Exhaust aftertreatment method and system

Abstract

Whilst an exhaust gas aftertreatment system having a specific catalyst reduction (SCR) system is operating in a regeneration mode, the DEF dosing rate (70a) is reduced to a regeneration test dosing rate (70b). NOx level data from sensors upstream and downstream of the SCR are analysed to determine an actual reduction in NOx level achieved (72). This is compared with an expected NOx level reduction achievable at the regeneration test dosing rate (74). An actual NOx reduction rate higher than the expected NOx reduction rate is indicative that regeneration is not complete. An actual NOx reduction rate within a tolerance of the expected NOx reduction rate is indicative that regeneration is complete, and the regeneration mode can be terminated. An exhaust gas after treatment system configured to carry out the method is claimed.

Description

EXHAUST AFTERTREATMENT METHOD AND SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not applicable.FIELD

[0002] Embodiments of the present disclosure relate generally to an exhaust aftertreatment system and to a method for removing reductant deposits in an exhaust aftertreatment system.BACKGROUND

[0003] There is a rising demand for cleaner and more efficient internal combustion engines, especially diesel engines. In response to these demands, new standards continue to be proposed for reduction of exhaust emissions and in particular reduction of particulate and nitrogen oxides (NOX) emissions.

[0004] Exhaust aftertreatment systems (EATS) in engine exhaust systems have been developed to meet these standards. Known EATS include a selective catalytic reduction (SCR) system for NOXreduction. The SCR system includes a dosing module for introducing a reductant into the exhaust flow upstream of a SCR catalyst. The reductant reacts with the SCR catalyst to reduce NOXlevels in the exhaust. Commonly used reductants include anhydrous ammonia (NH3) and aqueous ammonia (NH4OH).

[0005] It is also known to use a urea (COfNHzh) solution as a reductant. The urea solution is commonly referred to as a diesel exhaust fluid (DEF) and when added to a hot exhaust gas flow, the urea vaporizes, decomposing to produce ammonia (NH3) and carbon dioxide (CO2). The NH3 reacts with the SCR catalyst to convert NOXand NH3 into nitrogen gas (N2) and water vapor (H2O). The SCR system may also include an ammonia slip catalyst (ASC) to remove excess levels of NH3 not fully utilized in the SCR process from the exhaust gases. The ASC is conveniently incorporated in a SCR unit downstream of the SCR catalyst.

[0006] In the known SCR systems, the reductant (which term includes DEF) may form a liquid film on wall surfaces within the exhaust line. If the temperature is not sufficientlyhigh and / or the flow rate of the exhaust gas low, the reductant may crystallize, causing a build-up of deposit formations in the exhaust system. This forms an obstacle to exhaust gas flow. Reductant deposits in the exhaust system can be removed by a process referred to as regeneration, in which the exhaust gas temperature is raised to melt the deposits. A method of regeneration for removing reductant deposits is disclosed in is disclosed in U.S. Patent Application Publication No. 2012 / 0216510 Al, published 30thAugust 2012 to Xu et al. Regeneration can be a relatively slow process and to comply with exhaust gas emission regulations, regeneration needs to be kept as short as possible. It is desirable therefore to be able to monitor the regeneration process to determine when the reductant deposits have been sufficiently removed that the regeneration procedure can be terminated.SUMMARY

[0007] In an aspect of the invention there is provided a computer implemented method for determining when a regeneration procedure to remove reductant deposits in an exhaust aftertreatment system for treating exhaust gases received from an internal combustion engine (ICE) is sufficiently completed for the regeneration procedure to be terminated according to claim 1. Further optional features are set out in claims dependent on claim 1.

[0008] The method may comprise terminating the regeneration mode after a predefined time limit if the criteria for terminating the regeneration mode under step iii) are met before the predefined time limit expires. The predefined time limit may be in the range to 1 to 3 hours and may be around 2 hours.

[0009] In another aspect of the invention, there is provided an exhaust aftertreatment system for treating exhaust gases received from an internal combustion engine (ICE) according to claim 11. Further optional features are set out in the claims dependent on claim 11.

[0010] The control system may be configured to terminate the regeneration mode after a predefined time limit if the criteria for terminating the regeneration mode under step iii) are met before the predefined time limit expires. The predefined time limit may be in the range to 1 to 3 hours and may be around 2 hours.

[0011] Within the scope of this application it should be understood that the various aspects, embodiments, examples and alternatives set out herein, and individual featuresthereof may be taken independently or in any possible and compatible combination. Where features are described with reference to a single aspect or embodiment, it should be understood that such features are applicable to all aspects and embodiments unless otherwise stated or where such features are incompatible.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] One or more embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0013] FIG. 1 is a schematic illustration of an agricultural vehicle in the form of a tractor comprising an exhaust aftertreatment system;

[0014] FIG. 2 illustrates schematically an embodiment of an exhaust aftertreatment system for use I the vehicle of FIG. 1;

[0015] FIG. 3 is a graph illustrating a DEF dosing rate strategy for use when determining when regeneration is satisfactorily complete; and

[0016] FIG. 4 is a graph illustrating an alternative DEF dosing rate strategy for use when determining when regeneration is satisfactorily complete.DETAILED DESCRIPTION

[0017] The invention will be described with reference to the Figures.

[0018] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the apparatus, systems and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the apparatus, systems and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0019] As used herein, the terms "comprising," "including," "containing," "characterized by," and grammatical equivalents thereof are inclusive or open-ended termsthat do not exclude additional, unrecited elements or method steps, but also include the more restrictive terms "consisting of" and "consisting essentially of" and grammatical equivalents thereof.

[0020] As used herein, the term "may" with respect to a material, structure, feature, or method act indicates that such is contemplated for use in implementation of an embodiment of the disclosure, and such term is used in preference to the more restrictive term "is" so as to avoid any implication that other, compatible materials, structures, features, and methods usable in combination therewith should or must be excluded.

[0021] As used herein, the term "configured" refers to a size, shape, material composition, and arrangement of one or more of at least one structure and at least one apparatus facilitating operation of one or more of the structure and the apparatus in a predetermined way.

[0022] As used herein, the singular forms following "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0023] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0024] As used herein, spatially relative terms, such as "beneath," "below," "lower," "bottom," "above," "upper," "top," "front," "rear," "left," "right," and the like, may be used for ease of description to describe one element's or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Unless otherwise specified, the spatially relative terms are intended to encompass different orientations of the materials in addition to the orientation depicted in the figures.

[0025] As used herein, the term "substantially" in reference to a given parameter, property, or condition means and includes to a degree that one of ordinary skill in the art would understand that the given parameter, property, or condition is met with a degree of variance, such as within acceptable manufacturing tolerances. By way of example, depending on the particular parameter, property, or condition that is substantially met, the parameter, property, or condition may be at least 90.0% met, at least 95.0% met, at least 99.0% met, or even at least 99.9% met.

[0026] As used herein, the term "about" used in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter).

[0027] FIG. 1 illustrates schematically a vehicle 10, especially in the form of an agricultural tractor. The tractor 10 comprises a chassis 12, an operator cab 14, a front axle 16 and a rear axle 18. The tractor 10 has an engine compartment 20 housing an internal combustion engine (indicated schematically at 22) which selectively provides drive to the front and / or rear axles 16, 18 through a transmission. The internal combustion engine 22 in this example is specifically a diesel engine which burns diesel fuel with atmospheric air and produces power and waste gases. The waste gases are commonly referred to as exhaust gases and are rich in particulates and nitrous oxides NO and NO2, referred to collectively as NOx. An exhaust system, indicated generally at 24 receives exhaust gases from the engine 22 and includes an exhaust aftertreatment system (indicated generally at 26 in FIG.2) operative to remove at least some NOx from the exhaust gases before they are released to atmosphere. The exhaust aftertreatment system may be enclosed by a housing 27 as illustrated in FIG. 1.

[0028] FIG. 2 illustrates schematically part of the exhaust system 24 of the tractor 10 which incorporates an example of an exhaust aftertreatment system 26 for treating exhaust gas from the combustion engine, and which is configured to operate a method of regeneration to remove reductant deposits in accordance with an aspect of the present invention.

[0029] The exhaust aftertreatment system 26 defines a gas flow path 28 through which exhaust gases from the engine 22 flow in the direction of arrow X, which indicates the direction of flow of the gases from an upstream inlet end 28a to a downstream outlet end 28b. The outlet end 28b may be fluidly coupled with an exhaust tail pipe, which in an embodiment may include a vertical stackpipe 30 through which the exhaust gases are released into the atmosphere.

[0030] The exhaust aftertreatment system 26 may include a diesel oxidation catalyst (DOC) 32 and a diesel particulate filter (DPF) 34 to reduce particulate mass and number emissions. The DPF may be a catalysed soot filter (CSF) in which the DPF has a catalytic coating, typically of precious metal.

[0031] The exhaust aftertreatment system 26 includes a selective catalytic reduction (SCR) system configured to reduce a level of nitrogen oxides (NOx) in the exhaust gas. The SCR system may be located downstream of the DOC 32 and DPF 34 where these are present.

[0032] The SCR system includes a dosing module 36 for introducing a reductant in the form of a DEF into the exhaust flow, a mixer 38 for mixing the DEF in the exhaust gas and a SCR catalyst 40 in a SCR unit 42 downstream of the mixer. The DEF is vapourised in hot exhaust gases, decomposing to produce ammonia (NH3) and carbon dioxide (CO2). The ammonia derived from this decomposition can then react with the NOx in the catalyst brick 40, to convert the NOx to nitrogen gas and water vapour.

[0033] The SCR catalyst 40 may include any suitable catalyst provided that the catalyst is capable of catalyzing the above-mentioned conversion of NOx, in the presence of the nitrogen oxides reductant, to nitrogen and water. The catalyst may, for example, include one or more base metal oxides, e.g. vanadium, molybdenum and / or tungsten oxides, supported on a support material, e.g. a porous ceramic material, such as titanium dioxide.

[0034] As is known in the art, the SCR system may also comprise an NH3 slip catalyst (ASC) 44 for oxidising NH3 to remove excess levels of NH3 not fully utilised in the SCR process (known as NH3 slip) from the exhaust gases. An ASC may be conveniently incorporated in the SCR unit 42 downstream of the SCR catalyst 40 but many other arrangements are possible. The ammonia slip catalyst is configured to minimize or prevent downstream passage, in other words "slip", of unreacted ammonia. To this end, the ammonia slip catalyst may catalyze conversion of ammonia to nitrogen and water.

[0035] In an embodiment as illustrated, the SCR catalyst 40 and the ASC 44 may be provided in a single catalyst brick which includes a monolith coated with nitrogen oxides reduction catalyst, and whose downstream portion is also coated with ammonia slip catalyst. However, in alternative embodiments the SCR unit may have two catalyst bricks a first brick coated with nitrogen oxides reduction catalyst and a second brick coated with ammonia slip catalyst. In a further embodiment, the second brick may be a monolith coated with nitrogen oxides reduction catalyst, and whose downstream portion is coated with ammonia slip catalyst.

[0036] The exhaust aftertreatment system 26 includes an electronic control system 46 with a controller, indicated schematically at 48 in FIG. 2, which may be in the form of one or more electronic control units (ECU). The, or each, ECU 48 comprises programmable processing means, for example microcontroller CPUs, and memory and is configured and programmed to control and regulate operation of the exhaust aftertreatment system depending on operating conditions in accordance with pre-defined protocols. The electroniccontrol system 46 is typically part of an engine management system and may be part of a vehicle management system controlling various other functions of the vehicle such as the transmission. The functions of the ECU 48 may be carried out by a single ECU or by number of separate ECUs interconnected as part of a network, which may be a CAN bus system (e.g., ISOBUS), for example.

[0037] The electronic control system 46 also includes sensors for monitoring various operating parameters of the exhaust aftertreatment system 26. These include an upstream NOx sensor 50 for sensing concentration levels of NOx in the exhaust gases upstream of the DOC 32 and a downstream NOx sensor 52 for sensing concentration levels of NOx in the exhaust gases downstream of the SCR unit 42. In this context, the term "upstream" used in relation to the NOx sensor 50 refers to a NOx sensor located upstream of the SCR system and the term "downstream" used in the relation to the NOx sensor 52 refers to a NOx sensor located downstream of the SCR system. Comparing the relative NOx concentration levels detected by these two sensors enables the degree of NOx reduction achieved by the SCR system to be determined.

[0038] The electronic control system may also include the following sensors:• a first temperature sensor 54 for sensing the exhaust gas temperature (EGT) upstream of the DOC 32;• a first pressure sensor 56 for sensing the exhaust back pressure upstream of the DOC 32;• a differential pressure sensor 58 for measuring the pressure difference in the exhaust gasses across the DOC 32 and DPF 34 (alternatively this may be configured to measure the pressure difference in the exhaust gasses across the DPF 34 only);• a second temperature sensor 60 for sensing the EGT downstream of the DPF 34;• a third temperature sensor 62 for sensing the EGT proximal to the inlet to the SCR unit 42; and• a fourth temperature sensor 64 for sensing the EGT downstream of the SCR unit 42.

[0039] The sensors provide inputs for use by the ECU 48 in regulating operation of the exhaust aftertreatment system in a variety of operating conditions. Control of the exhaust aftertreatment system 26 may be carried out using a combination of mathematical modelling to predict operating conditions and parameters at various locations within the system andclosed loop feedback control, both using inputs from the various sensors. Inputs from other sensors associated with the engine 22 and / or the exhaust gas system upstream of the exhaust aftertreatment system may also be utilised. These may provide data relating to engine state, speed, load and temperatures, for example, as inputs to the exhaust aftertreatment control system. It will be appreciated that the sensor system as described above is an exemplary embodiment only and that the disclosure is not limited to use with EATS having such a sensor system.

[0040] Dosing of the DEF is controlled by the ECU 48 and may be controlled using a model-based DEF dosing control strategy. DEF dosing is allowed only when the engine is running, and the DEF dosing strategy is adjusted according to the particular operating state of the engine and exhaust aftertreatment.

[0041] Usually, the exhaust aftertreatment 26 is operated in a NOx reduction mode when the engine is running, and the exhaust gases are at an appropriate temperature. In the NOx reduction mode, the ECU 48 utilizes data from the two NOx sensors 50, 52 to determine a NOx reduction dosing rate at which the DEF is introduced into the exhaust gas flow by the dosing module 36. The NOx reduction dosing rate is typically selected to achieve the required tailpipe emissions of NOx while minimizing NH3 slip and excessive use of DEF. The NOx reduction dosing rate may be selected dependent at least in part on the NOx level detected by the upstream NOx sensor 50 and its selection may also take other operating conditions of the engine and / or exhaust aftertreatment into consideration. The NOx reduction dosing rate may be set according to a pre-determined dosing map or look-up table, which may be populated using data obtained from testing. In alternative embodiments, the NOx reduction dosing rate may be determined by the one or more controllers based on predefined protocols which may be established using data obtained from testing. In an embodiment, the NOx reduction dosing rate may be determined by mathematical modelling.

[0042] The ECU 48 generates one or more control signals which is / are communicated to the dosing module 36 to cause the dosing module 36 to deliver DEF at the NOx reduction dosing rate. The ECU 48 may compare data from the upstream and downstream NOx sensors 50, 52 to determine the level of NOx reduction achieved and compare this with an expected level of NOx reduction for the selected NOx reduction dosing rate underthe present operating conditions, which may also be obtained from a look-up table or map. This provides a control feed-back and the ECU 48 may be configured to vary the NOxreduction dosing rate where the actual NOx reduction detected does not match the expected NOx reduction or where the concentration of NOx detected by the downstream NOx sensor are outside of acceptable levels. In alternative embodiments, values for predicted NOx reduction may be determined by the one or more controllers based on predefined protocols. In an embodiment, the predicted NOx reduction may be determined by mathematical modelling. In an embodiment, a predicted NOx reduction rate may be determined from the following equation:Predicted NOx reduction rate = (measured upstream NOx - predicted downstream NOx) / measured upstream NOx - Equation 1.

[0043] Periodically, the exhaust aftertreatment 26 is operated in a regeneration mode (which may alternatively be referred to as a reductant deposit removal mode) in which the temperature of the exhaust gases is raised sufficiently to melt reductant (DEF) deposits in the exhaust system. In an embodiment, the exhaust gases may be raised to a temperature in the range of 350°C to 650°C during regeneration. Exhaust gas temperatures in the range of 450°C to 550°C have been found to be particularly effective at removing reductant deposits whilst keeping the surface temperature of the exhaust system within acceptable limits. However, the required exhaust gas temperature for effective regeneration can be higher or lower than the ranges indicated above depending on vehicle and exhaust system requirements. Entry into the regeneration mode may be triggered on a periodic basis. In an embodiment, the ECU may be programmed to enter the regeneration mode after a set number of operating hours, which in an embodiment could be anywhere between 20 to 100 or more operating hours. Alternatively, entry into the regeneration mode may be trigged in response to inputs to the ECU 48 indicative of a need to remove reductant deposits to keep the effectiveness of the EAT system within acceptable limits. In embodiments, the ECU 48 may be programmed to enter a regeneration mode in response to inputs indicative that the exhaust back pressure is high (e.g., above a predetermined limit) or that the NOx conversion rate is low compared to an expected NOx conversion rate for the DEF dosing rate over a period of time, or combination of these. The frequency with which regeneration is required depends on various factors which include vehicle operation conditions, exhaust line design, and ambient conditions. Accordingly, the frequency at which reductant deposit removal is required can vary significantly.

[0044] Usually, reductant deposits are found in the region of the exhaust aftertreatment system close to the dosing module 16, including the mixer 38 and at least the upstream end of the SCR unit 42. As the DEF deposits are melted, NH3 is released from the deposits into the exhaust gas stream passing through the SCR unit 42. The NH3 released as the DEF deposits are melted adds to the level of NH3 in the exhaust gases interacting with the SCR catalyst 40 and so affects the level of NOx conversion / reduction.

[0045] According to an aspect of the invention, when the exhaust aftertreatment system 26 is operating in the regeneration mode, the electronic control system 46 carries out a method to determine when reductant deposits have been removed sufficiently that the regeneration mode can be terminated. The method uses data obtained from the upstream and downstream NOx sensors 50, 52. As part of the method, for at least some of the time whilst operating in the regeneration mode, the reductant dosing is set to a rate which is lower than the NOx reduction dosing rate that would otherwise be selected if the system were operating in a NOx reduction mode. This reduced reductant dosing rate will be referred to as a "regeneration test dosing rate". In setting the regeneration test dosing rate, the control system 46 may determine an appropriate NOx reduction dosing rate for the operating conditions and then apply a reduction to determine the regeneration test dosing rate. The reduction may be a percentage reduction, say a reduction of at least 20%, or a reduction of at least 30%, or a reduction of at least 40%, or a reduction of at least 50% or a reduction of at least 60%, or a reduction of at least 70%, or a reduction of at least 80%, or a reduction of at least 90%. In an embodiment, the regeneration test dosing rate may be a fixed value that is sufficiently low that it would always be less than an appropriate NOx reduction dosing rate. In this case, the ECU 48 may simply apply the fixed regeneration test dosing rate without determining an appropriate NOx reduction dosing rate. In an embodiment, the regeneration test dosing rate is zero. In this case, the ECU 48 may not determine an appropriate NOx reduction dosing rate but may simply stop reductant dosing. Selection of the regeneration test dosing rate may take into account the need to ensure that the NOx levels emitted from the exhaust system do not exceed permitted limits during regeneration. Thus, in some applications, a regeneration test dosing rate of zero may not be appropriate and a higher regeneration test dosing rate adopted. The electronic control system 46 generates one or more suitable control signals that are forward to the dosing module 36 to cause the dosing module to deliver reductant into the exhaust gas flow at the regeneration test dosing rate.

[0046] Whilst DEF is being introduced at the reduced, regeneration test dosing rate, the control system 46 compares NOx level data received from the upstream and downstream NOx sensors 50, 52 to determine the actual NOx reduction achieved. The control system 46 compares the actual NOx reduction achieved to an expected level of NOx reduction achievable by the SCR system at the regeneration test dosing rate of DEF under the current operating conditions of the engine and exhaust aftertreatment system. Data regarding expected NOx reduction levels may be stored in a look-up table or map accessible to the ECU 48, the data for which may be obtained by testing. In alternative embodiments, values for predicted NOx reduction may be determined by the one or more controllers based on predefined protocols, which may be established using data obtained by testing. In an embodiment, the predicted NOx reduction may be determined by mathematical modelling and may make use of equation 1 as discussed above.

[0047] If the actual level of NOx reduction achieved is higher than the expected level of NOx reduction, this is an indication that DEF deposits in the exhaust system are being melted, releasing NH3 into the exhaust gases which is contributing to the reduction of NOx in the SCR unit 42. This is an indication that regeneration is not sufficiently complete. However, if the level of NOx reduction achieved is substantially the same as that expected at the regeneration test dosing rate, this indicates that no further DEF deposits are melting and releasing additional NH3 the exhaust gases. This indicates that regeneration is complete and that the regeneration mode can be terminated.

[0048] Typically, the ECU 48 will apply a time delay after the DEF dosing rate has been reduced to the regeneration test dosing rate before determining the actual NOx reduction achieved and comparing this with the expected NOx reduction. This allows the system to reach a steady state operation at the reduced, regeneration test dosing rate. The length of the time delay required is dependent on several factors such as the SCR catalyst temperature (response time) and SCR catalyst ammonia load level at that temperature. Typically, a suitable time delay may be in the region of 20 seconds to 5 minutes. Furthermore, the ECU 48 may be configured to determine that regeneration is complete provided that the actual NOx reduction rate is within a predefined threshold amount of the expected NOx reduction rate to allow for a margin of error. For example, the ECU 48 may be configured to determine that regeneration is complete even if the actual NOx reduction rate is above the expected NOx reduction rate by no more than a predetermined amount. The predeterminedamount can be set at any suitable level but in an embodiment is in the range of 5% to 20%, or within the range of 10% to 15% of the expected NOx reduction rate. However, predetermined amounts higher or lower than the ranges specified above can be used as appropriate to any given system and the current operating conditions. In embodiments, the ECU may be programmed to stop the regeneration mode only when it determines that the actual NOx reduction has fallen to the appropriate level for a predetermined period of time. This is to ensure that the exhaust line is a clean as possible so as not to leave small deposits that can act as a "seed" for further deposit build up. A suitable period of time may be in the region of 3 to 5 minutes but could be longer or shorter than this. Accordingly, in embodiments, the system may apply criteria for determining that regeneration is complete and can be terminated which require the actual NOx reduction rate to have fallen to within a predetermined threshold amount of the expected NOx reduction rate for a given period of time.

[0049] The actual NOx reduction rate for comparison with the expected NOx reduction rate may be determined substantially continuously or periodically during the testing phase. In an embodiment, the actual NOx reduction rate is determined on a substantially continuous basis with the results averaged over a time period and the average value used for comparison with the expected NOx reduction rate. The determined actual NOx reduction rate may be averaged over a time period in the range of 10 to 30 seconds for example.

[0050] Once the ECU 48 determines that the criteria to terminate regeneration have been met (i.e., that regeneration is complete and that no, or only small amounts of DEF deposits are being melted), it is operative to stop the regeneration mode and may then operate the exhaust aftertreatment system 26 in the normal NOx reduction mode if this is appropriate for the operating conditions of the engine and / or exhaust aftertreatment. Use of the method to determine when regeneration to remove reductant deposits is substantially complete enables the regeneration mode to be kept as short as possible whilst also ensuring that the regeneration process is effective.

[0051] The control system 46 may be configured to carry out the method to determine when the regeneration mode is complete only after the exhaust aftertreatment system 26 has been operating in the regeneration mode for a period of time. The control system may select an appropriate period of time based on an estimate of the required timefor successful regeneration. Where the control system determines that the actual NOx reduction has not fallen to an appropriate level to stop regeneration, it may be configured to continue to operate the exhaust aftertreatment system in the regeneration mode and to subsequently repeat the test method as necessary until the actual NOx reduction is determined to have fallen to meet the criteria for of termination the regeneration mode and the regeneration mode is terminated.

[0052] In an embodiment, the control system 46 maintains the DEF dosing rate at the regeneration test dosing rate whilst in the regeneration mode and analyses the NOx level data from the upstream and downstream NOx sensors 50, 52 until it determines that the criteria for terminating the regeneration mode have been met. This is illustrated in FIG. 3, which is a graph illustrating the DEF dosing rate and the actual NOx reduction rate against time along the X axis. The DEF dosing rate is indicated by line 70 and a typical actual NOx reduction rate expected for the DEF dosing rate is indicated by line 72. The DEF dosing rate 70 is reduced from the NOx reduction dosing rate 70a to the regeneration test dosing rate 70b when the system enters the regeneration mode, or at least whilst the system is in the regeneration mode and is held at that level until the regeneration mode is terminated. As illustrated by line 72, the actual NOx reduction rate will typically start to decline when the DEF dosing rate is reduced. The actual NOx reduction rate is compared to the expected NOx reduction rate (indicated by line 74) as described above until it is determined to have fallen to the expected NOx reduction rate for the DEF regeneration test dosing rate. Once the system determines that the actual NOx reduction rate has fallen to the expected NOx reduction rate 74 and the criteria for terminating the regeneration mode have been met, the regeneration mode is terminated. System 26 will typically be returned to the NOx reduction mode and the DEF dosing rate is raised to the NOx reduction rate 70a. As illustrated, the system 26 may apply a time delay after the actual NOx reduction rate 72 has fallen to the expected NOx reduction rate 74 before ending the regeneration mode. As the DEF dosing rate 70 is increased, the actual NOx reduction rate 72 increases to the usual level for normal running under the NOx reduction DEF dosing rate 70a. In the example illustrated, the regeneration test dosing rate 70b is above zero to help maintain NOx reduction at a rate that keeps emission of NOx is within acceptable limits during regeneration. However, in other embodiments the regeneration test dosing rate may be lower and could be zero.

[0053] FIG. 4 illustrates an alternative strategy for modifying the DEF dosing rate whilst the system is operating in the regeneration mode. FIG. 4 is a graph showing the DEF dosing rate and the actual NOx reduction rate against time along the X axis. The DEF dosing rate is indicated by line 70' and the actual NOx reduction rate detected is indicated by line 78. When the system enters the regeneration mode, the DEF dosing rate is reduced from the NOx reduction mode 70'a to a regeneration dosing rate 70'b. This is lower than the NOx dosing rate 70'a but is not sufficiently low to be used as a regeneration test dosing rate. The DEF regeneration dosing rate 70'b is selected to maintain NOx reduction at an acceptable level during regeneration considering the levels of NH3 released into the exhaust gases as the crystalized ammonia deposits are melted during the regeneration process. Periodically, the DEF dosing rate 70' is lowered to a regeneration test dosing rate 70'c and the calculated actual NOx reduction rate 78 compared to the NOx reduction rate expected at the regeneration test DEF dosing rate which is indicated by line 74. If system 26 determines that the actual NOx reduction rate 78 has not fallen sufficiently to meet the criteria to terminate regeneration after a period of time, the DEF dosing rate 70' is raised back to the regeneration dosing rate 70'b for a period before the test method is repeated. The test method is repeated periodically until the system 26 determines that criteria to terminate regeneration have been met and the regeneration mode is terminated. Usually the system will return to the NOx reduction mode and the DEF dosing rate returned to the NOx reduction dosing rate 70'a. FIG. 4 illustrates two test cycles where the DEF dosing rate 70' is reduced to the regeneration test dosing rate 70'c but the system can go through more than two test cycles and can carry out as many test cycles as are necessary until the criteria to terminate the regeneration mode are determined to have been met. As illustrated in FIG. 4, the system 26 may apply a time delay after the actual NOx reduction rate 78 has fallen to the expected NOx reduction rate 74 at the regeneration test dosing rate 70'c before ending the regeneration mode and the raising the DEF dosing rate back to the NOx reduction dosing rate 70'a. In a further alternative, the system may not apply a regeneration DEF dosing rate 70'b but simply maintain the NOx reduction dosing rate 70'a during regeneration and periodically lower the DEF dosing rate to the regeneration test dosing rate 70'c and carry out the test method according to an aspect of the present invention to determine when regeneration is satisfactorily complete, and the regeneration mode can be terminated.

[0054] The system may be configured so that it will only operate in the regeneration mode for up to a pre-defined (maximum) period of time. For example, a time limit in the range of one to three hours may be set. In an embodiment, a time limit of two hours is set. If the criteria for terminating the regeneration mode have not been met within the time limit, the regeneration mode is stopped and the system may return to the NOx reduction mode. In this event, the system may generate an error message to indicate that regeneration has not been successful. The error message may be displayed or otherwise made known to the driver e.g., as an error message (which may be a code or icon) on a display screen. Alternatively, or additionally, an error message or signal may be sent to system remote from the vehicle. This may be a central monitoring system for the vehicle for example.

[0055] The ECU 48 may be in communication with one or more sensors and / or devices associated with the internal combustion engine 22 and may be equipped with a data carrier. The ECU 48 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the internal combustion engine 22. Note, dashed lines are used to indicate communication between the ECU 48 and the various sensors and devices, but some are omitted for clarity.

[0056] The ECU 48 may include at least one digital central processing unit (CPU) in communication with a memory system and an interface bus. The at least one CPU may be configured to execute instructions stored as a program in the memory system and to send and receive signals to and from the interface bus. The memory system may include various storage types including optical storage magnetic storage, solid state storage, and other nonvolatile memory. The interface bus may be configured to send, receive, and modulate analogue and / or digital signals to / from the various sensors and control devices such as the dosing module 36. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control of the exhaust aftertreatment system 26 and possibly also the internal combustion engine 22.

[0057] It should be appreciated that the method as described above can be carried out on any exhaust aftertreatment system 26 having a SCR system including a reductant dosing module and SCR catalyst, NOx sensors upstream and downstream of the SCR system and a suitable control system 46. This is true regardless of whether or not other components such as a DOC, DPF, or ASC are present or the particular configuration of the exhaust aftertreatment system. Similarly, it should be appreciated that apart from the requirementfor upstream and downstream NOx sensors 50, 52, the method can be applied to and by a wide variety of exhaust aftertreatment systems having different sensor configurations.

[0058] Whilst embodiments of an exhaust aftertreatment system and method in accordance with the present disclosure have been described in relation to an agricultural vehicle 10 in the form of a tractor, it should be understood that the disclosed exhaust aftertreatment system and method can be applied to a range of vehicles and machines (whether static or mobile) which use an internal combustion engine and especially a diesel engine. This includes, without limitation, tracked vehicles, combine harvesters, industrial and construction vehicles, and generators. Furthermore, whilst the invention has been described in relation to an exhaust aftertreatment configured to receive exhaust gases from a diesel engine, the principles may be applied where the exhaust aftertreatment system is used in respect of an engine which burns an alternative fuel such as hydrogen. In this case, the exhaust aftertreatment may have an oxidation catalyst (OC) upstream of and adjacent to a particulate filter (PF) which are adapted to the type of fuel burned in place of the DOC and the DPF. Typically, the OC and PF would be constructed and function in similar manner to a DOC and DPF but would be configured for use with the particular fuel. Similarly, the DEF may be referred to simply as an exhaust fluid (EF) or a reductant where the engine is not a diesel engine. The principles of the method for determining when regeneration to remove reductant deposits is complete can be adapted for use in exhaust aftertreatment systems using any type of reductant to reduce pollutants in the exhaust gases where the reductant forms deposits in the system and where regeneration to remove the reductant deposits releases catalyst into the gas stream which affect the amount of pollutant removed by the SCR catalyst.

[0059] Still other embodiments involve a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) having processor-executable instructions configured to implement one or more of the techniques presented herein.

[0060] The invention is not limited to the embodiments or examples described herein and may be modified or adapted without departing from the scope of the present invention.

[0061] All references cited herein are incorporated herein in their entireties. If there is a conflict between definitions herein and in an incorporated reference, the definition herein shall control.

Claims

CLAIMSWhat is claimed is:

1. A computer implemented method for determining when a regeneration procedure to remove reductant deposits in an exhaust aftertreatment system for treating exhaust gases received from an internal combustion engine (ICE) is sufficiently completed for the regeneration procedure to be terminated, the method for use in an exhaust aftertreatment system comprising: a. an exhaust gas flow path for exhaust gases received from an internal combustion engine (ICE) flowing in a direction from upstream to downstream; b. a specific catalyst reduction (SCR) system in the exhaust gas flow path for reducing levels of NOx in the exhaust gases, the SCR system including a dosing module for introducing a reductant into the flow of exhaust gases and a SCR catalyst downstream of the dosing module; c. an upstream NOx sensor located upstream of the dosing module and a downstream NOx sensor located downstream of the SCR catalyst; d. a control system comprising one or more controllers configured to receive NOx level data from each of the upstream and downstream NOx sensors and to analyse the NOx level data received from the upstream and downstream NOx sensors to determine a change in the NOx level in the exhaust gases between the upstream and downstream NOx sensors, the control system also configured to generate and output one or more control signals for controlling operation of the dosing module; e. the exhaust aftertreatment system being selectively operable in either one of a NOx reduction mode and a regeneration mode, wherein in the regeneration mode a regeneration procedure is undertaken to remove reductant deposits from the exhaust system; f. the control system configured to regulate the dosing module to introduce reductant into the exhaust gases at a NOx reduction dosing rate when the exhaust aftertreatment system is operating in the NOx reduction mode based on the NOx level detected by the upstream NOx sensor;g. the method comprising, with the exhaust aftertreatment system operating in the regeneration mode: i. the control system regulating the dosing module to introduce reductant into the exhaust gases at regeneration test dosing rate lower than a NOx reduction dosing rate appropriate to the NOx level detected at the upstream NOx sensor; ii. whilst the reductant is being introduced at the regeneration test dosing rate, the control system analysing NOx level data received from the upstream and downstream NOx sensors to determine an actual reduction in NOx level between the upstream and downstream NOx sensors; iii. the control system comparing the determined actual NOx reduction with a predicted NOx reduction at the reduced regeneration test dosing rate; and either:

1. if the actual NOx reduction is higher than the predicted NOx reduction by at least a threshold amount, continuing to operate the exhaust aftertreatment in the regeneration mode; or2. if the actual NOx reduction is not higher than the predicted NOx level reduction by the at least a threshold amount, terminating the regeneration mode.

2. A method according to claim 1, wherein, following a determination that the actual NOx reduction is higher than the predicted NOx reduction by at least the threshold amount, periodically repeating the method until a determined actual NOx reduction is no longer higher than a predicted NOx reduction by the at least a threshold amount and terminating the regeneration mode.

3. A method according to claim 2, wherein following a determination that the actual NOx reduction is higherthan the predicted NOx reduction by at least the threshold amount, the method comprises maintaining the reductant dosing rate at the regeneration test dosing rate and periodically repeating steps ii) and iii) until a determined actual NOx reduction is not higher than a predicted NOx reduction by the at least a threshold amount and the regeneration mode is terminated.

4. A method according to claim 2, wherein the method comprises reducing the DEF dosing rate to a regeneration dosing rate lower than the NOx reduction dosing rate but higher than the regeneration test dosing rate when the exhaust aftertreatment system is operating in the regeneration mode and periodically carrying out steps i) to iii) until a determined actual NOx reduction is not higher than a predicted NOx reduction by the at least a threshold amount and the regeneration mode is terminated, wherein following each determination that the actual NOx reduction is higher than the predicted NOx reduction by at least the threshold amount in step iii), the DEF dosing rate is raised back to the regeneration dosing rate to continue to operate the exhaust aftertreatment in the regeneration mode.

5. A method according to claim 2, wherein, following a determination that the actual NOx reduction is higher than the predicted NOx reduction by at least the threshold amount, the method comprises increasing the reductant dosing rate to the NOx reduction dosing rate for a period of time before repeating steps i) to iii) until a determined actual NOx reduction is not higher than a predicted NOx reduction by the at least a threshold amount and the regeneration mode is terminated.

6. A method according to any one of claims 1 to 5, wherein the control system is configured to apply a time delay after the reductant dosing rate is set to the regeneration test dosing rate before determining an actual NOx level reduction in step ii).

7. A method according to any one of claims 1 to 6, wherein the step of comparing a determined actual NOx reduction with a predicted NOx reduction for the regeneration test dosing rate comprises comparing the determined actual NOx reduction with values for the predicted NOx reduction stored in a lookup-table or map accessible to the one or more controllers or with values for predicted NOx reduction calculated by the one or more controllers based on predefined protocols.

8. A method according to any one of claims 1 to 6, wherein the method is initiated only after the exhaust aftertreatment system has been operating in the regeneration mode for a pre-determined amount of time.

9. A method according to any one of claims 1 to 8, wherein the reductant is a diesel exhaust fluid which may be ammonia, urea, or an aqueous urea solution.

10. A method according to any one of claims 1 to 9, wherein the regeneration test dosing rate is at least 20%, or at least 30%, or at least 40%, or at least 50% or at least 60%, or at least 70%, or at least 80%, or at least 90%, lower than the NOx reduction dosing rate, or wherein the regeneration test dosing rate is zero.

11. An exhaust aftertreatment system for treating exhaust gases received from an internal combustion engine (ICE) comprising: a. an exhaust gas flow path for exhaust gases received from an internal combustion engine (ICE) flowing in a direction from upstream to downstream; b. a specific catalyst reduction (SCR) system in the exhaust gas flow path for reducing levels of NOx in the exhaust gases, the SCR system including a dosing module for introducing a reductant into the flow of exhaust gases and a SCR catalyst downstream of the dosing module; c. an upstream NOx sensor located upstream of the dosing module and a downstream NOx sensor located downstream of the SCR catalyst; d. a control system comprising one or more controllers configured to receive NOx level data from each of the upstream and downstream NOx sensors and to analyse the NOx level data received the upstream and downstream NOx sensors to determine a change in the sensed NOx level in the exhaust gases between the upstream and downstream NOx sensors, the control system also configured to generate and output one or more control signals for controlling operation of the dosing module; e. the exhaust aftertreatment system being selectively operable in either one of a NOx reduction mode and a regeneration mode, wherein in the regeneration mode a regeneration procedure is undertaken to remove reductant deposits from the exhaust system; f. the control system being configured to regulate the dosing module to introduce reductant into the exhaust gases at a NOx reduction dosing rate when the exhaust aftertreatment system is operating in the NOx reduction mode based on the NOx level detected by the upstream NOx sensor; g. wherein the control system is configured to determine when a regeneration procedure to remove reductant deposits is sufficiently completed for theregeneration procedure to be terminated when the SCR system is operating in the regeneration mode by: i. regulating the dosing module to introduce reductant into the exhaust gases at regeneration test dosing rate lower than a NOx reduction dosing rate appropriate to the NOx level detected at the upstream NOx sensor; ii. receiving and analysing NOx level data from the upstream and downstream NOx sensors to determine an actual reduction in NOx between the upstream and downstream NOx sensors at the regeneration test reductant dosing rate; iii. compare the determined actual NOx reduction with a predicted NOx reduction for the reduced regeneration test dosing rate; and either:

1. if the actual NOx reduction is higher than the predicted NOx reduction by at least a threshold amount, continuing to operate the exhaust aftertreatment in the regeneration mode; or2. if the actual NOx reduction is not higher than the predicted NOx reduction by the at least a threshold amount, terminating the regeneration mode.

12. An exhaust aftertreatment system according to claim 11, wherein, following a determination that the actual NOx reduction is higher than the predicted NOx reduction by at least the threshold amount, the control system is configured to periodically compare a determined actual NOx reduction achieved at the regeneration test dosing rate of the reductant with a predicted NOx reduction for the reduced regeneration test dosing rate until a determined actual NOx reduction is not higher than a predicted NOx reduction by the at least a threshold amount and the regeneration mode terminated.

13. An exhaust aftertreatment system according 12, wherein, following a determination that the actual NOx reduction is higher than the predicted NOx reduction by at least the threshold amount, the control system is configured to maintain the reductant dosing rate at the regeneration test dosing rate and to periodically compare a determined actual NOx reduction achieved at the regeneration test dosing rate of the reductant with a predicted NOx reduction for the reduced regeneration test dosingrate until a determined actual NOx reduction is not higher than a predicted reduction NOx by the at least a threshold amount and the regeneration mode is terminated.

14. An exhaust aftertreatment system according to claim 12, wherein, the control system is configured to reduce the DEF dosing rate to a regeneration dosing rate lower than the NOx reduction dosing rate but higher than the regeneration test dosing when the exhaust aftertreatment system is operating in the regeneration mode and to periodically carry out steps i) to iii), the control system configured to raise the DEF dosing rate back to the regeneration dosing rate following each determination that the actual NOx reduction is higher than the predicted NOx reduction by at least the threshold amount in step iii).

15. An exhaust aftertreatment system according to claim 12, wherein, following a determination that the actual NOx reduction is higher than the predicted NOx reduction by at least the threshold amount, the control system is configured to increase the reductant dosing rate to the NOx reduction dosing rate for a period of time before subsequently reducing the reductant dosing rate to the regeneration test dosing rate and again comparing a determined actual NOx reduction achieved at the regeneration test dosing rate with a predicted NOx reduction for the reduced regeneration test dosing rate, the control system configured to periodically cycle though this procedure until a determined actual NOx reduction at the regeneration test dosing rate is not higher than a predicted NOx reduction by the at least a threshold amount and the regeneration mode terminated16. An exhaust aftertreatment system according any one of claims 11 to 15, wherein the control system is configured to apply a time delay after the reductant dosing rate is set to the regeneration test dosing rate before determining an actual NOx level reduction for the regeneration test dosing rate.

17. An exhaust aftertreatment system according any one of claims 11 to 16, wherein the step of comparing a determined actual NOx level reduction with a predicted NOx level reduction for the reduced regeneration test dosing rate comprises comparing the determined actual NOx level reduction with values for the predicted NOx reduction stored in a lookup-table or map accessible to the one or more controllers or withvalues for predicted NOx reduction calculated by the one or more controllers based on predefined protocols.

18. An exhaust aftertreatment system according any one of claims 11 to 17, wherein the control system is configured to determine when a regeneration procedure to remove reductant deposits is sufficiently completed for the regeneration procedure to be terminated only after the exhaust aftertreatment system has been operating in the regeneration mode for a pre-determined amount of time.

19. An exhaust aftertreatment system according any one of claims 11 to 18, wherein the reductant is a diesel exhaust fluid which may be ammonia or urea and maybe an aqueous urea solution.

20. An exhaust aftertreatment system according any one of claims 11 to 19, wherein the regeneration test dosing rate is at least 20%, or at least 30%, or at least 40%, or at least 50% or at least 60%, or at least 70%, or at least 80%, or at least 90%, lower than the NOx reduction dosing rate or, wherein the regeneration test dosing rate is zero.

Images