WO2018071030A1

WO2018071030A1 - Systems and methods for model based catalyst diagnostics

Info

Publication number: WO2018071030A1
Application number: PCT/US2016/056880
Authority: WO
Inventors: Avra Brahma; Pardis KHAYYER; Pingen CHEN
Original assignee: Cummins Inc.
Priority date: 2016-10-13
Filing date: 2016-10-13
Publication date: 2018-04-19

Abstract

An apparatus includes a constituent storage model circuit, a detection circuit, and a notification circuit. The constituent storage model circuit is structured to determine a model state value based at least in part on a constituent flux value across a catalyst in an exhaust system. The detection circuit is communicably coupled to the constituent storage model circuit, and structured to compare the model state value to a model value threshold. The notification circuit is communicably coupled to the detection circuit, and structured to selectively provide a notification in response to the comparison of the model state value and the model value threshold.

Description

SYSTEMS AND METHODS FOR MODEL BASED CATALYST DIAGNOSTICS

TECHNICAL FIELD

[0001] The present disclosure relates to exhaust aftertreatment systems. More particularly, the present disclosure relates to operating an aftertreatment diagnostic system.

BACKGROUND

[0002] Emission regulations for internal combustion engines have become more stringent over recent years. Environmental concerns have motivated the implementation of stricter emission requirements for internal combustion engines throughout much of the world. Governmental agencies, such as the Environmental Protection Agency (EPA) in the United States, carefully monitor the emission quality of engines and set acceptable emission standards, to which all engines must comply. For example, the California Air Resources Board (CARB) requires engine systems to diagnose any sensors used in emissions control systems for errors that may affect emission levels.

[0003] Three-Way catalysts are a key component of emissions control systems in

Stoichiometric Spark-Ignited engines, such as those fueled by gasoline, ethanol, and natural gas. CARB requires engine systems to monitor the three-way catalyst(s) for any malfunctions that might lead to system emissions exceeding a pre-defined threshold.

SUMMARY

[0004] One embodiment relates to an apparatus that includes a constituent storage model circuit, a detection circuit, and a notification circuit. The constituent storage model circuit is structured to determine a model state value based at least in part on a constituent flux value across a catalyst in an exhaust system. The detection circuit is communicably coupled to the constituent storage model circuit and structured to compare the model state value to a model value threshold. The notification circuit is communicably coupled to the detection circuit and structured to selectively provide a notification in response to the comparison of the model state value and the model value threshold. [0005] Another embodiment relates to a system that includes an exhaust gas treatment system including a catalyst and a controller in communication with the exhaust gas treatment system. The controller is structured to determine a model state value of a constituent storage model based at least in part on a constituent flux across the catalyst and an exhaust gas characteristic, compare the model state value to a model value threshold, and trigger an action in response to the comparison of the model state value and the model value threshold.

[0006] Another embodiment relates to a method. The method includes receiving, by a controller in an exhaust gas system, operation data regarding the exhaust gas system, and determining, by the controller, a model state value based on the operation data. The model state value is indicative of a constituent flux across a catalyst in the exhaust gas system. The method also includes comparing, by the controller, the model state value to a model value threshold, and triggering, by the controller, an action based on the comparison of the model state value to the model value threshold.

[0007] These and other features, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0008] FIG. 1 is schematic diagram of an exhaust aftertreatment system with a controller, according to an example embodiment.

[0009] FIG. 2 is a schematic of the controller used with the exhaust aftertreatment system of FIG. 1, according to an example embodiment.

[0010] FIG. 3 is a schematic of a catalyst used in the exhaust aftertreatment system of FIG. 1, according to an example embodiment.

[0011] FIG. 4 is a schematic of a diagnostic system of the controller, according to an example embodiment.

[0012] FIG. 5 is a flow chart of a first diagnostic method, according to an example

embodiment. [0013] FIG. 6 is a flow chart of a second diagnostic method, according to an example embodiment.

[0014] FIG. 7 is a graph of air-to-fuel ratios over time, according to an example embodiment.

[0015] FIG. 8 is a flow chart of a third diagnostic method, according to an example embodiment.

DETAILED DESCRIPTION

[0016] Following below are more detailed descriptions of various concepts related to, and implementations of, methods, apparatuses, and systems for model based catalyst diagnostics. The various concepts introduced above and discussed in greater detail below may be implemented in any number of ways, as the concepts described are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

[0017] Referring the Figures generally, the various embodiments disclosed herein relate to systems, apparatuses, and methods for operating an engine system and monitoring or diagnosing a catalyst of an exhaust aftertreatment system (e.g., a three-way catalyst). The engine system includes an internal combustion engine that in one embodiment is a spark- ignition engine. In other embodiments, another engine type making use of stoichiometric combustion may be used. For example, a compression-ignition engine (e.g., a diesel engine) may be arranged to operate using an exhaust aftertreatment system as described herein. The engine system also includes an engine exhaust pipe that provides engine exhaust gases to a catalyst. A catalyst exhaust pipe is connected to the catalyst and provides treated exhaust gas to a muffler or another component of the exhaust aftertreatment system. An engine control system includes a controller, a first exhaust gas oxygen sensor (EGO) arranged to sense a condition of the engine exhaust gas, and a second EGO arranged to sense a condition of the treated exhaust gas. This sensor may be located after the Three-way catalyst or at any location upstream such that there is a volume of the catalyst between it and the first Oxygen sensor. The Oxygen sensors may be heated or unheated, or of the switching or wide-band types. [0018] The engine control system monitors the catalyst to confirm that the catalyst is functioning according to a threshold or standard (e.g., such as those set by a government organization, such as the EPA or CARB). In other words, the engine control system monitors the catalyst to confirm that the criteria pollutant emissions in the treated exhaust gas are below a predefined emissions threshold. The engine control system uses a model of how the catalyst should react and/or treat the engine exhaust gas to generate a model state indicative of a predicted nominal performance. The model state is then compared to actual results detected by the EGO sensors. The comparison can be used to determine the level to which the catalyst is stored or depleted of oxygen compared to the model or a maximum capacity, thereby providing an indication of the functionality of the catalyst. Based on the comparison, the engine control system may take an action, such as providing a notification or indication that the catalyst is failing, has failed, or needs to be replaced and/or serviced.

[0019] As shown in FIG. 1, an engine system 20 includes an engine 24, an engine exhaust pipe 28 that receives engine exhaust gases from the engine 24, a catalytic converter 32 including a catalyst 36 that receives the engine exhaust gas from the engine exhaust pipe 28 and treats the engine exhaust gases, a catalyst exhaust pipe 40 that receives the treated exhaust gases from the catalytic converter 32, and a downstream component 44 such as a muffler or another aftertreatment component. The engine system 20 also includes an engine control system 48 that includes a controller 52, a first exhaust gas oxygen sensor (EGO) 56 that communicates with the controller 52 and is positioned to detect a characteristic of the engine exhaust gas, and a second EGO 60 that communicates with the controller 52 and is positioned to detect a characteristic of the treated exhaust gas. In one embodiment, the catalytic converter 32 is part of a larger exhaust aftertreatment system that may include the controller 52 and the sensors 56, 60 as well as other components.

[0020] The engine 24 can be an internal combustion engine such as a spark-ignition engine fueled by gasoline, natural gas, ethanol, propane, or another fuel suitable for spark-ignition.

The engine 24 can be a compression-ignition engine fueled by diesel, or another fuel suitable for compression-ignition. The engine 24 can include a combustion chamber and an exhaust port or manifold that couples to the engine exhaust pipe 28 to contain the engine exhaust gases.

Many designs and arrangements of engines and engine exhaust pipes may be used with the embodiments described herein and the engine and engine exhaust pipe shown and described are to be construed as non-limiting examples.

[0021] In one embodiment, the catalytic converter 32 includes a three-way catalyst 36 and is intended to be used with spark-ignition engines. In another embodiment, the catalyst may be a two-way catalyst intended to be used with a compression-ignition engine, or another type of catalyst that benefits from a monitoring system.

[0022] The catalyst exhaust pipe 40 and the downstream component 44 receive the treated exhaust gases from the catalytic converter 32 and may perform other emissions treatment steps, and may muffle the noise of the engine 24. The arrangement of the catalyst exhaust pipe 40 and the downstream component 44 are non-limiting examples.

[0023] As shown in FIG. 2, the controller 52 includes a processing circuit 64 and a

communication interface 68 structured to communicate with the first EGO 56, the second EGO 60, the engine 24, and a display 72. The communication interface 68 may receive signals from the first EGO 56, the second EGO 60, and the engine 24, provide operation instructions to the engine 24, and provide display or alert information to the display 72. In one embodiment, the display 72 is a data port on the engine 24 or in a vehicle associated with the engine 24.

[0024] The processing circuit 64 includes a processor 76, a memory 80, and a diagnostic circuit 84. The processor 76 can include a notification circuit, and may be implemented as a general-purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a digital signal processor (DSP), a group of processing components, or other suitable electronic processing components. The memory 80 (e.g., RAM, ROM, Flash Memory, hard disk storage, etc.) may store data and/or computer code for facilitating the various processes described herein. The memory 80 may be communicably connected to the processor 76, the diagnostic circuit 84, and the communication interface 68 and structured to provide computer code or instructions to the processor 76 for executing the processes described in regard to the controller 52. Additionally, the memory 80 may be or include tangible, non-transient volatile memory or non-volatile memory. Accordingly, the memory 80 may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described herein.

[0025] The diagnostic circuit 84 includes various circuits (e.g., processor and memory circuits having executable code stored therein)for completing the activities described herein. More particularly, the diagnostic circuit 84 includes circuits structured to operate components of the engine 24 and the aftertreatment system. While various circuits with particular functionality are shown in FIG. 2, it should be understood that the controller 52, memory 80, and diagnostic circuit 84 may include any number of circuits for completing the functions described herein and that any number of the circuits described may be combined into a single circuit. For example, the activities and functionalities of the circuits of the diagnostic circuit 84 may be embodied in the memory 80, or combined in multiple circuits or as a single circuit. Additional circuits with additional functionality may be included. Further, it should be understood that the controller 52 may further control other vehicle activity beyond the scope of the present disclosure.

[0026] The diagnostic circuit 84 includes an engine circuit 88 structured to control various operations of the engine 24 as well as communicate with various sensors arranged in the engine 24; a fuel circuit 92 structured to monitor an amount of fuel provided to the engine 24 or a characteristic of the fuel provided to the engine 24; an oxygen in circuit 96 structured to communicate with the first EGO 56 and to analyze the signals provided by the first EGO 56; an oxygen out circuit 100 structured to communicate with the second EGO 60 and to analyze the signals provided by the second EGO 60; a lambda circuit 104 structured to communicate with the engine circuit 88, the fuel circuit 92, the oxygen in circuit 96, and the oxygen out circuit 100 and to determine an air-to-fuel equivalence ratio of the treated exhaust gas (outlet lambda o_ut); a theta circuit 108 structured to determine a model state Θ of the catalyst 36 based on a model; a timer circuit 112; and an oxygen storage circuit 116 structured to communicate with the lambda circuit 104, the theta circuit 108 and the timer circuit 112, and to determine an oxygen storage capacity of the catalyst 36.

[0027] As shown in FIG. 3, the catalyst 36 receives engine exhaust gas from the engine exhaust pipe 28 including an inlet quantity of oxygen Ri_n. An adsorbed quantity of oxygen R_ad_S of the gaseous oxygen is adsorbed into the catalyst 36 and a desorbed quantity of oxygen Rd_es is released back into the gaseous oxygen (this being a simplified representation of the Oxygen Storage material reduction phenomenon). A slip quantity of oxygen R_sii_P exits the catalytic converter 32 with the treated exhaust gas. The mass flow rates of the inlet quantity of oxygen Rin, the adsorbed quantity of oxygen R_ad_S, the desorpted quantity of oxygen Rd_es, and the slip quantity of oxygen R_si_ip can be determined by the diagnostic circuit 84. More specifically, the oxygen in circuit 96 monitors the first EGO 56, and communicates with the timer circuit 112 to determine an inlet oxygen mass flow rate rhi_n. The oxygen out circuit 100 monitors the second EGO 60, and communicates with the timer circuit 112 to determine a slip oxygen mass flow rate m_sii_P. The oxygen storage circuit 116 communicates with the oxygen in circuit 96 and the oxygen out circuit 100 and determines, based at least in part on the inlet oxygen mass flow rate rhin and the slip oxygen mass flow rate m_siip, an adsorption mass flow rate m_ad_S and a desorpted mass flow rate hides-

[0028] As shown in FIG. 4, the controller 52 utilizes various inputs to produce the model state Θ and an estimated outlet lambda _est- The engine circuit 88 and the fuel circuit 92 determine how much fuel is added to the combustion chamber, the engine 24 combusts the fuel in the presence of air, and the engine exhaust gases pass into the engine exhaust pipe 28. The oxygen in circuit 96 then communicates with the first EGO 56 and the oxygen in circuit 96 determines a mass flow rate of inlet air m_Air in the engine exhaust gas. The oxygen in circuit 96 also communicates with the lambda circuit 104 to determine an inlet lambda (λι_η) of the engine exhaust gas. Using the mass flow rate of inlet air riiAir and the inlet lambda λι_η, the engine circuit 88 determines inlet oxygen mass flow rate rhi_n into the catalyst 36.

[0029] The theta circuit 108 receives the inlet oxygen mass flow rate rhi_n from the engine circuit 88 and optionally communicates with the lambda circuit 104, the oxygen out circuit 100, and the oxygen storage circuit 116 to determine a model state Θ based on the model. How the model is used to determine the model state Θ may depend at least in part on an operating parameter of the engine 24. Exemplary models and model states Θ will be discussed below. [0030] The lambda circuit 104 receives the inlet oxygen mass flow rate r i_n from the engine circuit 88 and optionally communicates the oxygen out circuit 100 and the oxygen storage circuit 1 16 to determine the estimated outlet lambda _out, est-

[0031] As shown in FIG. 5, a first method 200 of diagnosing the catalyst 36 using the diagnostic circuit 84 includes initiating the method 200 by starting the engine 24 at step 202. At step 204, the theta circuit 108 resets the model state Θ to a default value of, for example, zero (0) or one (1). At step 206, the diagnostic circuit 84 runs the model to determine a new model state Θ. This generated model state Θ will represent a normal or properly functioning catalyst 36 (e.g., based on a life of the catalyst in terms of years in use, runtime, miles driven). Once the model state Θ is established, the method 200 proceeds to step 208 and checks for enabling conditions. In one embodiment, the enabling conditions include a temperature of the catalyst (as measured by a catalyst temperature probe or estimated via a model) being greater than a catalyst temperature threshold, the mass flow rate of inlet air riiAir in the engine exhaust gas being below an inlet air threshold, the amount of fuel added to the combustion chamber being greater than a fuel threshold, and there being no fuel cut action where fuel is being inhibited from entering the combustion chamber (e.g., braking). In one embodiment, the enabling conditions are met when the outlet lambda X_oUt undergoes a lean breakthrough and is not experiencing a fuel cut. A lean breakthrough occurs when the outlet lambda transitions from stoichiometric (e.g., ^^=1) to a lean ratio (e.g., λ_οώ>1). In some embodiments, the enabling condition may include the outlet lambda X_oUt switching from lean (e.g., _out>l) to rich (e.g. X_oUt<=l).

[0032] If the enabling conditions are not met in step 208, the method 200 continues to update the model state Θ to represent the catalyst 36 at step 206. If the enabling conditions are met in step 208, the diagnostic circuit 84 begins monitoring the catalyst 36 using model based diagnostics at step 210. During monitoring, the model state Θ and the outlet lambda _out are updated by the theta circuit 108 and the lambda circuit 104, respectively.

[0033] At step 212, the oxygen storage circuit 116 compares the model state Θ to a theta threshold, and the outlet lambda _out to a corresponding lambda threshold. If the model state Θ is less than the theta threshold and the outlet lambda X_oUt is greater than the lambda threshold, then the timer circuit 1 12 increments the timer at step 214. Because the model state Θ is representing a properly functioning catalyst 36, the outlet lambda should be close to the model state Θ within a predefined tolerance. If the model state Θ is less than the theta threshold, that indicates that the outlet lambda Xo_Ut should also be below the lambda threshold. The model state Θ and the outlet lambda Xo_Ut are both indications of the oxygen storage capacity of the catalyst 36. Again, the model state Θ is based on a model, and the outlet lambda is based on measurements.

[0034] After the timer is incremented at step 214, the timer value is compared to a timer threshold at step 216. If the timer value exceeds the timer threshold, then a fault is triggered at step 218 and sent to the display 72 from the processor 76 via the communication interface 68. The comparison between the timer value and the timer threshold lowers the likelihood of a false or inaccurate fault being triggered. In one embodiment, the timer threshold is between about thirty and about thirty-two seconds (30-32 seconds). In some embodiments, the timer threshold may be between about thirty seconds and about sixty seconds.

[0035] In one embodiment, the model is dependent at least in part on the inlet oxygen mass flow rate r i_n and an oxygen capacity Mc_ap,o2 of the catalyst 36 determined by the oxygen storage circuit 1 16. For example, the model state Θ may be defined as the following when running lean:

Θ = 0.23^■ rh_in ^■ F(A_in), /j (0)}],

where Θ is the model state (theta) over time as a function of the model state (theta), Mc_ap, 02 is an oxygen capacity of the catalyst, Ki is a constant, rh_in is a mass flow rate of air passing through the catalyst, and F(A_in) is a function of the air-to-fuel equivalence ratio (lambda).

[0036] For example, the model state Θ may be defined as the following when running rich:

Θ =

where Θ is the model state (theta) over time as a function of the model state (theta), Mc_ap, 02 is an oxygen capacity of the catalyst, K₂ is a constant, rh_in is a mass flow rate of air passing through the catalyst, F(A_in) is a function of the air-to-fuel equivalence ratio (lambda), and is a stoichiometric air-to-fuel ratio.

[0037] In some embodiments, the method 200 may utilize the timer circuit 112 to monitor the time that the model state Θ predicts that the treated exhaust gas from a nominal healthy system would be rich while the outlet lambda X_oUt indicates that the treated exhaust gas from the actual catalyst is actually lean. If a ratio of the actual lean time to the maximum theoretically allowed lean time is greater than a threshold, then the timer value is incremented.

[0038] As shown in FIG. 6, a second method 300 of diagnosing the catalyst 36 using the diagnostic circuit 84 includes initiating the method 300 by starting the engine 24 at step 302. At step 304, the theta circuit 108 resets the model state Θ to a default value of zero (0) or one (1). At step 306, the diagnostic circuit 84 runs the model to determine a new model state Θ. Steps 302, 304, and 306 of the method 300 are similar to the steps 202, 204, and 206 of the method 200 and may be conducted by the controller 52 simultaneously, or the steps 202, 204, 206 and the steps 302, 304, 306 may be the same.

[0039] At step 308, the diagnostic circuit 84 monitors for an enabling condition. An exemplary enabling condition may be a fuel cut event where fuel is inhibited from entering the combustion chamber of the engine 24 (e.g., during braking). If no fuel cut event has occurred, then the method 300 returns to step 306. If a fuel cut has occurred at step 308, then the method proceeds to step 310 and starts monitoring the catalyst 36. During monitoring, the model state Θ and the outlet lambda are updated by the theta circuit 108 and the lambda circuit 104, respectively.

[0040] At step 312, the oxygen storage circuit 116 determines if a lean breakthrough has occurred at the second EGO 60. If no lean breakthrough has occurred, then the diagnostic circuit 84 continues to monitor at step 310. When a lean breakthrough occurs (e.g., outlet lambda X_oUt <= 1), then the oxygen storage circuit 116 begins to monitor the model state Θ. In this case, the model state Θ is an indication of theoretical oxygen flux of the catalyst 36 (e.g., based on at least the adsorption mass flow rate m_ads and/or the desorbed mass flow rate hides)- The oxygen storage circuit 116 continues to monitor the model state Θ, until the model state Θ indicates a modelled lean breakthrough at step 316.

[0041] After observing a lean breakthrough on the second EGO sensor 60, the oxygen storage circuit 116 calculates an integrated oxygen flux from the time of the actual signal breakthrough to the time of the modelled breakthrough. For example, the oxygen storage circuit 116 may utilize a function as follows to determine the integrated oxygen flux:

Integrated Oxygen Flux = f^tm m_in(t)dt , where t_m is the time of the modelled lean breakthrough, t_s is the time of the actual lean breakthrough, and m_in is the inlet oxygen mass flow rate.

[0042] FIG. 7 shows a first line 318 of the model predicted outlet lambda over time and a second line 320 of the actual measured outlet lambda X_oUt over time according to an example embodiment. The integrated oxygen flux can be found between the first line 318 and the second line 320 between the time of actual lean breakthrough t_s and the modelled lean breakthrough t_m. The graph may help to visualize the value of the integrated oxygen flux.

[0043] As further shown in FIG. 6, once the integrated oxygen flux is determined at step 316, the integrated oxygen flux is compared to an oxygen flux threshold at step 322. If the integrated oxygen flux is larger than the oxygen flux threshold, then a fault is triggered at step 324 and an alert or notification is sent to the display 72 via the communication interface 68.

[0044] In some embodiments, the diagnostic circuit 84 uses a time difference between the actual lean breakthrough and the modelled lean breakthrough to identify a fault. The method 300 identifies when a healthy catalyst would fill with oxygen and compares that theoretically healthy catalyst to the actual catalyst 36 and how it is reacting. The method 300 allows the diagnostic circuit 84 to identify when the catalyst 36 has degraded past an acceptable threshold. In other words, when the difference between the mass of oxygen adsorbed by the actual catalyst 36 and the mass of oxygen adsorbed by the modelled catalyst is greater than a threshold value, a fault is triggered. In some embodiments, the method 300 is not dependent on the first EGO 56 and may operate independent of the oxygen in circuit 96. [0045] As shown in FIG. 8, a third method 400 of diagnosing the catalyst 36 using the diagnostic circuit 84 includes initiating the method 400 by starting the engine 24 at step 402. At step 404, the theta circuit 108 resets the model state Θ to a default value of zero (0) or one (1). At step 406, the diagnostic circuit 84 runs the model to determine a new model state Θ. At step 410, the diagnostic circuit 84 monitors for an enabling condition (e.g., a fuel cut or fuel cut exit). When the enabling condition is met, the method 400 proceeds to step 412 and the catalyst 36 is monitored.

[0046] The method 400 can utilize a non-recursive non-Kalman filter based method. For example, the equations described above may be used by the method 400 and the model parameter K₂ may be continually tuned (adapted) while monitoring occurs at step 412. The model parameter K₂ determined in the method 400 is representative of a parameter that indicates an age of the catalyst 36. In one embodiment, the parameter Mc_ap, 02 is an oxygen storage capacity of the catalyst 36. The oxygen storage capacity may be determined based at least in part on oxygen flux in/out of the catalyst 36, and/or measurements based on the first EGO 56 and the second EGO 60. The model parameter K₂ may be calculated in a feedback loop and determined at step 414. The model parameter K₂ is compared to a threshold at step 416. The capacity threshold represents an oxygen capacity that would not meet standards or otherwise indicates that the catalyst 36 needs maintenance or replacement. If the model parameter K₂ or M_Cap, 02 is less than the capacity threshold, a fault is triggered at step 418 and sent to the display 72 via the communication port 68.

[0047] In some embodiments, a method includes monitoring an oxygen flux across a three- way catalyst, developing an oxygen storage model based at least in part on the oxygen flux, outputting a model state (theta) from the oxygen storage model, monitoring an air-to-fuel equivalence ratio (lambda) of a flow of exhaust gas, comparing the model state (theta) to a theta threshold, comparing the air-to-fuel equivalence ratio (lambda) to a lambda threshold, incrementing a timer if the model state (theta) is less than the theta threshold and the air-to-fuel equivalence ratio is greater than or equal to the lambda threshold, and triggering a fault condition if the timer exceeds a time threshold. [0048] In one embodiment, incrementing the timer includes incrementing a lambda lean time when the air-to-fuel equivalence ratio (lambda) is greater than one, and incrementing a theta lean time when the model state (theta) is greater than the theta threshold. Additionally, triggering a fault condition may include comparing a ratio of the lambda lean time to the theta lean time to the time threshold.

[0049] In one embodiment, the time threshold is between about thirty seconds and about thirty- two seconds. In one embodiment, the oxygen storage model is representative of a three-way catalyst with a maximum oxygen capacity. In one embodiment, the oxygen storage model is not based on the monitored air-to-fuel equivalence ratio (lambda).

[0050] In one embodiment, when the air-to-fuel equivalence ratio (lambda) is greater than one, outputting the model state (theta) includes utilizing the following equation:

Θ = 0.23^■ πι_Μτ ^■ F(A_in), /i (0)}],

where Θ is the model state (theta) over time as a function of the model state (theta), Mc_ap, 02 is an oxygen capacity of the three-way catalyst, Ki is a constant, m_{Air in} is a mass flow rate of air passing through the three-way catalyst, and F(A_in) is a function of the air-to-fuel equivalence ratio (lambda).

[0051] In one embodiment, when the air-to-fuel equivalence ratio (lambda) is less than one, outputting the model state (theta) includes utilizing the following equation:

Θ = min \ K₂ ^■ 0.23^■ m_{Air in} ^■ F (A_in)^■ j_j^- , f₂ (0)

V" Cap,( where Θ is the model state (theta) over time as a function of the model state (theta), Mc_ap, 02 is an oxygen capacity of the three-way catalyst, K₂ is a constant, m_{Air in} is a mass flow rate of air passing through the three-way catalyst, F(A_in) is a function of the air-to-fuel equivalence ratio (lambda), and is a stoichiometric air-to-fuel ratio.

[0052] In some embodiments, a method includes recognizing a fuel cut event, monitoring an air-to-fuel equivalence ratio (lambda) of a flow of exhaust gas, identifying a lean breakthrough when a three-way catalyst has been substantially fully oxidized, developing an actual oxygen flux as a function of the time between the fuel cut event and the lean breakthrough, developing a predicted oxygen flux as a function of an oxygen storage model, developing an integrated oxygen flux based at least in part on a difference between the predicted oxygen flux and the actual oxygen flux, and triggering a fault condition if the integrated oxygen flux exceeds a threshold.

[0053] In one embodiment, predicted oxygen flux and the actual oxygen flux are functions of time. In one embodiment, the oxygen storage model is representative of a three-way catalyst with a maximum oxygen capacity. In one embodiment, developing the integrated oxygen flux includes estimating an amount of excess oxygen consumed by the predicted oxygen flux compared to the actual oxygen flux. In one embodiment, the oxygen storage model is not based on the monitored air-to-fuel equivalence ratio (lambda).

[0054] In one embodiment, when the air-to-fuel equivalence ratio (lambda) is greater than one, the predicted oxygen flux is based at least in part on the following equation:

where Θ is the model state (theta) over time as a function of the model state (theta), Mc_ap, 0₂ is an oxygen capacity of the three-way catalyst, Ki is a constant, rh_{Air in} is a mass flow rate of air passing through the three-way catalyst, and F(A_in) is a function of the air-to-fuel equivalence ratio (lambda).

[0055] In one embodiment, when the air-to-fuel equivalence ratio (lambda) is less than one, the predicted oxygen flux is based at least in part on the following equation:

Θ =

where Θ is the model state (theta) over time as a function of the model state (theta), Mc_ap, 02 is an oxygen capacity of the three-way catalyst, K₂ is a constant, m_{Air in} is a mass flow rate of air passing through the three-way catalyst, F(A_in) is a function of the air-to-fuel equivalence ratio (lambda), and is a stoichiometric air-to-fuel ratio.

[0056] In some embodiments, a method includes developing an oxygen storage model, developing a predicted oxygen flux of a three-way catalyst as a function of the oxygen storage model, monitoring an air-to-fuel equivalence ratio (lambda) of a flow of exhaust gas, developing an actual oxygen flux as a function of the air-to-fuel equivalence ratio (lambda), updating the oxygen storage model in view of the actual oxygen flux, and triggering a fault condition when the predicted oxygen flux is less than a threshold.

[0057] In one embodiment, the predicted oxygen flux and the actual oxygen flux are functions of time. In one embodiment, the oxygen storage model is representative of a three-way catalyst with a maximum oxygen capacity in view of the actual oxygen flux. In one embodiment, the oxygen storage model utilizes a non-recursive non-Kalman filter based methodology. In one embodiment, the method further includes triggering the development of the predicted oxygen flux when the flow of exhaust gas undergoes a lean-to-rich transition.

[0058] It should be understood that no claim element herein is to be construed under the provisions of 35 U.S.C. § 1 12(f), unless the element is expressly recited using the phrase "means for." The schematic flow chart diagrams and method schematic diagrams described above are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of representative embodiments. Other steps, orderings, and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the methods illustrated in the schematic diagrams. Further, reference throughout this specification to "one embodiment", "an embodiment", "an example

embodiment", or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment", "in an embodiment", "in an example embodiment", and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0059] Additionally, the format and symbols employed are provided to explain the logical steps of the schematic diagrams and are understood not to limit the scope of the methods illustrated by the diagrams. Although various arrow types and line types may be employed in the schematic diagrams, they are understood not to limit the scope of the corresponding methods. Indeed, some arrows or other connectors may be used to indicate only the logical flow of a method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of a depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the

corresponding steps shown. It will also be noted that each block of the block diagrams and/or flowchart diagrams, and combinations of blocks in the block diagrams and/or flowchart diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and program code.

[0060] Many of the functional units described in this specification have been labeled as circuits, in order to more particularly emphasize their implementation independence. For example, a circuit may be implemented as a hardware circuit comprising custom very-large- scale integration (VLSI) circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A circuit may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

[0061] As mentioned above, circuits may also be implemented in machine-readable medium for execution by various types of processors. An identified circuit of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions, which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified circuit need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the circuit and achieve the stated purpose for the circuit. Indeed, a circuit of computer readable program code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within circuits, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices, and may exist, at least partially, merely as electronic signals on a system or network.

[0062] The computer readable medium (also referred to herein as machine-readable media or machine-readable content) may be a tangible computer readable storage medium storing the computer readable program code. The computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. As alluded to above, examples of the computer readable storage medium may include but are not limited to a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), an optical storage device, a magnetic storage device, a holographic storage medium, a micromechanical storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain and/or store computer readable program code for use by and/or in connection with an instruction execution system, apparatus, or device.

[0063] The computer readable medium may also be a computer readable signal medium. A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electrical, electro-magnetic, magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport computer readable program code for use by or in connection with an instruction execution system, apparatus, or device. As also alluded to above, computer readable program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, Radio Frequency (RF), or the like, or any suitable combination of the foregoing. In one embodiment, the computer readable medium may comprise a combination of one or more computer readable storage mediums and one or more computer readable signal mediums. For example, computer readable program code may be both propagated as an electro-magnetic signal through a fiber optic cable for execution by a processor and stored on RAM storage device for execution by the processor.

[0064] Computer readable program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The computer readable program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone computer-readable package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0065] The program code may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks.

[0066] Accordingly, the present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

WHAT IS CLAIMED IS:

1. An apparatus comprising:

a constituent storage model circuit structured to determine a model state value based at least in part on a constituent flux value across a catalyst in an exhaust system;

a detection circuit communicably coupled to the constituent storage model circuit, the detection circuit structured to compare the model state value to a model value threshold; and

a notification circuit communicably coupled to the detection circuit, the notification circuit structured to selectively provide a notification in response to the comparison of the model state value and the model value threshold.

2. The apparatus of claim 1, further comprising a timer circuit structured to increment a timer responsive to the comparison.

3. The apparatus of claim 2, wherein the timer circuit is further structured to increment the timer responsive to the model state value being less than the model value threshold and a measured exhaust gas characteristic being greater than a characteristic threshold.

4. The apparatus of claim 1, wherein the model state value is indicative of a mass of oxygen stored in a nominal healthy catalyst, and wherein a measured exhaust gas characteristic is indicative of a mass of oxygen stored in a failed catalyst.

5. The apparatus of claim 1, wherein the notification includes activation of an indicator light.

6. The apparatus of claim 1, wherein the detection circuit is structured to adapt a model parameter during a fuel cut or a fuel cut exit in a feedback loop and the model parameter value is indicative of an oxygen capacity health of the catalyst.

7. The apparatus of claim 1, further comprising a monitoring circuit structured to monitor the constituent flux;

wherein the detection circuit is structured to develop an integrated constituent flux and provide the notification based on the integrated constituent flux being greater than an integrated flux threshold.

8. The apparatus of claim 1, wherein the model state value is updated over time as a function of the constituent flux.

9. The apparatus of claim 1, further comprising an air-to-fuel circuit structured to monitor an air-to-fuel equivalence ratio;

wherein the detection circuit is structured to compare the air-to-fuel equivalence ratio to a lambda threshold.

10. The apparatus of claim 1, further comprising an air-to-fuel circuit structured to monitor an air-to-fuel equivalence ratio;

wherein the model state value is based at least in part on the air-to-fuel equivalence ratio.

11. A system comprising:

an exhaust gas treatment system including a catalyst; and

a controller in communication with the exhaust gas treatment system, the controller structured to:

determine a model state value of a constituent storage model based at least in part on a constituent flux across the catalyst and an exhaust gas characteristic;

compare the model state value to a model value threshold; and trigger an action in response to the comparison of the model state value and the model value threshold.

12. The system of claim 11, wherein the comparison of the model state value and the model value threshold indicates a fault state of the catalyst.

13. The system of claim 11, wherein the exhaust gas characteristic is an air-to-fuel equivalence ratio.

14. The system of claim 11, wherein the controller is structured to determine an estimated excess oxygen consumption of a nominal healthy catalyst compared to the catalyst during a rich-to-lean transition.

15. The system of claim 11, wherein the controller is structured to trigger the action in response to the model state being less than the model threshold value and the exhaust gas characteristic being greater than a characteristic threshold.

16. A method comprising:

receiving, by a controller in an exhaust gas system, operation data regarding the exhaust gas system;

determining, by the controller, a model state value based on the operation data, the model state value indicative of a constituent flux across a catalyst in the exhaust gas system;

comparing, by the controller, the model state value to a model value threshold; and

triggering, by the controller, an action based on the comparison of the model state value to the model value threshold.

17. The method of claim 16, wherein the model state is indicative of an oxygen flux during a lean breakthrough, and wherein the action is a fault condition triggered in response to the model state being less than the model threshold value.

18. The method of claim 17, wherein the fault condition is triggered in response to the model state being less than the model threshold value and in response to an air-to-fuel equivalence ratio being greater than an air-to-fuel equivalence ratio threshold.

19. The method of claim 16, further comprising comparing a flux ratio of the model state and a flux ratio threshold, and trigging the action in response to the flux ratio exceeding the flux ratio threshold.

20. The method of claim 16, further comprising updating the constituent storage model in response to the constituent flux, wherein the action is triggered in response to the model state being less than the model threshold value.