JPS63219847A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To accurately control an air fuel ratio to a target value by changing a control constant on the basis of the detected data from a linear output type O2 sensor disposed in the lower side of a catalyst, and calculating a feedback compensative quantity on the basis of the result from the comparison between the output from a Z output type O2 sensor disposed in the upper side of the catalyst and a reference value corresponding to a theory air fuel ratio. CONSTITUTION:A control circuit 10 receives the detected data from an air flow meter 3, crank angle sensors 5 and 6, a water temperature sensor 9, a Z output type O2 sensor 13 disposed in the upper side of a catalyst converter 12, a linear output type O2 sensor in the lower side thereof, and so on. The control circuit 10 compares the output of the Z output type O2 sensor with the reference value corresponding to the theory air fuel ratio, and calculates the air fuel ratio feedback compensative quantity on the bases of both the comparison result and a control constant set from the comparison of the output of the linear output type O2 sensor 15 with the reference value corresponding to the air fuel ratio depending on operational condition.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides air-fuel ratio sensors (herein, oxygen concentration sensors (02 sensors)) on the upstream and downstream sides of a catalytic converter.
), and relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control using a downstream 02 sensor in addition to air-fuel ratio feedback control using an upstream 02 sensor.

[Conventional technology]

In simple air-fuel ratio feedback control (single 02 sensor system), the 02 sensor that detects oxygen concentration is installed at a location in the exhaust system as close to the combustion chamber as possible, that is, at the gathering part of the exhaust manifold upstream of the catalytic converter. Improving the accuracy of air-fuel ratio control is hindered by variations in sensor output characteristics. It takes 02
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 02 sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream 02 sensor is performed. In addition, a double 0□ sensor system that performs air-fuel ratio feedback control using a downstream 02 sensor has already been proposed (
Reference: Japanese Patent Application Laid-Open No. 58-48756), this double 0
In the two-sensor system, the 02 sensor installed downstream of the catalytic converter has a lower response speed than the upstream 02 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 02 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 performing 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 02 sensor. In fact, as shown in Figure 2, in a single 02 sensor system, 02
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, but with the double 02 sensor system, even if the output characteristics of the upstream 02 sensor deteriorate,
Exhaust emission characteristics are not deteriorated. That is, double 0
□In the sensor system, good exhaust emissions are guaranteed as long as the downstream 02 sensor maintains stable output characteristics.

[Problem that the invention seeks to solve]

In the double 02 sensor system described above, the upstream 0
□Both the sensor and the 02 sensor on the downstream side are of the type that has the Z output characteristics shown in Figure 3, that is, the stoichiometric air-fuel ratio (λ
= 1), only the stoichiometric air-fuel ratio can be detected, and as a result, during air-fuel ratio feedback control, the controlled air-fuel ratio usually becomes the stoichiometric air-fuel ratio. .

In this case, it is possible to set the controlled air-fuel ratio to the rich side or lean side by air-fuel ratio feedback control by using asymmetric skip processing, asymmetric integral processing, asymmetric delay processing, changing the comparison voltage VR, etc. cannot be accurately set to any rich air-fuel ratio or any lean air-fuel ratio.

Therefore, 1) When setting the control air-fuel ratio to the ``°slightly'' rich side during high loads with a lot of NoX emissions, 1i)) IC', Co
When setting the control air-fuel ratio to the "slightly" lean side during light loads with high emissions, iii) When setting the control air-fuel ratio to the "slightly" lean side during idling, when catalyst exhaust odor is likely to occur, etc. As a result, there are still problems such as deterioration of emissions, deterioration of fuel efficiency, deterioration of drivability, or abnormal odor of the catalyst exhaust.

Therefore, an object of the present invention is to provide a double air-fuel ratio sensor system that can accurately obtain a target air-fuel ratio.

[Means for solving problems]

The means for solving the above problems are shown in Figures 1A and 1B.
As shown in the figure.

In Figure 1A, the upstream side of a catalytic converter for purifying exhaust gas installed in the exhaust system of an internal combustion engine has an output that detects the concentration of a specific component in the exhaust gas and changes suddenly at the stoichiometric air-fuel ratio of the exhaust gas. A Z-output type air-fuel ratio sensor that generates a A fuel ratio sensor is provided. The first comparison means is the output of the Z output type air-fuel ratio sensor.
1 is compared with a first reference value VR1 corresponding to the stoichiometric air-fuel ratio. On the other hand, the reference value calculation means calculates a second reference value corresponding to the air-fuel ratio according to predetermined operating parameters of the engine,
The second comparing means compares the output I of the linear output type air-fuel ratio sensor with a second reference value IR, and the control constant updating means adjusts the air-fuel ratio feedback control constant, for example, the skip amount, according to the comparison result of the second comparing means. RSR and RSL are updated at a predetermined update rate ΔR3. The air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to the comparison result of the first comparison means and the air-fuel ratio feedback control constants RSR and RSL, and the air-fuel ratio adjustment means calculates the air-fuel ratio correction amount FAF according to the air-fuel ratio correction amount FAF. This is used to adjust the air-fuel ratio of the engine.

In FIG. 1B, a difference calculation means and an update rate calculation means are added to the components shown in FIG. 1A. That is, the difference calculation means calculates the difference Δ■ between the output of the linear output type air-fuel ratio sensor and the second reference value IR, and the update speed calculation means calculates the update speed ΔRS according to the ΔI.

[For production]

According to the means shown in FIG. 1A, the output ■ of the linear output type air-fuel ratio sensor approaches the second reference value ■2 corresponding to the target air-fuel ratio by air-fuel ratio feedback control based on the output of the linear output type air-fuel ratio sensor.

As a result, the control air-fuel ratio approaches the target air-fuel ratio.

Furthermore, according to the means shown in FIG. 1B, the speed of the air-fuel ratio feedback control is made variable according to the difference ΔI between the output of the linear output type air-fuel ratio sensor and the second reference value IR corresponding to the target air-fuel ratio. That is, the speed of the air-fuel ratio feedback control is made variable according to the difference between the control air-fuel ratio and the target air-fuel ratio. As a result, the control air-fuel ratio quickly approaches the target air-fuel ratio.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 4, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. The airflow meter 3 directly measures the amount of intake air, and includes a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30 degrees 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 10, 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, Co, and NOX in the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
On the upstream side of the catalytic converter 12, a Z output type 02 sensor 13 having the output characteristics shown in FIG. A sensor 15 is provided. That is, the upstream O2 sensor 13 outputs different output voltages to the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
occurs in the A/D converter 101, whereas the downstream side 0□
The sensor 15 generates a larger output current as the air-fuel ratio becomes leaner, and this output current is generated by the current/voltage conversion circuit 100.
The voltage is converted into a voltage by a resistor (for example, a resistor) and then supplied to the A/D converter 101. In addition.

In this case, a constant voltage, for example, 0.2 to 0.5v, is applied to the downstream 02 sensor 15, but this applied voltage changes in two or three steps depending on the air-fuel ratio range for high precision control. You may let them.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for determining whether the throttle valve 16 is fully closed or not, and this output signal is supplied to the input/output interface 102 of the control circuit 10. Ru.

The control circuit 10 is configured as a microcomputer, for example, and includes a current/voltage conversion circuit 100 and an A/D converter 1.
01, input/output interface 102, CPU10
3, a ROM 104, a RAM 105, a backup RAN 106, a tarlock generation circuit 107, etc. are provided.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7. That is, in the routine described later, when the fuel injection amount TAU is calculated, the fuel injection jLTAU 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 the clock signal (not shown) and its carrier terminal finally reaches the ``1'' level, the flip-flop 109
is set, and the drive circuit 110 stops energizing the fuel injection valve 7. That is, the combustion injection valve 7 is energized by the above-mentioned fuel injection amount TAU, and therefore, an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

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

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

The operation of the control circuit 10 shown in FIG. 4 will be explained below.

FIG. 6 shows a first air-fuel ratio feedback control routine for calculating an air-fuel ratio correction coefficient FAF based on the output of the upstream 0□ sensor 13, and is executed every predetermined period of time, for example, every 4 ms.

In step 601, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 02 sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value (for example, 60 degrees Celsius), while the engine is starting, during a post-start increase, during warm-up increase, during acceleration increase (asynchronous injection), during power increase, the output of the upstream 02 sensor 13 has never crossed the reference value, fuel cut is in progress (i.e. idle switch 1
7 is on (LL=“1”) and the rotational speed Ne is above a predetermined value), 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 627 and the air-fuel ratio correction coefficient FAF is set to 1.0. Note that FAF may be set to a value immediately before the end of closed loop control. In this case, step 62
Proceed directly to step 8. Alternatively, it may be an average value or a learned value (value of backup RAM 106) during closed loop control. On the other hand, if the closed loop condition is met, step 602
Proceed to.

In step 602, the output Vl of the upstream 02 sensor 13 is
is A/D converted and taken in, and in step 603 it is determined whether V is less than the comparison voltage VR1, for example 0.45V. In other words, it is determined whether the air-fuel ratio is rich or lean. If lean (V+≦VRI), it is determined in step 604 whether the delay counter CDLY is positive or not, and CDLY>
If Otare is selected, Stellaf6o5NiteCDLY is set to O, and the process proceeds to step 606. In steps 607 and 608, the delay counter CDLY is guarded at the minimum value TDL. In this case, when the delay counter CDLY reaches the minimum value TDL, the air-fuel ratio flag F1 is set to "0" (lean) in step 609. Note that the minimum value TDL is a lean delay time for maintaining the determination that the rich state is present even if there is a change from rich to lean in the output of the upstream °02 sensor 13, and is defined as a negative value. Ru. On the other hand, if rich (Vl>VlI), step 810
Determine whether the delay counter CDLY is negative or not at C.
If DLY<0, set CDLY to 0 in step 611.
Then, the process proceeds to step 612. Steps 613, 61
4, the delay counter CDLY is guarded at the maximum value TDR, and in this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F1 is set to "1°° (rich)" at step 615. value T
DR is a rich delay time for maintaining the determination that the engine is in a lean state even if the output of the upstream 0□ sensor 13 changes from lean to rich, and is defined as a positive value.

In step 616, it is determined whether the sign of the 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, then in step 617, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag F1. If it is a reversal from rich to lean, it is increased in a skip manner as FAF←FAF 1 RSR in step 618, and conversely, if it is a reversal from lean to rich, it is skipped as FAF-FAF-RSL in step 619. decrease. In other words, skip processing is performed. If the sign of the air-fuel ratio flag F1 is not inverted in step 616, integration processing is performed in steps 620, 621, and 622.

That is, in step 620, it is determined whether F1="o" or not, and if F1="0" (lean), step 621
FAF −FAF + K IR, and on the other hand, F1
="1" (rich), FAF in step 622
+-FAF-KIL. Here, the integral constant KIR
(KIL) is set sufficiently small compared to the skip constants RSR and RSL, that is, KIR(KIL)<RS
R (RSL). Therefore, step 621 gradually increases the fuel injection amount in the lean state (F1="0"),
Step 622 gradually reduces the fuel injection amount in the rich state (F1="1").

The air-fuel ratio correction coefficient FAF calculated in steps 618, 619, 621, and 622 is
24 and is guarded at a maximum value of 1.2, for example, and
In steps 625 and 626, it is guarded at a minimum value of 0.8, for example. As a result, if the air-fuel ratio correction coefficient FAF becomes too small or too large for some reason, the air-fuel ratio of the engine is controlled using that value to prevent over-lean or over-rich conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 628.

FIG. 7 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 6. 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. 7 (A>), the delay counter CD
As shown in FIG. 7(B), LY is counted up in a rich state and counted down in a lean state. As a result, as shown in FIG. 7(C), a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed. For example, even if the air-fuel ratio signal A/F changes from lean to rich at time tl, the delayed air-fuel ratio signal A/F changes from lean to rich.
/F' is maintained lean for the rich delay time TDR and then changes to rich at time t2. Even if the air-fuel ratio signal A/F changes from rich to lean at
L) After being kept rich for a considerable amount, it changes to lean at time L4. However, the air-fuel ratio signal A/F at time ts
, b, , ty, when inverted in a period shorter than the rich delay time TDR, it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, the air-fuel ratio signal after the delay processing at the time A/F' 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. 7(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 02 sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts RSR and RSL as first air-fuel ratio feedback control constants, and an integral constant KI.
A system that makes variable R, KIL, delay time [IR, TD[, or comparison voltage VR of the output v1 of the upstream O2 sensor 13], and a system that introduces the second air-fuel ratio correction coefficient FAF2. be.

For example, if the rich skip amount RSR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is decreased, the control air-fuel ratio can be shifted to the rich side. If you make it bigger,
The control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount RSR 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 amount R5R and the lean skip amount R8L according to the output of the downstream 02 sensor 15. Also, the Ricci integral constant K
If IR is increased, the controlled air-fuel ratio can be shifted to the rich side, and even if the lean integral constant KIL is decreased, the controlled air-fuel ratio can be shifted to the rich side;
If KIR is increased, the controlled air-fuel ratio can be shifted to the lean side, and even if the rich integral constant KIR is decreased, the controlled air-fuel ratio can be shifted to the lean side. Therefore, the downstream O2 sensor 15
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 .

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) > Rich delay time (TDR
), the control 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 02 sensor 15. Furthermore, if the comparison voltage V Rl is increased, the control air-fuel ratio can be shifted to the rich side, and the comparison voltage V R1
By decreasing , the control air-fuel ratio can be shifted to the lean side. Therefore, depending on the output of the downstream side 02 sensor 15, the comparison voltage V
The air-fuel ratio can be controlled by correcting Rl.

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor has its own advantages. For example, the delay time allows for very delicate air-fuel ratio adjustment, and the skip amount can be controlled with good response without lengthening the air-fuel ratio feedback period unlike the delay time. Therefore, naturally, two or more of these variable amounts can be used in combination.

A double ○2 sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described with reference to FIG.

FIG. 8 shows a second air-fuel ratio feedback control routine that calculates the skip amounts R5R and RSL based on the output of the downstream 02 sensor 15, and is executed at predetermined intervals, for example, every IS. In steps 801 to 804, downstream 0
2 sensor 15 to determine whether the condition is a closed loop condition or not. For example, in addition to the failure of the closed loop condition determined by the upstream 02 sensor 13 (step 801), the cooling water temperature THW is lower than a predetermined value (for example, 70°C) (step 802).
, when the throttle valve 16 is fully closed (LL="1") (step 803), the downstream side 02 sensor 15 is activated during fuel cut.
The closed loop condition is not satisfied when the output current I never crosses the reference value, that is, when the downstream sensor 15 is not activated as a linear output type (step 804), and in other cases, the closed loop condition is not met. The condition is satisfied. If it is not a closed loop condition, proceed directly to step 820. In this case, RSR and RSL are held at the values immediately before the end of the closed loop. Note that RSR and RSL are average values or learned values during closed loop control (values of backup RAM 106).
But that's fine.

If the closed loop condition is satisfied by the downstream 02 sensor 15, the process advances to step 805. In Ste Nobu 805, RA
The basic injection amount TAUP and rotational speed Ne are read out from M105, and the reference current value IR, which is the target air-fuel ratio, is calculated by interpolation using a two-dimensional map.

Next, in step 806, the output current of the downstream side 02 sensor 15 (in this case, actually the current/voltage conversion circuit 10
0 output voltage V) is A/D converted and taken in, step 8
At step 07, it is determined whether the current value is greater than or equal to the reference current value 12, that is, it is determined whether the air-fuel ratio is richer or leaner than the target air-fuel ratio.

In step 807, if E≧R (lean), the process proceeds to steps 808-813; on the other hand, if I<IR, the process proceeds to steps 814-819.

In step 808, RSR-RSR+ΔRS (constant value) is set, that is, the rich ski knob amount R3R is increased to shift the air-fuel ratio to the rich side. Stereo knobs 809 and 810 guard the RSR to the maximum value MAX, for example 7.5%. Furthermore, RSL← at Step 7 811
R5L-ΔRS, that is, lean skip ff1R
3L to shift the air-fuel ratio to the rich side.

In steps 812 and 813, RSL is set to the minimum value MIN.
For example, guard at 2.5%.

On the other hand, when IIIR (rich), Ste Knob 8
At step 14, RSR+-R5R-ΔRS is set, that is, the rich skip amount R3R is decreased to shift the air-fuel ratio to the lean side. In steps 815 and 816, the RSR is guarded at the minimum value MIN. Further, in step 817, RSL is set to 4-RSL+ΔRS, that is, the lean skip amount R5L is increased to shift the air-fuel ratio to the lean side. In steps 818 and 819, the RSL is set to the maximum MA
Guard with X.

The RSR and RSL calculated as described above are stored in the RAM 105.
The routine ends at step 823.

Note that FAF calculated during air-fuel ratio feedback,
RSR and RSL are temporarily changed to other values FAF', RSR',
R5L' and stored in the backup RAM 106. By using these values during air-fuel ratio oven loop control, drivability movements such as during restart, immediately after startup, or when the 0□ sensor is inactive can be changed. It is also useful for improving sex. The minimum value MIN in FIG. 8 is a value at a level that does not impair transient followability, and the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

Note that in step 805, one or two of the other engine parameters Q/Ne, Q, intake air pressure PM, vehicle speed spD, and throttle valve opening TA may be used instead.

In this way, air-fuel ratio feedback control is performed so that the output current of the downstream O2 sensor 15 becomes the reference current value IR (target air-fuel ratio) determined by the engine parameters.

FIG. 9 is a modification example of FIG. 8, and step 8 of FIG.
Steps 901 and 902 between step 06 and step 807
is added to make the skip amount ΔR3 variable. In step 901, the difference Δ■ between the output current value of the downstream side 02 sensor 15 and the reference current value value is calculated, that is,
The difference between the current control air-fuel ratio and the target air-fuel ratio is calculated, and in step 902, the skip 1Rs is calculated based on this difference Δ■.
The update rate ΔR3 of R and RSL is calculated. Then, the process advances to step 807.

In other words, the farther the control air-fuel ratio is from the target air-fuel ratio, the faster the update rate ΔR3 of the skip amounts RSR and RSL is increased, so the control air-fuel ratio quickly approaches the target air-fuel ratio.

FIG. 10 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360° CA.

In step 1001, the intake air amount data Q and rotational speed data Ne are read from the RAM 105, and the basic injection amount T is read out.
Calculate ΔUP. For example, TA[IP←α・Q/Ne
(α is a constant). At step 1002, RAM10
5, the cooling water temperature data THW is read out, and a warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the ROM 104. In step 1003, the final injection amount TAU is set as TAU−TAUP−FAF・(FWL+β+1)+
Calculate by γ. Note that β and γ are correction amounts determined by other driving blood parameters. Then step 1
At step 004, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. This routine then ends in step 1005. 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.

Note that the first air-fuel ratio feedback control is performed every 4 ms.
In addition, the second air-fuel ratio feedback control is performed every 1 second, because the air-fuel ratio feedback control is mainly controlled by the upstream 0□ sensor, which has good responsiveness, and is controlled by the downstream 02 sensor, which has poor responsiveness. This is to follow.

It is also applicable to a double 02 sensor system that corrects other control constants in air-fuel ratio feedback control by the upstream O2 sensor, such as the integral constant, delay time, and comparison voltage VRl of the upstream O2 sensor, using the output of the downstream 0° sensor. , and double 02 which also introduces a second air-fuel ratio correction factor.
The present invention can also be applied to sensor systems. Moreover, controllability can be improved by simultaneously controlling two of the skip amount, integral constant, and delay time. Furthermore, one of the skip amounts RSR and RSL may be fixed and only the other variable, one of the integral constants KIR and KIL may be fixed and only the other variable, or the delay time TDR, It is also possible to have one of the TDLs fixed and the other variable.

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

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

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the amount of air bleed from the carburetor to control the main system passage and The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into the slow system passage, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1001 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure depending on the intake air amount and the rotational speed of the engine, and in step 1003 The supplied air amount corresponding to the final fuel injection amount TAU is calculated.

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, since a linear output type is used as the downstream air-fuel ratio sensor, it is possible to accurately obtain any target air-fuel ratio, thereby reducing exhaust emissions, improving fuel efficiency, This is useful for improving drivability, reducing catalyst exhaust odor, etc.

[Brief explanation of drawings]

Figure 1 is an overall block diagram for explaining the present invention in detail, Figure 2 is a single 02 sensor system and double 0□
An exhaust emission characteristic diagram explaining the sensor system; FIGS. 3 and 5 are output characteristic diagrams of the 02 sensor; FIG. 4 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; 6, 8, 9, and 10 are flowcharts for explaining the operation of the control circuit in FIG. 4, and FIG.
FIG. 4 is a timing diagram for supplementary explanation of the flowchart in the figure. 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 11! I (second) ○, sensor, 17...idle switch.

Claims (1)

[Scope of Claims] 1. A catalytic converter installed in the exhaust system of an internal combustion engine for purifying exhaust gas; and a catalytic converter installed upstream of the catalytic converter to detect the concentration of a specific component in the exhaust gas and purify the exhaust gas. a Z-output type air-fuel ratio sensor that generates an output that suddenly changes at a stoichiometric air-fuel ratio; a linear output type air-fuel ratio sensor that generates an output; a first comparing means that compares the output of the Z output type air-fuel ratio sensor with a first reference value corresponding to a stoichiometric air-fuel ratio; and a predetermined operating parameter of the engine. a reference value calculation means for calculating a second reference value corresponding to the corresponding air-fuel ratio; a second comparison means for comparing the output of the linear output type air-fuel ratio sensor with the second reference value; control constant updating means for updating an air-fuel ratio feedback control constant at a predetermined update rate according to the comparison result of the first comparison means; and an air-fuel ratio correction amount according to the comparison result of the first comparison means and the air-fuel ratio feedback control constant. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio correction amount calculation means for calculating the air-fuel ratio correction amount; 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. A catalytic converter installed in the exhaust system of an internal combustion engine to purify exhaust gas; and a catalytic converter installed upstream of the catalytic converter that detects the concentration of specific components in the exhaust gas and detects sudden changes in the stoichiometric air-fuel ratio of the exhaust gas. a Z-output type air-fuel ratio sensor that generates an output of -type air-fuel ratio sensor; a first comparing means for comparing the output of the Z-output type air-fuel ratio sensor with a first reference value corresponding to a stoichiometric air-fuel ratio; a reference value calculation means for calculating a second reference value, a difference calculation means for calculating a difference between the output of the linear output type air-fuel ratio sensor and the second reference value, and a difference calculation means for calculating an update speed according to the difference. update speed calculation means for calculating; second comparison means for comparing the output of the linear output type air-fuel ratio sensor with the second reference value; and air-fuel ratio feedback control according to the comparison result of the second comparison means. control constant updating means for updating a constant at the update rate; air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the comparison result of the first comparison means and the air-fuel ratio feedback control constant; An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means for adjusting an air-fuel ratio of the engine according to a fuel ratio correction amount.