JPH11241632A - Control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control system for an internal combustion engine having an exhaust emission control device with NOx absorbent contained which suppresses the increase of NOx exhaust and improves fuel combustion. SOLUTION: Degradation of an exhaust emission control device is read from memory means (S101) to determine degradation correction factor KCAT to correct final target air-fuel ratio factor and delay angle θigCAT to correct delay angle of ignition timing (S102, S103) according to the degradation. Thus, when degradation of the exhaust emission control device is low, the air-fuel ratio of air-fuel mixture fed to an engine and ignition timing of the engine are controlled to implement best fuel consumption. When degradation of the exhaust emission control device is high, air-fuel ratio of air-fuel mixture and ignition timing are controlled to decrease the amount of NOx contained in exhaust gas fed to the exhaust emission control device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine provided with an exhaust gas purifying device having an exhaust system containing a nitrogen oxide absorbent.

[0002]

2. Description of the Related Art When the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine is set leaner than the stoichiometric air-fuel ratio (so-called lean burn control is executed), the emission amount of nitrogen oxides (hereinafter referred to as "NOx") is reduced. Because of the tendency to increase, a technique for purifying exhaust gas by providing an exhaust gas purifying device incorporating a NOx absorbent that absorbs NOx in an exhaust system of an engine has been conventionally known.

This NOx absorbent has an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, and when the oxygen concentration in the exhaust gas is relatively high (there is a large amount of NOx) (hereinafter referred to as "exhaust gas lean state"). On the other hand, in the state where 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 large (hereinafter referred to as “exhaust gas rich state”), NOx is absorbed. NOx is released. In an exhaust gas purifying apparatus having a built-in 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.
The CO is oxidized and discharged as water vapor and carbon dioxide.

Since the amount of NOx that can be absorbed by the NOx absorbent is naturally limited, it is not possible to continue only the lean burn control for a long time. Therefore, the absorbed NOx
The air-fuel ratio is temporarily enriched to release
release NOx from the x absorbent and release of N
An air-fuel ratio control method for reducing Ox has been conventionally known (JP-A-6-294319). Less than,
This temporary enrichment is referred to as "reduction enrichment."

[0005] However, even when the reduction enrichment is performed, the NOx absorbent gradually deteriorates as it is used, and the purification rate of the exhaust gas purifier decreases with the deterioration. The NOx amount increases. In order to suppress such an increase in the amount of exhausted NOx,
The NOx concentration in the exhaust gas is measured, and it is determined whether or not the NOx absorbent has deteriorated based on a difference between the measured NOx concentration and the reference NOx concentration. There is known one in which the flow rate (EGR amount) is increased (JP-A-5-113157).
According to this method, even if the NOx absorbent is deteriorated, the amount of NOx generated in the internal combustion engine can be reduced by increasing the amount of EGR, thereby being discharged to the outside. An increase in the NOx amount is suppressed.

[0006]

However, according to the above-mentioned conventional method, increasing the EGR amount during lean burn control leads to deterioration of combustion, so that precise control of the EGR amount is required. Control of the EGR amount controls the duty ratio of the EGR valve provided in the exhaust gas recirculation passage, and does not detect the amount of exhaust gas finally recirculated to the intake system. However, there is a problem that it is difficult to prevent deterioration of combustion.

[0007] The present invention has been made in view of the above points, and an internal combustion engine provided with an exhaust gas purifying apparatus having a built-in NOx absorbent can suppress NOx emissions and improve fuel efficiency. It is an object of the present invention to provide a control device.

[0008]

According to a first aspect of the present invention, there is provided an exhaust system for an internal combustion engine, wherein the air-fuel ratio of exhaust gas is leaner than a stoichiometric air-fuel ratio. Exhaust gas purifying means containing a nitrogen oxide absorbent for absorbing nitrogen oxides in exhaust gas, and air for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to a predetermined air-fuel ratio leaner than the stoichiometric air-fuel ratio In a control device for an internal combustion engine having a fuel ratio control means and a deterioration degree detecting means for detecting the degree of deterioration of the exhaust gas purifying means, when the degree of deterioration detected by the deterioration degree detecting means is small, the lean side The predetermined air-fuel ratio is set to the air-fuel ratio at which the fuel efficiency is the best, and when the degree of deterioration detected by the deterioration degree detecting means is large, the lean-side predetermined air-fuel ratio is set to Characterized in that it comprises a lean air-fuel ratio setting means for setting the air-fuel ratio exhaust of the object is reduced.

According to this configuration, when the deterioration degree detected by the deterioration degree detecting means is small, the predetermined air-fuel ratio on the lean side is set to the air-fuel ratio at which the fuel efficiency is the best, and the deterioration detected by the deterioration degree detecting means is set. When the degree is large, the predetermined air-fuel ratio on the lean side is set to an air-fuel ratio at which emission of nitrogen oxides from the internal combustion engine is reduced.

That is, when the degree of deterioration is small, the lean-side predetermined air-fuel ratio is set with priority given to fuel efficiency, and when the degree of deterioration becomes large, the lean-side predetermined air-fuel ratio is controlled with priority given to suppression of NOx emission over fuel efficiency. Is done. Therefore, it is possible to suppress NOx emission and improve fuel efficiency.

According to a second aspect of the present invention, there is provided a nitrogen oxidizing device provided in an exhaust system of an internal combustion engine for absorbing nitrogen oxides in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. Exhaust gas purifying means incorporating a substance absorbent, air-fuel ratio controlling means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to a predetermined air-fuel ratio leaner than the stoichiometric air-fuel ratio, and ignition timing of the internal combustion engine. In a control device for an internal combustion engine having an ignition timing control means for controlling to a predetermined ignition timing and a deterioration degree detecting means for detecting the degree of deterioration of the exhaust gas purifying means, the deterioration degree detected by the deterioration degree detecting means is When the ignition timing is small, the predetermined ignition timing is set to an ignition timing at which fuel efficiency is best, and when the deterioration degree detected by the deterioration degree detecting means is large, the predetermined ignition timing is retarded. Characterized in that it comprises a setting means.

According to this configuration, when the deterioration degree detected by the deterioration degree detecting means is small, the predetermined ignition timing is set to the ignition timing at which the fuel efficiency is the best, and the deterioration degree detected by the deterioration degree detecting means is large. At this time, the predetermined ignition timing is set to an ignition timing that is delayed from the ignition timing at which the fuel efficiency is best.

That is, when the degree of deterioration is small, the predetermined ignition timing is set giving priority to the fuel consumption, and when the degree of deterioration becomes large, the predetermined ignition timing is set giving priority to suppressing the NOx emission amount over the fuel consumption. Therefore, it is possible to suppress NOx emission and improve fuel efficiency.

[0014]

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

FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as “engine”) and a control device therefor according to an embodiment of the present invention. For example, an intake pipe 2 of a four-cylinder engine 1 is shown.
Is provided with a throttle valve 3 in the middle of the process. 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. The fuel injection valve 6 is provided with a fuel pump (not shown). And is electrically connected to the ECU 5, and the opening time of the fuel injection valve 6 is controlled by 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 attached 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.
Is attached. The NE sensor 10 includes the engine 1
A TDC signal pulse is output and supplied to the ECU 5 at a crank angle position before the predetermined crank angle with respect to the top dead center (TDC) at the start of the intake stroke of each cylinder (at every 180 ° crank angle in a four-cylinder engine).

The ignition plug 13 of each cylinder of the engine 1
It is electrically connected to the ECU 5. The ECU 5 determines the ignition timing θig of the ignition plug 13 by a method described later, and operates the ignition plug 13 at the determined ignition timing θig.

The exhaust pipe 12 is provided with an exhaust gas purifier 16 for purifying exhaust gas.
It incorporates a NOx absorbent that absorbs NOx and a catalyst that has an oxidizing and reducing action.

The exhaust gas purifying device 16 is in a state where 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). In the gas lean state), NOx
On the other hand, when 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 large (exhaust gas rich state), It has the property of reducing absorbed NOx. The exhaust gas purification device 16 is made of, for example, barium oxide (Ba0) and platinum (Pt). If NOx is absorbed to the limit of the NOx absorption capacity of the exhaust gas purifying device, that is, to the maximum NOx absorption amount, the NOx cannot be absorbed any more. Therefore, the air-fuel ratio is reduced and enriched to release and reduce NOx. In this reduction enrichment, if the degree of enrichment is too small, the reduction of released NOx will be insufficient, while if the degree of enrichment is too large, H
Since the emission amounts of C and CO increase, it is possible to maintain good exhaust gas characteristics by appropriately controlling the degree of the enrichment of the reduction enrichment.

The upstream and downstream positions of the exhaust gas purifying device 16 are respectively provided with a proportional air-fuel ratio sensor (hereinafter referred to as "LAF").
Sensor) 14 and an oxygen concentration sensor (hereinafter referred to as “O
2) 15 are provided. This LAF
The sensor 14 outputs an electric signal substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas, and supplies the electric signal to the ECU 5. Also,
The O2 sensor 15 has a characteristic that its electromotive force changes abruptly before and after the stoichiometric air-fuel ratio, and before and after the stoichiometric air-fuel ratio, the output signal is inverted from a lean signal to a rich signal or from a rich signal to a lean signal. That is, the output signal of the O2 sensor 15 has a high level with respect to the reference value VO2REF on the rich side of the exhaust gas, and has a low level with respect to the reference value VO2REF on the lean side. Here, the reference value VO2REF is set to a value near the center value of the O2 sensor output VO2. The output signal of the O2 sensor 15 is also supplied to the ECU 5.

The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value to a digital signal value. 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.

Based on the various engine parameter signals described above, the CPU 5b performs various operations in an air-fuel ratio feedback control region (including a lean burn control region) and a plurality of specific operation regions in which the air-fuel ratio feedback control is not performed, as described later. The engine operating state is determined, and according to the determined engine operating state, based on the following equation (1):
The fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated.

TOUT = TI × KCMDM × KLAF × K1 + K2 (1) Here, TI is the basic fuel injection time of the fuel injector 5 and is determined according to the engine speed NE and the intake pipe absolute pressure PBA. The TI map for determining the TI value is stored in the storage unit 5c.

KCMDM is a final target air-fuel ratio coefficient,
It is calculated by correcting a target air-fuel ratio KCMD set as described later. The target air-fuel ratio coefficient KCMD is
Since it 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, it is also called a target equivalent ratio.

KLAF is an air-fuel ratio correction coefficient, LA
The air-fuel ratio calculated from the detection value of the F sensor 14 is set to match the target air-fuel ratio coefficient KCMD.

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.

Further, the CPU 5b calculates the ignition timing θig of the engine 1 according to the following equation (2) according to the engine operating state, and drives the ignition plug 13 based on the calculated ignition timing θig.

Θig = θigM + θigCR + θigCAT (2) Here, θigM is a basic ignition timing set in accordance with, for example, the engine speed NE and the intake pipe absolute pressure PBA, and the θig map stored in the storage unit 5c is obtained. Calculated by reference. θigCR is a correction coefficient calculated according to another engine parameter (for example, engine water temperature TW or the like). θigCAT is a retard correction amount set according to the degree of deterioration of the exhaust gas purification device 16 as described later.

Further, the CPU 5b detects the degree of deterioration of the exhaust gas purification device 16 by measuring the inversion time of the output VO2 of the O2 sensor 15.

FIG. 2 is a flowchart of processing for calculating the target equivalent ratio KCMD and calculating the air-fuel ratio correction coefficient KLAF by PID control so that the detected equivalent ratio KACT matches the target equivalent ratio KCDMD. This processing is performed, for example, by T
It is executed in synchronization with the generation of the DC signal pulse.

First, in step S1, the target equivalence ratio KC
Calculate MD. The target equivalent ratio KCMD is basically
It is calculated according to the engine speed NE and the intake pipe absolute pressure PBA, and is changed to a value corresponding to the operating state in a low-temperature state of the engine coolant temperature TW or a predetermined high-load operating state.

In step S2, the target equivalent ratio KCMD is corrected by the following equation, and the final target air-fuel ratio coefficient KCMD is corrected.
Calculate M.

KCMDM = KCMD × KETC × KCAT (3) Here, KETC is a fuel cooling correction coefficient, and is set so as to increase as the target equivalent value KCMD increases. The fuel cooling correction is performed taking into account that the target equivalent ratio KCMD increases and the fuel cooling effect by the injection increases as the fuel injection amount increases. KCAT is a deterioration correction coefficient set according to the degree of deterioration of the exhaust gas purification device 16 as described later. The deterioration correction is a correction performed in consideration of the fact that when the exhaust gas purification device 16 deteriorates, the amount of NOx emitted to the outside increases.

In step S3, FIG. 3 and FIG.
Is performed, and in step S4,
The detection value of the LAF sensor 14 is converted into an equivalent ratio to calculate a detected equivalent ratio KACT. In the following step S5, P is determined based on the deviation between the detected equivalent ratio KACT and the target equivalent ratio KCMD.
By the ID control, the detected equivalent ratio KACT is changed to the target equivalent ratio KC.
The air-fuel ratio correction coefficient KLAF is calculated so as to match MD. After the calculation of the air-fuel ratio correction coefficient KLAF, the present process ends.

FIGS. 3 and 4 are flowcharts of the reduction enrichment control process executed in step S3 of FIG.

In step S11 of FIG. 3, it is determined whether or not a feedback control flag FLAFFB indicating "1" indicates that the engine 1 is in an operation state in which feedback control is performed in accordance with a value detected by the LAF sensor 14. If FLAFFB = 1 and the operation state in which the feedback control is executed is determined, "0" indicates that the operation state is the operation state in which the lean burn control for setting the air-fuel ratio to the lean side of the stoichiometric air-fuel ratio is executed. Lean burn control flag F
It is determined whether or not KBSMJG is "0" (step S1).
2) When FKBSMJG = 0 and the operation state in which the lean burn control is executed, the target equivalent ratio KCMD
Is equal to or less than a predetermined equivalent ratio KCMDLB (for example, 0.98) set to a value slightly leaner than the stoichiometric air-fuel ratio (step S13).

If any one of the steps S11 to S13 is negative (NO), the reduction enrichment flag FR indicating "1" indicates that the reduction enrichment is being executed.
ROK is set to “0” and the counter CTRR
Is set to the first predetermined value CTRINT1 (step S14), and the process ends without executing the reduction enrichment.

When all of the answers of steps S11 to S13 are affirmative (YES), that is, when the condition for executing the lean burn control is satisfied, the process proceeds to step S15.
A CTSV map (not shown) is searched, and the counter CT is searched.
The RR increment value CTSV is calculated. The CTSV map is
This is a map in which an increment value CTSV is set according to the engine speed NE and the intake pipe absolute pressure PBA. The CTSV value increases as the engine speed NE increases and the intake pipe absolute pressure PBA increases. Is set to

In the following step S16, the counter CTR
The value of R is incremented by the increment value CTSV, and then the value of the counter CTRR is increased to the first predetermined value CTRRIN.
It is determined whether it is equal to or greater than a predetermined threshold value CTRACT smaller than T1 (step S17). Immediately after the condition for executing the lean burn control is satisfied, the counter CTRR is set to the first predetermined value CTRINT1 (step S14).
Therefore, CTRR ≧ CTRACT, and step S1
Proceed to 8.

In step S18, it is determined whether or not the reduction enrichment flag FRROK is "1". At first, FRR
Since OK = 0, this is set to "1" (step S19), and the routine proceeds to step S21, where the engine speed NE is set.
Is the first predetermined rotational speed NKCMDRRL (for example, 1000
rpm> NE, NKCMDR
RL, the engine speed NE is higher than the first predetermined speed NKCMDRRL.
It is determined whether it is higher than MDRRH (for example, 2000 rpm) (step S22). And NE ≦ NKC
When MDRRL is in the low rotation speed range, the down count timer tmRR is set to a predetermined time TMR for low rotation.
RL (for example, 300 msec) (step S2
5) When NKCMDRRL <NE ≦ NKCMDDRRH and the engine is in the middle rotation range, the timer tmRR is set to the predetermined time TM for medium rotation longer than the predetermined time TMRRL for low rotation.
RRM (for example, 500 msec) (step S
24) When NE> NKCMDRRH and the engine is in the high rotation range, the timer tmRR is set to the predetermined time TMR for medium rotation.
The predetermined time TMRRH for high rotation longer than RM (for example, 80
0 msec) (step S23), and the process proceeds to step S26.

In step S26, steps S23 and S23 are executed.
The timer tmRR set in 24 or S25 is started. Next, a KCMDRR map (not shown) is searched to calculate a reduction enrichment target equivalent ratio KCMDRR (step S28), and a final target air-fuel ratio coefficient KCMDM is set to the reduction enrichment target equivalent ratio KCMDRR (step S28).
29), end this processing.

The KCMDRR map indicates the engine speed N
Is a map in which the reduction-enrichment target equivalent ratio KCMDRR is set in accordance with E and the intake pipe absolute pressure PBA. As the engine speed NE increases, the intake pipe absolute pressure PB
It is set so that the KCMDRR value increases as A increases. Note that all the set values are values larger than 1.0.

When the reduction enrichment flag FRROK is set to "1" in step S19 and the reduction enrichment is started, the answer in step S18 becomes affirmative (YES), and the process proceeds to step S27, where the timer tmRR is reset. It is determined whether the value is “0”. At first, since tmRR> 0, the process proceeds to step S28. When tmRR = 0, the reduction enrichment flag FRROK is set to “0” (step S30), and the counter CTRR is set to the predetermined threshold CT.
Second predetermined value CTRRINT2 smaller than RRACT
(For example, 0) (step S31), and the reduction enrichment ends. When steps S30 and S31 are executed, the final target air-fuel ratio coefficient KCMDM holds the value calculated in step S2 in FIG. 2, so that the lean burn control is started.

Thereafter, steps S16 and S17 are repeatedly executed, that is, lean burn control is executed, and
When the value of the counter CTRR reaches the predetermined threshold value CTRACT, the process proceeds to step S18 and the subsequent steps to execute the reduction enrichment.

In the present embodiment, in order to prevent the deterioration of the exhaust emission, the air-fuel ratio (target air-fuel ratio coefficient KCMD) of the air-fuel mixture supplied to the engine 1 according to the degree of deterioration of the exhaust gas purification device 16 and the engine 1 Is corrected. The degree of deterioration of the exhaust gas purifying device 16 is determined by executing an O2 feedback processing routine (not shown) when the detection of deterioration of the exhaust gas purifying device is permitted based on the operating state of the engine 1 and the output of the O2 sensor 15 at this time. VO
The determination is made by detecting the inversion time of No. 2.

More specifically, when the detection of deterioration of the exhaust gas purifying device is permitted based on the operating state of the engine 1, L
According to the outputs of the AF sensor 14 and the O2 sensor 15, FIG.
Then, the lean burn control performed according to the flowchart shown in FIG. That is, the O2 feedback correction coefficient KO2 is calculated, and the fuel injection amount Tout is calculated by the following equation (4), thereby controlling the fuel injection amount.

TOUT = Ti × KO2 × K3 + K4 (4) Here, Ti is a basic fuel injection time in the O2 feedback control at the time of detecting the deterioration of the exhaust gas purification device, and is expressed by the engine speed NE and the absolute pressure PBA in the intake pipe. Accordingly, it is calculated using the Ti map stored in the storage unit 5c. KO2 is an air-fuel ratio correction coefficient calculated according to the output VO2 of the O2 sensor 15. K3 and K4 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively.

During the execution of the O2 feedback control,
Times TL and KO from the occurrence of the special P-term PLSP for skipping the KO2 value in the decreasing direction until the O2 sensor output VO2 is inverted from the rich side to the lean side.
A predetermined time (n times) is measured for a time TR from the occurrence of the special P-term PRSP for skipping the binary value in the increasing direction to the inversion of the O2 sensor output VO2 from the lean side to the rich side. TLSUM, TRSU
M is calculated, and the determination time TCHK is calculated by the following equation (5).

TCHK = (TLSUM / nTL + TRSUM / nTR) (5) Here, the determination time TCHK decreases until the change in the air-fuel ratio of the air-fuel mixture supplied to the engine 1 appears as the output value of the O2 sensor 15. It means that time is getting faster. That is, the determination time TCHK indicates the degree of deterioration of the exhaust gas purification device 16, and the smaller the value of the determination time TCHK, the greater the degree of deterioration of the exhaust gas purification device 16. The obtained determination time TCHK is E
It is stored in the storage means 5c of the CU 5, and is used for correcting the target air-fuel ratio coefficient KCMD and the ignition timing θig according to the degree of deterioration.

The detection of the degree of deterioration of the exhaust gas purifying device 16 is not limited to such a method. For example, it is also possible to provide a NOx sensor at a position downstream of the exhaust gas purification device, and to detect the degree of deterioration of the exhaust gas purification device 16 by the NOx sensor. It is also possible to detect the degree of deterioration of the exhaust gas purification device 16 from the O2 sensor output VO2 when the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is switched from a lean value to a rich value.

FIG. 5 is a flowchart for explaining the control operation of the engine 1 according to the detected degree of deterioration.

First, in step S101, the determination time TCHK stored in the storage means 5c is fetched as the degree of deterioration of the exhaust gas purification device 16.

Next, the process proceeds to step S102, where a deterioration correction coefficient KCAT is calculated according to the degree of deterioration taken in.

Specifically, the determination time TCHK is set to a predetermined value t.
If it is longer than REF (for example, 2000 ms) and the degree of deterioration of the exhaust gas purification device 16 is small, the deterioration correction coefficient K
CAT is set to 1.0, and this value is applied to the above equation (1) to calculate the final target air-fuel ratio coefficient KCMDM. That is, when the degree of deterioration of the exhaust gas purification device 16 is small,
The air-fuel ratio of the air-fuel mixture supplied to the engine is set to an air-fuel ratio that gives the best fuel efficiency, giving priority to fuel efficiency.

The determination time TCHK is equal to a predetermined value tREF.
If it is shorter and the degree of deterioration of the exhaust gas purification device 16 is large, the deterioration correction coefficient KCAT is set by searching the KCAT table shown in FIG. That is, when the degree of deterioration of the exhaust gas purification device 16 is large, priority is given to reducing the NOx emission amount rather than improvement in fuel efficiency, and as the degree of deterioration increases (decrease the determination time TCHK), the deterioration correction coefficient KCAT is increased. To a smaller value.
As a result, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is made lean, and the air-fuel ratio (NOx-reduced air-fuel ratio) is controlled so that the NOx emission amount is reduced depending on the degree of deterioration of the exhaust gas purification device 16 at that time. Therefore, the amount of NOx discharged from the engine 1 to the exhaust gas purification device 16 is reduced, and the amount of NOx discharged to the outside is reduced.

The NOx reduction air-fuel ratio is set to a value within the range of 17 to 28 for a port injection type gasoline engine and 17 to 60 for a direct injection type engine. Here, the reason why the air-fuel ratio is set to a value of 17 or more is to avoid a region where the amount of NOx emission during the lean burn control is large. The maximum NOx reduction air-fuel ratio is set according to the type of the engine 1 in consideration of deterioration of combustion and fuel efficiency. Note that the value of the deterioration correction coefficient KCAT shown in the KCAT table is experimentally obtained.

Next, in step S103, a retard correction amount θigCAT of the ignition timing θig is calculated according to the detected degree of deterioration.

Specifically, as shown in FIG. 7, when the determination time TCHK is longer than a predetermined value tREF and the degree of deterioration of the exhaust gas purification device 16 is small, the retardation correction amount θigCA
T is set to 0, and this value is applied to the equation (2) to calculate the ignition timing θig. That is, the exhaust gas purification device 1
When the degree of deterioration of No. 6 is small, the ignition timing θig is set to an ignition timing (for example, 10 ° to 55 °) at which the fuel efficiency is the best.

The determination time TCHK is equal to a predetermined value tREF.
When the degree of deterioration of the exhaust gas purifying device 16 is shorter and the degree of deterioration of the exhaust gas purification device 16 is larger, the retard correction amount θigCAT becomes smaller as the degree of deterioration becomes larger (the determination time TCHK becomes shorter) with reference to the θigCAT table shown in FIG. Set to a value. Thus, the ignition timing θig is retarded when the degree of deterioration of the exhaust gas purification device 16 is small.

The ignition timing θig should be set to an optimum value that can obtain the air-fuel ratio originally set at that time. However, if the degree of deterioration of the exhaust gas purification device 16 is large by the above control, The NOx emission from the engine 1 to the exhaust gas purification device 16 is reduced according to the degree of deterioration. Thereby, the exhaust gas purification device 16
Can be prevented from increasing in the amount of NOx discharged from the engine 1 when the fuel cell deteriorates. Note that the value of the retard correction amount θigCAT shown in the θigCAT table is experimentally obtained.

As described above, according to the present embodiment, when the degree of deterioration of the exhaust gas purification device 16 is small, the air-fuel ratio and the ignition timing of the air-fuel mixture supplied to the engine 1 are determined based on the air-fuel ratio at which the fuel efficiency is the best. When the degree of deterioration of the exhaust gas purifying device 16 is large, priority is given to NOx emission over improvement in fuel efficiency, and the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is controlled by the exhaust gas purifying device. The NOx amount in the exhaust gas supplied to the exhaust gas 16 is set to the minimum air-fuel ratio and the ignition timing is retarded, so that NOx emission is suppressed regardless of the degree of deterioration of the exhaust gas purification device 16. Fuel efficiency can be improved.

[0066]

As described above, according to the first aspect of the present invention, when the detected degree of deterioration is small, the predetermined air-fuel ratio on the lean side is set to the air-fuel ratio at which the best fuel efficiency is obtained, and the detection is performed. When the degree of deterioration is large, the predetermined air-fuel ratio on the lean side is set to an air-fuel ratio at which emission of nitrogen oxides from the internal combustion engine is reduced, so that NOx emission is suppressed regardless of the degree of deterioration of the exhaust gas purifying means. In addition, fuel efficiency can be improved.

According to the second aspect of the invention, when the detected degree of deterioration is small, the predetermined ignition timing is set to the ignition timing at which the fuel efficiency is the best, and when the detected degree of deterioration is large, the predetermined ignition timing is delayed. Therefore, NOx emission can be suppressed and fuel efficiency can be improved irrespective of the degree of deterioration of the exhaust gas purifying means.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart of a process for executing air-fuel ratio feedback control according to an output of an air-fuel ratio sensor.

FIG. 3 is a flowchart of a process for executing return enrichment.

FIG. 4 is a flowchart of a process for executing return enrichment.

FIG. 5 is a flowchart illustrating a control operation of the internal combustion engine.

FIG. 6 shows a KCA for calculating a deterioration correction coefficient KCAT.
It is a T table.

FIG. 7 shows θi for calculating a retard correction amount θigCAT.
It is a gCAT table.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 5 electronic control unit 16 exhaust gas purification device

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 ZAB F01N 3/24 ZABE F02D 43/00 ZAB F02D 43/00 ZAB 301 301B 301E 45/00 ZAB 45/00 ZAB 312 312Z 322 322B

Claims (2)

[Claims] 1. An exhaust gas provided in an exhaust system of an internal combustion engine and having a built-in nitrogen oxide absorbent for absorbing nitrogen oxides in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. Gas purification means, air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to a predetermined air-fuel ratio leaner than the stoichiometric air-fuel ratio, and deterioration degree detection for detecting the degree of deterioration of the exhaust gas purification means Means for setting the lean-side predetermined air-fuel ratio to an air-fuel ratio at which fuel efficiency is best, when the degree of deterioration detected by the degree-of-deterioration detection means is small, and detecting the degree of deterioration. When the degree of deterioration detected by the means is large, lean air-fuel ratio setting means for setting the lean-side predetermined air-fuel ratio to an air-fuel ratio at which emission of the nitrogen oxides from the internal combustion engine is reduced is provided. Control apparatus for an internal combustion engine, characterized in that to obtain. 2. An exhaust gas provided in an exhaust system of an internal combustion engine and having a built-in nitrogen oxide absorbent for absorbing nitrogen oxides in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. Gas purification means, air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to a predetermined air-fuel ratio leaner than the stoichiometric air-fuel ratio, and ignition for controlling the ignition timing of the internal combustion engine to a predetermined ignition timing In a control device for an internal combustion engine having a timing control means and a deterioration degree detecting means for detecting the degree of deterioration of the exhaust gas purifying means, when the degree of deterioration detected by the deterioration degree detecting means is small, the predetermined ignition timing And ignition timing setting means for setting the ignition timing at which fuel efficiency is best, and delaying the predetermined ignition timing when the degree of deterioration detected by the degree of deterioration detection means is large. Control apparatus for an internal combustion engine, characterized.