Classifications

• • 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
  • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
  • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• • 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
  • F01N11/002—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• • 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
  • F01N11/007—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• • 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
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
• • 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
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/011—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more purifying devices arranged in parallel
• • 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
  • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
  • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
  • F01N3/0842—Nitrogen oxides
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/021—Introducing corrections for particular conditions exterior to the engine
  • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
  • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
  • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
  • F02D41/146—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
  • F02D41/146—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration
  • F02D41/1463—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration of the exhaust gases downstream of exhaust gas treatment apparatus
• • 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
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/08—Other arrangements or adaptations of exhaust conduits
  • F01N13/10—Other arrangements or adaptations of exhaust conduits of exhaust manifolds
  • F01N13/107—More than one exhaust manifold or exhaust collector
• • 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
• • 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
• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
  • F02D2041/1468—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an ammonia content or concentration of the exhaust gases
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
  • F02D41/1441—Plural sensors
• • 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 invention relates to a catalyst monitoring system and monitoring method.
• OBD on-board diagnostic
• a three-way catalyst is unable to sufficiently purify N0 ⁇ when the air-fuel ratio of the inflowing exhaust gas is leaner than the stoichiometric air-fuel ratio. Therefore, a lean burn engine, for example, that is able to operate at a leaner air-fuel ratio than the stoichiometric air-fuel ratio is equipped with a NO ⁇ catalyst in the exhaust passage. This N0 ⁇ catalyst is able to store N0 ⁇ when the air-fuel ratio of the exhaust gas is lean.
• Japanese Patent No. 3316066 describes a diagnostic system for an exhaust gas purifying apparatus as one type of OBD system for a lean burn engine.
• This diagnostic system is provided with a N0 ⁇ sensor downstream of a N0 ⁇ catalyst and integrates the amount of N0 ⁇ emission for a predetermined period of time based on the actual N0 ⁇ concentration detected by the NO ⁇ sensor. The diagnostic system then checks whether the NO ⁇ catalyst has failed based on that integrated value.
• i engine into the atmosphere may be classified into two categories, i.e., N0 ⁇ that passes through the N0 ⁇ catalyst during lean burn operation and N0 ⁇ that is discharged from the NO ⁇ catalyst during the rich spike control.
• the former N0 ⁇ that passes through the N0 ⁇ catalyst during lean burn operation is N0 ⁇ that was discharged from the engine and passed through the N0 ⁇ catalyst without being trapped by the NO ⁇ catalyst.
• the latter N0 ⁇ that is discharged from the N0 ⁇ catalyst during the rich spike control is N0 ⁇ that was stored in the NO x catalyst but then discharged from the N0 ⁇ catalyst without completely being reduced during the rich spike control.
• a limiting current N0 ⁇ sensor that is used in recent years responds to NH 3 as well as N0 ⁇ .
• a reducing agent such as unburned fuel
• the NO ⁇ sensor is unable to detect the concentration of only the N0 ⁇ because the N0 ⁇ sensor also responds to the NH 3 in the exhaust gas. Therefore, a N0 ⁇ sensor is unable to detect the amount of N0 ⁇ that is discharged from the N0 ⁇ catalyst during the rich spike control.
• OBD systems provided with N0 ⁇ sensors including the diagnostic system described in Japanese Patent No. 3316066, are designed to detect the NO ⁇ concentration with a N0 ⁇ sensor only during the lean burn operation, when the exhaust gas does not contain NH 3 .
• FIGS. 12 and 13 show the N0 ⁇ emissions regulation values and the OBD regulation values according to STEP IV in Europe and SULEV (Super Ultra-Low Emission Vehicle) in the United States.
• SULEV not only has a stringent N0 ⁇ emissions regulation value, but also has an extremely stringent OBD regulation value such as 1.75 times the NO x emissions regulation value. That is, the deterioration detection range is extremely small so deterioration of a N0 ⁇ catalyst is required to be diagnosed with extremely high accuracy.
• FIGS. 14A and 14B each show experimental data about NO x discharged from a lean burn engine system on a graph in which the horizontal axis represents time and the vertical axis represents the amount of N0 ⁇ emission.
• FIG. 14A shows a case using a NO ⁇ catalyst for Euro STEP IV and FIG. 14B shows a case using a NO x catalyst for US SULEV.
• the solid lines on the graphs represent data obtained using catalysts that correspond to the NO x emissions regulation values, i.e., catalysts that are not deteriorated.
• the broken lines in the graphs represent data obtained using catalysts that correspond to the OBD regulation value, i.e., catalysts that have deteriorated to a level where deterioration of the NO x catalyst must be detected according to OBD regulations.
• the NO x sensor detects the amount of NO x that passes through the N0 ⁇ catalyst during the lean burn operation, and deterioration of the N0 ⁇ catalyst may be determined by comparing the detected N0 ⁇ value with a predetermined determining value.
• the invention thus provides a catalyst monitoring system and monitoring method that accurately diagnoses deterioration of a NO x catalyst which is arranged in an exhaust passage of an internal combustion engine.
• a catalyst monitoring system includes an NO x catalyst which is arranged in an exhaust passage of an internal combustion engine; an NO x sensor which is arranged downstream of the NO x catalyst and detects a concentration of NO x ; air-fuel ratio controlling means for temporarily switching an air-fuel ratio of exhaust gas during operation of the internal combustion engine from a lean air-fuel ratio to a rich or a stoichiometric air-fuel ratio; calculating means for calculating an output integrated value of the NO x sensor by integrating an output from the NO x sensor at least during a period near the end of air-fuel ratio control; and diagnosing means for diagnosing deterioration of the NO x catalyst based on the output integrated value of the N0 ⁇ sensor.
• the N0 ⁇ sensor may be capable of detecting a concentration of NH 3 as well as the concentration of N0 ⁇ .
• the N0 ⁇ sensor may be a limiting current N0 ⁇ sensor.
• the period near the end of the air-fuel ratio control may be a period during which the output from the NO ⁇ sensor temporarily increases abruptly.
• the catalyst monitoring system may also include reducing agent amount calculating means for calculating an amount of reducing agent that has flowed into the N0 ⁇ catalyst during the air-fuel ratio control.
• the air-fuel ratio controlling means may end the air-fuel ratio control when the reducing agent amount reaches a predetermined amount.
• the diagnosing means may diagnose deterioration of the N0 ⁇ catalyst based on the output integrated value of the NO ⁇ sensor and the reducing agent amount.
• the catalyst monitoring system may also include reducing time measuring means for measuring a reducing time of N0 ⁇ according to the air-fuel ratio control.
• the diagnosing means may diagnose deterioration of the N0 ⁇ catalyst based on the output integrated value of the NO ⁇ sensor and the reducing time.
• the air-fuel ratio controlling means may start the air-fuel ratio control when the amount of N0 ⁇ that has flowed into the N0 ⁇ catalyst reaches a predetermined value.
• the catalyst monitoring system may also include an O 2 sensor which is arranged downstream of the NO ⁇ catalyst and detects a concentration of O 2 .
• the air-fuel ratio controlling means may end the air-fuel ratio control when an output from the O 2 sensor while the air-fuel ratio control is being executed becomes the rich air-fuel ratio.
• the diagnosing means may start to diagnose deterioration of the N0 ⁇ catalyst when a predetermined executing condition for determining deterioration is satisfied.
• the predetermined executing condition for determining deterioration may include: i) a condition that the internal combustion engine operate at a predetermined operating condition while the air-fuel ratio control is executed; and ii) a condition that a temperature of the N0 ⁇ catalyst be within a predetermined temperature range while the air-fuel ratio control is executed.
• the predetermined operating condition may include a condition that at least one from among a speed of the internal combustion engine, a throttle opening amount of the internal combustion engine, and an intake air amount of the internal combustion engine be within a predetermined range.
• the period near the end of the air-fuel ratio control may include a period during which the output from the NO ⁇ sensor temporarily increases abruptly due to NH 3 that is discharged from the N0 ⁇ catalyst.
• the calculating means may calculate the output integrated value of the N0 ⁇ sensor by integrating the product of a physical quantity corresponding to an amount of intake air flowing into the NO ⁇ catalyst multiplied by the output from the NO ⁇ sensor.
• the air-fuel ratio controlling means may end the air-fuel ratio control when the output current from the NO ⁇ sensor while the air-fuel ratio control is being executed corresponds to the rich air-fuel ratio.
• a catalyst monitoring method includes steps of: performing air-fuel ratio control that temporarily switches an air-fuel ratio of exhaust gas during operation of an internal combustion engine from a lean air-fuel ratio to a rich or a stoichiometric air-fuel ratio; calculating an output integrated value of an NO ⁇ sensor which is arranged downstream of an NO ⁇ catalyst in an exhaust passage of the internal combustion engine by integrating an output from the NO x sensor at least during a period near the end of the air-fuel ratio control; and diagnosing deterioration of the NO ⁇ catalyst based on the output integrated value of the NO ⁇ sensor.
• FIG. 1 is a schematic view of a system configuration according to a first example embodiment of the invention
• FIG. 2 is a sectional view of the structure of a N0 ⁇ sensor provided in the system shown in FIG. 1;
• FIG. 3 is a timing chart, with FIG. 3A showing the output from an A/F sensor, FIG. 3B showing the NO x concentration downstream of a N0 ⁇ catalyst, and FIG. 3C showing the output from a N0 ⁇ sensor;
• FIG. 4 is a flowchart illustrating a routine executed in the first example embodiment of the invention.
• FIG. 5 is a timing chart illustrating the various operations of the first example embodiment of the invention, with FIG. 5 A showing an integrated amount of N0 ⁇ that flows into a N0 ⁇ catalyst, FIG. 5B showing an air-fuel ratio control execution flag, FIG. 5C showing output from a downstream O 2 sensor, FIG. 5D showing output from an A/F sensor, FIG. 5E showing a reducing agent amount integrated value, FIG. 5F showing output from a N0 ⁇ sensor, and FIG. 5G showing a N0 ⁇ sensor output integrated value;
• FIG. 6 is a chart showing a reference determining value in the first example embodiment of the invention.
• FIG. 7 is a timing chart illustrating a method for calculating the reducing agent amount integrated value
• FIG. 8 is a chart showing a reference determining value in a second example embodiment of the invention.
• FIG. 9 is a chart showing a reference determining value in a third example embodiment of the invention.
• FIG. 10 is a schematic view of a system configuration according to a modified example of the first example embodiment of the invention.
• FIG. 11 is a timing chart illustrating a method for obtaining the reducing agent amount integrated value and a reducing time in the modified example
• FIG. 12 is a chart showing the NO x emissions regulation values and the OBD regulation values according to the Euro STEP IV emissions standards and the US SULEV emissions standards;
• FIG. 13 is a graph showing the NO ⁇ emissions regulation values and the OBD regulation values according to the Euro STEP IV emissions standards and the US SULEV emissions standards;
• FIG. 14A is a graph showing experimental data of the amount of N0 ⁇ discharged from a lean burn engine system when a N0 ⁇ catalyst for the Euro STEP IV emissions standards is used.
• FIG. 14B is a graph showing experimental data of the amount of NO ⁇ discharged from a lean burn engine system when a N0 ⁇ catalyst for the US SULEV emissions standards is used.
• FIG. 1 is a view of schematic view of a system configuration according to a first example embodiment of the invention.
• the system shown in FIG. 1 is provided with an internal combustion engine 10.
• the internal combustion engine 10 shown in the drawing is an in-line four cylinder type internal combustion engine having four cylinders "#1" to "#4".
• the invention is not limited to this, i.e., the number and arrangement of cylinders are not limited to this.
• the internal combustion engine 10 may operate by burning fuel at an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio (i.e., hereinafter, this air-fuel ratio will be referred to as "lean air-fuel ratio").
• the internal combustion engine 10 may be any one of a port injection type internal combustion engine in which fuel is injected into an intake port, an in-cylinder direct injection type internal combustion engine in which fuel is injected directly into the cylinder, or a combination of the two types internal combustion engines which employs both port injection and in-cylinder direct injection.
• the internal combustion engine 10 is a spark ignition type internal combustion engine but the invention may also be applied to a catalyst monitoring system of a compression ignition type internal combustion engine.
• the start catalysts 14 and 16 function as three-way catalysts that may simultaneously purify HC, CO, and NO ⁇ with the storage and release of oxygen when the air-fuel ratio of the inflowing exhaust gas is near the stoichiometric air-fuel ratio.
• "storage” used herein means retention of a substance (solid, liquid, gas molecules) in the form of at least one of adsorption, adhesion, absorption, trapping, occlusion, and others.
• the N0 ⁇ catalyst converter 18 functions as a NO ⁇ storage-reduction catalyst that stores N0 ⁇ when the air-fuel ratio of the inflowing exhaust gas is lean, and reduces the stored N0 ⁇ to N 2 when the air-fuel ratio of the inflowing exhaust gas is rich, thereby purifying N0 ⁇ , after which is then the released.
• This NO ⁇ storage-reduction catalyst 18 also has the ability to store oxygen and may function as a three-way catalyst when the internal combustion engine 10 operates at the stoichiometric air-fuel ratio.
• the N0 ⁇ catalyst 18 according to the first example embodiment is a high performance N0 ⁇ catalyst that is compatible with the stringent exhaust gas regulations
• an A/F sensor 20 is arranged upstream of the start catalyst 14
• an A/F sensor 22 is arranged upstream of the start catalyst 16
• an A/F sensor 24 is arranged upstream of the NO ⁇ catalyst 18
• a N0 ⁇ sensor 25 and an O 2 sensor 26 are arranged downstream of the N0 ⁇ catalyst 18.
• the A/F sensors 20, 22, and 24 are air-fuel ratio sensors that produce linear output signals which indicate the air-fuel ratio of the exhaust gas.
• the O 2 sensor 26 is an oxygen sensor that produces an output signal that abruptly changes depending on whether the air-fuel ratio of the exhaust gas becomes richer or leaner than the stoichiometric air-fuel ratio.
• the N0 ⁇ sensor 25 detects not only the concentration of N0 ⁇ concentration in the exhaust gas, but also the concentration of NH 3 (ammonia) in the exhaust gas. This N0 ⁇ sensor 25 will be described in detail later.
• a temperature sensor 28 that detects a temperature (bed temperature) TCAT of the NO x catalyst 18 is arranged in the NO x catalyst 18.
• the temperature TCAT of the N0 ⁇ catalyst 18 may not be directly detected, i.e., it may be estimated from the exhaust gas temperature detected by an exhaust gas temperature sensor provided upstream or downstream of the NO x catalyst 18.
• the temperature TCAT of the N0 ⁇ catalyst 18 may be estimated based on the operating state of the internal combustion engine 10.
• an intake system not shown, which draws in air and distributes the air to the cylinders is connected to the internal combustion engine 10.
• the system according to the first example embodiment includes an ECU (Electronic Control Unit) 30.
• This ECU 30 is electrically connected to, in addition to the sensors described above, various sensors that detect the engine speed NE, the intake air pressure PM, the intake air amount GA, and the throttle opening amount TH, and the like.
• the ECU 30 is also electrically connected to various actuators, such as fuel injectors, spark plugs, and a throttle valve.
• the internal combustion engine 10 operates by combustion at a lean air-fuel ratio within a predetermined operating range (hereinafter this operation will be referred to as "lean burn operation").
• lean burn operation N0 ⁇ is difficult to be purified in the start catalysts 14 and 16 so it is temporarily stored in the NO ⁇ catalyst 18.
• the ECU 30 executes rich spike control which temporarily switches the air-fuel ratio of the exhaust gas that flows into the N0 ⁇ catalyst 18 from a lean to a rich or the stoichiometric air-fuel ratio.
• N0 ⁇ that has stored in the N0 ⁇ catalyst 18 may be released from the N0 ⁇ catalyst 18 and thus reduced (i.e., purified).
• the method for temporarily switching the air-fuel ratio of the exhaust gas that flows into the N0 ⁇ catalyst 18 from the lean to the rich or the stoichiometric air-fuel ratio may be any one of the following methods: i.e., a method that switches the combustion air-fuel ratio of the internal combustion engine 10 from the lean to the rich or the stoichiometric air-fuel ratio, a method that injects additional fuel from an in-cylinder fuel injector during the latter half of the expansion stroke or during the exhaust stroke, or a method that injects fuel into the exhaust passage 12 upstream of the N0 ⁇ catalyst 18.
• rich spike control is executed by switching the combustion air-fuel ratio of the internal combustion engine 10 from the lean to the rich or the stoichiometric air-fuel ratio.
• FIG. 2 is a sectional view of the structure of a sensor portion of the N0 ⁇ sensor 25 provided in the system shown in FIG. 1.
• the N0 ⁇ sensor 25 in this first example embodiment is a limiting current NO ⁇ sensor.
• the sensor portion of the N0 ⁇ sensor 25 is made of six oxygen ion conducting solid electrolyte layers such as oxidized zirconia, which have been laminated together. These six solid electrolyte layers will hereinafter be referred to, in order from the top, as the first layer Li, the second layer L 2 , the third layer L 3 , the fourth layer L 4 , the fifth layer L 5 , and the sixth layer L 6 .
• a porous first diffusion-controlling member 50 and porous second diffusion-controlling member 51 are arranged between the first layer L 1 and the third layer L 3 .
• a first chamber 52 is formed between these diffusion-controlling members 50 and 51, and a second chamber 53 is formed between the second diffusion-controlling member 51 and the second layer L 2 .
• an atmospheric chamber 54 that is communicated with ambient air is formed between the third layer L 3 and the fifth layer L 5 .
• an outer end surface of the first diffusion-controlling member 50 contacts the exhaust gas. Accordingly, the exhaust gas flows into the first chamber 52 via the first diffusion-controlling member 50 such that the first chamber 52 fills up with exhaust gas.
• a negative electrode side first pump electrode 55 is formed on an inner peripheral surface of the first layer L 1 that faces the first chamber 52
• a positive electrode side first pump electrode 56 is formed on an outer peripheral surface of the first layer L 1 .
• Voltage is applied by a first pump voltage supply 57 between these first pump electrodes 55 and 56.
• oxygen in the exhaust gas inside the first chamber 52 contacts the negative electrode side first pump electrode 55 and turns into oxygen ions.
• These oxygen ions flow inside the first layer L 1 toward the positive electrode side first pump electrode 56. Accordingly, the oxygen in the exhaust gas inside the first chamber 52 moves inside the first layer L 1 and is drawn out to the outside. The amount of oxygen drawn out to the outside at this time increases as the voltage of the first pump voltage supply 57 increases.
• a reference electrode 58 is formed on an inner peripheral surface of the third layer L 3 that faces the atmospheric chamber 54.
• oxygen ions move inside the solid electrolyte layer from the side where the oxygen concentration is high toward the side where the oxygen concentration is low.
• the oxygen concentration in the atmospheric chamber 54 is higher than the oxygen concentration in the first chamber 52 so the oxygen inside the atmospheric chamber 54 receives a charge from contacting the reference electrode 58 and as a result, turns into oxygen ions.
• the voltage of the first pump voltage supply 57 is feedback controlled so that this voltage Vo becomes equal to the voltage generated when the oxygen concentration in the first chamber 52 is 1 ppm. That is, the oxygen in the first chamber 52 is drawn out through the first layer Li so that the oxygen concentration in the first chamber 52 becomes 1 ppm. This enables the oxygen concentration in the first chamber 52 to be maintained at 1 ppm.
• the negative electrode side first pump electrode 55 is made of material with low N0 ⁇ reducing ability, such as an alloy of gold Au and platinum Pt, for example. Therefore, almost none of the NO ⁇ in the exhaust gas is reduced in the first chamber 52 so the N0 ⁇ flows into the second chamber 53 through the second diffusion-controlling member 51. Meanwhile, a negative electrode side second pump electrode 60 is formed on the inner peripheral surface of the first layer Li that faces the second chamber 53. Voltage is applied by a second pump voltage supply 61 between the negative electrode side second pump electrode 60 and the positive electrode side first pump electrode 56. When voltage is applied between these pump electrodes 60 and 56, the oxygen in the exhaust gas inside the second chamber 53 contacts the negative electrode side second pump electrode 60 and turns into oxygen ions.
• the voltage of the second pump voltage supply 61 is feedback controlled so that this voltage Vi becomes equal to the voltage generated when the oxygen concentration in the second chamber 53 is 0.01 ppm. That is, the oxygen in the second chamber 53 is drawn out through the first layer L 1 so that the oxygen concentration in the second chamber 53 becomes 0.01 ppm. This enables the oxygen concentration in the second chamber 53 to be maintained at 0.01 ppm.
• the negative electrode side second pump electrode 60 is made of material with low NO ⁇ reducing ability, such as an alloy of gold Au and platinum Pt, for example. Therefore, almost none of the N0 ⁇ in the exhaust gas is reduced even if the N0 ⁇ contacts the negative electrode side second pump electrode 60. Meanwhile, a negative electrode side pump electrode 63 for detecting N0 ⁇ is formed on the inner peripheral surface of the third layer L 3 that faces the second chamber 53. This negative electrode side pump electrode 63 is made of material with high NO ⁇ reducing ability, such as rhodium Rh or platinum Pt, for example.
• the N0 ⁇ inside the second chamber 53 that is, the NO that actually makes up a substantial portion in the NO ⁇ , is separated into N 2 and O 2 on the negative electrode side pump electrode 63.
• a constant voltage 64 is applied between this negative electrode side pump electrode 63 and the reference electrode 58, and as a result, the resultant O 2 on the negative electrode side pump electrode 63 turns into oxygen ions which move inside the third layer L 3 toward the reference electrode 58.
• a current I 1 indicated by reference numeral 65 which is proportional to the amount of these oxygen ions, flows between the negative electrode side pump electrode 63 and the reference electrode 58.
• the ammonia NH 3 in the exhaust gas is separated into NO and H 2 O (4NH 3 + 5O 2 ⁇ 4NO + 6H 2 O) in the first chamber 52, and the resultant NO flows into the second chamber 53 through the second diffusion-controlling member 51.
• This NO is separated into N 2 and O 2 on the negative electrode side pump electrode 63, and the resultant O 2 turns into oxygen ions that move in the third layer L 3 toward the reference electrode 58.
• the current Ii is proportional to the NH 3 concentration in the exhaust gas so the NH 3 concentration in the exhaust gas is detected from the current Ii .
• the N0 ⁇ sensor 25 simultaneously detects both NO ⁇ and NH ? in the exhaust gas in principle. Therefore, when NH 3 is present in the exhaust gas, the current Ii of the NO ⁇ sensor 25 (hereinafter, this current Ii will simply be referred to as the "output of the N0 ⁇ sensor 25") is the combined value of the output according to N0 ⁇ and the output according to NH 3 .
• an electric heater 67 for heating the sensor portion of the NO x sensor 25 is provided between the fifth layer L 5 and the sixth layer L 6 .
• This electric heater 67 heats the sensor portion of the N0 ⁇ sensor 25 up to between 700 0 C and 800 0 C.
• FIG. 3 is a timing chart, with FIG. 3 A showing the output from the A/F sensor 24, FIG. 3B showing the NO ⁇ concentration downstream of the NO ⁇ catalyst 18, and FIG. 3C showing the output from the N0 ⁇ sensor 25.
• the NO ⁇ catalyst 18 is also provided with a catalyst such as platinum Pt which has a reducing function so when the air-fuel ratio becomes rich, ammonia NH 3 may be produced in the NO ⁇ catalyst 18.
• the ammonia NH 3 is used to reduce the NO ⁇ that is released from the N0 ⁇ catalyst 18 so almost no ammonia NH 3 is discharged from the NO x catalyst 18.
• ammonia NH 3 is no longer consumed to reduce the NO ⁇ so ammonia NH 3 is discharged from the N0 ⁇ catalyst 18 at this time.
• ammonia NH 3 flows to the downstream side of the NO ⁇ catalyst 18 near the time when the rich spike control ends (i.e., time t2).
• This ammonia NH 3 is detected by the NO ⁇ sensor 25 somewhat late due to the delay in movement of the exhaust gas. Therefore, as shown in FIG. 3C, the output from the NO ⁇ sensor 25 temporarily increases abruptly near the time when the rich spike control ends.
• the NO ⁇ concentration also increases near the rime that the rich spike control ends due to the effect from the N0 ⁇ that is discharged, as described above. However, at this time the N0 ⁇ concentration rises only slightly compared to the rise in the output from the N0 ⁇ sensor 25.
• the difference between the amount of NO x that has passed through the NO x catalyst 18 that has not yet deteriorated during lean burn operation and the amount of N0 ⁇ that has passed through the N0 ⁇ catalyst 18 that has deteriorated corresponding to the OBD regulation value (hereinafter simply referred to as the "deteriorated NO x catalyst 18") is extremely low. Therefore, even if the N0 ⁇ that has passed through an N0 ⁇ catalyst 18 is detected by the N0 ⁇ sensor 25, it is difficult to detect deterioration of the N0 ⁇ catalyst 18. Accordingly, deterioration of the N0 ⁇ catalyst 18 is required to be detected from the difference in the amounts of N0 ⁇ that has discharged from the N0 ⁇ catalyst 18 during rich spike control. However, as described above, ammonia NH 3 flows out downstream of the N0 ⁇ catalyst 18 following rich spike control so it is not easy to obtain the discharged amount of only NO ⁇ from the output of the N0 ⁇ sensor 25.
• the inventors have discovered that deterioration of the NO ⁇ catalyst 18 may be accurately diagnosed based on a value which indicates the integrated output of the N0 ⁇ sensor 25 near the time that the rich spike control ends (hereinafter this value will be referred to as the "N0 ⁇ sensor output integrated value NO x SCNT").
• the discharged amount of N0 ⁇ increases as the NO ⁇ catalyst 18 deteriorates, but this is due to a decrease in reducing efficiency.
• the ammonia NH 3 that was produced in the exhaust gas is being consumed to reduce the N0 ⁇ that has been released from the N0 ⁇ catalyst 18, the ammonia NH 3 will not flow downstream of the N0 ⁇ catalyst 18.
• the reducing efficiency decreases, ammonia NH 3 becomes difficult to be consumed to reduce N0 ⁇ .
• more ammonia NH 3 becomes to flow downstream of the N0 ⁇ catalyst 18. Accordingly, it may be said that the discharged amount of NO ⁇ increases as the amount of ammonia NH 3 that flows downstream of the N0 ⁇ catalyst 18 increases.
• the majority of the output from the N0 ⁇ sensor 25 near the time when the rich spike control ends is due to the ammonia NH 3 so there is a correlation between the amount of ammonia NH 3 that flows downstream of the N0 ⁇ catalyst 18 and the N0 ⁇ sensor output integrated value NO ⁇ SCNT near the time when the rich spike control ends. Accordingly, it may be estimated that the discharged amount of N0 ⁇ increases as the N0 ⁇ sensor output integrated value NO ⁇ SCNT increases near the time when the rich spike control ends.
• deterioration of the N0 ⁇ catalyst 18 may be diagnosed based on the N0 ⁇ sensor output integrated value NOxSCNT that deeply correlates with the discharged amount of N0 ⁇ during rich spike control, which makes it possible to more accurately diagnose deterioration.
• FIG. 4 is a flowchart of a routine executed by the ECU 30 in the first example embodiment in order to diagnose deterioration of the NO ⁇ catalyst 18. This routine is executed repeatedly at predetermined intervals of time.
• FIGS. 5 A to 5G is a timing chart that illustrates the various operations of the first example embodiment. The operations including the rich spike controls which are executed three times are shown in FIGS. 5Ato 5G.
• the routine shown in FIG. 4 first, the value of NO ⁇ IN that indicates the integrated amount of N0 ⁇ flowing into the NO ⁇ catalyst 18 is read (step 100).
• FIG. 5A shows this N0 ⁇ IN.
• the relationship between the load and speed of the internal combustion engine 10 and the amount of NO ⁇ generated per unit time is checked beforehand by experimentation. This relationship is stored in the ECU 30 in advance. The ECU 30 then calculates the amount of N0 ⁇ generated per unit time at the actual load and speed of the internal combustion engine 10 based on that relationship, and calculates the integrated value of that amount of NO ⁇ generated per unit time as NO ⁇ IN.
• FIG. 5B shows a rich spike control execution flag FR.
• FR When rich spike control is being executed, FR equals 1.
• FR When rich spike control is not being executed, FR equals 0.
• NO ⁇ IN is reset after NO ⁇ that has been stored in the N0 ⁇ catalyst 18 is released by execution of rich spike control. That is, NO ⁇ IN represents an (estimated value of the) amount of N0 ⁇ that has flowed into the NO ⁇ catalyst 18 between after rich spike control ended and before the next rich spike control ends.
• the method for calculating the NO ⁇ IN is not limited to the method of estimating the NO ⁇ IN from the operating state of the internal combustion engine 10. That is, an NO ⁇ sensor capable of detecting the N0 ⁇ concentration may be arranged upstream of the NO ⁇ catalyst 18 and the N0 ⁇ IN may be calculated based on the output from this NO ⁇ sensor.
• rich spike control starts when N0 ⁇ IN, i.e., the amount of NO ⁇ that has flowed into the NO ⁇ catalyst 18, reaches a predetermined value ⁇ . Therefore, when N0 ⁇ IN is read in step 100, it is determined whether that N0 ⁇ IN is equal to or greater than the predetermined value a (step 102). If N0 ⁇ IN has not yet reached the predetermined value cc in step 102, then the NO ⁇ sensor output integrated value NOxSCNT is updated by integrating the output NO ⁇ S from the N0 ⁇ sensor 25 detected in this cycle of the routine (step 104). Then, this cycle of the routine ends.
• FIG. 5F shows the output NO x S from the NO x sensor 25 and FIG. 5G shows the NO x sensor output integrated value NO x SCNT.
• the NO x sensor output integrated value NO x SCNT is calculated by integrating the NO x sensor output NO x S from the time that rich spike control starts until the time that the next rich spike control starts. Therefore, when it is determined in step 102 that the NO x IN has reached the predetermined value ⁇ , integration of the last NO x S ends (step 106).
• NO x SCNT R indicates a value that NO x sensor output NO x S has been integrated for the period during which the majority of the NO x sensor output NO x S is due to the ammonia NH 3 produced during the rich spike control.
• NO X SCNT L indicates a value that NO x sensor output NO x S has been integrated for the period during which the majority of the NO x sensor output NO x S is due to the NO x that passes through the NO x catalyst 18 during lean burn operation.
• step 106 a process for calculating the NO X SCNT R is also executed. More specifically, as shown in FIG. 5G, it may be determined that the majority of the NO x sensor output NO x S is due to the ammonia NH 3 during the period when the NO x sensor output NO x S temporarily increases abruptly. Therefore, the integrated value of the NO x sensor output NO x S during this period may be made NO X SCNT R , and the integrated value of the NO x sensor output NO x S during a period other than this period may be made NO X SCNT L .
• step 108 rich spike control for this cycle starts (step 108), following the step 106 and then the NO x sensor output NO x S starts to be integrated for this cycle (step 110).
• FIG. 5C shows the output O 2 S from the O 2 sensor downstream of the NO x catalyst 18.
• the rich spike control ends when the output O 2 S from the O 2 sensor 26 becomes a rich output. Therefore, while the rich spike control is being executed, it is determined whether the output O 2 S from the O 2 sensor 26 has become a rich output (step 112). When it is determined that the output O 2 S from the O 2 sensor 26 has become a rich output, the rich spike control for this cycle ends (step 114).
• This deterioration determining condition more specifically consists of the two conditions. These conditions are: (1) that an operating condition (such as the engine speed NE, the throttle opening amount TH, or the intake air amount GA) when rich spike control is executed be within a predetermined range; and (2) that the temperature TCAT of the NO ⁇ catalyst 18 when the rich spike control is executed be within a predetermined temperature range.
• an operating condition such as the engine speed NE, the throttle opening amount TH, or the intake air amount GA
• Condition (1) above is a condition provided so that only data obtained when the rich spike control is executed under predetermined operating conditions in which there is no sudden acceleration or deceleration or the like is used as the basis for the catalyst deterioration determination in order to prevent an erroneous determination due to a calculation error of the N0 ⁇ IN or the like.
• Condition (2) above is a condition to prevent an erroneous determination due to the effect of the temperature of the NO ⁇ catalyst 18. That is, the storage-reduction ability of the N0 ⁇ catalyst 18 changes depending on its temperature. Therefore, condition (2) above is provided so that only data obtained when the rich spike control is executed in a temperature range in which the storage-reduction ability of the N0 ⁇ catalyst 18 is regarded as being constant is used as the basis for the catalyst deterioration determination.
• step 116 If it is determined in step 116 that the deterioration determining condition is not satisfied, then it may be determined that catalyst deterioration determination should not be performed. Therefore, in this case, the routine for this cycle directly ends. On the other hand, if it is determined in step 116 that the deterioration determining condition is satisfied, catalyst deterioration determination is performed as follows. First, the NO X SCNT R that was calculated in step 106 is compared with a predetermined reference determining value ⁇ (step 118). As described above, it may be determined that the larger NOXSCNTR, which indicates the integrated N0 ⁇ sensor output NO ⁇ S near the time that the rich spike control ends, the more ammonia NH 3 has flowed out downstream of the NO ⁇ catalyst 18.
• the NO X SCNT R is equal to or greater than the reference determining value ⁇ in step 118, it is determined that the NO ⁇ catalyst 18 is deteriorated (step 120).
• the NO X SCNT R is less than the reference determining value ⁇ , it is determined that the N0 ⁇ catalyst 18 is normal (i.e., not deteriorated) (step 122).
• FIG. 6 is a graph showing a plurality of experimental data plotted on a coordinate system in which the horizontal axis represents the temperature TCAT of the N0 ⁇ catalyst 18 and the vertical axis represents the N0 ⁇ sensor output integrated value NO X SCNT R .
• the black squares represent experimental data obtained with an N0 ⁇ catalyst 18 in which level of the discharged amount of N0 ⁇ corresponds to the emissions regulation value (hereinafter this catalyst will be referred to as "normal catalyst (X)").
• the black diamonds represent experimental data obtained with a N0 ⁇ catalyst 18 in which level of the amount of N0 ⁇ discharged corresponds to the OBD regulation value (hereinafter this catalyst will be referred to as "deteriorated catalyst (Y)").
• this catalyst hereinafter this catalyst will be referred to as "deteriorated catalyst (Y)"
• the normal catalyst (X) may be reliably differentiated from the deteriorated catalyst (Y) by setting the reference determining value ⁇ to a value such as that shown by the straight line in FIG. 6.
• extremely high diagnostic accuracy may be obtained by diagnosing deterioration of the N0 ⁇ catalyst 18 based on the N0 ⁇ sensor output integrated value NOXSCNTR which correlates with the amount of N0 ⁇ that has been discharged during rich spike control.
• the reference determining value ⁇ is constant regardless of the temperature TCAT of the N0 ⁇ catalyst 18.
• the reference determining value ⁇ may be changed according to the TCAT.
• the reference determining value ⁇ may be changed according to another operating condition of the internal combustion engine 10.
• the NO x sensor output integrated value NO x SCNT is separated into N0 ⁇ SCNT R and NO X SCNT L and catalyst deterioration determination of the N0 ⁇ catalyst 18 is performed based on the NOXSCNT R .
• the invention is not limited to this method of determination.
• catalyst deterioration determination may be performed based on the NO x sensor output integrated value NO x SCNT before the NO x SCNT is separated into NO X SCNT R and N0 ⁇ SCNT L because the value of NO X SCNT L is small compared with the value of NO X SCNT R and thus has little effect. Also, it is also possible to calculate only the NO X SCNT R from the start. That is, in the invention, the integration period of the NO x sensor output NO x S on which the catalyst deterioration determination is based need only include the period of time during which the output of the NO x sensor 25 abruptly increases temporarily due to the ammonia NH 3 near the time when the rich spike control ends.
• the NO x sensor output integrated value NO x SCNT is calculated by integrating the NO x sensor output NO x S.
• the method for calculating the NO x sensor output integrated value NO x SCNT is not limited to this.
• the NO x sensor output integrated value NO x SCNT may also be calculated by integrating the product of a physical quantity corresponding to the amount of air flowing into the NO x catalyst 18 (i.e., corresponding to the inflow gas amount) multiplied by the NO x sensor output NO x S.
• the air amount flowing into the NO x catalyst 18 may be calculated based on, for example, the intake air amount GA detected by an airflow meter, the fuel injection quantity, or the output from the A/F sensor 24.
• the rich spike control ends when the output from the O 2 sensor 26 downstream of the NO x catalyst 18 becomes a rich output.
• the rich spike control may be ended using the O 2 sensor function or the A/F sensor function of the NO x sensor 25.
• the air-fuel ratio of the exhaust gas may be detected from the current I 2 of the NO x sensor 25 as described with reference to FIG 2. Accordingly, the rich spike control may be ended when this current I 2 corresponds to a rich air-fuel ratio. In this case, it is no longer necessary to provide the O 2 sensor 26 downstream of the N0 ⁇ catalyst 18 so costs may be reduced.
• the rich spike control ends when the output from the O 2 sensor 26 downstream of the N0 ⁇ catalyst 18 becomes a rich output.
• the rich spike control ends when the amount of reducing agent that has flowed into the NO ⁇ 18 reaches a predetermined value ⁇ after the rich spike control starts.
• FIG. 7 is a timing chart illustrating a method for calculating a reducing agent amount integrated value RFCNT. More specifically, the upper drawing in FIG. 7 shows the change in the reducing agent amount integrated value RFCNT, as well as the lower drawing in FIG. 7 shows the output AFS 2 from the A/F sensor 24, i.e., the air-fuel ratio AFS_2 of the exhaust gas that flows into the N0 ⁇ catalyst 18.
• the reducing agent amount integrated value RFCNT is a value indicative of the amount of reducing agent that has flowed into the N0 ⁇ catalyst 18 due to the rich spike control, and is calculated according to the following expression.
• RFCNT 2 0- e - > the amount of reducing agent per unit time multiplied by the ECU calculation cycle) ... (1)
• the amount of reducing agent per unit time may be calculated according to the following expression.
• the reducing agent amount integrated value RFCNT may be successively calculated by the ECU 30 based on the foregoing Expressions (1) and (2).
• the rich spike control ends when the reducing agent amount integrated value RFCNT that is calculated as described above reaches the predetermined value ⁇ . Therefore, the total amount of reducing agent supplied during rich spike control may be constant each time.
• the amount of the reducing agent may change depending on the deterioration level of the N0 ⁇ catalyst 18. For example, when the deterioration level of the NO ⁇ catalyst 18 is extremely high and the N0 ⁇ storage amount is extremely small, all of N0 ⁇ that was stored is soon reduced so the output from the O 2 sensor 26 soon becomes the rich output. As a result, the rich spike control soon ends so the amount of reducing agent becomes extremely small. When the amount of reducing agent is small, the amount of ammonia NH 3 produced is also small.
• the N0 ⁇ sensor output integrated value NO ⁇ SCNT is calculated to be small regardless of whether the deterioration level of the NO ⁇ catalyst 18 is extremely high so there is a possibility that the NO ⁇ catalyst 18 will be erroneously determined to be normal.
• the amount of reducing agent during rich spike control may be made constant so the amount of ammonia NH 3 produced may also be made constant.
• the amount of ammonia NH 3 is made constant, the amount of ammonia NH 3 that flows out downstream of the NO x catalyst 18, i.e., the NO ⁇ sensor output integrated value NO ⁇ SCNT, may be made to more accurately correlate with the discharged amount of NO ⁇ , i.e., with the reducing efficiency. Therefore, according to this modified example, an erroneous determination such as that described above may be more reliably prevented, which makes it possible to more accurately diagnose deterioration of the N0 ⁇ catalyst 18.
• the "air-fuel ratio controlling means" of the invention may be realized by the ECU 30 executing steps 108 and 114
• the "calculating means” of the invention may be realized by the ECU 30 executing steps 104, 106, and 110
• the "diagnosing means” of the invention may be realized by the ECU 30 executing steps 118 and 120, and 122.
• the reducing agent amount integrated value RFCNT may be regarded as the "reducing agent amount” of the invention.
• the "reducing agent amount calculating means" of the invention may be realized by the ECU 30 calculating the reducing agent amount integrated value RFCNT based on Expressions (1) and (2) above.
• the "air-fuel ratio controlling means” of the invention may be also realized by the ECU 30 ending the rich spike control when the reducing agent amount integrated value RFCNT reaches the predetermined value ⁇ .
• deterioration determination of the NO ⁇ catalyst 18 is performed by comparing the NO ⁇ sensor output integrated value NO X SCNT R with the reference determining value ⁇ (step 118 of the routine in FIG. 4).
• deterioration determination of the NO ⁇ catalyst 18 is performed by comparing the quotient NO X SCNT R / RFCNT of the NO x sensor output integrated value NO X SCNT R divided by the amount of reducing agent that has flowed into the NO x catalyst 18 (i.e., the reducing agent amount integrated value RFCNT), with the reference determining value.
• FIG. 8 is a graph in which experimental data using the same catalyst as in FIG. 6 is plotted on a coordinate system in which the horizontal axis represents the temperature TCAT of the NO x catalyst 18 and the vertical axis represents the quotient of NO X SCNT R / RFCNT. That is, in FIG. 8, the black squares represent experimental data of the normal catalyst (X) while the black diamonds represent experimental data of the deteriorated catalyst (Y). Incidentally, the rich spike control end condition was set such that the output from the O 2 sensor 26 downstream of the N0 ⁇ catalyst 18 be a rich output. As can be seen from FIG. 8, in this second example embodiment, the normal catalyst (X) may be reliably differentiated from the deteriorated catalyst (Y) by setting the reference determining value as shown by the sloped straight line in FIG. 8.
• the quotient of NO X SCNTR / RFCNT is a value that represents the percentage of reducing agent that has passed through the N0 ⁇ catalyst 18 without being consumed to reduce the N0 ⁇ that has been released from the N0 ⁇ catalyst 18, with respect to the entire amount of the reducing agent that flowed into the N0 ⁇ catalyst 18. Therefore, it may be said that the quotient of NO X SCNT R / RFCNT is a value that more accurately represents the reducing efficiency of the NO x catalyst 18. Therefore, according to this second example embodiment, even greater diagnostic accuracy is able to be obtained by diagnosing deterioration of the NO x catalyst 18 by comparing the quotient of NOXSCNT R / RFCNT with the reference determining value.
• the reference determining value becomes lower as the temperature TCAT of the NO x catalyst 18 during rich spike control increases. This is thought to be because the temperature TCAT of the NO x catalyst 18 is high when the internal combustion engine 10 is operating at a high load.
• the intake air amount GA is large so even if the amount of ammonia NH 3 that passes through the N0 ⁇ catalyst 18 is the same, the concentration of the ammonia NH 3 is lower.
• the N0 ⁇ sensor output NO ⁇ S is smaller so the NO x sensor output integrated value NOXSCNT R is also smaller. Therefore, the reference determining value is thought to become lower as the temperature TCAT of the NO x catalyst 18 increases.
• the reference determining value may be a constant value regardless of the temperature TCAT of the NO x catalyst 18.
• the specific process of the second example embodiment is as follows.
• the ECU 30 successively calculates the reducing agent amount integrated value RFCNT according to the same method that is used in the modified example of the first example embodiment described above while the rich spike control is being executed.
• the quotient of NO X SCNT R / RFCNT is calculated by dividing the N0 ⁇ sensor output integrated value NO X SCNT R by the reducing agent amount integrated value RFCNT at the time that the rich spike control ends.
• a reference determining value is obtained according to the relationship shown in FIG. 8 based on the temperature TCAT of the N0 ⁇ catalyst 18. This reference determining value is then compared with the quotient of NO X SCNT R / RFCNT.
• step 120 If the quotient of NO X SCNT R / RFCNT is equal to or greater than the reference determining value, it is determined that the NO x catalyst 18 is deteriorated (step 120). Meanwhile, if the quotient of NO X SCNT R / RFCNT is less than the reference determining value, it is determined that the N0 ⁇ catalyst 18 is normal (step 122).
• the second example embodiment is similar to the first example embodiment so further description will be omitted.
• the reducing agent amount integrated value RFCNT may be regarded as the "reducing agent amount” of the invention.
• the "reducing agent amount calculating means" of the invention may be also realized by the ECU 30 calculating the reducing agent amount integrated value RFCNT, and the "diagnosing means" of the invention may be also realized by the ECU comparing the quotient of NO X SCNT R / RFCNT with the reference determining value and diagnosing deterioration of the NO x catalyst 18.
• deterioration determination of the NO x catalyst 18 is performed by comparing the quotient of NO X SCNT R / TR S , which is the quotient of the NO x sensor output integrated value NOXSCNT R divided by a reducing time TR S according to rich spike control, with a reference determining value.
• the reducing time T RS is the time for which the rich spike control is continued, as shown in FIG. 5B, but the reducing time TR S is not limited to this.
• the reducing time T RS may also be the time for which the output from the A/F sensor 24 upstream of the N0 ⁇ catalyst 18 is maintained at a rich output.
• FIG. 9 is a graph in which experimental data using the same catalyst as in FIG. 6 is plotted on a coordinate system in which the horizontal axis represents the temperature TCAT of the N0 ⁇ catalyst 18 and the vertical axis represents the quotient of NO X SCNT R / T RS . That is, in FIG. 9 the black squares represent experimental data obtained with the normal catalyst (X) and the black diamonds represent experimental data obtained with the deteriorated catalyst (Y). Incidentally, the rich spike control end condition was set such that the output from the O 2 sensor 26 downstream of the N0 ⁇ catalyst 18 be a rich output. As can be seen from FIG. 9, in this third example embodiment, the normal catalyst (X) may be reliably differentiated from the deteriorated catalyst (Y) by setting the reference determining value as shown by the sloped straight line in FIG. 9.
• the amount of reducing agent that flows into the N0 ⁇ catalyst 18 i.e., the reducing agent amount integrated value RFCNT
• the quotient of NOXSCNTR / T RS may be used as the similar indicator to the quotient of NOXSCNT R / RFCNT in the second example embodiment. Therefore, greater diagnostic accuracy may be also obtained according to the third example embodiment, just as in the second example embodiment.
• the specific process of the third example embodiment is as follows.
• the ECU 30 measures the reducing time T RS while the rich spike control is being executed.
• the quotient of NO X SCNTR / T RS is calculated by dividing the N0 ⁇ sensor output integrated value NO x S CNT R by the reducing time T RS .
• a reference determining value is obtained according to the relationship shown in FIG. 9 based on the temperature TCAT of the N0 ⁇ catalyst 18.
• This reference determining value is then compared with the quotient of NOXSCNTR / TR S - If the quotient of NO X SCNT R / T RS is equal to or greater than the reference determining value, it is determined that the NO x catalyst 18 is deteriorated (step 120). Meanwhile, if the quotient of NO X SCNT R / TR S is less than the reference determining value, it is determined that the N0 ⁇ catalyst 18 is normal (step 122).
• the third example embodiment is similar to the first example embodiment so further description will be omitted.
• the "reducing time measuring means" of the invention may be realized by the ECU 30 measuring the reducing time T RS .
• the "diagnosing means" of the invention may be also realized by the ECU comparing the quotient of NO X SCNT R / T RS with the reference determining value and diagnosing deterioration of the N0 ⁇ catalyst 18.
• FIG. 10 is a schematic view of a system configuration according to a modified example of the first example embodiment of the invention.
• an O 2 sensor 27 that produces an output signal which suddenly changes when the air-fuel ratio of the exhaust gas becomes richer or leaner than the stoichiometric air-fuel ratio, is arranged upstream of the N0 ⁇ catalyst 18 instead of the A/F sensor 24.
• the system shown in FIG. 10 is similar to the system shown in FIG. 1.
• the O 2 sensor 27 arranged upstream of the N0 ⁇ catalyst 18 will be referred to as the "upstream O 2 sensor 27" and the O 2 sensor 26 arranged downstream of the N0 ⁇ catalyst 18 will be referred to as the "downstream O 2 sensor 26".
• FIG. 11 is a timing chart illustrating a method for obtaining the reducing agent amount integrated value RFCNT and the reducing time TR S in this modified example. More specifically, the upper drawing in FIG. 11 shows the output from the downstream O 2 sensor 26, the intermediate drawing in FIG. 11 shows the output from the upstream O 2 sensor 27, and the lower drawing in FIG. 11 shows an output which is either the output from one of the A/F sensors 20 or 22 arranged upstream of the start catalysts 14 and 16, or the output which is the average of both outputs from the A/F sensors 20 and 22 (hereinafter referred to as "A/F sensor output").
• the reducing agent starts to flow into the N0 ⁇ catalyst 18. Then when all of the oxygen and N0 ⁇ that have been stored in the NO ⁇ catalyst 18 are used up by the reducing agent, exhaust gas of a rich air-fuel ratio starts to pass through to the downstream side of the N0 ⁇ catalyst 18. As a result, the output of the downstream O 2 sensor 26 changes from lean to rich (time t3).
• the amount of reducing agent that has flowed into the N0 ⁇ catalyst 18 may be calculated based on the A/F sensor output from time t2 to time t3 (the portion with hatching in FIG. 11). Also, the reducing time T RS may be obtained by measuring the time from time t2 to time t3.
• the amount of oxygen and N0 ⁇ stored in the N0 ⁇ catalyst 18 may be calculated from the reducing agent amount integrated value RFCNT.
• deterioration determined may also be performed with extremely high accuracy by combining the deterioration determination results of the N0 ⁇ catalyst 18, which was obtained based the amount of oxygen and NO ⁇ stored in the N0 ⁇ catalyst 18, with deterioration determination results which was obtained using the N0 ⁇ sensor 25 described above.

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