JPH0718363B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (O ₂ sensor)) upstream and downstream of a catalytic converter.
The provided, 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 O ₂ sensor in the upstream side.

[Conventional technology]

In simple air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor that detects the oxygen concentration is provided at a location in the exhaust system that is as close to the combustion chamber as possible, that is, at the collective portion of the exhaust manifold that is upstream from the catalytic converter. , O ₂ sensor's output characteristic variation hinders improvement of air-fuel ratio control accuracy. In order to compensate for such variations in the output characteristics of the O ₂ sensor, variations in parts such as the fuel injection valve, and changes over time or over time, a second O ₂ sensor is provided downstream of the catalytic converter and the upstream O ₂ sensor is used. A double O ₂ sensor system has already been proposed that performs air-fuel ratio feedback control by a downstream O ₂ sensor in addition to air-fuel ratio feedback control (see JP-A-58-58).
48756 publication). In this double O ₂ sensor system, the O ₂ sensor provided downstream of the catalytic converter is
Although it has a low response speed as compared with the O ₂ sensor, it has an advantage that variation in output characteristics is small for the following reason.

(1) Since the exhaust gas temperature is low downstream of the catalytic converter, 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 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 O ₂ sensor output characteristic deteriorates, the exhaust emission characteristic is directly affected, whereas in the double O ₂ sensor system, the upstream side Exhaust emission characteristics do not deteriorate even if the output characteristics of the O ₂ sensor deteriorate. That is, in the double O ₂ sensor system, good exhaust emission is guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics.

[Problems to be solved by the invention]

However, in the double O ₂ sensor system downstream
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, the output of the downstream O ₂ sensor is delayed due to the O ₂ storage effect of the catalytic converter (three-way catalyst). 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, and as a result, CO, HC
When the output of the downstream O ₂ sensor changes from rich to lean, which causes deterioration of emissions and fuel efficiency, on the other hand, the air-fuel ratio upstream of the catalytic converter has already deviated to the lean side by more than the theoretical air-fuel ratio. As a result, there is a problem that NOx emission is deteriorated and drivability is deteriorated.

Explaining the O ₂ storage effect of the three-way catalyst, the three-way catalyst purifies NOx, CO, and HC at the same time, and its purification rate η is shown by the dashed line in FIG. The purification rate of NOx is larger on the rich side than (λ = 1), and the purification rates of CO and HC are large on the lean side (HC is not shown, but has the same tendency as CO). As a result, the required purification rate η is η. If so, the controllable air-fuel ratio window w is very narrow (w = w ₁ ), and therefore, the air-fuel ratio feedback control for the stoichiometric air-fuel ratio should also be originally performed within this range (w ₁ ). However, three-way catalyst, O ₂ that reacted fuel ratio uptake of O ₂ when the lean, CO when the air-fuel ratio becomes rich, and O ₂ was incorporated at the time of lean crowded preparative HC Since the air-fuel ratio feedback control has a storage effect and positively utilizes such an O ₂ storage effect, the air-fuel ratio is controlled at an optimum frequency and amplitude. As a result, as shown by the solid line in FIG. 3, the purification rate η is improved during the air-fuel ratio feedback control, and the controllable air-fuel ratio window w is substantially wide (w
= W ₂ ).

Therefore, an object of the present invention is to substantially increase the response speed of the downstream air-fuel ratio sensor (O ₂ sensor) to reduce CO, HC,
It is to prevent the deterioration of NOx, emission, fuel consumption, drivability, etc.

[Means for solving problems]

A configuration for solving the above problems is shown in FIG.

In FIG. 1, first and second air-fuel ratio sensors for detecting a specific component concentration in exhaust gas are provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine. Each is provided. The control constant calculation means is an air-fuel ratio feedback control constant, for example, the skip amounts RSR, RSL, depending on the output V ₂ of the downstream (second) air-fuel ratio sensor.
However, after reversing from the rich to lean or lean to rich with respect to the target air-fuel ratio of the output V ₂ of the downstream side air-fuel ratio sensor, the update speed of the air-fuel ratio feedback control constant per unit time is changed from before the reversal. Increase and then decrease. As a result, the air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to the air-fuel ratio feedback control constants RSR, RSL and the output V ₁ of the upstream (first) air-fuel ratio sensor.
The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount.

[Work]

According to the above-mentioned means, the average air-fuel ratio upstream of the catalytic converter changes rapidly at the rich / lean change point of the downstream side air-fuel ratio sensor, but gradually changes thereafter.

〔Example〕

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control system 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 air flow meter 3 directly measures the intake air amount, and has a built-in potentiometer to generate an output signal of an analog voltage proportional to the intake air amount. This output signal is the A / D converter 101 with built-in multiplexer of the control circuit 10.
Is being supplied to. The distributor 4 includes a crank angle sensor 5 whose axis generates a reference position detecting pulse signal every 720 ° converted into a crank angle, and a reference position detecting pulse signal every 30 ° converted into a crank angle. A crank angle sensor 6 for generating is provided. The pulse signals of the 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 supplied to the 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 of the cooling water THW
Generates an electric signal of analog voltage according to. 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 toxic components HC, CO, and NOx in the exhaust gas.

A first O ₂ sensor 13 is provided on the exhaust manifold 11, that is, on the upstream side of the catalytic converter 12, and a second O ₂ sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12. . The O ₂ sensors 13 and 15 generate electric signals according to the concentration of oxygen components in the exhaust gas. That is, the O ₂ sensor 13,1
5 is an A / D converter 101 that outputs different output voltage by the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the theoretical air-fuel ratio.
Occurs in. The control circuit 10 is configured as, for example, a microcomputer, and in addition to the A / D converter 101, the input / output interface 102, and the CPU 103, the ROM 104, the RAM 105, the backup RAM 106, the 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 are for controlling the fuel injection valve 7. That is, when the fuel injection amount TAU is calculated in the routine described later, the fuel injection amount T
The AU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, drive circuit 1
10 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and finally its carry-out terminal becomes the "1" level, the flip-flop 109 is set and the drive circuit 110 causes the fuel injection valve 7 to operate. Stop energizing. That is, the above-mentioned fuel injection amount TA
Only U, the fuel injection valve 7 is energized, and therefore the fuel injection amount TAU
The amount of fuel corresponding to is sent to the combustion chamber of the engine body 1.

The CUP 103 generates an interrupt when the A / D conversion of the A / D converter 101 is completed, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6, the clock generation circuit 107.
When an interrupt signal from is received.

The intake air amount data Q of the air flow meter 3 and the cooling water temperature data THW 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. Further, the rotation speed data Ne is calculated by the interrupt of the crank angle sensor 6 every 30 ° CA and is calculated by the RAM1.
It is stored in the predetermined area of 05.

FIG. 5 shows 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, which is executed every predetermined time, for example, 4 ms.

In step 501, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied. For example, when the cooling water temperature is equal to or lower than a predetermined value, during engine start, during starting increase, during warm-up increase, during power increase, when the output signal of the upstream O ₂ sensor 13 has never been reversed,
The closed loop condition is not satisfied during the fuel cut, and the closed loop condition is satisfied in other cases. When the closed loop condition is not satisfied, the routine proceeds to step 527, where the air-fuel ratio correction coefficient FAF is set to 1.0. FAF may be set to a value immediately before the end of closed loop control. In this case, the process proceeds directly to step 528. On the other hand, if the closed loop condition is satisfied, step 50
Go to 2.

In step 502, the output V ₁ of the upstream O ₂ sensor 13 is A / D converted and tackled, and in step 503, V ₁ is compared voltage V _R1
It is determined whether 0.45V or less, that is, whether the air-fuel ratio is rich or lean, that is, the air-fuel ratio is lean (V ₁ ≤
If V _R1 ), skip counter 504 with delay counter CDLY
Is determined to be positive. If CDLY> 0, CDLY is set to 0 in step 505, and the routine proceeds to step 506. In step 506, the delay counter CDLY is decremented by 1, and steps 507 and 50 are performed.
At 8, the delay counter CDLY is guarded with the minimum value TDL.
In this case, when the delay counter CDLY reaches the minimum value TDL, the first air-fuel ratio flag F1 is set to "0" (lean) in the skip 509. 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 510 whether the delay counter CDLY is negative, and if CDLY <0, skip
CDLY is set to 0 at 511, and the process proceeds to step 512. Step 51
In 2, the delay counter CDLY is incremented by 1, and steps 513 and 5 are performed.
At 14, the delay counter CDLY is guarded with the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, at step 515 the first air-fuel ratio flag F1
Is set to “1” (rich). The maximum value TDR is the upstream O ₂
It is a rich delay time for holding the determination that the lean state is present even if the output of the sensor 13 changes from lean to rich, and is defined by a positive value.

In step 516, it is determined whether or not the sign of the first air-fuel ratio flag F1 is inverted, that is, it is determined whether or not the air-fuel ratio after the delay process is inverted. If the air-fuel ratio is reversed,
At step 517, according to the value of the first air-fuel ratio flag F1,
Determine whether the reversal from rich to lean or from lean to rich. If it is inversion from rich to lean, in step 518 FAF ← FAF + RSR is increased in a skip manner. Conversely, if it is inversion from lean to rich, in step 519 FAF ← FAF−RSL is skipped. Reduce.
That is, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted at step 512, integration processing is performed at steps 520, 521 and 522. That is, in step 520, it is determined whether or not F1 = "0". If F1 = "0" (lean), then in step 521 FAF ←
Set FAF + KIR, and if F ₁ = “1” (rich), set FAF ← FAF + KIL in step 522. Where the integration constant KI
L and KIR are set sufficiently smaller than the skip constants RSR and RSL, that is, KIL, KIR <RSR and RSL. Therefore, step 521 gradually increases the fuel injection amount in the lean state (F1 = “0”), and step 522 is in the rich state (F1 = “0”).
The fuel injection amount is gradually reduced by "1").

The air-fuel ratio correction coefficient FAF calculated in steps 518, 519, 521, 522 is guarded at a minimum value, for example 0.8, at steps 523, 524, and at a maximum value, for example, at steps 525, 526.
Guarded at 1.2. Thus, when the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF calculated as described above is stored in the RAM 105, and this routine ends at step 582.

FIG. 6 is a timing diagram for supplementarily explaining the operation according to the flowchart of FIG. When the rich / lean air-fuel ratio signal A / F is obtained from the output of the upstream O ₂ sensor 13 as shown in FIG. 6 (A), the delay counter CDLY becomes rich as shown in FIG. 6 (B). The state is counted up, and the lean state is counted down. As a result,
As shown in FIG. 6 (C), the 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 ₁ , the delay-processed air-fuel ratio signal A / F ′ is held lean for the rich delay time TDR and then at time t ₂ Changes to rich. Even the air-fuel ratio signal A / F at time t ₃ is changed from rich to lean, the delayed air-fuel-fuel ratio signal A / F 'is the time after being held rich only equivalent lean delay time (-TDL) t Change to lean at ₄ . However, the air-fuel ratio signal A /
When F ′ is inverted in the short period of the rich delay time TDR as at times t ₅ , t ₆ , and t ₇ , it takes time for the delay counter CDLY to reach the maximum value TDR, and as a result, at time t ₈ . The air-fuel ratio signal A / F 'after the delay processing is inverted. That is, the air-fuel ratio signal A / F ′ after the delay processing becomes more stable than the air-fuel ratio signal A / F before the delay processing. In this way, the air-fuel ratio correction coefficient FAF shown in FIG. 6D 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 as the first air-fuel ratio feedback control constants, the integration constants KIR, KIL, the delay times TDR, TDL, or the output V ₁ of the upstream O ₂ sensor 13 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 the lean skip amount
Even if RSL is reduced, the control air-fuel ratio can be shifted to the rich side,
On the other hand, if the lean skip amount RSL is increased, the control air-fuel ratio can be shifted to the lean side, and the rich skip amount RSR
The control air-fuel ratio can be shifted to the lean side even if is decreased. 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 control air-fuel ratio can be shifted to the lean side even if the rich integration constant KIR is reduced. Therefore, the air-fuel ratio can be controlled by correcting the rich integration constant KIR and the lean integration constant KIL according to 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 times TDR and TDL according to 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, the comparison voltage V _R1
The control air-fuel ratio can be shifted to the lean side by decreasing. Therefore, the air-fuel ratio can be controlled by correcting the comparison voltage V _R1 according to 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 delicate adjustment of the air-fuel ratio, and the skip amount enables control with good response without lengthening the feedback cycle of the air-fuel ratio like the delay time. Therefore, these variable amounts can naturally be used in combination of two or more.

A double O ₂ sensor system in which the skip amount as the air-fuel ratio feedback control constant is variable will be described with reference to FIG. 7.

FIG. 7 shows a second air-fuel ratio feedback control routine for calculating the skip amounts SRS, RSL based on the output of the downstream O ₂ sensor 15, which is executed every predetermined time, for example, 512 ms. In step 701, it is determined whether or not the downstream O ₂ sensor 15 is in a closed loop condition. For example, upstream O ₂ sensor 13
When the closed loop condition is not satisfied, the output signal of the downstream O ₂ sensor 15 is also not inverted once by, when the downstream O ₂ sensor 15 is faulty, etc. is both a closed-loop condition is not satisfied, otherwise closed loop The condition is met. If it is not a closed loop condition, the process proceeds to steps 722 and 723, and the skip amounts RSR and RSL are set to constant values RSR ₀ and RSL ₀ . For example, RSR ₀ = 5% RSL ₀ = 5%. The skip amounts RSR and RSL may be values immediately before the end of the closed loop control. In this case, the process proceeds directly to step 724.

If it is a closed loop, the process proceeds to step 702, where the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and captured. Then step 7
In 03, it is determined whether or not V ₂ is the comparison voltage V _R2 or less, for example, 0.55 V, that is, it is determined whether the air-fuel ratio is rich or lean.
The comparison voltage V _R2 is higher than the comparison voltage V _R1 of the output of the upstream O ₂ sensor 13 in consideration of the difference in output characteristics due to the influence of raw gas and the deterioration speed on the upstream and downstream sides of the catalytic converter 12. Although it is set high, this setting may be arbitrary.

If V ₂ ≤V _R2 (lean) in step 703, step 70
4, the second air-fuel ratio flag F2 is set to "0", and conversely V ₂
If> V _R2 (rich), the routine proceeds to step 705, where the second air-fuel ratio flag F2 is set to "1".

In step 706, it is determined whether or not the second air-fuel ratio flag F2 has been inverted, that is, whether or not the output V _{2 of the} downstream O ₂ sensor 15 has been inverted. If it is reversed, proceed to step 707,
The initial value A is set to the correction amount ΔRS of the skip amounts RSR and RSL, that is, ΔRS ← A. Note that A can be a constant value or variable according to the load parameters Q, Ne and the like. On the other hand, if not reversed, the correction amount ΔRS is multiplied by a predetermined ratio k (<1) in step 708. That is, ΔRS ← ΔRS · k.

Therefore, after the inversion, when the routine of FIG. 7 is executed n times, ΔRS becomes ΔRS = A · Kn. That is, the correction amount ΔRS sharply increases immediately after the output V ₂ of the downstream O ₂ sensor 15 is inverted, and then gradually decreases.

Next, at step 709, it is judged if the second air-fuel ratio flag F2 is "0". As a result, if F2 = "0" (lean), the routine proceeds to steps 710 to 715, while F2 = "1" (rich)
If so, proceed to steps 716-721.

In step 710, RSR ← RSR + ΔRS, that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side. In steps 711 and 712, the RSR is guarded with the maximum value MAX, for example 6.2%. Further, in step 713, RSL
← RSL-ΔRS, that is, the lean skip amount RSL is decreased to shift the air-fuel ratio to the rich side. Steps 714,71
At 5, the RSL is guarded with the minimum value MIN, for example 2.5%.

On the other hand, when F2 = "1" (rich) in step 709, RSR ← RSR-ΔRS is set in step 716, that is, the rich skip amount RSR is decreased and the air-fuel ratio is shifted to the lean side. In steps 717 and 718, RSR is guarded with the minimum value MIN. Further, in step 719, 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 720 and 721, RSL is guarded by the minimum value MAX.

After the RSR and RSL calculated as described above are stored in the RAM 105, this routine ends at step 724.

The RSR and RSL calculated during the air-fuel ratio feedback can be converted into a single value and stored in the backup RAM 106, which is also useful for improving the drivability at the time of restart or the like. The minimum value MIN in FIG. 7 is a value at which the transient followability is not impaired, and the maximum value MAX is a value at which the deterioration of drivability due to the air-fuel ratio fluctuation does not change.

FIG. 8 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. RA in step 801
The intake air amount data Q and the rotation speed data Ne are read from M105 to calculate the basic injection amount RAUP. For example TAUP ← α
・ Q / Ne (α is a constant). In step 802, the cooling water temperature data THW is read from the RAM 105 and stored in the ROM 104 1
The warm-up increase value FWL is interpolated by the dimensional map. In step 803, the final injection amount TAU is calculated as TAU ← TAUP ・ FAF ・ (FW
Calculate by L + β) + γ. Note that β and γ are correction amounts that are determined by other operating state parameters. Then
In step 804, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 805, this routine ends.

As described above, when the time corresponding to the injection amount TAU elapses, the flip-flop 109 is reset by the carry-out signal of the down counter 108 and the fuel injection ends.

FIG. 9 is a timing chart for explaining the air-fuel ratio A / F on the upstream side of the catalyst obtained by the flow charts of FIGS. 5, 7 and 8. When the output V ₂ of the downstream O ₂ sensor 15 changes as shown in FIG. 9 (A), the second air-fuel ratio flag F2 changes as shown in FIG. 9 (B). As a result, the downstream O ₂ sensor 15
If the output V ₂ is lean (F2 = “0”), as shown in FIGS. 9 (D) and 9 (E), the rich skip amount RSR is rapidly increased immediately after the inversion, and thereafter gradually increased. Immediately after reversing the lean skip amount RSL, the lean skip amount is sharply decreased and thereafter, the output V _{2 of} the downstream O ₂ sensor 15 is rich (F2 =
If it is “1”), the rich skip amount RSR is sharply reduced immediately after reversal and then gradually decreased, and the rich skip amount RS
Immediately after L is inverted, it is rapidly increased and then gradually increased. When the skip amounts RSR, RSL thus change as shown in FIGS. 9D and 9E, the air-fuel ratio correction coefficient FAF is calculated by the routine shown in FIG. RSL is reflected in the air-fuel ratio correction factor FAF, so
As shown in FIG. 9 (F), the air-fuel ratio A / F on the upstream side of the catalyst (which shows a tendency opposite to that of the air-fuel ratio correction coefficient FAF) is immediately after the output V ₂ (F2) of the downstream O ₂ sensor 15 is reversed. Changes significantly, then changes slightly. As a result, the amplitude of the air-fuel ratio A / F becomes smaller.

When the air-fuel ratio correction coefficient FAF is skip-controlled by a constant value ΔRS according to the output V ₂ (F2) of the downstream O ₂ sensor 15 as in the conventional case, as shown by the dotted line in FIG. The amplitude of the air-fuel ratio A / F becomes large.

In step 708 of FIG. 7, the correction amount ΔRS is reduced by the proportion k (<1), but it may be reduced by subtracting a predetermined amount.

The first air-fuel ratio feedback control is performed every 4 ms, and the second air-fuel ratio feedback control is performed every 512 ms. The air-fuel ratio feedback control is mainly controlled by the upstream O ₂ sensor with good responsiveness. This is because the downstream O ₂ sensor, which has poor responsiveness, is used as a control.

Further, other control constants in the air-fuel ratio feedback control by the upstream O ₂ sensor, such as delay time, integration constant,
The present invention can be applied to a double O ₂ sensor system that corrects the above by the output of the downstream O ₂ sensor, 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, delay time, and integration constant. Further, it is possible to fix a fixed one of the skip amounts RSR and RSL and change only the other, or fix one of delay delay times TDR and TDL and change only the other, or a rich integration constant.
It is also possible to fix one of KIR and lean integration constant KIL 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 rotation speed. However, depending on the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may be calculated.

Furthermore, in the above-described embodiment, the internal combustion engine in which the fuel injection amount is controlled by the fuel injection valve is shown, but the present invention can be applied to a carburetor type internal combustion engine. For example, to control the air-fuel ratio by adjusting the intake air amount of the engine with the electric air control valve (EACV),
The air bleed amount of the carburetor is adjusted by the electric bleed air control valve to control the air-fuel ratio by introducing air into the main passage and the slow passage, and the amount of secondary air sent to the exhaust system of the engine is adjusted. The present invention can be applied to things that are adjusted. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 801 is determined by the carburetor itself, that is, in accordance with the intake pipe negative pressure according to the intake air amount and the rotation speed of the engine. At, the supply air amount corresponding to the final fuel injection amount TAU is calculated.

Furthermore, although the O ₂ sensor is used as the air-fuel ratio sensor in the above-described embodiment, 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, the response speed of the downstream side air-fuel ratio sensor is substantially increased by increasing the amount of change in the air-fuel ratio feedback control constant immediately after the inversion of the output of the downstream side air-fuel ratio sensor, It is possible to prevent a large shift in the air-fuel ratio upstream of the catalyst, and thus to prevent emission deterioration, fuel consumption deterioration, drivability deterioration, and the like.

[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 an O _{2 of a} three-way catalyst. FIG. 4 is a graph for explaining a storage effect, FIG. 4 is an overall schematic view showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention, and FIGS. 5, 7, and 8 are control circuits of FIG. 6 is a timing chart for supplementary explanation of the flow chart of FIG. 5, FIG. 9 is a timing chart of the upstream of the catalyst obtained by the flow charts of FIG. 5, FIG. 7, and FIG. It is a timing chart for explaining an air-fuel ratio. 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.

Claims (7)

[Claims] 1. A first and a second detector, which are provided on an upstream side and a downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, respectively, for detecting a concentration of a specific component in the exhaust gas. And an air-fuel ratio feedback control constant according to the output of the second air-fuel ratio sensor, and from rich to lean or from lean to the target air-fuel ratio of the output of the second air-fuel ratio sensor. Control constant calculation means for increasing the update speed of the air-fuel ratio feedback control constant per unit time after reversal to rich and for decreasing it after reversal, and output of the air-fuel ratio feedback control constant and the first air-fuel ratio sensor Air-fuel ratio correction amount calculation means for calculating the air-fuel ratio correction amount according to the above, and air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount. Ratio control device. 2. The internal combustion engine according to claim 1, wherein the control constant calculation means performs the gradual calculation speed decrease of the air-fuel ratio feedback control constant at a predetermined ratio at predetermined time intervals. Air-fuel ratio controller. 3. The internal combustion engine according to claim 1, wherein the control constant calculation means performs the gradual calculation speed decrease of the air-fuel ratio feedback control constant by a predetermined amount at predetermined time intervals. Air-fuel ratio controller. 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is a skip control constant. 5. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is an integral control constant. 6. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is a delay time. 7. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio feedback control constant is a comparison voltage of the output of the first air-fuel ratio sensor.