JPH10131790A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fluctuate an air-fuel ratio forcibly, and improve an exhaust gas characteristic by changing a rich side continuation time and a lean side continuation time independently from each other, changing a cycle of forcible fluctuation of the air-fuel ratio, and setting its change rate according to a deviation between an output of an oxygen concentration sensor and a prescribed reference value. SOLUTION: A rich side continuation time for deviating an air-fuel ratio continuously to a rich side, and a lean side continuation time for deviating the air-fuel ratio continuously to a lean side, are changed by cycle change means independently from each other, on the basis of an output of an O2 sensor 15 arranged between an upstream side housing part 13a and a downstream side housing part 13b in an exhaust gas emission control device 13 for purifying exhaust gas. In the cycle change means, a change rate of the rich side or lean side continuation time is set according to a deviation between the output of the O2 sensor 15 and a prescribed reference value. An air-fuel ratio which is adapted to purifying capacity is fluctuated forcibly, and performance of the device 13 is exhibited to a maximum level so as to improve an exhaust gas characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus for improving exhaust gas characteristics by forcibly changing the air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine. About.

[0002]

2. Description of the Related Art A technique for improving the purification efficiency of an exhaust gas purifying apparatus that purifies exhaust gas by using a catalyst by forcibly changing an air-fuel ratio (perturbation of an air-fuel ratio) has been known. I have. The mode of this forced fluctuation,
For example, a method of controlling the center value of the forced fluctuation or the ratio of the control time to the rich side and the control time to the lean side based on the output of the oxygen concentration sensor mounted on the downstream side of the exhaust gas purification device is a special technique. This is disclosed in Japanese Unexamined Patent Publication No. Hei 2-11841.

[0003]

However, the above-mentioned conventional method does not take into account the deterioration of the catalyst in the exhaust gas purification device, more specifically, the change in the oxygen storage capacity of the catalyst. In some cases, the air-fuel ratio is forced to fluctuate beyond the storage capacity and the exhaust gas characteristics are rather deteriorated.

The present invention has been made in view of this point, and the exhaust gas purifying apparatus performs forced fluctuation of the air-fuel ratio in accordance with the purifying ability of the exhaust gas purifying apparatus so as to maximize the performance of the exhaust gas purifying apparatus. It is an object of the present invention to provide an air-fuel ratio control device capable of improving gas characteristics.

[0005]

According to a first aspect of the present invention, there is provided an exhaust gas purifying means provided in an exhaust system of an internal combustion engine, wherein the exhaust gas purifying means is provided on a downstream side or inside the exhaust gas purifying means. Air-fuel ratio control of an internal combustion engine, comprising: an oxygen concentration sensor provided; In the device, based on the output of the oxygen concentration sensor, a rich-side duration time for continuously biasing the air-fuel ratio to the rich side, and a lean-side duration time for continuously biasing the air-fuel ratio to the lean side. The cycle changing means sets the amount of change of the rich-side or lean-side continuation time according to the deviation between the output of the oxygen concentration sensor and a predetermined reference value. Features That.

According to a second aspect of the present invention, in the air-fuel ratio control device according to the first aspect, the air-fuel ratio control device is provided upstream of the exhaust gas purifying means and outputs a signal proportional to the oxygen concentration in the exhaust gas. A fuel ratio sensor, and feedback control means for performing feedback control so that an air-fuel ratio of the air-fuel mixture supplied to the engine in accordance with an output signal of the air-fuel ratio sensor matches a target air-fuel ratio. The target air-fuel ratio is periodically changed.

According to the air-fuel ratio control device of the first aspect, the rich-side duration time for continuously deviating the air-fuel ratio toward the rich side from the stoichiometric air-fuel ratio and the lean-side duration time for continuously deviating to the lean side. Are independently changed to change the period of the forced fluctuation of the air-fuel ratio, and the amount of this change is set according to the deviation between the output of the oxygen concentration sensor and a predetermined reference value.

According to the second aspect of the present invention, the feedback control is performed such that the target air-fuel ratio periodically fluctuates and the air-fuel ratio of the air-fuel mixture supplied to the engine matches the target air-fuel ratio. .

[0009]

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 an “engine”) and a control device therefor according to an embodiment of the present invention. For example, a throttle is provided in the middle of an intake pipe 2 of a four-cylinder engine 1. A valve 3 is provided. 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 fuel injection 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. The engine speed (NE) sensor 10 and the CRK sensor 11 are mounted around a camshaft (not shown) of the engine 1 or around a crankshaft.
The engine speed sensor 10 outputs a pulse (hereinafter referred to as a “TDC signal pulse”) at a predetermined crank angle position every time the crankshaft of the engine 1 rotates 180 degrees, and the CRK sensor 11 outputs a pulse at each predetermined crank angle, for example, 45 degrees. And outputs a signal pulse (hereinafter referred to as “CRK signal pulse”) at the crank angle position of
It is supplied to CU5.

The exhaust pipe 12 is provided with an exhaust gas purifier 13 for purifying exhaust gas.
Is configured such that an upstream storage section 13a and a downstream storage section 13b, each storing an exhaust gas purification catalyst, are stored in one container (container). At a position upstream of the exhaust gas purification device 13, a wide-range air-fuel ratio sensor (hereinafter referred to as "LAF sensor") 14 for detecting an air-fuel ratio based on the oxygen concentration in the exhaust gas or the degree of oxygen deficiency is mounted. An O2 sensor 1 for detecting the oxygen concentration in the exhaust gas is provided between the upstream storage section 13a and the downstream storage section 13b.
5 is attached. The LAF sensor 14 outputs an electric signal substantially proportional to the air-fuel ratio and supplies the electric signal to the ECU 5. O
The second sensor 15 supplies an electric signal (SVO2) corresponding to the oxygen concentration in the exhaust gas to the ECU 5. The exhaust gas purification device 13 has a catalyst temperature (TCA) for detecting its temperature.
T) The detected catalyst temperature TCA with the sensor 16 attached
An electric signal corresponding to T is supplied to the ECU. Note that O
The two sensors 15 may be mounted on the downstream side of the downstream storage section 13b.

The ECU 5 is further connected to a vehicle speed sensor (VH) 17 for detecting the speed of a vehicle on which the engine 1 is mounted, and an atmospheric pressure (PA) sensor 18. Detection signals from these sensors are supplied to the ECU 5. Is done.

The intake pipe 2 is connected to a canister (not shown) for adsorbing the fuel vapor generated in the fuel tank via a passage 19, and a purge control valve 20 is provided in the passage 19. I have. The purge control valve 20 is provided by the ECU 5
And its opening and closing are controlled by the ECU 5. The purge control valve 20 is opened in a predetermined operation state of the engine 1, and supplies the fuel vapor stored in the canister to the intake pipe 2.

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. 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, the CPU 5b performs various engine operation states in an air-fuel ratio feedback control region or a plurality of specific operation regions in which the air-fuel ratio feedback control is not performed (hereinafter referred to as "open loop control region"). And, in accordance with the determined engine operating state, the T
The fuel injection time TOUT of the fuel injection valve 6 synchronized with the DC signal pulse is calculated.

[0019]

## EQU00001 ## TOUT = TIM.times.KAF.times.KCMD.times.K1 + K2 where TIM is a basic fuel amount, specifically, the fuel injection valve 5.
The basic fuel injection time is determined by searching a TI map set according to the engine speed NE and the intake pipe absolute pressure PBA. The TI map indicates the engine speed NE.
In the operating state corresponding to the intake pipe absolute pressure PBA, 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.

KAF is an air-fuel ratio correction coefficient, which is calculated according to the output of the LAF sensor 14 during the air-fuel ratio feedback control, and is set to a value corresponding to each operation region in the open loop control region.

KCMD is a target air-fuel ratio coefficient calculated according to the engine operating state, as described later. 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. In the present embodiment, the perturbation (forced fluctuation) of the air-fuel ratio is determined by the target air-fuel ratio coefficient K
This is performed by changing the CMD.

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 in accordance with 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 condition. Purge control valve 2
0 opening / closing control is performed.

FIG. 2 is a flowchart of the LAF feedback processing executed when the execution condition of the air-fuel ratio feedback control is satisfied. This processing is executed by the CPU 5b every time a TDC signal pulse is generated.

In step S1, the target air-fuel ratio coefficient KCM
A KCMD calculation process (FIG. 3) for calculating D is executed, and in step S2, a KAF for calculating an air-fuel ratio correction coefficient KAF
The calculation processing (FIG. 18) is executed. Hereinafter, the contents of these processes will be described in detail.

FIG. 3 is a flowchart of the KCMD calculation process. In step S11, the target air-fuel ratio coefficient KCM
SVO2 feedback processing for calculating an SVO2 correction coefficient KCMDSO2, which is one of the correction coefficients used for calculating D, based on the output SVO2 of the O2 sensor 15 (FIG. 4)
Execute Next, a TW correction coefficient KCMDTW is calculated according to the engine coolant temperature TW (step S12), a target air-fuel ratio coefficient KCMD is calculated by the following equation 2 (step S13), and the process is terminated.

[0027]

KCMD = KBS × KCMDW × KCMDSO2 Here, KBS is a basic value of the target air-fuel ratio coefficient KCMD, and is set according to the engine speed NE and the intake pipe absolute pressure PBA.

FIGS. 4 and 5 are flowcharts of the SVO2 feedback processing executed in step S11 of FIG.

In step S21, a KKPRTTW table shown in FIG. 6 is searched according to the engine coolant temperature TW to calculate a coolant temperature correction coefficient KKPRTTW. The water temperature correction coefficient KKPRTTW is a correction coefficient KPRTR for the rich-side duration TPRTR and a correction coefficient KPRTL for the lean-side duration TPRTL described below (hereinafter, when both correction coefficients are collectively expressed, the “duration correction coefficient K
PRTi (i = R, L) ") (step S27, step S221 in FIG. 14).

In step S22, SVO2 shown in FIG.
An F / B execution condition determination process is executed. This processing is performed in O2
SVO2 correction coefficient K corresponding to output SVO2 of sensor 15
This is for determining the execution condition of the calculation of the CMDSVO2.

In step S81 of FIG. 7, it is determined whether or not a predetermined fail-safe process is being executed. If the fail-safe process is being executed, a continuation time correction coefficient K to be described later is used.
The learning value KPRTREF of PRTi is set to "1.0" (step S82), it is determined that the SVO2F / B execution condition is not satisfied, and the SVO2F / B execution flag FSO2F is determined.
B is set to "0" (step S86). Step S
If the answer to 81 is negative (NO), the PID control flag FPIDFB indicating by "1" that the PID control is being executed.
Is determined to be "1" (step S84).

If FFIDFB = 0 and the air-fuel ratio feedback control is not being executed, the process proceeds to step S8.
6 and when FFIDFB = 1, the engine speed NE is set to the predetermined upper and lower limit values NESO2H and NESO2L.
(For example, 5000 rpm and 1000 rpm, respectively) and the absolute pressure PBA in the intake pipe is equal to a predetermined upper and lower limit value PBSO2H, PBSO2L (for example, 660 respectively).
mmHg, 210 mmHg) and whether the engine coolant temperature TW is higher than a predetermined coolant temperature TWSO2L (for example, 5 ° C.) (step S85). And
When the answer is negative (NO), the process proceeds to step S86, and when the answer is affirmative (YES), it is determined that the execution condition is satisfied.
The SVO2F / B execution flag FSO2FB is set to "1" (step S87), and the process ends.

Returning to FIG. 4, in step S23, SVO2
It is determined whether the F / B execution flag FSO2FB is “1”. If FSO2FB = 0 and the SVO2F / B execution condition is not satisfied, the enrichment processing end flag indicating the end of the air-fuel ratio enrichment processing by “1” FO2LEAN (Step S
45) is set to “0” (step S24), and SV
Median value KSO2CENT of O2 correction coefficient KCMDSO2
And the SVO2 correction coefficient KCMDSO2 are both "1.
"0" (steps S25 and S26). Then
The correction coefficient KKPRTTW calculated in step S21 is applied to the following equation 3 to calculate a duration correction coefficient KPRTi.

[0034]

KPRTi = KPRTREF × KKPRTTW Here, KPRTREF is a learning value of the duration correction coefficient KPRTi calculated by the processing of FIG. 17 described later.

In the following steps S28 to S31, the limit processing of the KPRTi value calculated in step S27 is performed. That is, when the duration correction coefficient KPRTi exceeds a predetermined upper limit value KPRTLMTH (for example, 1.7), KPRTi = KPRTLMTH is set (step S2).
8, S29), a predetermined lower limit KPRTLMTL (for example,
0.3), KPRTi = KPRTLMT
L (steps S30 and S31), and KPRTLMTL
If ≦ KPRTi ≦ KPRTLMTH, the process immediately proceeds to step S66. In step S66, a down count timer tKP referred to in step S67 described below.
Predetermined time TMKPRTRN for RTRN (for example, 10 seconds)
Is set and started, and this processing ends.

If FSO2FB = 1 in step S23 and the SVO2F / B execution condition is satisfied, it is determined whether the activation flag FnSO2 indicating "1" that the O2 sensor 15 is activated is "1". Determine (Step S4
1) If FnSO2 = 0 and not activated, the timer tKPRTRN is set to the predetermined time TMKP
Set and start RTRN (step S42),
Proceed to step S45.

If FnSO2 = 1 and the O2 sensor 15 is activated in step S41, it is determined whether or not the enrichment end flag FSO2LEAN is "1" (step S43). If the conversion process has been completed, the process immediately proceeds to step S45. If FSO2LEAN = 0, it is determined whether or not the O2 sensor output SVO2 is equal to or greater than a predetermined lower limit SVO2LMTL (step S44), and SVO2 <SVO2.
If it is LMTL and the amount of stored oxygen in the exhaust gas purification device 13 is large, the air-fuel ratio enrichment process of steps S48 to S50 is performed. That is, the central value KSO2CENT of the perturbation is increased by a predetermined addition term DKSO2P (step S48), and it is determined whether or not the central value KSO2CENT is larger than the rich predetermined value KSO2RICH (step S49), and KSO2CENT ≦ KSO2.
Immediately when it is RICH, and KSO2CENT>
If KSO2RICH, KSO2CENT = K
As SO2RICH (step S50), step S50
Go to 51. Thus, the center value KSO2CENT is
The value is gradually increased to the rich side predetermined value KSO2RICH.

In step S51, the timer tKPRTRN is set to the predetermined time TMKPRTRN in the same manner as in step S42.
Is set and started, and the process proceeds to step S61.

The enrichment process in steps S48 to S50 is performed immediately after the fuel cut.
Since the amount of oxygen stored in the fuel cell 3 increases, the air-fuel ratio is made rich to prevent deterioration of exhaust gas characteristics.

SVO2 ≧ SVO2L by enrichment processing
When MTL is reached, the process proceeds to step S45, where the enrichment end flag FSO2LEAN is set to "1", and then the central value KSO2CENT is reduced by a predetermined value DKSO2M (step S46). Then, it is determined whether or not center value KSO2CENT is smaller than “1.0”, and KSO2CEN is determined.
When T ≧ 1.0, the process proceeds to step S51, where K
When SO2CENT <1.0, KSO2CEN
Assuming that T = 1.0 (Step S52), Step S61
Proceed to.

In step S61, the SV shown in FIGS.
An O2 correction coefficient KCMDSO2 calculation process is executed, and in step S62, a KPRTi calculation process shown in FIGS. Next, the change amount D of the throttle valve opening θTH
It is determined whether the absolute value of TH (= θTH (k) −θTH (k−1)) is smaller than a predetermined change amount DTHKPRTL (for example, 3.5 deg) (step S63), and | DTH
When | <DTHKPRTL, the absolute pressure P in the intake pipe
BA change amount DPBA (= PBA (k) −PBA (k−
It is determined whether the absolute value of 1)) is smaller than a predetermined change amount DPBKPRTL (for example, 50 mmHg) (step S64). When | DPBA | <DPBKPRTL, the change amount DNE (= NE) of the engine speed NE is determined. (K)
-NE (k-1)) is equal to the predetermined change amount DNEKPRTL.
It is determined whether it is smaller than (for example, 300 rpm) (step S65). (K) and (k-1)
These are added to represent the current value and the previous value, respectively. In particular, parameters without (k), (k-1), etc.
This time represents the value.

If the answer in any of steps S63 to S65 is negative (NO), the process proceeds to step S66,
If all the answers are affirmative (YES) and the engine operation state is stable, it is determined whether or not the value of the timer tKPRTRN started at step S66 or the like is “0” (step S67). When tKPRTRN> 0, the process is immediately terminated, and when tKPRTRN = 0, a learning value KPRTREF calculation process (FIG. 17) is executed (step S68), and the process is terminated.

FIGS. 8 and 9 are flowcharts of the SVO2 correction coefficient KCMDSO2 calculation process executed in step S61 of FIG.

In step S101, the activation flag FnSO
2 to determine whether or not FnSO2 = 0 and O
When the second sensor 15 is not activated, the idle flag F indicating "1" indicates that the engine is idle.
It is determined whether or not IDLE is "1" (step S10).
5). When FIDLE = 1, the variation width KCMD from the perturbation center value KSO2CENT
Rich side duration TPR of PRT and perturbation
The basic values of the TR and the lean-side duration TPRTL (hereinafter referred to as the “basic value of the duration”) TMPRT are respectively set to predetermined values KCMDPSTI and TMPR for idle before activation.
It is set to TSTI (for example, 500 msec) (step S107), and the process proceeds to step S108. Also, FID
When LE = 0 and not in the idle state (when in the off-idle state), the fluctuation width KCMDPRT and the duration basic value TMPRT are respectively set to the predetermined values KCMDPST and TMPRTST for off-idle before activation (for example, 300).
msec) (step S106), and the process proceeds to step S108.

When FnSO2 = 1 and the O2 sensor 15 is activated in step S101, it is determined whether or not the idle flag FIDLE is "1" (step S1).
02), when FIDLE = 1, the fluctuation width KCMD
The PRT and the duration basic value TMPRT are converted into predetermined values for idle KCMDPIDL and TMPRTIDL, respectively.
(For example, 1 sec) (step S103),
Proceed to step S108. When FILDE = 0 and the engine is in the off-idle state, a map (not shown) set according to the engine speed NE and the intake pipe absolute pressure PBA is searched to obtain the fluctuation width KCMDPRT and the continuation time base. Determine the value TMPRT (Step S1)
04).

In step S108, the engine speed N
E and an SVREF table set as shown in FIG. 10 according to the intake pipe absolute pressure PBA, and a reference value SV
Calculate REF. In the SVREF table, the absolute pressure PBA in the intake pipe is set to a first predetermined pressure PBSVREF1 (for example, 1).
A line L1 applied when the pressure is equal to or less than 10 mmHg) and a line L2 applied when the pressure is equal to or more than the second predetermined pressure PBSVREF2 (for example, 660 mmHg) are set.
If BSVREF1 <PBA <PBSVREF2, a reference value SVREF is calculated by interpolation.

In the following step S109, the previous SVO2
It is determined whether or not the F / B execution flag FSO2FB is “0”. If FSO2FB = 1 also last time, the process immediately proceeds to step S121. If FSO2FB = 0 and the current time becomes “1”, the following is performed. Is performed (steps S110 to S115). That is, the inversion request flag F indicating "1" to request the inversion of the bias direction of the air-fuel ratio (transition from the lean side to the rich side or vice versa).
PRTCNG is set to “0” (step S110),
It is determined whether or not the O2 sensor output SVO2 is equal to or less than the reference value SVREF (step S111).

When SVO2 ≦ SVREF, in order to start the perturbation from the rich deviation of the air-fuel ratio,
The perturbation flag FPRT indicating that the rich-side deviation control is being executed is set to "1" (step S112), and the rich-side continuation time TPRTR is calculated by the following equation 5, and the calculated value is calculated. The countdown timer tPRT is set and started (step S113), and the process proceeds to step S121.

[0049]

[Mathematical formula-see original document] TPRTR = TMPRT * KPRTR Here, TMPRT is determined in steps S103, S104 and S104.
The basic value of the duration set in 106 or S107, KP
RTR is a rich-side continuation time correction coefficient calculated in the processing of FIGS.

On the other hand, in step S111, SVO2> SVR
If EF, the perturbation flag F is set to start the perturbation from the lean deviation of the air-fuel ratio.
While setting the PRT to "0" (step S11)
4) The lean side duration time TPRTL is calculated by the following equation 6, the calculated value is set in the timer tPRT and started (step S115), and the process proceeds to step S121.

[0051]

(6) TPRTL = TMPRT × KPRTL Here, TMPRT is performed in steps S103, S104, and S104.
The basic value of the duration set in 106 or S107, KP
RTL is a lean-side continuation time correction coefficient calculated in the processing of FIGS.

In step S121, KCMDSO2 inversion determination processing (FIG. 11) is executed. In this process, it is determined whether or not the direction of deviation of the air-fuel ratio should be reversed as described later.
Set G to "1".

In a succeeding step S122, it is determined whether or not the perturbation flag FPRT is "1".
= 1, that is, during execution of the rich-side deviation control,
It is determined whether or not the inversion request flag FPRTCNG is "1" (step S123). If FPRTCNG = 0, the SVO2 correction coefficient KCMDSO is calculated by the following equation (7).
2 (step S124) (FIG. 12, t2 to t).
4), and the process ends.

[0054]

KCMDSO2 = KSO2CENT + KCMDPRT where KSO2CENT is the central value of perturbation (see FIG. 4, steps S46 to S52), KCMDPR
T is the fluctuation range set in steps S103, S104, and the like.

In step S123, FPRTCNG =
If it is 1, and the inversion request is made, the SVO2 correction coefficient KCMDSO2 is decreased by a predetermined value DKCMDSO2 (step S125), and the KCMDSO2 value is set to the central value K.
It is determined whether or not SO2CENT or more (step S12)
6). This process is immediately terminated while KCMDSO2 ≧ KSO2CENT (see t4 to t5 in FIG. 12). When KCMDSO2 <KSO2CENT, the perturbation flag F is set to shift to the lean side bias control.
The PRT is set to "0" (step S127), and the SVO2 correction coefficient KCMDSO2 is calculated by the following equation (step S128).

[0056]

KCMDSO2 = KSO2CENT−KCMDPRT Next, the lean-side duration time TPRTL is calculated by the above equation 6, set to the timer tPRT and started (step S129), and the inversion request flag FPRPCNG.
Is returned to “0” (step S130) (FIG. 12, t5).
Reference), and terminates this processing.

On the other hand, in step S122, when FPRT = 0 and the lean side deviation control is being executed, the inversion request flag FPR
It is determined whether TCNG is "1" (step S13).
1) When FPRTCNG = 0, the SVO2 correction coefficient KCMDSO2 is calculated by the above equation 8 (step S132) (see t5 to t7 in FIG. 12), and this processing ends.

In step S131, FPRTCNG =
If it is 1, and the inversion request is made, the SVO2 correction coefficient KCMDSO2 is increased by a predetermined value DKCMDSO2 (step S133), and the KCMDSO2 value becomes the central value K.
It is determined whether or not SO2CENT or less (step S13)
4). This process is immediately terminated while KCMDSO2 ≦ KSO2CENT (see t7 to t8 in FIG. 12), and when KCMDSO2> KSO2CENT, the perturbation flag F is set to shift to the rich-side bias control.
The PRT is set to "1" (step S135), and the SVO2 correction coefficient KCMDSO2 is calculated by the equation (7) (step S136).

Next, the rich side continuation time TPRTR is calculated by the above equation 5, set in the timer tPRT and started (step S137), and the inversion request flag FP
The RTCNG is returned to “0” (step S138) (see t8 in FIG. 12), and the present process ends.

As described above, according to this processing, when the inversion request is made, the SVO2 correction coefficient KCMDSO2 is changed to the central value KC
It gradually changes toward MDCENT, and the central value KCMD
When CENT is reached, the deviation control on the opposite side is started. By this repetition, the KCMDSO2 value changes as shown in FIG. 12A, and the perturbation of the air-fuel ratio is executed.

FIG. 11 is a flowchart of the KCMDSO2 inversion determination process in step S121 in FIG.

In step S151, the previous SVO2F /
It is determined whether or not the B execution flag FSO2FB is “0”. If FSO2FB = 0, the delay counter cPRTDLY is set to “0” (step S15).
8), a delay flag FPRTDLY which is similarly set slightly after the perturbation flag FPRT (FIG. 1)
2 (d) is the same as the perturbation flag FPRT (step S159), and the break flag FSO2BREAK, which is set to "1" at the time of break determination (steps S164 and S167) described later, is set to "0". (Step S160), the process proceeds to step S161.

In step S151, FSO2FB =
If it is 1, the previous perturbation flag FPR
It is determined whether or not T has been inverted (step S152). If T has not been inverted, the delay counter cPRTDLY is incremented by a predetermined number NPRTLY if it has not been inverted.
(For example, 8) (step S153), and the process proceeds to step S154.

At step S154, it is determined whether or not the value of the delay counter cPRTDLY is "0".
While DLY> 0 (FIG. 12, t2 to t3, t5 to t
6, t8 to t9), the count value is decremented by "1" (step S157), and step S161 is performed.
Proceed to. When cPRTDLY = 0 (FIG. 1)
2, t3, t6, t9) are delay flags FPRTD
LY is set equal to the perturbation flag FPRT (step S155), and the break flag FSO2BREAK is set.
Is set to “0” (step S156), and step S156
Proceed to 161.

In step S161, the delay flag F
It is determined whether or not PRTDLY is “1”, and
When = 1, the O2 sensor output SVO2 becomes equal to the reference value SVREF by a predetermined voltage DSVREF (for example, 0.06
V) or not (Step S1)
62). If this answer is affirmative (YES), the timer tP
It is determined whether the value of RT is "0" (step S16).
9), while tPRT> 0 (FIG. 12, before t1, t
2 to t4 and t5 to t7), the present process is immediately terminated.
After that, when tPRT = 0 (FIG. 12, t1, t7),
Proceeding to step S170, the inversion request flag FPRTCN
G is set to "1" to request a reversal (instructs reversal of the air-fuel ratio bias direction).

In step S162, SVO2> (SVRE)
F + DSVREF) (this is called “break” in this specification. As described later, the O2 sensor output SVO2 decreases and SVO2 <(SVREF−DSVR).
EF), the break flag FSO2BREAK is set to "1" (step S1).
63). That is, when FRPTDLY = 1 and the O2 sensor output SVO2 changes beyond the predetermined voltage DSVREF in the rich direction during the execution of the rich-side deviation control, it is determined that the oxygen stored in the exhaust gas purification device has been exhausted. As described below, an inversion request is made if the conditions of steps S164 and S168 are satisfied.

In step S164, the value of the timer tPRT becomes (TMPRT × (KPRTR-KPRTLMTL)).
It is determined whether or not: Here, TMPRT × KPRT
R is the rich side duration time TPRTR (Equation 5), and TMPRT × KPRTLMTL corresponds to the lower limit value TPRTMMIN of the rich side duration time TPRTR. Therefore, in step S164, tPRT> (TMPRT ×
(KPRTR−KPRTLMTL)), the execution time of the rich side deviation control is equal to the lower limit value TPRTMI.
Since this means that the number has not reached N, the present process is terminated without making a reversal request. This is because the reaction time in the exhaust gas purification device is insufficient when the period of the perturbation is too short, and the purification performance is reduced.

If the answer to step S164 is affirmative (YES), it is further determined whether the value of the perturbation flag FPRT and the value of the delay flag FPRTDLY are not equal (step S168), and FPRT @ FPR.
When it is TDLY (FIG. 12, t2 to t3, t5 to t
(6, t8 to t9) immediately after the inversion request has been made, the process is terminated without making the inversion request. Meanwhile FPRT
= FPRTDLY, the step S170
Then, the inversion request flag FPRPCNG is set to "1" (t4 in FIG. 12), and this processing ends.

If FRPTDLY = 0 in step S161, the same processing as steps S162 to S164 is performed. That is, the O2 sensor output SVO2 is equal to the reference value S
It is determined whether or not the value is equal to or greater than a value obtained by subtracting the predetermined voltage DSVREF from VREF (step S165).
In the case of (ES), the process proceeds to step S169. In step S165, SVO2 <(SVREF-DSVREF)
When a break occurs, the break flag F
SO2BREAK is set to “1” (step S16)
6). That is, when FRPTDLY = 0 and the O2 sensor output SVO2 changes beyond the predetermined voltage DSVREF in the lean direction during the execution of the lean-side deviation control, oxygen is discharged beyond the oxygen storage capacity of the exhaust gas purification device. If the conditions are satisfied, the reversal request is made if the conditions of steps S167 and S168 are satisfied as described below.

In step S167, the value of the timer tPRT becomes (TMPRT × (KPRTL-KPRTLMTL)).
It is determined whether or not: Here, TMPRT × KPRT
L is the lean-side duration TPRTL (Equation 6), and TMPRT × KPRTLMTL corresponds to the lower limit value TPRTMMIN of the lean-side duration TPRTL. Therefore, in step S167, tPRT> (TMPRT ×
(KPRTL-KPRTLMTL), the execution time of the lean side deviation control is equal to the lower limit value TPRTMI.
Since this means that the number has not reached N, the present process is terminated without making a reversal request. On the other hand, when the answer to step S167 is affirmative (YES), the process proceeds to step S168.

As described above, according to the processing of FIG. 11, the duration TPRTR or T
When the PRTL has elapsed (t1, t7 in FIG. 12), or when a break has occurred even before the lapse of the duration TPRTR or TPRTL (t4 in FIG. 12), the inversion request flag FPRTCNG is set to “1”. An inversion request is made.

As described above, when a break occurs, a reversal request is made even before the lapse of the duration TPRTR or TPRTL, so that the bias in the oxygen accumulation state of the catalyst in the exhaust gas purification device 13 is quickly corrected. And good exhaust gas characteristics can be maintained.

FIGS. 13 and 14 show steps S62 of FIG.
6 is a flowchart of a KPRTi calculation process in FIG.

In step S201, the delay flag F
It is determined whether or not PRTDLY has been inverted, and if not, this process ends immediately. That is, the processing of step S202 and subsequent steps is performed by using the delay flag FPRTDLY.
Is executed only immediately after is inverted.

If the delay flag FPRTDLY is inverted, it is determined whether or not the activation flag FnSO2 is "1" (step S202). If FnSO2 = 0 and the O2 sensor 15 has not been activated yet, step S2
At 21, the duration correction coefficient KPRTi is set to the learning value KPRT.
REF × water temperature correction coefficient KKPRTTW is set (formula 3), the duration correction coefficient KPRTi is initialized, and the process proceeds to step S225.

If it is determined in step S202 that FnSO2 = 1 and the O2 sensor 15 is activated, zone determination is performed in accordance with the O2 sensor output SVO2 (step S2).
03 to S205). That is, the O2 sensor output SVO2
And a predetermined upper limit value SVO having a relationship as shown in FIG.
2LMTH (for example, 0.85V), (reference value SVREF
+ Predetermined voltage DSVREF), reference value SVREF, (reference value SVREF-predetermined voltage DSVREF), predetermined lower limit value S
VO2LMTL (for example, 0.2V), and SVO
When 2> SVO2LMTH, the zone parameter S
FBZONE = 5 (Steps S203 and S20)
7), (SVREF + DSVREF) <SVO2 ≦ SV
When O2LMTH, the zone parameter SFBZO
NE = 4 (Steps S203, S204, S20)
9), (SVREF−DSVREF) ≦ SVO2 ≦ (S
(VREF + DSVREF), the zone parameter SFBZONE = 3 is set (steps S203 and S20).
4, S205, S217), SVO2LMTL ≦ SVO
When 2 <(SVREF-DSVREF), the zone parameter SFBZONE = 2 is set (step S203).
To S206, S212), SVO2 <SVO2LMTL
, The zone parameter SFBZONE = 1 is set (steps S203 to S206, S215).

Further, when SFBZONE = 4, O2
The current value SVO2 (k) of the sensor output is the previous value SVO2
It is determined whether or not (k-1) or less (step S210),
When SFBZONE = 2, it is determined whether or not the current value SVO2 (k) of the O2 sensor output is equal to or greater than the previous value SVO2 (k-1) (step S213). When SFBZONE = 5 or SFBZON.
When E = 4 and SVO2 (k)> SVO2 (k-1) (the SVO2 value is increasing), the rich-side correction term DKPRTR and the lean-side correction term DKPRTL are each set to a fifth predetermined value. DKPRTR5 and DKPRTL
5 (step S208), and SFBZONE = 4
When SVO2 (k) ≦ SVO2 (k−1) (the SVO2 value is decreasing), the rich correction term DKPRTR and the lean correction term DKPRTL are respectively set to the fourth predetermined values DKPRTR4 and DKPRTL4. (Step S211), and when SFBZONE = 3, the rich-side correction term DKPRTR and the lean-side correction term DKPRTL are respectively set to the third predetermined value DKPRT.
R3 and DKPRTL3 are set (step S21).
8) SFBZONE = 2 and SVO2 (k) ≧ S
VO2 (k-1) (SVO2 value is increasing)
At this time, the rich-side correction term DKPRTR and the lean-side correction term DKPRTL are respectively set to the second predetermined value DKPRTR.
2 and DKPRTL2 (step S214),
When SFBZONE = 1 or SFBZONE = 2
If SVO2 (k) <SVO2 (k-1) (the SVO2 value is decreasing), the rich correction term DKPRTR and the lean correction term DKPRTL are respectively set to the first predetermined values DKPRTR1 and DKPRTL1. (Step S216). Here, the first to fifth predetermined values are set as follows. That is, DKP
RTR5 <DKPRTR4 <0 <DKPRTR3 <DK
PRTR2 <DKPRTR1 and DKP
RTL1 <DKPRTL2 <0 <DKPRTL3 <DK
It is set so that PRTL4 <DKPRTL5.

In a succeeding step S222, it is determined whether or not the delay flag FPRTDLY is "1".
When LY = 0 and immediately after the transition from the rich-side deviation control to the lean-side deviation control, the rich-side correction term DKPRTR is added to the rich-side duration correction coefficient KPRTR (step S223), while FPRTDLY = 1. If it is immediately after the shift from the lean side deviation control to the rich side deviation control, the lean side duration correction coefficient KPRT
The lean correction term DKPRTL is added to L (step S
224), and proceed to step S225.

In step S225 and thereafter, a limit process for the calculated duration correction coefficient KPRTi is performed. That is, the duration correction coefficient KPRTi is equal to the predetermined upper limit value KPRT.
If it exceeds LMTH, KPRTi = KPRTLMT
H (steps S225 and S226), and when the duration correction coefficient KPRTi falls below the predetermined lower limit value KPRTLMTL, KPRTi = KPRTLMTL (steps S227 and S228). Otherwise, the process ends immediately.

According to the processing of FIGS. 13 and 14, the rich-side duration correction coefficient KPRTR and the lean-side duration correction coefficient KPRTL are independently changed, and the period of the perturbation is changed. By performing perturbation suitable for the purifying ability of the device, the exhaust gas characteristics can be improved by maximizing the performance of the exhaust gas purifying device, and at the center of the perturbation due to the deviation of the output characteristics of the LAF sensor 14. Even when the value deviates from the desired value, by changing each of the rich-side or lean-side durations TPRTR and TPRTL,
The center value of the substantial perturbation can always be kept optimal.

The zone parameter SFBZONE =
3 and the O2 sensor output SVO2 is equal to the reference value SVREF.
When they are in the vicinity, the correction terms DKPRTR, DKPRTL
Is set to a positive value having a small absolute value, and the amount of one correction of the duration correction coefficient KPRTi is suppressed to a small value (FIG. 1).
6, before t11, after t14).

Further, when SFBZONE = 2 and the O2 sensor output SVO2 is decreasing (t11 to t1 in FIG.
2) Or, if SFBZONE = 1 and SVO2
When the value greatly shifts to the lean side (t12 to t12 in FIG.
13), the rich-side correction term DKPRTR is set to a first predetermined value DKPRTR1 having a relatively large positive value, and the lean-side correction term DKPRTR is set to a first predetermined value having a relatively large negative absolute value. Since it is set to DKPRTL1, the correction amount of the duration correction coefficient KPRTi for one time becomes large, and both the rich-side duration TPRTR and the lean-side duration TPRTL are quickly corrected.

Then, the O2 sensor output SV
When the increase tendency of O2 is maintained and the area enters the area of SFBZONE = 2 (t13 to t14 in the figure), the correction term DKPRTR
And DKPRTL are both set to the second predetermined values DKPRTR2 and DKPRTL2 whose absolute values are smaller, so that the amount of one correction of the duration correction coefficient KPRTi becomes smaller, and after time t14, the region shifts to the area of SFBZONE = 3. I do.

Although not shown, the O2 sensor output S
When VO2 is largely deviated in the rich direction, the duration correction coefficients KPRTR and KPRTR in the direction opposite to that of FIG.
The PRTL is respectively corrected, and the correction amount at one time is a large value (DKPRTR) when the SVO2 value is increasing at SFBZONE = 4 and when the SVO2 value is increasing.
5, DKPRTL5), and when the SVO2 value enters the area of SFBZONE4 while decreasing, a smaller value (DK
PRTR4, DKPRTL4).

FIG. 17 is a flowchart of the process for calculating the learning value KPRTREF executed in step S68 of FIG.

In step S241, it is determined whether or not a predetermined time TMSO2ST (for example, 180 seconds) has elapsed after the start of the engine. If not, the process ends immediately. Immediately after the start, the condition of the catalyst in the exhaust gas purification device 13 is not stabilized. After a lapse of a predetermined time TMSO2ST, the delay flag FPRTD
It is determined whether or not LY has been inverted (step S242),
If immediately after the reversal, the zone parameter SFBZON
It is determined whether E is "3" (step S243). If it is not immediately after the inversion of the delay flag FPRTDLY or if SFBZONE is not 3, the present process is immediately terminated.

When the delay flag FPRTDLY has just been changed and SFBZONE = 3, it is determined whether both the rich-side duration correction coefficient KPRTR and the lean-side duration correction coefficient KPRTL are 1.0 or more (step S244). If both or either one is smaller than 1.0, it is determined whether both are smaller than 1.0 (step S245). As a result, if one of them is 1.0 or more and the other is less than 1.0, this processing is immediately terminated. If both are less than 1.0, the learning value KPRTREF is corrected in step S246, If both are greater than or equal to 1.0, the learning value KP is determined in step S249.
Modify RTREF.

In step S246, the correction term DKPRT is subtracted from the previously calculated learning value KPRTREF to obtain a new learning value KPRTREF. When the duration correction coefficients KPRTR and KPRTL are both smaller than 1.0, the zone parameter SFBZONE = 4 or 5 immediately after the end of the rich-side deviation control, and the rich-side duration correction coefficient KPRTR is corrected in a decreasing direction. Immediately after the end of the side deviation control, the zone parameter SFBZONE
= 1 or 2 and the lean-side duration correction coefficient KPRT
This is because the correction of L in the decreasing direction indicates that the oxygen storage capacity of the exhaust gas purifying device has decreased. Next, it is determined whether or not the value is smaller than a predetermined lower limit KPRTLMTL (step S247). KPRT
As soon as REF ≧ KPRTLMTL,
When PRTREF <KPRTLMTL, KPR
TREF = KPRTLMTL (Step S24)
8), end this processing.

On the other hand, in step S249, a correction term DKPRT is added to the learning value KPRTREF calculated up to the previous time to obtain a new learning value KPRTREF. When the duration correction coefficients KPRTR and KPRTL are both equal to or greater than 1.0, the zone parameter SFBZONE = 1, 2 or 3 immediately after the end of the rich-side deviation control, and the rich-side duration correction coefficient KPRTR is corrected in the increasing direction. , The zone parameter SFBZON immediately after the end of the lean side deviation control.
E = 1, 2, or 3, and the lean-side duration correction coefficient K
This is because the PRTL has been corrected in the increasing direction, so that the oxygen storage capacity of the exhaust gas purification device is considered to be larger than the capacity originally assumed. Step S104 in FIG.
Is set assuming that the catalyst in the exhaust gas purifying device is slightly deteriorated, and the “initial assumed capacity” corresponds to the map set value. It means oxygen storage capacity. This is because, if a map of the basic duration TMPRT is set assuming a new catalyst, the exhaust gas characteristics may be deteriorated until a learning effect appears when a deteriorated catalyst is used.

Next, it is determined whether or not the learned value KPRTREF is larger than a predetermined upper limit KPRTLMTH (step S250). Immediately when KPRTREF ≦ KPRTLMTH, and KPRTREF> KPRTLMT
If it is H, KPRTREF = KPRTLMTH (step S251), and this processing ends.

According to the processing of FIG. 17, the rich-side duration correction coefficient KPRTR and the lean-side duration correction coefficient KPR
When both TLs become larger than 1.0, the learning value K
When PRTREF is corrected in the increasing direction, and when the rich-side duration correction coefficient KPRTR and the lean-side duration correction coefficient KPRTL are both smaller than 1.0, the learning value KPRTREF is corrected in the decreasing direction. As a result, if there is a difference between the initially assumed oxygen storage capacity (purification capacity) of the exhaust gas purification device and the actual oxygen storage capacity, the learning value KPRTREF is corrected according to the difference. It is possible to obtain an optimal learning value that matches the oxygen storage capacity of the engine. As a result, the performance of the exhaust gas purifying device can always be maximized and good exhaust gas characteristics can be obtained.

The learning value KPRTREF is stored in the RAM which is backed up by the battery even when the ignition switch is turned off, and is used for setting the initial value of the duration correction coefficient KPRTi at the next operation (FIG. 4, step S27, FIG. 14, step S221). If the battery is removed, the value is set to 1.0.

Next, the KAF calculation processing of step S2 in FIG. 2, that is, the calculation processing of the air-fuel ratio correction coefficient KAF based on the output of the LAF sensor 14, will be described with reference to FIGS.

FIG. 18 is a flowchart of the KAF calculation process. First, a KPI for calculating a PID correction coefficient KPID is shown.
Execute the D calculation process (FIG. 19) (Step S31)
2). Next, the air-fuel ratio correction coefficient KAF is calculated in step S31.
The PID correction coefficient KPID calculated in step 2 is set (step S313), and a limit check process is performed to limit the KAF value to a range between predetermined upper and lower limits (step S31).
4), end this processing.

FIG. 19 is a flowchart of the KPID calculation process in step S312 of FIG.

In step S331, it is determined whether or not the previous PID control flag FpidFB was "1".
Immediately when IDFB = 1, and FFIDFB
If = 0, the previous value KIF (k-1) of the integral term KIF of the PID control is set as the air-fuel ratio correction coefficient KAF (step S332), and the process proceeds to step S333.

In step S333, a proportional term KPF, an integral term KIF, and a derivative term KDF are calculated by the following equation (9).

[0098]

KPF = KPLAF × DKCMD KIF (k) = KILAF × DKCMD + KIF (k−
1) KDF = KDLAF × DDKCMD Here, KPLAF, KILAF and KDLAF are control gains, and DKCMD is a deviation between the target air-fuel ratio and the detected air-fuel ratio. Specifically, the target equivalence ratio (target air-fuel ratio coefficient) The difference between KCMD and the detected equivalent ratio KACT calculated based on the output of the LAF sensor 14 (= KCMD−KA
CT). DDKCMD is the deviation DKCMD.
(= DKCMD (k) −DKCMD (k−
1)).

In the following steps S334 to S337, limit processing of the integral term KIF is performed. That is, when the KIF value is within the range of the predetermined upper and lower limit values O2LMTH and O2LMTL (O2LMTL ≦ KIF ≦ O2LMTH), and when KIF <O2LMTL, KIF =
As the O2LMTL (step S336), the KIF
If> O2LMTH, KIF = O2LMTH (step S337), and the process proceeds to step S338.

In step S338, the PID correction coefficient KPID is calculated by adding the integral term KIF, the proportional term KPF, and the derivative term KDF. Next, the PID correction coefficient KPID
Is smaller than the predetermined lower limit O2LMTL (step S339). If KPID <O2LMTL, the integral term KIF is set to the previous value (step S339).
341), the PID correction coefficient KPID is set to a predetermined lower limit O2L
The MTL is set (step S342), and the process ends. If KPID ≧ O2LMTL in step S339, the PID correction coefficient KPID is set to the predetermined upper limit O2L.
It is determined whether or not it is greater than MTH (step S34).
0), if KPID ≦ O2LMTH, the process is immediately terminated. If KPID> O2LMTH, the integral term KIF is held at the previous value (step S34).
3) The PID correction coefficient KPID is set to a predetermined upper limit O2LMT.
H is set (step S344), and the process ends.

According to the processing of FIG. 19, the PID correction coefficient KPID is calculated by the PID control so that the detected equivalent ratio KACT matches the target equivalent ratio KCMD.

Note that the present invention is not limited to the above-described embodiment, and various modifications are possible. For example, in the above-described embodiment, the case where the air-fuel ratio is feedback-controlled by the PID control has been described.

In the above-described embodiment, the feedback control is performed using the air-fuel ratio correction coefficient KAF such that the detected equivalent ratio KACT based on the output of the LAF sensor 14 matches the target air-fuel ratio coefficient KCMD. The perturbation of the air-fuel ratio may be performed by applying only the target air-fuel ratio coefficient KCMD to Expression 1 without using the coefficient KAF.

[0104]

As described above in detail, according to the air-fuel ratio control apparatus of the first aspect, the rich-side continuation time in which the air-fuel ratio is continuously deviated to the rich side from the stoichiometric air-fuel ratio and the lean-side continuation time are continued. And the period of the forced fluctuation of the air-fuel ratio is changed by independently changing the lean duration time to be deviated.
Since this change amount is set in accordance with the deviation between the output of the oxygen concentration sensor and the predetermined reference value, the air-fuel ratio that is compatible with the purifying capacity of the exhaust gas purifying device is forcibly changed to maximize the performance of the exhaust gas purifying device. And the exhaust gas characteristics can be improved to the maximum, and even if the center value of the forced fluctuation deviates from the desired value, the substantial center value is always maintained optimally by changing the duration on the rich side or lean side. In addition, even when the rich or lean duration time deviates from the optimum value, it can be quickly corrected.

According to the air-fuel ratio control device of the second aspect, feedback control is performed such that the target air-fuel ratio periodically fluctuates and the air-fuel ratio of the air-fuel mixture supplied to the engine matches the target air-fuel ratio. Therefore, the actual air-fuel ratio can be accurately controlled to the target air-fuel ratio.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration 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 feedback process based on an output of a LAF sensor.

FIG. 3 is a flowchart of a KCMD calculation process.

FIG. 4 is a flowchart of an SVO2 feedback process of FIG. 3;

FIG. 5 is a flowchart of an SVO2 feedback process of FIG. 3;

FIG. 6 is a diagram showing a table used in the processing of FIG. 4;

FIG. 7 is a flowchart of an SVO2F / B execution condition determination process of FIG. 4;

8 is a flowchart of a KCMDSO2 calculation process of FIG.

FIG. 9 is a flowchart of a KCMDSO2 calculation process of FIG. 5;

FIG. 10 is a diagram showing a table used in the processing of FIG. 8;

FIG. 11 is a flowchart of a KCMDSO2 inversion determination process in FIG. 9;

FIG. 12 is a diagram for explaining the processing of FIGS. 8, 9 and 11;

FIG. 13 is a flowchart of a KPRTi calculation process of FIG.

FIG. 14 is a flowchart of a KPRTi calculation process of FIG. 5;

FIG. 15 is a diagram for explaining zone parameters (SFBZONE) set in the processing of FIG. 13;

FIG. 16 is a diagram for explaining the processing in FIGS. 13 and 14;

FIG. 17 is a flowchart of a KPRTREF calculation process of FIG. 5;

FIG. 18 is a flowchart of a KAF calculation process of FIG. 2;

FIG. 19 is a flowchart of a KPID calculation process in FIG. 18;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Electronic control unit (ECU) 6 Fuel injection valve 12 Exhaust pipe 13 Exhaust gas purification device 14 Wide area air-fuel ratio sensor 15 Oxygen concentration sensor

Claims (2)

[Claims] 1. An exhaust gas purifying means provided in an exhaust system of an internal combustion engine, an oxygen concentration sensor provided downstream or inside the exhaust gas purifying means, and an air-fuel ratio of an air-fuel mixture supplied to the engine. An air-fuel ratio control device for an internal combustion engine including an air-fuel ratio changing unit that periodically fluctuates between a stoichiometric air-fuel ratio between a rich side and a lean side, based on an output of the oxygen concentration sensor. The rich-side duration that continues to bias toward the
A period changing means for independently changing a lean-side duration for continuously biasing the air-fuel ratio to the lean side,
The air-fuel ratio control device for an internal combustion engine, wherein the cycle changing means sets a change amount of the rich or lean continuation time according to a deviation between an output of the oxygen concentration sensor and a predetermined reference value. 2. An air-fuel ratio sensor provided upstream of the exhaust gas purifying means and outputting a signal proportional to the oxygen concentration in the exhaust gas, and supplies the signal to the engine in accordance with an output signal of the air-fuel ratio sensor. 2. A feedback control means for performing feedback control so that an air-fuel ratio of an air-fuel mixture coincides with a target air-fuel ratio, wherein the air-fuel ratio changing means periodically changes the target air-fuel ratio. An air-fuel ratio control device for an internal combustion engine according to the above.