JP2569460B2 - 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. _{The present} invention relates to an air-fuel ratio control device for an internal combustion engine that corrects a feedback control constant in air-fuel ratio feedback control using an upstream O ₂ sensor based on outputs of _two sensors.

[Conventional technology]

In general, a basic injection amount of a fuel injection valve is calculated according to an intake air amount (or intake air pressure) and a rotation speed of an engine, and an O ₂ sensor that detects a concentration of a specific component, for example, an oxygen component in the exhaust gas of the engine. The basic injection amount is corrected according to the air-fuel ratio correction coefficient FAF calculated based on the signal, and the actually supplied fuel amount is controlled according to the corrected injection amount. This control is repeated to finally make the air-fuel ratio of the engine converge within a predetermined range. With such air-fuel ratio feedback control, the air-fuel ratio can be controlled within a very narrow range near the stoichiometric air-fuel ratio.Thus, the three-way catalytic converter provided in the exhaust system, that is, the C contained in the exhaust gas,
The digestive ability of the catalytic converter that simultaneously purifies the three harmful components of O, HC, and NO _X can be kept high.

In the above-described air-fuel ratio feedback control (single O ₂ sensor system), the O ₂ sensor for detecting the oxygen concentration is provided in a portion of the exhaust system as close as possible to the fuel chamber, that is, at a portion of the exhaust manifold upstream of the catalytic converter. However, variations in the output characteristics of the O ₂ sensor have hindered the improvement of the air-fuel ratio control accuracy. The causes of the variation in the output characteristics of the O ₂ sensor are as follows.

(1) individual differences of the O ₂ sensor itself; (2) non-uniform mixing of the exhaust gas at the O ₂ sensor due to tolerances in mounting parts such as the fuel injection valve and the exhaust gas recirculation valve to the engine; (3) Changes in the output characteristics of the O ₂ sensor over time or over time.

Also, O Outside ₂ sensor, a fuel injection valve, an exhaust gas recirculation amount, time or secular change of the engine condition such as a tappet clearance, the non-uniformity of mixing of the exhaust gas due to manufacturing variations is changed and expanded There is.

A second O ₂ sensor is provided downstream of the catalytic converter in order to compensate for the variation in the output characteristics of the O ₂ sensor and the variation in components, aging or aging.
First O ₂ in O ₂ catalytic converter upstream from the output of sensor
Double O ₂ sensor system for correcting the delay time in the air-fuel ratio feedback control by the sensor is already known (see JP 55-37562, JP-Sho 58-48755, JP-Sho 58-72647 No.). That is, in the normal single O ₂ sensor system, even if the O ₂ sensor output is changed to the lean signal from the rich signal assumes a fixed time-rich signal, conversely, the O ₂ sensor output is changed to the rich signal from lean signal a certain time even if is subjected to delay processing of regarded as lean signal, thereby, but to stabilize the air-fuel ratio feedback control, double O ₂ sensor system described above, the downstream O a certain time of the delay processing It is variable according to the output of _two sensors. In this case, although the O ₂ sensor provided on the downstream side of the catalytic converter has a low response speed as compared with the upstream O ₂ sensor, it has an advantage that variation in output characteristics is small for the following reason. I have.

(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 an 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. In other words, even if the upstream O ₂ sensor deteriorates, the exhaust gas emission can be minimized by correcting the delay time by the downstream O ₂ sensor. In fact, as shown in FIG. 2, in a single O ₂ sensor system, O ₂
When the output characteristics of the sensor deteriorate, the exhaust emission characteristics are directly affected. On the other hand, in the double O ₂ sensor system, even if the output characteristics of the upstream O ₂ sensor deteriorate, the exhaust emission characteristics do 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]

However, in the above-mentioned double O ₂ sensor system, the control center of the upstream O ₂ sensor deteriorates due to the deterioration of the upstream O ₂ sensor. Therefore, as the delay time increases, the response speed (control frequency) decreases accordingly. There is a problem that control accuracy is reduced.

Also, in FIG. 4 of JP-A-58-72647,
The delay time is guarded by the maximum value,
Although the reduction in response speed can be prevented to some extent, when the delay time reaches the maximum value, the correction of the delay time by the downstream O ₂ sensor is also substantially stopped, and the function of the double O ₂ sensor system is not exhibited. There is.

For example, as shown in FIG. 3A, the deterioration of the upstream O ₂ sensor is relatively light, and the rich delay time TD is regarded as a lean state even if the output of the upstream O ₂ sensor changes from lean to rich.
Even if the output of R and the upstream O ₂ sensor changes from rich to lean, it is considered as rich.
When set to 2 ms, the control frequency of the upstream O ₂ sensor is about 1.3 Hz, whereas as shown in FIG. 3B,
As the upstream O ₂ sensor deteriorates, as a result, when the rich delay time TDR is set to 8 ms, the lean delay time TDL is set to 256 ms.
Thus, the control frequency of the upstream O ₂ sensor is 0.93 Hz, and the response is deteriorated by about 30%, which may cause surging.

[Means for solving the problem]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to prevent a decrease in response speed and to minimize a change in a fluctuation width of an air-fuel ratio correction coefficient to thereby prevent deterioration of drivability and emission of an air-fuel ratio of an internal combustion engine. In providing a control device, the means of which are shown in FIG.

In FIG. 1, upstream and downstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine,
First and second air-fuel ratio sensors for detecting specific component concentrations in exhaust gas are provided respectively. The skip constant calculating means calculates a new skip constant obtained by increasing or decreasing the skip constants RSR and RSL according to the output of the second air-fuel ratio sensor. The air-fuel ratio adjusting means uses this skip constant,
An air-fuel ratio correction amount is calculated according to the output of the first air-fuel ratio sensor. The calculation of the new skip constant by the skip constant calculation means gradually increases the rich skip constant RSR and gradually decreases the lean skip constant RSL,
Conversely, when the output of the second air-fuel ratio sensor is rich,
The rich skip constant RSR is gradually reduced and the rich skip constant RSL is gradually increased.

[Action]

According to the above-described means, if the output of the downstream air-fuel ratio sensor is lean, the rich skip amount is gradually increased by a predetermined value, and the lean skip amount is gradually decreased by the same amount. The fuel ratio is shifted to the rich side, and conversely,
If the output of the downstream air-fuel ratio sensor is rich, the lean skip amount is gradually increased by a predetermined value and the rich skip amount is gradually decreased by the same amount, so that the air-fuel ratio is shifted to the lean side. You. As a result, in the present invention, since the ratio of the increase / decrease of the rich skip amount and the lean skip amount is the same, the skip amount when the set air-fuel ratio is changed does not become large, and the air-fuel ratio becomes rough from lean to lean. The total width of the skip amount from the rich to the rich can be made constant, the change in the fluctuation width of the air-fuel ratio correction coefficient can be minimized, and the drivability and emission are improved.

〔Example〕

 Hereinafter, embodiments of the present invention will be described 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 an intake passage 2 of an engine main body 1. The air flow meter 3 directly measures the amount of intake air, and has a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to the A / D converter 101 with built-in multiplexer in the control circuit 10.
Is supplied to 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 the 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 a fuel supply system to an 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 detects the temperature THW of the cooling water.
Generates an electric signal of an analog voltage corresponding to. This output is also supplied to the A / D converter 101.

Three harmful components HC in the exhaust gas downstream of the exhaust system from the exhaust manifold 11, CO, catalytic converter 12 housing the three-way catalyst that simultaneously purifies NO _X is provided.

A first O ₂ sensor 13 is provided in the exhaust manifold 11, that is, upstream of the catalytic converter 12, and a second O ₂ sensor 15 is provided in an 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 13,1
5 generates an output voltage which differs depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio in the A / D converter 101 via a buffer circuit (not shown) of the control circuit 10.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface 10
2.In addition to CPU103, ROM104, RAM105, backup RAM10
6. A clock generation circuit 107 and the like are provided. Note that the backup RAM 106 is directly connected to a battery (not shown), so that even if an ignition switch (not shown) is turned off, the stored contents of the backup RAM 106 do not disappear.

In the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110
Is to control the 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 its carry-out terminal finally becomes “1” level, the flip-flop 109 is reset and the drive circuit 110 is reset.
Stops the energization of the fuel injection valve 7. 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 6 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 an interruption of the crank angle sensor 6 at every 30 ° C.
It is stored in a predetermined area of M105.

FIG. 5, FIG. 7A, FIG. 7B, FIG.
This will be described with reference to the flowchart of FIG.

Figure 5 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 501, the upstream O ₂ of the air-fuel ratio by the sensor loop (feedback) condition is determined whether or not satisfied. During engine start, during fuel increase operation after start, during warm-up increase operation, during power increase operation, during lean control, upstream side
When the O ₂ sensor is in the inactive state or the like, the closed loop condition is not satisfied in any case, and in other cases, the closed loop condition is satisfied. The determination of the active / inactive state of the upstream O ₂ sensor is performed by the RAM 105.
This is performed by reading out the water temperature data THW and determining whether THW ≧ 70 ° C. once or determining whether the output level of the upstream O ₂ sensor has once increased or decreased. If the closed loop condition is not satisfied, the routine proceeds to step 517, where the air-fuel ratio correction coefficient FAF is set to 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 502.

In step 502, V ₁ is determined whether or not the comparison voltage V _R1 for example 0.45V or less uptake, at step 503 the output V ₁ of the upstream O ₂ sensor 13 converts A / D, that is, the air-fuel ratio Determine whether it is rich or lean. If lean (V ₁ ≦ V _R1), the delay counter CDLY 1 is subtracted at step 504, to guard the delay counter CDLY minimum value TDR in step 505 and 506. Note that the minimum value TDR is a rich delay time for maintaining the determination that the output is the lean state even when the output of the upstream O ₂ sensor changes from lean to rich, and is defined as a negative value. . On the other hand, rich (V ₁ >
If V _R1 ), in step 507 the delay counter CDLY
Is added to the delay counter C at steps 508 and 509.
Guard DLY with maximum value TDL. Note that the maximum value TDL is a lean delay time for holding a determination that the output is in a rich state even when there is a change from rich to lean in the output of the upstream O ₂ sensor, and is defined as a positive value. .

Here, the reference of the delay counter CDLY is set to 0, and CDLY
When ≧ 0, the air-fuel ratio after the delay processing is regarded as rich, and CD
When LY <0, the air-fuel ratio after the delay processing is regarded as lean.

In step 510, it is determined whether or not the sign of the delay counter CDLY 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 inverted, in step 511, whether the air-fuel ratio is changed from rich to lean,
Determine whether the transition is from lean to rich. If the transition is from rich to lean, then at step 512, FAF ← FAF + RSR
In contrast, if the inversion is from lean to rich, in step 513, FAF is reduced in a skipping manner as FAF-FAF-RSL. That is, skip processing is performed.

If the sign of the delay counter CDLY has not been inverted at step 510, integration processing is performed at steps 514, 515, 516. That is, at step 514, it is determined whether or not CDLY <0, and if CDLY <0 (lean), the FAF is determined at step 515.
If ← FAF + KI, on the other hand, if CDLY ≧ 0 (rich), then at step 516, FAF ← FAF−KI. Where the integration constant K
I is set sufficiently smaller than the skip constant RSR (RSL), that is, KI << RSR (RSL). Therefore, step 515 gradually increases the fuel injection amount in the lean state (CDLY <0), and step 516 gradually reduces the fuel injection amount in the rich state (CDL ≧ 0).

The air-fuel ratio correction coefficient FAF calculated in steps 512, 513, 515, 516 is a minimum value, for example, 0.8 and a maximum value, for example, 1.2.
In this way, if 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 with that value to prevent over-rich or over-lean. prevent.

The FAF calculated as described above is stored in the RAM 105, and this routine ends in step 518.

FIG. 6 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. Rich as shown in FIG. 6 by the output of the upstream O ₂ sensor 13 (A), when the air-fuel ratio A / F is obtained, the delay counter CDLY is
As shown in FIG. 6 (B), the count is incremented in the rich state and is counted down in the lean state. As a result, as shown in FIG. 6 (C), a delayed air-fuel ratio signal A / F '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 'is the time after being held lean only the rich delay time (-TdR) It changes to the rich at t _2. Even if the change the air-fuel ratio A / F from rich to lean at time t _3,
The delayed air-fuel-fuel ratio signal A / F 'is changed to a lean at time t ₄ after being held rich only equivalent lean delay time TDL. However, when the air-fuel ratio signal A / F is reversed in a shorter period of time than the rich delay time (-TdR) as the time _{t 5, t 6, t 7} , takes time delay counter CDLY crosses the reference value 0 as a result, the air-fuel ratio signal a / F after the delay is reversed at time t _8. That is, the air-fuel ratio signal A / F 'after the delay processing is more stable than the air-fuel ratio signal A / F before the delay processing. Thus, the stable air-fuel ratio signal A / F ′ after the delay processing
Based on this, the air-fuel ratio correction coefficient FAF shown in FIG. 6 (D) is obtained.

If the delay times TDR and TDL are set appropriately, the upstream O
The control air-fuel ratio of the air-fuel ratio feedback control by the _two sensors 13 can be shifted to the rich side or the lean side. For example, if rich delay time (-TDR)> lean delay time (TDL) is set, the control air-fuel ratio can shift to the rich side, and conversely, lean delay time (TDL)> rich delay time (-TDR). If so, the control air-fuel ratio can shift to the lean side. That is,
Delay time in accordance with the output of the downstream O ₂ sensor 15 TDR, can control the air-fuel ratio by correcting the TDL. However,
In this case, as described above, as the delay time increases, the response speed (control frequency) decreases. Therefore, in the present invention, the delay time TDR, although TDL are variable, the adjustment is auxiliary, the upstream O ₂ sensor 13 air-fuel ratio shift to the feedback control the air-fuel ratio richer or leaner by the This is mainly performed by making the skip amounts RSR and RSL variable. 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 reduced, the control air-fuel ratio can be shifted to the rich side. Further, if the lean skip amount RSL is increased, the control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount RSR is reduced, the control air-fuel ratio can be shifted to the lean side. Accordingly, the air-fuel ratio can be controlled by correcting the rich skip amount RSR and the lean skip amount RSL in accordance with the output of the downstream O ₂ sensor. In addition, the skip amount
Only when RSR or RSL exceeds the maximum value MAX, the delay time TDR or TDL is increased by the amount by which the skip amount RSR or RSL is limited by the maximum value MAX, thereby adjusting the control center of the air-fuel ratio.

Figure 7A is a second air-fuel ratio feedback control routine for calculating the skip amounts RSR, RSL and the delay time TDR, TDL in accordance with the output of the downstream O ₂ sensor 15 is executed at predetermined time, for example 1s . In step 701, the upstream O ₂
It is determined whether a closed loop condition of the air-fuel ratio by the sensor is satisfied. This step is substantially the same as step 501 of FIG. 5, O ₂ sensor activation determination and the like are different.

If the closed loop condition is not satisfied, the process proceeds to step 722 to 725, the skip amounts RSR, RSL, TDR, constant value TDL RSR _o, RSL _o, T
DR _o and TDL _o . For example, RSR _o = 5% / s RSL _o = 5% / s TDR _o = −12 (corresponding to 48 ms) TDL _o = 6 (corresponding to 24 ms).

If the closed-loop condition is satisfied, the process proceeds to step 702, whether the downstream O ₂ output voltage V ₂ of the A / D conversion to the incorporation of the sensor 15, V ₂ is the comparison voltage V _R2 eg 0.55V or less at step 703 Is determined. That is, it is determined whether the air-fuel ratio is rich or lean. Note that the comparison voltage V _R2 in step 703 is determined by taking into account the output characteristics due to the influence of raw gas and the output characteristics due to the difference in the speed of deterioration because each O ₂ sensor is located before and after the catalyst, as shown in FIG. higher is set than the comparison voltage V _R1 at the step 502.

When lean (V ₂ ≦ VR ₂ ), in step 704, RSR ← RSR + ΔRS. However, ΔRS is a constant value, for example, 0.5
% / S. By repeating this, the air-fuel ratio is shifted to the rich side by gradually increasing the rich skip amount RSR. In step 705, it is determined whether or not the RSR has exceeded a maximum value MAX (for example, equivalent to 10%), that is, whether or not RSR> MAX. If RSR ≦ MAX, the process proceeds to step 710. On the other hand, if RSR> MAX, at step 706, RSR ← MAX is set, and the rich skip amount RSR is guarded at the maximum MAX. When step 706 is executed in this manner, the correction of the air-fuel ratio to the rich side is limited accordingly, so that in step 707, the rich delay time TDR is set to TDR ← TDR−ΔTD. However, ΔTD is a constant value, for example, 4 ms /
s. Further, in step 708, the lean delay time
Let TDL be TDL ← TDL−ΔTD. That is, the rich delay time (-TDR) is gradually increased, and the lean delay time TDL is gradually decreased, thereby shifting the air-fuel ratio to the rich side. In step 709, the delay times TDR and TDL are guarded at the minimum value from the viewpoint of ensuring stable response operation, and guarded at the maximum value from the viewpoint of preventing a decrease in response speed (control frequency). For example,
The rich delay time TDR is from -75 (equivalent to 300 ms) to -2 (8 ms
Equivalent), and the lean delay time TDL
Is guarded in the range of 2 (corresponding to 8 ms) to 75 (corresponding to 300 ms).

Further, in step 710, RSL ← RSL−ΔRS, and this is repeated to obtain the lean skip amount RSL.
Is gradually reduced to further shift the air-fuel ratio to the rich side. In steps 710 and 711, the lean skip amount RSL is guarded by the minimum value MIN (for example, equivalent to 3%).

Further, when rich in step 703 (V ₂ > V _R2 ), in step 713 RSL ← RSL + ΔRS, and by repeating this, the lean skip amount RSL
Is gradually increased to shift the air-fuel ratio to the lean side. In step 714, the RSL is set to the maximum value MAX (for example, equivalent to 10%).
Is determined, that is, whether or not RSL> MAX is satisfied.
If RSL ≦ MAX, proceed to step 711, while RSL> MAX
If so, at step 715, RSL ← MAX is set, and the lean skip amount RSL is guarded at the maximum value MAX. Step like this
When 714 is executed, the correction to the lean side of the air-fuel ratio is limited by that amount.
DR is set to TDR ← TDR + ΔTD, and in step 717, the lean delay time TDL is set to TDL ← TDL + ΔTD. That is, while gradually decreasing the rich delay time (-TDR), gradually increasing the lean delay time TDL,
Thereby, the air-fuel ratio is shifted to the lean side. Steps
In step 718, the delay times TDR and TDL are guarded by the minimum value and the maximum value as in step 709.

Further, in step 719, RSR ← RSR−ΔRS, and this is repeated to obtain the rich skip amount RSR.
Is gradually reduced to further shift the air-fuel ratio to the lean side. In steps 720 and 721, the rich skip amount RSR is guarded by the minimum value MIN.

After the RSR, RSL, TDR, and TDL calculated as described above are stored in the RAM 105, the routine ends in step 726.

Note that the minimum value MIN in FIG. 7A, for example, a value equivalent to 3% is a level at which the transient followability is not impaired.
The maximum value MAX, for example, a value equivalent to 10%, is a level at which drivability does not deteriorate due to air-fuel ratio fluctuation.

Thus, according to the routine of Figure 7A, if the output of the downstream O ₂ sensor 15 is lean, the rich skip amount RSR
Is gradually increased, and the lean skip amount RSL is gradually reduced, whereby the air-fuel ratio is shifted to the rich side. Furthermore, when the rich skip amount RSR reaches the maximum value MAX, the lip skip amount RSR is guarded at the maximum value MAX, and the air-fuel ratio can be further shifted to the rich side by correcting the delay times TDR and TDL. ing. On the other hand, if the rich output of the downstream O ₂ sensor 15 is increased lean skip amount RSL is gradually and is decreased rich skip amount RSR is gradually Thus, the air-fuel ratio is shifted to the lean side. Furthermore, when the lean skip amount RSL reaches the maximum value MAX, the lean skip amount RSL is guarded at the maximum value MAX, and the air-fuel ratio can be further shifted to the lean side by correcting the delay times TDR and TDL. ing.

FIG. 7B shows a modification of FIG. 7A. In FIG. 7B,
7A, steps 727, 728, 20704 'to 710', 71
3 'to 719' are added. That is, when it is determined in step 703 that the engine is lean (V ₂ ≦ VR ₂ ), it is determined in step 727 whether or not the engine is the first lean operation, that is, whether or not a change point from rich to lean is determined. If it is the first lean, RSR ← RSR + ΔRS ′ in step 704 ′. Here, ΔRS ′ is a constant value, and ΔRS ′ >> ΔRS. That is, the RSR is increased in a skip manner, and in steps 705 'and 706', the RSR is guarded at the maximum value MAX as in steps 705 and 706. In steps 707 'and 708', TDR ← TDR−ΔTD ′ TDL ← TDL−ΔTD ′ where ΔTD ′ is a constant value and ΔTD ′ >> ΔTD. That is, the rich delay time (-TDR) is increased in a skip manner, and the lean delay time TDL is reduced in a skip manner, thereby shifting the air-fuel ratio to the rich side. In step 709 ', the delay time is
Guard TDR and TDL with minimum and maximum values. Further, at step 710, RSL is decreased stepwise as RSL ← RSL−ΔRS ′, and at steps 711 and 712, the RSR is guarded with the minimum value MIN. When it is determined in step 703 that the air conditioner is rich (V ₂ > V _R2 ), step 728
It is determined whether or not is the first rich state, that is, whether or not it is a transition point from lean to rich. If it is the first rich, RSL ← RSL + ΔRS ′ in step 713 ′. That is, the RSL is increased in a skip manner, and in steps 714 'and 715', the RSL is guarded at the maximum value MAX, as in steps 714 and 715. In steps 714 'and 715', TDR ← TDR + ΔTD ′ TDL ← TDL + ΔTD ′, that is, the rich delay time (−TDR) is reduced in a skipping manner, and the lean delay time TDL is increased in a skipping manner. As a result, the air-fuel ratio is shifted to the rich side. In step 718 ′, the delay time is the same as in step 718.
Guard TDR and TDL with minimum and maximum values. Further, in step 719 ', RSR is reduced stepwise as RSR ← RSR-ΔRS', and in steps 720 and 721, the RSL is guarded with the minimum value MIN.

Thus, for the first lean at step 727,
And in the case of the first rich in step 728, the skip amounts RSR and RSL are skip-controlled, and further, the skip amount RS
When R and RSL are skip-controlled, the skip amounts RSR and RSL
Reaches the maximum value MAX, the delay times TDR and TDL are skip-controlled, while if not the first lean at step 727 and the first rich at step 728, the skip amounts RSL and RSR and the delay time TDR , TDL are integrated and controlled as in the case of FIG. 7A. As a result, the transient followability of the skip amounts RSR and RSL is improved.

Furthermore, FAF, RS calculated during air-fuel ratio feedback
R, RSL, TDR, TDL are once other values FAF ', RSR', RSL ', TDR', T
It can be converted to DL 'and stored in the backup RAM 106, which is useful for improving drivability at the time of restart or the like.

FIG. 8 shows an injection amount calculation routine which is executed at every predetermined crank angle, for example, every 360 ° CA. At step 801, the intake air amount data Q and the rotation speed data Ne are read from the RAM 105 to calculate the basic injection amount TAUP. For example, TA
UP ← KQ / Ne (K is a constant). RAM 105 in step 802
Further, the cooling water temperature data THW is read out, and the warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in the RAM 104. This warm-up increase value FWL is, as shown in the figure, the current cooling water temperature THW.
Is set so as to become smaller as the value rises.

In step 803, the final injection amount TAU is calculated by TAU ← TAUP · FAF · (1 + FWL + α) + β. Note that α and β are correction amounts determined by other operating state parameters, for example, correction amounts determined by a signal from a throttle position sensor (not shown) or a signal from an intake air temperature sensor, a battery voltage, and the like. Is stored. Next, at 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 has elapsed, the flip-flop 107 is reset by the carry-out signal of the down counter 106, and the fuel injection ends.

FIG. 9 is a timing chart for explaining the air-fuel ratio correction coefficient FAF obtained by the flowcharts of FIGS. 5 and 7B. When the output voltage V ₁ of the upstream O ₂ sensor 13 changes as shown in FIG. 9 (A), of FIG. 5 step 502
The result of the comparison is as shown in FIG. 9 (B). As a result, as shown in FIG. 9 (C), the air-fuel ratio correction coefficient FAF is gradually reduced by the time constant KI when the output of the upstream O ₂ sensor 13 is rich, and when the output of the upstream O ₂ sensor 13 is lean, the time constant is It is gradually increased at KI. When switching between rich and lean, FAF is RSL
Or skip only RSR. In the FIG. 9 (C), Yes and skip amount RSL, the RSR constant, correction by the downstream O ₂ sensor 15 is not considered. The ninth
In FIG. 6C, for simplicity of illustration, no delay processing is performed (for the delayed waveform, refer to the waveform in FIG. 6C). On the other hand, when the output voltage V ₂ of the downstream O ₂ sensor 15 changes as shown in FIG. 9 (D), the comparison result at step 703 of Figure 7B is as the Figure 9 (E). As a result, as shown in FIG. 9 (F), the rich skip amount RSR is gradually increased by the time constant ΔRS when the output of the downstream O ₂ sensor 15 is lean, and by the time constant ΔRS when the output of the downstream O ₂ sensor 15 is lean. The rich skip amount RSR is gradually reduced by ΔRS ′ at times t ₁ , t ₃ , and t ₅ when the rich and lean are inverted. Moreover, the rich skip amount RSR is at time t ₂ reaches the maximum value MAX, as shown in FIG. 9 (H), the rich delay time TDR and the lean delay time TDL is gradually reduced in the time constant Delta] TD. In this case, the lean delay time TDL is kept at the minimum value and does not change.

Also, as shown in FIG. 9 (G), the lean skip amount
RSL, the output of the downstream O ₂ sensor 15 is gradually reduced by the constant ΔRS time if lean, gradually increased in constant ΔRS time if lean, also reversed when t ₁ between the rich and lean,
At t ₃ and t ₅ , the lean skip amount RSL is skip-controlled by ΔRS ′. Furthermore, the lean skip amount RSR is the maximum value M
At time t ₄ reaches the AX, as shown in FIG. 9 (H),
Rich delay time TDR and lean delay time TDL have time constant Δ
It is gradually increased by TD. In this case, the rich delay time TDL is held at the maximum value and does not change.

Also, when the downstream O ₂ sensor 15 reverses between rich and lean,
At t ₁ , t ₃ , and t ₅ , the rich delay time TDR and the lean delay time TDL are also skipped by ΔTD ′ as shown in FIG. 9 (H).

Figure 9 (F), (G), as shown in (H), the skip amount RSR, RSL, delay time TDR, the TDL is changed in accordance with the output of the downstream O ₂ sensor 15, FIG. 9 (C) The air-fuel ratio correction coefficient FAF changes as shown by the solid line in FIG. 9 (I).
The dotted line in FIG. 9 (I) is the same as the solid line in FIG. 9 (C).

In the case of the routine in FIG. 7A, FIG.
Although there is no change in the skip amounts ΔRS ′ and ΔTD ′ in (G) and (H), the air-fuel ratio correction coefficient FAF is shown in FIG.
Are similar to those shown in FIG.

Thus, the delay times TDR with mainly variably controlled skip amounts RSR, the RSL in accordance with the output of the downstream O ₂ sensor 15, TDL
Accordingly, the control center of the air-fuel ratio correction coefficient FAF can be made variable by performing the variable control, so that the control center of the air-fuel ratio can be made variable.

The first air-fuel ratio feedback control is performed every 4 ms.
Also, the reason why the second air-fuel ratio feedback control is performed every 1 s is that the air-fuel ratio feedback control is mainly performed by the upstream O ₂ sensor with good responsiveness, and the downstream O ₂ sensor with poor responsiveness. This is because the control is performed in accordance with the control.

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

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 supply amount to the intake system is controlled by the fuel injection valve 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 supply amount corresponding to the basic injection amount TAUP in step 801 in FIG. 8 is determined by the carburetor itself,
That is, it is determined according to the intake-air negative pressure according to the intake air amount and the rotational speed of the engine, and at step 803 in FIG. 8, 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-described embodiment is constituted by a microcomputer, that is, a digital circuit, it may be constituted by an analog circuit.

〔The invention's effect〕

FIG. 10 is a graph for explaining the effect of the present invention. That is, when there is no deterioration of the upstream air-fuel ratio sensor and there is no deviation of the control center of the air-fuel ratio A / F, the control frequency is almost 2 Hz. If the upstream air-fuel ratio sensor deteriorates and the control center of the air-fuel ratio A / F deviates by 10%, if the air-fuel ratio deviation is corrected by correcting the delay time as in the past, the control frequency becomes approximately 1.3 Hz. On the other hand, when the air-fuel ratio deviation is corrected by the correction of the skip amount and the delay time as in the present invention, the control frequency becomes approximately 1.8 Hz.

Thus, according to the present invention, if the output of the downstream air-fuel ratio sensor is lean, the rich skip amount is gradually increased by a predetermined value, and the lean skip amount is gradually decreased by the same amount. Therefore, the air-fuel ratio is shifted to the rich side. Conversely, if the output of the downstream air-fuel ratio sensor is rich, the lean skip amount is gradually increased by a predetermined value, and the rich skip amount is gradually increased by the same amount. Therefore, the air-fuel ratio is shifted to the lean side. As a result, in the present invention, since the ratio of the increase / decrease of the rich skip amount and the lean skip amount is the same, the skip amount when the set air-fuel ratio is changed does not become large, and the air-fuel ratio becomes rough from lean to lean. This can be solved by making the total width of the skip amount from the rich to the rich constant, and improving the drivability and emission by minimizing the change in the fluctuation width of the air-fuel ratio correction coefficient.

[Brief description of the drawings]

FIG. 1 is a 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 FIGS. 3A and 3B are O ₂ sensors. FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention, and FIGS. 5, 7A, 7B, and 8 are FIGS. 6 is a timing chart for supplementary explanation of the flowchart of FIG. 5, and FIG. 9 is a timing chart for supplementary explanation of the flowcharts of FIGS. 6 and 7B. FIG. 10 is a graph for explaining the effect of the present invention. 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 (first) O ₂ sensor, 15
... downstream (second) O ₂ sensor.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takatoshi Masui 1 Toyota Town Toyota City Toyota Motor Corporation (72) Inventor Toshiyasu Katsuno 1 Toyota Town Toyota City Toyota Motor Corporation 72 Inventor Toshio Tanahashi 1 Toyota Town, Toyota City Inside Toyota Motor Corporation (56) Reference JP-A-58-72647 (JP, A) JP-A-54-33916 (JP, A) JP-A-61-65041 ( JP, A) JP-A-61-185634 (JP, A) JP-A-61-215434 (JP, A) JP-B-57-3815 (JP, B2)

Claims (2)

(57) [Claims] A first and a second air-fuel ratio sensor for detecting a concentration of a specific component in exhaust gas is provided upstream and downstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine. When the output of the first air-fuel ratio sensor indicates rich or lean, an air-fuel ratio correction coefficient (FAF) is corrected by an integration constant (KI) as an air-fuel ratio feedback constant, and the first air-fuel ratio is corrected. When the output of the fuel ratio sensor is inverted, the air-fuel ratio correction coefficient (FAF) is corrected by a skip constant (RSR, RSL) as an air-fuel ratio feedback constant, and the output of the second air-fuel ratio sensor is used as the first air-fuel ratio sensor. An air-fuel ratio control device for compensating for variations in output characteristics and changes over time, wherein a new skip constant is calculated by increasing or decreasing the skip constants (RSR, RSL) according to the output of the second air-fuel ratio sensor. S An air-fuel ratio adjusting unit that calculates an air-fuel ratio correction amount in accordance with an output of the first air-fuel ratio sensor using the skip constant. When the output of the air-fuel ratio sensor is lean, the skip constant (RSR) of the air-fuel ratio correction amount when the output of the first air-fuel ratio sensor is inverted from rich to lean is gradually increased (step 704). The skip constant (RSL) of the air-fuel ratio correction amount when the output of the first air-fuel ratio sensor is inverted from lean to rich is gradually reduced (step 710).
When the output of the second air-fuel ratio sensor is rich, the skip constant (RSR) of the air-fuel ratio correction amount when the output of the first air-fuel ratio sensor is inverted from rich to lean is gradually reduced (step 719) and gradually increasing the skip constant (RSL) of the air-fuel ratio correction amount when the output of the first air-fuel ratio sensor is inverted from lean to rich (step 713). Fuel ratio control device. 2. When the output of the second air-fuel ratio sensor is inverted from rich to lean, the skip constant calculating means is configured to output the air-fuel ratio when the output of the first air-fuel ratio sensor is inverted from rich to lean. Skip constant (RSR) for fuel ratio correction amount
And the skip constant (RSL) of the air-fuel ratio correction amount when the output of the first air-fuel ratio sensor is changed from lean to rich is skipped (step 710 ') (step 710'). ') Conversely, when the output of the second air-fuel ratio sensor is inverted from lean to rich, the skip constant of the air-fuel ratio correction amount when the output of the first air-fuel ratio sensor is inverted from rich to lean (RS
R) is skipped (step 719 '), and the skip constant (RSL) of the air-fuel ratio correction amount when the output of the first air-fuel ratio sensor is inverted from lean to rich is increased (step 719'). The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein step 713 ').