KR100906880B1 - How to Monitor Catalytic Efficiency of Lean Knox Traps - Google Patents
How to Monitor Catalytic Efficiency of Lean Knox Traps Download PDFInfo
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- KR100906880B1 KR100906880B1 KR1020080029456A KR20080029456A KR100906880B1 KR 100906880 B1 KR100906880 B1 KR 100906880B1 KR 1020080029456 A KR1020080029456 A KR 1020080029456A KR 20080029456 A KR20080029456 A KR 20080029456A KR 100906880 B1 KR100906880 B1 KR 100906880B1
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- 230000003197 catalytic effect Effects 0.000 title claims abstract description 10
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 68
- 239000001301 oxygen Substances 0.000 claims abstract description 68
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 68
- 239000003054 catalyst Substances 0.000 claims abstract description 52
- 238000000034 method Methods 0.000 claims abstract description 35
- 238000012544 monitoring process Methods 0.000 claims abstract description 34
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 28
- 238000002347 injection Methods 0.000 claims abstract description 8
- 239000007924 injection Substances 0.000 claims abstract description 8
- 239000002283 diesel fuel Substances 0.000 claims description 4
- 239000000446 fuel Substances 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000033228 biological regulation Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
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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
- F01N9/00—Electrical control of exhaust gas treating apparatus
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60Y—INDEXING SCHEME RELATING TO ASPECTS CROSS-CUTTING VEHICLE TECHNOLOGY
- B60Y2400/00—Special features of vehicle units
- B60Y2400/90—Driver alarms
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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
- F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
- F01N2550/02—Catalytic activity of catalytic converters
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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
- F01N2560/025—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting O2, e.g. lambda sensors
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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
- F01N2900/0416—Methods of control or diagnosing using the state of a sensor, e.g. of an exhaust gas sensor
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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
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- Combustion & Propulsion (AREA)
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- General Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Combined Controls Of Internal Combustion Engines (AREA)
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Abstract
본 발명은 린 녹스 트랩 시스템의 전단 및 후단에 장착된 산소센서를 이용하여 린 녹스 트랩의 촉매 효율을 모니터링하는 린 녹스 트랩의 촉매 효율 모니터링 방법에 관한 것이다.The present invention relates to a catalytic efficiency monitoring method of a lean nox trap, which monitors the catalytic efficiency of a lean nox trap using oxygen sensors mounted at the front and rear ends of the lean nox trap system.
본 발명의 린 녹스 트랩의 촉매 효율 모니터링 방법은 2차 분사 인젝터를 통하여 NOx를 환원시키기 위한 환원제를 공급하는 제1 단계와; 린 녹스 트랩의 전단에 장착된 산소센서를 통하여 상기 환원제의 공급량을 측정하고, 상기 린 녹스 트랩의 후단에 장착된 산소센서를 통하여 환원되는 산소량을 측정하는 제2 단계와; 상기 환원되는 산소량이 제1 한계값보다 작은가를 판단하는 제3 단계와; 상기 환원되는 산소량이 제1 한계값보다 작으면, 상기 환원되는 산소량이 제2 한계값보다 작은가를 판단하는 제4 단계와; 상기 환원되는 산소량이 상기 제2 한계값보다 작으면, 상기 린 녹스 트랩 촉매 효율이 저하되었다라고 판단하고, 경고등을 점등하는 제5 단계를 포함한다.The catalyst efficiency monitoring method of the lean knox trap of the present invention includes a first step of supplying a reducing agent for reducing NOx through a secondary injection injector; A second step of measuring a supply amount of the reducing agent through an oxygen sensor mounted at a front end of the lean nox trap and measuring an amount of oxygen reduced through an oxygen sensor mounted at a rear end of the lean nox trap; A third step of determining whether the reduced amount of oxygen is less than a first threshold value; A fourth step of determining whether the amount of reduced oxygen is less than a second limit value when the amount of reduced oxygen is smaller than a first limit value; If the amount of oxygen to be reduced is less than the second threshold value, it is determined that the lean Knox trap catalyst efficiency is lowered, and a fifth step of turning on a warning light.
Description
본 발명은 린 녹스 트랩의 촉매 효율 모니터링 방법에 관한 것으로, 특히 린 녹스 트랩 시스템의 전단 및 후단에 장착된 산소센서를 이용하여 린 녹스 트랩의 촉매 효율을 모니터링하는 린 녹스 트랩의 촉매 효율 모니터링 방법에 관한 것이다.The present invention relates to a method for monitoring the catalytic efficiency of a lean nox trap, and more particularly, to a method for monitoring the catalytic efficiency of a lean nox trap using an oxygen sensor mounted at the front and the rear of the lean nox trap system. It is about.
배기가스에 포함된 NOx를 제거하기 위한 기술의 하나로, 연료 린(Lean) 구간 중 촉매에 흡장된 NOx를 연료 리치(rich) 구간의 디젤 연료를 환원제로 이용하여 환원시킴으로써 배기가스에서 NOx를 제거하는 린 녹스 트랩(Lean NOx Trap 이하, LNT) 시스템이 있다.As a technology for removing NOx contained in exhaust gas, NOx is removed from exhaust gas by reducing NOx stored in catalyst in fuel lean section by using diesel fuel in fuel rich section as a reducing agent. There is a Lean NOx Trap (LNT) system.
LNT 시스템은 주행 시간이 증가하면 NOx의 변환 효율이 떨어진다. 따라서, 북미 및 유럽의 디젤 배기 규제에서는 NOx 규제치 초과를 방지하기 위하여 LNT의 촉매 효율을 모니터링하도록 규정하고 있다.In LNT systems, the conversion efficiency of NOx decreases as the driving time increases. Therefore, diesel exhaust regulations in North America and Europe require that the catalyst efficiency of LNT be monitored to prevent exceeding NOx limits.
LNT의 촉매 효율을 모니터링하기 위해서는 NOx 센서가 필요하다. 그런데, NOx 센서가 고가임에 따라 LNT의 촉매 효율을 모니터링하기 위하여 LNT 시스템에 NOx 센서를 설치하게 되면 원가가 상승하는 문제점이 있다.A NOx sensor is needed to monitor the catalyst efficiency of the LNT. However, as the NOx sensor is expensive, there is a problem in that the cost increases when the NOx sensor is installed in the LNT system to monitor the catalyst efficiency of the LNT.
따라서, 본 발명의 목적은 LNT 시스템의 전단 및 후단에 장착된 산소센서를 이용하여 LNT의 촉매 효율을 모니터링하는 LNT의 촉매 효율 모니터링 방법을 제공하는 것이다.Accordingly, an object of the present invention is to provide a catalyst efficiency monitoring method of LNT that monitors catalyst efficiency of LNT using oxygen sensors mounted at the front and rear ends of the LNT system.
상기의 목적을 달성하기 위하여, 본 발명의 실시 예에 따른 린 녹스 트랩 촉매 효율 모니터링 방법은 2차 분사 인젝터를 통하여 NOx를 환원시키기 위한 환원제를 공급하는 제1 단계와; 린 녹스 트랩의 전단에 장착된 산소센서를 통하여 상기 환원제의 공급량을 측정하고, 상기 린 녹스 트랩의 후단에 장착된 산소센서를 통하여 환원되는 산소량을 측정하는 제2 단계와; 상기 환원되는 산소량이 제1 한계값보다 작은가를 판단하는 제3 단계와; 상기 환원되는 산소량이 제1 한계값보다 작으면, 상기 환원되는 산소량이 제2 한계값보다 작은가를 판단하는 제4 단계와; 상기 환원되는 산소량이 상기 제2 한계값보다 작으면, 상기 린 녹스 트랩 촉매 효율이 저하되었다라고 판단하고, 경고등을 점등하는 제5 단계를 포함한다.In order to achieve the above object, the lean Knox trap catalyst efficiency monitoring method according to an embodiment of the present invention comprises a first step of supplying a reducing agent for reducing NOx through the secondary injection injector; A second step of measuring a supply amount of the reducing agent through an oxygen sensor mounted at a front end of the lean nox trap and measuring an amount of oxygen reduced through an oxygen sensor mounted at a rear end of the lean nox trap; A third step of determining whether the reduced amount of oxygen is less than a first threshold value; A fourth step of determining whether the amount of reduced oxygen is less than a second limit value when the amount of reduced oxygen is smaller than a first limit value; If the amount of oxygen to be reduced is less than the second threshold value, it is determined that the lean Knox trap catalyst efficiency is lowered, and a fifth step of turning on a warning light.
상기 린 녹스 트랩 촉매 효율 모니터링 방법은 상기 환원되는 산소량이 상기 제1 한계값보다 작지 않으면, 경고등을 점등하는 단계를 더 포함한다.The lean knox trap catalyst efficiency monitoring method further comprises the step of turning on a warning light if the amount of reduced oxygen is less than the first limit value.
상기 제1 한계값은 린 녹스 트랩 시스템이 차량에서 이탈되었을 것으로 예상되는 산소량이며, 상기 제2 한계값은 린 녹스 트랩 촉매 효율이 저하되었다라고 판 단할 수 있는 산소량이다.The first threshold is the amount of oxygen that the lean knox trap system is expected to leave the vehicle, and the second threshold is the amount of oxygen that can determine that the lean knox trap catalyst efficiency is degraded.
상기 환원제의 공급량은 상기 린 녹스 트랩의 전방에 장착된 산소센서 신호의 면적이고, 상기 환원되는 산소량은 상기 린 녹스 트랩의 후방에 장착된 산소센서 신호의 면적이다.The supply amount of the reducing agent is the area of the oxygen sensor signal mounted in front of the lean knox trap, and the reduced oxygen amount is the area of the oxygen sensor signal mounted at the rear of the lean knox trap.
상기 린 녹스 트랩 촉매 효율 모니터링 방법은 상기 제2 단계에서 측정한 상기 환원되는 산소량을 이용하여, 상기 NOx의 환원에 사용된 환원제의 양을 계산하는 단계와; 제2 단계에서 측정한 상기 환원제의 공급량에서 상기 NOx의 환원에 사용된 환원제의 양을 차감하여 환원제의 슬립량을 계산하는 단계와; 상기 환원제의 공급량 대비 상기 환원제의 슬립량의 양의 비가 일정비를 초과하는가를 판단하는 단계와; 상기 환원제의 공급량 대비 상기 환원제의 슬립량의 양의 비가 일정비를 초과하면, 경고등을 점등하는 단계를 더 포함한다.The lean knox trap catalyst efficiency monitoring method includes calculating an amount of a reducing agent used to reduce the NOx by using the amount of reduced oxygen measured in the second step; Calculating a slip amount of the reducing agent by subtracting the amount of the reducing agent used to reduce the NOx from the supply amount of the reducing agent measured in the second step; Determining whether a ratio of the amount of slip amount of the reducing agent to the supply amount of the reducing agent exceeds a predetermined ratio; When the ratio of the amount of the slip amount of the reducing agent to the supply amount of the reducing agent exceeds a certain ratio, further comprising the step of lighting a warning light.
상기 환원제는 디젤 연료에 포함된 HC이다.The reducing agent is HC contained in the diesel fuel.
상기 린 녹스 트랩 촉매 효율 모니터링 방법은 알피엠을 읽어드려 차량이 아이들 상태인가를 판단하는 단계와; 차량이 아이들 상태이면, 상기 린 녹스 트랩 촉매의 온도와 SOx 로딩 양을 읽어드려 상기 린 녹스 트랩의 촉매가 일정 온도 미만이고 SOx 로딩 양이 일정량 미만인가를 판단하는 단계와; 상기 린 녹스 트랩의 촉매가 일정 온도 미만이고 SOx 로딩 양이 일정량 미만이면 상기 제1 단계 내지 제5 단계를 수행한다.The lean Knox trap catalyst efficiency monitoring method may include: reading an LPPM to determine whether the vehicle is in an idle state; If the vehicle is in an idle state, reading the temperature of the lean knox trap catalyst and the amount of SOx loading to determine whether the catalyst of the lean knox trap is below a certain temperature and the amount of SOx loading is less than a certain amount; When the catalyst of the lean knox trap is below a certain temperature and the amount of SOx loading is less than a certain amount, the first to fifth steps are performed.
상기와 같이, 본 발명의 실시 예에 따른 LNT 촉매 효율 모니터링 방법은 LNT 시스템의 전단 및 후단에 장착된 산소센서를 이용하여 LNT의 촉매 효율을 모니터링한다. 따라서, 본 발명의 실시 예에 따른 LNT 촉매 효율 모니터링 방법은 LNT의 촉매 효율을 모니터링하기 위한 NOx 센서를 제거함으로써 원가를 절감할 수 있다.As described above, the LNT catalyst efficiency monitoring method according to an embodiment of the present invention monitors the catalytic efficiency of the LNT using oxygen sensors mounted at the front and rear ends of the LNT system. Therefore, the LNT catalyst efficiency monitoring method according to an embodiment of the present invention can reduce the cost by removing the NOx sensor for monitoring the catalyst efficiency of the LNT.
이하, 도 1 및 도 2를 참조하여 본 발명의 바람직한 실시 예에 대하여 설명하기로 한다.Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 1 and 2.
도 1은 본 발명의 실시 예에 따른 LNT 촉매 효율 모니터링 방법을 나타내는 순서도이다.1 is a flowchart illustrating a method for monitoring LNT catalyst efficiency according to an embodiment of the present invention.
본 발명의 실시 예에 따른 LNT 촉매 효율 모니터링 방법은 아이들 상태에서 LNT 촉매 효율 모니터링을 실시한다. 따라서, 본 발명의 LNT 촉매 효율 모니터링 방법은 먼저, RPM을 읽어드려(S10), 현재 차량이 아이들(Idle) 상태인가를 판단한다(S12). S12 단계의 판단 결과, 차량이 아이들 상태이면, 본 발명의 LNT 촉매 효율 모니터링 방법은 LNT 촉매의 온도와 SOx 로딩(Loading) 양을 읽어드려(S14), LNT 촉매가 일정 온도 미만이고 SOx 로딩 양이 일정량 미만인가를 판단한다(S16). LNT 촉매는 LNT 촉매가 일정 온도를 넘어가면 효율이 급격히 저하된다. 따라서, 본 발명의 LNT 촉매 효율 모니터링 방법은 LNT 촉매 효율 모니터링을 실시하기에 앞서, LNT 촉매가 일정 온도를 넘어가는가를 판단하고, 넘어가면 LNT 촉매 효율 모니터링을 실시하지 않는다. 그리고, SOx의 로딩 양이 일정량 이상이면, SOx의 환 원이 실시됨에 의하여 LNT 촉매 효율이 저하될 수 있으므로, LNT 촉매 효율 모니터링이 SOx의 환원의 실시 등에 의하여 방해받지 않도록 SOx의 로딩 양이 일정량 이상이면 실시하지 않는다.The LNT catalyst efficiency monitoring method according to an embodiment of the present invention performs LNT catalyst efficiency monitoring in an idle state. Therefore, in the LNT catalyst efficiency monitoring method of the present invention, first, by reading the RPM (S10), it is determined whether the current vehicle (idle) state (S12). As a result of the determination in step S12, when the vehicle is in the idle state, the LNT catalyst efficiency monitoring method of the present invention reads the temperature and SOx loading amount of the LNT catalyst (S14), and the LNT catalyst is below a predetermined temperature and the SOx loading amount is increased. It is determined whether or not less than a predetermined amount (S16). LNT catalyst is rapidly reduced efficiency when the LNT catalyst exceeds a certain temperature. Therefore, the LNT catalyst efficiency monitoring method of the present invention determines whether the LNT catalyst exceeds a predetermined temperature before performing the LNT catalyst efficiency monitoring, and does not perform the LNT catalyst efficiency monitoring. If the loading amount of SOx is greater than or equal to a certain amount, the LNT catalyst efficiency may be reduced by reducing SOx, so that the loading amount of SOx is not less than a certain amount so that the monitoring of LNT catalyst efficiency is not hindered by implementation of reduction of SOx. If not, do not perform.
본 발명의 LNT 촉매 효율 모니터링 방법은 S16 단계의 판단 결과, LNT 촉매가 일정 온도 미만이고 SOx 로딩 양이 일정량 미만이면, 2차 분사 인젝터를 통하여 NOx를 제거하기 위한 환원제(이하, HC)로 디젤 연료를 공급한다(S18). 그런 다음, LNT 시스템의 전단에 장착된 산소센서를 통하여 HC의 공급량을 측정하고, LNT 시스템의 후단에 장착된 산소센서를 통하여 환원되는 산소량을 측정한다(S20).In the LNT catalyst efficiency monitoring method of the present invention, if the LNT catalyst is less than the predetermined temperature and the SOx loading amount is less than the predetermined amount, the fuel is diesel fuel as a reducing agent (hereinafter, HC) for removing NOx through the secondary injection injector. Supply (S18). Then, the amount of HC supplied is measured through an oxygen sensor mounted at the front of the LNT system, and the amount of oxygen is reduced through an oxygen sensor mounted at the rear of the LNT system (S20).
도 2는 2차 분사를 통한 HC 공급 이후에 LNT의 전방에 장착된 산소센서와 후방에 장착된 산소센서가 측정하는 값을 나타내는 그래프이다.2 is a graph showing values measured by an oxygen sensor mounted at the front of the LNT and an oxygen sensor mounted at the rear after HC supply through the secondary injection.
0.5 ~ 1.5s 사이의 짧은 순간에 2차 분사를 통해 HC가 공급되면, LNT의 전방에 장착된 산소센서는 도 2에 도시된 바와 같이, 0.5 ~ 1.5s 사이의 짧은 순간에 연료 리치 상태라는 것을 측정한다. 즉, LNT의 전방에 장착된 산소센서는 2차 분사를 통해 HC가 분사되면, 산소센서 신호의 면적으로부터 HC의 공급량을 측정한다. 그리고, LNT의 후방에 장착된 산소센서는 산소센서 신호의 면적으로부터 환원되는 산소량을 측정한다. LNT의 후방에 장착된 산소센서는 a와 같이 면적이 작은 신호를 출력할 수도 있으면, b와 같이 면적이 큰 신호를 출력할 수도 있다.When HC is supplied through the secondary injection at a short time between 0.5 and 1.5 s, the oxygen sensor mounted in front of the LNT is in a fuel rich state at a short time between 0.5 and 1.5 s, as shown in FIG. Measure That is, when HC is injected through the secondary injection, the oxygen sensor mounted in front of the LNT measures the HC supply amount from the area of the oxygen sensor signal. The oxygen sensor mounted on the rear of the LNT measures the amount of oxygen reduced from the area of the oxygen sensor signal. The oxygen sensor mounted on the rear of the LNT may output a signal having a large area, such as b, if it may output a signal having a small area.
본 발명의 LNT 촉매 효율 모니터링 방법은 LNT의 후방에 장착된 산소센서를 통한 환원되는 산소량이 측정되면, NOx의 환원에 사용된 HC 양을 계산한다(S22). 그리고, 본 발명의 LNT 촉매 효율 모니터링 방법은 LNT의 전방에 장착된 산소센서 가 측정한 HC 양에서 NOx의 환원에 사용된 HC 양을 차감하여 NOx의 환원에 사용되지 않은 HC 양 즉, HC 슬립량을 계산한다(S24).The LNT catalyst efficiency monitoring method of the present invention calculates the amount of HC used for reduction of NOx when the amount of oxygen reduced through the oxygen sensor mounted to the rear of the LNT is measured (S22). In addition, the LNT catalyst efficiency monitoring method of the present invention subtracts the amount of HC used for reducing NOx from the amount of HC measured by an oxygen sensor mounted in front of the LNT, that is, the amount of HC not used for reducing NOx, that is, the HC slip amount. Calculate (S24).
그런 다음, 본 발명의 LNT 촉매 효율 모니터링 방법은 LNT의 후방에 장착된 산소센서가 측정한 환원되는 산소량이 제1 한계값보다 작은가를 판단하여(S26), 작으면, 경고등을 점등한다(S28). 이때, 제1 한계값은 LNT 시스템이 차량에서 이탈되었을 것으로 예상되는 LNT의 후방에 장착된 산소센서가 측정한 산소량이다. S26 단계에서 LNT의 후방에 장착된 산소센서가 측정한 환원되는 산소량이 제1 한계값보다 작지 않으면, LNT의 후방에 장착된 산소센서가 측정한 환원되는 산소량이 제2 한계값보다 작은가를 판단한다(S30). 이때, 제2 한계값은 LNT 촉매 효율이 저하되었다라고 판단할 수 있는 LNT의 후방에 장착된 산소센서가 측정한 산소량이다. S30 단계의 판단 결과, LNT의 후방에 장착된 산소센서가 측정한 산소량이 제2 한계값보다 작으면, 본 발명의 LNT 촉매 효율 모니터링 방법은 LNT 촉매 효율이 저하되었다라고 판단하고, 경고등을 점등한다(S28). 여기서, 제1 및 제2 한계값은 실험을 통하여 얻어지는 값으로 공급되는 HC 양에 대비하여 정하여져 있다.Then, the LNT catalyst efficiency monitoring method of the present invention determines whether the amount of reduced oxygen measured by the oxygen sensor mounted to the rear of the LNT is less than the first limit value (S26), if it is small, turns on the warning light (S28) . At this time, the first limit value is the amount of oxygen measured by an oxygen sensor mounted to the rear of the LNT in which the LNT system is expected to be separated from the vehicle. If the amount of reduced oxygen measured by the oxygen sensor mounted to the rear of the LNT in step S26 is not less than the first limit value, it is determined whether the amount of reduced oxygen measured by the oxygen sensor mounted to the rear of the LNT is smaller than the second limit value. (S30). At this time, the second limit value is the amount of oxygen measured by the oxygen sensor mounted to the rear of the LNT, which can be judged that the LNT catalyst efficiency is lowered. As a result of the determination in step S30, if the amount of oxygen measured by the oxygen sensor mounted to the rear of the LNT is less than the second limit value, the LNT catalyst efficiency monitoring method of the present invention determines that the LNT catalyst efficiency is reduced, and lights a warning light. (S28). Here, the first and the second limit values are determined relative to the amount of HC supplied as the value obtained through the experiment.
그리고, 본 발명의 LNT 촉매 효율 모니터링 방법은 HC 공급량에 대한 HC 슬립량에 대한 비가 일정비를 초과하는가를 판단한다(S32). S32의 판단 결과, HC 공급량에 대한 HC 슬립량에 대한 비가 일정비를 초과하면, 공급되는 HC 양에 비하여 HC 슬립량이 많다는 것으로, NOx의 환원을 위하여 너무 많은 연료가 공급되고 있는 것이므로, 연비가 나빠진다. 따라서, 본 발명의 LNT 촉매 효율 모니터링 방법은 HC 공급량에 대한 HC 슬립량에 대한 비가 일정비를 초과하면, 또한 경고등을 점등 하여(S34) 이를 사용자에게 알린다. 여기서, HC 공급량에 대한 HC 슬립량에 대한 비가 일정비는 실험을 통하여 얻어지는 값으로 공급되는 HC 양에 대비하여 정하여져 있다.In addition, the LNT catalyst efficiency monitoring method of the present invention determines whether the ratio of the HC slip amount to the HC feed amount exceeds a predetermined ratio (S32). As a result of the determination in S32, when the ratio of the HC slip amount to the HC supply amount exceeds a certain ratio, the HC slip amount is larger than the HC amount supplied, and because too much fuel is supplied for the reduction of NOx, Falls out. Therefore, the LNT catalyst efficiency monitoring method of the present invention, if the ratio of the HC slip amount to the HC feed amount exceeds a certain ratio, also turns on the warning light (S34) to inform the user. Here, the ratio of the HC slip amount to the HC feed amount is determined relative to the HC amount supplied to the value obtained through the experiment.
도 1은 본 발명의 실시 예에 따른 LNT 촉매 효율 모니터링 방법을 나타내는 순서도,1 is a flowchart showing a method for monitoring LNT catalyst efficiency according to an embodiment of the present invention;
도 2는 2차 분사를 통한 HC 공급 이후에 LNT의 전방에 장착된 산소센서와 후방에 장착된 산소센서가 측정하는 값을 나타내는 그래프이다.2 is a graph showing values measured by an oxygen sensor mounted at the front of the LNT and an oxygen sensor mounted at the rear after HC supply through the secondary injection.
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