Title of Invention

A METHOD OF REGULATING AN AMOUNT OF NH3 STORAGE IN A CATALYST OF AN EXHAUST AFTER TREATMENT SYSTEM

Abstract

A method of regulating an amount of NH3 stored in a catalyst of an exhaust after-treatment system includes determining a mass of NH3 into the catalyst based on a dosing rate of a dosing agent that is injected into an exhaust stream upstream of the catalyst and determining a mass of NH3 out of the catalyst. An accumulated mass of NH3 within the catalyst is calculated based on the mass of NH3 into the catalyst and the mass of NH3 out of the catalyst. The dosing rate is regulated based on the accumulated mass of NH3 within the catalyst.

Full Text

General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 EXCESS NH3 STORAGE CONTROL FOR SCR CATALYSTS FIELD [0001] The present disclosure relates to exhaust treatment systems, and more particularly to an excess NH3 storage control for an exhaust treatment system including a selective catalytic reduction (SCR) catalyst. BACKGROUND [0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. [0003] Internal combustion engines combust an air and fuel mixture to generate drive torque. The combustion process generates exhaust that is exhausted from the engine to atmosphere. The exhaust contains nitrogen oxides (NOx), carbon dioxide (C02), carbon monoxide (CO) and particulates. NOx is a term used to describe exhaust gases that consist primarily of nitrogen oxide (NO) and nitrogen dioxide (N02). An exhaust after-treatment system treats the exhaust to reduce emissions prior to being released to atmosphere. In an exemplary exhaust after-treatment system, a dosing system injects a dosing agent (e.g., urea) into the exhaust upstream of a selective catalytic reduction (SCR) catalyst. The exhaust and dosing agent mixture reacts over the SCR catalyst to reduce the NOx levels released to atmosphere. [0004] The dosing agent reacts with NOx on the SCR catalyst to accomplish the NOx reduction. More specifically, the dosing agent breaks down 1 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 to form ammonia (NH3), which is the reductant utilized to react with the NOx. The following exemplary, chemical relationships describe the NOx reduction: [0005] To perform the above-described NOx reduction, the SCR catalyst stores NH3 therein. For an SCR catalyst to perform effectively, the NH3 storage level must be maintained at an adequate level. More specifically, the NOx reduction or conversion efficiency is dependent upon the NH3 storage level. In order to maintain high conversion efficiency under various operating conditions, the NH3 storage must be maintained. However, as the temperature of the SCR catalyst increases, the NH3 level must be reduced to avoid NH3 slip (i.e., excess NH3 being released from the SCR catalyst), which can reduce the conversion efficiency of the catalyst. SUMMARY [0006] Accordingly, the present disclosure provides a method of regulating an amount of NH3 stored in a catalyst of an exhaust after-treatment system. The method includes determining a mass of NH3 into the catalyst based on a dosing rate of a dosing agent that is injected into an exhaust stream upstream of the catalyst and determining a mass of NH3 out of the catalyst (i.e., consumed in the catalyst). An accumulated mass of NH3 within the catalyst is calculated based on the mass of NH3 into the catalyst and the mass of NH3 out 2 General Motors No. GP-308601 -PTE-CD Attorney Docket No. 8540P-000442 of the catalyst. The dosing rate is regulated based on the accumulated mass of NH3 within the catalyst. [0007] In one feature, the mass of NH3 out of the catalyst is determined based on signals generated by NOx sensors that are located upstream and downstream of the catalyst, respectively. [0008] In another feature, the method further includes determining a conversion efficiency of the catalyst based on a temperature of the catalyst. The mass of NH3 out of the catalyst is determined based on a base dosing rate (i.e., stoichiometric) and the conversion efficiency. [0009] In still another feature, the method further includes monitoring a catalyst temperature and setting the accumulated mass of NH3 within the catalyst equal to zero when the catalyst temperature exceeds a threshold temperature. In this manner, the areas of operation, in which the catalyst does not have any storage potential, are accounted for. [0010] In yet other features, the method further includes defining a maximum NH3 storage mass of the catalyst based on a catalyst temperature. The dosing rate is regulated based on the maximum NH3 storage mass. An excess NH3 storage ratio is calculated based on the accumulated mass of NH3 within the catalyst and the maximum NH3 storage mass, wherein the dosing rate is regulated based on the excess NH3 storage ratio. For example, an adjustment factor is determined based on the excess NH3 storage ratio, wherein the dosing rate is regulated based said adjustment factor. The dosing agent is regulated to maintain the excess NH3 storage ratio to be less than 1. 3 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 [0011] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. DRAWINGS [0012] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. [0013] Figure 1 is a functional block diagram of an engine system including an exhaust treatment system including a selective catalytic reduction (SCR) catalyst; [0014] Figure 2 is a flowchart illustrating exemplary steps that are executed by the excess NH3 storage control of the present disclosure; [0015] Figure 3 is a functional block diagram of exemplary modules that execute the excess NH3 storage control; [0016] Figure 4 is a functional block diagram of exemplary modules that are used to determine a cumulative NH3 value into the SCR catalyst; [0017] Figure 5A is a functional block diagram of exemplary modules that are used to determine a cumulative NH3 value out of the SCR catalyst; [0018] Figure 5B is a functional block diagram of exemplary, alternative modules that are used to determine the cumulative NHS value out of the SCR catalyst; and 4 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 [0019] Figure 6 is a functional block diagram of exemplary modules that are used to determine an excess NH3 storage multiplier in accordance with the excess NH3 storage control of the present disclosure. DETAILED DESCRIPTION [0020] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. [0021] Referring now to Figure 1, an exemplary vehicle system 10 is schematically illustrated. The vehicle system 10 includes an engine system 12, an exhaust after-treatment system 14. The engine system 12 includes an engine 16 having a cylinder 18, an intake manifold 20 and an exhaust manifold 22. Air flows into the intake manifold 20 through a throttle 24. The air is mixed with fuel and the air and fuel mixture is combusted within the cylinder 18 to drive a piston (not shown). Although a single cylinder 18 is illustrated, it is appreciated that the engine 12 may include additional cylinders 18. For example, engines having 2, 3, 4, 5, 6, 8, 10, 12 and 16 cylinders are anticipated. The fuel is provided from a fuel source 26 and is injected into the air stream using an injector 28. A fuel level 5 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 sensor 30 is responsive to the amount of fuel within the fuel source 26. It is anticipated that the present disclosure can be implemented in both lean burn gasoline engines and diesel engines. [0022] Exhaust is produced through the combustion process and is exhausted from the cylinder 18 into the exhaust manifold 22. The exhaust after- treatment system 14 treats the exhaust flowing therethrough to reduce emissions before being released to the atmosphere. The exhaust after-treatment system 14 includes a dosing system 32, a diesel oxidation catalyst (DOC) 34, a NOx sensor 36, a NOx sensor 37 and a catalyst 38 that is preferably provided as a selective catalytic reduction (SCR) catalyst. [0023] The NOx sensor 36 is deemed the upstream NOx sensor and the NOx sensor 37 is deemed the downstream NOx sensor, relative to the catalyst 38. Both NOx sensors 36, 37 are responsive to a NOx level of the exhaust and generate respective signals based thereon. An upstream NOx mass flow rate (mN0XUS) is determined based on the signal generated by the NOx sensor 36. Similarly, a downstream NOx mass flow rate {mN0XDS) is determined based on the signal generated by the NOx sensor 37. [0024] Temperature sensors TA, TB and Tc are located at various points along the emissions path. For example, the temperature sensor TA is located upstream of the DOC 34, the temperature sensor TB is located upstream of the catalyst 38 and the temperature sensor Tc is located downstream of the catalyst 38. The DOC 34 reacts with the exhaust to reduce emission levels of the exhaust. It is also anticipated that a diesel particulate filter (DPF) 40 may be 6 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 located downstream from the catalyst 30 that filters diesel particulates to further reduce emissions. It is anticipated that the order of the SCR catalyst and the DPF can be reversed. [0025] The dosing system 32 includes a dosing agent injector 42, a dosing agent storage tank 44 and a dosing agent supply sensor 46. The dosing system 32 selectively injects a dosing agent (e.g., urea) into the exhaust stream to further reduce emissions. More specifically, the rate at which the dosing agent is injected into the exhaust stream {mDA) is determined based on the signals generated by one or more of the various sensors described herein. The exhaust and dosing agent mixture reacts within the catalyst 38 to further reduce exhaust emissions. [0026] A control module 50 regulates flow of the dosing agent based on the excess NH3 storage control of the present disclosure. The excess NH3 storage control keeps track of the mass of NH3 supplied into (mm3IN) and out of (mNH3our)tne catalyst 38. Furthermore, the excess NH3 storage control makes corrections based on where the calculated storage amount is with respect to a maximum NH3 storage capacity (mmiMAX) of the catalyst 38. [0027] mNH3IN is determined based the dosing agent or reductant (e.g., urea) input mass flow rate (i.e., mDA). rhDA is known and is determined based on the signal generated by the upstream NOx sensor 36. mNH3IN is further determined based on the exhaust flow rate, which is calculated based on MAF, a known fuel flow rate and other constants. mm30UT is the amount of NH3 that 7 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 reacts with NOx within the catalyst 38 and is calculated based on the difference between mmxus, mNOWS and a time delta (dt). A set of constants is used to convert this difference to an NH3 mass out of the catalyst 38 {mNH30UT) (i.e., NH3 consumed). The difference (Amm3) between mm3m and mm30m is provided as the mass of NH3 stored in the catalyst 38. [0028] The stored NH3 (Amm3) is compared to mm3MAX, which is determined based on a temperature of the catalyst 38 (TCAT). mNH3IN is adjusted to keep AmNH3 at a desired fraction of mm3MAX. In one embodiment, a simple ratio 0EXCSNH3) is implemented. As another embodiment, a closed-loop control setpoint is provided as a fraction of mNH3MAX. In this manner, NH3 release from the catalyst 38 that results from thermal transients can be reduced. [0029] The mass flow rate of NH3 supplied into the catalyst 38 (mNH3IN) (e.g., provided in g/s) is calculated based on mDA, provided in g/hour, the concentration of the dosing agent (DACONC), the molecular weight of the dosing agent (DAMw) (e.g., 60.06 g/mol in the case of urea), the molecular weight of NH3 (NH3MW) (e.g., 17.031 g/mol) and the known decomposition factor of the dosing agent with respect to NH3 (koec)- DACONC is determined as the percentage of dosing agent to dosing agent solution (e.g., 32.5% indicates 0.325 parts dosing agent to 1 part dosing agent solution). koEc is provided in mol NH3 per mol dosing agent (e.g., in the case of urea, 1 mol of urea decomposes to 2 moles of NH3; kDEc = 2). mNH3IN is calculated in accordance with the following relationship: 8 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 where 3600 is a time conversion factor (k-riME) of seconds per hour. [0030] mm30UT (e.g., provided in g/s) is the mass flow rate of NH3 consumed in the catalyst 38 and is calculated based on rhN0XUS, provided in g/s, mN0XDS, provided in g/s, the molecular weight of the NOx (NOXMW) and NH3MW (e.g., 17.031 g/mol). NOxMw is variable, however, any NOXMW can be used (e.g., N02 = 46.055 g/mol), because it cancels in the relationships described herein. ™miour 's calculated in accordance with the following relationship: X varies from 1 to 1.333 depending on the upstream % of N02. mNOXUS and mmxDS are calculated in accordance with the following relationship: where ff^EXH 's the mass flow rate of the exhaust and EXHMW is the molecular weight of the exhaust gas (e.g., provided in g of exhaust / mol of exhaust). [0031] Both mNmm and mm30ur are multiplied by a time increment (dt) (e.g., 1 second) to provide mNHVN and mNHlom, respectively, which are provided in grams. AmNH3 is determined as the difference between mNH1[N and mmJ0UT and is deemed the excess NH3 that is stored in the catalyst 38. AmNr]3 (e.g., or mNH3iN and mNH3our before calculating Amm3) can be integrated to provide a 9 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 cumulative value over time (&mmiCUM)- &mNH3cuM is divided by mNHZMAX to provide JEXCSNH3. [0032] JEXCSNH3 is used as an input to a look-up table to look up an excess storage multiplier value (kExcssTORE), which is fed back to the control module 50 to trim mM. The look-up table is stored in memory and is calibrated in such a way to make the kExcssTORE equal to 1 at some desired storage ratio ODSR) of NH3STOREMAX- For example, if IEXCSNH3 is less than JDSR. kExcssTORE is set to be greater than 1 and vise versa. In one embodiment, this function is executed by a closed-loop control (e.g., a PID control module). [0033] It is preferable to control the JDSR to be sufficiently below 1 to avoid NH3 slip from occurring. In order to reduce accumulated errors, AmNmcuM is reset during high temperature catalyst operation where no significant NH3 storage occurs (i.e., when TCAT is greater than a threshold temperature (TTHR))- The catalyst temperature (TCAT) is determined based on a temperature sensor signal (e.g., from one or more of the temperature sensors TA, TB, Tc and/or a temperature sensor integrated into the catalyst (not shown)). As TCAT increases NH3STOREMAX decreases, thereby raising the JEXCSNH3. This causes less dosing agent, and thus less NH3, to be dosed to the catalyst 38. By resetting ^mNHZCUM, NH3 release from the catalyst 38 is reduced. [0034] As mentioned above, NH3STOREMAX is the maximum possible NH3 stored at a given TCAT- Described below is a method of determining NH3STOREMAX- The catalyst 38, and exhaust after-treatment system for that matter, is stabilized to a constant temperature and the catalyst is purged of all 10 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 stored NH3 (i.e., by providing no dosing agent, and thus no incoming NH3, to the catalyst). At this point, ^mm3CUM is reset to 0 g. At some time (to), the dosing agent, and thus NH3, supply is turned back on with an excess NH3 to NOx molar ratio. The conversion efficiency of the downstream NOx sensor 37 and the upstream NOx sensor 36 will stabilize at a maximum value and at some latter time (ti) will start decreasing (i.e., when the downstream NOx sensor 37 detects NH3). At this point, Amm3ClM is read to provide an approximate NH3STOREMAX value. The conversion efficiency is determined in accordance with the following relationship: [0035] Referring now to Figure 2, exemplary steps that are executed by the excess NH3 control will be described in detail. In step 200, control determines whether TCAT is greater than TJHR- If TCAT is greater than TTHR, control sets &mm3CUM equal to zero in step 202 and loops back to step 200. If TCAT is not greater than TTHR, control determines mm3IN in step 204. Control determines mm3Qm in step 206. In step 208, control calculates AmmiCUM. In step 210, control determines mm3MAX . [0036] Control calculates 1EXCSNH3 based on mNH3MAX and &mNH3CUM in step 212. In step 214, control determines kExcssTORE based on JEXCSNH3- Control regulates mDA based on KEXCSSTORE in step 216 and control ends. It is anticipated, however, that the above-described, exemplary control will continue 11 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 to loop through steps 200 to 216 at a pre-determined time interval or rate while the engine is running. [0037] Referring now to Figure 3, exemplary modules that execute the excess NH3 control will be described in detail. The exemplary modules include a mNHim module 300, a mNH30UT module 302, a summer module 304, a dosing agent control module 306 and a comparator module 308. The mNH3iN module 300 determines mm3IN based on mDA, as described in detail above. The mNH3our module 302 determines mNm0UT based on mmxus and mN0XDS, as described in detail above and in further detail with respect to Figure 5A below. Alternatively, the mm30UT module 302 determines mm30UT based on rhDAaASE), as described in further detail with respect to Figure 5B below. mDA(BASE) is the stoichiometric NH3 quantity. [0038] The summer module 304 determines AmNH3 as the difference between mNH3BI and mm30UT. The dosing agent control module 306 monitors AfflW3C[/M and regulates mDA based thereon. The dosing agent control module 306 also selectively resets Amffl3CW, as described in detail above, based on a signal from the comparator module 308. More specifically, the comparator module 308 compares TCAT to TTHR- If TCAT is greater than TTHR, the signal from the comparator module 308 indicates that AmNHXUU should be reset. If TCAT is not greater than TTHR, the signal from the comparator module 308 indicates that &mNH3CUM should not be reset. 12 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 [0039] Referring now to Figure 4, exemplary modules that are used to calculate mNH3m will be described in detail. The exemplary modules include a first multiplier module 400, a first divider module 402, second and third multiplier modules 404, 406, respectively, a second divider module 408, a fourth multiplier module 410 and an addition module 412. The modules 400, 402, 404, 406, 408 process mDA, DACONC, DAMW, koEc, NH3MW and kTiME in accordance with Equation 1, described above, to provide mmim. The fourth multiplier module 410 multiplies mNH3IN by dt to provide mNHim. The addition module 412, which may be optionally provided, accumulates the mmim values to provide a cumulative mNH3IN \mNH3INCUM )• [0040] Referring now to Figure 5A, exemplary modules that are used to calculate mNH30UT will be described in detail. The exemplary modules include a summer module 500, a divider module 502, first, second and third multiplier modules 504, 505, 506, respectively, and an addition module 508. The modules 500, 502, 504, 505 process mN0XUS, mN0XDS, NOXMW and NH3Mw to provide mNin0UT. The third multiplier module 506 multiplies mm30UT by dt to provide mwhow The addition module 508, which may be optionally provided, accumulates the mm30UT values to provide a cumulative mNH30UT (mNH30UrcUM). It is again noted that the molar ratio X between NH3 and NOx varies from 1 to 1.333 depending on the upstream % of NO2. 13 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 [0041] Referring now to Figure 5B, alternative exemplary modules that are used to calculate mm30UT will be described in detail. As discussed in further detail below, the exemplary modules initially calculate mm30UT based on wmm and a conversion efficiency (CE(%)) of the catalyst. CE(%) is determined based on several factors including, but not limited to, TCAT. space velocity and N02 ratio. [0042] The exemplary modules include a first multiplier module 510, a first divider module 512, second, third and fourth multiplier modules 514, 516, 517 respectively, a second divider module 518, a fifth multiplier module 520 a third divider module 522, a sixth multiplier module 524 and an addition module 526. The modules 510, 512, 514, 516, 517, 518 process mM(BASE), DACONC, DAMW, kDEc, NH3MW and kTiME in accordance with Equation 1, described above, to provide mm3lN. The third divider module divides CE(%) by 100 to provide a decimal value of the conversion efficiency, which is then multiplied by mm3IN in the fifth multiplier module 520 to provide mNH30UT. The sixth multiplier module 524 multiplies mm30UT by dt to provide mm30m. The addition module 526, which may be optionally provided, accumulates the mm30UT values to provide MNHIOUTCVM ■ Again, the molar ratio X between NH3 and NOx varies from 1 to 1.333 depending on the upstream % of NO2. [0043] Referring now to Figure 6, exemplary modules that are used to determine I a mwH3MAx module 600, an addition module 602, a division module 604 and a 14 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 kexcssTORE module 606. The mmmAX module 600 determines mNmMAX based on TCAT and VCAT, as discussed above. The addition module 602 accumulates the AmNflJ values to provide &mNH3CUM. If, however, the addition modules 412 and 508, 526 of Figures 4 and 5A, 5B are included, the addition module 602 can be foregone because AmNH3CUM will be provided based on mmjJNC[JM and rnmwmcuM from the addition modules 412 and 508, 526. If the addition modules 412 and 508, 526 are not provided, the addition module 602 is provided. The division module 604 determines JEXCSNH3 as a ratio between AmNH3CUM and mmiMAX . The kExcssTORE module 606 KEXCSSTORE determines kExcssTORE, as discussed in detail above. [0044] Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims. 15 General Motors No. GP-308601 -PTE-CD Attorney Docket No. 8540P-000442 CLAIMS What is claimed is: 1. A method of regulating an amount of NH3 stored in a catalyst of an exhaust after-treatment system, comprising: determining a mass of NH3 into the catalyst based on a dosing rate of a dosing agent that is injected into an exhaust stream upstream of the catalyst; determining a mass of NH3 out of the catalyst; calculating an accumulated mass of NH3 within the catalyst based on said mass of NH3 into the catalyst and said mass of NH3 out of the catalyst; and regulating said dosing rate based on said accumulated mass of NH3 within the catalyst. 2. The method of claim 1 wherein said mass of NH3 out of the catalyst is determined based on signals generated by NOx sensors that are located upstream and downstream of the catalyst, respectively. 3. The method of claim 1 further comprising determining a conversion efficiency of the catalyst based on a temperature of the catalyst, wherein said mass of NH3 out of the catalyst is determined based on a base dosing rate and said conversion efficiency. 16 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 4. The method of claim 1 further comprising: monitoring a catalyst temperature; and setting said accumulated mass of NH3 within the catalyst equal to zero when said catalyst temperature exceeds a threshold temperature. 5. The method of claim 1 further comprising determining a maximum NH3 storage mass of the catalyst based on a catalyst temperature, wherein said dosing rate is regulated based on said maximum NH3 storage mass. 6. The method of claim 5 further comprising calculating an excess NH3 storage ratio based on said accumulated mass of NH3 within the catalyst and said maximum NH3 storage mass, wherein said dosing rate is regulated based on said excess NH3 storage ratio. 7. The method of claim 6 further comprising determining an adjustment factor based on said excess NH3 storage ratio, wherein said dosing rate is regulated based said adjustment factor. 8. The method of claim 6 wherein said dosing agent is regulated to maintain said excess NH3 storage ratio to be less than 1. 17 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 9. An exhaust after-treatment system that regulates an amount of NH3 stored in a catalyst thereof, comprising: a first module that determines a mass of NH3 into the catalyst based on a dosing rate of a dosing agent that is injected into an exhaust stream upstream of the catalyst; a second module that determines a mass of NH3 out of the catalyst; a third module that calculates an accumulated mass of NH3 within the catalyst based on said mass of NH3 into the catalyst and said mass of NH3 out of the catalyst; and a fourth module that regulates said dosing rate based on said accumulated mass of NH3 within the catalyst. 10. The exhaust after-treatment system of claim 9 wherein said mass of NH3 out of the catalyst is determined based on signals generated by NOx sensors that are located upstream and downstream of the catalyst, respectively. 11. The exhaust after-treatment system of claim 9 further comprising a fifth module that determines a conversion efficiency of the catalyst based on a temperature of the catalyst, wherein said mass of NH3 out of the catalyst is determined based on a base dosing rate and said conversion efficiency. 18 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 12. The exhaust after-treatment system of claim 9 further comprising a temperature sensor that monitors a catalyst temperature, wherein said fourth module sets said accumulated mass of NH3 within the catalyst equal to zero when said catalyst temperature exceeds a threshold temperature. 13. The exhaust after-treatment system of claim 9 further comprising a fifth module that determines a maximum NH3 storage mass of the catalyst based on a catalyst temperature, wherein said dosing rate is regulated based on said maximum NH3 storage mass. 14. The exhaust after-treatment system of claim 13 further comprising a sixth module that calculates an excess NH3 storage ratio based on said accumulated mass of NH3 within the catalyst and said maximum NH3 storage mass, wherein said dosing rate is regulated based on said excess NH3 storage ratio. 15. The exhaust after-treatment system of claim 14 further comprising a seventh module that determines an adjustment factor based on said excess NH3 storage ratio, wherein said dosing rate is regulated based said adjustment factor. 16. The exhaust after-treatment system of claim 14 wherein said dosing agent is regulated to maintain said excess NH3 storage ratio to be less than 1. 19 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 17. A method of regulating an amount of NH3 stored in a catalyst of an exhaust after-treatment system, comprising: determining a mass of NH3 into the catalyst based on a dosing rate of a dosing agent that is injected into an exhaust stream upstream of the catalyst; determining a mass of NH3 out of the catalyst; calculating an accumulated mass of NH3 within the catalyst based on said mass of NH3 into the catalyst and said mass of NH3 out of the catalyst; determining a maximum NH3 storage mass of the catalyst; calculating an excess NH3 storage ratio based on said maximum NH3 storage mass and said accumulated mass of NH3 within the catalyst; and regulating said dosing rate based on said excess NH3 storage ratio to maintain said excess NH3 storage ratio to be less than 1. 18. The method of claim 17 wherein said mass of NH3 out of the catalyst is determined based on signals generated by NOx sensors that are located upstream and downstream of the catalyst, respectively. 19. The method of claim 17 further comprising determining a conversion efficiency of the catalyst based on a temperature of the catalyst, wherein said mass of NH3 out of the catalyst is determined based on a base dosing rate and said conversion efficiency. 20 General Motors No. GP-308601-PTE-CD Attorney Docket No. 8540P-000442 20. The method of claim 17 further comprising: monitoring a catalyst temperature; and setting said accumulated mass of NH3 within the catalyst equal to zero when said catalyst temperature exceeds a threshold temperature. 21. The method of claim 17 further comprising determining said maximum NH3 storage mass of the catalyst based on at least one of a catalyst temperature and a catalyst volume. 22. The method of claim 21 further comprising determining an adjustment factor based on said excess NH3 storage ratio, wherein said dosing rate is regulated based said adjustment factor. Dated this 4th day of MARCH, 2008 21 A method of regulating an amount of NH3 stored in a catalyst of an exhaust after-treatment system includes determining a mass of NH3 into the catalyst based on a dosing rate of a dosing agent that is injected into an exhaust stream upstream of the catalyst and determining a mass of NH3 out of the catalyst. An accumulated mass of NH3 within the catalyst is calculated based on the mass of NH3 into the catalyst and the mass of NH3 out of the catalyst. The dosing rate is regulated based on the accumulated mass of NH3 within the catalyst.

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00431-kol-2008-abstract.pdf

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00431-kol-2008-description complete.pdf

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00431-kol-2008-form 3.pdf

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431-KOL-2008-(03-09-2013)-ABSTRACT.pdf

431-KOL-2008-(03-09-2013)-ANNEXURE TO FORM 3.pdf

431-KOL-2008-(03-09-2013)-CLAIMS.pdf

431-KOL-2008-(03-09-2013)-CORRESPONDENCE.pdf

431-KOL-2008-(03-09-2013)-FORM-1.pdf

431-KOL-2008-(03-09-2013)-FORM-2.pdf

431-KOL-2008-(03-09-2013)-PA.pdf

431-KOL-2008-(03-09-2013)-PETITION UNDER RULE 137.pdf

431-KOL-2008-(16-07-2014)-CORRESPONDENCE.pdf

431-KOL-2008-(16-07-2014)-OTHERS.pdf

431-kol-2008-ASSIGNMENT-1.1.pdf

431-KOL-2008-ASSIGNMENT.pdf

431-kol-2008-CANCELLED PAGES.pdf

431-KOL-2008-CORRESPONDENCE OTHERS 1.1.pdf

431-KOL-2008-CORRESPONDENCE OTHERS 1.2.pdf

431-kol-2008-CORRESPONDENCE.pdf

431-kol-2008-EXAMINATION REPORT.pdf

431-kol-2008-FORM 18-1.1.pdf

431-kol-2008-form 18.pdf

431-kol-2008-GPA.pdf

431-kol-2008-GRANTED-ABSTRACT.pdf

431-kol-2008-GRANTED-CLAIMS.pdf

431-kol-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

431-kol-2008-GRANTED-DRAWINGS.pdf

431-kol-2008-GRANTED-FORM 1.pdf

431-kol-2008-GRANTED-FORM 2.pdf

431-kol-2008-GRANTED-FORM 3.pdf

431-kol-2008-GRANTED-FORM 5.pdf

431-kol-2008-GRANTED-LETTER PATENT.pdf

431-kol-2008-GRANTED-SPECIFICATION-COMPLETE.pdf

431-kol-2008-PETITION UNDER RULE 137.pdf

431-KOL-2008-PRIORITY DOCUMENT.pdf

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431-kol-2008-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf