JP2000110655A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of suppressing the discharge of NOx during a lean operation, and of having an accurate misfire judging function exhibiting no erroneous judgment caused by making an air-fuel ratio richer for reducing NOx. SOLUTION: When the variable ΔM acting as a parameter indicating the fluctuation of engine revolutions is found to be smaller than the threshold of a misfire judgement, it is determined that the case is caused by misfire (S79). Just after a rich mixture forming flag FRICH is changed wherein it is indicated by (1) that reduction enrichment is being carried out, namely, in a transition condition just after an air-fuel ratio is changed as reduction enrichment rich, in place of a first misfire judging threshold MSLM 1 (S76) to be used for a condition other than the transition condition, misfire is judged by using a second misfire judging threshold MSLMT 2.

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 apparatus for purifying nitrogen oxides (NOx) in an exhaust system.
The present invention relates to an exhaust gas purifying apparatus provided with a NOx purifying apparatus having a built-in absorbent, and further having a misfire determination function for an internal combustion engine.

[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 to be leaner than the stoichiometric air-fuel ratio, the amount of NOx emission tends to increase. NO with built-in NOx absorbent
2. Description of the Related Art A technology for providing an x-purification device and purifying exhaust gas has been conventionally known. This NOx absorbent absorbs NOx when 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 is large) (hereinafter referred to as "exhaust gas lean state"). While
Conversely, when the air-fuel ratio is set near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is relatively low (hereinafter referred to as “exhaust gas rich state”),
It has the property of releasing absorbed NOx. In the exhaust gas rich state, the NOx purifying device including the NOx absorbent has a feature that NOx released from the NOx absorbent is H
Reduced by C and CO and discharged as nitrogen gas,
HC and CO are oxidized and discharged as water vapor and carbon dioxide.

Since the amount of NOx that can be absorbed by the above-mentioned NOx absorbent naturally has a limit, it is not possible to continue only lean operation for a long time. Therefore, in order to release the absorbed NOx, the air-fuel ratio is temporarily enriched to release the NOx from the NOx absorbent and release the NOx.
Conventionally, an air-fuel ratio control method that reduces the air-fuel ratio has been known (for example, Japanese Patent No. 2586739). Less than,
This temporary enrichment is called “reduction enrichment”.

According to the technique disclosed in this publication, the amount of NOx absorbed by the NOx absorbent is estimated according to the engine operating state such as the engine load and the engine speed, and the estimated N
When the Ox amount exceeds a predetermined allowable amount, reduction enrichment is executed.

When a misfire occurs in the internal combustion engine, unburned fuel is discharged as it is and deteriorates exhaust gas characteristics. Therefore, the occurrence of misfire is determined and the combustion state of the internal combustion engine is determined based on the frequency of occurrence. Conventionally, a technique for performing this is known (for example, JP-A-7-54704). According to the technique disclosed in this publication, a rotational fluctuation of the internal combustion engine is detected, and when the detected rotational fluctuation exceeds a reference value, it is determined that a misfire has occurred.

[0006]

As described above, NO
In the engine equipped with the x purification device, the air-fuel ratio is reduced and enriched intermittently during the lean operation, but the fuel supply amount fluctuates relatively sharply. Therefore, if the conventional misfire determination method as disclosed in Japanese Patent Laid-Open No. 7-54704 is applied as it is, it is erroneously determined that a misfire has occurred even though no misfire has occurred at the start or end of the reduction enrichment. There was a case.

The present invention has been made in view of this point, and has an exhaust gas having an accurate misfire determination function that suppresses the amount of NOx emission during lean operation and that does not have an erroneous determination caused by the reduction enrichment. It is intended to provide a purification device.

[0008]

In order to achieve the above object, the invention according to claim 1 is provided in an exhaust system of an internal combustion engine, and when the exhaust gas is in a lean state where the oxygen concentration in the exhaust gas is relatively high. Nitrogen oxide purifying means for absorbing nitrogen oxides in the exhaust gas and reducing the nitrogen oxides absorbed in an exhaust gas rich state where the oxygen concentration in the exhaust gas is relatively low, and an air-fuel ratio of a mixture supplied to the engine. During a lean operation that is set to a leaner side than the stoichiometric air-fuel ratio, the exhaust gas purifying apparatus for an internal combustion engine includes: a reducing unit that temporarily enriches the air-fuel ratio so that the exhaust gas becomes the exhaust gas rich state. The engine further includes misfire determination means for determining misfire of the engine. The misfire determination means has a different state in a transient state immediately after the air-fuel ratio has been changed by the reducing means, in a transition state other than the transition state. And performing misfire determination in a manner.

According to this configuration, in the transient state immediately after the change of the air-fuel ratio by the reducing means is performed, the misfire determination is performed by a method different from that in other than the transient state. By changing the misfire determination threshold value or changing the arithmetic expression for calculating the parameter indicating the fluctuation of the engine speed, it is possible to make an accurate misfire determination without erroneous determination due to the reduction rich. it can.

More specifically, the misfire determining means calculates a rotation fluctuation parameter indicating a rotation fluctuation of the engine, and determines that a misfire has occurred when the rotation fluctuation parameter becomes larger than a misfire determination threshold value. Then, in the transient state immediately after the change of the air-fuel ratio by the reducing means, the misfire determination means changes the misfire determination threshold to a larger value (a value that is hard to determine misfire) than in the other than the transient state, and determines the misfire. I do.

Alternatively, the misfire determination means makes a misfire determination in the transient state by changing an arithmetic expression used for calculating the rotation fluctuation parameter to a different one from the arithmetic expression used in the case other than the transient state. In this case, the arithmetic expression performs a filtering process on a rotational speed parameter having a value corresponding to the detected engine rotational speed, and the misfire determining unit determines that the degree of contribution of the rotational speed parameter detected in the transient state is small. It is desirable to change the arithmetic expression so as to be relatively small compared to the contribution of the rotation speed parameter detected in a state other than the transient state.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter, referred to as "engine") and a control device thereof, including an exhaust gas purification device according to an embodiment of the present invention. A throttle valve 3 is arranged in the intake pipe 2 of the engine 1. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, and outputs an electric signal corresponding to the opening of the throttle valve 3 to output an electronic control unit for engine control (hereinafter referred to as “ECU”) 5. To supply.

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 an 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.

A signal pulse (hereinafter referred to as a "CYL signal pulse") is provided around a camshaft or a crankshaft (not shown) of the engine 1 at a predetermined crank angle position of a specific cylinder of the engine 1.
A cylinder discriminating sensor (hereinafter referred to as “CYL sensor”) 12 at a crank angle position that is a predetermined crank angle before the top dead center (TDC) at the start of the intake stroke of each cylinder (the crank angle of 180 in a four-cylinder engine). T)
A TDC sensor 11 for generating a DC signal pulse, and one pulse (hereinafter referred to as a “CRK signal pulse”) at a constant crank angle (for example, 30 °) cycle shorter than the cycle of the TDC signal pulse
) Is provided, and a CYL signal pulse, a TDC signal pulse and a CRK signal (crank angle signal) pulse are supplied to the ECU 5.

The spark plug 19 of each cylinder of the engine 1
It is connected to the ECU 5 via the distributor 18.

The exhaust pipe 12 is provided with a NOx purifying device 16 as a nitrogen oxide purifying means. The NOx purifying device 16 includes a NOx absorbent that absorbs NOx and a catalyst for promoting oxidation and reduction. As the NOx absorbent, when the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set leaner than the stoichiometric air-fuel ratio, and when the oxygen concentration in the exhaust gas is relatively high (NOx is large), NOx On the other hand, in the exhaust gas rich state where the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is relatively low, NOx absorbed
A storage type having a characteristic of releasing NOx or an adsorption type of adsorbing NOx in an exhaust gas lean state and reducing it in an exhaust gas rich state is used. NO
The x purification device 16 is configured to perform N
In the exhaust gas rich state, NOx released from the NOx absorbent is reduced by HC and CO to be discharged as nitrogen gas, while HC and CO are oxidized to form steam and carbon dioxide. It is configured to be emitted as carbon. Storage type NO
As the x absorbent, for example, barium oxide (Ba0) is used. As the adsorption type NOx absorbent, for example, sodium (Na) and titanium (Ti) or strontium (Sr) and titanium (Ti) are used. In both the storage type and the adsorption type, for example, platinum (P
t) is used. This NOx absorbent generally has a characteristic that the higher the temperature, the easier it is to release the absorbed NOx.

When 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, NOx can no longer be absorbed, so that the air-fuel ratio is enriched to release and reduce NOx in a timely manner. That is, reduction enrichment is performed.

A proportional air-fuel ratio sensor 14 (hereinafter referred to as "LAF sensor 14") is mounted at an upstream position of the NOx purification device 16. The LAF sensor 14 detects the oxygen concentration (air-fuel ratio) in the exhaust gas. A substantially proportional electric signal is output and supplied to the ECU 5.

In the engine 1, the valve timing of the intake valve and the exhaust valve can be switched between two stages: 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. 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, and an electromagnetic valve and a hydraulic 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 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value into a digital signal value. 5b, various arithmetic programs executed by the CPU 5b, tables and maps used in the arithmetic programs,
Storage means 5c for storing calculation results and the like;
And an output circuit 5d for supplying a drive signal to the ignition plug 19
And so on.

The CPU 5b determines various engine operating states in the air-fuel ratio feedback control region and a plurality of specific operating regions in which the air-fuel ratio feedback control is not performed based on the various engine parameter signals described above. The fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated based on the following equation (1) according to the operating state.

TOUT = TI × KCMD × KLAF × K1 + K2 (1) Here, TI is a basic fuel injection time of the fuel injection valve 5, 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 is set such that the air-fuel ratio of the air-fuel mixture supplied to the engine substantially becomes the stoichiometric air-fuel ratio in the operating state corresponding to the engine speed NE and the intake pipe absolute pressure PBA on the map.

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

K1 and K2 are other correction coefficients and correction variables calculated in accordance with 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, and responds to the engine operating state. Then, a signal for driving the spark plug 19 is supplied to the spark plug 19 via the distributor 18.

FIG. 2 is a flowchart of a process for controlling the fuel supply of the engine 1. This processing is also performed at regular intervals.
This is executed by the PU 5b.

In step S12, it is determined whether the engine is in the lean operation, that is, the target air-fuel ratio coefficient K stored in step S17 described later during normal control in which the reduction enrichment is not performed.
It is determined whether or not the stored value KCMDB of the CMD is smaller than “1.0”. As a result, when KCMDB ≧ 1.0 and the lean operation is not being performed, the process immediately proceeds to step S16, where the target air-fuel ratio coefficient KCMD according to the engine operating state is set.
The normal fuel supply control using the above equation (1) is performed. Next, the target air-fuel ratio coefficient KCMD is stored as the storage value KCMDB (step S17), and the process ends.

If KCMDB <1.0 in step S12 and the engine is operating lean, the next step S14 is performed according to the engine speed NE and the intake pipe absolute pressure PBA.
(Step S)
13). The increment value ADDNOx is a parameter corresponding to the amount of NOx discharged per unit time during the lean operation, and is set so as to increase as the engine speed NE increases and as the intake pipe absolute pressure PBA increases. Have been.

At step S14, step S
The increment value ADDNOx determined in step 13 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 S15, it is determined whether or not the value of the NOx amount counter CNOx has exceeded the allowable value CNOxREF. If the answer is negative (NO), the routine proceeds to step S16, 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 S15, CNOx> CNOxR
When it becomes EF, the enrichment flag FRICH is set to "1" (step S18), and the reduction enrichment is performed to set the target air-fuel ratio coefficient KCMD to a value corresponding to an air-fuel ratio of about 14.0 (step S19). This reduction enrichment is performed over the enrichment time TRICH (for example, about 1 or 2 seconds).

In step S20, it is determined whether or not the reduction enrichment has been completed. If the reduction enrichment has not been completed, this processing is immediately terminated. If the reduction enrichment has been completed, the count value of the NOx amount counter CNOx is counted. Is reset to “0”, and the enrichment flag FRICH is set to “0”.
(Step S21). According to the processing of FIG. 2, during the lean operation, every time the value of the NOx amount counter CNOx reaches the allowable value CNOxREF, the enrichment flag FRICH is set to “1”, the reduction enrichment is performed, and the NOx absorbent Is reduced.

Next, the misfire determination process of the engine 1 will be described with reference to FIGS. FIG. 3 is a diagram showing an overall configuration of a misfire determination process of the engine 1 (executed by the CPU 5b). FIG. 3A shows a CRK process which is executed in synchronism with each generation of the CRK signal pulse. In this process, the CRK signal pulse generation time interval (a parameter proportional to the reciprocal of the engine speed) is shown. ) Is calculated (hereinafter referred to as “first average value”) TAVE (step S3).
1). FIG. 2B shows a TDC process executed in synchronism with the generation of each TDC signal pulse. In this process, the average value of the first average value TAVE calculated by the CRK process (hereinafter referred to as “the The amount of change ΔM of M (referred to as “average value of 2”) is calculated (step S41), and it is determined whether or not misfire has occurred in the engine 1 based on the amount of change ΔM (step S42).

FIG. 4 is a flowchart of the process for calculating the first average value TAVE in step S31 of FIG. 3A.

In step S51, the generation time interval CRMe (n) of the CRK signal pulse is measured. In particular,
As shown in FIG. 5, every time the crankshaft rotates 30 degrees, CRMe (n), CRMe (n + 1), CRMe (n +
2) is measured.

In step S52, 1 is obtained by the following equation (2).
The first average value TAVE (n) is calculated as the average value of 12 CRMe values from the previous measurement value CRMe (n-11) to the latest measurement value CRMe (n).

(Equation 1)

In this embodiment, since the CRK signal pulse is generated every time the crankshaft rotates 30 degrees, the first average value TAVE (n) is an average value corresponding to one rotation of the crankshaft. By performing such an averaging process, a primary vibration component of the engine rotation for one cycle of one rotation of the crankshaft, that is, a mechanical error (a manufacturing error, an installation error, etc.) ) Can be removed. TAVE (n)
The engine speed NE is calculated based on the value.

FIG. 6 is a flowchart of the ΔM calculation processing in step S41 of FIG. 3B.

In step S61, the following equation (3) is used.
The calculated value TAVE (n−5) five times before the first average value TAVE
6 TAs from 5) to the latest calculated value TAVE (n)
A second average value M (n) is calculated as the average value of the VE values.

(Equation 2)

In the present embodiment, the engine 1 is a four-cylinder four-cycle engine, and ignition is performed in any one of the cylinders every time the crankshaft rotates 180 degrees. Therefore, the second average value (n) is an average value of the first average value TAVE (n) for each ignition cycle. By performing such averaging processing, it is possible to remove a secondary vibration component represented as a torque fluctuation of the engine rotation due to combustion, that is, a vibration component of a crankshaft half rotation cycle. The averaging process corresponds to a low-pass filter process for attenuating low frequency components.

In the following step S62, high-pass filter processing of the second average value M (n), that is, processing of attenuating high-frequency components, is performed by the following equation (4). The second average value after the high-pass filter processing is FM (n).

FM (n) = b (1) × M (n) + b (2) × M (n−1) + b (3) × M (n−2) −a (2) FM (n−1) −a (3) FM (n−2) (4) where b (1) to b (3), a (2), and a (3) are filter coefficients, for example, 0.2096, −0, respectively. .4192,
The values are set to 0.2096, 0.3557, and 0.1940. Further, FM (0) and FM (1) each have a value of 0, and the equation (4) is applied to n having a value of 2 or more.

By this high-pass filter processing, M
(N) The low-frequency component of about 10 Hz or less included in the value is removed, and the influence of vibration transmitted from the drive system to the engine (for example, vibration caused by torsion of the crankshaft, road surface vibration transmitted from the tire, etc.) can be removed. it can.

In a succeeding step S63, a change amount ΔM (n) of the second average value FM (n) subjected to the high-pass filtering is performed.
Is calculated by the following equation (5). ΔM (n) = FM (n) −FM (n−1) (5)

The second after the high-pass filter processing is performed.
Since the polarity of the average value FM (n) is inverted with respect to the M (n) value, if a misfire occurs in the engine 1, the M (n) value increases, so the FM (n) value decreases in the negative direction. Increase
The ΔM (n) value also tends to increase in the negative direction. That is, the absolute value | ΔM (n) | of the variation ΔM (n) corresponds to the rotation fluctuation parameter of the engine 1, and when a misfire occurs, the absolute value | ΔM (n) | tends to increase.

FIG. 7 is a flowchart of a process for performing misfire determination and misfire cylinder discrimination based on the change amount ΔM calculated as described above.

In step S71, it is determined whether or not the monitoring execution condition, that is, whether misfire determination can be performed. The monitoring execution condition is satisfied, for example, when the engine water temperature TW, the intake air temperature TA, the engine speed NE, and the like are within a predetermined range.

When the monitor execution condition is not satisfied, the value of the counter CTR defining the period of the transient state immediately after the change of the air-fuel ratio accompanying the execution of the reduction enrichment is set to "0" (step S72), and this processing is executed. finish. On the other hand, when the monitor execution condition is satisfied, whether the enrichment flag FRICH indicating that reduction enrichment is being performed is indicated by “1” has been inverted, that is, whether the flag FRICH has changed from 0 to 1 or from 1 to 0 Is determined (step S73). If the answer is negative (NO), the value of the counter CTR is decremented by "1" (step S74), and the counter CT is decremented.
It is determined whether or not the value of R is “0” (Step S7)
5). Since the value of the counter CTR does not take a negative value, step S74 is performed with the count value “0”.
Is executed, the value “0” is maintained. In that case, the process proceeds from step S75 to step S76,
The change amount ΔM is equal to the first misfire determination threshold value MSLMT1 (<0).
It is determined whether or not (| ΔM | is larger than | MSLMT1 |). Here, the negative misfire determination threshold M
SLMT1 is read from a map set according to the engine speed NE and the engine load (intake pipe absolute pressure PBA). The absolute value of the misfire determination threshold value MSLMT1 is set to decrease as the engine speed NE increases, and set to increase as the engine load increases.

When the answer to step S76 is negative (NO), that is, when ΔM ≧ MSLMT1, the program ends immediately, and the answer to step S76 is affirmative (YES).
That is, when ΔM <MSLMT1 holds, it is determined that a misfire has occurred in the previously ignited cylinder (step S7).
9). As described above, when a misfire occurs, ΔM
(N) The value increases in the negative direction. Also,
The reason why misfire is determined to have occurred in the previous ignition cylinder is that a delay is generated by the high-pass filter processing.

If the answer in step S73 is affirmative (YE
S), that is, immediately after the enrichment flag FRICH is inverted, the counter CTR is set to a predetermined value NTR (for example, 6) that determines the period of the transient state (step S7).
7) The change amount ΔM is equal to the second misfire determination threshold value MSLMT2
It is determined whether it is smaller than (<0) (Step S7)
8). The second misfire determination threshold value MSLMT2 is a determination threshold value for a transient state, and is set to a value smaller than the first misfire determination threshold value MSLMT1, that is, MSLMT2 <MSLMT.
1 (| MSLMT2 |> | MSLMT1 |). Specifically, a first misfire determination threshold value MSLMT1 is calculated according to the engine speed NE and the intake pipe absolute pressure PBA, and MSLMT2 = MSL.
It is calculated as MT1-DLMT. DLMT is a positive predetermined value. Thereby, the second misfire determination threshold value MSLM
T2 is set to a value that is more difficult to determine as misfire as compared with the first misfire determination threshold value MSLMT1, that is, a value corresponding to a larger rotation fluctuation.

If it is determined in step S78 that ΔM ≧ MSLMT2, the process immediately ends, and ΔM <MSLMT2
Is established, it is determined that a misfire has occurred in the previously ignited cylinder (step S79). When the counter CTR is set to the predetermined value NTR in step S77,
Until TR = 0 (6TD when NTR = 6)
(C period) is determined to be in a transient state immediately after the air-fuel ratio change, and steps S73, S74, S76, and S78 are repeatedly executed. After CTR = 0, step S7 is performed.
The process proceeds from S5 to S76.

According to the processing of FIG. 7, in the transient state immediately after the change of the air-fuel ratio due to the reduction enrichment, the first misfire determination threshold value MSL is used instead of the first misfire determination threshold value MSLMT1.
Second misfire determination threshold MSLM having an absolute value greater than MT1
Since misfire determination is performed using T2, it is possible to prevent erroneous determination that a misfire has occurred without a misfire due to rotation fluctuations of the engine 1 caused by an air-fuel ratio change accompanying the enrichment with reduction.

In this embodiment, steps S13 to S13 in FIG.
S15 and S18 to S21 correspond to the reduction means, and the processing of FIG. 3, more specifically, the processing of FIG. 7 corresponds to the misfire determination means,
Absolute value of variation ΔM (n) and misfire determination threshold MSLMT
The absolute values of 1, MSLMT2 correspond to the rotation fluctuation parameter and the misfire determination threshold, respectively.

(Second Embodiment) In the present embodiment, in the transient state immediately after the change of the air-fuel ratio due to the reduction enrichment, instead of changing the misfire determination threshold value, the process of calculating the change amount ΔM is performed. The arithmetic expression of the average value M (n) of No. 2 is changed.

FIG. 8 is a flowchart of the ΔM calculation process in the present embodiment.
Steps S1, S62 and S63 are the same processing steps as in the first embodiment shown in FIG.

In step S101 of FIG. 8, it is determined whether or not the enrichment flag FRICH has been inverted. If not, the value of the counter CTR is decremented by "1" (step S102). It is determined whether or not the value is “0” (step S103).
When step S104 described later is not executed, the value of the counter CTR is “0”, and therefore, step S61 is performed.
Then, the second average value M (n) is calculated by the equation (3) as in the first embodiment.

On the other hand, in step S101, the enrichment flag F
If the RICH has just been inverted, the counter CTR
Is set to a predetermined value NTR (step S104), and a second average value M (n) is calculated by the following equation (6) (step S105).

(Equation 3)

Here, c (0), c (1), c (2),
c (3), c (4) and c (5) are each smaller than 1 and c (0) + c (1) + c (2) + c (3) +
It is a weighting coefficient where c (4) + c (5) = 1. More specifically, assuming that the first average value TAVE (n) immediately after the inversion of the enrichment flag FRICH is TAVE (n0), the value TAVE immediately after the inversion in the arithmetic expression (expression (6)) in step S105. Weight coefficients c (0) to c (5) are set such that the contribution of (n0) is relatively smaller than the contribution of the other first average value TAVE (n). Note that the arithmetic expression (Equation (3)) used in the operation of step S61 is represented by the weighting factors c (0) to c (c) in Expression (6).
This corresponds to the case where (5) is all set to 1/6.

After execution of step S61 or S105,
Steps S62 and S63 are executed in the same manner as in the first embodiment, and high-pass filter processing and calculation of the amount of change ΔM are performed.

When the counter CTR is set to the predetermined value NTR in step S104, step S105 is executed until CTR = 0, and the second average value M (n) is calculated by equation (6). The setting of the weighting coefficients c (0) to c (5) is, for example, when NTR = 6, when CTR = 6, c (0) is a relatively small value as compared with the other coefficients. When CTR = 5, c (1) is set to a relatively small value as compared with other coefficients, and when CTR = 4, c (2) is set as compared with other coefficients. When CTR = 3, c (3) is set to a relatively small value compared with other coefficients, and when CTR = 2, c (4) is set to c (4). When CTR = 1, c (5) is set to a relatively small value compared to the other coefficients.

FIG. 9 is a flowchart of misfire determination and misfire cylinder discrimination processing in this embodiment, in which steps S72, S73 to S75, S77, and S78 in FIG. 7 are deleted. That is, the monitor execution condition is satisfied,
When the change amount ΔM is smaller than the first misfire determination threshold value MSLMT1, the previous cylinder is determined to be misfire. In this embodiment,
The other points are the same as those of the first embodiment.

As described above, in the present embodiment, in the transient state immediately after the change of the air-fuel ratio due to the reduction enrichment, the second state
Is changed, and the second average value M (n) is calculated such that the weight of the first average value TAVE (n0), which is greatly affected by the change in the air-fuel ratio, is reduced. Therefore, the second average value M ((n) is prevented from greatly fluctuating, and the misfire does not occur due to the rotation fluctuation of the engine 1 caused by the air-fuel ratio change accompanying the reduction enrichment. It is possible to prevent erroneous determination of misfire.

In this embodiment, steps S13 to S13 in FIG.
S15 and S18 to S21 correspond to the reduction means, the processing in FIG. 8 corresponds to the misfire determination means, the CRK signal pulse generation time interval CRMe (n) corresponds to the rotation speed parameter, and the change amount ΔM (n) The absolute value corresponds to the rotation fluctuation parameter.

The present invention is not limited to the embodiment described above, and various modifications are possible. For example, in step S62, low-frequency components are removed by high-pass filtering, but high-frequency components are removed together with low-frequency components by band-pass filtering.
The fluctuation component in the engine rotation in the normal state where no misfire has occurred may be removed. Engine 1
The fuel is not limited to being injected into the intake pipe, but may be directly injected into the combustion chamber of each cylinder.

[0069]

As described above in detail, according to the present invention, in the transient state immediately after the change of the air-fuel ratio by the reducing means is performed, the misfire determination is performed by a method different from that in other than the transient state. So, for example, in the transient state,
By changing the determination threshold value for misfire determination or changing an arithmetic expression for calculating a parameter indicating a change in engine speed, an accurate misfire determination without erroneous determination due to reduction enrichment is performed. be able to.

[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 to an internal combustion engine.

FIG. 3 is a flowchart illustrating an overall configuration of a misfire determination process.

FIG. 4 is a flowchart of a process for calculating a first average value (TAVE).

FIG. 5 shows parameters (CRM) corresponding to the engine speed.
It is a figure for explaining the relation between measurement of e) and crankshaft rotation angle.

FIG. 6 is a parameter (ΔM) indicating rotation fluctuation of the engine.
It is a flowchart of a process of calculating.

FIG. 7 is a flowchart of a process for performing misfire determination and misfire cylinder discrimination.

FIG. 8 is a parameter (ΔM) indicating engine speed fluctuation.
9 is a flowchart (second embodiment) of a process for calculating the.

FIG. 9 is a flowchart (second embodiment) of a process for performing misfire determination and misfire cylinder discrimination.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Electronic control unit (reduction means, misfire determination means) 6 Fuel injection valve 10 Crank angle sensor 12 Exhaust pipe 16 NOx purification device 19 Spark plug

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 305 F02D 41/04 305A F-term (Reference) 3G084 BA03 BA05 BA09 BA15 DA04 DA29 EB08 EB22 FA02 FA10 FA11 FA17 FA20 FA24 FA26 FA29 FA34 FA38 3G091 AB05 AB09 BA16 CB03 CB07 EA01 EA06 EA07 EA09 EA13 EA16 EA34 FB10 3G301 JA08 JA23 LA01 MA01 NA08 NB14 NC02 PA07A PA10A PA11A PB05A PC09A PD02A PE02A PE08A

Claims (1)

[Claims] 1. An exhaust system for an internal combustion engine, which absorbs nitrogen oxides in the exhaust gas when the exhaust gas is in a lean state where the oxygen concentration in the exhaust gas is relatively high, and the oxygen concentration in the exhaust gas is relatively low. A nitrogen oxide purifying means for reducing nitrogen oxides absorbed in an exhaust gas rich state, and an air-fuel ratio of an air-fuel mixture supplied to the engine is set to a leaner side than a stoichiometric air-fuel ratio. An exhaust gas purifying apparatus for an internal combustion engine, comprising: a reducing means for temporarily enriching the air-fuel ratio so as to be in an exhaust gas rich state. In a transient state immediately after the air-fuel ratio is changed by the reducing means, misfire determination is performed by a different method than in a state other than the transient state. Location.