JPH03160134A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve convergency of control air-fuel ratio by adjusting air-fuel ratio in accordance with a rough adjusting item, gradually changed in inverse proportion to detected air-fuel ratio, and skipping and integration each O2 storage item, gradually changed in accordance with the displacement for a theoretical air-fuel ratio corresponding value of the detected air-fuel ratio. CONSTITUTION:A ternary catalyst (b) and an air-fuel ratio sensor (c), positioned in the downstream side of this catalyst (b), are respectively arranged in an exhaust passage (a) of an internal combustion engine. Here a rough adjusting item, gradually changed to a lean or rich side in inverse proportion to an output of the air-fuel ratio sensor (c), is calculated by a means (d). While the output of the air-fuel ratio sensor (c) is displaced to a rich or lean side by not less than a predetermined value from a theoretical air-fuel ratio equivalent value. A skipping O2 storage item, respectively being a fixed negative or positive value, is calculated by a means (e). Further, in a condition similar to the above described, a gradually decreased or increased integration O2 storage item is calculated by a means (f). In accordance with the above described each item, air-fuel ratio of the internal combustion engine is adjusted by a means (g).

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (Ox sensor)) downstream of a catalytic converter, and detects the air-fuel ratio by an 02 sensor downstream of the catalyst. The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs fuel ratio feedback control.

? Prior Art] As air-fuel ratio feedback control using an 02 sensor, a single O! There is a single 02 sensor system based on a sensor, and a double 02 sensor system based on two 02 sensors installed upstream and downstream of the catalyst, and furthermore,
There are two types of single O sensor systems: one in which an O2 sensor is provided upstream of the catalyst, and one in which an O2 sensor is provided downstream of the catalyst.

In a single 02 sensor system in which the 02 sensor is installed upstream of the catalyst, the 02 sensor is installed at a location in the exhaust system as close as possible to the combustion chamber, that is, upstream from the catalytic converter and at the gathering point of the famous exhaust manifold. Non-equilibrium degree (non-uniformity) For example, the presence of 02 even though the air-fuel ratio is rich, the inversion timing of the Ot sensor is shifted, and in a multi-cylinder engine, it is affected by the air-fuel ratio dispersion between cylinders, Therefore, the 02 sensor cannot detect the average air-fuel ratio, and as a result, there is a problem in that the accuracy of controlling the air-fuel ratio is low.

? On the other hand, a single O2 sensor with an O2 sensor installed downstream of the catalyst! The sensor system solves the problem of exhaust gas imbalance and non-detection of the average air-fuel ratio. O!
The responsiveness of the sensor is low, and therefore the responsiveness of the air-fuel ratio feedback control system deteriorates, resulting in a problem in that the catalyst is unable to fully demonstrate its performance, leading to deterioration in emissions. Furthermore, in a double O sensor system in which 02 sensors are provided upstream and downstream of the catalyst, air-fuel ratio feedback control is performed by the downstream 02 sensor in addition to air-fuel ratio feedback control by the upstream 02 sensor. For example, the downstream side 02 sensor detects the average air-fuel ratio, and the result is reflected in the value of the skip control constant etc. of the air-fuel ratio feedback control by the upstream side 02 sensor to perform overall air-fuel ratio control.

Therefore, as long as the downstream 02 sensor maintains stable output characteristics, good exhaust emissions are guaranteed.

However, in the double Ox sensor system,
The cost is high because it requires two 02 sensors, and
If the air-fuel ratio feedback control period by the upstream 02 sensor decreases due to changes over time, etc., there is a problem that the performance of the catalyst cannot be fully demonstrated.

For this reason, the applicant has already developed a forced automatic control waveform (forced oscillation waveform) with a predetermined amplitude and a predetermined frequency in a single Ox sensor system in which an O sensor is provided downstream of the catalyst.
has proposed a method in which the center value of is changed according to the output of the downstream 02 sensor (see Japanese Patent Laid-Open No. 1-66441). That is, as shown in FIG. 2, the output V of the downstream 02 sensor. When X changes, the center value (rough adjustment term) ^PC of the forced automatic control waveform Apt is changed according to the output VOX of the downstream 02 sensor. In this case, downstream O
t sensor output V. If 8 is lean, coarse adjustment term A
FC is gradually increased, while downstream O, the output V of the sensor. When X is rich, the coarse adjustment term APc is gradually reduced. In other words, the coarse adjustment term AFC is integrally controlled.

As shown in Figure 3, this is near the stoichiometric air-fuel ratio (λ=1).
When the forced automatic control waveform swings (AFs = AFS).

), the catalyst can maximize its purification performance, but when the air-fuel ratio on the rich side (λ<1) or the air-fuel ratio on the lean side (λ>
Even if the forced automatic control waveform swings in 1) (AFs+.A
Fsz) The purification performance of the catalyst cannot be demonstrated. Therefore, in order to bring the forced automatic control waveform AFss or ^psz closer to AFso so as to exhibit the purification performance of the catalyst, a rough adjustment term (integral term) is used. This is the introduction of

? [Problems to be Solved by the Invention] However, in the conventional device described above, there is a problem that highly accurate air-fuel ratio control cannot be performed in a vehicle where a situation in which the 02 storage effect cannot be exerted frequently occurs.

For example, if the air-fuel ratio of the gas containing the catalyst deviates significantly from the stoichiometric air-fuel ratio, and if this deviation continues for a long time, the three-way catalyst
When the Ox storage effect cannot be exerted due to large fluctuations in the 2 storage amount compared to the 02 storage amount under normal conditions, the conventional device described above simply controls the center value of the forced automatic control waveform by integral control. Therefore, the convergence of the controlled air-fuel ratio to the stoichiometric air-fuel ratio is poor, and as a result, the purification performance of the catalyst cannot be exhibited, leading to deterioration of emission.

For this reason, the applicant proposed that when the output of the downstream 02 sensor deviates significantly from the stoichiometric air-fuel ratio equivalent value to the rich side or lean side by a predetermined value or more, the 02 storage term AFcc+
It has already been proposed to shift (skip) the value of the coarse adjustment term AFc, which is the control center value, by introducing +o (skip term) (see: Japanese Patent Application No. 1-50161, 50).
985), this O! Since there is a limit to the air-fuel ratio correction width using only the storage term AFCCRO, the control center value AFc
If the range of air-fuel ratio fluctuation from
As expected, the convergence of the controlled air-fuel ratio to the stoichiometric air-fuel ratio is insufficient, and as a result, the purification performance of the catalyst cannot be exhibited, leading to deterioration of emissions.

Therefore, an object of the present invention is to take the above-mentioned prior application one step further and correct the control air-fuel ratio without undercorrecting even when the control air-fuel ratio fluctuates greatly from the stoichiometric air-fuel ratio due to fluctuations in the O estorage amount of the catalyst. It is an object of the present invention to provide an air-fuel ratio feedback control system that improves the convergence, fully exhibits the purification performance of a catalyst, and prevents deterioration of the emission curve by preventing the deterioration of the air-fuel ratio control flI accuracy due to the 02 storage effect.

[Means to solve the problem]

A means for solving the above problem is shown in FIG.

That is, a catalyst downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of a three-way catalyst provided in the exhaust passage of the internal combustion engine. The coarse adjustment term calculation means is the output V of the air-fuel ratio sensor. When X is lean, the air-fuel ratio sensor output V gradually changes to the lean side. A rough adjustment term AFc that gradually changes to the rich side when X is lean is calculated. The skip-like 02 storage term calculation means is the output ■ of the air-fuel ratio sensor. 8 is deviated from the stoichiometric air-fuel ratio equivalent value (vm) to the rich side by a predetermined value or more (V ox > V
z) becomes a constant negative value (18FCCIIOF),
Air-fuel ratio sensor output V. Skip-like 0, which becomes a constant positive value (AFcc*or) when
Calculate the storage term (±AFCCROP). Further, the integral 02 storage term calculation means gradually decreases the output V of the air-fuel ratio sensor when the output VOX of the air-fuel ratio sensor deviates from the stoichiometric air-fuel ratio equivalent value to the Lynch side by a predetermined value or more (Vox>Vg). An integral Ot storage term (AFccRot) that gradually increases when X deviates from the stoichiometric air-fuel ratio equivalent value to the lean side by a predetermined value or more (VOX<V+) is calculated.

The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine in accordance with the coarse adjustment term ^Fc, the skipped o storage term (±AFCCIIOF), and the integral 02 storage term (AFcc++ot).

[For production]

According to the above-mentioned means, 02 storage term A of the above-mentioned earlier application
Fc. . A skip-like 02 storage term AFC corresponding to
CIIOF plus integral O! Storage term AFcci
This version introduces oa. Its operation is shown in FIG. In other words, if the output VOX of the air-fuel ratio sensor deviates to the rich side by a larger amount than the stoichiometric air-fuel ratio equivalent value ■7, that is, if it is in the R 95 region of FIG.
2 storage term is assumed to be AFCCIOP (constant value), and on the other hand, the output V of the air-fuel ratio sensor. 8 deviates from the stoichiometric air-fuel ratio equivalent value VR to the lean side, that is, the fourth
If it is in the L jI area of Figure (A), the skip-like 02 storage term is set to 10 AFCCROF (Figure 4 (C)).
. At this time, an integral 02 storage term AFCCROi that gradually increases or decreases is calculated (fourth
Figure (D)). As a result, a skip Ox storage term and an integral 02 AFC +AFCCROP +AFccioi with storage term added
The air-fuel ratio is adjusted according to (FIG. 4(E)). Therefore, the output of the air-fuel ratio sensor ■. If 8 is significantly shifted to the region R or L, the integral 02 storage term AP is added to the skip Ot storage term - AFCCCROP.
(Since cmot contributes to the controlled air-fuel ratio, the convergence of the controlled air-fuel ratio is improved. [Example] Fig. 5 is an overall schematic diagram showing an air-fuel ratio control device for an internal combustion engine according to the present invention. Fig. 5 , an air flow meter 3 is provided in the intake passage 2 of the engine body 1.The air flow meter 3 directly measures the amount of intake air, and has a built-in potentiometer to generate an analog voltage proportional to the amount of intake air. This output signal is supplied to the A/D converter 101 with a built-in multiplexer of the control circuit 10.The distributor 4 has a reference signal that is rotated every 720 degrees in terms of crank angle. A crank angle sensor 5 that generates a position detection pulse signal and a crank angle sensor 6 that generates a reference position detection pulse signal every 30'' in terms of crank angle are provided.

The pulse signals of these crank angle sensors 5 and 6 are supplied to the human output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake boat for each cylinder.

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body 1. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. This output is also supplied to the A/D converter 101.

The exhaust system downstream of the exhaust manifold 11 contains three toxic components in the exhaust gas: FIC, CO, and No. A catalytic converter 12 is provided that accommodates a three-way catalyst that simultaneously purifies the air.

An 02 sensor l4 is provided in the exhaust pipe 13 on the downstream side of the catalytic converter 12. The 02 sensor 14 generates an electrical signal according to the concentration of oxygen components in the exhaust gas. That is, the 02 sensor 14 outputs different output voltages to the control circuit 1 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
0 is generated in the A/D converter 101. The control circuit 10 is
For example, it is considered as a microcomputer, and A/D
Converter 101, human output interface 102, CPU
In addition to 103, a ROM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, etc. are provided.

The throttle valve 15 of the intake passage 2 also includes an idle switch 1 for detecting whether the throttle valve 15 is fully closed.
6 is provided, and this output signal is supplied to the input/output interface 102 of the control circuit 10.

17 is a secondary air intake valve which supplies secondary air to the exhaust pipe 11 during deceleration or idling, and
This is to reduce Co emissions.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7. That is, in the routine described later, when the fuel injection amount TAU is calculated, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, the down count 108 receives the clock signal (
(not shown), and finally the borrow-out terminal is
1" level, the flip-flop 109 is set and the drive circuit 110 stops energizing the fuel injection valve 7. In other words, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, and therefore , an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 10.
1, the input/output interface 102
When the crank angle sensor 6 transmits a pulse signal, when the interrupt signal from the clock generation circuit 107 is received, etc.

The intake air amount data Q and the cooling water temperature data THW of the air flow meter 3 are taken in by an A/D conversion routine executed at predetermined time intervals and stored in a predetermined area of the RAM 105. That is, data Q and THW in RAM 105 are updated at predetermined time intervals. Further, the rotational speed data Ne is calculated by the interruption of the crank angle sensor 6 every 30'' CA, and is stored in a predetermined area of the RAM 105.

FIG. 6 shows a routine for calculating the fine adjustment term ^F, which is executed every predetermined period of time, for example, 4 ms. In step 601, it is determined whether the air-fuel ratio feedback condition is met. For example, when the cooling water temperature is below a predetermined value, e.g. 70'C, while the engine is starting, or when increasing the amount after starting,
During warm-up increase, power increase, fuel cut, and when throttle valve l6 is fully closed (LL="l"), the rotational speed Ne,
Vehicle speed, idle switch 16 signal L L, cooling water IT
When secondary air is being introduced based on Hw, etc., when the load is light, when Ot sensor l4 is not activated, etc., the air-fuel ratio feed bank condition is unreasonable.
In other cases, the air-fuel ratio feedback condition is valid.

When the air-fuel ratio feedback condition is unfavorable, the process proceeds directly to step 613. If the air-fuel ratio feedback condition is satisfied, the process proceeds to step 602.

In step 602, O, the output of the sensor 14 ■. A for 8
/D conversion and import, and reference voltage ■8 in step 603
For example, compare it with 0.45V. As a result, VOX≦V
If R (lean), the air-fuel ratio flag XOX is set to "O" (lean) in step 604, and it is determined in step 605 whether or not the previous air-fuel ratio flag xoxo is "1# (rich)." , only when the flag XOX is inverted from "1" (rich) to "0'(lean)", the fine adjustment term AFT is changed to Δ in step 607, as shown in FIG.
AF, (constant value). And step 612
Proceed to. On the other hand, in step 603, VOX>V (
rich), the air-fuel ratio flag XO is set in step 608.
X is set to "1' (rich), and the step 609 determines whether the previous air-fuel ratio flag xoxo is "0" (lean). As a result, the flag XOX changes from "0" (lean) to "1". (Rich), as shown in FIG. 7, the fine adjustment term AFf is changed to −ΔAF,
(constant value). Then, the process advances to step 612.

In step 612, the output V of the 02 sensor 14 is determined in the routine shown in FIG. 8, which will be described later. Calculate the reversal period of X? Clear the counter CNT.

The routine then ends at step 613.

In this way, according to the routine shown in FIG. 6, the fine adjustment term AFr of the skipped waveform is calculated every time the output of the O2 sensor 14 is reversed, as shown in FIG. In other words, an automatic control waveform can be obtained from the output of the 02 sensor 14 itself. In other words, control of the fine adjustment term AFt corresponds to skip control.

FIG. 8 shows a routine for calculating the coarse adjustment term AFC, which is executed every predetermined period of time, for example, 64 ms. In step 801, similarly to step 601 in FIG. 6, it is determined whether an air-fuel ratio feedback condition is met. As a result, the flow of steps 802 to 807 is executed only when the air-fuel ratio feedback condition is satisfied. That is,
In the step 802, the counter CNT is set to a constant value KCN.
It is determined whether T has been reached. In addition, the counter CNT
is the output V of the 02 sensor 14 as described above. It is cleared every time X is reversed. Therefore, at the beginning, the process proceeds from step 802 to step 803, where the counter CNT is counted up by +1, and the process proceeds to step 808. When counter CNT reaches KCNT, i.e. time KCN
After T x 64 ms have elapsed, the flow in step 802 proceeds to steps 804-807.

In step 804, the counter CNT is cleared, and in step 805, it is determined by the air-fuel ratio flag XOX whether the current catalyst downstream air-fuel ratio is lean ("0"> or rich ("1"). As a result, whether it is lean or If step 806
The rough adjustment term AFC is increased by ΔAFC (constant value) at step 807, and on the other hand, if it is rich, ΔAF is increased at step 807.
Decrease by c. Then, the process advances to step 808.

Note that the value ΔAF. are steps 607 and 611 in FIG.
This is smaller than the skip amount ΔAFf used in . That is, ΔAFC <ΔAF. Therefore, as shown in FIG. 9, if the air-fuel ratio is lean (XOX="O"), the coarse adjustment term AFc is Δ
The rough adjustment term AFC is gradually increased by AFC, and if the air-fuel ratio is rich (XOX='"l"), the coarse adjustment term AFC is gradually decreased by ΔAF. In other words, the control of the coarse adjustment term AF corresponds to integral control. Furthermore, the convergence of the air-fuel ratio can be improved by introducing skip control every time the air-fuel ratio is reversed into the coarse adjustment term ^F.

Substantial execution or non-execution of the coarse adjustment term calculation routine in FIG. 8 means substantial non-execution of the fine adjustment term calculation routine in FIG.
Each depends on the execution. That is, when the air-fuel ratio downstream of the catalyst deviates from the stoichiometric air-fuel ratio, VOX≦Vl
('J 7> or Vox>V* (rich), therefore, fj & adjustment term AFt by the routine in Figure 6 is ΔAF or -ΔAF
As a result, step 61
2 does not clear the counter CNT. On the other hand, in this case, the coarse adjustment term AFC according to the routine of FIG.
CNTX is gradually increased or decreased every 64ms.

In other words, the coarse adjustment term 8F is controlled rather than the fine adjustment term AP.

Conversely, when the air-fuel ratio downstream of the catalyst converges to the stoichiometric air-fuel ratio, the output of the 02 sensor 14 is ■. , is frequently inverted,
In other words, the output V of the Oz sensor 14. The inversion period of X becomes shorter, and the fine adjustment term AP is frequently
Repeat the pause. In this case, counter CNT is cleared by step 612 of FIG. 6 before reaching KCNT, so that the flow in step 802 of FIG. 8 always proceeds to step 803. In other words, the rough adjustment term A
There is no increase or decrease in FC, therefore, control of the coarse adjustment term AFc is prohibited and its value is held, and only the fine adjustment term AFt is controlled.

Figure 10 is O! This is a routine for calculating the storage term AFcc*o, and is executed every predetermined time, for example, every 16 ms. In step 1001, similarly to step 601 in FIG. 6, it is determined whether the air-fuel ratio feedback condition is established. As a result, if the air-fuel ratio feedback condition is not valid, the process directly proceeds to step 1011, and only if the air-fuel ratio feedback condition is valid, the process proceeds to step 1002.

In step 1002, the output V of the 02 sensor 14 is determined. A/D convert and import X, step 1003, 100
．． V at 1. Determine X. That is, as shown in FIG. 11, O~1. The OVO interval is divided into three, that is, 0 to V, {lean (L) region) ■1 to V,
(Stoichiometric air-fuel ratio (S) region) V2 ~ 1.0 V ('
Jychi(R)? It is divided into three regions (iI region), and it is determined in which of these regions the VOX is located. That is, 0≦
If Vox<Vl (Ljl region), step 1005
At step 1006, the integral 02 storage amount APcc*ot is gradually increased as AFcc*ot ←AFcco*ot+ΔAFcc++o (constant value), and at step 1006, the 02 storage term A
FcCRO is defined as AFCCRO←AFCCilOF+＾pcc*ot, where AFCCROP is a skip-like 02 storage term (constant value), and AFCCROF >ΔAFI:CIIO. In other words, in the L 9M region, as shown in FIG.
+AFccxo) increases gradually with an update rate of Δ^Fcc*o after shifting by the value AFCCIIOP.

Also, if ■,≦VOX≦■2 (S area), in step 1007, the integral 02 storage amount Apcc++
. ．． AFcc*oi ←0, and in step 1008, 02 storage term AFc
Let c*o be AFCCIIG ←O. In other words, in the R 9M range, as shown in FIG. 11, the air-fuel ratio correction coefficient FAF is the value AFr +AFC
It depends only on Furthermore, vIllX≧V z ( R
eI region), in step l009, the integral 0
2 storage amount AFcciot, AFCCRO5←AFCC. OROf−ΔAFcc*a (constant value) is gradually decreased, and in step 1010, 02 storage term 8FCCRO is calculated as AFcc*o? −AFcc*or +AFccioi. That is, in the R region, as shown in FIG. 11, the air-fuel ratio correction coefficient FAF is shifted by the value AFCCROP and then gradually decreases at an update rate of Δ^FCCIIO.

The routine of FIG. 10 then ends at the steno panel 1011.

In this way, the O2 storage term AFCCRO is an integral O2 storage term AFCCRO that gradually increases or decreases in addition to the Schinopian 02 storage term AFCCROp.
By introducing O+, the convergence of the controlled air-fuel ratio can be improved.

FIGS. 12, 13, and 15 show modifications of FIG. 10. In the routine of FIG. 10, the 02 storage term AFCCRO is always held at O in the S area, but in these modified examples, the 02 storage term 11pcc+to is not held at O even in the S area.

That is, FIGS. 12 and 13 are integral 02 straight?
The term AFcc*oi is the output of the 02 sensor 14 in the S region. L until 8 is reversed. By holding the value immediately before the change from the JI region (or R region) to the S Si region, the convergence of the control air-fuel ratio is further improved. 02 sensor output V in either lean side area or lynch side area. In order to prevent deterioration of the purification performance of the catalyst due to X staying for a long time, a delay process is introduced. Hereinafter, FIGS. 12, 13, and 15 will be described in detail.

In FIG. 12, steps 1007 .
Stenops 1201 and 1202 are provided in place of 1008.

That is, in step 1201, the integral 02 storage term A is calculated by the routine shown in FIG. 13 or 15.
Processes Fcc*ot, and in step 1202 O2
Let the storage term AFct*o be 8FCCROi-AFccaoi. That is, in the S area, the integral O2 storage term 8FCCROi is reflected.

FIG. 13 is a routine showing an example of the S area processing step 1201 of FIG. 12. Namely, Stemp? 301
Now, the output V of the O2 sensor 14. It is determined whether the air-fuel ratio downstream of the catalyst is lean or rich depending on whether X is less than or equal to VII, and as a result, step 1302. At 1303, an air-fuel ratio flag XOX is set. In step 1304, it is determined whether the air-fuel ratio has been reversed by comparing the previous air-fuel ratio flag value XOXO and the current air-fuel ratio flag value XOX. As a result, only when the air-fuel ratio is reversed, step 13
At 05, clear the integral 02 storage term 8FCCROi. Then, in step 1306, XOX
This routine ends in step 1307 in preparation for the next execution.

That is, according to the routine of FIG. 13, the integral 02 storage term AFcciot is the output of the air-fuel ratio sensor 14, as shown in FIG. Immediately after X enters the S region, it is not cleared, and the air-fuel ratio sensor l4 output ■. It is cleared only when X is reversed. Therefore, 02 sensor 1
4 output V. X is from L region (or R eM region) to S
Even if it moves to the ol area, 02 storage term AFCc. (
Strictly speaking, the integral 02 storage term AFccgoi )
Is the stoichiometric air-fuel ratio of the controlled air-fuel ratio due to the contribution of ? The convergence speed of will be increased.

Next, FIG. 15 will be explained. In FIG. 15, the following flags and counters are introduced.

XS (one "1"): Flag indicating that the output VOX of the 02 sensor 14 is in the S region, Flag XDLY: Integral 02 storage term AFcc*
Flag for delaying the start of oi update, CNTD
: Counter for measuring delay time.

In step 1501, the output V of the 02 sensor 14 is determined by determining whether the flag XS is "O" (outside the S region).
. It is determined whether or not X enters the S'nM region for the first time.

As a result, the output V of the O2 sensor 14. If X enters the S area after starting from the LeN area or the R area, the flag XS is set in step 1502 (XS-"1').
, steps 1503, 1500. : Performs more delayed processing. That is, in step 1503, the delay processing flag XDLY is set (XDLY - "'1"), and in step 1504, the delay time (:NTDO
Set it to D. This starts delay processing.

Also, the output V of the O2 sensor 14. When X is reversed, that is, the output V of the 02 sensor 14. Delay processing also occurs in steps 1505 to 1510 when X crosses reference voltage V.
Start with. That is, 02 at step 15o5
Output V of sensor 14. Determine whether X is lean (■.8≦■ or rich, and as a result, step 1506.150
At step 7, the air-fuel ratio flag XoX is set and reset. In step 1508, the previous value XOXO and the current value XOX
By comparing the output V of the air-fuel ratio sensor 14. X
Determine whether or not has been reversed. Only in the case of inversion, the previous value XOXO is replaced with the current value XOX in step 15o9, and the integral 02 storage term A is replaced in step 151o.
Clear FCCIO▲ and step 1503.1504
Delay processing will begin. In addition, step 1
Clearing the integral o2 storage term AFcc*o+ at 510 is the same as in the routine of FIG.

0, the output V of the sensor 14. , unless it enters the STJ region for the first time or crosses the reference voltage vR.
” Flows 1511 to 1517 are executed.

In step numbers 1511 to 1513, the counter CNTD
A delay time CTDO is measured, and the process proceeds to steps 1514 to 1517 only when the delay time has elapsed. Note that if the output VOX of the 02 sensor 14 is reversed before the measurement is completed, the delay time CNTD is set again, so the delay time is extended.

When the delay time has elapsed, the delay processing flag XDLY is reset (XDLY="0") in step 1514, and the integral 02 storage term 1'lpcc*at is integrated in steps 1515 to 1517.

The routine then ends at step 1518.

Note that the flag XS is reset when the output of the 02 sensor l4 falls outside the SKN range, that is, into the L region and the R region.

According to the routine in FIG. 15, as shown in FIG.
02 sensor 14 output V. X is the lean side of the SSM region (V
1 to vR) or the rich side (vll-vz) for a long time, 0! Storage term A
By introducing FCCRO (=AFcei+oi), the controlled air-fuel ratio is directed toward the stoichiometric air-fuel ratio. In addition,
The output V of the 02 sensor 14 after entering the S area from the LSfi area (or R area). Until the inversion of X, the integral is 0
2 storage term AFccs+ot is held as in FIG. 14.

FIG. L7 is an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360'' CA.Step 1
At step 701, the intake air amount data Q and rotational speed data Ne are read out from the RAM 105, and the basic injection amount ↑AtlP is calculated. For example, assume that TAUP←α·Q/Ne (α is a constant). In step 1702, the final injection amount TAU is determined as TAU+TAUP ・(＾Ft→−AFc+＾Fcc
Calculate by *o+β)+r. Note that β and T are correction amounts determined by other operating state parameters.

Next, in step 1703, the injection amount TAU is set in the down counter 108 and the flip-flop 1 is set.
Set 09 to start fuel injection. This routine then ends in step l704.

As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the borrow-out signal of the down counter 108, and the fuel injection ends.

FIG. 18 shows a routine for making use of the self-oscillation term (forced oscillation term) AFs.
executed every time. In step 1801, similarly to step 601 in FIG. 6, it is determined whether the air-fuel ratio feedback condition is met. As a result, if the air-fuel ratio feedback condition is not established, the process directly proceeds to step 181O, and only if the air-fuel ratio feedback condition is established, the process proceeds to step 1802. In step 1802, it is determined whether the counter CNTS has reached T/2 of the period T. In other words, the counter CNTS is incremented by +1 in step 1809, and the counter CNTS is incremented by +1 in step 1809 every CNTS = T /2.
Proceed to 3-1808.

That is, in step 1803, the counter CNTS is cleared, and in step 1804, the self-oscillation flag
It is determined whether the IC is "ON" or not, and if XSIC="0", the self-oscillation term AFs is set to -Δ^F,
(constant value), and in step 1806 the flag
is reversed to “゜1”. As a result, the counter CN
When TS reaches T/2, the flow of step 1804 continues to step 1807 . Proceed to 1808. In step 1807, the self-oscillation term AFs is set to ΔAF. Then, in step 1808, the flag XSTC is inverted to "O".

This routine then ends at step 1810.

In this way, according to the routine of FIG.
As shown in the figure, the automatic oscillation waveform of constant amplitude (ΔAF.) and Shuho T can be observed.

FIG. 20 shows an injection amount calculation routine when an automatic oscillation waveform is added, and step 1702 in FIG. 17 is replaced with a stem 2001. That is, the final injection amount T
AU is TAU ←-TAUP- (8Fr+AFg+AFc+AFcc
*o+β)+γ.

That is, the automatic oscillation term AF3 also replaces the fine adjustment term AF. In this case, the amplitude and frequency of the automatic oscillation waveform should be set to fully demonstrate the purification performance of the three-way catalyst.
Disturbances in the air-fuel ratio due to the introduction of the automatic oscillation term AFS are minimized.

In the above embodiment, the fine adjustment term AF is introduced, but the coarse adjustment term AFC and the 02 storage term apcc*
Air-fuel ratio control is possible even by introducing only o.

Furthermore, instead of the air flow meter, a Karman vortex sensor, a heat wire sensor, or the like may be used as the intake air amount sensor.

Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the amount of air bleed from the carburetor to control the main system passage and slow air. The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into system passages, devices that adjust the amount of air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step l701 is determined by the carburetor itself,
That is, it is determined according to the intake pipe negative pressure corresponding to the intake air amount and the rotational speed of the engine, and the supplied air amount corresponding to the final fuel injection amount TAU is calculated in step 1702.

Further, in the above-described embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a C○ sensor, a lean mixture sensor, etc. may also be used. In particular, T as an air-fuel ratio sensor
Using the iOz sensor improves control responsiveness and prevents overcorrection due to the output of the downstream air-fuel ratio sensor.

Further, although the embodiments described above are implemented using a microcomputer or digital circuit, it may also be implemented using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, since the 02 storage term that also includes the integral 02 storage term that changes integrally is introduced, it is possible to improve the convergence of the control air-fuel ratio without undercorrecting, and therefore, the emission Moreover, the control frequency is maintained high, and therefore the purification performance of the catalyst can be maximized.

[Brief explanation of the drawing]

Figure 1 is a block circuit diagram showing the basic structure of the present invention, Figure 2 is a timing diagram explaining the problem to be solved by the present invention, and Figure 3 is a diagram showing the relationship between the forced automatic control waveform and the catalyst purification function. FIG. 4 is a timing diagram explaining the action of the present invention; FIG. 5 is an overall schematic diagram showing the air-fuel ratio control device for an internal combustion engine according to the present invention; FIGS. 6, 8, 10, Figure 12, Figure 13, 1st
5, 17, 18, and 20 are flowcharts for explaining the operation of the control circuit in FIG. 5, FIG. 7 is a timing diagram supplementary to the flowchart in FIG. 6, and FIG. 11 is a timing diagram supplementary to the flowchart in FIG. 10; FIG. 14 is a timing diagram supplementary to the flowchart in FIGS. 12 and 13; FIG. 16 is a timing diagram that supplements the flowcharts in FIGS. 12 and 15, and FIG. 19 is a timing diagram that supplements the flowchart in FIG. 18.

Claims (1)

[Claims] 1. Three-way catalyst (12) provided in the exhaust passage of an internal combustion engine
and a catalyst downstream air-fuel ratio sensor (14) that is provided in the exhaust passage downstream of the three-way catalyst and detects the air-fuel ratio of the engine; and when the output of the air-fuel ratio sensor is rich, it gradually changes to the lean side. coarse adjustment term calculation means for calculating a coarse adjustment term (AF_C) that gradually changes to the rich side when the output of the air-fuel ratio sensor is lean; and the output (V_O_X) of the air-fuel ratio sensor is a value equivalent to the stoichiometric air-fuel ratio. (V_R) becomes a certain negative value (-AF_C_C_R_O_P_) when it deviates to the rich side by a predetermined value or more, and when the output of the air-fuel ratio sensor deviates from the stoichiometric air-fuel ratio equivalent value to the lean side by a predetermined value or more. Constant positive value (
a skipped O_2 storage term calculation means for calculating a skipped O_2 storage term (±AF_C_C_R_O_P), which is AF_C_C_R_O_P); Integral O_
an integral O_2 storage term calculating means for calculating a 2 storage term (AF_C_C_R_O_i); and an air-fuel ratio for adjusting the air-fuel ratio of the engine according to the rough adjustment term, the skipped O_2 storage term, and the integral O_2 storage term. An air-fuel ratio control device for an internal combustion engine, comprising: an adjusting means.