EMISSIONS CONTROL SYSTEM OF A COMBUSTION ENGINE EXHAUST SYSTEM

Abstract

An emissions control system includes a Selective Catalytic Reduction device adapted to reduce emissions, an injector adapted to inject a reductant into the device, a NOx sensor disposed downstream of the device, a controller, an iterative model, and a table. The controller is configured to perform short and long term control by confirming at least one short term criteria is met. Once confirmed, the controller calculates a normalized model error utilizing the model and a signal received from the sensor, and integrates the normalized model error. If the integrated normalized model error exceeds a threshold, the controller proceeds toward the long term control. If a long term criteria is met, a current long term factor and the integrated normalized model error is applied to the table to determine a new long term factor. The new long term factor is multiplied against an energization time of the injector.

Description

INTRODUCTION

The present disclosure relates to exhaust systems for internal combustion engines, and more particularly to exhaust systems using adaptive Selective Catalytic Reduction (SCR) systems for emission control.

Exhaust gas emitted from an internal combustion engine, particularly a diesel engine, is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NO_x”) as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions, typically disposed on catalyst supports or substrates, are provided in an engine exhaust system as part of an after-treatment system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.

Exhaust gas treatment systems typically include Selective Catalytic Reduction (SCR) devices. An SCR device includes a substrate having an SCR catalyst disposed thereon to reduce the amount of NO_x in the exhaust gas. The typical exhaust treatment system also includes a reductant delivery system that injects a reductant such as, for example, ammonia (NH3), urea (CO(NH2)2, and other reductants. The SCR device makes use of NH3 to reduce the NO_x. For example, when the proper amount of NH3 is supplied to the SCR device under the proper conditions, the NH3 reacts with the NO_x in the presence of the SCR catalyst to reduce the NO_x emissions. If the reduction reaction rate is too slow, or if there is excess ammonia in the exhaust, ammonia can slip from the SCR. On the other hand, if there is too little ammonia in the exhaust, NO_x conversion efficiency will be decreased.

SUMMARY

An emissions control system according to one, non-limiting, embodiment of the present disclosure treats exhaust gas of a combustion engine. The system includes a Selective Catalytic Reduction (SCR) device adapted to reduce emissions, a reductant injector adapted to inject a reductant into the SCR device, a downstream NO_x sensor disposed downstream of the SCR device, a controller, an iterative model, and a lookup table. The controller includes a processor and an electronic storage medium. The iterative model and the lookup table are stored in the electronic storage medium. The processor is configured to perform short term and long term adaptive control by confirming at least one short term enablement criteria is met. Once confirmed, the processor calculates a normalized chemical model error utilizing, in-part, the iterative model and a downstream NO_x signal received from the downstream NO_x sensor. The processor then integrates the normalized chemical model error to produce an integrated normalized chemical model error, and confirms that the integrated normalized chemical model error exceeds an error threshold. The processor may then proceed toward the long term adaptive control, and confirms at least one long term adaptation enablement criteria is met. A current long term adaptive factor and the integrated normalized chemical model error is then applied to the lookup table to determine a new long term adaptive factor. The new long term adaptive factor is multiplied against an energization time of the reductant injector.

Additionally to the foregoing embodiment, the emissions control system includes an upstream NO_x sensor disposed upstream of the reductant injector and the SCR device, wherein the processor is configured to receive an upstream NO_x signal from the upstream NO_x sensor to calculate the normalized chemical model error.

In the alternative or additionally thereto, in the foregoing embodiment, the normalized chemical model error is associated with the difference between a model-predicted NO_x level taken from the iterative model, and an actual NO_x level taken form the downstream NO_x signal.

In the alternative or additionally thereto, in the foregoing embodiment, the normalized chemical model error is normalized by magnitude.

In the alternative or additionally thereto, in the foregoing embodiment, the at least one short term enablement criteria includes at least one of a normalized error being greater than a first threshold, a NO_x gradient being less than a second threshold, a reductant-consumed being greater than a third threshold, a temperature being greater than a fourth threshold and less than a fifth threshold, a temperature gradient being less than a sixth threshold, a reductant storage level deviation being less than a seventh threshold, and a combustion mode.

In the alternative or additionally thereto, in the foregoing embodiment, the at least one long term enablement criteria includes at least one of the normalized error being greater than an eighth threshold, the NO_x gradient being less than a ninth threshold, the reductant consumed is greater than a tenth threshold, the temperature is greater than an eleventh threshold and less than a twelfth threshold, the temperature gradient is less than a thirteenth threshold, the reductant storage deviation is less than a fourteenth threshold, and the combustion mode.

In the alternative or additionally thereto, in the foregoing embodiment, the at least one short term enablement criteria is independent from the at least one long term enablement criteria.

An emissions control system for treating exhaust gas of a combustion engine according to another, non-limiting, embodiment includes a Selective Catalytic Reduction (SCR) device, a first NO_x sensor, and a controller. The controller is configured to perform short term and long term adaptive control by comparing a first NO_x measurement from the first NO_x sensor with a predicted NO_x value based at least in-part on an initial chemical model. In response to a short term enablement criteria being met, the controller calculates a normalized chemical model error, integrates the normalized chemical model error, and calculates a new long term adaptive factor if the integrated normalized chemical model error exceeds a threshold.

Additionally to the foregoing embodiment, the emissions control system includes a lookup table stored in the controller and configured to cross reference a current long term adaptive factor to the integrated normalized chemical model error to calculate the new long term adaptive factor.

In the alternative or additionally thereto, in the foregoing embodiment, the normalized chemical model error is equal to a delta between the first NO_x measurement and a predicted NO_x value based on the initial chemical model, and normalized based on magnitude.

In the alternative or additionally thereto, in the foregoing embodiment, the first NO_x sensor is located downstream from the SCR device.

In the alternative or additionally thereto, in the foregoing embodiment, the emissions control system includes a second NO_x sensor, wherein the normalized chemical model error is based on the initial chemical model, the first NO_x measurement, and an upstream NO_x measurement from the second NO_x sensor located upstream from the SCR device, and wherein the first NO_x sensor is located downstream from the SCR device.

In the alternative or additionally thereto, in the foregoing embodiment, the emissions control system includes a temperature sensor configured to send a temperature measurement to the controller, wherein the initial chemical model is generated by the controller and is at least based on the temperature measurement, the upstream NO_x measurement, and the first NO_x measurement.

In the alternative or additionally thereto, in the foregoing embodiment, the enablement criteria is a short term enablement criteria.

In the alternative or additionally thereto, in the foregoing embodiment, the short term enablement criteria includes at least one of a normalized error being greater than a first threshold, a NO_x gradient being less than a second threshold, a reductant-consumed being greater than a third threshold, a temperature being greater than a fourth threshold and less than a fifth threshold, a temperature gradient being less than a sixth threshold, a reductant storage level deviation being less than a seventh threshold, and a combustion mode.

In the alternative or additionally thereto, in the foregoing embodiment, the long term adaptive factor determination is conducted when a long term adaptation enablement criteria is met.

In the alternative or additionally thereto, in the foregoing embodiment, the long term adaptation enablement criteria is independent from the short term enablement criteria.

In the alternative or additionally thereto, in the foregoing embodiment, the long term adaptation enablement criteria includes at least one of the normalized error being greater than an eighth threshold, the NO_x gradient being less than a ninth threshold, the reductant consumed is greater than a tenth threshold, the temperature is greater than an eleventh threshold and less than a twelfth threshold, the temperature gradient is less than a thirteenth threshold, the reductant storage deviation is less than a fourteenth threshold, and the combustion mode.

In the alternative or additionally thereto, in the foregoing embodiment, the eighth threshold is greater than the first threshold.

In the alternative or additionally thereto, in the foregoing embodiment, the emission control system includes a reductant injector, wherein the new long term adaptive factor is generally multiplied by an energization time of the reductant injector.

The above features and advantages, and other features and advantages of the disclosure, are readily apparent from the following detailed description when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only, in the following detailed description, the detailed description referring to the drawings in which:

FIG. 1 is a schematic of a motor vehicle including an internal combustion engine and an exhaust system according to one or more embodiments;

FIG. 2 is a schematic of the exhaust system including an emissions control system;

FIG. 3 is a schematic of an SCR device of the emissions control;

FIG. 4 is a lookup table stored in and applied by a controller of the SCR device as part of a Long Term Adaptive (LTA) control feature; and

FIG. 5 is a flowchart of a method for adaptive SCR control and Long Term Adaptive (LTA) entry.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module refers to processing circuitry that may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory module that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

A motor vehicle, in accordance with an aspect of an exemplary embodiment, is indicated generally at 20 in FIG. 1. Motor vehicle 20 is shown in the form of a pickup truck. It is to be understood that motor vehicle 20 may take on various forms including automobiles, commercial transports, marine vehicles, and the like. Motor vehicle 20 includes a body 22 having an engine compartment 24, a passenger compartment 26, and a cargo bed 28.

An Internal Combustion Engine (ICE) system 30 of the motor vehicle 20 may include a combustion engine 32, an exhaust system 34, and a controller 36. The engine compartment 24 may generally house the combustion engine 32. Examples of combustion engines 32 may include a diesel engine, a gasoline or heptane engine, and others.

The engine 32 of the ICE system 30 may include a plurality of reciprocating pistons attached to a crankshaft, which may be operably attached to a driveline, such as a vehicle driveline, to power a vehicle (e.g., deliver tractive torque to the driveline). For example, the ICE system 30 may be any engine configuration or application, including various vehicular applications (e.g., automotive, marine, and the like), as well as various non-vehicular applications (e.g., pumps, generators, and the like). While the ICE system may be described in a vehicular context (e.g., generating torque), other non-vehicular applications are within the scope of this disclosure. Therefore, when reference is made to a vehicle, such disclosure should be interpreted as being applicable to any application of the ICE system 30.

Moreover, the ICE system 30 may generally represent any device capable of generating an exhaust gas stream generally directed and treated by the exhaust system 34. The exhaust gas may include and chemical species or mixture of chemical species; in gaseous, liquid, or solid form, that may require treatment. In one example, the exhaust gas may generally include gaseous (e.g., NO_x, O₂), carbonaceous, and/or particulate matter species. An exhaust gas stream may contain a mixture of one or more NO_x species, one or more liquid hydrocarbon species, and one more solid particulate species (e.g., ash). It should be further understood that the embodiments disclosed herein may be applicable to treatment of effluent streams not comprising carbonaceous and/or particulate matter species. Exhaust gas particulate matter generally includes carbonaceous soot, and other solid and/or liquid carbon-containing species which are germane to combustion engine exhaust gas, or form within the exhaust system 34.

With reference to FIG. 2, the exhaust system 34 of the ICE system 30 may include at least a portion of the controller 36, an exhaust gas conduit 38 (i.e., exhaust manifold and pipe), and an emissions control system 40. The exhaust gas conduit generally extends, and is in fluid communication with, the combustion engine 32 and a tail pipe 42 of the exhaust gas conduit 38 that may be located at the rear of the vehicle body 22. The emissions control system 40 is fluidically connected to the exhaust gas conduit 38, such that exhaust gas (see arrows 44) that passes through the conduit 38 is treated by the emissions control system 40 to reduce emissions before exiting to ambient through the tail pipe 42. The emissions control system 40 also facilitates the control and monitoring of the storage of one, or more, Nitrogen Oxides (NO_x), and/or treatment materials, to control the exhaust emissions produced by the combustion engine 32.

The emissions control system 40 may include an Oxidation Catalyst (OC) device 46, a Selective Catalytic Reduction (SCR) assembly 48, particulate filter devices (not shown), and other exhaust treatment devices. The SCR assembly 48 may be located downstream of the OC device 46 with respect to the exhaust conduit 38.

The OC device 46 of the emissions control system 40 may be one of various flow-through, oxidation catalyst devices known in the art. The OC device 46 may include a flow-through metal or ceramic monolith substrate 50. The substrate 50 may be packaged in a stainless steel shell or canister having an inlet and an outlet in fluid communication with the exhaust gas conduit 38. The substrate 50 may include an oxidation catalyst compound disposed thereon. The oxidation catalyst compound may be applied as a washcoat and may contain platinum group metals such as platinum (Pt), palladium (Pd), rhodium (Rh) or other suitable oxidizing catalysts, or combination thereof. The OC device 46 is useful in treating unburned gaseous and non-volatile HC and CO, that are oxidized to form carbon dioxide and water. A washcoat layer includes a compositionally distinct layer of material disposed on the surface of the monolithic substrate 50 or an underlying washcoat layer. A catalyst may contain one or more washcoat layers, and each washcoat layer may have unique chemical catalytic functions.

The SCR assembly 48 of the emissions control system 40 may be adapted to receive exhaust gas 44 treated by the OC device 46, and/or originating from the combustion engine 32, and reduce Nitrogen Oxide (NO_x) constituents in the exhaust gas 44. NO_x constituents may include N_yO_x species, wherein y>0 and x>0. Non-limiting examples of NO_x may include NO, NO₂, N₂O, N₂O₂, N₂O₃, N₂O₄, and N₂O₅. More particularly, the SCR assembly 48 may convert NO_x to diatomic nitrogen (N₂) and water.

The SCR assembly 48 may include at least a portion of the controller 36, an SCR device or canister 52, an upstream NO_x sensor 54, a downstream NO_x sensor 56, at least one temperature sensor 58, at least one pressure sensor 60, a reductant injector 62, and a reductant supply source 64. The SCR device 52 is in fluid communication with the exhaust gas conduit 44 for treatment of the exhaust gas 44. The NO_x sensor 54 may be located upstream of the SCR device 52 and downstream of the OC device 46 for measuring NO_x constituents in the exhaust gas 44 before the exhaust gas enters the SCR device 52. The NO_x sensor 56 may be located downstream of the SCR device 52 for measuring NO_x constituents in the exhaust gas 44 after the exhaust gas exits the SCR device 52. The temperature sensor 58 may be located upstream of the SCR device 52 and downstream of the reductant injector 62 for measuring exhaust gas temperature. Although the SCR device 52 is illustrated downstream from the OC device 46, it is contemplated and understood that the SCR device 52 may be located upstream from the OC device 46.

The at least one pressure sensor 60 (e.g., differential pressure sensor) may be adapted to determine the pressure differential across the SCR device 52. Although a single differential pressure sensor 60 is illustrated, it is appreciated that a plurality of pressure sensors may be used to determine the pressure differential of the SCR device 52. For example, a first pressure sensor may be disposed at an inlet of the SCR device 52 and a second pressure sensor may be disposed at an outlet of the SCR device 52. Accordingly, the difference between the pressure detected by the second pressure sensor and the pressure detected by the first pressure sensor may indicate the pressure differential across the SCR device 52. It should be noted that in other examples, the sensors may include different, additional, or fewer sensors than the sensors 54, 56, 58, 60 described.

The reductant injector 62 of the SCR assembly 48 may be generally mounted to the exhaust gas conduit 38 upstream of the SCR device 52 (i.e., between the upstream NO_x sensor 54 and the temperature sensor 58), and is configured to disperse a controlled amount of a reductant 66 into the flow of exhaust gas 44. The reductant 66 is stored and supplied to the injector 62 by the reductant supply source 64, and may be in the form of a gas, a liquid, or an aqueous solution (e.g., aqueous urea solution). The reductant 66 may be mixed with air in the injector 62 to aid in the dispersion of the injected spray. The SCR device 52 utilizes the reductant 66, such as ammonia (NH₃), to reduce the NO_x.

The SCR device 52 of the SCR assembly 48 may include a substrate 68. The substrate 68 may generally be a particulate filter (PF), such as a diesel particulate filter (DPF) coated with a SCR catalyst and adapted to filter or trap carbon and other particulate matter from the exhaust gas 44. The substrate 68 generally includes an inlet and an outlet in fluid communication with exhaust gas conduit 38. In another example, the substrate may be a flow-through monolith type of substrate that may generally be made of ceramic. Further examples of substrates 68 may include wound or packed fiber filters, open cell foams, sintered metal fibers, and others. The emissions control system 40 may also perform a regeneration process that regenerates the substrate 68 by burning-off the particulate matter trapped in the filter substrate.

A catalyst containing washcoat disposed on the substrate 68, (i.e., a flow through catalyst or a wall flow filter) may reduce NO_x constituents in the exhaust gas 44. The catalyst containing washcoat may contain a zeolite and one or more base metal components such as iron (Fe), cobalt (Co), copper (Cu), or vanadium (V), which can operate efficiently to convert NO_x constituents of the exhaust gas 44 in the presence of NH₃. In one or more examples, a turbulator (i.e., mixer, not shown) may also be disposed within the exhaust conduit 38 in close proximity to the injector 62 and/or the SCR device 52 to further assist in thorough mixing of the reductant 66 with the exhaust gas 44, and/or even distribution throughout the SCR device 52. It is understood that catalyst compositions for the SCR function, and NH₃ oxidation function, may reside in discrete washcoat layers on the substrate 68 or, alternatively, the compositions for the SCR and NH₃ oxidation functions may reside in discrete longitudinal zones on the substrate 68.

The body of the substrate 68 may, for example, be a ceramic brick, a plate structure, or any other suitable structure such as a monolithic honeycomb structure that includes several hundred to several thousand parallel flow-through cells per square inch, although other configurations are suitable. Each of the flow-through cells may be defined by a wall surface on which the SCR catalyst composition can be washcoated. The body of the substrate 68 may be formed from a material capable of withstanding the temperatures and chemical environment associated with the exhaust gas 44. Some specific examples of materials that may be used include ceramics such as extruded cordierite, α-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia, zirconium silicate, sillimanite, petalite, or a heat and corrosion resistant metal such as titanium or stainless steel. For example, the substrate 68 may comprise a non-sulfating TiO₂ material. The body of the substrate 68 may be a PF device, as will be discussed below.

The SCR catalyst composition is generally a porous and high surface area material which can operate efficiently to convert NO_x constituents in the exhaust gas 44 in the presence of the reductant 66 (e.g., ammonia). In some embodiments the zeolite may be a β-type zeolite, a Y-type zeolite, a ZM5 zeolite, or any other crystalline zeolite structure such as a Chabazite or a USY (ultra-stable Y-type) zeolite. The zeolite may comprise Chabazite or SSZ. Suitable SCR catalyst compositions may have high thermal structural stability, particularly when used in tandem with the substrate 68 as a particulate filter (PF) device or when incorporated into a SCRF device, which are regenerated via high temperature exhaust soot burning techniques.

The SCR catalyst composition may optionally further comprise one or more base metal oxides as promoters to further decrease the SO₃ formation and to extend catalyst life. The one or more base metal oxides may include WO₃, Al₂O₃, and MoO₃. In one embodiment, WO₃, Al₂O₃, and MoO₃ may be used in combination with V₂O₅.

The SCR catalyst (i.e., substrate 68) generally uses the reductant 66 to reduce NO_x species (e.g., NO and NO₂) to unregulated components. Such components include one or more of species which are not NO_x species, such as diatomic nitrogen (N₂), nitrogen-containing inert species, or species which are considered acceptable emissions. The reductant 66 may be ammonia (NH₃), such as anhydrous ammonia or aqueous ammonia, or generated from a nitrogen and hydrogen rich substance such as urea (CO(NH₂)₂). Additionally or alternatively, the reductant 66 may be any compound capable of decomposing or reacting in the presence of the exhaust gas 44 and/or heat to form ammonia. Equations (1)-(5) provide exemplary chemical reactions for NO_x reduction involving ammonia:

6NO+4NH₃→5N₂+6H₂O   (1)

4NO+4NH₃+O₂→4N₂+6H₂O   (2)

6NO₂+8NH₃→7N₂+12H₂O   (3)

2NO₂+4NH₃+O₂→3N₂+6H₂O   (4)

NO+NO₂+2NH₃→2N₂+3H₂O   (5)

It should be appreciated that Equations (1)-(5) are merely illustrative, and are not meant to confine the SCR device 52 to a particular NO_x reduction mechanism or mechanisms, nor preclude the operation of other mechanisms. The SCR device 52 may be configured to perform any one of the above NO_x reduction reactions, combinations of equations (1) through (5) NO_x reduction reactions, and other NO_x reduction reactions.

The reductant 66 may be diluted with water, where heat (e.g., from the exhaust) evaporates the water, and ammonia is supplied to the SCR device 52. Non-ammonia reductants may be used as a full or partial alternative to ammonia as desired. In embodiments where the reductant 66 includes urea, the urea reacts with the exhaust gas 44 to produce ammonia that is supplied to the SCR device 52. Reaction (6) below provides an exemplary chemical reaction of ammonia production via urea decomposition:

CO(NH₂)₂+H₂O→2NH₃+CO₂   (6)

It should be appreciated that Equation (6) is merely illustrative, and is not meant to confine the urea or other reductant 66 decomposition to a particular single mechanism, nor preclude the operation of other mechanisms.

The substrate 68 (i.e., SCR catalyst) may store the reductant 66 for interaction with the exhaust gas 44. The SCR device 52 has a reductant capacity, or an amount of reductant or reductant derivative it is capable of storing. The amount of reductant 66 stored within the SCR device 52 relative to the SCR catalyst capacity of the substrate 68 may be referred to as the SCR “reductant loading”, and may be indicated as a percent (%) loading (e.g., 90% reductant loading). During operation of SCR device 52, injected reductant 66 is stored in the SCR catalyst of the substrate 68 and consumed during reduction reactions with undesired NO_x species and must be continually replenished. Determining the precise amount of reductant 66 to inject is critical to maintaining exhaust gas emissions at acceptable levels. Insufficient levels of reductant 66 within the SCR device 52 may result in undesirable NO_x species emissions, referred as NO_x breakthrough, that may exit the exhaust outlet pipe 42. Excessive levels of reductant 66 injected into the SCR device 52 may result in undesirable amounts of reductant 66 passing through the SCR device 52 unreacted, or exiting the SCR device 52 as an undesired reaction product, also referred to as reductant slip. Reductant slip and NO_x breakthrough may also occur when the SCR catalyst of the substrate 68 is below a “light-off” temperature. SCR dosing logic may be utilized by the controller 36 to command reductant dosing.

The controller 36 may be adapted to be in electronic communication with aspects of the combustion engine 32, the reductant supply source 64, the injector 62, the sensors 54, 56, 58, 60, and other components of the ICE system 30. The controller 36 may include a processor 70 (e.g., microprocessor) and an electronic storage medium 72 that may be computer writeable and readable. In one embodiment, the controller 36 may be an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and an electronic memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

In operation, the processor 70 of the controller 36 may execute the SCR dosing logic stored in the storage medium 72, and may further receive and process NO_x signals (see arrows 74, 76 in FIG. 2) from the respective NO_x sensors 54, 56 that are indicative of NO_x levels in the exhaust gas 44 and proximate to the respective sensor location along the exhaust gas conduit 38. Similarly, the processor 70 may receive and process a temperature signal (see arrow 78) from the temperature sensor 58, and a pressure signal (see arrow 80) from the pressure sensor 60.

A reductant injection dosing rate (e.g., grams per second) may be determined by the processor 70 by applying a SCR chemical model 82 and processing a feedback signal (see arrow 84) from the reductant supply source 64 of the injector 62. Generally, the SCR chemical model 82, combined with the feedback signal 84 and the upstream NO_x signal 74, assists in generating a prediction of the amount of reductant 66 stored in the SCR device 52. The SCR chemical model 82 may further predict NO_x levels of the exhaust gas 44 discharged from the SCR device 52. Over time, the SCR chemical model 82 may be updatable by one or more process values. For example, the SCR chemical model 82 may be updatable by a short term correction factor.

Referring to FIG. 3, the exhaust gas 44 is generally illustrated flowing through the SCR device 52. The controller 36 may be configured to measure the flow rate (F) of gas volume, and concentration (C) of the gas. For example, the emissions control system 40 determines an input flow-rate (see arrow 86) of NO_x as FC_NOx,in, where F is the volume of the incoming gas 44, and C_NOx,in is the inlet concentration of NO_x in the incoming exhaust gas 44. Similarly, an input flow-rate (see arrow 88) of FC_NH3,in is the volume of the flow-rate of NH₃ (i.e., a reductant) in the incoming exhaust gas 44, C_NH3,in being the inlet concentration of NH₃. Further, compensating for the amount of adsorption (see arrow 90) and amount of desorption (see arrow 92), and the amounts reacted on the catalyst surface, the controller 36 may determine C_NH3 as the SCR concentration of NH₃, and C_NOx as SCR concentration of NO_x. Accordingly, FC_NOx is the NO_x outlet volume flow rate (see arrow 94) of NO_x through the outlet of the SCR device 52. In one or more examples, the controller 36 may determine W_NOxFC_NOx as mass flow rate of NO_x, where W_NOx is the molecular weight of NO_x. Similarly, for NH₃, the outlet volume flow rate (see arrow 96) is FC_NH3 with the mass flow rate of NH₃ being W_NH3FC_NH3.

Referring again to FIG. 2, the controller 36 controls operation of the injector 62 based in-part on the chemical model 82 and a desired reductant storage setpoint to determine an amount of reductant 66 to be injected, as described herein. The controller 36 may determine a long term factor (i.e., a long term correction coefficient) corresponding to the reductant storage based on monitoring the one or more sensors 54, 56, and may more precisely control the amount of injected reductant provided by the injector 62. For example, the controller 36 determines a reductant injector energizing time, long term, correction coefficient to further reduce or eliminate discrepancy between the chemical model 82 and actual NO_x emissions at the outlet of the SCR device 52. Alternatively, or in addition, the controller 36 determines a reductant set-point correction (i.e., a short term correction factor) to reduce or eliminate discrepancy between the chemical model 82 and actual NO_x emissions at the outlet of the SCR device 52. That is, the chemical model 82 may be updatable by the short term correction factor, and the long term factor taken from a lookup table 100 (see FIG. 4) may be applied directly to the DEF injector control (i.e., controller 36). Accordingly, the supply of reductant 66 may be utilized more efficiently. The controller 36 may control the amount of reductant supplied to the SCR device 52 to regulate the reductant storage level (i.e., amount stored by the substrate 68).

In one or more examples, the percentage of NOx that is removed from the exhaust gas 44 entering the SCR device 52 may be referred to as a conversion efficiency of the SCR device 52. The controller 36 may determine the conversion efficiency of the SCR device 52 based on the NOx_in and NOx_out signals 74, 76 generated by the respective NOx sensors 54, 56. For example, the controller 36 may determine the conversion efficiency of the SCR device 52 based on the following equation:

SCR_eff=(NOx_in−NOx_out)/NOx_in   (7)

Reductant (e.g., NH₃) slip may also be caused because of an increase in the temperature of the SCR catalyst. For example, NH₃ may desorb from the SCR catalyst of the substrate 68 when the temperature increases at times when the NH₃ storage level is near to the maximum NH₃ storage level. NH₃ slip may also occur due to an error (e.g., storage level estimation error) or faulty component (e.g., faulty injector) of the emissions control system 34.

Typically, the controller 36 estimates an NH₃ storage level of the SCR device 52 based on the chemical model 82. In one or more examples, the NH₃ storage set-point (“set-point”) is capable of being calibrated. That is, the NH₃ storage set-point may be a function of exhaust flow rate and temperature. Based on the current exhaust flow and temperature, the set-point may be defined.

The controller 36 uses the chemical model 82 to estimate the current storage level of NH₃ in the SCR device 52, and the storage level governor provides feedback to the injection controls to determine the injection rate of reductant to provide NH₃ for reactions according to the chemical model 82, and to maintain a target storage level. The set-point may indicate a target storage level for given operating conditions (e.g., a temperature of the SCR catalyst of the substrate 68). Accordingly, the set-point may indicate a storage level (S) and a temperature (T) of the SCR device 52, see FIG. 3. The set-point may he denoted as (S, T). The controller 36 controls the reductant injector 62 to manage the amount of reductant injected into the exhaust gas 44 to adjust the storage level of the SCR device 52 to the set-point. For example, the controller 36 commands the injector 62 to increase or decrease the storage level to reach the set-point when a new set-point is determined. Additionally, the controller 36 commands the reductant injector 62 to increase or decrease the storage level to maintain the set-point when the set-point has been reached.

The controller 36 may use the chemical model 82 of the SCR catalyst of the substrate 68 to predict the NO_x concentration in the exhaust gases 44 entering the SCR device 52. Further, based on the predicted NO_x concentration, the controller 36 may determine an amount of NH₃ needed to dose the exhaust gases 44 to satisfy the emissions threshold. The controller 36 may implement an adaptive semi-closed loop control strategy to maintain the performance of the SCR device 52 according to the chemical model 82, where the controller continuously learns one or more parameters associated with the chemical model 82 according to the ongoing performance of the motor vehicle 20.

In one or more examples, the predetermined value may be determined based on a specified statistic such as a standard deviation, for example 1.5 standard deviations. Further, the predetermined value may be calibrated to a modeled downstream NO_x value. The measured downstream NO_x is thus normalized against the expected error of the downstream NO_x sensor 56. The normalized error, 1.5 in this example, may then be compared to the threshold for entry into steady state slip detection logic. The predetermined value of the concentration of the NO_x that is used as the threshold for comparison, in such cases, is computed based on the earlier values of the NO_x measured by the NO_x sensor 56. In other words, in the above scenario, the 37.5 ppm is used as the threshold value because 37.5 is the 1.5 standard deviation value of earlier NO_x measurements. It should be noted that in one or more examples, the NO_x measurement and predicted value used may be a NO_x flow rate, or any other NO_x attribute (i.e., instead of the NO_x concentration).

A dosing governor (not shown) may be controlled by the controller 36, and is configured to monitor the reductant storage level (i.e., in the substrate 68 of the SCR device 52) generally predicted by the SCR chemical model 82, and compares the predicted reductant storage level to a preprogrammed, desired, reductant storage level. Deviations between the predicted reductant storage level and the desired reductant storage level may be continuously monitored, and a dosing adaptation (i.e., both the short term correction factor and the long term factor) may be triggered to increase or decrease reductant dosing in order to eliminate or reduce the deviation.

For example, the reductant dosing rate may be adapted to achieve a desired NO_x concentration or flow rate in the exhaust gas 44 downstream of the SCR device 52, or achieve a desired NO_x conversion rate. A desired conversion rate may be determined by many factors, such as the characteristics of SCR catalyst type and/or operating conditions of the ICE system 30 (e.g., engine 32 operating parameters). To achieve an optimal reductant dosing rate, the short term correction factor may be applied to the SCR chemical model 82 that generally represents the modeled NH3 storage. If the modeled and requested storage differ, then dosing is modified to achieve the desired storage. That is, the long term factor may be applied directly to the injector energizing time, and may increase or decrease dosing accordingly. The short term correction may be applied instantaneously, but the long term correction is applied only after a period of time.

Over time, inaccuracies of the SCR chemical model 82 may compound to appreciative errors between modeled SCR reductant storage level and actual storage level. Accordingly, the SCR chemical model 82 may be continuously corrected to minimize or eliminate errors. One method for correcting the SCR chemical model 82 includes comparing the modeled SCR discharge exhaust gas NO_x levels to the actual NO_x levels, measured by the downstream NO_x sensor 56, to determine a discrepancy, and subsequently correcting the SCR chemical model 82 to eliminate or reduce the discrepancy. Because the downstream NO_x sensor 56 may be cross-sensitive to the reductant 66 and the exhaust gas NO_x, it is critical to distinguish between reductant measurements and NO_x measurements as reductant slip may otherwise be confused with insufficient NO_x conversion.

A passive analysis technique may be used to distinguish between reductant measurements and NO_x measurements, is a correlation method that includes comparing the upstream NO_x concentration, measured by the upstream NO_x sensor 54, to the downstream NO_x concentration, measured by the downstream NO_x sensor 56. If the difference in concentration shows a diverging trend (i.e., an increasing difference), this may indicate an increase or decrease in reductant slip. The correlation analysis identifies when the measurements from the downstream NO_x sensor 56 is following the pattern of measurements from the upstream NO_x sensor 54 (i.e., the two sensor measurements are moving alike). The correlation is a statistical measure of the strength and direction of a linear relationship between the two NO_x sensors 54, 56.

For example, the comparison includes a correlation method which includes comparing the downstream NO_x concentration with the upstream NO_x measurements, or the predicted NO_x measurements, wherein diverging concentration directions can indicate an increase or decrease in reductant slip. For example, if the upstream NO_x concentration decreases and downstream NO_x concentration increases, reductant slip can be identified as increasing. Similarly, if the upstream NO_x concentration increases and downstream NO_x concentration decreases, reductant slip can be identified as decreasing. Thus, the divergence between the two sequences of NO_x measurements can be used to determine a dosing status of the SCR device 52.

Alternatively, or in addition, the comparison may include a frequency analysis. NO_x signals 74, 76 generated by the NO_x sensors 54, 56 may include multiple frequency components (e.g., high frequency and low frequency) due to the variation of the NO_x and reductant concentrations during the modulation/demodulation. High frequency signals generally relate only to NO_x concentration, while low frequency signals generally relate to both NO_x concentration and reductant concentration. High frequency signals for upstream NO_x and downstream NO_x are isolated and used to calculate a SCR NO_x conversion ratio, which is then applied to the isolated, low-pass, upstream NO_x measurement to determine a low frequency downstream NO_x measurement. The calculated low frequency downstream NO_x measurement is then compared to the actual isolated low frequency downstream NO_x measurement, wherein a deviation between the two values may indicate reductant slip.

A drawback of passive analysis techniques (i.e., short term techniques), such as the correlation method and frequency method described above, is the reliance on proper operation of two NO_x sensors 54, 56. For example, a faulty upstream NO_x sensor 54 may generate a NO_x signal 74 that is lower than the actual NO_x level proximate the upstream NO_x sensor causing the SCR chemical model 82 to predict higher reductant storage levels than the actual storage level. Accordingly, NO_x breakthrough would be incorrectly identified as reductant slip, and reductant dosing would be commanded such that NO_x breakthrough would be exacerbated (i.e., reductant dosing would be decreased). Further, the SCR chemical model 82 would be updated using the inaccurate upstream NO_x measurement, and the exacerbated NO_x breakthrough would endure. Additionally or alternatively, in a similar manner, a reductant slip may be incorrectly interpreted as NO_x breakthrough.

In general, the passive analysis, or short term, techniques may be used to partially predict the presence of NH3 slip and/or NOx breakthrough. However, merely applying the short term techniques will not compensate for system drift, part-to-part variations, and other factors, thus causing the wrong slip decisions to be made, leading to wrong short term storage level corrections. Wrong short term storage level corrections may lead to the wrong long term adaptation decisions. That is, if a system drift issue is present, merely applying any short term technique may cause saturation of the NH3 slip and/or NO_x breakthrough predictions. Therefore, the emissions control system 40 applies both a short term correction and a long term correction. More specifically, a long term adaptation that is only dependent on accumulated error is applied.

Referring to FIG. 4, a map or lookup table 100 may be stored in the electronic storage medium 72 of the controller 36 (see FIG. 1) for use by the processor 70 when executing a Long Term Adaptive (LTA) control as part of the SCR assembly 48 of the emissions control system 34. The table 100 may include multiple rows of integrated short term normalized error categories, or values, 102 that include both NH3 slip error rows and NO_x breakthrough error rows. That is, the normalized error relative to NH3 slip includes multiple values 102S (i.e., rows) expressed as positive values, and the normalized error relative to NO_x breakthrough includes multiple values 102B (i.e., rows). The multitude of columns in the lookup table 100 are associated with current long term adaptation factors 104. In operation, the processor 70 of the controller 36 cross references the current long term adaptation factor 104 to the integrated short term normalized error 102 to determine a new long term adaptation factor 106.

Referring to FIG. 5, a flowchart of a method 200 for adaptive SCR control and Long Term Adaptive (LTA) entry is illustrated. The method 200 may be implemented by the controller 36 and/or one or more electric circuits. The method 200 may be implemented by execution of logic that may be provided or stored in the form of computer readable and/or executable instructions in the storage medium 72 of the controller 36. At block 202, at least one short term enablement criteria is met. Examples of short term enablement criteria include: a normalized chemical model error is greater than a first threshold, a NO_x gradient is less than a second threshold, a reductant (e.g., NH3) consumed is greater than a third threshold (i.e., SCR device stability), a temperature window (i.e., a temperature being greater than a fourth threshold and less than a fifth threshold), a temperature gradient being less than less than a sixth threshold, a reductant storage level deviation being less than a seventh threshold, and a combustion mode.

The normalized chemical model error being greater than the first threshold, and as part of the short term enablement, may be generally the difference between the model predicted NO_x from SCR chemical model 82 and the actual NO_x normalized by magnitude. The NO_x gradient being less than a second threshold, and as part of the short term enablement, may be a rate of change (e.g., ppm/s) of NO_x entering the SCR device 52. A large gradient may be an indicator of a highly transient vehicle maneuver where corrections are desirable. The reductant (e.g., NH3) consumed being greater than a pre-established threshold is generally a stability criteria for the SCR device 52.

The temperature window, as part of the short term enablement, is generally indicative of a temperature being higher than a low temperature threshold and less than a high temperature threshold. The temperature window criteria may allow alignment of short term correction with the operating range where the SCR chemical model 82 is most accurate. That is, the SCR chemical model 82 may not be as accurate at very low temperatures where performance is reduced, or at very high temperatures when there is a propensity of NH3 slip.

The temperature gradient being less than the sixth threshold criteria, and as part of the short term enablement, is indicative of a rate of change of temperature at the inlet of the SCR device 52. A large gradient may be an indicator of a highly transient vehicle maneuver where exhaust correction may be undesirable.

The reductant storage level deviation being less than a seventh threshold criteria, and as part of the short term enablement, allows alignment of short term correction with the operating range where the SCR chemical model 82 is most accurate. The SCR chemical model 82 may not be as accurate when the actual reductant storage level on the SCR catalyst is much higher or lower than the setpoint (i.e., seventh threshold).

The combustion mode criteria allows blocking of short term correction on combustion mode (e.g., DPF regeneration, SCR warmup, and others). Certain combustion modes may have a higher propensity for increased temperatures, decreased storage levels, and increased NH3 slip. Under such modes, or conditions, short term corrections should be avoided.

At block 204, and if the short term enablement criteria is met, the controller may calculate the normalized chemical model error. Inputs for the normalized chemical model error include the signals 74, 76 from the respective upstream and downstream NO_x sensors 54, 56, and the SCR chemical model 82. The SCR chemical model 82 may be formed and developed from inputs associated with the temperature sensor 58, the NO_x sensors 54, 56, and the previous SCR chemical model 82 contained within the controller 36. The normalized chemical model error may equal the delta between the measured NO_x associated with the downstream NO_x signal 76 and the modeled, or predicted, downstream NO_x that is normalized based on magnitude of values.

At block 206, the normalized chemical model error, associated with short term control, is integrated. In one example, the task rate for this integration may be about fifty milliseconds. At block 208, if the integrated normalized chemical model error exceeds a threshold, the method 200 may proceed toward a long term adaptive factor determination. At block 210 and proceeding with the long term adaptive factor determination, a determination of whether long term adaptation enablement criteria is met. The long term adaptation enablement criteria(s) may be similar to the short term adaptation enablement criteria(s) except that the respective thresholds may be different. That is, the thresholds between the long term adaptation enablement criteria(s) may be independent from the short term adaptation enablement criteria(s). Generally, all thresholds may be SCR strategy and hardware dependent.

Examples of long term enablement criteria may include: the normalized error is greater than an eighth threshold, the NO_x gradient is less than a ninth threshold, the reductant (e.g., NH3) consumed is greater than a tenth threshold (i.e., SCR device stability), the temperature is greater than an eleventh threshold and less than a twelfth threshold, a temperature gradient is less than a thirteenth threshold, a reductant storage deviation is less than a setpoint (i.e., fourteenth threshold), and the combustion mode.

In one embodiment, the normalized error threshold for the long term adaptation (i.e., eighth threshold) may be substantially larger than the normalized error threshold for the short term correction (i.e., first threshold). Furthermore, the various thresholds of the long term adaptation enablement criteria may be about twice as large as the respective thresholds of the short term adaptation criteria. In other embodiments, the thresholds may be about equivalent.

At block 212, and if the long term adaptation enablement criteria is met, the integrated normalized chemical model error 102 and the current long term adaptive factor 104 are utilized as inputs for the map or lookup table 100 to determine a new (i.e., subsequent) long term adaptive factor 106. For example, if the integrated short term normalized error 102 is 0.3 (i.e., an integrated short term normalized error associated with NH3 slip) and the current long term adaptation factor is about 0.8, the new long term adaptation factor 106 would be about 0.77 (i.e., as an example portrayal). The new long term adaptation factor 106 may then be used to compensate for system drift and/or part-to-part variation. In, one example, the new long term adaptation factor 106 may generally multiply the DEF injector energizing time (i.e., the amount of time the injector remains open).

The technical solutions described herein facilitate improvements to emissions control systems used in combustion engines, such as those used in vehicles. For example, the technical solutions determine storage correction and adaptation based on integration of a smaller error than what is used to enter a steady state reductant slip detection logic, the error indicative of a difference between downstream NO_x sensor measurement and downstream NO_x model. Such improvements facilitate prevention of cycling of steady state reductant slip detection when the NO_x error is just high enough to cause a steady state reductant slip detection event, but the error is low enough to cause the system to cycle in and out of the steady state reductant slip detection without any adapts.

Further advantages and benefits include a system 40 configured to treat short term and long term adaptation independently. This independence contributes toward improved adaptation robustness, decreased false failures, and a reduction in the potential for DEF crystallization.

While the above disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from its scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiments disclosed, but will include all embodiments falling within the scope thereof.

Claims

1. An emissions control system for treating exhaust gas of a combustion engine, the emissions control system comprising:

a Selective Catalytic Reduction (SCR) device adapted to reduce emissions;

a reductant injector adapted to inject a reductant into the SCR device;

a downstream NOx sensor disposed downstream of the SCR device;

a controller including a processor and an electronic storage medium;

an iterative model stored in the electronic storage medium; and

a lookup table stored in the electronic storage medium, and wherein the processor is configured to perform short term and long term adaptive control by: confirming at least one short term enablement criteria is met; calculating a normalized chemical model error utilizing in-part the iterative model and a downstream NOx signal received from the downstream NOx sensor; integrating the normalized chemical model error to produce an integrated normalized chemical model error; confirming that the integrated normalized chemical model error exceeds an error threshold; proceeding toward the long term adaptive control; confirming at least one long term adaptation enablement criteria is met; applying a current long term adaptive factor and the integrated normalized chemical model error to the lookup table to determine a new long term adaptive factor; and multiplying the new long term adaptive factor against an energization time of the reductant injector.

2. The emissions control system set forth in claim 1, further comprising:

an upstream NOx sensor disposed upstream of the reductant injector and the SCR device, wherein the processor is configured to receive an upstream NOx signal from the upstream NOx sensor to calculate the normalized chemical model error.

3. The emissions control system set forth in claim 1, wherein the normalized chemical model error is associated with the difference between a model-predicted NOx level taken from the iterative model, and an actual NOx level taken form the downstream NOx signal.

4. The emissions control system set forth in claim 3, wherein the normalized chemical model error is normalized by magnitude.

5. The emissions control system set forth in claim 1, wherein the at least one short term enablement criteria includes at least one of a normalized error being greater than a first threshold, a NOx gradient being less than a second threshold, a reductant-consumed being greater than a third threshold, a temperature being greater than a fourth threshold and less than a fifth threshold, a temperature gradient being less than a sixth threshold, a reductant storage level deviation being less than a seventh threshold, and a combustion mode.

6. The emissions control system set forth in claim 5, wherein the at least one long term enablement criteria includes at least one of the normalized error being greater than an eighth threshold, the NOx gradient being less than a ninth threshold, the reductant consumed is greater than a tenth threshold, the temperature is greater than an eleventh threshold and less than a twelfth threshold, the temperature gradient is less than a thirteenth threshold, the reductant storage deviation is less than a fourteenth threshold, and the combustion mode.

7. The emissions control system set forth in claim 1, wherein the at least one short term enablement criteria is independent from the at least one long term enablement criteria.

8. An emissions control system for treating exhaust gas of a combustion engine, the emissions control system comprising:

a Selective Catalytic Reduction (SCR) device;

a first NOx sensor; and

a controller configured to perform short term and long term adaptive control by: comparing a first NOx measurement from the first NOx sensor with a predicted NOx value based at least in-part on an initial chemical model, and in response to a short term enablement criteria being met: calculating a normalized chemical model error; integrating the normalized chemical model error; and calculating a new long term adaptive factor if the integrated normalized chemical model error exceeds a threshold.

9. The emissions control system set forth in claim 8, further comprising:

a lookup table stored in the controller and configured to cross reference a current long term adaptive factor to the integrated normalized chemical model error to calculate the new long term adaptive factor.

10. The emissions control system set forth in claim 9, wherein the normalized chemical model error is equal to a delta between the first NOx measurement and a predicted NOx value based on the initial chemical model, and normalized based on magnitude.

11. The emissions control system set forth in claim 10, wherein the first NOx sensor is located downstream from the SCR device.

12. The emissions control system set forth in claim 8, further comprising:

a second NOx sensor, wherein the normalized chemical model error is based on the initial chemical model, the first NOx measurement, and an upstream NOx measurement from the second NOx sensor located upstream from the SCR device, and wherein the first NOx sensor is located downstream from the SCR device.

13. The emissions control system set forth in claim 12, further comprising:

a temperature sensor configured to send a temperature measurement to the controller, wherein the initial chemical model is generated by the controller and is at least based on the temperature measurement, the upstream NOx measurement, and the first NOx measurement.

14. The emission control system set forth in claim 9, wherein the enablement criteria is a short term enablement criteria.

15. The emission control system set forth in claim 14, wherein the short term enablement criteria includes at least one of a normalized error being greater than a first threshold, a NOx gradient being less than a second threshold, a reductant-consumed being greater than a third threshold, a temperature being greater than a fourth threshold and less than a fifth threshold, a temperature gradient being less than a sixth threshold, a reductant storage level deviation being less than a seventh threshold, and a combustion mode.

16. The emission control system set forth in claim 15, wherein the long term adaptive factor determination is conducted when a long term adaptation enablement criteria is met.

17. The emission control system set forth in claim 16, wherein the long term adaptation enablement criteria is independent from the short term enablement criteria.

18. The emission control system set forth in claim 16, wherein the long term adaptation enablement criteria includes at least one of the normalized error being greater than an eighth threshold, the NOx gradient being less than a ninth threshold, the reductant consumed is greater than a tenth threshold, the temperature is greater than an eleventh threshold and less than a twelfth threshold, the temperature gradient is less than a thirteenth threshold, the reductant storage deviation is less than a fourteenth threshold, and the combustion mode.

19. The emission control system set forth in claim 18, wherein the eighth threshold is greater than the first threshold.

20. The emission control system set forth in claim 8, further comprising:

a reductant injector, wherein the new long term adaptive factor is generally multiplied by an energization time of the reductant injector.