JP2518254B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

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

[Conventional technology]

In simple air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor that detects oxygen concentration is provided in the exhaust system as close as possible to the combustion chamber, that is, at the exhaust manifold upstream of the catalytic converter. In addition, the variation in the output characteristics of the O ₂ sensor hinders the improvement of the air-fuel ratio control accuracy. Such O ₂ component variation variation and the fuel injection valve and the output characteristics of the sensor, to compensate for time or secular change, a second O ₂ sensor disposed downstream of the catalytic converter, by the upstream O ₂ sensor Downstream O ₂ in addition to air-fuel ratio feedback control
Double O ₂ with air-fuel ratio feedback control by sensor
Sensor systems have already been proposed (see:
-48756 publication). In this double O ₂ sensor system,
O ₂ sensor provided downstream of the catalytic converter, compared with the upstream O ₂ sensor, but has a low response speed,
There is an advantage that the variation in output characteristics is small for the following reasons.

(1) Since the exhaust gas temperature is low downstream of the catalytic converter, there is little thermal effect.

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

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

Therefore, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor. Actually, as shown in FIG. 2, in the single O ₂ sensor system, when the output characteristic of the O ₂ sensor deteriorates, the exhaust emission characteristic is directly affected, whereas in the double O ₂ sensor system, the upstream Even if the output characteristic of the side O ₂ sensor deteriorates, the exhaust emission characteristic does not deteriorate. That is, in the double O ₂ sensor system, good exhaust emissions are guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics.

[Problems to be solved by the invention]

Problems of the rich skip amount RSR and the lean skip amount RSL as the air-fuel ratio feedback control by the output V ₂ of the downstream O ₂ sensor 15 will be described with reference to the timing chart of FIG. In FIG. 3, V ₂ is the output of the downstream O ₂ sensor 15, and τ _H and τ _L are exhaust gas control delays. In FIG. 3, the rich skip amount RSR (lean skip amount RSL is RS
Changes symmetrically with R) is the output V _{2 of the} downstream O ₂ sensor 15.
And the comparison voltage V _R2 (for example, 0.55V) are calculated in an integrated manner according to the comparison result. That is, if V ₂ ≦ V _R2 (lean), the rich skip amount RSR increases at a constant update speed ΔRS, and if V ₂ > V _R2 (rich), the rich skip amount R
SR decreases at a constant update rate ΔRS. Thus, for example, when the control delay due to transport delay of the intake air quantity Q is smaller exhaust gas (tau _L) as large as the output V ₂ of the downstream O ₂ sensor 15 has changed from lean to rich, the downstream O ₂ sensor 15 Although the control air-fuel ratio is already on the rich side by the air-fuel ratio feedback control by the output V ₂ of
From this time point, the rich skip amount RSR changes from a large value to the lean direction. As a result, the control air-fuel ratio requires a relatively long time for the average becomes the stoichiometric air-fuel ratio, inviting HC, increased CO emissions, the deterioration catalytic exhaust odor like fuel economy, on the contrary, the downstream O ₂ sensor 15 When the output V ₂ of the engine changes from rich to lean, the rich skip amount RS even though the control air-fuel ratio is already largely lean due to the air-fuel ratio feedback control by the output V ₂ of the downstream O ₂ sensor 15.
R starts to change from a small value to the rich direction. As a result, it takes a relatively long time for the average of the control air-fuel ratio to reach the stoichiometric air-fuel ratio, which causes a problem of increasing NOx emissions and deteriorating drivability. That is, the swing range of the rich skip amount RSR (lean skip amount RSL) becomes large. Therefore, if the update speed ΔRS is reduced (the update speed ΔRS is increased) in order to reduce the swing width, the intake air amount Q is large and the control delay due to the exhaust gas transportation delay is originally small (τ _H ) May unnecessarily deteriorate the control air-fuel ratio. On the contrary, if the update speed ΔRS is increased (the update speed ΔRS is decreased), the control air-fuel ratio may hunt when the intake air amount Q is large and the exhaust gas transportation delay is small.

Thus, in the double O ₂ sensor system downstream side
Since the O ₂ sensor is located downstream of the catalytic converter, it produces a rich or lean output after a certain time delay. That is, there is a delay in the transportation of exhaust gas. Therefore, when the output of the downstream O ₂ sensor changes from lean to rich, the air-fuel ratio upstream of the catalytic converter has already deviated to the rich side from the stoichiometric air-fuel ratio, resulting in deterioration of HC and CO emissions and fuel consumption. When the output of the downstream O ₂ sensor changes from rich to lean, on the contrary, the air-fuel ratio upstream of the catalytic converter has already deviated to the lean side by more than the theoretical air-fuel ratio. ,
There is a problem that it causes deterioration of NOx emission and deterioration of drivability.

Therefore, the object of the present invention is to substantially increase the response speed of the downstream air-fuel ratio sensor (O ₂ sensor) by increasing the HC, C
It is intended to prevent deterioration of O, NOx emissions, deterioration of fuel efficiency, generation of a catalyst odor of exhaust gas, deterioration of drivability, and the like.

[Means for solving problems]

The means for solving the above problem is shown in FIG. In FIG. 1, an upstream side and a downstream side of a catalytic converter CC _RO for purifying exhaust gas provided in an exhaust system of an internal combustion engine are respectively detected on the upstream side and the downstream side to detect the concentration of a specific component in the exhaust gas. An air-fuel ratio sensor is provided. On the other hand, the update speed calculation means calculates the air-fuel ratio feedback control constant update speed ΔRS according to the engine parameter relating to the exhaust gas transportation delay of the engine, for example, the intake air amount Q, and the control constant calculation means calculates the air-fuel ratio feedback control constant update speed ΔRS. Then, the air-fuel ratio feedback control constants such as the skip amounts RSR and RSL are calculated according to the output V ₂ of the downstream side air-fuel ratio sensor. Then, 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, RSL and the output V ₁ of the upstream side air-fuel ratio sensor, and the air-fuel ratio adjustment means calculates the air-fuel ratio correction amount FAF. The air-fuel ratio of the engine is adjusted accordingly.

[Work]

According to the above-mentioned means, the update speed of the air-fuel ratio feedback control constant changes according to the exhaust gas transportation delay, and the amplitude of the air-fuel ratio feedback control constant becomes substantially constant regardless of the exhaust gas transportation delay.

〔Example〕

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

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 3, an air flow meter 3 is provided in an intake passage 2 of an engine body 1. The airflow meter 3 directly measures the intake air amount and incorporates a potentiometer to generate an output signal of an analog voltage proportional to the intake air amount. This output signal is output from the A / D converter 1 with built-in multiplexer in the control circuit 10.
Supplied to 01. The distributor 4 has a crank angle sensor 5 whose axis generates, for example, a reference position detection pulse signal every 720 ° in terms of crank angle, and a reference position detection pulse signal in every 30 degrees which is converted into crank angle. A generated crank angle sensor 6 is provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to an input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

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

The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 is the temperature TH of the cooling water.
Generates an electric signal of analog voltage 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 HC, CO, and NOx in the exhaust gas.

The exhaust manifold 11 has a catalytic converter 12
A first O ₂ sensor 13 is provided on the upstream side, and a second O ₂ sensor 15 is provided on the exhaust pipe 14 downstream of the catalytic converter 12. The O ₂ sensors 13 and 15 generate an electric signal corresponding to the concentration of the oxygen component in the exhaust gas. That is, the O ₂ sensor 1
3,15 are different output voltages depending on whether the air-fuel ratio is leaner or richer than the theoretical air-fuel ratio.
Occurs at 01.

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

The control circuit 10 is configured as, for example, a microcomputer, and includes an A / D converter 101, an input / output interface 102,
In addition to CPU103, ROM104, RAM105, backup RAM106,
A clock generation circuit 107 and the like are provided.

Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 include the fuel injection valve 7
Is for controlling. That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and the carry-out terminal finally becomes "1" level, the flip-flop 109 is set and the drive circuit 110 sets the fuel injection valve 7 Stop energizing. That is, the fuel injection valve 7 is energized by the above-described fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

Note that the CPU 103 generates an interrupt when the A / D conversion of the A / D converter 101 ends, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6,
When an interrupt signal from 7 is received, and so on.

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

According to the present invention, by making the update speed ΔRS variable according to the transportation delay of exhaust gas, in this case, the intake air amount Q,
Renewal of skip amount RSR (RSL) shown in Fig. 3 eliminates fluctuation of the fluctuation amount due to delay of transportation of exhaust gas, that is, as shown in Fig. 5, the fluctuation amount of skip amount RSR (RSL) is almost equal. It is a constant control.

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

Figure 6 is a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream O ₂ sensor 13 is executed at a predetermined time, for example, 4ms each.

In step 601, the air-fuel ratio of the closed loop by the upstream O ₂ sensor 13 (feedback) condition is determined whether or not satisfied. For example, if the cooling water temperature is a specified value (for example, 60
(° C) or below, during engine start, during starting increase, during warm-up increase, during acceleration increase (asynchronous injection), during power increase, upstream side
When the output V ₁ of the O ₂ sensor 13 never crosses the reference value, the fuel is being cut (that is, the idle switch 17 is on (LL = "1") and the rotation speed Ne is equal to or higher than 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 routine proceeds to step 627, where 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 the closed loop control. In this case, go directly to step 628. Also, FAF
May be an average value or a learning value (value of backup RAM 106) at the time of closed loop control. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 602.

In step 602, the output V ₁ of the upstream O ₂ sensor 13 is A / D-converted to work, and in step 603, it is determined whether or not V ₁ is the comparison voltage V _R1, for example, 0.45 V or less. That is, it is determined whether the air-fuel ratio is rich or lean. If lean (V ₁ ≦ V _R1 ), it is determined in step 604 whether the delay counter CDLY is positive, and if CDLY> 0, CDLY is set to 0 in step 605.
And proceed to step 606. In step 606, CDLY is counted down, in steps 607 and 608, the delay counter CDLY is guarded by the minimum value TDL, and in this case, when the delay counter CDLY reaches the minimum value TDL, step 609 is performed.
Then, the first air-fuel ratio flag F1 is set to "0" (lean). The minimum value TDL is a lean delay time for holding the determination that the output is rich, even if there is a change from rich to lean in the output of the upstream O ₂ sensor 13, and is defined as a negative value. It On the other hand, if rich (V ₁ > V _R1 ), it is determined in step 610 whether the delay counter CDLY is negative, and if CDLY <0, CDLY is set to 0 in step 611,
Go to step 612. In step 612, CDLY is incremented, and in steps 613 and 614, the delay counter CDLY is guarded by the maximum value TDR. In this case, the delay counter CDL
When Y reaches the maximum value TDR, the first step 615
The air-fuel ratio flag F1 of is set to "1" (rich). It should be noted that the maximum value TDR is a rich delay time for holding a judgment that the output is a lean state even if there is a change from lean to rich in the output of the upstream O ₂ sensor 13, and is defined as a positive value. It

In step 616, it is determined whether or not the sign of the first air-fuel ratio flag F1 has been inverted, that is, whether or not the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, it is determined in step 617 whether the reversal is from rich to lean or from lean to rich, depending on the value of the first air-fuel ratio flag F1. If the inversion is from rich to lean, then in a step 618, FAF ← FAF + RSR is increased in a skipping manner. Conversely, if the inversion is from lean to rich, in a step 619, FAF ← FAF−RSL is skipped. Decrease.
That is, skip processing is performed. If the sign of the first air-fuel ratio flag F1 is not reversed in step 616, step
Integral processing is performed at 620, 621 and 622. That is, step 620
In step 621, it is determined that FAF ← FAF + KIR, while on the other hand, F1 = “0” (lean)
If “1” (rich), FAF ← FAF−KIL in step 622
And Where the integration constant KIR (KIL) is the skip constant RS
It is set sufficiently smaller than R and RSL, that is, KIR
(KIL) <RSR (RSL). Therefore, step 621 gradually increases the fuel injection amount in the lean state (F1 = "0"),
In step 622, the fuel injection amount is gradually reduced in the rich state (F1 = "1"). The air-fuel ratio correction coefficient FAF calculated in steps 618, 619, 621 and 622 is guarded with a maximum value of 1.2 in steps 623 and 624 and with a minimum value of 0.8 in steps 625 and 626. This allows
For some reason, the air-fuel ratio correction factor FAF becomes too small,
Alternatively, when it becomes too large, the value is used to control the air-fuel ratio of the engine to prevent over lean or over rich.

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

FIG. 7 is a timing chart for supplementarily explaining 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 O ₂ sensor 13 as shown in FIG. 7 (A), the delay counter CDLY becomes
As shown in FIG. 7 (B), the count is performed in a rich state and the count is reduced in a lean state. As a result, as shown in FIG. 7 (C), a delayed air-fuel ratio signal A / F '(corresponding to the flag F1) is formed. For example, the air-fuel ratio signal A / F is changed from lean to rich at time t _1, the air-fuel ratio signal A / F which is delayed processed 'at time t ₂ after being held lean only the rich delay time TDR Change richly. Also the air-fuel ratio signal A / F from the rich at time t ₃ is changed to the lean air-fuel ratio signal A / F which is delayed processed '
Changes to lean at time t ₄ after being held rich only equivalent lean delay time (-TDL). However, if the air-fuel ratio signal A / F is inverted in a period shorter than the rich delay time TDR as at times t ₅ , t ₆ , and t ₇ , the delay counter CDLY will have the maximum value TD.
It takes time to reach R, and as a result, the delayed air-fuel ratio signal A / F ′ is inverted at time t ₈ . That is, the air-fuel ratio signal A / F ′ after the delay processing is the air-fuel ratio signal A before the delay processing.
Stable compared to / F. Thus, the air-fuel ratio correction coefficient FAF shown in FIG. 7D 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 O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, the skip amounts RSR, RSL, the integration constants KIR, KIL, the delay times TDR, TDL, or the output V ₁ of the upstream O ₂ sensor 13 as the first air-fuel ratio feedback control constant are determined. There are a system that makes the comparison voltage V _R1 variable, and a system that introduces the second air-fuel ratio correction coefficient FAF2.

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 RSL is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean skip amount RSL is increased. , The control air-fuel ratio can be shifted to the lean side, and the rich skip amount
You can shift to lean side even if RSR is reduced. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount RSR and the lean skip amount RSL according to the output of the downstream O ₂ sensor 15. Also, if the rich integration constant KIR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean integration constant KIL is decreased, the control air-fuel ratio can be shifted to the rich side, while if the lean integration constant KIL is increased. , The control air-fuel ratio can be shifted to the lean side, and the rich integration constant KI
Even if R is made small, the control air-fuel ratio can be shifted to the lean side.
Accordingly, the air-fuel ratio can be controlled by correcting the rich integration constant KIR and the lean integration constant KIL in accordance with the output of the downstream O ₂ sensor 15. If rich delay time TDR> lean delay time (-TDL) is set, the control air-fuel ratio can shift to the rich side, and conversely, if lean delay time (-TDL)> rich delay time (TDR) is set, control can be performed. The air-fuel ratio can shift to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay time TDR, the TDL in accordance with the output of the downstream O ₂ sensor 15. Furthermore, it shifts the control air-fuel ratio by increasing the comparison voltage V _R1 to the rich side, also, possible shifts the control air-fuel ratio by decreasing the reference voltage V _R1 to the lean side. Accordingly, the air-fuel ratio can be controlled by correcting the reference voltage V _R1 in accordance with the output of the downstream O ₂ sensor 15.

Each of these skip amount, integration constant, delay time, and comparison voltage can be made variable by the downstream O ₂ sensor. For example, the delay time allows very fine adjustment of the air-fuel ratio, and the skip amount can be controlled with good response without lengthening the air-fuel ratio feedback cycle unlike the delay time. Therefore, these variable amounts can be used in combination of two or more.

Referring to FIG. 8 will be described double O ₂ sensor system in which the skip amounts as an air-fuel ratio feedback control constant to a variable.

Figure 8 is skip amount based on the output of the downstream O ₂ sensor 15 RSR, a second air-fuel ratio feedback control routine for calculating the RSL, is executed at predetermined time, for example, 1s. In steps 801 to 803, it is determined whether or not the closed loop condition by the downstream O ₂ sensor 15 is satisfied. For example, when the closed-loop condition is not satisfied by the upstream O ₂ sensor 13 (step 801 which is the same as step 601) and when the cooling water temperature THW is below a predetermined value (for example, 70 ° C.) (step 802), the throttle valve 1
When 6 is fully closed (LL = “1”) (step 803), etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If it is not a closed loop condition, the process proceeds to step 819. In this case, RSR and RSL are held at the values immediately before the end of the closed loop, but they may be average values or learning values during closed loop control.

If the closed loop condition by the downstream O ₂ sensor 15 is satisfied,
Proceed to steps 804-817. In step 804, the update speed ΔRS of the rich skip amount RSR and the lean skip amount RSL is calculated. That is, the intake air amount data Q is read from the RAM 105 and the update speed ΔRS is interpolated and calculated by the one-dimensional map. In this case, when the intake air amount Q increases, the exhaust gas transportation delay decreases, so the update speed ΔRS increases, and conversely, when the intake air amount Q decreases, the exhaust gas transportation delay increases. , The update rate ΔRS is reduced.

In step 805, takes in the output V ₂ of the downstream O ₂ sensor 15 is converted A / D, is V ₂ at step 806 to determine whether the comparison voltage V _R2 or less. That is, it is determined whether the air-fuel ratio is lean or rich. As a result, if V ₂ ≦ V _R2 (lean), the process proceeds to steps 807 to 811. On the other hand, if V ₂ > V _R2 (rich), the process proceeds to steps 812 to 817.

In step 807, RSR ← RSR + ΔRS is set, that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side. In steps 808 and 809, RSR is guarded at the maximum value MAX, for example 7.5%. In addition, in step 815 RSL
← RSL−ΔRS, that is, the air-fuel ratio is shifted to the rich side by reducing the rich skip amount RSL. Step 811,81
In 2, the RSL is guarded with the minimum value MIN, for example, 2.5%.

On the other hand, when V ₂ > VR ₂ (rich), RSR ← RSR−ΔRS is set in step 813, that is, the rich skip amount RSR
To shift the air-fuel ratio to the lean side. Step
In 814 and 815, RSR is guarded by the minimum value MIN. Further, in step 816, RSL ← RSL + ΔRS is set, that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. In steps 817 and 818, RSL is guarded with the maximum value MAX.

After the RSR and RSL calculated as described above are stored in the RAM 105, this routine ends at step 819. In the routine of FIG. 8, the update rate of the rich skip amount RSR and the update rate of the lean skip amount RSL are symmetrical (identical), but they may be asymmetric. Although the intake air amount Q is used as the engine parameter related to the exhaust gas transportation delay in step 804, other parameters such as the rotation speed Ne, the intake pipe pressure, Q / Ne, and the throttle valve opening may be used.

In addition, FAF, RSR,
RSL can be temporarily changed to other values FAF ′, RSR ′, RSL ′ and stored in the backup RAM 106.By using these values during the air-fuel ratio open loop control, for example, at the time of restart or immediately after starting, etc. It also helps improve driving motility when the O ₂ sensor is inactive. The minimum value MIN in FIG. 8 is a value at which the transient followability is not impaired, and the maximum value MAX is a value at which driveability does not deteriorate due to air-fuel ratio fluctuations.

FIG. 9 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 901, the intake air amount data Q and the rotation speed data are read from the RAM 105.
Ne is read and the basic injection amount TAUP is calculated. For example, TA
UP ← α · Q / Ne (α is a constant). RAM in step 902
The cooling water temperature data THW is read from 105, and the warm-up increase value FWL is interpolated by the one-dimensional map stored in the ROM 104.
In step 903, the final injection amount TAU is calculated by TAU ← TAUP · FAF · (FWL + β + 1) + γ. Here, β and γ are correction amounts determined by other operation state parameters. Then step 904
Then, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start the fuel injection. Then, in step 905, this routine ends. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carry-out signal of the down counter 108, and the fuel injection ends.

The first air-fuel ratio feedback control is performed every 4ms.
The second air-fuel ratio feedback control is performed every 1 s because the air-fuel ratio feedback control is mainly performed by the upstream O ₂ sensor with good response and the downstream O ₂ sensor with poor response is used. This is because the control is performed subordinately.

Further, other control constants in the air-fuel ratio feedback control by the upstream O ₂ sensor, such as the integration constant, the delay time, the comparison voltage V _R1 of the upstream O ₂ sensor, etc. are corrected by the output of the downstream O ₂ sensor by double O ₂ The present invention can be applied to a sensor system and also to a double O ₂ sensor system that introduces a second air-fuel ratio correction coefficient. In addition, controllability can be improved by simultaneously controlling two of the skip amount, the integration constant, and the delay time. In addition, skip amount RSR, RSL
It is also possible to fix one of them and make only the other variable,
It is possible to fix one of the integration constants KIR and KIL and make only the other variable, or to fix one of the delay times TDR and TDL and make the other variable.

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

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

Further, in the above-described embodiment, the internal combustion engine in which the fuel injection valve controls the fuel injection amount to the intake system is described. However, the present invention can be applied to a carburetor-type internal combustion engine. For example, the air-fuel ratio is controlled by adjusting the intake air amount of the engine using an electric air control valve (EACV).
Electric bleed air control valve adjusts the air bleed amount of the carburetor to control the air-fuel ratio by introducing air into the main passage and the slow passage, and controls the amount of secondary air sent to the exhaust system of the engine. The present invention can be applied to a device to be adjusted. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 901 is determined by the carburetor itself, that is, determined in accordance with the intake pipe negative pressure corresponding to the intake air amount and the engine speed, and step 903. Then, the supply air amount corresponding to the final fuel injection amount TAU is calculated.

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

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

〔The invention's effect〕

As described above, according to the present invention, since the update speed of the air-fuel ratio feedback control constant is changed according to the transportation delay of the exhaust gas, overcorrection of the air-fuel ratio feedback control constant due to the transportation delay of the exhaust gas can be performed. It is possible to prevent a large deviation of the control air-fuel ratio, and it is useful for reducing exhaust emission, improving fuel efficiency, reducing unpleasant odor of catalyst exhaust, and preventing deterioration of drivability.

[Brief description of drawings]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention, FIG. 2 is an exhaust emission characteristic diagram for explaining a single O ₂ sensor system and a double O ₂ sensor system, and FIG. 3 is to be solved by the present invention. FIG. 4 is a timing chart for explaining problems, 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, and FIG. 5 is timing for explaining an operation according to the present invention. FIG. 6, FIG. 8, FIG. 8 and FIG. 9 are flow charts for explaining the operation of the control circuit of FIG. 4, and FIG. 7 is a timing chart for supplementary explanation of the flow chart of FIG. 1 ... Engine main body, 3 ... Air flow meter, 4 ... Distributor, 5,6 ... Crank angle sensor, 10 ... Control circuit, 12 ... Catalytic converter, 13 ... Upstream side (first) O ₂ Sensor, 15 …… Downstream (second) O ₂ sensor, 17 …… Idle switch.

Claims (2)

(57) [Claims] 1. A catalytic converter for purifying exhaust gas, which is provided in an exhaust system of an internal combustion engine, and an upstream, which is provided on each of an upstream side and a downstream side of the catalytic converter, for detecting a concentration of a specific component in the exhaust gas. Side, downstream side air-fuel ratio sensor, according to the engine parameters related to the exhaust gas transportation delay of the engine, when the exhaust gas transportation delay is large, the update rate of the air-fuel ratio feedback control constant is calculated to be slow, the exhaust gas When the transportation delay is small, the control constant update speed calculation means for calculating so that the update speed of the air-fuel ratio feedback control constant becomes faster; and the air-fuel ratio according to the output of the downstream side air-fuel ratio sensor at the air-fuel ratio feedback control constant update speed. Control constant calculation means for calculating a feedback control constant, the air-fuel ratio feedback control constant and the upstream side air-fuel ratio sensor Air-fuel ratio correction amount calculation means for calculating the air-fuel ratio correction amount according to the output of the sensor, and air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount. Fuel ratio control device. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the engine parameter is an intake air amount of the engine.