JPH09126014A - Air fuel ratio control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the temperature rise without deteriorating the exhaust performance when the manifold catalyst is hot. SOLUTION: The air fuel ratio feedback control is realized based on the signal from an O2 sensor on the upstream side of the manifold catalyst, the temperature of the manifold catalyst is detected (to be estimated from the running condition), and when it is hot, the proportional control of the air fuel ratio feedback correction factor is delayed to reduce the control responsiveness (A). Perturbation of the air fuel ratio at the inlet of the manifold catalyst is increased thereby. When the temperature of the manifold catalyst is normal, the feedback control of the air fuel ratio is realized based on the signal from the O2 sensor on the upstream side of the manifold catalyst, and when the manifold catalyst is hot, the feedback control of the air fuel ratio is realized based on the signal from the O2 sensor on the downstream side of the manifold catalyst (B).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control device for preventing burnout / deterioration of an exhaust gas purification catalyst provided in an engine exhaust passage.

[0002]

2. Description of the Related Art Conventionally, as an air-fuel ratio control system for an internal combustion engine of this type, there is one disclosed in, for example, Japanese Patent Laid-Open No. 63-38648. It detects the temperature of the catalyst,
When this exceeds a predetermined value, the conversion center of the air-fuel ratio is shifted to the rich side to reduce the conversion rate of the catalyst and prevent temperature rise due to reaction heat, thereby preventing deterioration of the catalyst. Is.

Specifically, a delay time is provided from when the output of the O ₂ sensor cuts the slice level to when the rich / lean judgment is made, and the delay time at the lean → rich judgment is made large when the catalyst temperature is high. The control center of the air-fuel ratio is shifted to the rich side.

[0004]

However, in such a conventional air-fuel ratio control system for an internal combustion engine, since the control center of the air-fuel ratio is shifted to the rich side, not only the upstream side catalyst (manifold catalyst) is used. , Downstream catalyst (underfloor catalyst)
However, the conversion rate at 1 is also reduced, so that there is a problem in that CO and HC emissions are increased.

In view of such conventional problems, it is an object of the present invention to prevent burning and deterioration of the catalyst without deteriorating the exhaust performance.

[0006]

Therefore, in the invention according to claim 1, as shown in FIG. 1 (A), the engine exhaust passage is provided with an upstream side catalyst and a downstream side catalyst for exhaust gas purification,
An upstream side catalyst is provided with an air-fuel ratio detecting means for detecting an air-fuel ratio based on the exhaust gas composition on the upstream side, and an air-fuel ratio feedback control means for feedback-controlling the fuel supply amount to the engine so that the detected air-fuel ratio becomes the stoichiometric air-fuel ratio. In an air-fuel ratio control device for an internal combustion engine, catalyst temperature detection means for detecting the temperature of the upstream side catalyst, and when the detected catalyst temperature is equal to or higher than a predetermined value, the air-fuel ratio is detected regardless of whether the detected air-fuel ratio is rich or lean. The fuel ratio feedback control means is provided with responsiveness lowering means for lowering the responsiveness of the air-fuel ratio control to the detected air-fuel ratio.

That is, when the temperature of the upstream side catalyst is equal to or higher than a predetermined value, regardless of whether the detected air-fuel ratio is rich or lean,
By reducing the responsiveness of the air-fuel ratio control to the detected air-fuel ratio,
Air-fuel ratio perturbation (pertur) at the upstream catalyst inlet
By increasing the bation, the conversion rate of the upstream side catalyst is lowered, and the temperature rise of the catalyst due to the heat of reaction is prevented. Even in this case, since the control center of the air-fuel ratio is stoichiometric, the air-fuel ratio at the downstream side catalyst inlet is also balanced by the upstream side catalyst, and the amplitude of the air-fuel ratio does not become excessive. Since it is controlled near the stoichiki, the deterioration of emission can be suppressed.

According to the second aspect of the present invention, the air-fuel ratio feedback control means includes proportional control means for increasing or decreasing the air-fuel ratio feedback correction coefficient by a predetermined proportional constant when the lean rich of the detected air-fuel ratio is reversed, and the detected air-fuel ratio. Integral control means for increasing / decreasing the air-fuel ratio feedback correction coefficient by a predetermined integration constant at predetermined time intervals in accordance with the lean / rich state, and fuel supply amount correction means for correcting the fuel supply amount by the air-fuel ratio feedback correction coefficient. The responsiveness lowering means is a proportional control delay means for delaying an increase / decrease in the proportional amount of the air-fuel ratio feedback correction coefficient in the proportional control means.

By delaying the proportional control of the air-fuel ratio feedback correction coefficient, it is possible to increase the perturbation of the air-fuel ratio while keeping the air-fuel ratio control center stoichiometric. In the invention according to claim 3, the responsiveness lowering means suspends the integral control means while delaying the increase / decrease of the proportional constant of the air-fuel ratio feedback correction coefficient in the proportional control means, and the air-fuel ratio feedback It is characterized in that the correction coefficient is held.

This makes it possible to make more effective use of the effect of the delay in proportional control. In the invention according to claim 4, the responsiveness lowering means controls the air-fuel ratio feedback correction coefficient by the integral control means while delaying the increase / decrease of the proportional constant of the air-fuel ratio feedback correction coefficient in the proportional control means. It is characterized in that it increases or decreases in the same direction as before the inversion of the detected air-fuel ratio.

As a result, the perturbation can be increased. The invention according to claim 5 is characterized in that responsiveness reduction degree varying means for varying the degree of responsiveness reduction by the responsiveness reduction means according to the exhaust gas flow rate is provided. When the exhaust gas flow rate is large, the time to reach the maximum storage amount of the catalyst is shortened, so that the decrease in responsiveness is suppressed and the amplitude of the downstream catalyst inlet air-fuel ratio is prevented from becoming excessive.

According to the sixth aspect of the present invention, as shown in FIG. 1 (B), the engine exhaust passage is provided with an upstream side catalyst and a downstream side catalyst for exhaust purification, while the upstream side catalyst is based on the exhaust gas composition upstream. An air-fuel ratio of an internal combustion engine including first air-fuel ratio detection means for detecting an air-fuel ratio, and first air-fuel ratio feedback control means for feedback-controlling a fuel supply amount to the engine so that the detected air-fuel ratio becomes a stoichiometric air-fuel ratio. In the fuel ratio control device, while the second air-fuel ratio detecting means for detecting the air-fuel ratio based on the exhaust gas composition of the upstream side catalyst downstream is provided, the catalyst temperature detecting means for detecting the temperature of the upstream side catalyst, and the detected When the catalyst temperature is equal to or higher than a predetermined value, fuel is supplied to the engine so that the air-fuel ratio detected by the second air-fuel ratio detecting means becomes the stoichiometric air-fuel ratio instead of the first air-fuel ratio feedback control means. It is obtained so as to provide a second air-fuel ratio feedback control means for feedback control.

When the temperature of the upstream side catalyst is above a predetermined value,
By performing feedback control of the air-fuel ratio based on the exhaust composition of the upstream side catalyst downstream, by increasing the perturbation of the air-fuel ratio at the upstream side catalyst inlet, while suppressing the deterioration of emissions, while suppressing the deterioration of the upstream side catalyst Prevents temperature rise. In this case, perturbation of the air-fuel ratio can be obtained according to the deterioration state (O ₂ storage amount) of the upstream side catalyst. In other words, in order to reduce the conversion rate of the upstream side catalyst to the target, the new catalyst has a larger storage amount than the deteriorated catalyst, so it is necessary to further increase the perturbation, but this can be achieved. .

[0014]

Embodiments of the present invention will be described below. FIG. 2 is a system diagram showing an embodiment of the present invention. First, this will be described. Air is sucked from the air cleaner 2 into the combustion chamber of each cylinder of the internal combustion engine 1 mounted on the vehicle via the intake duct 3, the throttle valve 4, the intake manifold 5, and each intake valve 6. Each branch of the intake manifold 5 is provided with a fuel injection valve 7 for each cylinder.

The fuel injection valve 7 is an electromagnetic fuel injection valve which is energized by a solenoid to open the valve, and deenergized to close the valve. The fuel injection valve 7 is energized by a drive pulse signal from a control unit 14 described later to open the valve. Then, the fuel pumped by a fuel pump (not shown) and adjusted to a predetermined pressure by the pressure regulator is injected and supplied. A spark plug 8 is provided in each combustion chamber of the engine 1 to ignite sparks to ignite and burn the air-fuel mixture.

Exhaust gas from each combustion chamber of the engine 1 is
It is led from each exhaust valve 9 to an upstream side catalyst (hereinafter referred to as “mani catalyst”) 11 via an exhaust manifold 10. Furthermore,
Downstream catalyst (hereinafter “underfloor catalyst”) via the exhaust duct 12
It is led to 13. Control unit 14 is C
It is equipped with a microcomputer including a PU, a ROM, a RAM, an A / D converter, an input / output interface, etc., receives input signals from various sensors, performs arithmetic processing as described later, and operates the fuel injection valve 7. To control.

As the various sensors, a crank angle sensor 15 capable of detecting the engine speed N together with the crank angle from the crankshaft or camshaft rotation of the engine 1, the intake duct 3
An air flow meter 16 for detecting the intake air flow rate Q and a throttle sensor for detecting the opening TVO of the throttle valve 4.
17 (including an idle switch that is turned on when the throttle valve 4 is fully closed), a water temperature sensor 18 that detects the cooling water temperature TW of the engine 1, and a rich exhaust air-fuel ratio upstream of the manifold catalyst 11 at the collecting portion of the exhaust manifold 10. An upstream O ₂ sensor 19 that outputs a signal according to lean, and further a downstream O ₂ sensor that outputs a signal according to rich / lean of the exhaust air-fuel ratio downstream of the manifold catalyst 11 (upstream of the underfloor catalyst 13) Twenty etc. are provided. Although not shown, a signal from the start switch is also used.

Next, the contents of the arithmetic processing of the control unit 14 will be described with reference to the flow charts of FIGS. FIG. 3 is a flowchart of the catalyst temperature determination routine, which is executed in time synchronization. In step 1 (denoted as S1 in the figure, the same applies hereinafter), the start switch is turned on.
If it is ON (at the time of starting), it is determined whether or not step 2
Then, the timer TM1 for measuring the elapsed time after starting is cleared, and in step 3, referring to the table of FIG. 6, the function f of the water temperature TWINT at the time of starting detected by the water temperature sensor 18
As, the warm-up time T1 = f (TWINT) is estimated.
When the start switch is OFF, in step 4, the timer TM1 for measuring the elapsed time after starting is counted up.

In step 5, referring to the map of FIG. 7,
Function g of engine speed N and basic fuel injection amount (load) TP
As, the steady catalyst temperature TCA = g (N, TP) is estimated. In step 6, a timer (elapsed time after starting) TM1
Is compared with the warm-up time T1, and when TM1 ≧ T1, it is determined in step 7 whether or not the water temperature TW detected by the water temperature sensor 18 is equal to or higher than a predetermined value TW1.

As a result, TM1 <T1 or TW <TW1
If, then the process proceeds to step 8 and it is estimated that the catalyst temperature TC = the steady-state catalyst temperature TCA. Then, the routine proceeds to step 11, where the flag F1 = 0 is set to indicate that the catalyst is at the normal temperature. In step 12, the flag F3 = 0 is set in order to cancel the delay. When TM1 ≧ T1 and TW ≧ TW1, the routine proceeds to step 9, where the catalyst temperature TC is estimated by the weighted average of the steady catalyst temperature TCA as in the following equation.

TC = [(n-1) / n] .TC + (1 / n) .TCA In this embodiment, the catalyst temperature TC is estimated and detected from the engine operating state, but is directly detected by the sensor. You may make it detect it intentionally. Then, in step 10, it is determined whether the estimated catalyst temperature TC is equal to or higher than a predetermined value TC1.

As a result, when TC <TC1, the routine proceeds to step 11, where a flag F1 = 0 is set to indicate that the catalyst is at normal temperature. In step 12, the flag F3 = 0 is set in order to cancel the delay. When TC ≧ TC1, the routine proceeds to step 13, where the flag F1 = 1 is set to indicate that the catalyst temperature is high. Also, in step 14, in FIG.
As a function h of the engine speed N and the basic fuel injection amount (load) TP, the delay time T2 = h
Set (N, TP).

The delay time T2 may be a constant value, but when the exhaust gas flow rate is large, the time to reach the maximum storage amount of the catalyst becomes short, so it is desirable to shorten the delay time T2. This is because if the delay time T2 is too long, the amplitude of the underfloor catalyst inlet air-fuel ratio becomes large. Therefore, in this embodiment, the delay time T2 is shortened in the region where the exhaust gas flow rate is larger than that in the engine operating state.

FIG. 4 is a flow chart of the air-fuel ratio feedback control routine, which is executed in time synchronization. In step 21, it is judged whether or not it is the air-fuel ratio feedback (F / B) control condition, and if it is not the control condition, step 22
Then, the air-fuel ratio feedback correction coefficient α is clamped to 1.0, and this routine ends.

In step 23, the signal OS1 of the upstream O ₂ sensor 19 is read, and in step 24, the signal OS1 is compared with a predetermined slice level SL1 and OS1≤SL1.
If it is, it is determined in step 25 that F2 = 0 (lean), and O
When S1> SL1, in step 26, F2 = 1 (rich)
Is determined. Then, the process proceeds to step 27, but step 27
The subsequent description will be described separately for the case of the catalyst normal temperature and the case of the catalyst high temperature.

[Catalyst Normal Temperature; F1 = 0] Step
At 27, it is determined whether or not the flag F2 is inverted, and when inverted (during rich / lean inversion), the routine proceeds to step 28. In step 28, it is determined whether or not the flag F1 = 1 (catalyst high temperature), and if the flag F1 = 0 (catalyst normal temperature), the process proceeds to step 29.

In step 29, it is judged whether or not the flag F2 = 1 (rich). If the flag F2 = 0 (lean), it means that the rich-to-lean inversion is in effect, so in step 30, the air-fuel ratio feedback correction coefficient is determined. α is a predetermined proportional constant P _L
Increase by minutes. On the contrary, when the flag F2 = 1 (rich), the lean-> rich reversal is being performed, and therefore, in step 31, the air-fuel ratio feedback correction coefficient α is set to the predetermined proportional constant P _R.
Reduce by a minute.

As a result of the judgment in step 27, when non-inversion,
Go to step 32. In step 32, flag F1 = 1
It is determined whether or not (catalyst high temperature), and flag F1 = 0 (catalyst communication).
If the temperature is room temperature), go to step 33. In step 33,
It is determined whether or not the flag F2 = 1 (rich), and the flag F2
= 0 (lean), the air-fuel ratio feed in step 34
The back correction coefficient α is set to a predetermined integration constant I_LIncrease by minutes.
On the contrary, if the flag F2 = 1 (rich), in step 35
The air-fuel ratio feedback correction coefficient α is set to a predetermined integration constant I_R
Reduce by a minute. Incidentally, I _L<< P_L, I_R<< P_RIt is.

[Catalyst High Temperature; F1 = 1] Step 27
Then, it is determined whether or not the flag F2 is inverted, and when it is inverted (when rich / lean is inverted), the routine proceeds to step 28. In step 28, it is determined whether or not flag F1 = 1 (catalyst high temperature). If flag F1 = 1 (catalyst high temperature), step 28
Proceed to 36.

At step 36, the flag F3 is set to 1 to start the delay, and at step 37, the delay time measuring timer TM2 is cleared and the present routine is ended. After that, when the process proceeds to step 32 in the determination at step 27, it is determined at step 32 whether or not the flag F1 = 1 (catalyst high temperature). If the flag F1 = 1 (catalyst high temperature), the process proceeds to step 38.

In step 38, it is determined whether or not flag F3 = 1 (during delay), and flag F3 = 1 (during delay).
If so, the process proceeds to step 39 to count up the delay time measuring timer TM2. And step
At 40, it is determined whether or not the timer TM2 has reached the predetermined delay time T2, and if it is within the delay time T2, this routine is ended. During this delay, the air-fuel ratio feedback correction coefficient α is held.

When the delay time T2 elapses, the flag F3 is set to 0 in step 41 to cancel the delay. Then, the process proceeds from step 29 to step 30 or 31, and the proportional constant to the air-fuel ratio feedback correction coefficient α is added. Is added. After that, since F3 = 0 is determined in step 38, the process proceeds from step 33 to step 34 or 35, and the integral constant is added to the air-fuel ratio feedback correction coefficient α.

By such control, the air-fuel ratio feedback correction coefficient α when the catalyst temperature is high changes as shown in FIG. FIG. 5 is a flowchart of a fuel injection amount calculation routine, which is executed in time synchronization or rotation synchronization. In step 51, the basic fuel injection amount TP is calculated from the intake air flow rate Q detected by the air flow meter 16 and the engine speed N detected by the crank angle sensor 15 according to the following equation.
Is calculated.

TP = K · Q / N (K is a constant) In step 52, from the basic fuel injection amount TP, the air-fuel ratio feedback correction coefficient α, and the battery voltage-dependent voltage correction amount TS, according to the following equation, The fuel injection amount TI is calculated. TI = TP · α + TS When the fuel injection amount TI is calculated, a drive pulse signal having a pulse width of TI is output to the fuel injection valve 7 of the injection cylinder at a predetermined timing synchronized with the engine rotation, and fuel injection is performed. Be seen.

Thus, when the manifold catalyst 11 is at a high temperature,
By delaying the proportional control after reversing the air-fuel ratio rich / lean and increasing the perturbation of the air-fuel ratio at the inlet of the manifold catalyst 11, the conversion rate of the manifold catalyst 11 is reduced,
The temperature rise of the manifold catalyst 11 due to the heat of reaction is prevented. Even in this case, since the control center of the air-fuel ratio is stoichiometric, the air-fuel ratio at the inlet of the underfloor catalyst 13 is also balanced by the manifold catalyst 11, and the amplitude of the air-fuel ratio does not become excessive. Since it is controlled near the stoichiki, the deterioration of emission can be suppressed.

In this embodiment, the upstream O ₂ sensor 19
Corresponds to the air-fuel ratio detecting means. Further, the routine of FIG. 4 and the routine of FIG. 5 correspond to the air-fuel ratio feedback control means, and particularly the steps 29 to 31 of FIG. 4 are proportional control means,
The steps 33 to 35 in FIG. 4 correspond to the integral control means, and the step 52 in FIG. 5 corresponds to the fuel supply amount correcting means. Further, the routine of FIG. 3 corresponds to the catalyst temperature detecting means. Further, steps 28, 32, 36 to 37, 38 to 41 in FIG. 4 correspond to the response lowering means (proportional control delay means). Further, the step 14 in FIG. 3 corresponds to the response lowering degree varying means.

Next, another embodiment of the present invention will be described. In this embodiment, the flow chart of FIG. 10 is executed in place of the flow chart of FIG. 4 of the above-mentioned embodiment, and in the above-mentioned embodiment, the air-fuel ratio feedback correction coefficient α is held during the delay of the proportional control. In contrast,
During the delay, the air-fuel ratio feedback correction coefficient α is integrated and controlled in the same direction as before the inversion.

Therefore, in this embodiment, during the delay, that is, after executing step 37 or step 40, the routine directly proceeds to step 42 without terminating the routine.
In step 42, it is determined whether or not the flag F2 = 1 (rich). If the flag F2 = 0 (lean), the process proceeds to step 35 to further control to the lean side in the same direction as before the reversal, and the air-fuel ratio is advanced. The feedback correction coefficient α is set to a predetermined integration constant I
Reduce by _R. When the flag F2 = 1 (rich),
In order to further control to the rich side in the same direction as before the reversal, the routine proceeds to step 34, where the air-fuel ratio feedback correction coefficient α is increased by the predetermined integration constant I _L.

By such control, the air-fuel ratio feedback correction coefficient α when the catalyst temperature is high changes as shown in FIG. In this way, during the delay, by performing the integral control in the same direction as before the reversal, it is possible to further increase the perturbation of the air-fuel ratio. However, an upper limit and a lower limit are set for the air-fuel ratio feedback correction coefficient α so that the amplitude of the air-fuel ratio does not become excessively large.

Therefore, step 43 is provided after the steps 30, 31, 34 and 35 so that the limiter processing of α is performed. Specifically, as shown in the subroutine in FIG. 11, in step 101, the air-fuel ratio feedback correction coefficient α is compared with the upper limit value αmax, and if α> αmax, the step
At 102, limit to α = αmax. Further, in step 103, the air-fuel ratio feedback correction coefficient α is compared with the lower limit value αmin, and if α <αmin, in step 104 it is limited to α = αmin.

Next, still another embodiment of the present invention will be described. In this example, the mani catalyst 11
The air-fuel ratio feedback control is performed by the upstream O ₂ sensor 19, and when the catalyst temperature is high, the air-fuel ratio feedback control is performed by the O ₂ sensor 20 downstream of the manifold catalyst 11 (upstream of the underfloor catalyst 13).

Specifically, the flowchart of FIG. 13 is executed instead of the flowchart of FIG. 4 of the above-described embodiment.
The flowchart of FIG. 3 may be basically the same, but the processes of steps 12 and 14 are unnecessary. FIG. 13 is a flowchart of the air-fuel ratio feedback control routine, which is executed in time synchronization.

In step 61, it is judged whether or not it is the air-fuel ratio feedback (F / B) control condition. If it is not the control condition, in step 62 the air-fuel ratio feedback correction coefficient α
Is clamped to 1.0 and this routine ends. In step 63, it is determined whether or not flag F1 = 1 (catalyst high temperature). If flag F1 = 0 (catalyst normal temperature), step 64
If the flag F1 = 1 (catalyst high temperature), go to step 68.

In the case of the catalyst normal temperature, in step 64, the signal OS1 of the upstream O ₂ sensor 19 is read, and in step 65,
The signal OS1 is compared with a predetermined slice level SL1. If OS1 ≦ SL1, it is determined in step 66 that F2 = 0 (lean), and if OS1> SL1, it is determined in step 67 that F2 = 1 (rich). To do. If the catalyst temperature is high, the signal OS2 of the downstream O ₂ sensor 20 is read in step 68, the signal OS2 is compared with a predetermined slice level SL2 in step 69, and when OS2 ≦ SL2, in step 70 F2 = It is determined to be 0 (lean), and when OS2> SL2, it is determined in step 71 that F2 = 1 (rich).

After this, the routine proceeds to step 72, where it is judged whether or not the flag F2 is inverted, and when it is inverted (when rich / lean is inverted), it proceeds to step 73. In step 73,
It is determined whether or not the flag F2 = 1 (rich), and the flag F2
If = 0 (lean), it means that the rich-to-lean reversal is being performed. Therefore, at step 74, the air-fuel ratio feedback correction coefficient α
Is increased by a predetermined proportional constant P _L. Conversely, flag F2 =
In the case of 1 (rich), since lean-> rich is being reversed, the air-fuel ratio feedback correction coefficient α is decreased by a predetermined proportional constant P _R in step 75.

When it is determined in step 72 that there is no reversal, step
Proceed to 76. In step 76, flag F2 = 1 (rich)
It is determined whether or not, and if the flag F2 = 0 (lean),
In step 77, the air-fuel ratio feedback correction coefficient α is increased by the predetermined integration constant I _L. On the contrary, when the flag F2 = 1 (rich), the air-fuel ratio feedback correction coefficient α is decreased by a predetermined integration constant I _R in step 78.

After this, the routine proceeds to step 79, where the limiter processing of the air-fuel ratio feedback correction coefficient α is performed according to the subroutine shown in FIG. Thus, when the manifold catalyst 11 is at the normal temperature, the O ₂ sensor 19 upstream of the manifold catalyst 11
More air-fuel ratio feedback control is performed, but when the manifold catalyst 11 is at a high temperature, the O of the downstream of the manifold catalyst 11 (upstream of the underfloor catalyst 13)
By performing the air-fuel ratio feedback control by the ₂ sensor 20, by increasing the perturbation of the air-fuel ratio at the inlet of the manifold catalyst 11, while suppressing the deterioration of emissions,
It is possible to prevent the temperature of the manifold catalyst 11 from rising.

In this embodiment, the upstream O ₂ sensor 19
Corresponds to the first air-fuel ratio detecting means, and the downstream O ₂ sensor 20
Corresponds to the second air-fuel ratio detecting means. Further, the routine of FIG. 3 corresponds to the catalyst temperature detecting means. Further, steps 64 to 67 and steps 72 to 78 of the routine of FIG. 13 correspond to the first air-fuel ratio feedback control means, and steps 63, 68 to 71 and steps 72 to 78 of the routine of FIG. Second
Corresponds to the air-fuel ratio feedback control means.

[0049]

As described above, according to the invention of claim 1, when the upstream side catalyst is at a high temperature, the response of the air-fuel ratio control to the detected air-fuel ratio is irrespective of whether the detected air-fuel ratio is rich or lean. By lowering the property and increasing the perturbation of the air-fuel ratio at the inlet of the upstream catalyst, it is possible to prevent the burning and deterioration of the upstream catalyst without deteriorating the emission.

According to the second aspect of the present invention, by delaying the proportional control of the air-fuel ratio feedback correction coefficient, it is possible to easily achieve the effect. According to the invention of claim 3, by holding the air-fuel ratio feedback correction coefficient while delaying the proportional control, it is possible to further utilize the effect of the delay of the proportional control.

According to the fourth aspect of the present invention, while the proportional control is delayed, the integral control is continued in the same direction as before the inversion, so that the perturbation can be further increased. According to the fifth aspect of the invention, by varying the degree of decrease in responsiveness according to the exhaust gas flow rate, it is possible to obtain the effect of being able to respond to changes in the characteristics of the catalyst.

According to the sixth aspect of the invention, when the upstream side catalyst is at a normal temperature, air-fuel ratio feedback control is performed based on the exhaust gas composition upstream of the upstream side catalyst, while when the upstream side catalyst is at a high temperature, the upstream side catalyst is upstream. By performing air-fuel ratio feedback control based on the exhaust composition of the downstream side catalyst, the perturbation of the air-fuel ratio at the upstream side catalyst inlet is increased, thereby suppressing the deterioration of emissions and burning the upstream side catalyst. The effect of preventing deterioration can be obtained.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of the present invention.

FIG. 2 is a system diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart of a catalyst temperature determination routine.

FIG. 4 is a flowchart of an air-fuel ratio feedback control routine.

FIG. 5 is a flowchart of a fuel injection amount calculation routine.

[Fig. 6] Characteristic diagram of warm-up time

FIG. 7: Characteristic diagram of steady-state catalyst temperature

FIG. 8 is a characteristic diagram of delay time.

FIG. 9 is a diagram showing how the air-fuel ratio feedback correction coefficient changes.

FIG. 10 is a flowchart of an air-fuel ratio feedback control routine showing another embodiment of the present invention.

FIG. 11 is a flowchart of a subroutine for α limiter processing.

FIG. 12 is a diagram showing how the air-fuel ratio feedback correction coefficient changes.

FIG. 13 is a flowchart of an air-fuel ratio feedback control routine showing still another embodiment of the present invention.

[Explanation of symbols]

1 Internal Combustion Engine 7 Fuel Injection Valve 10 Exhaust Manifold 11 Upstream Catalyst (Mani Catalyst) 12 Exhaust Duct 13 Downstream Catalyst (Underfloor Catalyst) 14 Control Unit 15 Crank Angle Sensor 16 Air Flow Meter 18 Water Temperature Sensor 19 Upstream O ₂ Sensor 20 Downstream Side O ₂ sensor

Claims (6)

[Claims] 1. An engine exhaust passage is provided with an upstream side catalyst and a downstream side catalyst for purifying exhaust gas, and an air-fuel ratio detecting means for detecting an air-fuel ratio based on an exhaust gas composition upstream of the upstream side catalyst and a theoretical detected air-fuel ratio. In an air-fuel ratio control device for an internal combustion engine, which comprises an air-fuel ratio feedback control means for feedback-controlling the amount of fuel supplied to the engine so as to obtain an air-fuel ratio, catalyst temperature detection means for detecting the temperature of the upstream side catalyst, and When the catalyst temperature is equal to or higher than a predetermined value, responsiveness lowering means for lowering the responsiveness of the air-fuel ratio control to the detected air-fuel ratio in the air-fuel ratio feedback control means is provided regardless of whether the detected air-fuel ratio is rich or lean. An air-fuel ratio control device for an internal combustion engine, characterized in that 2. The air-fuel ratio feedback control means adjusts the air-fuel ratio feedback correction coefficient by a predetermined proportional constant when lean-rich of the detected air-fuel ratio is reversed, and proportional control means for adjusting the lean-rich of the detected air-fuel ratio. And an air-fuel ratio feedback correction coefficient for increasing or decreasing the air-fuel ratio feedback correction coefficient by a predetermined integration constant, and a fuel supply amount correction means for correcting the fuel supply amount by the air-fuel ratio feedback correction coefficient. The property reducing means is a proportional control delay means for delaying an increase / decrease in the proportional amount of the air-fuel ratio feedback correction coefficient in the proportional control means.
An air-fuel ratio control device for an internal combustion engine according to the above. 3. The responsiveness lowering means suspends the integral control means while delaying the increase / decrease of the proportional proportion constant of the air-fuel ratio feedback correction coefficient in the proportional control means, so as to adjust the air-fuel ratio feedback correction coefficient. The air-fuel ratio control device for an internal combustion engine according to claim 2, which holds the air-fuel ratio. 4. The responsiveness lowering means detects the air-fuel ratio feedback correction coefficient by the integral control means while delaying the increase / decrease of the proportional constant of the air-fuel ratio feedback correction coefficient in the proportional control means. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein the air-fuel ratio control device increases or decreases in the same direction as before the reversal. 5. The responsiveness decrease degree varying means for varying the degree of responsiveness decrease by the responsiveness decreasing means according to the exhaust gas flow rate is provided. An air-fuel ratio control device for an internal combustion engine as set forth in. 6. An engine exhaust passage is provided with an upstream side catalyst and a downstream side catalyst for exhaust gas purification, and first air-fuel ratio detecting means for detecting an air-fuel ratio based on the exhaust gas composition upstream of the upstream side catalyst.
An air-fuel ratio control device for an internal combustion engine, comprising: a first air-fuel ratio feedback control means for feedback-controlling a fuel supply amount to an engine so that a detected air-fuel ratio becomes a stoichiometric air-fuel ratio. A second air-fuel ratio detecting means for detecting the air-fuel ratio based on the above is provided, while a catalyst temperature detecting means for detecting the temperature of the upstream side catalyst and a first catalyst when the detected catalyst temperature is equal to or higher than a predetermined value. Instead of the air-fuel ratio feedback control means, second air-fuel ratio feedback control means for feedback-controlling the fuel supply amount to the engine so that the air-fuel ratio detected by the second air-fuel ratio detection means becomes the stoichiometric air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, comprising: