JPH0613857B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention provides an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ sensor)) on the upstream side and the downstream side of a catalytic converter, and O ₂ relates to an air-fuel ratio control apparatus for an internal combustion engine which performs air-fuel ratio feedback control by the O ₂ sensor downstream in addition to the air-fuel ratio feedback control by the sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor for detecting the oxygen concentration is provided at a location in the exhaust system as close to the combustion chamber as possible, that is, at a collective portion of the exhaust manifold upstream of the catalytic converter. , O ₂ sensor output characteristics vary, which hinders improvement of air-fuel ratio control accuracy. Such O ₂
A second O ₂ sensor is provided downstream of the catalytic converter in order to compensate for variations in output characteristics of the sensor, variations in parts such as the fuel injection valve, and changes over time or over time.
A double O ₂ sensor system has already been proposed which performs air-fuel ratio feedback control by a downstream O ₂ sensor in addition to air-fuel ratio feedback control by an upstream O ₂ sensor. In this double O ₂ sensor system, the O ₂ sensor provided on the downstream side of the catalytic converter has a lower response speed than the upstream O ₂ sensor, but the variation in the output characteristics is small for the following reasons. Have advantages.

(1) Downstream of the catalytic converter, the exhaust temperature is low, so there is little thermal effect.

(2) Downstream of the catalytic converter, various poisons are trapped in the catalyst, so the amount of poisoning of the downstream O ₂ sensor is small.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to the equilibrium state.

Therefore, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor. In fact, as shown in FIG. 2, in a single O ₂ sensor system, O ₂
When the output characteristic of the sensor deteriorates, it directly affects the exhaust emission characteristic, whereas in the double O ₂ sensor system, even if the output characteristic of the upstream O ₂ sensor deteriorates,
Exhaust emission characteristics do not deteriorate. In other words, double O
_{In a two-} sensor system, good exhaust emission is guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics.

[Problems to be solved by the invention]

In the above-described double O ₂ sensor system, the air-fuel ratio change speed is changed according to the output of the downstream O ₂ sensor, so that the vehicle surging degree changes accordingly.
Especially, when the air-fuel ratio correction coefficient FAF is skipped, the vehicle surging degree becomes large. This is due to torque fluctuations due to a sudden change in the air-fuel ratio. This is remarkable in the system in which the skip amount in the air-fuel ratio feedback control is changed by the downstream O ₂ sensor.

In this case, the relationship between the skip amount RS of the air-fuel ratio correction coefficient FAF and the vehicle surging degree D is shown in FIG. 3, and the vehicle surging degree D is easily felt during a light load (intake air amount Q: small), On the other hand, when the load is high (intake air amount Q: large), it is difficult to experience, so the upper limit LU of the skip amount RS of the air-fuel ratio correction coefficient FAF at the allowable vehicle surging degree D _max is different. However, in general, the upper limit value L of the skip amount RS of the air-fuel ratio correction coefficient FAF regardless of whether the load is light or high.
U is constant. Therefore, if the skip amount RS upper limit value is uniformly determined so that the surging degree is equal to or less than D _max when the load is low, emphasizing the reduction of the surging of the vehicle, the emission becomes large at the time of the high load and the light load becomes large. Although the air-fuel ratio change width is large compared to the time, the air-fuel ratio change width becomes relatively small. As a result, H
There is a problem that it causes an increase in C, CO and NO _x emissions.

It should be noted that if the change width of the air-fuel ratio is small, optimal control cannot be performed for the catalyst, causing an increase in HC, CO, and NO _x emissions.

[Means for solving problems]

An object of the present invention is to provide a double air-fuel ratio sensor system that achieves both prevention of vehicle surging at light load and securing of emission performance at high load, and its means is shown in FIG.

In FIG. 1, first and second air-fuel ratio sensors for detecting a specific component concentration in exhaust gas are provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine. Each is provided. The constant calculation means is a constant rich skip amount RSR involved in the air-fuel ratio feedback control according to the output V ₂ of the downstream (second) air-fuel ratio sensor.
, Calculate the lean skip amount RSL. The constant upper limit calculation means is a constant RSR, RS that is involved in air-fuel ratio feedback control.
The upper limit LU of L is the speed SPD of the vehicle equipped with the engine,
The engine speed Ne, the load Q / Ne, the intake air amount Q, the intake air pressure PM, and the throttle valve opening degree TA are calculated according to one of the operating condition parameters. The larger the operating condition parameter, the larger the upper limit LU. Set. As a result, the upper limit guard means guards the constants RSR, RSL involved in the air-fuel ratio feedback control with the upper limit LU. The air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FA according to the output V ₁ of the upstream (first) air-fuel ratio sensor and the constants RSR, RSL involved in the guarded air-fuel ratio feedback control.
Computes F. Then, the air-fuel ratio adjusting means determines the air-fuel ratio correction amount.
It adjusts the air-fuel ratio of the engine according to FAF.

[Action]

According to the above-mentioned means, the constants RSR, RSL involved in the air-fuel ratio feedback control are increased when the load is high compared to when the load is light.
Since the upper limit value LU of is set to be large, the change width of the air-fuel ratio can be increased.

〔Example〕

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

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control system 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 intake air amount, and has a built-in potentiometer to generate an output signal of an analog voltage proportional to the intake air amount. This output signal is supplied to the A / D converter 101 with a built-in multiplexer in the control circuit 10. In Distributor 4,
For example, a crank angle sensor 5 whose axis generates a reference position detecting pulse signal every 720 ° converted to a crank angle and a crank angle sensor which generates a reference position detecting pulse signal every 30 ° converted to a crank angle 6 is provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to the input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

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

The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 is the temperature of the cooling water THW
Generates an electric signal of analog voltage according to. This output is also supplied to the A / D converter 101.

An exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, CO, and NO _x in the exhaust gas.

The exhaust manifold 11 includes the catalytic converter 1
A first O ₂ sensor 13 is provided on the upstream side of 2, and a _second O ₂ sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12. The O ₂ sensors 13 and 15 generate electric signals according to the concentration of oxygen components in the exhaust gas. That is, the O ₂ sensors 13 and 15 generate different output voltages in the control circuit 10 to the A / D converter 101 depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface.
In addition to 102 and CPU 103, ROM 104, RAM 105, backup RAM 106, clock generation circuit 107, etc. are provided.

Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 are for controlling the fuel injection valve 7. That is, when the fuel injection amount TAU is calculated in the routine described later, 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, when the down counter 108 counts a clock signal (not shown) and finally its carry-out terminal becomes "1" level, the flip-flop 109 is set and the driving circuit is set.
110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is biased by the above-mentioned fuel injection amount TAU, and therefore,
An amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

It should be noted that the interrupt generation of the CPU 103 is caused by the A / D converter 101
This is, for example, when the I / O interface 102 receives the pulse signal of the crank angle sensor 6 at the end of the / D conversion, when the interrupt signal from the clock generation circuit 107 is received, and the like.

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

FIG. 5 shows a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, 4 ms.

In step 501, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied. For example, when the cooling water temperature is below a specified value,
The closed loop condition is not satisfied during engine start, during post-start increase, during warm-up increase, during power increase, when the output signal of the upstream O ₂ sensor 13 has never been inverted, during fuel cut, etc. In the case, the closed loop condition is satisfied.
When the closed loop condition is not satisfied, the routine proceeds to step 521, where the air-fuel ratio correction coefficient FAF is set to 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 502.

At step 502, the output V ₁ of the upstream O ₂ sensor 13 is A / D converted and taken in, and at step 503, it is judged whether or not V ₁ is the comparison voltage V _R1 or less than 0.45 V, that is,
Determine whether the air-fuel ratio is rich or lean. Lean (V ₁ ≤
If it is V _R1 ), the first delay counter CDLY 1 is decremented by 1 in step 504, and the first delay counter CDLY 1 is guarded by the minimum value TDR 1 in steps 505 and 506. The minimum value TDR 1 is the rich delay time for holding the determination that the output of the upstream O ₂ sensor 13 is in the lean state even if there is a change from lean to rich,
Defined with a negative value. On the other hand, if rich (V ₁ > V _R1 ), in step 507, the first delay counter CDLY 1
Is incremented by 1 and the first delay counter CDLY 1 is guarded with the maximum value TDL 1 in steps 508 and 509. It should be noted that the maximum value TDL 1 is a lean delay time for holding the determination that the output is the rich state even if the output of the upstream O ₂ sensor 13 changes from rich to lean, and is defined as a positive value. To be done.

Here, the reference of the first delay counter CDLY 1 is set to 0, the air-fuel ratio after delay processing is considered rich when CDLY 1> 0, and the air-fuel ratio after delay processing is lean when CDLY 1 ≦ 0. Shall be regarded.

In step 510, it is determined whether or not the sign of the first delay counter CDLY 1 is inverted, that is, it is determined whether or not the air-fuel ratio after the delay processing is inverted. If the air-fuel ratio has been reversed, it is determined in step 511 whether it is reversal from rich to lean or reversal from lean to rich. If it is a reverse from rich to lean, FAF ← FA in step 512
F + RSR is increased in a skip manner, and conversely, if lean to rich inversion, then in step 513 FAF ← FAF −
RSL and skip reduction. That is, skip processing is performed.

If the sign of the first delay counter CDLY1 is not inverted in step 510, integration processing is performed in steps 514, 515 and 516. That is, in step 514, CDLY 1 <0
If CDLY 1 ≤ 0 (lean), step 515 sets FAF ← FAF + KI. If CDLY 1> 0 (rich), step 516 sets FAF ← FAF + KI. Here, the integration constant KI is set sufficiently smaller than the skip constants RSR, RSL, that is, KI <RSR (RSL)
Is. Therefore, step 515 is in the lean state (CDLY 1
≦ 0), the fuel injection amount is gradually increased, and step 516 gradually decreases the fuel injection amount in the rich state (CDLY1> 0).

The air-fuel ratio correction coefficient FAF calculated in steps 512, 513, 515 and 516 is guarded at steps 517 and 518 with a minimum value of 0.8, and at steps 519 and 520 with a maximum value of 1.2. As a result, when the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF calculated as described above is stored in the RAM 105, and this routine ends at step 522.

Note that step 521 in FIG. 5 can be omitted, and in this case, the value immediately before the end of the air-fuel ratio feedback control is used as FAF.

FIG. 6 is a timing diagram for supplementarily explaining the operation according to the flowchart of FIG. When the rich / lean air-fuel ratio signal A / F1 is obtained from the output of the upstream O ₂ sensor 13 as shown in FIG. 6 (A), the first delay counter CDLY 1 is shown in FIG. 6 (B). As shown, the rich state is counted up and the lean state is counted down. As a result, as shown in FIG. 6C, the delayed air-fuel ratio signal A / F1 'is formed. For example,
Also at time t ₁ the air-fuel ratio signal A / F1 is changed from lean to rich, the air-fuel ratio signal A / F1 delayed processed 'the time t ₂ after being held lean only the rich delay time (-TDR1) Changes to rich. Also the air-fuel ratio signal A / F1 from the rich at time t ₃ is changed to the lean air-fuel ratio signal A / F1 delayed processed 'at time t ₄ after being held rich only lean delay time TDL 1 equivalent Changes to lean. However, the air-fuel ratio signal A / F1 changes from time t ₅ , t ₆ ,
When inverted in a period shorter than the rich delay time (-TDR1) like t ₇ , it takes time for the first delay counter CDLY 1 to cross the reference value 0. As a result, after the delay processing at time t ₈ . Of the air-fuel ratio signal A / F1 'is inverted. That is,
The air-fuel ratio signal A / F1 'after the delay processing is more stable than the air-fuel ratio signal A / F1 before the delay processing. In this way, the sixth signal is generated based on the stable air-fuel ratio signal A / F1 'after the delay processing.
The air-fuel ratio correction coefficient FAF 1 shown in FIG.

Next, the second air-fuel ratio feedback control by the downstream O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, skip amounts RSR, RSL as delay constants involved in the first air-fuel ratio feedback control, delay times TDR 1, TDL 1, integration constant KI (in this case, rich integration constant KI1R and lean There are a system in which the integration constant KI1L is set separately) or a system in which the comparison voltage V _R1 of the output V ₁ of the upstream O ₂ sensor 13 is variable, and a system in which a second air-fuel ratio correction coefficient FAF 2 is introduced.

For example, if the rich skip amount RSR is increased, the control air-fuel ratio can be shifted to the rich side, and the lean skip amount is increased.
Even if RSL is reduced, the control air-fuel ratio can be shifted to the rich side,
On the other hand, if the lean skip amount RSL is increased, the control air-fuel ratio can be shifted to the lean side, and the rich skip amount RSR
The control air-fuel ratio can be shifted to the lean side even if is decreased. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount RSR and the lean skip amount RSL according to the output of the downstream O ₂ sensor 15. In addition, the rich delay time (-
TDR1)> lean delay time (TDL1), the control air-fuel ratio can shift to the rich side, and conversely, lean delay time (TDL1)
By setting 1)> rich delay time (-TDR1), the control air-fuel ratio can shift to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR 1 and TDL 1 according to the output of the downstream O ₂ sensor 15. Furthermore, if the rich integration constant KI1R is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean integration constant KI1L is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean integration constant KI is increased.
If 1L is increased, the control air-fuel ratio can shift to the lean side,
Further, the control air-fuel ratio can be shifted to the lean side even if the rich integration constant KI1R is reduced. Therefore, the downstream O ₂ sensor 15
The air-fuel ratio can be controlled by correcting the rich integration constant KI1R and the lean integration constant KI1L according to the output of. Furthermore, if the comparison voltage V _R1 is increased, the control air-fuel ratio can be shifted to the rich side, and if the comparison voltage V _R1 is decreased, the control air-fuel ratio can be shifted to the lean side. Therefore, the downstream O ₂
The air-fuel ratio can be controlled by correcting the comparison voltage V _R1 according to the output of the sensor 15.

A double O ₂ sensor system in which the skip amount as a constant involved in the air-fuel ratio feedback control is variable will be described with reference to FIGS. 7 and 8.

FIG. 7 is a second air-fuel ratio feedback control routine for calculating the skip amounts RSR, RSL based on the output of the downstream O ₂ sensor 15, and is executed every predetermined time, for example, every 1 s. In step 701, it is judged whether or not the closed loop condition by the downstream O ₂ sensor 15 is satisfied. For example, when the coolant temperature is below a predetermined value, when the output signal of the downstream O ₂ sensor 15 is also not reversed once, when the downstream O ₂ sensor 15 is faulty, even closed-loop condition is one during a transient operation or the like The condition is not satisfied, and in other cases, the closed loop condition is satisfied. If it is not a closed loop condition, the process proceeds to steps 728 and 729, and the skip amounts RSR and RSL are set to constant values RSR ₀ and RSL ₀ . For example, RSR ₀ = 5% RSL ₀ = 5%. Note that steps 728 and 729 can be deleted. In this case, the value immediately before the end of the air-fuel ratio feedback control is used.

If it is a closed loop, the process proceeds to step 702, where the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and fetched, and the step is performed.
At 703, it is determined whether or not V ₂ is the comparison voltage V _R2, for example, 0.55 V or less, that is, it is determined whether the air-fuel ratio is rich or lean. It should be noted that the comparison voltage V _R2 is more than the comparison voltage V _R1 of the output of the upstream O ₂ sensor 13 in consideration of the difference in output characteristics due to the influence of raw gas and the deterioration speed on the upstream and downstream of the catalytic converter 14. Set high. If lean (V ₂ ≦ V _R2 ), the second delay counter CDLY 2 is decremented by 1 in step 704, and steps 705 and 706 are executed.
, Guards the second delay counter CDLY 2 with the minimum value TDR 2. The minimum value TDR 2 is a rich delay time for maintaining a lean state even when there is a change from lean to rich, and is defined by a negative value. On the other hand, rich (V
If _2> V _R2), the second delay counter CDLY 2 in step 707 by adding 1 to the guard second delay counter CDLY 2 at the maximum value TDR 2 at step 708 and 709. The maximum value TDR 2 is a lean delay time for maintaining the rich state even when there is a change from rich to lean, and is defined by a positive value.

Again, the reference of the second delay counter CDLY 2 is set to 0, the air-fuel ratio after delay processing is regarded as rich when CDLY 2> 0, and the air-fuel ratio after delay processing is set to lean when CDLY 2 ≦ 0. Shall be regarded.

In step 710, the intake air amount data Q is read from the RAM 105 and it is determined whether or not Q> Q ₁ , and in step 11,
It is determined whether or not Q> Q ₂ . Note that Q ₁ <Q ₂ ,
For example, Q ₁ = 20 m ³ / h and Q ₂ = 80 m ³ / h. As a result, if Q ≦ Q ₁ , in step 712, the upper limit LU of the skip amounts RSR, RSL is set to 4%, and Q ₁ <Q
If ≤Q ₂ , LU is set to 6% in step 713, and Q≤
If Q ₂ , in step 714 the LU is set to 8%. In this way, as the parameter Q increases, the skip amount
Increase the upper limit LU of RSR and RSL. The upper limit LU may be obtained as a value that continuously changes by interpolation calculation, and instead of the intake air amount Q, the vehicle speed SPD, rotation speed Ne, load Q / Ne, throttle valve opening TA Calculation may be performed, and interpolation calculation may be performed using a map based on these two or more operating state parameters.

At step 715, the second delay counter CDLY 2 becomes CDLY.
It is determined whether or not 2 ≦ 0. As a result, if CDLY 2 ≦ 0, it is determined that the air-fuel ratio is lean and the routine proceeds to steps 716 to 721, while if CDLY 2> 0, it is determined that the air-fuel ratio is rich. Then, proceed to steps 722-727.

In step 716, RSR ← RSR + ΔRS (fixed value
0.08%), that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side. Steps 717, 71
In 8, RSR is guarded by the upper limit LU. Further, in step 719, RSL ← RSL−ΔRS is set, that is, the lean skip amount RSL is decreased and the air-fuel ratio is shifted to the rich side. In steps 720 and 721, the RSL is guarded by the lower limit value, for example, 2.5%.

On the other hand, if rich (V ₂ > V _R2 ), step 722
At this time, RSR ← RSR−ΔRS, that is, the rich skip amount RSR is decreased and the air-fuel ratio is shifted to the lean side. In steps 723 and 724, RSR is guarded with a lower limit value of 2.5%. Further, in step 725, RSL ←← RSL + ΔRS (constant value), that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. Steps 726, 727
Then, RSL is guarded by the upper limit LU.

After the RSR and RSL calculated as described above are stored in the RAM 105, this routine ends at step 730.

FAF, RSR, RS calculated during air-fuel ratio feedback
L can be temporarily converted to other values FAF ′, RSR ′, RSR ′ and stored in the backup RAM 106.
It is also useful for improving drivability when restarting.
The lower limit value of 2.5% in FIG. 7 is a level value at which transient followability is not impaired.

As described above, according to the routine of FIG. 7, if the output of the downstream O ₂ sensor 15 is lean, the rich skip amount RS
R is gradually increased, and the lean skip amount RSL is gradually decreased, whereby the air-fuel ratio is shifted to the rich side. When the output of the downstream O ₂ sensor 15 is rich, the rich skip amount RSR is gradually reduced and the lean skip amount RSL is gradually increased, whereby the air-fuel ratio is shifted to the lean side.

FIG. 8 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 801,
The intake air amount data Q and the rotation speed data Ne are read from the RAM 105 to calculate the basic injection amount TAUP. Eg TA
UP ← KQ / Ne (K is a constant). At step 802
The cooling water temperature data THW is read from the RAM 105 and the warm-up increase value FWL is interpolated by the one-dimensional map stored in the ROM 104. In step 803, the final injection amount TAU is calculated by TAU ← TAUPFAF (FWL + α) + β. Note that α and β are correction amounts determined by other operating state parameters. Next, at step 804, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 805, this routine ends.

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

The first air-fuel ratio feedback control is performed every 4 ms, and the second air-fuel ratio feedback control is performed every 1 s. The main reason for the air-fuel ratio feedback control is control by the upstream O ₂ sensor with good responsiveness. This is because the control is performed by the downstream O ₂ sensor having poor responsiveness.

Further, other constants related to the air-fuel ratio feedback control by the upstream O ₂ sensor, such as delay time, integration constant,
Double O _{2 that} corrects etc. by the output of the downstream O ₂ sensor
The present invention can be applied to a sensor system and also to a double O ₂ sensor system that introduces a second air-fuel ratio correction coefficient. In addition, controllability can be improved by simultaneously controlling two of the skip amount, delay time, and integration constant. Furthermore, one of the skip amounts RSR, RSL can be fixed and only the other can be made variable, or one of the delay times TDR1, TDL 1 can be fixed and only the other can be made variable, or the rich integration constant It is also possible to fix one of KIR and lean integration constant KIL and make the other variable.

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

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

Further, although the internal combustion engine in which the fuel injection amount is controlled by the fuel injection valve is shown in the above-mentioned embodiment, the present invention can be applied to a carburetor type internal combustion engine. For example, the electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and the electric bleed air control valve adjusts the air bleed amount of the carburetor to adjust the main system passage and the slow passage. The present invention can be applied to a device that controls the air-fuel ratio by introducing air into the system passage, a device that adjusts the amount of secondary air sent to the exhaust system of the engine, and the like. In this case,
The basic fuel injection amount corresponding to the basic injection amount TAUP in step 801 is determined by the carburetor itself, that is, in accordance with the intake pipe negative pressure corresponding to the intake air amount and the engine speed, and in step 803 the final fuel injection is performed. The amount of supply air corresponding to the amount TAU is calculated.

Furthermore, although the O ₂ sensor is used as the air-fuel ratio sensor in the above-described embodiment, a CO sensor, a lean mixture sensor, or the like can be used.

Further, although the above-mentioned embodiment is constituted by the microcomputer, that is, the digital circuit, it may be constituted by the analog rotation.

〔The invention's effect〕

As described above, according to the present invention, when the load is high compared to when the load is high, a constant involved in the air-fuel ratio feedback control, for example, RSR, the upper limit LU of RSL is set to a large value, so that the variation range of the air-fuel ratio is reduced. Can be relatively large, so
Optimum control of the catalyst becomes possible, and HC, CO, N
O _x emissions can be reduced.

[Brief description of drawings]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention, and FIG. 2 is a single O ₂ sensor system and a double O ₂ sensor system.
FIG. 3 is a graph showing the relationship between a constant involved in air-fuel ratio feedback control and vehicle surging degree, and FIG. 4 is an air-fuel ratio control device for an internal combustion engine according to the present invention. An overall schematic diagram showing an embodiment, FIGS. 5, 7, and 8 are flowcharts for explaining the operation of the control circuit of FIG. 3, and FIG. 6 is a supplementary description of the flowchart of FIG. It is a timing diagram. 1 ... Engine body, 3 ... Air flow meter, 4 ... Distributor, 5, 6 ... Crank angle sensor, 10 ... Control circuit, 12 ... Catalytic converter, 13 ... Upstream side (first) O ₂ Sensor, 15 ... Downstream (second) O ₂ sensor.

Claims (1)

[Claims] 1. A first and a second detector, which are respectively provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, for detecting a concentration of a specific component in the exhaust gas. An air-fuel ratio sensor, a constant calculating means for calculating a constant involved in the air-fuel ratio feedback control according to the output of the second air-fuel ratio sensor, and an upper limit value of the constant involved in the air-fuel ratio feedback control of the engine. A constant upper limit value calculating means for calculating according to the operating condition parameter and setting the upper limit value larger as the operating condition parameter increases, and an upper limit value guard means for guarding a constant involved in the air-fuel ratio feedback control with the upper limit value. And an air-fuel ratio correction amount is calculated according to the output of the first air-fuel ratio sensor and a constant involved in the guarded air-fuel ratio feedback control. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio correction amount calculation means; and an air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount.