with a very great probability that said NOx sensor 255, 265 is defective. Said predetermined threshold value Tvl is a suitable value.

According to one aspect of the present invention, the determination of whether said NOx sensor 255, 265 is defective may in a similar manner comprise the step of considering whether said NOx level, in connection with said rate of change H' exceeding said predetermined value H'max, fails below a predetermined threshold value Tv2. If said NOx level fails below said predetermined threshold value Tv2, in connection with said rate of change H' exceeding said predetermined value H'max, it may be determined with a very great probability that said NOx sensor 255, 265 is defective. Said predetermined threshold value Tv2 is a suitable value. Said threshold values Tvl and Tv2 are also illustrated in the diagrams described with reference to Figures 3b-3f.

The size of said rate of change H' is an absolute amount of said rate of change if. Said rate of change H' may thus also be negative, as displayed in Figure 3a after the point in time T2.

When it is confirmed that said size of said determined rate of change HP exceeds a certain predetermined value H'max, said determined rate of change H' in Figure 3a is compared with an expected rate of change H'exp, Said expected rate of change H'exp is determined based on an expected NOx level, where said expected NOx level is obtained through a calculation model wherein the engine's operating modes may be used as parameters in said model, or through an NOx level which is determined continuously with a corresponding NOx sensor 255, 265 arranged in said exhaust pipe 290, The expected NOx level is represented by curve 2 in Figure 3a, In Figure 3a it may be concluded that, at the point in time T2, the determined rate of change H' exceeds a predetermined value H'max, At the point in time T2, or at a point in time which corresponds to the point in time T2 in Curve 2, which represents said expected NOx level, it may be detected that the expected rate of change H'exp does not correspond to said determined rate of change H'. Thus it may be concluded that said NOx sensor 255, 265 in Figure 3a is defective.

Figure 3a shows a time period, during which said size of said determined rate of change H^! exceeds said predetermined value H'max, followed by a time period T3- T4 with an increased determined NOx level H2 compared to a determined NOx level HI during a time period T0-T1 before said time period, during which said size of said determined rate of change H' exceeds said predetermined value H'max. Said determined NOx level varies over time, so that a mean value of said NOx level may be used to carry out said comparison of the NOx level before and after said time period, during which said size of said determined rate of change H' exceeds said predetermined value H'exp, in the description below, HI and H2 should be interpreted as mean values of the NOx level during a time period.

Where said NOx sensor 255, 265 has been confirmed to be defective, an error code associated with an increased NOx level H2 is generated in case of an increased value H2 after a time period, during which said determined rate of change H^! exceeds said predetermined value H'exp. According to one embodiment, said error code associated with a defective NOx sensor 255, 265 may replace an error code associated with an increased NOx level H2. Said error code associated with a defective NOx sensor is generated where said increased NOx level H2 is not expected. In Figure 3a, curve 2, representing the expected NOx level, indicates that said increase of H2 is not expected since the expected NOx level does not show any increase in the NOx level after said time period, during which said size of said determined rate of change H' exceeds said predetermined value H'exp. According to one embodiment, said error code associated with a defective NOx sensor may be generated where said increase in the NOx level H2 after the point in time Tl is expected, but where said increase in the NOx level after the point in time Tl differs by more than a predetermined value from said expected increased NOx level. Said NOx sensor 255, 265 may be placed in any location in the exhaust pipe 290, e.g. upstream or downstream of the SCR catalyst 270.

With reference to Figure 3b, a diagram is displayed where the NOx level in exhausts from an engine 206 is specified as a function of time T. The NOx level is specified in terms of ppm. The time T is specified in terms of seconds (s).

Figure 3b shows that the measured NOx level may also have a negative lowest value. With reference to Figure 3c, a diagram is displayed where the NOx level is specified as a function of time T. The NOx level is specified in terms of ppm. The time T is specified in terms of seconds (s). The size of said rate of change H' is an absolute amount of said rate of change. Said rate of change H¹ may thus also be negative, as is the case at the point in time Tl in Figure 3c,

Figure 3c shows that a time period, where said size of said determined rate of change H¹ exceeds said predetermined value H'max, is followed by a time period T2- T3 with a lower determined NOx level H2 compared to a determined NOx level Hi during a time period T0-T1 before said time period, during which said size of said determined rate of change H' exceeds said predetermined value H'max. Where said NOx sensor 255, 265 has been confirmed defective, as said determined rate of change H^! exceeds said predetermined value HP at the point in time Tl, and as said rate of change is not consistent with an expected rate of change H'exp in said NOx level, an error code is generated at the lower value H2, which is associated with a lower NOx level H2. According to one embodiment, said error code associated with a defective NOx sensor 255, 265 may replace a generated error code associated with a lower NOx level H2. Said error code is generated when said lower NOx level H2 is not expected, in Figure 3c, curve 2, which represents the expected NOx level, indicates that said decrease of H2 is not expected, since the expected NOx level does not indicate any reduction of the NOx level. According to one embodiment, said error code associated with a defective NOx sensor 255, 265 may be generated where said increase in the NOx level H2 after the point in time Tl is expected, but where said decrease in the NOx level after the point in time Tl differs by more than a predetermined value from said expected increased NOx level. With reference to Figure 3d, the NOx level is specified as a function of time T. The NOx level is specified in terms of ppm. The time T is specified in terms of seconds (s). Figure 3d shows an example, where a time period, during which said size of said determined rate of change H' exceeds said predetermined value H'max, is followed by a time period T2-T3 with a determined NOx level H2 which is consistent with a determined NOx level HI during a time period TQ-T1 before said time period, during which said size of said determined rate of change H' exceeds said predetermined value H'max. Thus, no error code associated with a defective NOx sensor is genera ted, according to the example embodiment illustrated in Figure 3d.

With reference to Figure 3e, a diagram is displayed where the NOx Ievei is specified as a function of time T. The NOx ievei is specified in terms of ppm. The time T is specified in terms of seconds (s).

The detected NOx level, continuously determined with an NOx sensor 255, 265 arranged in an exhaust pipe 290 which leads exhausts from an engine 206, is represented by a curve 1 in Figure 3d. Curve 2 represents a reference curve, either continuously determined with a corresponding NOx sensor 255, 265 arranged in the exhaust pipe 290, or calculated with the help of a calculation model. Herein it is indicated that, at the point in time Tl, a size of said rate of change H' is detected where said size exceeds said predetermined value H'max. After a comparison with an expected rate of change H'exp it may be confirmed that said NOx sensor is defective, as a size of said rate of change H', where said size exceeds said predetermined value H'max at the point in time Tl, is not consistent with an expected rate of change H'exp. With reference to Figure 3f, a diagram is displayed where the NOx ievei is specified as a function of time T. The NOx level is specified in terms of ppm. The time T is specified in terms of seconds (s). The detected NOx Ievei, continuously determined with an NOx sensor 255, 265 arranged in an exhaust pipe 290 which leads exhausts from an engine 206, is represented by curve 1 in Figure 3f. Curve 2 represents a reference curve, either continuously determined with a corresponding NOx sensor 255, 265 arranged in the exhaust pipe 290, or calculated with the help of a calculation model. Herein it is indicated that, at the point in time TO, a size of said rate of change H' is detected where said size exceeds said predetermined value H'max. After a comparison with an expected rate of change H'exp it may be concluded that said determined rate of change H' at the point in time TO is expected. Further, at the points in time Tl, T2, T3, and T4 it may be concluded that said NOx sensor is defective, as a size of said rate of change HP, where said size exceeds said predetermined value H'max at the points in time Tl, T2, T3, and T4, is not consistent with an expected rate of change H'exp. According to one embodiment, a registration of a number of occurring cases X, where the size of said rate of change exceeds said predetermined value H'exp and where said occurring cases are not expected, is carried out. In cases where said number of occurring cases X exceeds a predetermined number Xmax during a predetermined time period, it is treated as a reliable indication that said NOx sensor 255, 265 is defective. Said time period may, according to one example embodiment, be between 5 seconds and 60 minutes. Said time period may, according to one example embodiment, be between 1 and 24 hours. Said predetermined number Xmax may be between 1 and 20, or between 1 and 100, or between 1 and 1,000.

With reference to Figure 3g, a diagram is displayed, where the rate of change H' in the NOx level is specified as a function of time T. The rate of change in said NOx level is specified in terms of ppm/second. The time T is specified in terms of seconds (s). Figure 3g shows said determined rate of change H', said expected rate of change H'exp and said predetermined vaiue H'max.

Figure 3g indicates that, at the point in time TO, said determined rate of change H' exceeds said predetermined vaiue H'max. This indicates that an NOx sensor, which has measured the NOx levels based on which said rate of change H' had been calculated, is defective. At the point in time TO it is also displayed that said expected rate of change H'exp exceeds said predetermined value H'max. Thus, a defective NOx sensor may not be concluded at the point in time TO.

At the point in time Tl, said determined rate of change H' exceeds the predetermined value H'max. This indicates that an NOx sensor, which has measured the NOx levels based on which said rate of change H' had been calculated, is defective. As said rate of change H' at the point in time Tl is not expected, which may be detected by comparing H' with said expected rate of change H'exp, it may be concluded at the point in time Tl that an NOx sensor, which measured the NOx levels based on which said rate of change H' was calculated, is defective.

Figure 4a schematically illustrates a flow chart of a method to detect and manage at least one defective NOx sensor 255, 265 arranged in an exhaust pipe 290 from an engine 206. The method comprises a method step s401.

The method step $401 includes the steps:

- to determine a rate of change H¹ in said continuously determined NOx level;

- to compare a size of said rate of change H' with a predetermined vaiue H'max; and

- in cases where said size of said rate of change H' exceeds said predetermined value H'max, to treat it as an indication that said NOx sensor 255; 265 is defective. The method is completed after step s401.

Figure 4b schematically illustrates a flow chart of a part of a method to detect at least one defective NOx sensor 255, 265 arranged in an exhaust pipe 290 from an engine 206, according to one aspect of the present invention.

The method comprises an initial method step s410. The method step s410 may comprise the step of activating the method according to the invention. Said activation may be carried out by an operator of the vehicle 100. Said activation may be carried out by garage staff or service staff in a garage or a service facility, respectively. Said activation may take place through said presentation device 280 and/or said communications device 285. Said activation may occur automatically when said engine 206 is started. The method step s410 comprises the step of continuously determining an NOx level in exhausts in an exhaust pipe 290. The method step s410 comprises the step of determining a rate of change H' in said continuously determined NOx level.

Following the method step s410, a subsequent method step s420 is completed.

The method step s420 comprises the step of comparing the size of said rate of change H' with a predetermined value H'max. Said comparison may be carried out continuously. The method step s420 comprises the step, in cases where said size of said rate of change H' exceeds said predetermined value H'max, to treat it as an indication that said NOx sensor 255; 265 is defective.

Following the method step s420, a subsequent method step s430 is completed.

The method step s430 comprises the step of comparing said rate of change H' of said continuously determined NOx level, determined with at least one of the first NOx sensor 255 and the second NOx sensor 265, with an expected rate of change H'exp in said NOx ieveL Said expected rate of change H'exp in said NOx level is determined with a corresponding NOx sensor, arranged in said exhaust pipe 290 and/or a calculation model. According to one example, said rate of change H' of said continuously determined NOx levei determined with the first NOx sensor 255 may be compared with an expected rate of change H'exp in said NOx level, determined with the second NOx sensor 265, or vice versa.

Following the method step s430, a subsequent method step s440 is completed. The method step s440 comprises the step, in case a size of said determined rate of change H' exceeds a predetermined value H'max, and where said rate of change H' differs from said expected rate of change H'exp in said NOx level, to treat it as a confirmed defect in said NOx sensor 255; 265. Following the method step s440, a subsequent method step s450 is completed.

The method step s450 comprises the step, in case a defect is confirmed in said NOx sensor 255; 265 and where a time period, during which said size of said determined rate of change H' exceeds said predetermined vaiue H'max, is followed by a time period with an increased determined NOx level compared to a determined NOx levei during a time period before said size of said determined rate of change H' exceeds said predetermined value Η', of generating an error code associated with a defective NOx sensor 255, 265.

Said NOx level usually varies over time so that e.g. a mean value of said NOx level HI, H2 during a time period before and after, respectively, a time period, during which said size of said determined rate of change H' exceeds said predetermined value H'max, may be used for said comparison.

If an increased NOx level H2, following a time period during which said size of said determined rate of change H', exceeds said predetermined value H'max compared with an NOx leve! HI before said time period is concluded, a subsequent method step s460 is carried out. In case an increased NOx level has not been confirmed, a subsequent method step s470 is carried out. The method step s460 includes the step:

in case a defect is confirmed in said NOx sensor 255, 265 and where a time period, during which said size of said determined rate of change exceeds said predetermined value H'max, is followed by a time period with an increased determined NOx level H2 compared to a determined NOx level HI during a time period before said size of said determined rate of change H' exceeds said predetermined value H', of generating an error code associated with a defective NOx sensor 255, 265. The method step s460 may also comprise the step of replacing a generated error code associated with an increased NOx level with said generated error code associated with a defective NOx sensor 255, 265.

Following the method step s460, a subsequent method step s470 is completed.

The method step s470 comprises an end or a continuation of the method according to the invention. A continuation of the method according to the invention entails that the method has started again according to the method step s410.

With reference to Figure 5, a diagram of an embodiment of a system 500 is shown. The control units 200 and 210, which are described with reference to Figure 2, may in one embodiment comprise the system 500. The device 500 includes a non- volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory part 530, wherein a computer program, such as an operative system, is stored to control the function of the unit 500. Further, the unit 500 includes 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-voiatile memory 520 also has a second memory part 540.

A computer program P is provided, which may comprise procedures to detect at least one defective NOx sensor 255, 265 arranged in an exhaust pipe 290 from an engine 290, comprising the steps:

- to continuously determine an NOx level in the exhausts from said engine 206 in said exhaust pipe 290 with said NOx sensor 255; 265;

- to determine a rate of change H' in said continuously determined NOx level;

- in cases where said size of said rate of change H' exceeds said predetermined value H'max, to treat it as an indication that said NOx sensor 255, 265 is defective.

The computer program P may comprise procedures for comparing said rate of change H^! in said continuously determined NOx level with an expected rate of change H'exp in said NOx level, where said expected rate of change H'exp in said NOx level is determined with a corresponding NOx sensor 255, 265 arranged in said exhaust pipe 290 and/or a calculation model. The computer program P may comprise procedures for comparing said rate of change H' in said continuously determined NOx level with an expected rate of change H 'exp in said NOx level, where said expected rate of change H'exp in said NOx level is determined with a calculation model, wherein said calculation mode! comprises the operating conditions of said engine.

The computer program P may comprise procedures to:

- determine, based on said comparison of said rate of change H' in said continuously determined NOx level with said expected rate of change H'exp in said NOx level, whether said rate of change H' is expected. The computer program P may comprise procedures, where said rate of change H' in said continuously determined NOx level differs from said expected rate of change H'exp in said NOx level, to treat this as a confirmed defect in said NOx sensor 255, 265.

The computer program P may comprise procedures to:

- in cases where a defect is confirmed in said NOx sensor 255, 265 and where a time period, during which said size of said determined rate of change H^! exceeds said predetermined value H'max, is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change H' exceeds said predetermined value H', to generate an error code associated with a defective NOx sensor 255, 265. The computer program P may comprise procedures to:

- in case where a defect is confirmed in said NOx sensor 255, 265 and a time period, during which said size of said determined rate of change H^! exceeds said predetermined value H'max, is followed by a time period with an increased determined !MOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change H' exceeds said predetermined value H^!, to replace a generated error code associated with an increased NOx level with said generated error code associated with a defective NOx sensor 255, 265. The computer program P may comprise procedures to:

- during a certain predetermined time period, register a number of cases X where the size of said rate of change H' exceeds said predetermined value H'max;

- compare the number of cases X, where the size of said rate of change H' exceeds said predetermined value H'max, with a predetermined number Xmax; and - in case said number of cases X exceeds said predetermined number Xrnax, to treat it. as a reliable indication that said NOx sensor 255, 265 is defective.

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 which is 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-voiatile 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, L230, L240, L25Q, L255, L260, L265, L280 and L285 may e.g. be connected to the data port 599 (see Figure 2), When data is received in the data port 599, it is temporarily stored in the second memory part 540. When in-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 regarding the NOx level upstream of the SCR catalyst 270. According to one embodiment, signals received in the data port 599 comprise information regarding the NOx level downstream of the SCR catalyst 270. The signals received in the data port 599 may be used by the device 500 to detect and manage at ieast one defective NOx sensor arranged in an exhaust pipe 290 from an engine 206, 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.

Claims

1. Method to detect at least one defective NOx sensor {255; 265) arranged in an exhaust pipe (290) from an engine (206), comprising the step:

- to continuously determine an NOx level in the exhausts from said engine

(206) in said exhaust pipe (290) with said NOx sensor (255, 265);

characterised by the steps:

- to determine a rate of change (H^!) in said continuously determined NOx level;

- to compare a size of said rate of change (Η') with a predetermined value

(H'max); and

- in cases where said size of said rate of change (Η') exceeds said predetermined value (H'max), to treat it as an indication that said NOx sensor (255; 265) is defective.

2. Method according to claim 1, comprising the step:

- to compare said rate of change (Η') in said continuously determined NOx level with an expected rate of change (H'exp) in said NOx level, where said expected rate of change (H'exp) in said NOx level is determined with a corresponding NOx sensor (255; 265) arranged in said exhaust pipe (290) and/or a calculation model.

3. Method according to claim 2, wherein said calculation mode! comprises operating conditions of said engine (206).

4. Method according to claim 2 or 3, comprising the step:

- to determine, based on said comparison of said rate of change (Η') in said continuously determined NOx level with said expected rate of change (H'exp) in said NOx level, whether said rate of change (Η') is expected.

5. Method according to any of claims 2-4, wherein, where said rate of change {H^!} in said continuously determined NOx level differs from said expected rate of change (H'exp) in said NOx level, to treat this as a confirmed defect in said NOx sensor (255; 265).

6. Method according to claim 5, comprising the step:

- in cases where a defect is confirmed in said NOx sensor (255; 265) and where a time period, during which said size of said determined rate of change (Η') exceeds said predetermined value (H'rnax), is followed by a time period with an increased determined NOx level compared to a determined

NOx level during a time period before said time period, during which said size of said determined rate of change (Η') exceeds said predetermined value (Η'), to generate an error code associated with a defective NOx sensor (255; 265).

7. Method according to claim 6, comprising the step:

NOx level during a time period before said time period, during which said size of said determined rate of change (Η') exceeds said predetermined value (H'rnax), to replace a generated error code associated with an increased NOx level with said generated error code associated with a defective NOx sensor (255; 265).

8. Method according to any of claims 1-7, comprising the step:

- during a certain predetermined time period, to register a number of cases (X) where the size of said rate of change (H^!) exceeds said predetermined value (H'rnax); - to compare the number of cases (X), where the size of said rate of change (H^!) exceeds said predetermined value (H'max), with a predetermined number (Xmax); and

^■ in case said number of cases (X) exceeds said predetermined number (Xmax), to treat it as a reliable indication that said NOx sensor (255; 265) is defective.

9. Device to detect at least one defective NOx sensor {255; 265) arranged in an exhaust pipe (290) from an engine (206), comprising:

- elements (255; 265) adapted to continuously determine an NOx level in exhausts from said engine (206) in said exhaust pipe (290),

characterised by:

^■ elements (200; 210; 500) adapted to determine a rate of change (H") in said continuously determined NOx Ievel;

- elements (200; 210; 500) adapted to compare a size of said rate of change

(H^!) with a predetermined value (H'max); and

- elements (200; 210; 500) adapted, in cases where said size of said rate of change (Η') exceeds said predetermined value (H'max), to treat it as an indication that said NOx sensor (255; 265) is defective.

10. Device according to claim 9, comprising:

^■ elements (200; 210; 500) adapted to compare said rate of change (Η') in said continuously determined NOx Ievel with an expected rate of change (H'exp) in said NOx Ievel.

11. Device according to claim 10, comprising:

- elements (200; 210; 500) adapted to determine, based on said comparison of said rate of change (Η') in said continuously determined NOx Ievel with said expected rate of change (H'exp) in said NOx ievel, whether said rate of change (Η') is expected.

12. Device according to claim 10 or 11, comprising:

- elements (200; 210; 500) adapted, where said rate of change (Η') in said continuously determined NOx level differs from said expected rate of change (H'exp) in said NOx level, to treat it as a confirmed defect in said NOx sensor (255; 265).

13. Device according to claim 12, comprising:

- elements (200; 210; 500) adapted, in cases where a defect is confirmed in said NOx sensor (255; 265) and where a time period, during which said size of said determined rate of change (Η') exceeds said predetermined value (H'max), is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change (Η') exceeds said predetermined value (Η'), to generate an error code associated with a defective NOx sensor (255; 265).

14. Device according to claim 13, comprising:

- elements (200; 210; 500) adapted, in cases where a defect is confirmed in said NOx sensor (255; 265) and where a time period, during which said size of said determined rate of change (Η') exceeds said predetermined value (H'max), is followed by a time period with an increased determined NOx level compared to a determined NOx level during a time period before said time period, during which said size of said determined rate of change (Η') exceeds said predetermined value (H^!), to replace a generated error code associated with an increased NOx level with said generated error code associated with a defective NOx sensor (255; 265).

15. Device according to any of claims 9-14, comprising: - elements (200; 210; 500} adapted, during a certain predetermined time period, to register a number of cases (X) where the size of said rate of change (Η') exceeds said predetermined value (H'max);

^■ elements (200; 210; 500) adapted to compare the number of cases (X), where the size of said rate of change (Η') exceeds said predetermined value

(H'max), with a predetermined number (Xmax); and

- elements (200; 210; 500) adapted, in case said number of cases (X) exceeds said predetermined number (Xmax), to treat it as a reliable indication that said NOx sensor (255; 265) is defective.

16. Motor vehicle (100, 110), comprising a device according to any of claims 9-15.

17. Motor vehicle (100; 110) according to claim 16, wherein the motor vehicle is one of a truck, a bus or a car.

18. Computer program (P) to detect at least one defective NOx sensor (255; 265) arranged in an exhaust pipe (290) from an engine (206), wherein said computer program (P) comprises program code to cause an electronic control device (200; 500) or another computer (210; 500} connected to the electronic control device (200; 500) to perform the steps according to any of claims 1-8.

19. Computer program product, comprising program code stored in a computer- readable medium., in order to perform the method steps according to any of claims 1-8, wherein said program code is executed in an electronic control device (200, 500) or in another computer (210, 500) connected to the electronic control device (200, 500).