JPS63195350A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the variation of air-fuel ratio at the upper stream of a catalyst by furnishing the first and the second O2 sensors, increasing the control constant as the rich continuing time and the lean continuing time of the second O2 sensor are made longer, and carrying out the feedback control by the constant and the detected value of the first O2 sensor. CONSTITUTION:A control circuit 10 computes a basic fuel injection quantity depending on the rotation frequencies from crank angle sensors 5 and 6 and the air intake amount from an air flow meter 3, and carrys out the feed back control of air-fuel ratio depending on the detected values of the first O2 sensor 13 and the second O2 sensor 15 which are furnished at the upper stream and at the lower stream of a catalyst converter 12 respectively. That is, the rich continuing time and the lean continuing time of the second O2 sensor 15 are measured, the skip amount and the integral constant are renewed larger as the said measurement is made larger, and the air-fuel ratio correction amount is computed from the output of the first O2 sensor 13, the renewed skip amount, and the renewed integral constant.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (OX sensors)) on the upstream and downstream sides of a catalytic converter.
0.0 on the upstream side. The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream Ot sensor in addition to air-fuel ratio feedback control using a sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single 0□ sensor system), the 0□ sensor that detects oxygen concentration is installed in the exhaust system as close to the combustion chamber as possible, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter. , variations in the output characteristics of the Ot sensor pose a problem in improving the control accuracy of the air-fuel ratio. It takes 02
In order to compensate for variations in sensor output characteristics, variations in components such as fuel injection valves, and changes over time or aging, a second Ot sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream AT sensor is performed. In addition, Double 0! performs air-fuel ratio feedback control using the downstream 02 sensor! Sensor systems have already been proposed (
Reference: Japanese Patent Application Laid-Open No. 58-48756). This double 0
In a two-sensor system, the 02 sensor installed downstream of the catalytic converter has a lower response speed than the upstream Ot sensor, but has the advantage of less variation in output characteristics for the following reasons. There is.

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

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream zero 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 an equilibrium state.

Therefore, as described above, by air-fuel ratio feedback control (double 02 sensor system) based on the outputs of the two 02 sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream Ot sensor. In fact, as shown in Figure 2, Shin.

In the double 02 sensor system, if the 02 sensor output characteristics deteriorate, it directly affects the exhaust emission characteristics, whereas in the double 02 sensor system, if the 02 sensor output characteristics deteriorate, the upstream 02
Even if the output characteristics of the sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, double 0. In the sensor system, good exhaust emissions are guaranteed as long as the downstream sensor maintains stable output characteristics.

[Problem that the invention seeks to solve]

However, double 0! Since the downstream Ot sensor in the sensor system is located downstream of the catalytic converter, it generates rich and lean outputs with a certain time delay. In other words, 0.0 of the catalytic converter (three-way catalyst). The output of the downstream Ot sensor is delayed due to the storage effect. Therefore, when the output of the downstream Ot sensor changes from lean to rich, the air-fuel ratio upstream of the catalytic converter has already shifted richer than the stoichiometric air-fuel ratio, and as a result, C
This causes deterioration of IC emissions, deterioration of fuel efficiency, and increase in catalyst exhaust odor. When the sensor output changes from rich to lean, the air-fuel ratio upstream of the catalytic converter has already deviated significantly from the stoichiometric air-fuel ratio to the lean side, resulting in worsening of NOx emissions, suffocation, sluggishness, surges, lack of power, etc. There is a problem in that the drivability of the vehicle is deteriorated.

Therefore, an object of the present invention is to substantially increase the response speed of the downstream air-fuel ratio sensor (Ox sensor) to reduce CO
, IIC, deterioration of NOx emissions, deterioration of fuel efficiency, increase in catalyst exhaust odor, deterioration of drivability, etc.

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG. In FIG. 1, first and second air-fuel ratio sensors for detecting the concentration of specific components in exhaust gas are provided on the upstream side of a catalytic converter for exhaust gas purification, which are provided in the exhaust system of an internal combustion engine;
Each is provided on the downstream side. The comparison means compares the output v2 of the downstream (second) air-fuel ratio sensor with a reference value ■□
The duration calculation means calculates the rich m duration TRN or the lean duration TLN of the comparison result of the comparison means. The update speed calculation means updates air-fuel ratio feedback control constants such as rich skip amount RSR and lean skip IR according to the calculated rich duration time TRH or lean duration time TLN.
3L update rate ΔRS is calculated. As a result, the air-fuel ratio feedback control constants R5R and R5L are updated using the update rate ΔRS calculated according to the comparison result of the comparison means. As a result, the air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to the air-fuel ratio feedback control constants RSR, R5L and the output V of the upstream (first) air-fuel ratio sensor. The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[For production]

According to the above means, the update rate of the air-fuel ratio feedback control constant increases as the output of the downstream air-fuel ratio sensor continues to be rich or lean, and the controlled air-fuel ratio quickly approaches the stoichiometric air-fuel ratio. become.

〔Example〕

FIG. 3 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. 3, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is supplied to the MA/D converter 101 in the multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720° in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30' in terms of crank angle. A crank angle sensor 6 is provided. 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 10.
3 interrupt 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 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components IC, GO, and NOx in exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
A first Ot sensor 13 is provided on the upstream side of the catalytic converter 12, and a second Ot sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12.

0, sensors 13 and 15 generate electrical signals according to the concentration of oxygen components in the exhaust gas. That is, 0□ sensor 13
, 15, the control circuit 10 outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
This occurs in the D converter 101.

The control circuit IO is configured as a microcomputer, for example, and includes an A/D converter 1011, an output interface 102, a ROM 104, a CPU 103, and a ROM 104:R.
An AM 105, a bank-up RAM 106, a clock generation circuit 107, and the like are provided.

Further, in the control circuit 10, a down counter lO8,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection ITAU becomes the down counter 1.
08 and 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 the clock signal (not shown) and finally its carrier terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 controls the fuel injection valve 7. Stop biasing. In other words, the above fuel injection amount TA
The fuel injection valve 7 is energized by U, and therefore the fuel injection amount T
An amount of fuel corresponding to the AU is sent to the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 1103 is caused by the A/D converter 1.
At the end of A/D conversion of 01, input/output interface 10
2 receives a pulse signal from the crank angle sensor 6, receives an interrupt signal from the clock generation circuit 107, etc.

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

FIG. 4 shows a first air-fuel ratio feedbank control routine that calculates an air-fuel ratio correction coefficient FAF based on the output of the upstream 02 sensor 13, and is performed for a predetermined period of time, for example, 4+am.
executed every time.

In step 401, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream Ot sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, e.g., 60°C, when the engine is starting, during the increase after starting, during warm-up, during increase in power, or when the output signal of the upstream 0□ sensor 13 has never been inverted. , fuel cut, etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If the closed loop condition is not satisfied, the process proceeds to step 427 and the air-fuel ratio correction coefficient FAF is set to 1.0. In this case, FAF may be a value immediately before the end of closed loop control or a learned value (value in backup RAM). On the other hand, if the closed loop condition is satisfied, the process proceeds to step 402.

In step 402, the output v1 of the upstream 02 sensor 13 is
is A/D converted and taken in, and in step 403 it is determined whether or not V is less than the comparison voltage V□, for example, 0.45V.
In other words, it determines whether the air-fuel ratio is rich or lean. In other words, if the air-fuel ratio is rich or lean (■1≦V),
In step 404, it is determined whether the delay counter CDLY is positive or not. If CDLY>0, in step 405, CDLY is set to 0, and the process proceeds to step 406. Step 4
In step 06, the delay counter CDLY is incremented by 1m, and in steps 407 and 408, the delay counter CDLY is guarded with the minimum value TDL.

In this case, when the delay counter CDLY reaches the minimum value TDL, the first air-fuel ratio flag F1 is set to "θ" (lean) in step 409.
L is a lean delay time for maintaining the determination that the fuel is in a rich state even if there is a change from rich to lean in the output of the upstream 01 sensor 13, and is defined as a negative value. On the other hand, if it is rich (V+ >Van), it is determined in step 410 whether the delay counter CDLY is negative or not, and if CDLY <0, it is determined in step 411 that the delay counter CDLY is negative or not.
Set DLY to 0 and proceed to step 412. Step 41
In step 2, the delay counter CDLY is incremented by 1, and in steps 413 and 414, the delay counter CDLY is guarded at the maximum value TDR.

In this case, when the delay counter CDLY reaches the maximum value TDR, the first air-fuel ratio flag F1 is set to l'' (rich) in step 415.
is upstream side O! This is a lean delay time for maintaining the determination that the lean state is present even if the output of the sensor 13 changes from lean to rich, and is defined as a positive value.

In step 416, it is determined whether the sign of the first air-fuel ratio flag F1 has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, in step 417, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the first air-fuel ratio flag F1. If it is a reversal from rich to lean, at step 418 PAP←FAF +R5R
On the contrary, if it is a reversal from lean to rich, FAF 4-FAF is increased in step 419.
- Decrease RSL and skip. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 412, integration processing is performed in steps 420, 421, and 422. That is, in step 420, Fl
- Determine whether or not it is “0”, and if F1 = “0” (lean), set FAF-pAP +KIR in step 421, and if F1 = “1” (rich), step 6
22, FAF 4-FAF +KIL. Here, the integral constants KIR and KIL are the skip constants RSR and RS
It is set sufficiently small compared to L, that is, KIR(
IL)<RSR(R5L). Therefore, step 421 gradually increases the fuel injection amount in a lean state (F1="0"), and step 422 gradually increases the fuel injection amount in a rich state (F1="0").
'1'') gradually decreases the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 418, 419, 421, and 422 is guarded at a minimum value such as 0.8 in steps 423 and 424, and is guarded at a maximum value such as 1.2 in steps 425 and 426. will be guarded. As a result, for some reason, the air-fuel ratio correction coefficient FA
If F becomes too large (or too small), the engine's air-fuel ratio is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 428.

FIG. 5 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 4. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 02 sensor 13 as shown in FIG. 5(A), the delay counter CD
As shown in FIG. 5 (I3), LY is counted up in the rich state and counted down in the lean state. As a result, as shown in FIG. 5(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, time 1. Even if the air-fuel ratio signal A/F changes from lean to rich, the delayed air-fuel ratio signal A
/F' is maintained lean for the rich delay time TDR and then changes to rich at time 1t.Even if the air-fuel ratio signal A/F changes from rich to lean at time 0 t, the delayed air The fuel ratio signal A/F' is determined by the lean delay time (-
After being held rich by an amount equivalent to TDL), it changes to lean at time t4. However, the air-fuel ratio signal A/F at time t
% +th, t', rich delay time TDR
If it reverses in a shorter period, the delay counter CDLY
It takes time for TDR to reach the maximum value, and as a result,
At time t, the air-fuel ratio signal A/F' after the delay process is inverted. In other words, the air-fuel ratio signal A/F' after the delay process is more stable than the air-fuel ratio signal A/F before the delay process. In this manner, the air-fuel ratio correction coefficient FAF shown in FIG. 5(D) is obtained based on the stable air-fuel ratio signal A/F' after the delay processing.

Next, the second air-fuel ratio feedback control by the downstream sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts R5R and RSL as the first air-fuel ratio feedback control constants, and an integral constant K.
IR, KIL, delay time 'I'OR, TDL.

Or the output of the upstream Ot sensor 13 ■Comparison voltage of 1■
A system that makes □ variable and a second air-fuel ratio correction coefficient FA
There is a system that introduces F2.

For example, if you increase Rich Skip 1iR3R,
The control air-fuel ratio can be shifted to the rich side, and even if the lean skip 1iRsL is decreased, the control air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount R3L is increased, the control air-fuel ratio can be shifted to the lean side, Further, even if the rich skip amount R3R is reduced, the control air-fuel ratio can be shifted to the lean side.

Therefore, the air-fuel ratio can be controlled by correcting the rich skip IRsR and the lean skip amount R3L according to the output of the downstream Ot sensor 15.

In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
On the other hand, increasing the lean integral constant KIL allows the controlled air-fuel ratio to be shifted to the lean side, and even if the rich integral constant KIR is decreased, the controlled air-fuel ratio cannot be shifted to the rich side. You can move to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIR and the lean integral constant KIL according to the output of the downstream 0□ sensor 15. If rich delay time TDR>lean delay time (-TDL) is set, the control air-fuel ratio can be shifted to the rich side, and conversely, lean delay time (-TDL)>>
By setting the rich delay time (TDR), the controlled air-fuel ratio can be shifted to the lean side.

That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream 0□ sensor 15. Furthermore, by increasing the comparison voltage Vllll, the control air-fuel ratio can be shifted to the rich side, and by decreasing the comparison voltage V□, the control air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage v1 according to the output of the downstream 0□ sensor 15, the air-fuel ratio can be controlled.

Referring to FIG. 6, the double 0.0. The sensor system will be explained.

FIG. 6 shows a second air-fuel ratio feedback control routine that calculates skip 1iRSR and RSL based on the output of the downstream Ot sensor 15.
executed every time. In step 601, downstream O! It is determined whether the sensor 15 is in a closed loop condition. For example, when the cooling water temperature is below a predetermined value, for example 70°C, the downstream side
．． The closed loop condition is not satisfied when the output signal of the sensor 15 never inverts, when the downstream Oz sensor 15 is out of order, during transient operation, on-idle (LL = “l”), etc. The closed loop condition is satisfied when . If it is not a closed loop condition, proceed to steps 617 and 618 1. The skip amounts R3R and RSL are set to a constant value RSRO.

Let it be R3Lo. For example, +11SR, ) = 5% RSL, = 5%. In this case as well, RSR and RSL are set to values immediately before the end of closed loop control or learned values (backup RAM
value).

If it is a closed loop, the process proceeds to step 602 and the downstream Ot
Output V of sensor 15! is A/D converted and imported, and in step 603, Vt≦vlI! (lean) or not. Note that the comparison voltage V□ is, for example, 0.55V. As a result, if V z ≦V ax (lean), the process proceeds to steps 604 to 614, and on the other hand, if v2>vo (rich), the process proceeds to steps 615 to 625.

In step 604, the second air-fuel ratio flag F2 is set to "O".
(lean) or not. As a result, F2="1
'' (rich), it means that the output v2 of the downstream Ot sensor 15 has reversed from rich to lean, so in step 606, the lean w1vt counter TLN is
is cleared, and the second air-fuel ratio flag F is cleared in step 607.
2 to "0" and proceed to step 608. Therefore, from now on, if the output vt of the downstream Ot sensor 15 maintains the lean output, the flow in step 604 is changed to step 60.
The process proceeds to step 5, where the lean continuation counter TLN is counted up, and the process proceeds to step 608.

In step 608, an update amount ΔR5 of the skip amounts RSR and RSL is calculated using a one-dimensional map stored in the ROM 104 based on the value of the lean continuation counter TLN.

Therefore, as shown in the block of step 608, the larger the lean continuation counter TLN, the more the update amount Δ
RS is calculated to be large. In steps 609 to 614, the skip amounts R3R and RSL are updated using the update amount ΔRS obtained in this manner.

That is, in step 609, RSR4-R5R+Δ
R3, that is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side. Step 610.6
In No. 11, the RSR is guarded at the maximum value MAX, for example, 7.5%. Furthermore, in step 612, R3L←RSL
-ΔRS, that is, the lean skip amount R3L is decreased to shift the air-fuel ratio to the rich side. Step 613
．． 614, set the RSL to the minimum value MIN, for example 2.5%.
Guard at.

Similarly, in step 615, the second air-fuel ratio flag F2
It is determined whether or not is “1” (rich). As a result, F
If 2 = “0” (lean), downstream side 0: sensor 1
Since the output Vt of 5 means that the lean state has been reversed to the rich state, the rich continuation counter TRH is cleared in step 617', and the second air-fuel ratio flag F2 is inverted to "l" in step 618. Proceed to step 619.

Therefore, from now on, downstream side 0. If the output 8 of the sensor 15 maintains the rich output, the flow at step 615 advances to step 616, where the rich continuation counter TRH is counted up, and the flow advances to step 619.

In step 619, the update amount ΔR5 of the skip amounts R3R and RSL is calculated using the one-dimensional map stored in the ROM 104 based on the value of the rich continuation counter TRH.

Here, as in step 608, as shown in the block of step 619, the rich 41 consecutive counter TR
The larger H becomes, the larger the update amount ΔR3 is calculated.

In steps 620 to 625, the skips 11R5R and RSL are updated using the update amount ΔR3 obtained in this way. That is, in step 620, RSR4-R
SR-ΔR5, that is, the rich skip amount R3R is decreased to shift the air-fuel ratio to the lean side. Step 6
In No. 21 and 622, the RSR is guarded at the minimum value MIN. Furthermore, in step 623, RSL←R3L−ΔR
In other words, the lean skip amount R3L is increased to shift the air-fuel ratio to the lean side. Step 624, 6
In No. 25, RSL is guarded at the minimum value MAX.

I? calculated as above? Sl? , ! ? SL is R1
After being stored in 1MLO5, the routine ends at step 628.

Note that RAF calculated during air-fuel ratio feedback,
Convert RSR and RSL to other values and bank up R.
These values can also be stored in the AM106, and can be used during air-fuel ratio oven loop control to improve drivability, for example, at restart, immediately after startup, or when the sensor is inactive. It's useful. The minimum value MIN in FIG. 6 is a value at which transient followability is not impaired, and the maximum value MIN is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In this way, when the update amount ΔRS of skip 1RsR and RSL is changed according to the rich or lean duration time TRH or TLN of the output v8 of the downstream O2 sensor 15, the control air-fuel ratio quickly moves toward the stoichiometric air-fuel ratio. become. Therefore, it is useful for reducing CD, IIC, NOx emissions, etc.

FIG. 7A shows a modification example of FIG. 6, and step 6 of FIG.
08, steps 701 to 703 are provided. That is, in step 701, intake air amount data Q is read out from the RAM 106, and it is determined whether Q>Qo (C high load). If high load state B (Q>Qo),
The process proceeds to step 702, and if the load condition 11i is low (Q≦Qo), the process proceeds to step 703. Step 702.703
Now, let's talk about RO based on Lean Continuation Counter TLN.
The reskip amount R is determined by the one-dimensional map stored in M104.
The update amount ΔR5 of SR and RSL is calculated, but when the load is high (
Q>Q,) The update amount ΔR3 is set to be larger than the update amount ΔR5 at the time of low load (Q≦QO).

As a result, the controlled air-fuel ratio largely shifts to the rich side.

Note that in step 702, dotted lines may be used instead of solid lines.

FIG. 7B also shows a modification of FIG. 6, in which steps 701' to 703' are provided in place of step 619 in FIG. That is, in step 701', RAM1
The intake air amount data Q is read from 06, and it is determined whether Q>Qo (high load). If it is a high load state (Q>Q,), the process proceeds to step 702' and a low load state a (Q≦Q,
), the process advances to step 703'. Step 702
', 703', both rich continuation counter TR
The update amount ΔRS of skip 1iR5R, RSL is calculated using the one-dimensional map stored in the ROM 104 based on H, but the update amount ΔRS during low load (Q≦Q,) is the same as the update amount ΔRS during high load (Q>Q, ). The amount is set to be larger than the amount ΔR5. As a result, the controlled air-fuel ratio largely shifts to the lean side. Note that in step 703', dotted lines may be used instead of solid lines.

In this way, the modified example in Fig. 7A allows the
By controlling the air-fuel ratio to the rich side, it is possible to prevent deterioration of drivability such as deterioration of NOx emissions, heavy breathing, sluggishness, surge, and lack of power. In addition, by setting the control air-fuel ratio to the lean side during low load (Q≦Q) according to the modification shown in FIG. 7B, it is possible to particularly reduce catalyst exhaust odor.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360°C. step 80
1, the basic injection amount TAUP is calculated by reading the intake air amount data Q and the rotational speed data Ne from the RAM 105. For example, assume that TAUP←α·Q/Ne (α is a constant). In step 802, the cooling water temperature data THW is read from the RAM 105, and a warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the ROM 104. In step 803, the final injection amount TAU is set as TAU - TAI
JP-FAF・(FIL+β+1)
Calculate by +r. Note that β and T are correction amounts determined by other operating state parameters. Next, in step 804, the injection 11 TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. The routine then ends at step 805. In addition, as mentioned above, the injection amount T
When the time corresponding to AU has passed, the down counter 10
The flip-flop 109 is activated by the carrier signal of 8.
is reset and fuel injection ends.

Also, the first air-fuel ratio feedback control is performed every 4 m, and the second air-fuel ratio feedback control is performed every 1 s, which is why the air-fuel ratio feedback control is performed on the upstream side 0! Mainly controlled by sensors, downstream 0. This is because control by the sensor is performed in a secondary manner.

Furthermore, a double 02 sensor system that corrects other control constants, such as delay time, integral constant, etc. in the air-fuel ratio feedback control by the upstream oxygen sensor, by the output of the downstream oxygen sensor, also has a second air-fuel ratio control constant. The invention can also be applied to double 0□ sensor systems that introduce correction factors. Furthermore, controllability can be improved by simultaneously controlling two of the skip amount, delay time, and integral constant. Furthermore, it is also possible to fix one of the skip amounts RSR and R5L and make only the other variable, and the delay time TDR,
It is also possible to fix one of TDL and make only the other variable, or to set the rich integral constant KIR, lean integral constant K
It is also possible to have one of the ILs fixed and the other variable.

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

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

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a capretor type internal combustion engine. For example, Electric Air Control Pulp (f!ACV)
The electric bleed air control valve adjusts the air bleed amount of the carburetor and introduces atmospheric air into the main system passage and slow system passage to control the air fuel ratio. The present invention can be applied to things such as those that control the exhaust system of an engine, and those that adjust the amount of secondary air sent into the exhaust system of an engine. In this case, the basic injection amount TAIJP in step 801
A corresponding basic fuel injection amount is determined by the carburetor itself, that is, depending on the intake pipe negative pressure depending on the intake air amount and the rotational speed of the engine, and in step 803, the supply air corresponding to the final fuel injection amount TAU is determined. The quantity is calculated.

Further, in the above embodiment, an Ox sensor is used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, etc. may also be used.

Furthermore, although the embodiments described above are constructed using a microcomputer, that is, a digital circuit, they may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, the response speed of the downstream air-fuel ratio sensor can be substantially increased.
It can prevent large deviations in the air-fuel ratio upstream of the catalytic converter, thus reducing emissions, fuel efficiency, and
It is possible to prevent an increase in catalyst exhaust odor, deterioration of drivability, etc.

[Brief explanation of the drawing]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 01 sensor system and a double 0□
Fig. 3 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention; Fig. 4, Fig. 6, Fig. 7A, and Fig. 7B. , FIG. 8 is a flowchart for explaining the operation of the control circuit of FIG. 3, and FIG. 5 is a timing diagram for supplementary explanation of the flowchart of FIG. 4. DESCRIPTION OF SYMBOLS 1... Engine body, 3... Air flow meter, 4... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter,
13...Upstream side (first) 0□ sensor, 15...Downstream side (second) 0□ sensor.

Claims (1)

[Scope of Claims] 1. A first catalytic converter installed on the upstream side and downstream side of a catalytic converter for purifying exhaust gas provided in the exhaust system of an internal combustion engine, and configured to detect the concentration of a specific component in the exhaust gas. a second air-fuel ratio sensor; a comparison means for comparing the output of the second air-fuel ratio sensor with a comparison reference value to determine whether it is rich or lean; and a rich duration time or a lean duration time as a comparison result of the comparison means. a duration calculation means for calculating; an update rate calculation means for calculating an update rate of the air-fuel ratio feedback control constant to increase as the calculated rich duration time or lean duration time increases; control constant updating means for updating an air-fuel ratio feedback control constant based on the calculated update rate; and air-fuel ratio correction for calculating an air-fuel ratio correction amount according to the output of the first air-fuel ratio sensor and the air-fuel ratio feedback control constant. An air-fuel ratio control device for an internal combustion engine, comprising: an 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. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the update rate is changed according to a load parameter of the engine.