JPH11303621A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decide the deterioration of an NOx absorbent accurately even when a three-dimensional catalyst is arranged at the upstream side of the NOx absorbent. SOLUTION: This device carries out a feedback control to control the air-fuel ratio to a theoretical air-fuel ratio, according to the output of an O2 sensor, at the downstream side of an NOx absorbent, and measures the deciding time TCHK (S22). And when the reduction rich operation of the NOx absorbent is carried out during a lean operation, a rich transfer time TNOx from the time when the air-fuel ratio is converted to the rich side to the time that the O2 sensor output exceeds a standard value SVREF is measured (S25). The deciding time TCHK and the rich transfer time TNOx are converted to deciding parameters OSCIDX and NSCIDX respectively (S23, S26), and the deterioration of the NOx absorbent is decided depending on the parameters (S27 to S30).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to an exhaust system having NOx (nitrogen oxide).
The present invention relates to an exhaust gas purifying apparatus having an absorbent and having a function of determining deterioration of the NOx absorbent.

[0002]

2. Description of the Related Art When a lean operation is performed in which the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine is set leaner than the stoichiometric air-fuel ratio, the amount of NOx emission tends to increase. A NOx absorbent that absorbs
A technique for purifying exhaust gas has been conventionally known. In this NOx absorbent, the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio, and the oxygen concentration in the exhaust gas is relatively high (NOx
(Hereinafter referred to as “exhaust gas lean state”), while absorbing NOx, the air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is low, and the HC and CO components are low. In a state with a large amount of NOx (hereinafter, referred to as an "exhaust gas rich state"), it has a characteristic of releasing the absorbed NOx. In an exhaust gas purifying apparatus incorporating this NOx absorbent, in an exhaust gas rich state, NOx released from the NOx absorbent is reduced by HC and CO and discharged as nitrogen gas, and HC and CO are oxidized. It is configured to be discharged as water vapor and carbon dioxide.

[0003] The amount of NOx that can be absorbed by the NOx absorbent naturally has a limit, and this limit value tends to decrease as the NOx absorbent deteriorates. For this reason, an air-fuel ratio sensor is arranged downstream of the NOx absorbent, and the air-fuel ratio enrichment (hereinafter referred to as “reduction enrichment”) for releasing the NOx absorbed by the NOx absorbent is executed. A method of determining the degree of deterioration of the NOx absorbent based on the time from the start to the time when the output of the air-fuel ratio sensor changes to a value indicating the rich air-fuel ratio has been conventionally known (Japanese Patent Laid-Open No. 8-232644). No.).

[0004]

However, in the case where a three-way catalyst is arranged upstream of the NOx absorbent in the exhaust passage of the engine together with the NOx absorbent, even if the above-mentioned reduction enrichment is started, the exhaust gas is exhausted by the three-way catalyst. Since HC and CO in the gas are oxidized, a delay occurs before the exhaust gas containing a large amount of HC and CO components actually flows into the NOx absorbent. Therefore, if the above-described conventional method is applied as it is, it is not possible to accurately determine the deterioration of the NOx absorbent.

The present invention has been made with a focus on this point. Even when a three-way catalyst is arranged upstream of the NOx absorbent, the exhaust gas is designed to accurately determine the deterioration of the NOx absorbent. It is intended to provide a purification device.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an exhaust system for an internal combustion engine, which includes a NOx absorbent for absorbing NOx in exhaust gas in an exhaust gas lean state, N absorbed in
NOx purification means for reducing Ox, a three-way catalyst provided upstream of the NOx purification means and having an oxygen storage capacity,
In an exhaust gas purifying apparatus for an internal combustion engine, which is provided downstream of the NOx purifying means and includes an exhaust concentration sensor for detecting a concentration of a specific component in exhaust gas, an air-fuel ratio of an air-fuel mixture supplied to the engine is theoretically determined. First detection means for detecting a reversal time of the output of the exhaust gas concentration sensor when the air-fuel ratio is switched from rich to lean or vice versa; and Second detection means for detecting a time when the output of the exhaust concentration sensor stagnates near the stoichiometric air-fuel ratio when the output is changed to the rich side after maintaining the lean side, and detection by the first and second detection means A deterioration determining means for determining deterioration of the NOx absorbent based on the result.

Here, the "predetermined time" is when the NOx absorbent is
The time required to absorb NOx up to the limit of the NOx absorption capacity, or a slightly shorter time. For example, the estimated NOx emission per unit time calculated according to the engine operating state is integrated, and the integrated value is calculated. Is the time required until reaches a predetermined allowable value.

According to this configuration, the three-way catalyst is purified by the inversion time of the output of the exhaust gas concentration sensor when the air-fuel ratio of the air-fuel mixture supplied to the engine is switched from rich to lean from the stoichiometric air-fuel ratio or vice versa. The output of the exhaust concentration sensor when the air-fuel ratio of the air-fuel mixture is changed to the rich side after maintaining the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio for a predetermined period of time is determined by the time when the output stagnates near the stoichiometric air-fuel ratio. The purification capability of the source catalyst and the NOx absorbent is detected, and the deterioration of the NOx absorbent is determined based on the two detection results. Therefore, it is possible to accurately determine the deterioration of the NOx absorbent except for the influence of the three-way catalyst.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram of a control device for an internal combustion engine (hereinafter referred to as an “engine”) including an exhaust gas purifying device according to an embodiment of the present invention. A throttle valve 3 is disposed in the middle of the pipe 2. The throttle valve 3 has a throttle valve opening (θT
H) The sensor 4 is connected, and outputs an electric signal corresponding to the opening degree of the throttle valve 3 and supplies it to an engine control electronic control unit (hereinafter referred to as “ECU”) 5.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of an intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The ECU 5 is electrically connected to the ECU 5 and controls a valve opening time of the fuel injection valve 6 based on a signal from the ECU 5.

On the other hand, an intake pipe absolute pressure (PBA) sensor 7 is provided immediately downstream of the throttle valve 3, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 7 is supplied to the ECU 5. . Further, an intake air temperature (TA) sensor 8 is mounted downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies the electric signal to the ECU 5.

The engine water temperature (TW) sensor 9 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5.

An engine speed (NE) sensor 10 is provided around a camshaft or a crankshaft (not shown) of the engine 1.
And a cylinder discrimination (CYL) sensor 11. The engine speed sensor 10 outputs a TDC signal pulse at a crank angle position before a predetermined crank angle with respect to the top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1 (every 180 ° crank angle in a four-cylinder engine). The cylinder discriminating sensor 11 outputs a cylinder discriminating signal pulse at a predetermined crank angle position of a specific cylinder. These signal pulses are supplied to the ECU 5.

The exhaust pipe 12 is provided with a three-way catalyst 16 and a NOx purifying means 17 constituting an exhaust gas purifying device. The NOx purifying means 17 is arranged downstream of the three-way catalyst 16.

The three-way catalyst 16 has an oxygen storage capacity, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set leaner than the stoichiometric air-fuel ratio, and the exhaust gas lean has a relatively high oxygen concentration in the exhaust gas. In this state, oxygen in the exhaust gas is accumulated, and conversely, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set to a richer side than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is low, and the HC and CO components are low. When the exhaust gas is rich, the accumulated oxygen has a function of oxidizing HC and CO in the exhaust gas.

The NOx purifying means 17 contains a NOx absorbent for absorbing NOx and a catalyst for promoting oxidation and reduction. As the NOx absorbent, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set leaner than the stoichiometric air-fuel ratio, and the oxygen concentration in the exhaust gas is relatively high (NOx is large) (exhaust gas lean state). Means that while storing NOx, the air-fuel ratio supplied to the engine 1 is set to be richer than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas is low, and the HC and CO components are high (exhaust gas rich state). Is a storage type having a characteristic of releasing stored NOx, or adsorbing NOx in an exhaust gas lean state and NOx in an exhaust gas rich state.
Use an adsorption type that reduces NOx purification means 1
In the exhaust gas lean state, NOx is absorbed by the NOx absorbent, while in the exhaust gas rich state, NOx absorbed by the NOx absorbent is reduced by HC and CO to be discharged as nitrogen gas. , C
O is configured to be oxidized and discharged as water vapor and carbon dioxide. As the storage type NOx absorbent, for example, barium oxide (Ba0) is used, and as the adsorption type NOx absorbent, for example, sodium (Na) and titanium (Ti) or strontium (Sr) and titanium (Ti) are used. For example, platinum (Pt) is used as a catalyst in both the storage type and the adsorption type. This NOx absorbent generally has a characteristic that the higher the temperature, the easier it is to release the absorbed NOx.

If NOx is absorbed up to the limit of the NOx absorbing capacity of the NOx absorbent, that is, up to the maximum NOx absorption amount, it becomes impossible to absorb NOx any more, so that the air-fuel ratio is enriched to release and reduce NOx in a timely manner. That is, N
Perform Ox reduction enrichment.

At a position upstream of the three-way catalyst 16, a proportional type air-fuel ratio sensor 14 (hereinafter referred to as "LAF sensor 14") is mounted. The LAF sensor 14 detects the oxygen concentration (air-fuel ratio) in the exhaust gas. An electric signal that is approximately proportional is output, and E
Supply to CU5. A binary oxygen concentration sensor 15 (hereinafter “O2 sensor 1”)
5 ") and its detection signal is
5 is supplied. This O2 sensor 15 has its output VO
2 has a characteristic that changes abruptly before and after the stoichiometric air-fuel ratio, and its output VO2 becomes higher on the rich side and lower on the lean side than the stoichiometric air-fuel ratio.

In the engine 1, the valve timing of the intake valve and the exhaust valve can be switched between a high-speed valve timing suitable for a high-speed rotation region of the engine and a low-speed valve timing suitable for a low-speed rotation region of the engine. It has a mechanism 30. The switching of the valve timing includes the switching of the valve lift amount. Further, when the low-speed valve timing is selected, one of the two intake valves is stopped to stabilize the air-fuel ratio even when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio. We have tried to ensure the combustion that we did.

The valve timing switching mechanism 30 switches the valve timing via a hydraulic pressure. An electromagnetic valve and a hydraulic pressure sensor for switching the hydraulic pressure are connected to the ECU 5. The detection signal of the oil pressure sensor is supplied to the ECU 5, and the ECU 5 controls the solenoid valve to control the switching of the valve timing according to the operating state of the engine 1.

The ECU 5 has an input circuit 5a having functions of shaping input signal waveforms from various sensors, correcting a voltage level to a predetermined level, converting an analog signal value to a digital signal value, and a central processing circuit ( The CPU 5b includes a storage unit 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.

The CPU 5b determines various engine operating states based on the various engine parameter signals described above, and according to the determined engine operating states,
Based on the following equation (1), a fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated.

TOUT = TI × KCMD × KLAF × K1 + K2 (1) Here, TI is a basic fuel injection time of the fuel injection valve 6, and TI is set according to the engine speed NE and the intake pipe absolute pressure PBA. Determined by searching the map. TI
The map shows the engine speed NE and the absolute pressure PB in the intake pipe.
In the operating state corresponding to A, the air-fuel ratio of the air-fuel mixture supplied to the engine is set to be substantially equal to the stoichiometric air-fuel ratio. That is, the basic fuel injection time TI has a value that is substantially proportional to the intake air amount (weight flow rate) of the engine. Therefore, the basic fuel injection time TI is set to a certain period TSU.
By integrating over M, a parameter corresponding to the integrated value of the exhaust gas flow rate discharged during that period can be obtained.

KCMD is a target air-fuel ratio coefficient. The engine speed NE, the intake pipe absolute pressure PBA, and the engine coolant temperature T
It is set according to the engine operating parameters such as W. The target air-fuel ratio coefficient KCMD is proportional to the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F / A, and takes a value of 1.0 at the stoichiometric air-fuel ratio.

The detected equivalent ratio KACT calculated from the detected value of the LAF sensor 14 is equal to the target equivalent ratio KCMD.
Is an air-fuel ratio correction coefficient calculated by PID control so as to coincide with The air-fuel ratio correction coefficient KLAF is determined by the three-way catalyst 1
The determination of the oxygen storage capacity of No. 6 is performed by feedback control according to the output of the O2 sensor 15 as described later.

K1 and K2 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, so that various characteristics such as fuel consumption characteristics and engine acceleration characteristics can be optimized according to the engine operating condition. Is determined to be a predetermined value.

The CPU 5b supplies a drive signal for opening the fuel injection valve 6 to the fuel injection valve 6 via the output circuit 5d based on the fuel injection time TOUT obtained as described above.

FIG. 2 is a flowchart of a process for calculating the fuel injection time TOUT and controlling the fuel supply of the engine 1. This process is executed at regular intervals.

In step S11, it is determined whether or not the engine is in the lean operation, that is, the stored value KCMDB of the target air-fuel ratio coefficient KCMD stored in step S19 described later during the normal control in which the NOx reduction enrichment is not performed becomes "1.0". It is determined whether KCMDB is smaller than 1.0, and if KCMDB ≧ 1.0 and the engine is not performing the lean operation, the process immediately proceeds to step S18, where the target air-fuel ratio coefficient KCMD and the like according to the engine operating state are set. ) Is performed. Next, the target air-fuel ratio coefficient KCMD is stored in the stored value KCM.
The data is stored as a DB (step S19), and the process ends.

If KCMDB <1.0 in step S11 and the engine is operating lean, the next step S13 is performed according to the engine speed NE and the intake pipe absolute pressure PBA.
(Step S)
12). The increment value ADDNOx is a parameter corresponding to the amount of NOx discharged per unit time during the lean operation, and is set to increase as the engine speed NE increases and the intake pipe absolute pressure PBA increases. Have been.

In step S13, step S
The increment value ADDNOx determined in step 12 is applied, and the NOx amount counter CNOx is incremented. This gives N
A count value corresponding to the Ox emission amount is obtained.

CNOx = CNOx + ADDNOx In the following step S14, it is determined whether or not the value of the NOx amount counter CNOx has exceeded an allowable value CNOxREF. If the answer is negative (NO), the routine proceeds to step S18, where normal fuel supply control is performed. Allowable value CN
Ox is set to a value corresponding to the NOx amount slightly smaller than the maximum NOx absorption amount of the NOx absorbent.

In step S14, CNOx> CNOxR
When EF is reached, the target air-fuel ratio coefficient KCMD is set to 14.
The NOx reduction enrichment is set to a value equivalent to about 0 (step S15). This NOx reduction enrichment is performed for a relatively short time, for example, about 1 or 2 seconds. In step S16, it is determined whether or not the NOx reduction enrichment has been completed. If the NOx reduction enrichment has not been completed, the present process is immediately terminated.
The count value of the Ox amount counter CNOx is reset to "0" (step S17). Therefore, until the NOx reduction enrichment ends, steps S14 to S15,
The process of S16 is repeatedly executed, and when the process is completed, the process proceeds from step S14 to S18.

According to the processing of FIG. 2, during lean operation, N
Each time the value of the Ox amount counter CNOx reaches the allowable value CNOxREF, the NOx reduction enrichment is performed, and the NOx absorbed by the NOx absorbent is released.

FIG. 3 is a flowchart of a process for judging the deterioration of the NOx absorbent.
This is executed by the PU 5b. The deterioration determination process is executed when the engine speed NE, the intake pipe absolute pressure PBA, the engine coolant temperature TW, the intake air temperature TA, and the like are within predetermined ranges and the engine is in a relatively stable operating state. You.

In step S20, it is determined whether or not an end flag FDONE indicating "1" indicating that the deterioration determination has been completed is "1". If FDONE = 1, the present process is immediately terminated. If FDONE = 0, it is determined whether or not the stoichiometric operation is being performed to set the target air-fuel ratio coefficient KCMD to "1.0" (step S21). If the stoichiometric operation is being performed, TCHK measurement processing is executed. (Step S
22). In the TCHK measurement process, proportional integration control of the air-fuel ratio is performed according to the output SVO2 of the O2 sensor 15, and the sensor output SVO2 is inverted from the lean side to the rich side with respect to the predetermined reference voltage SVREF, and the air-fuel ratio correction coefficient KLAF is calculated. The inversion time TL from the time when the output is changed in the lean direction by the proportional term PL to the time when the output SVO2 is inverted in the reverse direction,
And the output SVO2 is inverted from the rich side to the lean side with respect to the reference voltage SVREF, and the output SVO2 is changed from the time when the air-fuel ratio correction coefficient KLAF is changed in the rich direction by the proportional term PR.
The inversion time TR until the VO2 is inverted in the reverse direction is measured, and the determination time TCHK is calculated as the average value of these inversion times TL and TR. That is, as shown in FIG. 4, the O2 sensor output SVO2 is changed to a predetermined reference voltage SVRE.
F at the time when the lean side is reversed from the lean side to the rich side (t
At (1, t3), the air-fuel ratio correction coefficient KLAF is reduced stepwise by the proportional term PL, and thereafter, while the O2 sensor output SVO2 is higher than the reference voltage SVREF, the air-fuel ratio correction coefficient KLAF is gradually reduced, and the O2 sensor output is reduced. S
At the time (t2, t4) at which VO2 is inverted from the rich side to the lean side with respect to the reference voltage SVREF, the air-fuel ratio correction coefficient KLAF is increased stepwise by the proportional term PR, and thereafter, the O2 sensor output SVO2 is changed to the reference voltage SVREF.
While the temperature is lower than F, control for gradually increasing the air-fuel ratio correction coefficient KLAF is executed, and the inversion times TL, T
R is measured, and a determination time TCHK is calculated as an average value of these inversion times TL and TR. The measurement of the determination time TCHK is performed a plurality of times, and each measurement is averaged together with the measurement values obtained so far. Since the determination time TCHK decreases as the oxygen storage capacity of the three-way catalyst 16 decreases,
As a result, a parameter indicating the storage capacity of the three-way catalyst 16 can be obtained.

Since the determination time TCHK varies not only with the oxygen storage capacity of the three-way catalyst 16 but also with the exhaust gas flow rate, in step S23, the determination time TCHK is applied to the following equation (2) to determine the three-way catalyst determination parameter. OSCIDX
, The influence of the exhaust gas flow rate is corrected.

OSCIDX = TCHK × GAIRSUM (2) Here, GAIRSUM is an integrated value (hereinafter referred to as “flow rate integrated value”) of a parameter representing the exhaust gas flow rate during the TCHK measurement processing execution period TMSR. Specifically, it is an integrated value of the basic fuel injection time TI. Since the basic fuel injection time TI has a value that is substantially proportional to the intake air amount (weight flow rate) of the engine as described above, the basic fuel injection time TI is calculated by integrating the basic fuel injection time TI over the measurement processing execution period TMSR. A parameter corresponding to the integrated value of the flow rate of exhaust gas discharged during the period can be obtained.

By determining the oxygen storage capacity of the three-way catalyst using the three-way catalyst determination parameter OSCIDX calculated by using the above equation (2), the three-way catalyst is less affected by the operating state of the engine. Accurate determination can be performed over a wide range.

On the other hand, if it is determined in step S21 that the stoichiometric operation is not being performed, it is determined whether or not the lean operation is being performed (KCMDB <1.0) (step S24). If the lean operation is being performed, a TNOx measurement process is performed.

In the TNOx measurement process, NOx is added to the NOx absorbent.
This is a process of executing reduction enrichment in a state where x is absorbed and measuring a time TNOx during which the O2 sensor output SVO2 stagnates near a value corresponding to the stoichiometric air-fuel ratio at that time. More specifically, when executing the NOx reduction rich during the lean operation, as shown in FIG. 5, after the time point t11 when the target air-fuel ratio coefficient KCMD is changed to a value larger than 1.0, the O2 sensor output SVO2 From the time t13 when the voltage exceeds the predetermined voltage SV1, the O2 sensor output SVO2 changes to the reference voltage S
Rich transition time TN until time t12 when VREF is reached
Measure Ox. This measurement is performed a plurality of times, and each measurement is averaged together with the measurement values obtained so far. The predetermined voltage SV1 is a reference voltage SVREF corresponding to the stoichiometric air-fuel ratio.
(For example, 0.4 V)
Degree).

The rich transition time TNOx becomes longer as the absorption capacity of the NOx absorbent becomes larger.
A parameter for determining the NOx absorption capacity of the x absorbent can be obtained. However, the rich transition time TNOx also becomes shorter as the exhaust gas flow rate becomes larger, similarly to the above-mentioned determination time TCHK.
5 is applied to the following equation (3) to determine the NOx absorbent determination parameter NSCI.
DX is calculated (step S26).

NSCIDX = TNOX × GAIRSUM (3) Then, it is determined whether or not both the number of times nTCHK for measuring the determination time TCHK and the number of times nTNOX for measuring the rich transition time TNOx have reached a predetermined number n0 (for example, five times) (step). S27), nTCHK <n0 or nTNOX <
If n0, the process ends. If nTCK ≧ n0 and nTNOx ≧ n0, the three-way catalyst determination parameter OC from the NOx absorbent determination parameter NSCIDX is used.
It is determined whether the value obtained by subtracting SIDX is smaller than the reference value IDXREF (step S28). And NSC
If IDX-OSCIDX ≧ IDXREF, N
The Ox absorbent is determined to be normal (step S30), and NSC
If IDX-OSCIDX <IDXREF, NOx
It is determined that the absorbent has deteriorated (step S29). After execution of step S29 or S30, the end flag FDON
E is set to "1" (step S31), and this processing ends. Here, the reference value IDXREF is set to a value corresponding to, for example, the NOx absorbent having a NOx absorption capacity of about 50% of a new product.

As described above, the rich transition time TNOx varies depending on the NOx absorption capacity of the NOx absorbent and the exhaust gas flow rate. However, when the three-way catalyst 16 is provided further upstream, the three-way catalyst 16 It also depends on the oxygen storage capacity of That is, even if the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is changed to a richer side than the stoichiometric air-fuel ratio, HC and CO in the exhaust gas (feed gas) are reduced by the three-way catalyst 16.
Since the amount of HC and CO that are oxidized at the NOx absorbent and reach the NOx absorbent decreases, the rich transition time TNOx tends to be longer as the three-way catalyst 16 has a larger oxygen storage capacity. Therefore, in the present embodiment, the NOx absorbent determination parameter N
By subtracting the three-way catalyst determination parameter OSCIDX from the SCIDX, the influence of the oxygen storage capacity of the three-way catalyst 16 is eliminated, and the deterioration of the NOx absorbent is determined. This makes it possible to accurately determine the deterioration of the NOx absorbent.

In this embodiment, the O2 sensor 15 corresponds to an exhaust gas concentration sensor, and the TC2 in step S22 in FIG.
The HK measurement processing corresponds to the first detection means, the TNOx measurement processing in step S25 in the figure corresponds to the second detection means, and steps S23 and S26 to S30 in the figure correspond to the deterioration determination means.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the fuel injection valve 6 may be provided in each cylinder so as to inject fuel directly into the combustion chamber of the engine 1 instead of the intake pipe 2.

The exhaust gas concentration sensor is not limited to the oxygen concentration sensor, but may be a NOx concentration sensor for detecting the concentration of NOx in the exhaust gas.

[0049]

As described above in detail, according to the present invention, the output of the exhaust gas concentration sensor when the air-fuel ratio of the air-fuel mixture supplied to the engine is switched from rich to lean from the stoichiometric air-fuel ratio or vice versa. The purifying ability of the three-way catalyst is detected based on the inversion time, and the output of the exhaust gas concentration sensor when the air-fuel ratio of the air-fuel mixture is changed to the rich side after maintaining the air-fuel ratio on the lean side from the stoichiometric air-fuel ratio for a predetermined period of time is calculated. The purifying ability of the three-way catalyst and the NOx absorbent is detected based on the stagnant time, and the deterioration of the NOx absorbent is determined based on the two detection results. Therefore, it is possible to accurately determine the deterioration of the NOx absorbent except for the influence of the three-way catalyst.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine including an exhaust gas purification device according to an embodiment of the present invention and a control device thereof.

FIG. 2 is a flowchart of a process for performing fuel supply control.

FIG. 3 is a flowchart of a process for determining deterioration of a NOx absorbent.

FIG. 4 is a diagram illustrating a parameter measurement process for determining the oxygen storage capacity of the three-way catalyst.

FIG. 5 is a diagram for explaining a parameter measurement process for determining the NOx absorbing ability of the NOx absorbent.

[Explanation of symbols]

1 internal combustion engine 5 electronic control unit (first detecting means, second detecting means
12 exhaust pipe 15 oxygen concentration sensor (exhaust gas concentration sensor) 16 three-way catalyst 17 NOx purification means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 45/00 314 F02D 45/00 314Z

Claims (1)

[Claims] 1. An NO provided in an exhaust system of an internal combustion engine to absorb NOx in exhaust gas in an exhaust gas lean state.
a NOx purifying means which contains an x-absorbent and reduces NOx absorbed in an exhaust gas rich state; a three-way catalyst provided upstream of the NOx purifying means and having an oxygen storage capacity; and a downstream side of the NOx purifying means. And an exhaust gas purification device for an internal combustion engine, the exhaust gas purification device comprising: an exhaust gas concentration sensor for detecting the concentration of a specific component in the exhaust gas. First detecting means for detecting the reversal time of the output of the exhaust gas concentration sensor when the air-fuel ratio is switched to the side or vice versa, and after maintaining the air-fuel ratio of the air-fuel mixture leaner than the stoichiometric air-fuel ratio for a predetermined time. Second detection means for detecting a time when the output of the exhaust gas concentration sensor stagnates near the stoichiometric air-fuel ratio when the output is changed to the rich side; and detection detection by the first and second detection means. NOx based on the fruit
An exhaust gas purifying apparatus for an internal combustion engine, comprising: a deterioration determining means for determining deterioration of an absorbent.