Method for determining ammonia sensitivity of a nitrogen oxides sensor, a control system, and vehicle

Abstract

A method (400) for determining one or more of an ammonia (NH3) sensitivity and an ammonia sensitivity accuracy of a nitrogen oxides (NOx) sensor (280, 280', 381, 382, 382') configured downstream of a selective catalytic reduction catalyst (SCR; 220, 320, 330) is presented. The method comprises: - storing (420) selected values of a sampled sensor signal (Ssampl) of a nitrogen oxides sensor (280 381, 382) as one or more signal vectors (Vmax, Vmin, Vavg), being functions of one or more velocity zones (vz1, vz2, … vzn), for one or more time bins (Bin1, Bin2, Bin3), being associated with an operation time period of the nitrogen oxides sensor (280, 280', 381, 382, 382'), respectively; - comparing (440) one or more comparison values (vA, vB), being associated with at least one of the one or more the signal vectors (Vmax, Vmin, Vavg), with one or more threshold values (vA_th, vB_th), respectively; and - determining (450) one or more of the ammonia sensitivity and the ammonia sensitivity accuracy of the nitrogen oxides sensor (280, 280', 381, 382, 382').

Description

[0001] METHOD FOR DETERMINING ONE OR MORE OF AN AMMONIA SENSITIVITY AND AN AMMONIA SENSITIVITY ACCURACY OF A NITROGEN OXIDES SENSOR, A CONTROL SYSTEM CONFIGURED FOR CARRYING OUT THE METHOD, AND A VEHICLE COMPRISING THE CONTROL SYSTEM

[0002] Technical field

[0003] The present invention relates to a method for determining an ammonia NHs sensitivity and / or an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor, to a control system configured for determining an ammonia NHs sensitivity and / or an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor, and to a vehicle comprising the control system.

[0004] The invention also relates to a computer program and a computer program product, which implement the method according to the invention.

[0005] Background

[0006] The following background description constitutes a description of the background to the present invention, and thus need not necessarily constitute prior art.

[0007] In connection with increased government interests concerning pollution and air quality, primarily in urban areas, emission standards and regulations regarding emissions from combustion engines have been drafted in many jurisdictions.

[0008] Such emission standards often comprise requirements defining acceptable limits of exhaust emissions from combustion engines in for example vehicles. For example, emission levels of nitrogen oxides NOx, hydrocarbons CxHy, carbon monoxide CO and particles PM are often regulated by such standards for most types of vehicles. Vehicles equipped with combustion engines typically give rise to such emissions in varying degrees. In this document, the invention will be described mainly for its application in vehicles, i.e. for internal combustion engines. However, the invention may be used in substantially any application where combustion engines are used, for example in vessels such as ships or aeroplanes / helicopters, wherein regulations and standards for such applications limit emissions from the combustion engines.In an effort to comply with these emission standards and regulations, the exhausts caused by the combustion of the combustion engine are treated (purified).

[0009] A common way of treating exhausts from a combustion engine comprises a so-called catalytic purification process, which is why vehicles equipped with a combustion engine usually comprise at least one catalyst. There are different types of catalysts, where the different respective types may be suitable depending on for example the combustion concept, combustion strategies and / or fuel types which are used in the vehicles, and / or the types of compounds in the exhaust stream to be purified. In relation to at least nitrous gases (nitrogen monoxide, nitrogen dioxide), referred to below as nitrogen oxides NOx, vehicles often comprise at least one catalyst, wherein an additive is supplied to the exhaust stream resulting from the combustion in the combustion engine, in order to reduce nitrogen oxides NOx, primarily to nitrogen gas and aqueous vapour. This is described in more detail below.

[0010] Selective catalytic reduction (SCR) catalysts are a commonly used type of catalysts for this type of reduction, primarily for heavy goods vehicles. Selective catalytic reduction catalysts usually use ammonia NH3, or a composition from which ammonia may be generated / formed, as an additive to reduce the amount of nitrogen oxides NOx in the exhausts. The additive, for example urea, is injected into the exhaust stream resulting from the combustion engine upstream of the catalyst. The additive added to the catalyst is adsorbed (stored) in the catalyst, in the form of ammonia NH3, so that a redox-reaction may occur between nitrogen oxides NOx in the exhausts and ammonia NH3 available via the additive.

[0011] Summary

[0012] The emission standards and regulations become more and more stringent over time regarding the emissions from combustion engines, requiring a more and more efficient purification of the exhausts. Therefore, the control of the purification process needs to be improved. An improved control of the purification process may be achieved by extending the information basis for the control. Especially, the control of the purification process may also be based on the level of ammonia NH3 being present in the exhaust stream downstream of a selective catalytic reduction catalyst in the exhaust treatment system.For this reason, a nitrogen oxides NOx sensor positioned downstream of a selective catalytic reduction catalyst in the exhaust treatment system may be utilized for providing a measure of the ammonia NH3 in the exhaust stream. This is possible since the nitrogen oxides NOx sensor is cross-sensitive also to ammonia NH3. Thus, the cross-sensitive nitrogen oxides NOx sensor positioned downstream of a selective catalytic reduction catalyst may of course be used for measuring nitrogen oxides NOx, but may also also be used for measuring ammonia NH3 if its cross-sensitivity is taken advantage of.

[0013] However, the accuracy of the cross-sensitivity for the nitrogen oxides NOx sensors decreases with age, i.e. the sensor-to-sensor variation increases with age. It is therefore difficult to know or estimate the cross-sensitivity accuracy for individual nitrogen oxides NOx sensors. The cross-sensitivity is especially inaccurate at low flow velocities and high temperatures for the exhaust stream. The position of the crosssensitive nitrogen oxides NOx sensor downstream of a selective catalytic reduction catalyst in the exhaust treatment system may unfortunately result in that the exhaust stream has a low flow velocity when it comes in contact with the NOx sensor. The exhaust stream also has a high temperature in this downstream position of the nitrogen oxides NOx sensor.

[0014] The ageing causing an unknown cross-sensitivity accuracy may in conventional solutions force sensors to be replaced regularly in order to meet the requirements on the control of the purification process in the exhaust treatment system. The sensor replacements further need to be performed at an interval decided by the fastest ageing sensors, which means that most sensors will be replaced before they have degraded beyond the requirements on the control of the purification process.

[0015] It is therefore an objective of the present invention to provide a determination of one or more of an ammonia NH3 sensitivity and an ammonia NH3 sensitivity accuracy of a nitrogen oxides NOx sensor such that these problems are at least partly solved. According to a first aspect of the present invention, this objective is achieved through the above-mentioned method for determining one or more of an ammonia sensitivity and an ammonia sensitivity accuracy of a nitrogen oxides sensor configureddownstream of a selective catalytic reduction catalyst of an exhaust treatment system configured for treatment of an exhaust gas from an engine;

[0016] the method comprising:

[0017] - sampling a signal of the nitrogen oxides sensor to provide a sampled sensor signal; - storing selected values of the sampled sensor signal as one or more signal vectors for one or more time bins, respectively, wherein

[0018] -- each of the one or more signal vectors is a function of one or more velocity zones associated with a velocity of the exhaust gas; and

[0019] -- each of the one or more time bins is associated with an operation time period of the nitrogen oxides sensor;

[0020] - determining one or more comparison values associated with at least one of the one or more the signal vectors;

[0021] - comparing the one or more comparison values with one or more threshold values, respectively; and

[0022] - determining one or more of the ammonia sensitivity and the ammonia sensitivity accuracy of the nitrogen oxides sensor based on the comparison.

[0023] The determined ammonia sensitivity and / or ammonia sensitivity accuracy of the nitrogen oxides NOx sensor may for example be used for triggering an accurate diagnosis indicating that this specific nitrogen oxides NOx sensor individual needs to be replaced, for example due to ageing which has deteriorated its ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy.

[0024] The determined ammonia sensitivity and / or ammonia sensitivity accuracy of the nitrogen oxides NOx sensor may also be used for compensating for the ageing nitrogen oxides NOx sensor. Hereby, the operational lifetime of the nitrogen oxides NOx sensor is extended.

[0025] Thus, thanks to the proposed determination of the ammonia NHssensitivity and / or ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor, the sensor replacements can be done when the specific nitrogen oxides NOx sensor individual in question, and not the fastest ageing sensor in a group of sensors, reaches its design limit. This will prolong the time each nitrogen oxides NOx sensor individual can be used, and will thus also decrease the costs conventionally spent on sensorreplacements. Also, unnecessary service shop visits may be avoided, thereby minimizing the vehicle off road time. An accurate, robust and reliable control of the exhaust treatment system may thus be based on measures of ammonia NHs, without the need for a separate / additional ammonia NHs sensor, since the nitrogen oxides NOx sensor already being present in the exhaust treatment system will instead provide an accurate measurement of ammonia NHs. Thus, the hardware complexity is minimized by the presented solution.

[0026] Since the reliability of the ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor is hereby increased, the control of the exhaust treatment system may be performed more reliably and accurately, resulting in an improved purification of the exhaust gases.

[0027] According to an embodiment of the present invention, the determination of the one or more comparison values comprises:

[0028] - determining one or more points of at least one signal vector and one or more velocity values for the exhaust gas associated with the one or more points, respectively; and

[0029] - determining the one or more velocity values to be the one or more comparison values.

[0030] Hereby, the features of the nitrogen oxides NOx sensor related to the ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy associated with various velocities may efficiently be identified.

[0031] According to an embodiment of the present invention, the one or more points of the at least one signal vector are determined based on an inclination of the selected values of the at least one signal vector with decreasing velocities of the exhaust gas.

[0032] By analyzing the inclinations / slopes or the values of the signal vector, the points and the exhaust gas velocities at which the ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy decrease may easily and efficiently be found.

[0033] According to an embodiment of the present invention, at least one of the one or more points is determined as a point between a first signal vector interval and a secondsignal vector interval, the first signal vector interval and the second signal vector interval having differing inclinations.

[0034] The differing inclinations of the first signal vector interval and the second signal vector interval may hereby be utilized for efficiently identifying the points and the exhaust gas velocities at which the ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy are deteriorated. According to an embodiment, the individual inclinations for the various signal vector intervals should not exceed a first inclination level, at the same time as a total inclination for the total signal vector does not exceed a second inclination level.

[0035] According to an embodiment of the present invention, the one or more points of the at least one signal vector are determined based on a decrease of the selected values of the at least one signal vector with decreasing velocities of the exhaust gas.

[0036] The decreasing selected values of the at least one signal vector may thus be utilized for efficiently identifying the points and the exhaust gas velocities at which the ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy are deteriorated. Generally, ageing of a nitrogen oxides NOx sensor reduces its provided ammonia NH3 sensitivity while the ageing at the same time increases the sensor to sensor variation of the ammonia NH3 sensitivity, and thus decrease the accuracy.

[0037] According to an embodiment of the present invention, at least one of the one or more points is determined as a point where the selected values are decreased to a predetermined fraction of a maximum value of the selected values.

[0038] The predetermined fraction reduction of the selected values of the at least one signal vector may thus identify the points and the exhaust gas velocities at which the ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy are deteriorated. If the maximum value of the selected values is provided by an essentially non-aged / non-deteriorated / new nitrogen oxides NOx sensor, then the ammonia NH3 sensitivity may hereby be determined. However, if the maximum value of the selected values is provided by an at least partly aged nitrogen oxides NOx sensor, which has been in operation for some time, then the ammonia NH3 sensitivity accuracy may hereby be determined.According to an embodiment of the present invention, the determination of the one or more comparison values comprises:

[0039] - normalizing the one or more signal vectors with respect to at least one predetermined signal value to provide a normalized signal vector for each of the one or more time bins;

[0040] - determining one or more points of at least one normalized signal vector and one or more velocity values for the exhaust gas associated with the one or more points, respectively; and

[0041] - determining the one or more velocity values to be the one or more comparison values.

[0042] To base the determination of ammonia NH3 sensitivity and / or an ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor on normalized signal vectors for the time bins facilitates a calibration of different sensor versions. Also, the normalization of the one or more signal vectors provides for a uniform scaling of the one or more signal vectors, and thereby provides a reproduceable resolution of the one or more signal vectors.

[0043] According to an embodiment of the present invention, the determination of the one or more comparison values comprises:

[0044] - normalizing the one or more signal vectors with respect to at least one predetermined signal value to provide a normalized signal vector for each of the one or more time bins;

[0045] - subtracting an initial normalized signal vector of an initial time bin from a normalized signal vector of a subsequent time bin to provide a relative difference vector;

[0046] - determining one or more values of the relative difference vector to be the one or more comparison values.

[0047] The normalized signal vector of the initial time bin corresponds to values output by an essentially new / non-aged / non-deteriorated nitrogen oxides NOx sensor. Thus, the relative difference vector comprises vector values corresponding to the deviation from such a new / non-aged / non-deteriorated nitrogen oxides NOx sensor. Hereby, the values of the relative difference vector may directly be utilized as an indication of theageing and / or deterioration of the nitrogen oxides NOx sensor impacting the ammonia NHs sensitivity and an ammonia NHs sensitivity accuracy.

[0048] According to an embodiment of the present invention, the one or more comparison values are determined from the relative difference vector as one in the group of: - one or more minimal values of the relative difference vector;

[0049] - one or more maximal values of the relative difference vector; and

[0050] - a maximal difference between one or more maximal values of the relative difference vector and one or more minimal values of the relative difference vector.

[0051] The minimal and / or maximal values of the relative difference vector may be directly used as a basis for determining ageing and / or deterioration of the nitrogen oxides NOx sensor impacting the ammonia NHs sensitivity, i.e. may be utilized for determining the ammonia NHs sensitivity. The largest difference value between such maximal and minimal values may be directly used as a basis for determining ageing and / or deterioration of the nitrogen oxides NOx sensor impacting the ammonia NHs sensitivity accuracy, i.e. may be utilized for determining the ammonia NHs sensitivity accuracy.

[0052] According to an embodiment of the present invention, the method further comprises - dividing an initial normalized signal vector of an initial time bin by a subsequent normalized signal vector of a subsequent time bin to provide a relative adaptive constant vector;

[0053] - adjusting values of the sampled sensor signal based on the provided relative adaptive constant vector.

[0054] Hereby, the values of the sampled sensor signal are adjusted / adapted based on the ageing and / or deterioration of the nitrogen oxides NOx sensor. By introducing this adjustment / adaption of the values of the sampled sensor signal, the lifetime of an individual nitrogen oxides NOx sensor may be prolonged, since its ageing and / or deterioration affecting the ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy is compensated for. Thus, each sensor may be used for a longer time, which further reduces the costs for sensor service and / or replacements.According to an embodiment of the present invention, the at least one predetermined signal value utilized for the normalization is one or more in the group of:

[0055] - a highest value of the one or more signal vectors;

[0056] - one or more values of a signal vector for an initial time bin; and

[0057] - at least one value of a signal vector for an initial time bin, the at least one value being associated with a highest velocity of the exhaust gas for the initial time bin.

[0058] The highest value of the one or more signal vectors corresponds to an output by the nitrogen oxides NOx sensor for high velocities of the exhaust gas. Since the ammonia NH3 sensitivity and an ammonia NH3 sensitivity accuracy is essentially not deteriorated at such high exhaust gas velocities, these values may be seen as corresponding to values being output by a new / non-aged / non-deteriorated nitrogen oxides NOx sensor.

[0059] The signal vector of the initial time bin may also be seen as corresponding to values being output by a new / non-aged / non-deteriorated nitrogen oxides NOx sensor.

[0060] Thus, the highest values of the signal vectors and / or the signal vector of the initial time bin may be utilized as corresponding values for a new / non-aged / non-deteriorated nitrogen oxides NOx sensor. Hereby, the values of the normalized signal vector may be seen as corresponding to such a non-deteriorated nitrogen oxides NOx sensor, and may be directly used as a basis for determining ageing and / or deterioration of the nitrogen oxides NOx sensor, that impact the ammonia NH3 sensitivity and an ammonia NH3 sensitivity accuracy.

[0061] According to an embodiment of the present invention,

[0062] - each of the one or more signal vectors is further a function of a temperature of the exhaust gas;

[0063] - the determination of the one or more comparison values is based also on the temperature; and

[0064] - the comparison of the one or more comparison values with one or more threshold values, respectively, is based also on the temperature.

[0065] By extending the one or more signal vectors to also be functions of a temperature of the exhaust gas, an increased accuracy and reliability for the determination of theammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor is provided. Both the temperature of the exhaust gas and its velocity when passing by the nitrogen oxides NOx sensor may thus influence the output signal of the nitrogen oxides NOx sensor, which is here taken into consideration when the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor is determined.

[0066] According to an embodiment of the present invention,

[0067] - each of the one or more signal vectors is further a function of a concentration / level of ammonia in the exhaust gas;

[0068] - the determination of the one or more comparison values is based also on the concentration / level of ammonia; and

[0069] - the comparison of the one or more comparison values with one or more threshold values, respectively, is based also on the concentration / level of ammonia.

[0070] By extending the one or more signal vectors to also be functions of a concentration of ammonia in the exhaust gas, an increased accuracy and reliability for the determination of the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor is provided. Both the ammonia concentration in the exhaust gas and the velocity of the exhaust gas when passing by the nitrogen oxides NOx sensor may thus influence the output signal of the nitrogen oxides NOx sensor, which is here taken into consideration when the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor is determined.

[0071] According to an embodiment of the present invention, the determination of the one or more comparison values and the comparison of the one or more comparison values with one or more threshold values, respectively, is based also on one or more in the group of:

[0072] - a level of nitrogen oxides in the exhaust gas;

[0073] - a level of ammonia in the exhaust gas;

[0074] - a level of adsorbed ammonia in the exhaust treatment system upstream of the nitrogen oxides sensor; and- a reduction of nitrogen oxides in the exhaust treatment system upstream of the nitrogen oxides sensor.

[0075] To base the determination of the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor on more parameters of the exhaust gas and / or the exhaust treatment system increases the accuracy and reliability of the determination. The one or more comparison values may here be determined and / or the comparison of the one or more comparison values with one or more threshold values may here be performed based on measured and / or modelled signals and / or values associated with these parameters of the exhaust gas, the exhaust treatment system and / or the vehicle.

[0076] According to an embodiment of the present invention, the method is performed during one in the group of:

[0077] - idling of the engine;

[0078] - high idling of the engine;

[0079] - a normal operation of the engine;

[0080] - a set load operation of the engine; and

[0081] - a set speed operation of the engine.

[0082] Thus, the herein presented determination of the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor may be performed during various suitable operation modes of the vehicle. Such operation modes may be associated with operation of an engine and / or an exhaust treatment system of the vehicle in various control and / or diagnosis modes.

[0083] According to an embodiment of the present invention, the selected values of the sampled sensor signal comprise one or more in the group of:

[0084] - maximum values of the sampled sensor signal;

[0085] - average values of the sampled sensor signal;

[0086] - minimum values of the sampled sensor signal;

[0087] - a predetermined fraction of maximum values of the sampled sensor signal;

[0088] - a predetermined fraction of average values of the sampled sensor signal; and - a predetermined fraction of minimum values of the sampled sensor signal.Thus, values of the sampled sensor signal being suitable for the current situation, implementation and / or operation mode may be chosen for the determination of the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor. Hereby, a flexible solution is provided. The various type of values being selected have respective advantages. For example, the selection of maximum, average or minimum values is a low-complexity solution. The selection of fractions of maximum, average or minimum values provides for an accurate and robust determination of the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor, because possibly erroneous maximum and / or minimum end / tail values are neglected.

[0089] According to an embodiment of the present invention, the one or more threshold values are determined based on a relation between a maximum value of the sampled sensor signal and a minimum value of the sampled sensor signal.

[0090] Hereby, these threshold values are associated with a robustness of the control of the exhaust treatment system. The determination of the ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor, and a possible decision to exchange an aged nitrogen oxides NOx sensor, may thus be performed such that an accurate and reliable control of the exhaust treatment system is achieved.

[0091] According to an embodiment of the present invention, the velocity zones provide a resolution in a velocity domain according to one in the group of:

[0092] - a resolution in an interval of 0.5 m / s to 20 m / s; and

[0093] - a resolution of 3 m / s.

[0094] A suitable velocity resolution, which results in an accurate determination of the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor without causing too much computational burden, is hereby provided. In one embodiment, lower velocities of the exhaust gas may be represented with higher resolution in the velocity domain, i.e. with shorter velocity zone intervals.According to an embodiment of the present invention, the one or more time bins comprise:

[0095] - an initial time bin; and

[0096] - at least one sequential time bin.

[0097] The signal vector of the initial time bin comprises values corresponding to values being output by a new / non-aged / non-deteriorated nitrogen oxides NOx sensor. Thus, the values of this initial time bin signal vector are suitable to utilize as a reference signal vector for the determination of the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor.

[0098] According to an embodiment of the present invention, each of the one or more time bins covers a time period in the group of:

[0099] - a time period in an interval of 10 h to 1000 h

[0100] - a time period in an interval of 100 h to 1000 h; and

[0101] - a time period of 1000 h.

[0102] A suitable time resolution, which results in an accurate exhaust determination of the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor without causing too much computational burden, is hereby provided. As a non-limiting example, if each bin covers 1000 h, then the sampled signals for the last, i.e. most recent, 1000 h of operation are represented by the last bin, i.e. by most recent generated time bin.

[0103] According to an embodiment of the present invention, the nitrogen oxides sensor is configured upstream of an ammonia slip catalyst of the exhaust treatment system.

[0104] Thus, the herein presented determination of the ammonia NH3 sensitivity and / or the ammonia NH3 sensitivity accuracy may be efficiently utilized for nitrogen oxides NOx sensor in various positions in the exhaust treatment system, and in exhaust treatment systems having various layouts. When the cross sensitive nitrogen oxides NOx sensor is positioned downstream of a selective catalytic reduction catalyst and upstream of an ammonia slip catalyst of the exhaust treatment system, the level of ammonia NH3 sensed by the nitrogen oxides NOx sensor may be utilized as a basis for the control of the reductant dosing being performed upstream of the selectivecatalytic reduction catalyst and / or as a basis for the control of a coverage level of the selective catalytic reduction catalyst.

[0105] According to a second aspect of the present invention, the objective is achieved through a control system configured for determining one or more of an ammonia sensitivity and an ammonia sensitivity accuracy of a nitrogen oxides sensor configured downstream of a selective catalytic reduction catalyst of an exhaust treatment system configured for treatment of an exhaust gas from an engine;

[0106] the control system being configured to:

[0107] - sample a signal of the nitrogen oxides sensor to provide a sampled sensor signal; - store selected values of the sampled sensor signal as one or more signal vectors for one or more time bins, respectively, wherein

[0108] -- each of the one or more signal vectors is a function of one or more velocity zones associated with a velocity of the exhaust gas; and

[0109] -- each of the one or more time bins is associated with an operation time period of the nitrogen oxides sensor;

[0110] - determine one or more comparison values associated with at least one of the one or more the signal vectors;

[0111] - compare the one or more comparison values with one or more threshold values, respectively; and

[0112] - determine one or more of the ammonia sensitivity and the ammonia sensitivity accuracy of the nitrogen oxides sensor based on the comparison.

[0113] According to a third aspect of the present invention, the objective is achieved through a vehicle comprising a herein described control system.

[0114] According to a fourth aspect, the invention relates to a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the herein described methods.

[0115] The computer program has corresponding advantages as mentioned for the method according to the first aspect.According to a fifth eleventh, the invention relates to a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the herein described methods.

[0116] The computer-readable medium has corresponding advantages as mentioned for the method according to the first aspect.

[0117] It will be appreciated that all the embodiments described for the method aspects of the invention are applicable also to one or more of the control system aspect, the vehicle aspect, the computer program aspect and the computer-readable medium aspect of the invention. Thus, all the embodiments described for the method aspects of the invention may be performed / implemented by the herein described control system, vehicle, computer program and / or the computer-readable medium. The control system may also be a processing device, i.e. a device. The control system aspects, the vehicle aspect, the computer program aspect and the computer-readable medium aspect, and their embodiments, have advantages corresponding to the advantages mentioned above for the methods and their embodiments.

[0118] Brief list of figures

[0119] The invention will be illustrated in more detail below, along with the enclosed drawings, where similar references are used for similar parts, and where:

[0120] Figure 1 shows an example vehicle which may comprise a control system according to various aspects and embodiments of the present invention,

[0121] Figure 2 shows an example of an exhaust treatment system in which various aspects and embodiments of the present invention may be implemented,

[0122] Figure 3 shows an example of an exhaust treatment system in which various aspects and embodiments of the present invention may be implemented,

[0123] Figure 4 shows a flow chart for the method according to the aspects and embodiments of the invention,Figurer 5a-d show signal diagrams of comprising possible values of a sampled sensor signal of a nitrogen oxides NOx sensor, and a relation between the second VB and first VA velocities over time,

[0124] Figures 6a-b show signal diagrams of comprising possible values of a normalized signal vector of a nitrogen oxides NOx sensor,

[0125] Figure 7 schematically illustrates a control unit in which the aspects and embodiments of the present invention may be implemented,

[0126] Figure 8 schematically illustrates a distribution of a signal frequency of sampled sensor signal values, and

[0127] Figure 9 schematically illustrates an example time bin.

[0128] Description of preferred embodiments

[0129] Figure 1 schematically shows an example vehicle 100 comprising a powertrain. The powertrain comprises a combustion engine 101, which in a customary manner, via an output shaft 102 of the combustion engine 101 is connected to a gearbox 103 via a clutch 106. An output shaft 107 from the gearbox 103 may drive the wheels 113, 114 e.g. via a final drive 108, such as e.g. a customary differential, and the drive shafts 104, 105 connected to the said final drive 108.

[0130] The combustion engine 101, e.g. an internal combustion engine, may be controlled by the engine’s control system via a control device 115. Likewise, the clutch 106 and the gearbox 103 may be controlled by the vehicle’s control system, with the help of one or more applicable control devices (not shown). Naturally, the vehicle’s powertrain may also be of another type, such as a type with a conventional automatic gearbox, of a type with a hybrid driveline, etc.

[0131] The vehicle 100 also comprises an exhaust treatment / purification system 250, 350 for treatment / purification of exhaust emissions resulting from combustion in the combustion chamber of the combustion engine 101. The exhaust treatment system 250, 350 may be a herein described exhaust treatment system 250, 350, being controlled by a control system / arrangement / unit 190.Figure 2 shows an example exhaust treatment system 250, which may illustrate a so-called Euro Vl-system, in which the herein presented solution may be implemented. The exhaust treatment system 250 is connected to a combustion engine 201 e.g. via an exhaust conduit 202, wherein the exhausts generated at the combustion, that is to say the exhaust stream 203, is indicated with arrows. The exhaust stream 203 is led to a coated or uncoated diesel particulate filter (cDPF / DPF) 210. A coated diesel particulate filter is coated with a catalytically oxidising coating, for example comprising at least one precious metal. A diesel oxidation catalyst (DOC) may be arranged upstream of the coated or uncoated diesel particulate filter (cDPF / DPF) 210 in the exhaust treatment system 250. Thus, a coated or uncoated diesel particulate filter 210 and possibly a diesel oxidation catalyst are arranged downstream of the combustion engine 201 in the exhaust treatment system 250.

[0132] During the combustion in the combustion engine 201 , soot and ash are created, and the coated or uncoated diesel particulate filter 210 is used to catch the soot and ash. The exhaust stream 203 is here led through a filter structure, wherein soot and ash from the exhaust stream 203 are caught when passing through, and are stored in the coated or uncoated diesel particulate filter 210.

[0133] The catalytic coating in the coated diesel particulate filter 210, or alternatively in the oxidation catalyst, has several functions and is normally used primarily to oxidise, during the exhaust treatment, remaining hydrocarbons CxHy(also referred to as HC) and carbon monoxide CO in the exhaust stream 203 into carbon dioxide CO2 and water H2O. Also, a large fraction of the nitrogen monoxides NO occurring in the exhaust stream may be oxidised into nitrogen dioxide NO2. The oxidation of nitrogen monoxide NO into nitrogen dioxide NO2 is important to the nitrogen dioxide-based soot and ash oxidation in the filter, and is also advantageous at a potential subsequent reduction of nitrogen oxides NOx.

[0134] In this respect, the exhaust treatment system 250 further comprises a selective catalytic reduction (SCR) catalyst 220 arranged downstream of the coated or uncoated diesel particulate filter 210. The selective catalytic reduction catalyst 220 uses ammonia NH3, or a composition from which ammonia may be generated / formed, e.g. urea, as an additive for the reduction of nitrogen oxides NOxin the exhaust stream 203. After passing through the components of the exhaust treatment system, the exhaust stream is emitted into the environment at the tailpipe.

[0135] The reaction rate of this reduction is impacted, however, by the ratio between nitrogen monoxide NO and nitrogen dioxide NO2 in the exhaust stream, so that the reductive reaction is impacted in a positive direction by the previous oxidation of NO into NO2 in the coated diesel particulate filter, or alternatively in the oxidation catalyst.

[0136] The selective catalytic reduction catalyst 220 requires additives to reduce the concentration of a compound, such as for example nitrogen oxides NOx, in the exhaust stream 203. Such additive is injected into the exhaust stream downstream of the coated or uncoated particulate filter 210 and upstream of the selective catalytic reduction catalyst 220, shown in figure 2 as a dosing arrangement 270. Such additive is often ammonia NH3 and / or urea based, or consists of a substance from which ammonia NH3 may be extracted or released, and may for example consist of AdBlue, which basically consists of urea mixed with water. Urea forms ammonia NH3 at heating (thermolysis) and at heterogeneous catalysis on an oxidizing surface (hydrolysis), which surface may, for example, consist of titanium dioxide TiO2, within the selective catalytic reduction catalyst 220. The exhaust treatment system may also comprise a separate hydrolysis catalyst. The additive may be provided from a container / tank 275, and the dosing of the additive may be controlled by a control unit / system 290.

[0137] The exhaust treatment system 250 may, according to some embodiments, also be equipped with an ammonia slip-catalyst (ASC) 240, which is arranged downstream of the reduction catalyst arrangement 220 to oxidise an excess of ammonia that may remain after reduction catalyst arrangement 220, and / or to assist the reduction catalyst arrangement 220 with further reduction of NOx. Accordingly, the ammonia slip-catalyst ASC 240 may provide a potential for improving the system’s total conversion / reduction of NOx.

[0138] After passing through the components of the exhaust treatment system 250, the exhaust stream is emitted into the environment at the tailpipe 283 of the exhaust treatment system 350.The exhaust treatment system 250 may also be equipped with one or several sensors, such as one or several NOx and / or temperature sensors for the determination of nitrogen oxides and / or temperatures in the exhaust treatment system. One such sensor is a nitrogen oxides NOx sensor 280 positioned downstream of the selective catalytic reduction catalyst 220. If the exhaust treatment system 250 comprises an ammonia slip-catalyst 240, the nitrogen oxides NOx sensor 280 may, according to an embodiment, be positioned downstream of the reduction catalyst arrangement 220 and upstream of the ammonia slip-catalyst 240. According to another embodiment, the nitrogen oxides NOx sensor 280 is positioned downstream of the ammonia slip-catalyst 240. According to yet another embodiment, the nitrogen oxides NOx sensor 280 is positioned downstream of the reduction catalyst arrangement 220 and upstream of the ammonia slip-catalyst 240, and an additional nitrogen oxides NOx sensor 280’ is positioned downstream of the ammonia slip-catalyst 240. The nitrogen oxides NOx sensor 280, and the possible additional nitrogen oxides NOx sensor 280’, are connected to the control unit / system 290, and are configured to provide sensor signal information to the control unit / system 290. The herein presented method for determining an ammonia NHs sensitivity and / or an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor is applicable to the nitrogen oxides NOx sensor 280 and / or the additional nitrogen oxides NOx sensor 280’.

[0139] Figure 3 schematically shows another example of an exhaust treatment system 350, in which the herein presented solution may be implemented. The exhaust treatment system 350 is connected via an exhaust pipe 302 to a combustion engine 301.

[0140] Exhausts are generated at combustion in the engine 301 , and the exhaust stream 303 (indicated with arrows) is led to a first / upstream dosage device 371 , arranged to add an additive into the exhaust stream 303. A first / upstream selective catalytic reduction catalyst (SCRi) 330 is arranged downstream of the first / upstream dosage device 371. The first / upstream selective catalytic reduction catalyst 330 is arranged to reduce nitrogen oxides NOx in the exhaust stream 303, through the use of the additive added to the exhaust stream by the upstream dosage device 371. In moredetail, the first / upstream selective catalytic reduction catalyst 330 uses the additive, for example ammonia NH3, or a substance from which ammonia NH3 may be generated / formed / released, for the reduction of nitrogen oxides NOx in the exhaust stream 303. This additive may for example consist of the above mentioned AdBlue, and may be provided from a container / tank 375. The injection of the additive may be controlled by a control unit / system 390.

[0141] Downstream of the first / upstream selective catalytic reduction catalyst 330, the exhaust treatment system 350 further comprises a coated or uncoated diesel particulate filter (cDPF / DPF) 310. A coated diesel particulate filter is coated with a catalytically oxidising coating, for example comprising at least one precious metal for catching and oxidising soot and ash. A diesel oxidation catalyst (DOC) may be arranged upstream of the coated or uncoated diesel particulate filter (cDPF / DPF) 310 in the exhaust treatment system 350. Thus, a coated or uncoated diesel particulate filter 310 and possibly a diesel oxidation catalyst are arranged downstream of the first / upstream selective catalytic reduction catalyst 330 in the exhaust treatment system 350.

[0142] Downstream of the coated or uncoated particulate filter 310, the exhaust treatment system 350 comprises a second / downstream dosage device 372, which is arranged to supply additive to the exhaust stream 303, where such downstream additive comprises ammonia NH3, or a substance, for example AdBlue, from which ammonia NH3 may be generated / formed / released, as described above. The downstream additive may here be the same additive as the above mentioned additive injected by the upstream dosage device 371 , and may possibly also come from the same container / tank 375. Alternatively, the additives injected by the first / upstream 371 and second / downstream 372 dosage devices, respectively, may also be of different types and may come from different tanks. The injection by the second / downstream dosage device 372 may be controlled by a control unit / system 390.

[0143] According to an embodiment of the invention, an evaporation arrangement may be arranged at the first / upstream 371 and / or second / downstream 372 dosing arrangements, respectively, to increase the speed of the decomposition of urea intoammonia, and / or to mix the additive with the emissions, and / or to vaporise the additive.

[0144] The exhaust treatment system 350 also comprises a second / downstream reduction catalyst device (SCR2) 320, which is arranged downstream of the second / downstream dosage device 372. The second / downstream reduction catalyst device 320 is arranged to reduce nitrogen oxides NOx in the exhaust stream 303 through use of the additive injected by the second / downstream dosage device 372, and possibly also additive remaining in the exhaust stream 303 which was injected by the first / upstream dosage device 371.

[0145] According to an embodiment, the exhaust treatment system 350 may further comprise an ammonia slip catalyst arrangement (ASC) 340 arranged downstream of the second / downstream reduction catalyst device 320 for oxidation of a residue of additive in the exhaust stream 303, as shown in figure 3, respectively. The ammonia slip catalyst arrangement 340 removes an additive residue from the exhaust stream 303.

[0146] After passing through the components of the exhaust treatment system, the exhaust stream is emitted into the environment at the tailpipe 383 of the exhaust treatment system 350.

[0147] The exhaust treatment system 350 may also be equipped with one or several sensors, such as one or several NOx and / or temperature sensors for the determination of nitrogen oxide NOx concentrations and / or temperatures in the exhaust treatment system 350, respectively. One such sensor may be a first / upstream nitrogen oxides NOx sensor 381 positioned downstream of the first / upstream selective catalytic reduction catalyst 330. Another such sensor may be a second / downstream nitrogen oxides NOx sensor 382 positioned downstream of the second / downstream selective catalytic reduction catalyst 320. If the exhaust treatment system 350 comprises an ammonia slip-catalyst 340, the second / downstream nitrogen oxides NOx sensor 382 may, according to an embodiment, be positioned downstream of the second / downstream selective catalyticreduction catalyst 320 and upstream of the second / downstream ammonia slipcatalyst 340. According to another embodiment, the second / downstream nitrogen oxides NOx sensor 382 is positioned downstream of the ammonia slip-catalyst 240. According to yet another embodiment, the second / downstream nitrogen oxides NOx sensor 382 is positioned downstream of the second / downstream selective catalytic reduction catalyst 320 and upstream of the second / downstream ammonia slipcatalyst 340, and an additional second / downstream nitrogen oxides NOx sensor 382’ is positioned downstream of the ammonia slip-catalyst 240. The first and second nitrogen oxides NOx sensors 381 , 382, and the possible additional second nitrogen oxides NOx sensors 382’, are connected to the control unit / system 390, and are configured to provide sensor signal information to the control unit / system 390. The herein presented method for determining an ammonia NHs sensitivity and / or an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor is applicable to the first and second nitrogen oxides NOx sensors 381 , 382, and to the possible additional second nitrogen oxides NOx sensors 382’.

[0148] Through the use of the exhaust treatment system 350 shown in Figure 3, both the first / upstream selective catalytic reduction catalyst 330 and the second / downstream selective catalytic reduction catalyst 320 may be optimised with respect to a selection of catalyst characteristics for the reduction of nitrogen oxides NOx, and / or with respect to volumes for the first / upstream 330 and second / downstream 320 selective catalytic reduction catalysts, respectively.

[0149] The coated or uncoated particulate filter 310 may hereby be used to improve the efficiency, by taking into account how its thermal mass, i.e. its thermal inertia, impacts the temperature of the second / downstream selective catalytic reduction catalyst 320. By taking into account the thermal inertia of the coated or uncoated particulate filter 310, the first / upstream selective catalytic reduction catalyst 330 and the second / downstream selective catalytic reduction catalyst 320, respectively, may be optimised with respect to the specific temperature function each will experience.

[0150] The exhaust treatment system 350 reduces the amount of nitrogen oxides NOx in the exhaust stream in substantially all driving modes, comprising especially cold starts and throttle, that is to say increased requested torque.For each one of the first / upstream 330 and the second / downstream 320 selective catalytic reduction catalysts, its catalytic characteristics may be selected based on the environment to which it is exposed, or will be exposed to. Additionally, the catalytic characteristics for the first / upstream 330 and the second / downstream 320 reduction catalyst device may be adapted so that they may be allowed to operate in symbiosis with each other. The first / upstream 330 and the second / downstream 320 selective catalytic reduction catalyst may also comprise one or several materials, providing the catalytic characteristic. For example, transition metals such as vanadium and / or tungsten may be used, for example in a catalyst comprising V2Os / WO3 / TiO2. Metals such as iron and / or copper may also be comprised in the first / upstream 330 and / or second / downstream 320 selective catalytic reduction catalys, for example in a Zeolite-based catalyst.

[0151] A skilled person realises that the herein presented method for determining an ammonia NHs sensitivity and / or an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor is generally applicable to essentially any exhaust treatment system comprising a nitrogen oxides NOx sensor arranged downstream of a selective catalytic reduction catalyst.

[0152] According to an aspect of the present invention, a method for for determining one or more of an ammonia NHs sensitivity and an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ configured downstream of a selective catalytic reduction catalyst 220, 320, 330 of an exhaust treatment system 250, 350 configured for treatment of an exhaust gas 203, 303 from an engine 201 , 301.

[0153] Figure 4 shows a flow-chart diagram illustrating some aspects and embodiments of such a method 400.

[0154] Figures 5a-d schematically illustrate signal diagrams useful for explaining some features of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ having been identified when developing the herein presented solution. Figures 5a-d may therefore be useful for explaining the presented method 400 illustrated in figure 4.Figures 5a-c schematically illustrate examples of possible selected values of a sampled sensor signals Ssampi for one or more velocity zones vz1 , vz2, ... vzn associated with a velocity v of the exhaust gas 203, 303, where the sampled sensor signals Ssampi are provided by the nitrogen oxides NOx sensor 280, 381 , 382 for three time resolved bins, more in detail for an initial time bin Bin 1 in figure 5a, and for two sequential time bins Bin2, Bin3 in figures 5b-c. The selection of the values is described in detail below in connection with the second step 420 of the method.

[0155] According to various embodiments, each of the one or more time bins Bin 1 , Bin2, Bin3 covers an operation time period of the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ in an interval of 10 h to 1000 h, a time period in an interval of 100 h to 1000 h and / or a time period of 1000 h.

[0156] The sampled sensor signals Ssampi is sampled continuously, and the sampled values are stored as a function of the one or more velocity zones vz1 , vz2, ... vzn associated with a velocity v of the exhaust gas 203, 303. The velocity zones vz1 , vz2, ... vzn may be seen as a resolution of the function in the velocity domain. According to various embodiments, the velocity zones vz1 , vz2, ... vzn provide a resolution in an interval of 0.5 m / s to 20 m / s, or provide a resolution of 3 m / s. It may be noted that the velocity v and the velocity zones vz1 , vz2, ... vzn are associated with a dwell time tdweii for the exhaust gas 203 at the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’, as its cross-sensitivity depends on catalytic reactions occurring due to exposure time and temperature. The dwell time tdweii of the exhaust gas 203 is, as is well known associated with the velocity v of the exhaust gas 203; tdweii = k / v, where k is a constant.

[0157] The solid lines in each graph of figures 5a-c indicate maximal and minimal values of the sampled sensor signals Ssampi for that time bin. Thus, the values of the sampled sensor signals Ssampi are situated vertically between these solid lines. The dashed lines to the left in the graphs indicate that values of a sampled sensor signals Ssampi are unknown for very low velocities v of the exhaust gas 203, 303, e.g. for exhaust gas velocities for which no signals have been sensed and sampled.

[0158] If the graphs of figures 5a-c are compared, it may be noted that for an essentially new nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’, being schematicallyillustrated in the initial Bini of figure 5a, the cross-sensitivity of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’, i.e. the ammonia NHs sensitivity and the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is stable, i.e. is essentially not deteriorated. This may be concluded from the horizontal solid lines of the graph, indicating that the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ is not reduced with reducing exhaust gas velocities v, at least for known signal values. Thus, the horizontal solid lines indicate that the level of ammonia NHs in the exhaust stream 203, 303 being sensed by the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is essentially the same for different velocities v of the exhaust stream 203, 303, which is of course correct, because the ammonia NHs content in the exhaust stream does not vary with the velocity v. Thus, the crosssensitivity of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ illustrated in figure 5a is essentially not deteriorated.

[0159] However, for a nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ having been in operation for some time, being schematically illustrated in the second bin Bin2 of figure 5b, the cross-sensitivity of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’, i.e. the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ has been deteriorated. This may be concluded from the sloping solid lines to the left in the graph, for velocities lower than a second velocity VB, indicating that the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ is reduced with reduced exhaust gas velocities v for known signal values. The sloping lines indicate that the level of ammonia NHs in the exhaust stream 203, 303 being sensed by the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is reduced with reducing velocities v of the exhaust stream 203, 303, which is not correct, because the ammonia NHs content in the exhaust stream does not vary with the velocity v. Thus, the ammonia NHs sensitivity of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is here decreased for lower exhaust gas velocities v: v < VB; causing the solid lines of the graph to lower values with the lower velocities to the left in the graph.For a nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ having been in operation for a longer time, being schematically illustrated in the third bin Bin3 of figure 5c, the cross-sensitivity of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’, i.e. the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ has been even more deteriorated, and is relatively poor. It may be concluded from the sloping solid lines in the graph that the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ are reduced with reduced exhaust gas velocities v lower than a second velocity VB ; v < VB; for known signal values. It should be noted that the solid lines of the graph in figure 5c start sloping at the second velocity VB; V < VB; further to the right than the solid lines start sloping at the second velocity VB; V < VB; in the graph of figure 5b. In other words is the second velocity VB in figure 5c higher that the second velocity VB in figure 5b. Thus, the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is according to the graph of figure 5c already reduced at higher second velocities VB of the exhaust gas for the third time bin Bin3 in figure 5c than for the second time bin Bin2 shown in figure 5b. Thus, the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is even worse for the third time bin Bin3 in figure 5c, than it is for the second time bin Bin2 in figure 5b, since the reduction of the levels of ammonia NHs sensed by the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ are reduced also at higher values for the second velocity VB in figure 5c.

[0160] In figures 5a-c, a first velocity VA indicates the exhaust stream velocity from which there are available signal samples, and the second velocity VB indicates the exhaust stream velocity at which the slope / deterioration starts with reduced velocities. Figure 5d schematically shows values for a relation / quotient

[0161]

[0162] between the second VB and first VA velocities over time. It should be noted that the relationship / quotient VB I has increasing values with increasing time. This is in correlation with the graphs in figures 5a-c, in which the relationship / quotient VB I

[0163]

[0164] increases from the second bin Bin2 in figure 5b to the third bin Bin3 in figure 5c, due to the higher and higher values for the second velocity VB for longer operation times for the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’.The method 400, illustrated by the flow-chart in figure 4, explores these features of the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ illustrated in figures 5a-d to determine its ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy. The method steps of figure 4 may be performed in another order than illustrated in figure 4, as long as the information needed for performing a method step is available when the step is to be performed.

[0165] In a first step 410 of the method 400, a signal S of the nitrogen oxides sensor 280381, 382 is sampled to provide a sampled sensor signal Ssampi. This sampled sensor signal Ssampi may comprise values anywhere between the solid lines in the graphs of figures 5a-c.

[0166] In a second step 420, selected values of the sampled sensor signal Ssampi are stored as one or more signal vectors Vmax, Vmin, Vavgfor one or more time bins B in 1 , Bin2, Bin3, respectively. Each of the one or more signal vectors Vmax, Vmin, Vavgis here a function of one or more velocity zones vz1 , vz2, ... vzn associated with a velocity v of the exhaust gas 203, 303. Also, each of the one or more time bins Bin 1 , Bin2, Bin3 is associated with an operation time period of the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’, as explained above. Thus, for each time bin Bini, Bin2, Bin3, a set of values of the sampled sensor signal Ssampi may be selected as a signal vector Vmax, Vmin, Vavgbeing a function of one or more velocity zones vz1 , vz2, ... vzn.

[0167] According to an embodiment, values of the sampled sensor signal Ssampi being selected as the signal vector Vmax comprise maximum values of the sampled sensor signal SsamPi_max. Figure 5b illustrates a non-limiting example of such a signal vector Vmax, for which the highest / maximal sampled sensor signal Ssampi values are comprised in and arranged as a signal vector Vmax.

[0168] According to an embodiment, values of the sampled sensor signal Ssampi being selected as the signal vector Vavgcomprise average values of the sampled sensor signal SsamPi_avg. Figure 5b illustrates a non-limiting example of such a signal vector Vavg, for which the average / middle sampled sensor signal Ssampi values are comprised in and arranged as a signal vector Vavg.According to an embodiment, values of the sampled sensor signal Ssampi being selected as the signal vector Vmin comprises minimum values of the sampled sensor signal SsamPi_min. Figure 5b illustrates a non-limiting example of such a signal vector Vmin, for which the lowest / minimal sampled sensor signal Ssampi values are comprised in and arranged as a signal vector Vmin.

[0169] According to an embodiment, values of the sampled sensor signal Ssampi being selected as the signal vector Vmax comprises a predetermined fraction / portion Ssampl_max_frac of the maximum values of the sampled sensor signal. Thus, the signal vector Vmax would then be between the signal vector Vmin and the signal vector Vmax illustrated in figure 5b.

[0170] According to an embodiment, values of the sampled sensor signal Ssampi being selected as the signal vector Vavgcomprises a predetermined fraction / portion Ssampl_avg_frac of the average values of the sampled sensor signal. Thus, the signal vector Vagv would then be between the signal vector Vmin and the signal vector Vavgillustrated in figure 5b.

[0171] According to an embodiment, values of the sampled sensor signal Ssampi being selected as the signal vector Vmin comprises a predetermined fraction / portion Ssampl_min_frac of the minimum values of the sampled sensor signal.

[0172] The Selection of fractions Ssampl_max_frac, Ssampl_avg_frac, Ssampl_min_frac Of maximum, average or minimum values, respectively, provides for an accurate and robust determination of the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor, because possibly erroneous maximum and / or minimum end / tail values are neglected. This is schematically illustrated in the non-limiting example of figure 8, showing the distribution, e.g. a normal distribution of the signal value frequency for the values of the sampled sensor signal Asampi.

[0173] As shown in figure 8, most of the values, i.e. the highest signal frequency, of the sampled sensor signal Ssampi are centered around the average value.The predetermined fraction / portion Ssampi_avg_frac of the average values of the sampled sensor signal are the values in an interval around the average values 50%, for example between 33% and 67% of the maximum value.

[0174] The predetermined fraction / portion SsampL _max_frac of the maximum values of the sampled sensor signal are values excluding the maximum end / tail values, for example excluding values being 90% or more of the maximum value.

[0175] The predetermined fraction / portion Ssampi_min_frac of the minimum values of the sampled sensor signal are values excluding the minimum end / tail values, for example excluding values being 10% or less of the maximum value.

[0176] Thus, as illustrated in figure 8, these selection of fractions Ssampi_max_frac, SsamPi_avg_frac, Ssampi_min_frac of maximum, average, or minimum values exclude extreme end / tail values of the sampled sensor signal Ssampi. These extreme end / tail values of the sampled sensor signal Ssampi are prone to include errors, for example caused by electric problems of the sensor and / or measuring arrangement. The accuracy and robustness of the determination of the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor is therefore hereby improved.

[0177] The values are thus schematically illustrated in figures 5a-c as single curves / lines, although the actually sensed values of the sampled sensor signal Ssampi would also include some additional sensed values being spread around these schematically illustrated curves / lines. Extreme values, resulting from the sensor outputting minimum or maximum values, may interfere with, i.e. may affect, the selected minimal valued signal vector Vmin, or the selected maximal valued signal vector Vmax illustrated in figures 5a-c. Therefore, the minimum and maximum end / tail values of the sampled sensor signal are values excluded according to some embodiments, as explained above, to avoid such interference.

[0178] In a third step 430, one or more comparison values VA, VB associated with at least one of the one or more the signal vectors Vmax, Vmin, Vavgare determined. The one or more comparison values VA, VB are generally associated with a degradation of the nitrogen oxides NOx sensor, which causes a degradation / reduction of the values ofthe sampled sensor signal Ssampi. For example, as schematically illustrated in figures 5b-c, the comparison values VA, VB may, according to an embodiment, be velocity values determined based on the appearance of the one or more the signal vectors Vmax, Vmin, Vavg, i.e. based on a degradation / reduction in the amplitudes / values of the sampled sensor signal Ssampi. In the non-limiting examples shown in figures 5b-c, the comparison values VA, VB are situated where the degradation of the nitrogen oxides NOx sensor causes a reduction of the amplitudes / values of the sampled sensor signal Ssampi, i.e. causes an inclination change of the amplitudes / values of the sampled sensor signal Ssampi.

[0179] In a fourth step 440, the one or more determined comparison values VA, VB are compared with one or more threshold values VA_th, VB_th, respectively.

[0180] According to an embodiment, the one or more threshold values VA_th, VB_th are determined based on a relation between a maximum value SsamPi_max of the sampled sensor signal Ssampi and a minimum value Ssampi_min of the sampled sensor signal Ssampi. These threshold values VA_th, VB_th are hereby associated with the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor. Thus, the comparison of the comparison values VA, VB with the one or more threshold values VA_th, VB_th, respectively, provides a measure of the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor, which is an important measure for the controllability of the exhaust treatment system in which the nitrogen oxides NOx sensor is comprised.

[0181] In a fifth step 450, one or more of the ammonia NH3 sensitivity and the ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ are determined based on the comparison 440 of the one or more comparison values VA, VB and the one or more threshold values VA_th, VB_th, respectively.

[0182] For example, the determined ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ may be used for triggering a diagnosis indicating that the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ has a problem with the ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy, and needs to be replaced. For example, if the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is aged such that its ammonia NH3sensitivity and / or ammonia NH3 sensitivity accuracy has deteriorated to a level at which the sensor must be exchanged / serviced to provide sufficient accuracy for the exhaust treatment system control, this will be discovered by the determined ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy.

[0183] Thus, if the comparison of the one or more determined comparison values VA, VB with one or more threshold values VA_th, VB_th, respectively, reveals that that the ammonia NH3 sensitivity and / or ammonia NH3 sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ needs to be replaced, a service indication may be provided, e.g. in a driver interface.

[0184] According to various embodiments, the herein described method 400 may be perform ed / executed during idling of the engine 201, 301, during high idling of the engine 201 , 301 , during a normal operation of the engine 201 ,301 , during a set / fixed load operation of the engine 201 , 301 and / or during a set / fixed speed operation of the engine 201 , 301.

[0185] According to an embodiment, schematically illustrated in figures 5b-c, one or more points A, A’, B, B’ of at least one signal vector Vmax, Vmin, Vavgand one or more velocity values VA, VB for the exhaust gas 203 ,303 being associated with the one or more points A, A, B, B’ of at least one signal vector Vmax, Vmin, Vavg, respectively, are determined 431. Then, the one or more velocity values VA, VB are determined 432 to be the one or more comparison values VA, VB that will be used for the comparison 440 with the one or more threshold values VA_th, VB_th, respectively.

[0186] According to an embodiment, the one or more points A, A’, B, B’ of the at least one signal vector Vmax, Vmin, Vavgare determined 431a based on an inclination of the selected values of the at least one signal vector Vmax, Vmin, Vavgwith decreasing velocities v of the exhaust gas 203, 303.

[0187] Thus, as a non-limiting example illustrated in figures 5b-c, the varying inclinations / slopes of the signal vectors Vmax comprising maximum values of the sampled sensor signal SsamPi_max for the second Bin2 and third Bin3 time bins may here be analyzed. The one or more points A, B’, and therefore also the one or more associated velocity values VA, VB for the exhaust gas 203, 303, are then determinedbased on the inclination / slope analysis. As is understood by a skilled person, corresponding determinations of one or more points A, A’, B, B’, and one or more associated velocity values VA, VB may be made based on any one of the least one signal vector V max, Vmin, Vavg.

[0188] According to an embodiment, one of the one or more points B, B’ is determined 431a as a point between a first signal vector interval h and a second signal vector interval I2, where the first signal vector interval I1 and the second signal vector interval I2 have differing inclinations. Thus, as a non-limiting example illustrated in figures 5b-c, signal points B’ of the signal vectors Vmax comprising maximum values of the sampled sensor signal Ssampi_max for the second Bin2 and third Bin3 time bins, respectively, may here be determined 431a based on the differing inclinations / slopes of the first signal vector interval I1 and the second signal vector interval I2. Then, velocity values VB associated with the determined points B’ of the signal vectors Vmax is determined 432 to be comparison values VB to be used for the comparison 440 with the one or more threshold values VB_th. As is understood by a skilled person, corresponding determinations of one or more points A, A, B, B’, and one or more associated velocity values VA, VB may of course be made based on any one of the least one signal vector V max, Vmin, Vavg.

[0189] According to an embodiment, the one or more points A, A’, B, B’ of the at least one signal vector Vmax, Vmin, Vavg are determined 431b based on a decrease of the selected values of the at least one signal vector Vmax, Vmin, Vavgwith decreasing velocities v of the exhaust gas 203, 303. Thus, as a non-limiting example illustrated in figures 5b-c, the values of the signal vectors Vmax for the second Bin2 and third Bin3 time bins that are decreasing with decreasing velocities v of the exhaust gas 203, 303 may here be analyzed, and the one or more points A’, B’, and therefore also the one or more associated velocity values VA, VB for the exhaust gas 203, 303, are determined based on the analysis of the decrease of the vector values. Then, the one or more determined velocity values VA, VB are used for the comparison 440 with the one or more threshold values VA_th, VB_th, respectively.

[0190] According to an embodiment, at least one of the one or more points A, A, B, B’ is determined 431 b as a point where the selected values of the at least one signalvector Vmax, Vmin, Vavg have decreased to a predetermined fraction Sfrac of a maximum value Smax of the selected values of the at least one signal vector V max, Vmin, Vavg. Thus, as a non-limiting example illustrated in figure 5b, the point A’ of the signal vector Vmax comprising maximum values of the sampled sensor signal SsamPi_max for the second time bin Bin2 may here be determined 431 b as the point A where the selected values of the at least one signal vector Vmax have decreased to the predetermined fraction Sfrac of a maximum value Smax of the selected values in the signal vector Vmax. As another non-limiting example, the point A’ of the signal vector Vmax comprising maximum values of the sampled sensor signal SsamPi_max for the second time bin Bin2 may here be determined 431 b as the point A’ where the selected values of the at least one signal vector Vmax have decreased to the predetermined fraction Sfrac of a maximum value Smax of the selected values in the corresponding signal vector Vmax for the first time bin Bini . Then, the velocity value VA associated with the determined point A of the signal vector Vmax is determined 432 to be a comparison value VB to be used for the comparison 440 with the one or more threshold values VB_th. As is understood by a skilled person, corresponding determinations of one or more points A, A’, B, B’, and one or more associated velocity values VA, VB may of course be made based on any of the least one signal Vector Vmax, Vmin, Vavg.

[0191] According to an embodiment schematically illustrated in figures 6a-c, the one or more comparison values VA, VB are determined 430 by first normalizing 433 the one or more signal vectors Vmax, Vmin, Vavg with respect to at least one predetermined signal value to provide one or more normalized signal vector Vnormi , Vnorm2, Vnorm3 for of each of the one or more time bins B in 1 , Bin2, Bin3, respectively. The at least one predetermined signal value utilized for the normalization 433 may, according to various embodiments, be a highest value of the one or more signal vectors Vmax, Vmin, Vavg, one or more values of a signal vector Vmax, Vmin, Vavgfor the initial time bin Bini and / or at least one value of a signal vector Vmax, Vmin, Vavgfor the initial time bin Bini being associated with a highest velocity v of the exhaust gas for the initial time bin Bini.Then, one or more points A, B of one or more normalized signal vector Vnormi , Vnorm2, Vnorm3 and one or more velocity values VA, VB for the exhaust gas 203, 303 associated with the one or more points A, B, respectively, are determined 434.

[0192] The one or more velocity values VA, VB are then determined 435 to be the one or more comparison values VA, VB.

[0193] As explained above, the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ are then determined 450 based on the comparison 440 of these one or more comparison values VA, VB with one or more threshold values VA_th, VB_th, respectively.

[0194] According to an embodiment, the one or more points A, B of the one or more normalized signal vectors Vnormi, Vnorm2, Vnorms are determined based on an inclination of the normalized values of the one or more normalized signal vector Vnormi, Vnorm2, Vnorm3 with decreasing velocities v of the exhaust gas 203, 303.

[0195] Thus, as a non-limiting example illustrated in figures 6b-c, the varying inclinations / slopes of one or more of the second Vnorm2 and third Vnorm3 normalized signal vectors for the second Bin2 and third Bin3 time bins, respectively, may here be analyzed. The one or more points A, B, and therefore also the one or more associated velocity values VA, VB for the exhaust gas 203, 303, are then determined based on the inclination / slope analysis.

[0196] According to an embodiment, one B of the one or more points is determined as a point between a first signal vector interval h and a second signal vector interval I2, where the first signal vector interval I1 and the second signal vector interval I2 of the normalized signal vector Vnormi , Vnorm2, Vnorm3 have differing inclinations. Thus, as a non-limiting example illustrated in figures 6b-c, point B of one or more of the second Vnorm2 and third Vnorm3 normalized signal vectors for the second Bin2 and third Bin3 time bins, respectively, may here be determined based on the differing inclinations / slopes of the first signal vector interval I1 and the second signal vector interval I2. Then, the velocity value VB associated with the determined point B of one or more of the second Vnorm2 and third Vnorm3 normalized signal vectors for the second Bin2 and third Bin3 time bins, respectively, is determined 432 to be a comparisonvalue VB to be used for the comparison 440 with the one or more threshold values VB_th.

[0197] According to an embodiment, the one or more points A, B of the one or more normalized signal vectors Vnor i, Vnorm2, Vnorm3 are determined based on a decrease of the normalized values of the one or more normalized signal vector Vnormi , Vnorm2, Vnorm3 with decreasing velocities v of the exhaust gas 203, 303. Thus, as a nonlimiting example illustrated in figures 6b-c, the values of one or more of the second Vnorm2 and third Vnorm3 normalized signal vectors for the second Bin2 and third Bin3 time bins, respectively, may here be analyzed, and the one or more points A, B, and therefore also the one or more associated velocity values VA, VB for the exhaust gas 203, 303, are determined based on the analysis of the decrease of the normalized vector values. The hereby determined one or more velocity values VA, VB are then used for the comparison 440 with the one or more threshold values VA_th, VB_th.

[0198] According to an embodiment, at least one of the one or more points A, B is determined as a point where the one or more normalized values of the normalized signal vectors Vnormi, Vnorm2, Vnorm3 are decreased to a predetermined fraction Sfrac of a maximum value Smax of the normalized vector values. Thus, as a non-limiting example illustrated in figure 6b, point A of the second normalized signal vector Vnorm2 for the second time bin Bin2 may here be determined as the point A where values of the second normalized signal vector Vnorm2 have decreased to the predetermined fraction Sfrac of a maximum value Smax of the values in the second normalized signal vector Vnorm2. As another non-limiting example, point A of the second normalized signal vector Vnorm2 for the second time bin Bin2 may be determined as the point A where values of the second normalized signal vector Vnorm2 have decreased to the predetermined fraction Sfrac of a maximum value Smax of the values in the corresponding first normalized signal vector Vnormi for the first time bin Bini . Then, the velocity value VA associated with the determined point A of the second normalized signal vector Vnorm2 is determined 432 to be a comparison value VA to be used for the comparison 440 with the one or more threshold values VB_th. As is understood by a skilled person, corresponding determinations of one or more points A, B, and one ormore associated velocity values VA, VB may of course be made based on any of the one or more normalized signal vectors Vnor i, Vnorm2, Vnorm3.

[0199] According to an embodiment, the one or more comparison values are determined 430 by first normalizing 436 the one or more signal vectors Vmax, Vmin, Vavgwith respect to at least one predetermined signal value to provide one or more normalized signal vectors Vnormi , Vnorm2, Vnorm3 for the one or more time bins B in 1 , Bin2, Bin3, respectively. The at least one predetermined signal value utilized for the normalization 436 may, according to various embodiments, be a highest value of the one or more signal vectors Vmax, Vmin, Vavg, one or more values of a signal vector Vmax, Vmin, Vavgfor the initial time bin B in 1 and / or at least one value of a signal vector Vmax, Vmin, Vavgfor the initial time bin B in 1 being associated with a highest velocity v of the exhaust gas for the initial time bin Bin 1.

[0200] Then, an initial normalized signal vector Vnormi of an initial time bin Bini is subtracted 437 from a normalized signal vector Vnorm2, Vnorm3 of a subsequent time bin Bin2, Bin3 to provide a relative difference vector Vrei_diff. Thus, as a non-limiting example, the values of the initial normalized signal vector Vnormi shown in figure 6a may here be subtracted from the values of at least one of the second Vnorm2 and third Vnorm3 normalized signal vectors shown in figures 6b and 6c, respectively, in order to provide the relative difference vector Vrei_diff.

[0201] Then, one or more values of the relative difference vector Vrei_diff are determined 438 to be the one or more comparison values.

[0202] As explained above, the ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ are then determined 450 based on the comparison 440 of these one or more comparison values with one or more threshold values, respectively.

[0203] According to an embodiment, one or more minimal values of the relative difference vector Vrei_diff_min are here determined 438 to be one or more comparison values to be used for the comparison 440 with the one or more threshold values.According to an embodiment, one or more maximal values of the relative difference vector Vrei_diff_max are here determined 438 to be one or more comparison values to be used for the comparison 440 with the one or more threshold values.

[0204] According to an embodiment, a maximal difference Vrei_diff_sPan between one or more maximal values of the relative difference vector Vrei_diff_max and one or more minimal values of the relative difference vector Vrei_diff_min is here determined 438 to be a comparison value to be used for the comparison 440 with the one or more threshold values.

[0205] According to an embodiment, the values of the signal Ssampi are adjusted 470 in order to compensate for the varying the cross-sensitivity of the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’, i.e. the varying ammonia NHs sensitivity and / or the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’.

[0206] An initial normalized signal vector Vnormi of an initial time bin Bini is here first divided 460 by a subsequent normalized signal vector Vnorm2, Vnorms of a subsequent time bin Bin2, Bin3 to provide a relative adaptive constant vector Vrei_ad, which is a vector of adaption constants associated with the ageing of the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’. Then, the adaptive information at relevant flows / velocities, and according to some below described embodiments at relevant exhaust flows / velocities, exhaust temperatures and / or levels / concentrations of ammonia NHs, being provided by the relative adaptive constant vector Vrei_ad is utilized for adjusting 470 values of the sampled sensor signal Ssampi. For example, the sampled sensor signal Ssampi provided by the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ is corrected / adjusted by element-wise multiplication of the sampled sensor signal Ssampi with the adaptive information at relevant flows / velocities, and according to some below described embodiments at relevant exhaust flows / velocities, exhaust temperatures and / or levels / concentrations of ammonia NHs, of the relative adaptive constant vector Vrei_ad. According to an embodiment, the sampled sensor signal Ssampi is corrected / adjusted by multiplication with a value determined by interpolation of values of the relative adaptive constant vector Vrei_ad.Thus, by this correction / adjustment of for example the sampled sensor signal Ssampi on which the normalized signal vector Vnorm2 of the time bin Bin2 shown in figure 6b is based, the bending / slopes of this normalized signal vector Vnorm2 to the left of point B may be straighten out, i.e. the normalized signal vector Vnorm2 is compensated for the reduced ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ with reducing exhaust gas velocities.

[0207] According to an embodiment, an adaption vector AF is determined, which comprises scalar adaptation values determined and utilized for adjustment of the sampled sensor signal Ssampi. A normalized signal Vnorm_max_vei at a maximal exhaust flow / velocity of a time bin is here first divided by a subsequent normalized signal vector Vnorm of the same time bin to provide the adaption vector AF, which comprises the adaption values associated with the ageing of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’. Then, the adaption vector AF is utilized for adjusting values of the sampled sensor signal Ssampi for the same time bin. For example, the sampled sensor signal Ssampi provided by the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’ is corrected / adjusted by the scalar value of the adaption vector AF.

[0208] According to an embodiment, each of the one or more signal vectors V max, Vmin, Vavg is further a function of a temperature T of the exhaust gas 203, 303. Thus, each of the one or more signal vectors Vmax, Vmin, Vavgfor the one or more time bins B in 1 , Bin2, Bin3, respectively, is a function of the one or more velocity zones vz1 , vz2, ... vzn associated with the velocity v of the exhaust gas 203, 303 and is also a function of the temperature T of the exhaust gas 203, 303.

[0209] Thus, in each point in time, i.e. for each time bin, the effect of the temperature of the exhaust gas 203, 303 on the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is combined / superposed on the effect of the velocity v of the exhaust gas 203, 303 on the nitrogen oxides NOx sensor 280, 280’, 381, 382, 382’. Each of the one or more signal vectors Vmax, min, Vavg is a then a function of the combined / superimposed velocity-temperature zones z.Further, the herein described determination 430 of the one or more comparison values VA, VB is then based also on the temperature T of the exhaust gas 203, 303. Also, the herein described comparison 440 of the one or more comparison values VA, VB with one or more threshold values, respectively, is then based also on the temperature T of the exhaust gas 203, 303.

[0210] According to an embodiment, each of the one or more signal vectors V max, Vmin, Vavg is further a function of a level / concentration of ammonia NHs in the exhaust gas 203, 303. Thus, each of the one or more signal vectors Vmax, Vmin, Vavgfor the one or more time bins Bini, Bin2, Bin3, respectively, is a function of the one or more velocity zones vz1 , vz2, ... vzn associated with the velocity v of the exhaust gas 203, 303 and is also a function of the level / concentration of ammonia NHs in the exhaust gas 203, 303. Each of the one or more signal vectors Vmax, min, Vavg is a then a function of the combined / superimposed velocity-ammonia zones z. Possibly, each of the one or more signal vectors Vmax, Vmin, Vavg is a function of the temperature T of the exhaust gas 203, 303, as explained above. Each of the one or more signal vectors Vmax, min, Vavg is a then a function of the combined / superimposed velocity-ammonia-temperature zones z.

[0211] The herein described determination 430 of the one or more comparison values VA, VB is then based also on the level / concentration of ammonia NHs of the exhaust gas 203, 303, and possibly also on the temperature T of the exhaust gas 203, 303, as explained above.

[0212] Also, the herein described comparison 440 of the one or more comparison values VA, VB with one or more threshold values, respectively, is then based also on the level / concentration of ammonia NHs , and possibly also on the temperature T of the exhaust gas 203, 303, as explained above.

[0213] Figure 9 schematically illustrates some features of the herein presented embodiments of the method for determining an ammonia NHs sensitivity and / or an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor when it is performed based on all three of the velocity v of the exhaust gas 203, 303, thetemperature T of the exhaust gas 203, 303, and the level / concentration of ammonia NHs in the exhaust gas 203, 303.

[0214] As illustrated in figure 9 for one time bin, here exemplified as the time bin for 1000-2000h being chosen in accordance with the function bin choice based on the operation time t, the selected values of the sampled signal vector Ssampi have been selected as a signal vector in accordance with the function storage choices. These selected values of the signal vector may for example be maximum Vmax, minimum Vmin, average Vavg, or fractional values of the sampled signal vector Ssampi, as explained above. The selected values of the signal vector are here functions of the combined / superimposed velocity-ammonia zones z1, z2, ... zn, where the velozity zones vzn are exemplified as 0-3, 3-6, 6-9, 9-12, 9-15, and so on.

[0215] Within the illustrated time bin for 1000-2000h, three example bins for different temperature intervals are created in accordance with a function bin choice based the temperature T of the exhaust gas 203, 303. In this example, three temperature bins are created for the temperature interval of T < 300 °C, for the temperature interval of 300 °C < T < 400 °C, and for the temperature interval of 400 °C < T, respectively. For each such temperature bin, a signal vector is created as a function of the combined / superimposed velocity-ammonia zones z1, z2, ... zn, as herein described. The velocity zones, here exemplified as 0-3, 3-6, 6-9, 9-12, 9-15 m / s are

[0216] determ ined / chosen based on

[0217] Thus, the dependencies of all three of the velocity v of the exhaust gas 203, 303, the temperature T of the exhaust gas 203, 303, and the level / concentration of ammonia NHs in the exhaust gas 203, 303 are combined / superimposed to form multidimensional bins and representations of the sampled sensor signal Ssampi. These multidimensional bins and representations of the sampled sensor signal Ssampi are then used as a basis for the herein described determination 430 of the one or more comparison values VA, VB, and the herein described comparison 440 of the one or more comparison values VA, VB with one or more threshold values, respectively. Hereby, the determination of the ammonia NHs sensitivity and the ammonia NHs sensitivity accuracy for the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is based on all three of the velocity v of the exhaust gas 203, 303, the temperature T ofthe exhaust gas 203, 303, and the level / concentration of ammonia NHs in the exhaust gas 203, 303.

[0218] A skilled person understands that if one of the temperature T of the exhaust gas 203, 303 and the level / concentration of ammonia NHs in the exhaust gas 203, 303 is not taken it consideration by the method, that dimension / information is neglected in the example illustration in figure 9.

[0219] According to various embodiments, the herein described determination 430 of the one or more comparison values VA, VB is based also on modelled and / or measured values for a level of nitrogen oxides NOx in the exhaust gas 203, 303, a level / concentration of ammonia NHs in the exhaust gas 203, 303, a level of adsorbed ammonia NHs in the exhaust treatment system 250, 350 upstream of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’, and / or a reduction of nitrogen oxides NOx in the exhaust treatment system 250, 350 upstream of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’. The modelled values may here be determined based on a model of the exhaust treatment system 250, 350, or based on a model of one or more components of the exhaust treatment system 250, 350.

[0220] According to various embodiments, the herein described comparison 440 of the one or more comparison values VA, VB with one or more threshold values VA_th, VB_th, respectively, is based also on modelled and / or measured values for a level of nitrogen oxides NOx in the exhaust gas 203, 303, a level of ammonia NHs in the exhaust gas 203, 303, a level of adsorbed ammonia NHs in the exhaust treatment system 250, 350 upstream of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’, and / or a reduction of nitrogen oxides NOx in the exhaust treatment system 250, 350 upstream of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’. The modelled values may here be determined based on a model of the exhaust treatment system 250, 350, or based on a model of one or more components of the exhaust treatment system 250, 350.

[0221] According to an aspect, a control system 190, 290, 390 configured for determining one or more of an ammonia NHs sensitivity and an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ is presented. The nitrogenoxides NOx sensor 280, 280’, 381 , 382, 382’ is configured downstream of a selective catalytic reduction catalyst SCR 220, 320, 330 of an exhaust treatment system 250, 350 configured for treatment of an exhaust gas 203, 303 from an engine 201 , 301.

[0222] The control system 190, 290, 390 may be configured to execute the herein described method aspects and embodiments.

[0223] The control system 190, 290, 390 is thus configured to sample 410 a signal S of the nitrogen oxides sensor 280, 280’, 381 , 382, 382’ to provide a sampled sensor signal Ssampl.

[0224] The control system 190, 290, 390 is further configured to store 420 selected values of the sampled sensor signal Ssampi as one or more signal vectors Vmax, Vmin, Vavg fOT one or more time bins Bini, Bin2, Bin3, respectively, wherein

[0225] - each of the one or more signal vectors Vmax, Vmin, Vavgis a function of one or more velocity zones vz1 , vz2, ... vzn associated with a velocity v of the exhaust gas 203, 303; and

[0226] - each of the one or more time bins Bini , Bin2, Bin3 is associated with an operation time period of the nitrogen oxides sensor 280, 280’, 381, 382, 382’.

[0227] The control system 190, 290, 390 is also configured to determine 430 one or more comparison values VA, VB associated with at least one of the one or more the signal Vectors Vmax, Vmin, Vavg.

[0228] The control system 190, 290, 390 is further configured to compare 440 the one or more comparison values VA, VB with one or more threshold values VA_th, VB_th, respectively.

[0229] The control system 190, 290, 390 is further configured to determine 450 one or more of the ammonia NHs sensitivity and the ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ based on the comparison 440.

[0230] The hereby determined ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy of the nitrogen oxides NOx sensor 280, 280’, 381 , 382, 382’ may be used for triggering a diagnosis indicating that the nitrogen oxides NOx sensor 280, 280’,381 , 382, 382’ has a problem with the ammonia NHs sensitivity and / or ammonia NHs sensitivity accuracy, and possibly needs to be replaced.

[0231] According to an aspect, a vehicle 100 comprising a herein described control system 190, 290, 390 is presented.

[0232] The control system may be configured for executing / performing any of the embodiments for the method aspects described in this document.

[0233] A person skilled in the art will realise that a method for determining one or more of an ammonia NHs sensitivity and an ammonia NHs sensitivity accuracy of a nitrogen oxides NOx sensor according to the present invention may also be implemented in a computer program, which when executed in a computer will cause the computer to execute the method. The computer program usually forms a part of a computer program product 503, wherein the computer program product comprises a suitable digital non-volatile I permanent I persistent I durable storage medium on which the computer program is stored. Said non-volatile / permanent / persistent / durable computer readable medium consists of a suitable memory, e.g.: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash, EEPROM (Electrically Erasable PROM), a hard disk device, etc.

[0234] Figure 7 schematically shows a control device 500 / 190 / 290 / 390. The control device 500 / 190 / 290 / 390 comprises a calculation unit 501 , which may consist of essentially a suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP), ora circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC). The calculation unit 501 is connected to a memory unit 502, installed in the control device 500 / 190 / 290 / 390, providing the calculation device 501 with e.g. the stored program code and / or the stored data, which the calculation device 501 needs in order to be able to carry out calculations. The calculation unit 501 is also set up to store interim or final results of calculations in the memory unit 502.

[0235] Further, the control device 500 / 190 / 290 / 390 is equipped with devices 511 , 512, 513, 514 for receiving and sending of input and output signals, respectively. These inputand output signals may contain wave shapes, pulses, or other attributes, which may be detected as information by the devices 511, 513 for the receipt of input signals, and may be converted into signals that may be processed by the calculation unit 501. These signals are then provided to the calculation unit 501. The devices 512, 514 for sending output signals are arranged to convert the calculation result from the calculation unit 501 into output signals for transfer to other parts of the vehicle’s control system, and / or the component(s) for which the signals are intended.

[0236] Each one of the connections to the devices for receiving and sending of input and output signals may consist of one or several of a cable; a data bus, such as a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport) bus, or any other bus configuration; or of a wireless connection.

[0237] A person skilled in the art will appreciate that the above-stated computer can be constituted by the computing unit 501 and that the above- stated memory can be constituted by the memory unit 502.

[0238] Generally, control systems in modern vehicles consist of a communications bus system, consisting of one or several communications buses to connect a number of electronic control devices (ECUs), or controllers, and different components localised on the vehicle. Such a control system may comprise a large number of control devices, and the responsibility for a specific function may be distributed among more than one control device. Vehicles of the type shown, thus often comprise significantly more control devices than what is shown in Figures 1-3 and 7, which is well known to a person skilled in the art within the technology area.

[0239] As a person skilled in the art will realise, the control device 500 / 190 / 290 / 390 in figure 7 may comprise one or several of the control devices 190, 290 and 390 in figures 1-3, respectively.

[0240] The present invention, in the embodiment shown, is implemented in the control device 500 / 190 / 290 / 390. The invention may, however, also be implemented wholly or partly in one or several other control devices, already existing in the vehicle, or in a control device dedicated to the present invention.Here and in this document, control units, control entities or processing arrangements are sometimes described as being arranged for performing the methods and / or steps 410, 420, 430, 440, 450, 460, 470, 431, 431a, 431b, 432, 433, 434, 435, 436, 437, 438 according to the invention. This also includes that the units, entities or processing arrangements are designed to and / or configured to perform these method steps.

[0241] One or more control entities 610, 620, 630, 640, 650, 660, 670, 631, 631a, 631b, 632, 633, 634, 635, 636, 637, 638 may be arranged for performing the methods and / or steps. Such entities 610, 620, 630, 640, 650, 660, 670, 631, 631a, 631b, 632, 633, 634, 635, 636, 637, 638 may be arranged as separate entities, or may be logically separated but physically implemented in the same unit, or may be both logically and physically arranged together. These control entities 610, 620, 630, 640, 650, 660, 670, 631, 631a, 631b, 632, 633, 634, 635, 636, 637, 638 may for example correspond to groups of instructions, which can be in the form of programming code, that are input into, and are utilized by a processor / computing unit 501 when the entities are active and / or are utilized for performing its method steps, respectively. A person skilled in the art will also realise that the above control system 500 / 190 / 290 / 390 may be modified according to the different embodiments of the method according to the invention. In addition, the invention relates to the motor vehicle 100, for example a car, a truck or a bus, or another unit comprising at least one control system 500 / 190 / 290 / 390 according to the invention, such as for example a vessel.

[0242] The present invention is not limited to the embodiments of the invention described above, but relates to and comprises all embodiments within the scope of the enclosed independent claims.

Claims

Claims1. A method (400) for determining one or more of an ammonia (NHs) sensitivity and an ammonia (NHs) sensitivity accuracy of a nitrogen oxides (NOx) sensor (280, 280’, 381, 382, 382’) configured downstream of a selective catalytic reduction catalyst (SCR; 220, 320, 330) of an exhaust treatment system (250, 350) configured for treatment of an exhaust gas (203, 303) from an engine (201 , 301 ); the method (400) comprising:- sampling (410) a signal (S) of the nitrogen oxides (NOx) sensor (280381 , 382) to provide a sampled sensor signal (Ssampi);- storing (420) selected values of the sampled sensor signal (Ssampi) as one or more signal vectors (Vmax, Vmin, Vavg) for one or more time bins (Bini , Bin2, Bin3), respectively, wherein-- each of the one or more signal vectors (Vmax, Vmin, Vavg) is a function of one or more velocity zones (vz1 , vz2, ... vzn) associated with a velocity (v) of the exhaust gas (203, 303); and-- each of the one or more time bins (Bin 1 , Bin2, Bin3) is associated with an operation time period of the nitrogen oxides (NOx) sensor (280, 280’, 381 , 382, 382’); - determining (430) one or more comparison values (VA, VB) associated with at least one of the one or more the signal vectors (V max, Vmin, Vavg);- comparing (440) the one or more comparison values (VA, VB) with one or more threshold values (vA_th, VB_th), respectively; and- determining (450) one or more of the ammonia (NHs) sensitivity and the ammonia (NHs) sensitivity accuracy of the nitrogen oxides (NOx) sensor (280, 280’, 381 , 382, 382’) based on the comparison (440).

2. The method (400) as claimed in claim 1 , wherein the determination (430) of the one or more comparison values (VA, VB) comprises:- determining (431) one or more points (A, A, B, B’) of at least one signal vector (Vmax, Vmin, Vavg) and one or more velocity values (VA, VB) for the exhaust gas (203, 303) associated with the one or more points (A, A’, B, B’), respectively; and- determining (432) the one or more velocity values (VA, VB) to be the one or more comparison values (VA, VB).

3. The method (400) as claimed in claim 2, wherein the one or more points (A, A’, B, B’) of the at least one signal vector (Vmax, Vmin, Vavg) are determined (431a) based on an inclination of the selected values of the at least one signal vector (Vmax, Vmin, Vavg) with decreasing velocities (v) of the exhaust gas (203, 303).

4. The method (400) as claimed in claim 3, wherein at least one of the one or more points (B, B’) is determined (431a) as a point between a first signal vector interval (h) and a second signal vector interval (I2), the first signal vector interval (I1) and the second signal vector interval (I2) having differing inclinations.

5. The method (400) as claimed in claim 2, wherein the one or more points (A, A’, B, B’) of the at least one signal vector (Vmax, Vmin, Vavg) are determined (431b) based on a decrease of the selected values of the at least one signal vector (Vmax, Vmin, Vavg) with decreasing velocities (v) of the exhaust gas (203, 303).

6. The method (400) as claimed in claim 5, wherein at least one of the one or more points (A, A, B, B’) is determined (431 b) as a point where the selected values are decreased to a predetermined fraction (Sfrac) of a maximum value (Smax) of the selected values.

7. The method (400) as claimed in claim 1 , wherein the determination (430) of the one or more comparison values (VA, VB) comprises:- normalizing (433) the one or more signal vectors (Vmax, Vmin, Vavg) with respect to at least one predetermined signal value to provide a normalized signal vector (Vnor i, Vnorm2, Vnorms) for of each of the one or more time bins (B in 1 , Bin2, Bin3);- determining (434) one or more points (A, B) of at least one normalized signal vector (Vnormi, Vnorm2, Vnorm 3) and one or more velocity values (VA, VB) for the exhaust gas (203, 303) associated with the one or more points (A, B), respectively; and- determining (435) the one or more velocity values (VA, VB) to be the one or more comparison values (VA, VB).

8. The method (400) as claimed in claim 1 , wherein the determination (430) of the one or more comparison values comprises:- normalizing (436) the one or more signal vectors (Vmax, Vmin, Vavg) with respect to at least one predetermined signal value to provide a normalized signal vector (Vnormi,Vnorm2, Vnorms) for each of the one or more time bins (Bin 1 , Bin2, Bin3);- subtracting (437) an initial normalized signal vector (Vnorm-i) of an initial time bin (Bini) from a normalized signal vector (Vnorm2, Vnorms) of a subsequent time bin (Bin2, Bin3) to provide a relative difference vector (Vrei_diff);- determining (438) one or more values of the relative difference vector (Vrei_diff) to be the one or more comparison values.

9. The method (400) as claimed in claim 8, wherein the one or more comparison values are determined (438) from the relative difference vector (Vrei_diff) as one in the group of:- one or more minimal values of the relative difference vector (Vrei_diff_min);- one or more maximal values of the relative difference vector (Vrei_diff_max); and - a maximal difference (Vrei_diff_sPan) between one or more maximal values of the relative difference vector (Vrei_diff_max) and one or more minimal values of the relative difference vector (Vrei_diff_ .min).

10. The method (400) as claimed in any one of claims 8-9, further comprising- dividing (460) an initial normalized signal vector (Vnorm-i) of an initial time bin (Bin 1 ) by a subsequent normalized signal vector (Vnorm2, Vnorms) of a subsequent time bin (Bin2, Bin3) to provide a relative adaptive constant vector (Vrei_ad);- adjusting (470) values of the sampled sensor signal (Ssampi) based on the provided relative adaptive constant vector (Vrei_ad).

11. The method (400) as claimed in any one of claims 7-10, wherein the at least one predetermined signal value utilized for the normalization (433, 436) is one or more in the group of:- a highest value of the one or more signal vectors (V max, Vmin, Vavg);- one or more values of a signal vector (Vmax, Vmin, Vavg) for an initial time bin (B in 1 ); and- at least one value of a signal vector (Vmax, Vmin, Vavg) for an initial time bin (B in 1 ), the at least one value being associated with a highest velocity (v) of the exhaust gas for the initial time bin (B in 1 ).

12. The method (400) as claimed in any one of claims 1-11, wherein- each of the one or more signal vectors (Vmax, Vmin, Vavg) is further a function of a temperature (T) of the exhaust gas (203, 303);- the determination (430) of the one or more comparison values (VA, VB) is based also on the temperature (T); and- the comparison (440) of the one or more comparison values (VA, VB) with one or more threshold values, respectively, is based also on the temperature (T).

13. The method (400) as claimed in any one of claims 1-12, wherein- each of the one or more signal vectors (Vmax, Vmin, Vavg) is further a function of a concentration of ammonia (NHs) in the exhaust gas (203, 303);- the determination (430) of the one or more comparison values (VA, VB) is based also on the concentration of ammonia (NHs); and- the comparison (440) of the one or more comparison values (VA, VB) with one or more threshold values, respectively, is based also on the concentration of ammonia (NHs).

14. The method (400) as claimed in any one of claims 1-13, wherein the determination (430) of the one or more comparison values (VA, VB) and the comparison (440) of the one or more comparison values (VA, VB) with one or more threshold values (vA_th, VB_th), respectively, is based also on one or more in the group of:- a level of nitrogen oxides (NOx) in the exhaust gas (203, 303);- a level of ammonia (NHs) in the exhaust gas (203, 303);- a level of adsorbed ammonia (NHs) in the exhaust treatment system (250, 350) upstream of the nitrogen oxides (NOx) sensor (280, 280’, 381, 382, 382’); and - a reduction of nitrogen oxides (NOx) in the exhaust treatment system (250, 350) upstream of the nitrogen oxides (NOx) sensor (280, 280’, 381, 382, 382’).

15. The method (400) as claimed in any one of claims 1-14, wherein the method (400) is performed during one in the group of:- idling of the engine (201 , 301 );- high idling of the engine (201 , 301 );- a normal operation of the engine (201 , 301 );- a set load operation of the engine (201 , 301 ); and- a set speed operation of the engine (201 , 301 ).

16. The method (400) as claimed in any one of claims 1-15, wherein the selected values of the sampled sensor signal (Ssampi) comprise one or more in the group of:- maximum values of the sampled sensor signal (Ssampi_max);- average values of the sampled sensor signal (SsamPi_avg);- minimum values of the sampled sensor signal (SsamPi_min);- a predetermined fraction (Ssampi _max_frac) of maximum values of the sampled sensor signal;- a predetermined fraction (Ssampi _avg_frac) of average values of the sampled sensor signal; and- a predetermined fraction (Ssampi _min_frac) of minimum values of the sampled sensor signal.

17. The method (400) as claimed in any one of claims 1-16, wherein the one or more threshold values (vA_th, VB_th) are determined based on a relation between a maximum value (Ssampi_max) of the sampled sensor signal (Ssampi) and a minimum value (Ssampi_min) of the sampled sensor signal (Ssampi).

18. The method (400) as claimed in any one of claims 1-17, wherein the velocity zones (vz1, vz2, ... vzn) provide a resolution in a velocity domain according to one in the group of:- a resolution in an interval of 0.5 m / s to 20 m / s; and- a resolution of 3 m / s.

19. The method (400) as claimed in any one of claims 1-18, wherein the one or more time bins (Bin 1 , Bin2, Bin3) comprise:- an initial time bin (Bini); and- at least one sequential time bin (Bin2, Bin3).

20. The method (400) as claimed in any one of claims 1-19, wherein each of the one or more time bins (B in 1 , Bin2, Bin3) covers a time period in the group of: - a time period in an interval of 10 h to 1000 h- a time period in an interval of 100 h to 1000 h; and- a time period of 1000 h.

21. The method (400) as claimed in any one of claims 1 -20, wherein the nitrogen oxides (NOx) sensor (280, 280’, 381, 382, 382’) is configured upstream of an ammonia slip catalyst (ASC; 240, 340) of the exhaust treatment system (250, 350).

22. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of claims 1 -21.

23. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 -21.

24. A control system (190, 290, 390) configured for determining one or more of an ammonia (NHs) sensitivity and an ammonia (NHs) sensitivity accuracy of a nitrogen oxides (NOx) sensor (280, 280’, 381, 382, 382’) configured downstream of a selective catalytic reduction catalyst (SCR; 220, 320, 330) of an exhaust treatment system (250, 350) configured for treatment of an exhaust gas (203, 303) from an engine (201, 301);the control system (120) being configured to:- sample (410) a signal (S) of the nitrogen oxides sensor (280, 280’, 381 , 382, 382’) to provide a sampled sensor signal (Ssampi);- store (420) selected values of the sampled sensor signal (Ssampi) as one or more signal vectors (Vmax, Vmin, Vavg) for one or more time bins (Bini , Bin2, Bin3), respectively, wherein-- each of the one or more signal vectors (Vmax, Vmin, Vavg) is a function of one or more velocity zones (vz1 , vz2, ... vzn) associated with a velocity (v) of the exhaust gas (203, 303); and-- each of the one or more time bins (Bin 1 , Bin2, Bin3) is associated with an operation time period of the nitrogen oxides sensor (280, 280’, 381 , 382, 382’);- determine (430) one or more comparison values (VA, VB) associated with at leastone of the one or more the signal vectors (V max, Vmin, Vavg);- compare (440) the one or more comparison values (VA, VB) with one or more threshold values (vA_th, VB_th), respectively; and- determine (450) one or more of the ammonia (NH3) sensitivity and the ammonia (NH3) sensitivity accuracy of the nitrogen oxides (NOx) sensor (280, 280’, 381 , 382, 382’) based on the comparison (440).

25. A vehicle (100) comprising a control system (190, 290, 390) according to claim 24.

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