JPH02233843A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To bring the emission control performance of a catalyzer into full play by adjusting an air-fuel ratio with a second coarse control term if it is in a purge area of an evaporative purge system and a difference between first and second coarse control terms is more than the specified value, but in the other case, according to the first coarse control term, respectively. CONSTITUTION:Both first and second coarse control term operational means operate first and second coarse control terms AFCG, AFCE, gradually varied to the lean side when output of an air-fuel ratio sensor is rich but to the rich side at time of leanness respectively. At time of a purge area of an evaporative system, a difference AF between both these coarse control terms is operated, and when it is discriminated to be more than the specified value by a purge area discriminating means, air-fuel ratio control over an engine is performed according to the second coarse control term AFCE for evaporative generation and a forced automatic waveform AF. On the other hand, when it is out of the purge area, the term AFCE is held by a second hold means, and when the difference AF is less than the specified value, the air-fuel ratio is adjusted according to a first coarse control term AFCG for a nonevaporative generating are and a forced oscillating term AFs. Thus, the worsening of emission can be prevented.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention has an evaporative purge system and an air-fuel ratio sensor (herein, an oxygen concentration sensor (0, sensor)) on the downstream side of a catalytic converter. The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using an O2 sensor downstream of a catalyst.

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

In a single 0■ 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 to the combustion chamber as possible, that is, the catalyst controller. It is installed at the gathering part of the exhaust manifold upstream from the sensor, but due to non-equilibrium (non-uniformity) of the exhaust gas, for example, the presence of 02 even though the air-fuel ratio is rich, the reversal timing of the 0 Also, multi-cylinder engines are affected by air-fuel ratio variations between cylinders, so the 0■ sensor cannot detect the average air-fuel ratio, and as a result, there is a problem of low air-fuel ratio control accuracy. Ta.

On the other hand, in the case of a single 02 sensor system in which the 0■ sensor is installed downstream of the catalyst, although the imbalance of exhaust gas and non-detection of the average air-fuel ratio are resolved, the position of the 02 sensor is further away from the exhaust valve. However, depending on the catalyst capacity and purification performance (size of 02 storage effect, etc.)
The responsiveness of the sensor is low, and therefore the responsiveness of the air-fuel ratio feedback control system is deteriorated, and as a result, the performance of the catalyst cannot be fully demonstrated, leading to a problem of deterioration of emissions.

In addition, double 02 sensors are installed upstream and downstream of the catalyst.
In the sensor system, upstream O2? In addition to air-fuel ratio feedback control by the sensor, air-fuel ratio feedback control is performed by the downstream 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 can be maintained. It is proved. However, in the double 02 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, the catalyst performance cannot be fully demonstrated. There is a problem.

For this reason, the applicant has already developed a forced self-excitation control waveform (forced oscillation waveform) with a predetermined amplitude and a predetermined frequency in a single 02 sensor system in which a 0 sensor is provided downstream of the catalyst.
We have proposed a method in which the central value of 0 is changed according to the output of the downstream 0■ sensor.

That is, as shown in FIG. 2, the downstream side 02 cm? output V. When X changes, the forced self-excitation control waveform AF.
The center value (coarse adjustment term) AFC is changed according to the output VOX of the downstream 0■ sensor. In this case, the output V of the downstream 02 sensor. When X is lean, the coarse adjustment term AFc is gradually increased, while the output V of the downstream 02 sensor. X
is rich, the coarse adjustment term A F c is gradually reduced. In other words, the coarse adjustment term A F c is integrally controlled. As shown in Figure 3, this is near the stoichiometric air-fuel ratio (λ=1
), the forced self-excitation control waveform swings (AFS=AF.).

), the catalyst can maximize its purification performance, but even if the self-excitation control waveform swings at the rich side air-fuel ratio (λ×1) or the lean side air-fuel ratio (λ×1) (AFs+, AFs■
) The purification function of the catalyst cannot be achieved. Therefore, the above-mentioned coarse adjustment term (integral term) AFc is introduced in order to bring the self-excitation control waveform AFs+ or AFS2 closer to AFso so as to exhibit the purification performance of the catalyst.

? [Problems to be Solved by the Invention] However, in engines having an evaporative purge system, making the rough adjustment term variable according to the output of the downstream 0 sensor described above is problematic in areas where the evaporative purge system does not work. However, it becomes a problem in areas where the evaporative purge system works and a large amount of evaporative gas is generated. That is, when a large amount of evaporation occurs, the downstream 02 sensor indicates a rich output, and as a result, the rough adjustment term is erroneously learned to the lean side. When such erroneous learning causes the vehicle to fall outside the Evabo purge area, there is a problem in that it may lead to deterioration of NOx emissions, deterioration of drivability, etc.

As a solution to the above-mentioned problem, it is possible to divide the coarse adjustment term into two areas, one for the evaporative purge area and one for the outside of the evaporative purge area. This does not necessarily occur in large quantities, and therefore, the coarse adjustment term for the evaporative purge area will still be learned incorrectly.

Therefore, an object of the present invention is to provide an air-fuel ratio feedback control system that can fully demonstrate the purifying performance of a catalyst even in an engine having an evaporative purge system.

[Means to solve the problem]

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

In FIG. 1, the purge area determining means determines the purge area of the Evabo Burge system.

Further, a three-way catalyst is provided in the exhaust passage of the internal combustion engine, and furthermore, a catalyst downstream air-fuel ratio sensor for detecting the air-fuel ratio of the engine is provided downstream of the three-way catalyst. The first coarse adjustment term calculation means is the output V of the air-fuel ratio sensor. When X is rich, it gradually changes to the rich side, and the output V of the air-fuel ratio sensor. The first coarse adjustment term AFC that gradually changes to the rich side when X is lean
On the other hand, when the output VOX of the air-fuel ratio sensor is rich, the second rough adjustment term calculating means gradually changes to the lean side, and the output V of the air-fuel ratio sensor is calculated. A second coarse adjustment term A F c p that gradually changes to the rich side when X is lean is calculated.

When in the purge area of the Evabo system (XPGA=”
1”), the difference determining means is configured to distinguish between the first coarse adjustment term AFcc and the second coarse adjustment term AFcc.
The difference ΔAF between the rough adjustment term AFCE and the rough adjustment term AFCE is calculated, and it is determined whether the difference ΔAF is greater than or equal to a predetermined value. As a result, when the purge area of the Evabo system and the difference ΔAF is greater than a predetermined value,
PGA="1", XACHG-"1"), the first hold means stops the calculation of the first coarse adjustment term calculation means and holds the second coarse adjustment term AFcc. On the other hand,
When outside the purge area of the evaporative system (XPGA="0"), the first holding means stops the calculation of the second coarse adjustment term calculation means and holds the second coarse adjustment term AFCE. The forced self-excitation control waveform generation means generates a forced self-excitation control waveform A F s with a predetermined amplitude and a predetermined frequency. Then, when the air-fuel ratio adjustment means is in the purge area of the evaporative purge system and the difference ΔAF is greater than or equal to a predetermined value (XPGA
= "l n. coarse adjustment term AF
cc and forced self-excitation control waveform AF. The engine's air-fuel ratio is adjusted accordingly.

[For production]

According to the above-mentioned means, the first coarse adjustment term AFcG is used not only for the normal non-evaporation purge area but also for the area where a large amount of evaporation is not generated even in the evaporation purge area. On the other hand, the second coarse adjustment term AFcp is for the area where a large amount of evaporation is generated in the evaporative purge area. In other words, the evaporation purge area and the evaporation generation area usually do not coincide. Therefore, in the present invention, the rough adjustment term AFC is divided into AFcc for the non-evaporation generation area and AFCE for the evaporation generation area. That is, since the second coarse adjustment term AFcE is updated over the entire evaporation region, the degree of evaporation occurrence in this region is learned by the second coarse adjustment term AFcc. Therefore, if the degree of evaporation generation increases (XACHG
= "1"'), the influence of Evabo is the first coarse adjustment term AFcc
In order to prevent this from occurring, the update of the first coarse adjustment term AFcc is held and the air-fuel ratio is adjusted using the second coarse adjustment term AFcg.

〔Example〕

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 4, 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, has a built-in potentiometer, and generates an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 includes a crank angle sensor 5 that generates a pulse signal for detecting a reference position every 720 degrees in terms of crank angle, and a crank angle sensor 5 that detects a reference position every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided which generates a pulse signal. The pulse signals of these crank angle sensors 5 and 6 are supplied to the input/output interface 102 of the control circuit IO, and the output of the crank angle sensor 6 is sent to the CPU 1.
03's? supplied to the built-in terminal.

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 11C. A catalytic converter 12 is provided that accommodates a three-way catalyst that simultaneously purifies CD and NOx.

An 02 sensor 14 is provided in the exhaust pipe 13 downstream of the catalytic converter 12. The 02 sensor 14 generates an electrical signal according to the concentration of oxygen components in the exhaust gas. In other words, the 0■ 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 configured as a microcomputer, and A/D
Converter 101, input/output interface 102, CP[
Outside of I103, R(llMI04.RAM105
, a backup RAJO 6, a clock generation circuit 107, etc. are provided.

Further, the throttle valve 15 of the intake passage 2 receives a signal LL indicating whether the throttle valve 15 is fully closed or not, and a signal LL indicating whether the throttle valve 15 is fully closed or not.
Throttle sensor l that generates a signal TA indicating 50 degrees of opening
6 is provided, and the output signals LL and TA are supplied to the human output interface 102 and the A/D converter 101 of the control circuit 10, respectively.

17 is a barge port located near the throttle valve 15 (for example, 12 to 13 degrees); 18 is an air flow meter 3;
a purge air intake port located downstream of the fuel tank 19, which communicates with an activated carbon canister connected to the fuel tank 19 to form an evaporative purge system.

Further, in the control circuit 10, a down counter 108,
The flip-flop 109 and the drive circuit 110 are for controlling the fuel injection valve 7. That is, in the routine described below, when the fuel injection amount TAU is calculated, the fuel injection amount TAU is reset to the down counter 10g and the flip-flop knob 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and the borrow out terminal reaches the "1" level, the flip-flop 10
9 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 amount of fuel injection 1iTAU mentioned above, and therefore the fuel injection amount TAU
An amount of fuel corresponding to the amount of fuel 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 controller receives a pulse signal from the crank angle sensor 6, when it receives an interrupt signal from the clock generation circuit 107, etc.

The intake air amount data Q and 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 1050. 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. 5 shows a routine for calculating the fine adjustment term AF, which is executed every predetermined period of time, for example, 4 ms. That is, in step 501, it is determined whether the air-fuel ratio feedback condition is satisfied.

For example, when the cooling water temperature is below a predetermined value, for example 40°C,
The air-fuel ratio feedback condition is not satisfied during engine starting, during fuel increase after engine start, during warm-up fuel increase, during power increase, fuel cut, etc., and in other cases, the air-fuel ratio feedback condition is satisfied. If the air-fuel ratio feedback condition is not satisfied, the process directly proceeds to step 513. If the air-fuel ratio feedback condition is satisfied, the process proceeds to step 502. In step 502, the output V of the 02 sensor 14 is determined. X to A/D
It is converted and taken in, and in step 503 it is compared with a reference voltage V, for example 0.45V. As a result, VOX≦VR
(U), the air-fuel ratio flag XOX is set to "0# (lean)" in step 504, and the previous air-fuel ratio flag XOX [l is "1" (rich) in step 505.
Determine whether or not. As a result, the flag XOX is “1” (
Only when the value is reversed from “rich” to “0” (lean),
As shown in FIG. 6, in step 507, the fine adjustment term AF
Let t be ΔAF, (constant value). Then, the process advances to step 512. On the other hand, in step 503, VOX>V
If R (!J), the air-fuel ratio flag XOx is set to "1" (rich) in step 508, and step 50
At 9, the previous air-fuel ratio flag XOXO is “0” (lean)
Determine whether or not. As a result, the flag XOx is “0”
Only when the change is from "1'(lean)" to "1'(rich)," as shown in FIG.
Let Fr be -ΔAF.

Then, the process advances to step 512.

In step 512, the output V of the 02 sensor 14 is determined in the routine shown in FIG. 9, which will be described later. A counter CNT for calculating the inversion period of X is cleared.

The routine then ends at step 513.

In this manner, according to the routine shown in FIG. 5, the fine adjustment term AFT of the skipped waveform is calculated every time the output of the 02 sensor 14 is inverted, as shown in FIG.

In other words, a self-excitation control waveform can be obtained from the output of the 02 sensor 14 itself. In other words, control of the fine adjustment term AFr corresponds to sweep control.

FIG. 7 shows a region division processing routine for the rough adjustment term AFo, which is executed every predetermined time, for example, 16 ms. In addition,
This routine uses the flag XPGA indicating the Everbage area.
, and a flag XACHG indicating the evacuation generation area.

In step 701, the opening degree TA of the throttle valve 15 is set to A.
/D conversion and import, at throttle 702, TA>
It is determined whether TAo (a constant value, for example, 12 to 13 degrees) is reached. In other words, if TA>TAo, the purge port 17 is connected to the downstream side of the throttle valve 15, resulting in an evaporative purge state, and the process proceeds to step 703, where the evaporative purge area flag XPGA is set (XPGA="
1'). On the other hand, if TA≦TAO, the barge boat 17 is in communication with the upstream side of the throttle valve 15, and therefore the pressures of the barge air intake port 18 and the purge boat 17 are the same, resulting in a non-evaporation purge state. Proceeding to step 711, the evaporative purge area flag XPGA is reset (XPGA="0").

Only in the case of the evaporation purge area (XPGA="1"), the process proceeds to steps 704 to 710, and it is determined whether or not evaporation is occurring. In step 704, the first coarse adjustment term AF is calculated by the routine shown in FIG. 9, which will be described later.
Calculate the difference ΔAF between cc and the second rough adjustment term AFCE,
In step 705, it is determined whether ΔAF<0. If ΔAF<O, AFCE <-AFcc is determined in step 706 as erroneous learning. In other words, since the coarse adjustment term AFCE is exclusive to the evaporative purge area, A
Fcc≧AFC! It is. Therefore, AFCE >A
If it becomes Fcc, it may be changed to ^FcE4-AFcc.

In step 707, it is determined based on the difference ΔAF whether or not evaporation has occurred (a certain amount is large). That is, in step 707, it is determined whether ΔAF<M, (constant value),
At step 708, it is determined whether ΔAF>M2 (constant value). However, M1<M2, and as shown in FIG. 8, hunting of the flag XACHG, that is, hunting of the air-fuel ratio, is prevented by determining ΔAF in a hysteretic manner. As a result, if ΔAF<M+, the evaporation generation flag XACHG is reset (XACHG-“0”) in step 709 as it is assumed that no evaporation occurs (even if there is a small amount); on the other hand, if ΔAF>M2 In step 710, it is assumed that an evaporative engine has occurred.
G = “1”).

If M1≦ΔAF≦M2, the flag XACHG is not changed.

The routine then ends at step 712.

FIG. 9 shows the rough adjustment term AFcc. This is a routine for calculating AFCE, and is executed every predetermined period of time, for example, 64 ms. In step 901, step 50 in FIG.
1, it is determined whether the air-fuel ratio feedback condition is satisfied, and if the air-fuel ratio feedback condition is not satisfied, the process directly proceeds to step 913, and if the air-fuel ratio feedback condition is satisfied, the process proceeds to step 902. . In step 902, the counter CNT is set to a constant value K.
Determine whether CNT has been reached. In addition, counter C
NT is the output V of the 02 sensor l4 as described above. It is cleared every time X is reversed. Therefore, at the beginning, the process proceeds from step 902 to step 903, and the counter CN
Count up T by +1 and proceed to step 913. When count CNT reaches KCNT, that is, time K
After 64 ms of CNTX have elapsed, the flow in step 902 proceeds to steps 904-912.

In step 904, the counter CNT is cleared, and in step 905, it is determined from the air-fuel ratio flag XOX whether the current catalyst downstream air-fuel ratio is lean ("0") or rich ("1"). If the result is lean, step 906
Let the incremental value ΔAFC (constant value) of the rough adjustment term be AX,
On the other hand, if it is rich, the decrement value -ΔA is determined in step 907.
Set Fc to AX and proceed to step 908.

Note that the value △AFc is determined at steps 507 and 511 in FIG.
This is smaller than the skip amount ΔAFr used in . That is, ΔAFC<ΔA F r .

In step 908, the Everbage area flag XPGA
In step 909, it is determined whether the evaporation occurrence flag XACHG is "0" or not. As a result, if the everboverage area flag XPGA is "0" (non-everbage area), the value AX is
is used to update only the first coarse adjustment term AFcc. That is, AFcc, ← AFcc+AX is set, and the second rough adjustment term AFCE is held. Also,
If the evaporation barge area flag XPGA is "1" (evaporation barge area) and the evaporation occurrence flag XACHG is "0" (no evaporation occurrence), the value AX is used in step 911. AFc+
: Update both. That is, A Fca − A Fcc+ A XAFCE
- AFCE+AX. Furthermore, Evap purge area flag X! 'GA is "1" (Evabo barge area) and Evobo occurrence flag X
If ACliG is "1" (evaporation has occurred), only the second rough adjustment term AFCE is updated in step 912 using the value AX. That is, AFce←AFci+Aχ is set, and the first rough adjustment term AFCG is held.

This routine then ends in step 913.

Note that the flag XPGA in steps 908 to 912
The relationship between XACHG and the update of the coarse adjustment term is as follows.

In addition, the coarse adjustment term 8 Fcc, A according to the routine of FIG.
As shown in Fig. 10, if the air-fuel ratio is lean (XOX = "0"), FCE is gradually increased by ΔAFo, and if the air-fuel ratio is rich (XOX = "bi"), ΔAF
．． gradually decreased. In other words, control of the coarse adjustment term corresponds to integral control. However, it is also possible to add skip control every time xOx is reversed to improve the convergence of the air-fuel ratio to the stoichiometric air-fuel ratio.

FIG. 11 also shows the coarse adjustment term AFcc 1AFC[! 2 is a timing diagram showing changes in the two coarse adjustment terms, and the update and hold of the two coarse adjustment terms are controlled based on the values of the two flags XPG8 and XACHG. Note that the solid line represents the rough adjustment term AF that is actually used for fuel injection in the routine shown in FIG. 15, which will be described later.
It shows c. Furthermore, Fig. 12 also shows that the rough adjustment term APca
・This is a timing diagram showing changes in AFcp. Here, the second coarse adjustment term AFcE is equal to the first coarse adjustment term AFca.
This shows the case where it becomes larger. In this case, as described above, in step 706 of FIG.
+-AFcc.

Substantial execution or non-execution of the coarse adjustment term calculation routine in FIG. 9 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≦V.
(Lean) or V. Therefore, the fine adjustment term AF according to the routine of FIG. 5 is maintained at either ΔAff or -Δ8f, and as a result, the counter There is no clearing of CNT. On the other hand, in this case,
Coarse adjustment term AFcc or AFc according to the routine of FIG.
+: is gradually increased or decreased every 64 ms of KCNTX.

In other words, rather than controlling the fine adjustment term AFr, the coarse adjustment term AFr
Fcc or AFCE control is performed.

Conversely, when the catalyst downstream air-fuel ratio converges to the stoichiometric air-fuel ratio, the output V of the 02 sensor 14. Is X often reversed? It was carried out in
In other words, the output V of the sensor 14 is 0. The inversion period of X becomes shorter, and the fine adjustment term AF, frequently becomes ΔAfr. −ΔAf
, repeat the pause. In this case, count CNT is cleared by step 512 of FIG. 5 before reaching KCNT, so that the flow in step 902 of FIG. 9 always proceeds to step 903. That is, there is no increase or decrease in the coarse adjustment term AFC, and therefore, control of the coarse adjustment term AFcG or AFCE is prohibited and its value is held, and only the fine adjustment term AFf is controlled.

FIG. 13 is a timing diagram illustrating air-fuel ratio control according to the routines shown in FIGS. 5, 7, and 9.

In other words, before time t, the air desire ratio (V.X)
has shifted to the lean side, and in this case, the coarse adjustment term AF
Only cc or AFC2 is controlled. That is, it is an integral control period. Between times 1 and -12, the air-fuel ratio (
V ox ) has converged to the stoichiometric air-fuel ratio, but is still on the lean side. In this case, the fine adjustment term AFf is controlled every time the air-fuel ratio is reversed, and the
Is there a case where the reversal period is long? Therefore, the coarse adjustment term A
F c c or AFC. control is also performed. Time t2
From then on, the air-fuel ratio has completely converged to the stoichiometric air-fuel ratio, and as a result, the output VOX of the 0■ sensor 14 frequently crosses the reference voltage V1, and the inversion period becomes shorter. As a result, control of the coarse adjustment term AFCG or AFCE is prohibited,
Its value is held.

Obtained in this way. Fine adjustment term AFf and coarse adjustment term A
Sum with FC AFr +AFcc (or AFC!!
), and when the controlled air-fuel ratio catches up to the stoichiometric air-fuel ratio by coarse adjustment term control (integral control), self-denity ratio control (fine adjustment) is performed by the output of the 02 sensor 14 itself. As a result, the output reversal period of the 02 sensor 14 is short, that is, the control frequency is maintained high, and the purification performance of the catalyst can be maximized.In addition, coarse adjustment term control is prohibited (hold). As a result, over-correction of the air-fuel ratio due to the response delay of the 02 sensor 14 is eliminated, and the convergence of the control air-fuel ratio is also improved.

FIG. 14 shows a routine for generating a forced self-oscillation term (forced oscillation term) AFs, which is performed every predetermined time, for example, 4 m.
Executed every s. In step 1401, similarly to step 501 in FIG. 5, it is determined whether the air-fuel ratio feedback condition is satisfied. As a result, if the air-fuel ratio feedback condition is not satisfied, the process directly proceeds to step 1410, and only if the air-fuel ratio feedback condition is satisfied, the process proceeds to step 1402. In step 1402, it is determined whether the counter CNTS has reached T/2 of the synchronization T. In other words, the counter CNTS is incremented by +1 in step 1409, and every CNTS=T/2, the counter CNTS is incremented by +1 in step 1403.
Proceed to ~1408.

That is, in step l403, the counter CNTS is cleared, and in step 1404, it is determined whether the forced self-oscillation flag XSIC is "0" or not. If XSIC="0", the forced self-oscillation term is cleared in step 1405 AFs is set to -ΔAFS (constant value), and flag XSIC is inverted to "1" in step 1406. As a result, when the counter CNTS reaches T/2 again, the flow of step 1404 is changed to step 1407. Proceed to 1408. In step 1407, the forced self-oscillation term A F s
is set as ΔAFS, and the flag XSI is set in step 1408.
Invert C to "0".

The routine then ends at step 1410.

In this way, according to the routine of FIG.
A forced self-oscillation waveform with a constant amplitude (ΔAFs) and period T as shown in the figure can be generated. Note that the amplitude ΔAF. can also be reduced to an idle state (LL="1'").

FIG. 15 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA.

In step 1601, the intake air amount data Q and rotational speed data Ne are read from the RAM 105, and the basic injection amount T is read out.
Calculate AUP. For example, TAUP←α・Q/N
e (α is a constant). In step 1502, it is determined whether the evaporative purge area flag XPGA is "1" or not, and in step 1503, the evaporative purge area flag
It is determined whether or not is "1". As a result, only when the evaporative purge area flag XPGA is "1" in the evaporative purge area and the evaporative generation flag XACHG is "1" (evaporative generation), the process advances to step l504 and the second coarse adjustment term
Fc! Let be AFc.゛In other words, AFc ← A
Fcg. Otherwise, in step 1505, the first coarse adjustment term AFcc is set to AF. shall be. That is, the flag XPG
The relationship between A, XACHG and the coarse adjustment term AFc is as follows.

Next, in step 1506, the final injection jlTAU is
TAU ←TA [IP − (AFf+AFc 18F,
+β)+T1. Note that β and γ are correction amounts determined by other operating state parameters. Then,
At step 1507, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. And step 15
This routine ends at 08.

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.

Figure 16 is Figure 5, Figure 7, Figure 9, Figure 14, Figure 15.
FIG. 3 is a timing diagram illustrating air-fuel ratio control according to the routine shown in the figure. That is, the fine adjustment term A F r + forced self-oscillation term AF,S replaces the fine adjustment term A F r in FIG. In this case, the amplitude and frequency of the forced self-oscillation waveform are set so as to fully demonstrate the purification performance of the three-way catalyst, and disturbances in the air-fuel ratio due to the introduction of the forced self-oscillation term A F s are minimized.

In addition, in the above-mentioned embodiment, the coarse adjustment term AFo (AF
cc, 8F. I! ) is combined with the fine adjustment term AFr and the forced self-oscillation term AFs, but the present invention can also be applied to a case where only the fine adjustment term AF or the forced self-oscillation term AFs is combined.

Note that, 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.

Furthermore, in the above embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, lean mixture sensor, etc. may also be used.

Furthermore, the embodiments described above may be implemented using a microcomputer, that is, a digital circuit, or alternatively may be implemented using an analog circuit.

〔Effect of the invention〕

As described above, according to the present invention, when evaporation occurs in the evaporative purge system, the normal erroneous learning of the coarse adjustment term is eliminated, and as a result, deterioration of emissions can be prevented.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram showing the basic configuration of the present invention, Fig. 2 is a timing diagram explaining the problem in the prior application, Fig. 3 is a graph showing the relationship between the self-excitation control waveform and the catalyst purification function, and Fig. 4 The figures are overall schematic diagrams showing one embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention.
Figure 5 is a flowchart to explain the operation of the control circuit in Figure 4, Figure 6 is a timing diagram to supplement the flowchart in Figure 5, and Figure 8 is a supplementary flowchart in Figure 7. 13 is a timing diagram supplementary to the flowcharts in FIGS. 5, 7, and 9. FIGS. 10, 11, and IZ are flowcharts in FIGS. 7 and 9. FIG. 16 is a timing diagram supplementary explaining the flowcharts of FIGS. 5, 7, 9, and 14. ? ...Engine body, 3...Air 7 row meter,
...Distributor, 6...Crank angle sensor, 0...Control circuit, 12...Catalytic converter,
4...0■sensor, 17...barge boat,
Death: Barge air intake boat.

Claims (1)

[Claims] 1. An evaporative purge system (18), a purge area determining means for determining a purge area of the evaporative purge system, a three-way catalyst (12) provided in an exhaust passage of an internal combustion engine, and a catalyst downstream air-fuel ratio sensor (14) that is installed in the exhaust passage downstream of the three-way catalyst and detects the air-fuel ratio of the engine; a first coarse adjustment term calculation means that calculates a first coarse adjustment term (AF_C_G) that gradually changes to the rich side when the output of the air-fuel ratio sensor is lean; a second coarse adjustment term calculation means for calculating a second coarse adjustment term (AF_C_E) that gradually changes toward the rich side when the output of the air-fuel ratio sensor is lean; a difference determining means for calculating a difference (ΔAF) between the first coarse adjustment term and the second coarse adjustment term when the area is in the range, and determining whether the difference is greater than or equal to a predetermined value; a first holding means for stopping the calculation of the first coarse adjustment term calculation means and holding the first coarse adjustment term (AF_C_G) when the purge area and the difference is equal to or greater than the predetermined value; a second hold means for stopping the calculation of the second coarse adjustment term calculation means and holding the second rough adjustment term (AF_C_E) when the system is outside the purge area; and a purge area of the evaporative purge system. In addition, when the difference is greater than or equal to the predetermined value, the second rough adjustment term (AF_C
_E), and in other cases, adjusts the air-fuel ratio of the engine according to the first coarse adjustment term (AF_C_G); Air-fuel ratio control device for internal combustion engines.