US20220074332A1 - Method for controlling exhaust aftertreatment system for vehicles - Google Patents
Method for controlling exhaust aftertreatment system for vehicles Download PDFInfo
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- US20220074332A1 US20220074332A1 US17/168,467 US202117168467A US2022074332A1 US 20220074332 A1 US20220074332 A1 US 20220074332A1 US 202117168467 A US202117168467 A US 202117168467A US 2022074332 A1 US2022074332 A1 US 2022074332A1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N9/00—Electrical control of exhaust gas treating apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
- F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N9/00—Electrical control of exhaust gas treating apparatus
- F01N9/005—Electrical control of exhaust gas treating apparatus using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
- F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/14—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics having more than one sensor of one kind
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
- F01N2570/14—Nitrogen oxides
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/14—Arrangements for the supply of substances, e.g. conduits
- F01N2610/1453—Sprayers or atomisers; Arrangement thereof in the exhaust apparatus
- F01N2610/146—Control thereof, e.g. control of injectors or injection valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/04—Methods of control or diagnosing
- F01N2900/0406—Methods of control or diagnosing using a model with a division of the catalyst or filter in several cells
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/04—Methods of control or diagnosing
- F01N2900/0418—Methods of control or diagnosing using integration or an accumulated value within an elapsed period
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1602—Temperature of exhaust gas apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1616—NH3-slip from catalyst
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1621—Catalyst conversion efficiency
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1622—Catalyst reducing agent absorption capacity or consumption amount
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
Definitions
- the present disclosure relates to a method for controlling an exhaust aftertreatment system for vehicle engines.
- SCR urea-selective catalytic reduction
- the SCR apparatus allows ammonia formed by pyrolysis of urea in exhaust gas to react with nitrogen oxides (NO x ) with the aid of a catalyst so as to be purified into water and nitrogen.
- NO x nitrogen oxides
- Urea injected upstream from the SCR apparatus should be injected in an amount suitable for purifying nitrogen oxides (NO x ) in the exhaust gas.
- ammonia slip in which a surplus amount of ammonia which does not participate in reaction is exhausted, occurs and the excessively large amount of urea is consumed, and when an excessively small amount of urea is injected, unpurified nitrogen oxides (NO x ) are discharged.
- an ammonia sensor may be installed downstream from the SCR apparatus, but the ammonia sensor is expensive and thus the cost of the vehicle is increased.
- the present disclosure has been made in view of the above problems, and it is an object of the present disclosure to provide a method for controlling an exhaust aftertreatment system for vehicles in which ammonia slip of a selective catalytic reduction (SCR) apparatus may be prevented without providing an ammonia sensor downstream from the SCR apparatus so as to avoid an increase in vehicle costs, a suitable amount of urea may be injected in consideration of a change in purification efficiency due to aged deterioration of the SCR apparatus, and ultimately the SCR apparatus may purify NO x in exhaust gas into the optimum state so as to satisfy various regulations.
- SCR selective catalytic reduction
- a method for controlling an exhaust aftertreatment system for vehicles including: determining, by a controller, whether or not a designated regeneration operation is finished; accumulating, by the controller, a first amount of NO x emission measured by a rear end NO x sensor of a selective catalytic reduction (SCR) apparatus and a second amount of NO x emission calculated by an NO x emission amount model respectively for a designated first reference period of time immediately after the regeneration operation is finished; determining, by the controller, whether or not a difference between an accumulated value of the first amount of NO x emission and an accumulated value of the second amount of NO x emission exceeds a designated reference value when the first reference period of time has elapsed; and correcting, by the controller, a model purification efficiency used in the NO x emission amount model using a sensor purification efficiency acquired by a front end NO x sensor and the rear end NO x sensor of the SCR apparatus when the difference between the accumulated values
- the controller may correct the model purification efficiency by calculating an efficiency correction coefficient configured to make the model purification efficiency equal to the sensor purification efficiency, and multiplying the model purification efficiency by the efficiency correction coefficient.
- the controller may calculate the urea injection amount using a corrected NH 3 —NO x reaction ratio acquired by multiplying a NH 3 —NO x reaction ratio by a reaction ratio correction coefficient, which is a reciprocal of the efficiency correction coefficient.
- the method may further include, when a next regeneration operation is performed after the correcting the model purification efficiency, accumulating, by the controller, a third NO x emission amounts measured by the rear end NO x sensor of the SCR apparatus and a fourth NO x emission amounts calculated by the NO x emission amount model respectively for a designated second reference time immediately after the regeneration operation is finished, determining, by the controller, whether or not an accumulated value of the third NO x emission amounts measured by the rear end NO x sensor is greater than an accumulated value of the fourth NO x emission amounts calculated by the NO x emission amount model, and correcting, by the controller, an ammonia occludable amount of the SCR apparatus when the accumulated value of the third NO x emission amounts measured by the rear end NO x sensor is greater than the accumulated value of the fourth NO x emission amounts calculated by the NO x emission amount model.
- the controller may correct the ammonia occludable amount of the SCR apparatus by multiplying the ammonia occludable amount by a designated occlusion coefficient, and the occlusion coefficient may have a value in a range of 0 to 1.
- the controller may calculate the urea injection amount using a following equation,
- urea injection amount NO x inflow rate ⁇ (corrected NH 3 —NO x reaction ratio) ⁇ (corrected model purification efficiency)+(ammonia occludable amount ⁇ occlusion coefficient).
- the controller may gradually decrease the occlusion coefficient until a fifth NO x emission amount calculated by the rear end NO x sensor becomes equal to a sixth NO x emission amount calculated by the NO x emission amount model.
- the controller may calculate a corrected ammonia occludable amount by correcting the ammonia occludable amount of the SCR apparatus using the occlusion coefficient when the fifth NO x emission amount calculated by the rear end NO x sensor becomes equal to the sixth NO x emission amount calculated by the NO x emission amount model, and the controller may calculate the urea injection amount using a following equation and controls the calculated urea injection amount to be injected,
- urea injection amount NO x inflow rate ⁇ (corrected NH 3 —NO x reaction ratio) ⁇ (corrected model purification efficiency)+(corrected ammonia occludable amount).
- the controller may sequentially turn on a slip diagnosis flag after correcting the model purification efficiency, accumulate the third NO x emission amounts measured by the rear end NO x sensor of the SCR apparatus and the fourth NO x emission amounts calculated by the NO x emission amount model respectively for the first reference time immediately after the regeneration operation is finished, and determine whether or not an accumulated value of the third NO x emission amounts measured by the rear end NO x sensor is greater than an accumulated value of the fourth NO x emission amounts calculated by the NO x emission amount model, and correct the ammonia occludable amount of the SCR apparatus, when the slip diagnosis flag is turned on.
- the controller may turn off the slip diagnosis flag after the correcting the ammonia occludable amount of the SCR apparatus.
- the NO x emission amount model may be calculated using a following equation,
- NO x purification amount model NO x inflow rate ⁇ model purification efficiency
- FIG. 1 is a view exemplarily illustrating an exhaust aftertreatment system for vehicles to which the present disclosure is applicable;
- FIG. 2 is a flowchart illustrating a method for controlling an exhaust aftertreatment system for vehicles according to one embodiment of the present disclosure
- FIG. 3 is a graph showing accumulated values of NO x emission amounts as time passes
- FIG. 4 is a graph showing accumulated values of NO x emission amounts for a first reference time
- FIG. 5 is another graph showing accumulated values of NO x emission amounts for the first reference time
- FIG. 6 is a graph showing ammonia emission probability as time passes
- FIG. 7 is a graph showing accumulated values of NO x emission amounts for a second reference time.
- FIG. 8 is a graph showing a change in a value output by an NO x sensor depending on a change in an ammonia amount and a change in an NO x amount.
- FIG. 1 is a view exemplarily illustrating an exhaust aftertreatment system for vehicles to which the present disclosure is applicable, a selective catalytic reduction (SCR) apparatus 1 configured to purify nitrogen oxides (NO x ) in exhaust gas emitted from an engine is provided, a front end NO x sensor 3 configured to measure nitrogen oxides (NO x ) in the exhaust gas flowing into the SCR apparatus 1 and a urea injection apparatus 5 configured to inject urea are provided in a region upstream from the SCR apparatus 1 , and a rear end NO x sensor 7 configured to measure nitrogen oxides (NO x ) in the exhaust gas having passed through the SCR apparatus 1 is provided in a region downstream from the SCR apparatus 1 .
- SCR selective catalytic reduction
- front end does not necessarily mean the front end of the SCR apparatus 1 , and is to be interpreted as any arbitrary position upstream from the SCR apparatus 1 , which is suitable for measuring nitrogen oxides (NO x ) flowing into the SCR apparatus 1 .
- rear end does not necessarily mean the rear end of the SCR apparatus 1 , and is to be interpreted as any arbitrary position downstream from the SCR apparatus 1 , which is suitable for measuring nitrogen oxides (NO x ) emitted from the SCR apparatus 1 .
- a controller 9 receives signals from the front end NO x sensor 3 and the rear end NO x sensor 7 , and controls the urea injection apparatus 5 to inject urea.
- the controller 9 may be a computer or a processor such as a CPU, or more specifically, an electronic control unit (ECU) as an embedded system configured to control electrical systems in a vehicle.
- the controller 9 may be programmed to communicate with the front end NO x sensor 3 , the rear end NO x sensor 7 , and the urea injection apparatus 5 , so as to control the connected devices.
- no separate ammonia sensor is provided downstream from the SCR apparatus 1 .
- a method for controlling the exhaust aftertreatment system for vehicles includes determining, by the controller 9 , whether or not a designated regeneration operation is finished (S 10 ), accumulating, by the controller 9 , NO x emission amounts measured by the rear end NO x sensor 7 of the SCR apparatus 1 and NO x emission amounts calculated by an NO x emission amount model respectively for a designated first reference time immediately after the regeneration operation is finished (S 20 ), determining, by the controller 9 , whether or not a difference between an accumulated value of the NO x emission amounts measured by the rear end NO x sensor 7 and an accumulated value of the NO x emission amounts calculated by the NO x emission amount model exceeds a designated reference value when the first reference time has elapsed (S 30 ), and correcting, by the controller 9 , model purification efficiency used in the NO x emission amount model using sensor purification efficiency acquired by the front end NO x sensor 3 and the rear end NO x sensor 7 when the difference between the accumulated values exceeds the reference
- DPF diesel particulate filter
- the SCR apparatus 1 includes an SCR-catalyzed diesel particulate filter (SDPF), i.e., a conventional DPF with SCR coating, or is formed by supporting an SCR catalyst on a carrier, when the above operation of increasing the temperature to the level at which all occluded ammonia is removed is performed, the regeneration operation is regarded as being performed.
- SDPF diesel particulate filter
- the regeneration operation means regeneration of the DPF. Further, the operation of FIG. 2 is continuously performed repeatedly during the driving of the vehicle.
- the first reference time is set based on a time for which ammonia is not occluded in the SCR apparatus 1 because the temperature of the SCR apparatus 1 is raised due to the above regeneration operation.
- the carrier or the DPF of the SCR apparatus 1 is characterized in that ammonia is not occluded thereinto at a high temperature, and thus, during this time, an NO x purification amount and an NO x emission amount may be more precisely calculated using NO x and urea flowing into the SCR apparatus 1 and NO x discharged from the SCR apparatus 1 , without regard to an ammonia occlusion amount and an ammonia occludable amount in the SCR apparatus 1 . For this reason, in the present disclosure, this time is used.
- the first reference time is set based on the time for which occlusion of ammonia is not performed in the SCR apparatus 1 for the above-stated reason.
- the first reference time may be set to the time for which occlusion of ammonia is not performed in the SCR apparatus 1 , and further include a point in time at which some occlusion of ammonia is performed without affecting achievement of the objects of the present disclosure.
- the controller 9 determines the suitability of the NO x emission amount model by accumulating NO x emission amounts measured by the rear end NO x sensor 7 and NO x emission amounts calculated by the NO x emission amount model respectively for the first reference time immediately after the regeneration operation and determining whether or not a difference between accumulated values exceeds the reference value, as described above.
- a value suitable for determining whether or not the above NO x emission amount model and the model purification efficiency need to be corrected which is acquired by a great number of experiments and analyses, may be selected as the reference value, and the reference value may be set to 2% or the like, as exemplarily shown in FIG. 2 .
- NO x emission amount model is calculated using the following equation:
- the NO purification amount model is calculated using the following equation:
- NO x purification amount model NO inflow rate ⁇ model purification efficiency.
- the model purification efficiency may be a value which the controller 9 has as the purification efficiency of the SCR apparatus 1 , and the NO inflow rate may be measured by the front end NO sensor 3 .
- the NO emission amount is calculated using the model purification efficiency, and thus, when there is an error in the model purification efficiency, an error in the NO x emission amount calculated by the NO x emission amount model occurs.
- FIG. 3 is a graph showing accumulated values of NO x emission amounts as time passes, the graph shows the accumulated value of the NO x emission amounts measured by the rear end NO x sensor 7 of the SCR apparatus 1 and the accumulated value of the NO x emission amounts calculated by the NO x emission amount model and indicates occurrence of a difference therebetween, and such a difference indicates that there is an error in the model purification efficiency used in the NO x emission amount model.
- FIG. 3 also shows an accumulated value of NO x inflow rates calculated based on values measured by the front end NO x sensor 3 , and a difference between the accumulated value of NO x inflow rates and the accumulated value of the NO x emission amounts of the rear end NO x sensor 7 may be interpreted as an accumulated value of amounts of NO x purified by the SCR apparatus 1 .
- the controller 9 corrects the model purification efficiency by calculating an efficiency correction coefficient which makes the model purification efficiency equal to the sensor purification efficiency and multiplying the model purification efficiency by the efficiency correction coefficient.
- the sensor purification efficiency is calculated using an NO x inflow rate based on the measured value of the front end NO x sensor 3 and an NO x emission amount based on the measured value of the rear end NO x sensor 7 .
- a corrected model purification efficiency is calculated by multiplying the model purification efficiency by the efficiency correction coefficient, and thereafter, the controller 9 calculates a urea injection amount using the corrected model purification efficiency.
- the controller 9 calculates the urea injection amount using the corrected model purification efficiency calculated by multiplying the model purification efficiency by the efficiency correction coefficient
- the controller 9 calculates the urea injection amount using a corrected NH 3 —NO x reaction ratio calculated by multiplying a NH 3 —NO x reaction ratio by a reaction ratio correction coefficient which is the reciprocal of the efficiency correction coefficient.
- the controller 9 calculates the urea injection amount using the following equation, and then controls the urea injection apparatus 5 to inject the calculated urea injection amount:
- reaction ratio correction coefficient ⁇ efficiency correction coefficient 1.
- an error in the model purification efficiency in the current state is 10% and, in order to reduce the error, the model purification efficiency is corrected as follows.
- ammonia occludable amount used to calculate the urea injection amount is a constant which is merely added, and will thus be omitted for the purpose of brevity of description.
- FIG. 2 illustrates that the model purification efficiency is corrected, the model-based accumulated value is recalculated using the corrected model purification efficiency, the recalculated model-based accumulated value is compared with the sensor-based accumulated value, it is confirmed that a difference between the recalculated model-based accumulated value and the sensor-based accumulated value is less than the reference value, and then the corrected model purification efficiency is reflected as a learning value.
- FIG. 4 indicates that, when the sensor-based accumulated value is greater than the model-based accumulated value after the first reference time, the model-based accumulated value is recalculated using the above-corrected purification efficiency and the recalculated model-based accumulated value becomes the sensor-based accumulated value
- FIG. 5 indicates that, when the sensor-based accumulated value is less than the model-based accumulated value after the first reference time, the model-based accumulated value is recalculated using the above-corrected purification efficiency and the recalculated model-based accumulated values becomes the sensor-based accumulated value.
- reaction ratio correction coefficient is the reciprocal of the efficiency correction coefficient
- the reason why the reaction ratio correction coefficient is the reciprocal of the efficiency correction coefficient is to maintain the urea injection amount equal to the previous state thereof so as not to change actual purification efficiency in the present disclosure, because, if the purification efficiency of the exhaust aftertreatment system is lowered by correcting the model used to calculate the urea injection amount, the exhaust aftertreatment system is regarded as a defeated device, which is illegal.
- the SCR apparatus 1 may consistently maintain suitable purification in compliance with regulations while the model purification efficiency is corrected to a suitable value.
- the method for controlling the exhaust aftertreatment system for vehicles further includes, when a next regeneration operation is performed after correcting the model purification efficiency, accumulating, by the controller 9 , NO x emission amounts measured by the rear end NO x sensor 7 of the SCR apparatus 1 and NO x emission amounts calculated by the NO x emission amount model respectively for a designated second reference time immediately after the regeneration operation is finished (S 110 ), determining, by the controller 9 , whether or not an accumulated value of the NO x emission amounts measured by the rear end NO x sensor 7 is greater than an accumulated value of the NO x emission amounts calculated by the NO x emission amount model (S 120 ); and correcting, by the controller 9 , the ammonia occludable amount of the SCR apparatus 1 when the accumulated value of the NO x emission amounts measured by the rear end NO x sensor 7 is greater than the accumulated value of the NO x emission amounts calculated by the NO x emission amount model (S 130 ).
- the ammonia occludable amount of the SCR apparatus 1 used to calculate the urea injection amount is corrected depending on the situation in the next regeneration operation.
- the reason for this is to prevent ammonia slip in which, if a reduction in the ammonia occludable amount due to aged deterioration of the SCR apparatus 1 is not properly considered, the amount of unreacted ammonia is emitted downstream from the SCR apparatus 1 due to an excessive urea injection amount.
- the ammonia occlusion amount of the SCR apparatus 1 may be expressed using the following equation:
- ammonia occlusion amount urea injection amount ⁇ urea amount used to reduce NO x ⁇ urea amount oxidized ⁇ unreacted urea amount.
- the ammonia occludable amount is to be suitably corrected using the second reference time for which the above situation is maintained.
- the accumulated value of the NO x emission amounts measured by the rear end NO x sensor 7 i.e., the sensor-based accumulated value
- the accumulated value of the NO x emission amounts calculated by the NO x emission amount model i.e., the model-based accumulated value.
- the sensor-based accumulated value is greater than the model-based accumulated value, as shown in FIG.
- the amount of ammonia slipped downstream from the SCR apparatus 1 is erroneously sensed as an NO x emission amount by the rear end NO x sensor 7 and such erroneous sensing is caused by an error in the ammonia occludable amount used to calculate the urea injection amount.
- FIG. 8 is a graph exemplarily showing a change in a value output by the rear end NO x sensor 7 depending on a change in an ammonia amount and a change in an NO x amount, and the NO x sensor 7 , which has the property of measuring both NO x and ammonia, erroneously senses ammonia slipped downstream from the SCR apparatus 1 as the NO emission amount.
- the controller 9 corrects the ammonia occludable amount so as to ultimately reduce the urea injection amount to an optimum level, thereby being capable of preventing emission of ammonia based on the unnecessary urea injection amount.
- the controller 9 corrects the ammonia occludable amount of the SCR apparatus 1 by multiplying the ammonia occludable amount by a designated occlusion coefficient, and the occlusion coefficient has a value in the range of 0 to 1.
- the ammonia occludable amount will be gradually decreased due to aged deterioration of the SCR apparatus 1 , and thus, the corrected ammonia occludable amount may be easily calculated by multiplying the previous ammonia occludable amount by the occlusion coefficient which is within the range of 0 to 1.
- controller 9 calculates the urea injection amount using the following equation:
- urea injection amount NO x inflow rate ⁇ (corrected NH 3 —NO x reaction ratio) ⁇ (corrected model purification efficiency)+(ammonia occludable amount ⁇ occlusion coefficient).
- the controller 9 controls the urea injection apparatus 5 to inject the calculated urea injection amount into the front end of the SCR apparatus 1 , the controller finds the value of the occlusion coefficient by gradually decreasing the occlusion coefficient until the NO x emission amount calculated by the rear end NO x sensor 7 becomes equal to the NO x emission amount calculated by the NO x emission amount model.
- the controller 9 corrects the ammonia occludable amount of the SCR apparatus 1 using the value of the occlusion coefficient when the NO x emission amount calculated by the rear end NO x sensor 7 becomes equal to the NO x emission amount calculated by the NO x emission amount model, and calculates the urea injection amount using the corrected ammonia occludable amount using the following equation:
- urea injection amount NO x inflow rate ⁇ (corrected NH 3 —NO x reaction ratio) ⁇ (corrected model purification efficiency)+(corrected ammonia occludable amount).
- the controller 9 controls the urea injection apparatus 5 to inject the calculated urea injection amount, and thus allows the SCR apparatus 1 to exhibit the optimal purification function without emitting ammonia.
- the second reference time may be set to be equal to the first reference time or to be slightly different from the first reference time.
- the second reference time may be set based on a time for which all ammonia is removed from the SCR apparatus 1 because the temperature of the SCR apparatus 1 is still high immediately after the regeneration operation and new ammonia has not started to be occluded in the SCR apparatus 1 , and the second reference time may be set to a different time from the first reference time as needed.
- the second reference time is set to be equal to the first reference time
- the controller 9 sequentially turns on a slip diagnosis flag after correcting the model purification efficiency, accumulates NO x emission amounts measured by the rear end NO x sensor 7 of the SCR apparatus 1 and NO x emission amounts calculated by the NO x emission amount model respectively for the first reference time immediately after the regeneration operation is finished (S 110 ), and determines whether or not the accumulated value of the NO x emission amounts measured by the rear end NO x sensor 7 is greater than the accumulated value of the NO x emission amounts calculated by the NO x emission amount model (S 120 ), and corrects the ammonia occludable amount of the SCR apparatus 1 (S 130 ), when the slip diagnosis flag is turned on.
- the controller 9 may turn off the slip diagnosis flag after correcting the ammonia occludable amount of the SCR apparatus 1 , and thus, again correct the model purification efficiency depending on the situation immediately after the next regeneration operation is performed.
- the present disclosure provides a method for controlling an exhaust aftertreatment system for vehicles in which ammonia slip of an SCR apparatus may be prevented without providing an ammonia sensor downstream from the SCR apparatus so as to avoid an increase in vehicle costs, a suitable amount of urea may be injected in consideration of a change in purification efficiency due to aged deterioration of the SCR apparatus, and ultimately the SCR apparatus may purify NO x in exhaust gas into the optimum state so as to satisfy various regulations.
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Abstract
Description
- This application claims the benefit of priority to Korean Patent Application No. 10-2020-0116085, filed on Sep. 10, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.
- The present disclosure relates to a method for controlling an exhaust aftertreatment system for vehicle engines.
- Nitrogen oxides (NOx) included in exhaust gas generated when the engine of a vehicle is operated are a serious factor causing air pollution, and thus, a urea-selective catalytic reduction (SCR) apparatus is applied as an exhaust aftertreatment apparatus configured to purify nitrogen oxides (NOx) exhausted from the vehicle.
- The SCR apparatus allows ammonia formed by pyrolysis of urea in exhaust gas to react with nitrogen oxides (NOx) with the aid of a catalyst so as to be purified into water and nitrogen.
- Urea injected upstream from the SCR apparatus should be injected in an amount suitable for purifying nitrogen oxides (NOx) in the exhaust gas.
- When an excessively large amount of urea is injected, ‘ammonia slip’, in which a surplus amount of ammonia which does not participate in reaction is exhausted, occurs and the excessively large amount of urea is consumed, and when an excessively small amount of urea is injected, unpurified nitrogen oxides (NOx) are discharged.
- In order to prevent ammonia slip of the SCR apparatus, an ammonia sensor may be installed downstream from the SCR apparatus, but the ammonia sensor is expensive and thus the cost of the vehicle is increased.
- The above description has been provided to aid in understanding of the background of the present disclosure and should not be interpreted as conventional technology known to those skilled in the art.
- The present disclosure has been made in view of the above problems, and it is an object of the present disclosure to provide a method for controlling an exhaust aftertreatment system for vehicles in which ammonia slip of a selective catalytic reduction (SCR) apparatus may be prevented without providing an ammonia sensor downstream from the SCR apparatus so as to avoid an increase in vehicle costs, a suitable amount of urea may be injected in consideration of a change in purification efficiency due to aged deterioration of the SCR apparatus, and ultimately the SCR apparatus may purify NOx in exhaust gas into the optimum state so as to satisfy various regulations.
- In accordance with the present disclosure, the above and other objects can be accomplished by the provision of a method for controlling an exhaust aftertreatment system for vehicles, the method including: determining, by a controller, whether or not a designated regeneration operation is finished; accumulating, by the controller, a first amount of NOx emission measured by a rear end NOx sensor of a selective catalytic reduction (SCR) apparatus and a second amount of NOx emission calculated by an NOx emission amount model respectively for a designated first reference period of time immediately after the regeneration operation is finished; determining, by the controller, whether or not a difference between an accumulated value of the first amount of NOx emission and an accumulated value of the second amount of NOx emission exceeds a designated reference value when the first reference period of time has elapsed; and correcting, by the controller, a model purification efficiency used in the NOx emission amount model using a sensor purification efficiency acquired by a front end NOx sensor and the rear end NOx sensor of the SCR apparatus when the difference between the accumulated values exceeds the reference value.
- In the correcting the model purification efficiency, the controller may correct the model purification efficiency by calculating an efficiency correction coefficient configured to make the model purification efficiency equal to the sensor purification efficiency, and multiplying the model purification efficiency by the efficiency correction coefficient.
- When the controller calculates a urea injection amount using corrected model purification efficiency acquired by multiplying the model purification efficiency by the efficiency correction coefficient, the controller may calculate the urea injection amount using a corrected NH3—NOx reaction ratio acquired by multiplying a NH3—NOx reaction ratio by a reaction ratio correction coefficient, which is a reciprocal of the efficiency correction coefficient.
- The method may further include, when a next regeneration operation is performed after the correcting the model purification efficiency, accumulating, by the controller, a third NOx emission amounts measured by the rear end NOx sensor of the SCR apparatus and a fourth NOx emission amounts calculated by the NOx emission amount model respectively for a designated second reference time immediately after the regeneration operation is finished, determining, by the controller, whether or not an accumulated value of the third NOx emission amounts measured by the rear end NOx sensor is greater than an accumulated value of the fourth NOx emission amounts calculated by the NOx emission amount model, and correcting, by the controller, an ammonia occludable amount of the SCR apparatus when the accumulated value of the third NOx emission amounts measured by the rear end NOx sensor is greater than the accumulated value of the fourth NOx emission amounts calculated by the NOx emission amount model.
- The controller may correct the ammonia occludable amount of the SCR apparatus by multiplying the ammonia occludable amount by a designated occlusion coefficient, and the occlusion coefficient may have a value in a range of 0 to 1.
- The controller may calculate the urea injection amount using a following equation,
-
urea injection amount=NOx inflow rate×(corrected NH3—NOx reaction ratio)×(corrected model purification efficiency)+(ammonia occludable amount×occlusion coefficient). - While the controller controls the calculated urea injection amount to be injected into a front end of the SCR apparatus, the controller may gradually decrease the occlusion coefficient until a fifth NOx emission amount calculated by the rear end NOx sensor becomes equal to a sixth NOx emission amount calculated by the NOx emission amount model.
- The controller may calculate a corrected ammonia occludable amount by correcting the ammonia occludable amount of the SCR apparatus using the occlusion coefficient when the fifth NOx emission amount calculated by the rear end NOx sensor becomes equal to the sixth NOx emission amount calculated by the NOx emission amount model, and the controller may calculate the urea injection amount using a following equation and controls the calculated urea injection amount to be injected,
-
urea injection amount=NOx inflow rate×(corrected NH3—NOx reaction ratio)×(corrected model purification efficiency)+(corrected ammonia occludable amount). - When the second reference time is set to be equal to the first reference time, the controller may sequentially turn on a slip diagnosis flag after correcting the model purification efficiency, accumulate the third NOx emission amounts measured by the rear end NOx sensor of the SCR apparatus and the fourth NOx emission amounts calculated by the NOx emission amount model respectively for the first reference time immediately after the regeneration operation is finished, and determine whether or not an accumulated value of the third NOx emission amounts measured by the rear end NOx sensor is greater than an accumulated value of the fourth NOx emission amounts calculated by the NOx emission amount model, and correct the ammonia occludable amount of the SCR apparatus, when the slip diagnosis flag is turned on.
- The controller may turn off the slip diagnosis flag after the correcting the ammonia occludable amount of the SCR apparatus.
- The NOx emission amount model may be calculated using a following equation,
-
NOx emission amount model=NOx inflow rate−NOx purification amount model=NOx inflow rate×(1−model purification efficiency), - where, NOx purification amount model=NOx inflow rate×model purification efficiency.
- The above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
-
FIG. 1 is a view exemplarily illustrating an exhaust aftertreatment system for vehicles to which the present disclosure is applicable; -
FIG. 2 is a flowchart illustrating a method for controlling an exhaust aftertreatment system for vehicles according to one embodiment of the present disclosure; -
FIG. 3 is a graph showing accumulated values of NOx emission amounts as time passes; -
FIG. 4 is a graph showing accumulated values of NOx emission amounts for a first reference time; -
FIG. 5 is another graph showing accumulated values of NOx emission amounts for the first reference time; -
FIG. 6 is a graph showing ammonia emission probability as time passes; -
FIG. 7 is a graph showing accumulated values of NOx emission amounts for a second reference time; and -
FIG. 8 is a graph showing a change in a value output by an NOx sensor depending on a change in an ammonia amount and a change in an NOx amount. - Reference will now be made in detail to the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
-
FIG. 1 is a view exemplarily illustrating an exhaust aftertreatment system for vehicles to which the present disclosure is applicable, a selective catalytic reduction (SCR)apparatus 1 configured to purify nitrogen oxides (NOx) in exhaust gas emitted from an engine is provided, a front end NOx sensor 3 configured to measure nitrogen oxides (NOx) in the exhaust gas flowing into theSCR apparatus 1 and aurea injection apparatus 5 configured to inject urea are provided in a region upstream from theSCR apparatus 1, and a rear end NOx sensor 7 configured to measure nitrogen oxides (NOx) in the exhaust gas having passed through theSCR apparatus 1 is provided in a region downstream from theSCR apparatus 1. - Here, the term ‘front end’ does not necessarily mean the front end of the
SCR apparatus 1, and is to be interpreted as any arbitrary position upstream from theSCR apparatus 1, which is suitable for measuring nitrogen oxides (NOx) flowing into theSCR apparatus 1. In addition, the term ‘rear end’ does not necessarily mean the rear end of theSCR apparatus 1, and is to be interpreted as any arbitrary position downstream from theSCR apparatus 1, which is suitable for measuring nitrogen oxides (NOx) emitted from theSCR apparatus 1. - A
controller 9 receives signals from the front end NOx sensor 3 and the rear end NOx sensor 7, and controls theurea injection apparatus 5 to inject urea. - In the present disclosure, the
controller 9 may be a computer or a processor such as a CPU, or more specifically, an electronic control unit (ECU) as an embedded system configured to control electrical systems in a vehicle. Thecontroller 9 may be programmed to communicate with the front end NOx sensor 3, the rear end NOx sensor 7, and theurea injection apparatus 5, so as to control the connected devices. - In the present disclosure, no separate ammonia sensor is provided downstream from the
SCR apparatus 1. - Referring to
FIG. 2 , a method for controlling the exhaust aftertreatment system for vehicles according to the present disclosure includes determining, by thecontroller 9, whether or not a designated regeneration operation is finished (S10), accumulating, by thecontroller 9, NOx emission amounts measured by the rear end NOx sensor 7 of theSCR apparatus 1 and NOx emission amounts calculated by an NOx emission amount model respectively for a designated first reference time immediately after the regeneration operation is finished (S20), determining, by thecontroller 9, whether or not a difference between an accumulated value of the NOx emission amounts measured by the rear end NOx sensor 7 and an accumulated value of the NOx emission amounts calculated by the NOx emission amount model exceeds a designated reference value when the first reference time has elapsed (S30), and correcting, by thecontroller 9, model purification efficiency used in the NOx emission amount model using sensor purification efficiency acquired by the front end NOx sensor 3 and the rear end NOx sensor 7 when the difference between the accumulated values exceeds the reference value (S40). - Here, an operation of increasing a temperature to a level at which all ammonia occluded in the
SCR apparatus 1 may be removed by raising the temperature of theSCR apparatus 1 to 500° C. or higher, such as regeneration of a diesel particulate filter (DPF), is called a regeneration operation. - Therefore, if the
SCR apparatus 1 includes an SCR-catalyzed diesel particulate filter (SDPF), i.e., a conventional DPF with SCR coating, or is formed by supporting an SCR catalyst on a carrier, when the above operation of increasing the temperature to the level at which all occluded ammonia is removed is performed, the regeneration operation is regarded as being performed. - For reference, in the present disclosure, as exemplarily shown in
FIG. 2 , the regeneration operation means regeneration of the DPF. Further, the operation ofFIG. 2 is continuously performed repeatedly during the driving of the vehicle. - The first reference time is set based on a time for which ammonia is not occluded in the
SCR apparatus 1 because the temperature of theSCR apparatus 1 is raised due to the above regeneration operation. - That is, the carrier or the DPF of the
SCR apparatus 1 is characterized in that ammonia is not occluded thereinto at a high temperature, and thus, during this time, an NOx purification amount and an NOx emission amount may be more precisely calculated using NOx and urea flowing into theSCR apparatus 1 and NOx discharged from theSCR apparatus 1, without regard to an ammonia occlusion amount and an ammonia occludable amount in theSCR apparatus 1. For this reason, in the present disclosure, this time is used. - Therefore, the first reference time is set based on the time for which occlusion of ammonia is not performed in the
SCR apparatus 1 for the above-stated reason. Particularly, the first reference time may be set to the time for which occlusion of ammonia is not performed in theSCR apparatus 1, and further include a point in time at which some occlusion of ammonia is performed without affecting achievement of the objects of the present disclosure. - The
controller 9 determines the suitability of the NOx emission amount model by accumulating NOx emission amounts measured by the rear end NOx sensor 7 and NOx emission amounts calculated by the NOx emission amount model respectively for the first reference time immediately after the regeneration operation and determining whether or not a difference between accumulated values exceeds the reference value, as described above. - Here, a value suitable for determining whether or not the above NOx emission amount model and the model purification efficiency need to be corrected, which is acquired by a great number of experiments and analyses, may be selected as the reference value, and the reference value may be set to 2% or the like, as exemplarily shown in
FIG. 2 . - That is, referring to
FIG. 2 , when the difference between the accumulated value of the NOx emission amounts measured by the rear end NOx sensor 7 (i.e., a sensor-based accumulated value) and the accumulated value of the NOx emission amounts calculated by the NOx emission amount model (i.e., a model-based accumulated value) exceeds 2%, it is determined that the characteristics of theSCR apparatus 1 are changed into a state in which the NOx emission amount model and the model purification efficiency are unsuitable, and thus the NOx emission amount model and the model purification efficiency are corrected. - Here, the NOx emission amount model is calculated using the following equation:
-
NOx emission amount model=NO inflow rate−NOx purification amount model=NOx inflow rate×(1−model purification efficiency). - The NO purification amount model is calculated using the following equation:
- NOx purification amount model=NO inflow rate×model purification efficiency.
- The model purification efficiency may be a value which the
controller 9 has as the purification efficiency of theSCR apparatus 1, and the NO inflow rate may be measured by the front end NO sensor 3. - As described above, in the NO emission amount model, the NO emission amount is calculated using the model purification efficiency, and thus, when there is an error in the model purification efficiency, an error in the NOx emission amount calculated by the NOx emission amount model occurs.
-
FIG. 3 is a graph showing accumulated values of NOx emission amounts as time passes, the graph shows the accumulated value of the NOx emission amounts measured by the rear end NOx sensor 7 of theSCR apparatus 1 and the accumulated value of the NOx emission amounts calculated by the NOx emission amount model and indicates occurrence of a difference therebetween, and such a difference indicates that there is an error in the model purification efficiency used in the NOx emission amount model. - For reference,
FIG. 3 also shows an accumulated value of NOx inflow rates calculated based on values measured by the front end NOx sensor 3, and a difference between the accumulated value of NOx inflow rates and the accumulated value of the NOx emission amounts of the rear end NOx sensor 7 may be interpreted as an accumulated value of amounts of NOx purified by theSCR apparatus 1. - In correcting the model purification efficiency (S40), the
controller 9 corrects the model purification efficiency by calculating an efficiency correction coefficient which makes the model purification efficiency equal to the sensor purification efficiency and multiplying the model purification efficiency by the efficiency correction coefficient. - For reference, the sensor purification efficiency is calculated using an NOx inflow rate based on the measured value of the front end NOx sensor 3 and an NOx emission amount based on the measured value of the rear end NOx sensor 7.
- That is, a corrected model purification efficiency is calculated by multiplying the model purification efficiency by the efficiency correction coefficient, and thereafter, the
controller 9 calculates a urea injection amount using the corrected model purification efficiency. - Further, when the
controller 9 calculates the urea injection amount using the corrected model purification efficiency calculated by multiplying the model purification efficiency by the efficiency correction coefficient, thecontroller 9 calculates the urea injection amount using a corrected NH3—NOx reaction ratio calculated by multiplying a NH3—NOx reaction ratio by a reaction ratio correction coefficient which is the reciprocal of the efficiency correction coefficient. - That is, the
controller 9 calculates the urea injection amount using the following equation, and then controls theurea injection apparatus 5 to inject the calculated urea injection amount: -
urea injection amount=NOx inflow rate×(NH3—NOx reaction ratio×reaction ratio correction coefficient)×(model purification efficiency×efficiency correction coefficient)+(ammonia occludable amount)=NOx inflow rate×(corrected NH3—NOx reaction ratio)×(corrected model purification efficiency)+(ammonia occludable amount). - Here, reaction ratio correction coefficient×efficiency correction coefficient=1.
- For example, on the assumption that the sensor purification efficiency is 80% when the NH3—NOx reaction ratio is 0.37 and the model purification efficiency is 70%, an error in the model purification efficiency in the current state is 10% and, in order to reduce the error, the model purification efficiency is corrected as follows.
-
rea injection amount=NOx inflow rate×(0.37)×(0.7) <before correction> -
urea injection amount=NOx inflow rate×(0.37×0.875)×(0.7×1.142)=NOx inflow rate×(0.324)×(0.8) <after correction> - Here, 0.875×1.142=1.
- For reference, the ammonia occludable amount used to calculate the urea injection amount is a constant which is merely added, and will thus be omitted for the purpose of brevity of description.
- That is, in the above example, because the corrected model purification efficiency becomes 0.8 (80%) and is exactly equal to the sensor purification efficiency, an accumulated value of NOx emission amounts calculated by the NOx emission amount model using the corrected model purification efficiency (i.e., a recalculated model-based accumulated value) becomes equal to the sensor-based accumulated value, and thus, the error is removed.
-
FIG. 2 illustrates that the model purification efficiency is corrected, the model-based accumulated value is recalculated using the corrected model purification efficiency, the recalculated model-based accumulated value is compared with the sensor-based accumulated value, it is confirmed that a difference between the recalculated model-based accumulated value and the sensor-based accumulated value is less than the reference value, and then the corrected model purification efficiency is reflected as a learning value. - For reference,
FIG. 4 indicates that, when the sensor-based accumulated value is greater than the model-based accumulated value after the first reference time, the model-based accumulated value is recalculated using the above-corrected purification efficiency and the recalculated model-based accumulated value becomes the sensor-based accumulated value, andFIG. 5 indicates that, when the sensor-based accumulated value is less than the model-based accumulated value after the first reference time, the model-based accumulated value is recalculated using the above-corrected purification efficiency and the recalculated model-based accumulated values becomes the sensor-based accumulated value. - Here, the reason why the reaction ratio correction coefficient is the reciprocal of the efficiency correction coefficient is to maintain the urea injection amount equal to the previous state thereof so as not to change actual purification efficiency in the present disclosure, because, if the purification efficiency of the exhaust aftertreatment system is lowered by correcting the model used to calculate the urea injection amount, the exhaust aftertreatment system is regarded as a defeated device, which is illegal.
- Therefore, according to the present disclosure, in consideration of a change in the model purification efficiency due to aged deterioration of the
SCR apparatus 1, theSCR apparatus 1 may consistently maintain suitable purification in compliance with regulations while the model purification efficiency is corrected to a suitable value. - The method for controlling the exhaust aftertreatment system for vehicles according to the present disclosure further includes, when a next regeneration operation is performed after correcting the model purification efficiency, accumulating, by the
controller 9, NOx emission amounts measured by the rear end NOx sensor 7 of theSCR apparatus 1 and NOx emission amounts calculated by the NOx emission amount model respectively for a designated second reference time immediately after the regeneration operation is finished (S110), determining, by thecontroller 9, whether or not an accumulated value of the NOx emission amounts measured by the rear end NOx sensor 7 is greater than an accumulated value of the NOx emission amounts calculated by the NOx emission amount model (S120); and correcting, by thecontroller 9, the ammonia occludable amount of theSCR apparatus 1 when the accumulated value of the NOx emission amounts measured by the rear end NOx sensor 7 is greater than the accumulated value of the NOx emission amounts calculated by the NOx emission amount model (S130). - That is, when the regeneration operation is repeated, if a process of learning the corrected model purification efficiency in the previous regeneration operation is performed, the ammonia occludable amount of the
SCR apparatus 1 used to calculate the urea injection amount is corrected depending on the situation in the next regeneration operation. - The reason for this is to prevent ammonia slip in which, if a reduction in the ammonia occludable amount due to aged deterioration of the
SCR apparatus 1 is not properly considered, the amount of unreacted ammonia is emitted downstream from theSCR apparatus 1 due to an excessive urea injection amount. - Referring to
FIG. 6 , when regeneration of the DPF is repeated as time passes, the possibility of ammonia slip from theSCR apparatus 1 gradually increases as time passes, increases sharply when the possibility of ammonia slip exceeds a designated level, and is then eliminated due to regeneration of the DPF, and such a process is repeated. - The ammonia occlusion amount of the
SCR apparatus 1 may be expressed using the following equation: -
ammonia occlusion amount=urea injection amount−urea amount used to reduce NOx−urea amount oxidized−unreacted urea amount. - Here, accurate modeling of the amount of urea oxidized and the amount of urea which does not participate in reaction, i.e., the amount of urea which is occluded into the wall of the
SCR apparatus 1 but has a remarkably low reaction rate, or is occluded into the wall of theSCR apparatus 1 and does not thus actually participate in the reaction, is impossible, and as a result, precise detection of the ammonia occludable amount of theSCR apparatus 1 is impossible. - However, because all ammonia occluded in the
SCR apparatus 1 is removed and thus no ammonia is occluded in theSCR apparatus 1 immediately after the regeneration operation, such as regeneration of the DPF, is performed, in the present disclosure, the ammonia occludable amount is to be suitably corrected using the second reference time for which the above situation is maintained. - That is, because the model purification efficiency was corrected in the previous regeneration operation and the NOx emission amount model was corrected thereby, the accumulated value of the NOx emission amounts measured by the rear end NOx sensor 7 (i.e., the sensor-based accumulated value) for the second reference time should be almost equal to the accumulated value of the NOx emission amounts calculated by the NOx emission amount model (i.e., the model-based accumulated value). However, when the sensor-based accumulated value is greater than the model-based accumulated value, as shown in
FIG. 7 , it is regarded that the amount of ammonia slipped downstream from theSCR apparatus 1 is erroneously sensed as an NOx emission amount by the rear end NOx sensor 7 and such erroneous sensing is caused by an error in the ammonia occludable amount used to calculate the urea injection amount. - For reference,
FIG. 8 is a graph exemplarily showing a change in a value output by the rear end NOx sensor 7 depending on a change in an ammonia amount and a change in an NOx amount, and the NOx sensor 7, which has the property of measuring both NOx and ammonia, erroneously senses ammonia slipped downstream from theSCR apparatus 1 as the NO emission amount. - Therefore, when the sensor-based accumulated value for the second reference time is greater than the model-based accumulated value, as described above, the
controller 9 corrects the ammonia occludable amount so as to ultimately reduce the urea injection amount to an optimum level, thereby being capable of preventing emission of ammonia based on the unnecessary urea injection amount. - The
controller 9 corrects the ammonia occludable amount of theSCR apparatus 1 by multiplying the ammonia occludable amount by a designated occlusion coefficient, and the occlusion coefficient has a value in the range of 0 to 1. - That is, the ammonia occludable amount will be gradually decreased due to aged deterioration of the
SCR apparatus 1, and thus, the corrected ammonia occludable amount may be easily calculated by multiplying the previous ammonia occludable amount by the occlusion coefficient which is within the range of 0 to 1. - In more detail, the
controller 9 calculates the urea injection amount using the following equation: -
urea injection amount=NOx inflow rate×(corrected NH3—NOx reaction ratio)×(corrected model purification efficiency)+(ammonia occludable amount×occlusion coefficient). - While the
controller 9 controls theurea injection apparatus 5 to inject the calculated urea injection amount into the front end of theSCR apparatus 1, the controller finds the value of the occlusion coefficient by gradually decreasing the occlusion coefficient until the NOx emission amount calculated by the rear end NOx sensor 7 becomes equal to the NOx emission amount calculated by the NOx emission amount model. - That is, the
controller 9 corrects the ammonia occludable amount of theSCR apparatus 1 using the value of the occlusion coefficient when the NOx emission amount calculated by the rear end NOx sensor 7 becomes equal to the NOx emission amount calculated by the NOx emission amount model, and calculates the urea injection amount using the corrected ammonia occludable amount using the following equation: -
urea injection amount=NOx inflow rate×(corrected NH3—NOx reaction ratio)×(corrected model purification efficiency)+(corrected ammonia occludable amount). - The
controller 9 controls theurea injection apparatus 5 to inject the calculated urea injection amount, and thus allows theSCR apparatus 1 to exhibit the optimal purification function without emitting ammonia. - Here, the second reference time may be set to be equal to the first reference time or to be slightly different from the first reference time.
- That is, the second reference time may be set based on a time for which all ammonia is removed from the
SCR apparatus 1 because the temperature of theSCR apparatus 1 is still high immediately after the regeneration operation and new ammonia has not started to be occluded in theSCR apparatus 1, and the second reference time may be set to a different time from the first reference time as needed. - For reference, in the embodiment shown in
FIG. 2 , the second reference time is set to be equal to the first reference time, and thecontroller 9 sequentially turns on a slip diagnosis flag after correcting the model purification efficiency, accumulates NOx emission amounts measured by the rear end NOx sensor 7 of theSCR apparatus 1 and NOx emission amounts calculated by the NOx emission amount model respectively for the first reference time immediately after the regeneration operation is finished (S110), and determines whether or not the accumulated value of the NOx emission amounts measured by the rear end NOx sensor 7 is greater than the accumulated value of the NOx emission amounts calculated by the NOx emission amount model (S120), and corrects the ammonia occludable amount of the SCR apparatus 1 (S130), when the slip diagnosis flag is turned on. - The
controller 9 may turn off the slip diagnosis flag after correcting the ammonia occludable amount of theSCR apparatus 1, and thus, again correct the model purification efficiency depending on the situation immediately after the next regeneration operation is performed. - As is apparent from the above description, the present disclosure provides a method for controlling an exhaust aftertreatment system for vehicles in which ammonia slip of an SCR apparatus may be prevented without providing an ammonia sensor downstream from the SCR apparatus so as to avoid an increase in vehicle costs, a suitable amount of urea may be injected in consideration of a change in purification efficiency due to aged deterioration of the SCR apparatus, and ultimately the SCR apparatus may purify NOx in exhaust gas into the optimum state so as to satisfy various regulations.
- Although the exemplary embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.
Claims (10)
urea injection amount=NOx inflow rate×(corrected NH3—NOx reaction ratio)×(corrected model purification efficiency)+(ammonia occludable amount×occlusion coefficient), and
urea injection amount=NOx inflow rate×(corrected NH3—NOx reaction ratio)×(corrected model purification efficiency)+(corrected ammonia occludable amount).
NOx emission amount model=NOx inflow rate−NOx purification amount model=NOx inflow rate×(1−model purification efficiency),
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KR (1) | KR20220033793A (en) |
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CN116044551A (en) * | 2023-04-03 | 2023-05-02 | 潍柴动力股份有限公司 | Engine urea injection control method and device and vehicle |
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SE539382C2 (en) | 2012-07-05 | 2017-09-05 | Scania Cv Ab | SCR system and procedure for cleaning exhaust gases in an SCR system |
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