JPS63239332A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To secure an optional desired air-fuel ratio in an accurate manner, by using a linear output type as a downstream side sensor and having an air-fuel ratio feedback control constant set at each area of a driving state parameter, in the case of a device which installs each air-fuel ratio sensor in both up- and downstreams of catalytic converter rhodium. CONSTITUTION:A Z output type air-fuel ratio sensor 13 and a linear output type air-fuel ratio sensor 15 are installed in both up- and downstreams of catalytic converter rhodium 12 in an exhaust system, and output of the upstream side sensor 13 is compared with the first reference value conformed to a theoretical air-fuel ratio by a first comparing device A. Likewise, output of the downstream side sensor 15 is compared with the second reference value conformed to the air-fuel ratio, corresponding to a first driving parameter of an engine, operated by an operational device C, and according to the compared result, an air-fuel ration feedback control constant at each area of a second driving parameter of the engine is operated by an operational device D. And, according to this control constant and the compared result of the first comparing device A, the air-fuel ratio compensation value is operated by an operational device E, and the air-fuel ratio is regulated via a regulating device F.

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.
), and 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 an upstream Ot sensor.

[Conventional technology]

Various methods are known for air-fuel ratio feedback control. For example, there is a single Ot sensor system in which a linear output type 0□ sensor having the output characteristics shown in Fig. 2 is provided upstream of the catalyst, and air-fuel ratio feedback control is performed based on the output of this Ot sensor to obtain an arbitrary air-fuel ratio (see (Japanese Unexamined Patent Publication No. 58-198752), it is not possible to compensate for variations in the output characteristics of the 0□ sensor, variations in parts such as fuel injection valves, and changes over time or over time. As a solution to these drawbacks, there is a double 02 sensor system in which an O2 sensor is provided upstream and downstream of the catalyst, respectively.

In this case, if both the upstream and downstream Ot sensors are of the type having a Z output characteristic that suddenly changes at the stoichiometric air-fuel ratio as shown in FIG. 3, the controlled air-fuel ratio will normally be the stoichiometric air-fuel ratio. In this case, changing the controlled air-fuel ratio to the rich side or lean side by air-fuel ratio feedback control involves asymmetric skip processing, asymmetric integral processing, asymmetric delay processing, comparison voltage
8 or by oven loop control, but it is not possible to accurately set the control air-fuel ratio to an arbitrary rich air-fuel ratio or lean air-fuel ratio.

Therefore, by configuring both the upstream and downstream 02 sensors of the linear output type, or by configuring only the upstream 02 sensor of the linear output type, an arbitrary rich air-fuel ratio or linear air-fuel ratio can be obtained. be able to.

[Problem that the invention seeks to solve]

However, at least the above-mentioned linear output type 0. Double 0. equipped with a sensor. In sensor systems, linear output type O2 sensors usually have a thicker coating layer due to the 02 diffusion layer than Z output type 0□ sensors, and as a result, the response is lower (it takes time to pump up the 02). The problem is that the air-fuel ratio feedback control cycle may become longer, resulting in a reduction in the purification function of the catalyst, resulting in deterioration of emissions, deterioration of fuel efficiency, deterioration of drivability, or the occurrence of abnormal odors in the catalyst exhaust. There is also a Z output type O! downstream of the catalyst. When a sensor is used, there is also the problem that rich or lean air-fuel ratio control must be corrected based on estimates.

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 and has high responsiveness.

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG. That is, on the upstream side of a three-way catalyst for purifying exhaust gas installed in the exhaust system of an internal combustion engine, a catalyst detects the concentration of a specific component in the exhaust gas and generates an output that changes suddenly at the stoichiometric air-fuel ratio of the exhaust gas. A Z-output type air-fuel ratio sensor is provided, and on the downstream side of the three-way catalyst, there is a linear output type air-fuel ratio sensor that detects the concentration of a specific component of exhaust gas and generates a linear output according to the air-fuel ratio of the exhaust gas. is provided. The first comparison means compares the output v1 of the Z output type air-fuel ratio sensor with a first reference value Vll+ corresponding to the stoichiometric air-fuel ratio. On the other hand, the reference value calculation means calculates a second reference value IN! corresponding to the air-fuel ratio according to the first operating state parameter of the engine, for example, the vehicle speed SPD.
F, the second comparison means compares the output ■ of the linear output type air-fuel ratio sensor with the second reference value I□, and the control constant calculation means adjusts the engine according to the comparison result of the second comparison means. the second of
The air-fuel ratio feedback control constant for each region of the operating state parameter, for example, Q, for example, the skip amount R5R1.

Calculate R5Li. Then, 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 R3R1 and R3Li for each region of the second operating state parameter Q of the engine. The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[Operation] According to the above-described means, the output ■ of the linear output air-fuel ratio sensor is set to the second reference value ■■ r corresponding to the target air-fuel ratio by the air-fuel ratio feedback control based on the output of the linear output air-fuel ratio sensor. approach. Moreover, since the air-fuel ratio feedback control constants R3R1 and R3Li are provided for each region of the operating state parameter, for example, Q, the controlled 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 includes 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 which generates a signal. 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, the water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of cooling water. 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], 01.

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.
A Z output type 0□ sensor 13 having the output characteristics shown in FIG. A sensor 15 is provided. That is, the upstream 02 sensor 13 outputs different output voltages to the control circuit 10 depending on whether the air-fuel ratio is on the lean side or the lean side with respect to the stoichiometric air-fuel ratio.
This occurs in the A/D converter 101 of 0.
The sensor 15 outputs a larger output current I as the air-fuel ratio becomes leaner.
This output current I 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 this case, a constant voltage of, for example, 0.2 to 0.5 V is applied to the downstream 0□ sensor 15, but this applied voltage is divided into two stages or two depending on the air-fuel ratio range for high-precision control. It may be changed in three or more stages.

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, and this output signal is sent to the control circuit 100.
It is supplied to the input/output interface 102.

18 is a vehicle speed sensor whose output is sent to the vehicle speed formation circuit 1
11 to an input/output interface 102.

The control circuit 10 is configured as a microcomputer, for example, and includes a current/voltage conversion circuit 100, an A/D converter 101, an input/output interface 102 . CPU103
, outside the vehicle speed formation circuit 111, ROM 104, RA
M105, back amplifier RAM 106, clock 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 amount TAU is preset in the down counter 10B 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, the down counter 108 receives the clock signal (
(not shown), and finally the carrier terminal is “
When the level reaches 1, the flip-flop 109 is set and the drive circuit 110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body l.

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

The intake air amount data Q and cooling water temperature data THW of the air flow meter 3 are 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 an interrupt every 30'CA of the crank angle sensor 6 and 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. 5 shows a first air-fuel ratio feedback control routine that calculates an air-fuel ratio correction coefficient FAF based on the output of the upstream OT sensor 13, and is executed every predetermined period of time, for example, every 4 vas.

In step 501, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 0□ sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value (for example, 60°C), the output of the upstream 02 sensor 13 is I have never set a standard value such as 0.
When 35V is not crossed, the fuel is cut (i.e.
The closed-loop condition is not satisfied when the idle switch 17 is on (LL="l") and the rotational speed Ne is above a predetermined value, and the closed-loop condition is satisfied in all other cases.

If the closed loop condition is not satisfied, the process proceeds to step 527 and the air-fuel ratio correction coefficient FAF is set to 1.0. In addition, F.A.
F may be a value immediately before the end of closed loop control. In this case, proceed directly to step 528. 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 satisfied, the process proceeds to step 502.

In step 502, the output of the upstream 0□ sensor 13 is
is A/D converted and taken in, and in step 503 it is determined whether or not V is less than the comparison voltage □, for example, 0.45V.

In other words, it determines whether the air-fuel ratio is rich or lean. If lean (■1≦V□), it is determined in step 504 whether the delay counter CDLY is positive or not, and if CDLY>O, CDLY is set to O in step 505, and the process proceeds to step 506. In steps 607 and 508, the delay counter CDLY is guarded at the minimum value TDL, and in this case, when the delay counter CDLY reaches the minimum value TDL, the air-fuel ratio flag F1 is set to "0" in step 509.
(lean). Note that the minimum value TDL is 02 on the upstream side.
This is a lean delay time for maintaining the determination that the state is rich even if the output of the sensor 13 changes from rich to lean, and is defined as a negative value. On the other hand, if it is rich (V + > V tt + ), it is determined in step 510 whether the delay counter CDLY is negative or not, and if CDLY<0, the CD is detected in step 511.
Set LY to 0 and proceed to step 512. Step 513
At ゜514, the delay counter CDLY is set to the maximum value TD.
In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F1 is set to 11'' (rich) in step 515.

The maximum value TDR is a rich delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream AT sensor 13.
Defined as a positive value.

In step 516, 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 process has been reversed. If the air-fuel ratio is reversed, then in step 517, 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 to PAP 4-FAF +RSR in step 518, and conversely, if it is a reversal from lean to rich, it is skipped to FAF -PAP-RSL in step 519. decrease. In other words, skip processing is performed. If the sign of the air-fuel ratio flag F1 is not inverted in step 516, integration processing is performed in steps 520, 521, and 522. That is, in step 520, Fl-“
If Fl-“0” (lean), FAF −FAF +KIR is determined in step 521, and on the other hand, if Fl-“1” (rich), step 5 is determined.
At step 22, FAF←FAF-KIL. Here, the integral constant KIR(KTL) is set sufficiently small compared to the skip constants R3R and RSL, that is, KIR(K
IL) < RSR(RSL). Therefore, step 521 gradually increases the fuel injection amount in the lean state (Fl-“0”), and step 522 gradually increases the fuel injection amount in the rich state (Fl-“0”).
-“1”) to gradually reduce the fuel injection amount. The air-fuel ratio correction coefficient FAF calculated in steps 518, 519, 521, 522 is guarded at a maximum value of 1.2 in steps 523, 524, and
526, it is guarded at a minimum value, for example, 0.8. 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 528.

FIG. 6 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream Ot sensor 13 as shown in FIG. 6(A), the delay counter CD
As shown in FIG. 6(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 t, 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 time t, the air-fuel ratio signal A/F' subjected to the delay processing is delayed by the lean delay time (-T
DL) After being held rich by a considerable amount, it changes to lean at time t4. However, the air-fuel ratio signal A/F at time tS
rj&+t? When the inversion occurs in a period shorter than the rich delay time TDR, the delay counter CDLY reaches the maximum value T.
It takes time to reach DR, and as a result, time 1. The air-fuel ratio signal A/F' after the delay processing is inverted at . 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. 6CD) 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 O2 sensor 15 will be explained. The second air-fuel ratio feedback control includes skip amounts R3R, R3L as the first air-fuel ratio feedback control constants, and an integral constant K.
There is a system in which the comparison voltage v81 of IR, KIL, delay time TDR, TDL, or output V of the upstream O2 sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF2 is introduced.

For example, if the rich skip amount R3R is increased, the control air-fuel ratio can be shifted to the lean side, and even if the lean skip amount RSL 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 rich side. , the control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R3R is decreased, 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 R3R and the lean skip 11R3L according to the output of the downstream Ot 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 side 0□ 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 the engine.

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 0□ sensor 15. Furthermore, by increasing the comparison voltage Vi11, the control air-fuel ratio can be shifted to the rich side, and the comparison voltage Vllll
By decreasing , the control air-fuel ratio can be shifted to the lean side.

Therefore, by correcting the comparison voltage Vll+ according to the output of the downstream 0□ sensor 15, the air-fuel ratio can be controlled.

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 O2 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. 7 shows a second air-fuel ratio feedback control routine that calculates the skip amounts R3R and RSL based on the output of the downstream 0□ sensor 15, and is executed every predetermined period of time, for example, every 13 seconds. In steps 701 to 704, downstream 0
2 sensor 15 to determine whether the condition is a closed loop condition or not. For example, upstream O! In addition to the failure of the closed loop condition determined by the sensor 13 (step 701), when the cooling water temperature THW is below a predetermined value (for example, 70°C) (step 702)
, when the throttle valve 16 is fully closed (LL="1") (step 703), the downstream side 02 sensor 15 is activated during fuel cut.
The closed loop condition is not satisfied when the output current I of the output current I has never crossed the reference value, that is, when the downstream Ot sensor 15 is not activated as a linear output type (step 704), and in other cases. The closed loop condition is satisfied. If it is not a closed loop condition, proceed directly to step 728. In this case, R5H and RSL are held at the values immediately before the end of the closed loop.

Downstream side 0. If the closed loop condition is satisfied by the sensor 15, the process proceeds to step 705. In step 705, the vehicle speed SPD is fetched from the vehicle speed forming circuit 111, and in step 706
．． In step 709, if the product of the rate of change of the vehicle speed SPD <
Proceed to 12.713.

In step 707, the rich control rich skip amount R3l? is read from the backup RAM 106? (R) is read as R2H, and in step 708, the rich air-fuel ratio (λ<
Let the reference current value I, l corresponding to 1) be I REF.

Further, in step 710, the backup RAM 106
Then, the rich skip amount RSR(s) for stoichiometric air-fuel ratio control is read out and set as RSR, and in step 711, the reference current value O corresponding to the stoichiometric air-fuel ratio (λ=1) is set to ■1. shall be. Further, in step 712, backup l? AM10
6, the lean control rich skip amount RSR (L) is read out and set as RSR, and in step 713, the reference current value IL corresponding to the lean air-fuel ratio (λ>1) is set to 1□.

In this way, the reference current value IIIF, which is the target air-fuel ratio, is set for the steady state, acceleration state, and deceleration state.

Next, in step 714, the output current of the downstream AT sensor 15 (in this case, actually the current/voltage conversion circuit 10
0 output voltage ■) is A/D converted and taken in, step 7
At step 15, it is determined whether I is outside the reference current value 1jllFll, that is, it is determined whether the air-fuel ratio is richer or leaner than the target air-fuel ratio.

If I≧■□ (lean) in step 715, the process proceeds to steps 716 to 718; on the other hand, if l<1. □ If the result is A (rich), the process proceeds to steps 719 to 721.

In step 716, R3R←R3R+ΔRS (constant value) is set, that is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side. Step 717.7
In No. 18, the RSR is guarded at the maximum value MAX, for example, 7.5%. On the other hand, when I<I□F (rich),
In step 719, R3R←R3R-ΔRS is set, that is, the rich skip amount R3R is decreased to shift the air-fuel ratio to the lean side. In steps 720 and 721 RSR
is guarded at a minimum value MIN, for example, 2.5%.

In step 722, the lean skip amount R3L is set to R3
L-TR-RSR However, TR is the total skip amount, and is calculated using, for example, 10%.

In steps 723 and 725, the reference current value 11 is again determined to be a steady state, an acceleration state, or a deceleration state, for example! It is determined by the value of F. If it is in a steady state, the R3RO value is stored in the rich skip amount R3R (R) for rich control in the backup RAM 106, and if it is in an accelerated state, the RSR value is stored in the bank up RA? It is stored in the rich skip amount R3R(S) for stoichiometric air-fuel ratio control in 1106, and if it is in a deceleration state, the value of RSR is stored in the backup RA.
M106 lean control rich skip amount RSR (L)
Store in.

The routine then ends at step 728.

In Fig. 7, three types (It, 01IL) are prepared as the reference current value 111tF, which is the target air-fuel ratio, but more types may be prepared. I determined it, but
Other operating state parameters such as Q, Q/Ne, Ne
One or two of Sw & tracheal pressure and throttle valve opening may be used. Similarly, the number of regions for block learning of the skip amount R3R may be increased, and other driving state parameters other than vehicle speed SPD, Q, Q/Ne, Ne,
It may be one or two of intake pipe pressure, throttle valve opening, etc.

Note that the minimum value MIN in FIG. 7 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.

In this way, the downstream at sensor L as a linear output type
Air-fuel ratio feedback control is performed so that the output current □ of No. 5 becomes the reference current value □F (target air-fuel ratio) determined by the engine parameters.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360°C. Step 801
Then, the intake air amount data Q and the rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount TAUP. 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. Step 8
In 03, the final injection amount TAU is set as TAU←TAUP −
FAF ・(FWL+β+1) Calculated by 10γ.

Note that β and γ are correction amounts determined by other operating state parameters. Next, in step 804, injection 11
The 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. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

FIG. 9 is a timing diagram that supplements the flowcharts of FIGS. 5, 7, and 8.
The t sensor 13 is activated as a Z output type and V+ ≧0.
35V), the air-fuel ratio feedback control tTI by the upstream Ox sensor 13 starts. Next, at time t2, the downstream OT sensor 15 is activated as a linear output type.

In other words, when the output current of the downstream Ot sensor 15 during fuel cut, ■ exceeds a certain value (■≧811A),
Downstream side 0□ sensor 15 is activated and downstream side 02 sensor 1
5 starts air-fuel ratio feedback control. In the air-fuel ratio feedback control by the downstream side 02 sensor 15, the target air-fuel ratio, that is, the reference current value I, which differs depending on the acceleration state JLj (tt "" t3), the steady state (ts~t4), and the deceleration state U (t4~). =O, II.

(2) are set, and an air-fuel ratio feedbank control constant RSR is also prepared for each state. Therefore, the responsiveness of air-fuel ratio control is high, and emissions such as NOX are reduced to 0. Compared to the conventional type, both of which are Z output type.

Note that the first air-fuel ratio feedback control is performed every 4 ms.
Moreover, the second air-fuel ratio feedback control is performed every 1 second because the air-fuel ratio feedback control is performed on the upstream side 0! with good responsiveness. This is because control by the sensor is performed primarily, and control by the downstream 02 sensor, which has poor responsiveness, is performed secondary.

In addition, other control constants in the air-fuel ratio feedback control by the upstream 02 sensor, such as an integral constant, delay time, comparison voltage Vllll of the upstream 02 sensor, etc.
The present invention can be applied to a double 02 sensor system that corrects based on the output of the t sensor, and also to a double 02 sensor system that introduces a second air-fuel ratio correction coefficient. Moreover, controllability can be improved by simultaneously controlling two of the skip amount, integral constant, and delay time. Furthermore, one of the skip amounts R5R and RSL may be fixed and only the other variable, one of the integral constants XIR 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.

Furthermore, 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 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, and devices that adjust the amount of secondary air sent to the exhaust system of an engine. In this case, the basic fuel injection amount corresponding to the basic injection 1iTAUP in step 801 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure according to the intake air amount and the engine rotation speed, and the basic fuel injection amount corresponding to the basic injection 1iTAUP is determined in step 803. 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, a linear output type is used as the downstream air-fuel ratio sensor, and an air-fuel ratio feedback control constant is provided for each region of operating condition parameters, so that any target air-fuel ratio can be set accurately and quickly. Therefore, it is useful for reducing exhaust emissions, improving fuel efficiency, improving drivability, reducing catalyst exhaust odor, etc.

[Brief explanation of the drawing]

FIG. 1 is an overall block diagram for explaining the present invention in detail, FIGS. 2 and 3 are output characteristic diagrams of the Oz sensor, and FIG. 4 is an implementation of the air-fuel ratio control device for an internal combustion engine according to the present invention. An overall schematic diagram showing an example; Figures 5, 7, and 8 are flowcharts for explaining the operation of the control circuit in Figure 4; Figure 6 is a timing diagram for supplementary explanation of the flowchart in Figure 5. FIG. 9 is a timing diagram illustrating the present invention in detail. 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 Z output type Ot sensor, 15... Downstream linear output type Ot sensor, 17... Idle switch.

Claims (1)

[Claims] 1. A three-way catalyst for purifying exhaust gas provided in the exhaust system of an internal combustion engine, and a three-way catalyst provided upstream of the three-way catalytic converter to detect the concentration of a specific component in the exhaust gas. a Z-output type air-fuel ratio sensor that generates an output that suddenly changes at the stoichiometric air-fuel ratio of the exhaust gas; and a Z-output air-fuel ratio sensor that is installed downstream of the three-way catalyst and detects the concentration of a specific component of the exhaust gas and adjusts the air-fuel ratio of the exhaust gas. a linear output type air-fuel ratio sensor that generates a linear output corresponding to the stoichiometric air-fuel ratio; a first comparing means that compares the output of the Z-output type air-fuel ratio sensor with a first reference value corresponding to the stoichiometric air-fuel ratio; a reference value calculating means for calculating a second reference value corresponding to the air-fuel ratio according to the first operating parameter; and a second comparison unit for comparing the output of the linear output type air-fuel ratio sensor with the second reference value. a control constant calculation means for calculating an air-fuel ratio feedback control constant for each region of the second operating state parameter of the engine according to the comparison result of the second comparison means; and a comparison between the first comparison means. air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount according to the result and an air-fuel ratio feedback control constant for each region of a second operating state parameter of the engine; An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means for adjusting a fuel ratio; 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the first operating state parameter and the second operating state parameter are the same. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the first operating state parameter and the second operating state parameter are different. 4. When the engine is determined to be in a steady state based on the first operating state parameter of the engine, the second reference value is set to a value corresponding to a rich air-fuel ratio, and the engine is determined to be in a steady state based on the first operating state parameter of the engine. However, when it is determined that the engine is in an acceleration state, the second reference value is set to a value corresponding to the stoichiometric air-fuel ratio, and when the engine is determined to be in a deceleration state based on the first operating state parameter of the engine, the second reference value is set to a value corresponding to the stoichiometric air-fuel ratio. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the value is a value corresponding to a lean air-fuel ratio.