JPH07189778A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To improve a conversion ratio of a catalyst by detecting a catalyst temperature, and shifting a control average air-fuel ratio to a rich side when the catalyst temperature is not a specified estimated value. CONSTITUTION:A calculation means 35 calculates reference proportional partsPR, PL to be added at an inversion time, which serve for agreement of a control average air-fuel ratio with an air-fuel ratio to optimize a coversion ratio of a catalyst. A calculation means 36 calculates proportional part correction rates FPR, FPL for shifting the control average air-fuel ratio to a rich side when a detected value of a catalyst temperature is not an estimated temperature Tso. The reference proportional parts PL, PR are corrected by using the proportional part correction rates FPR, FPL. The corrected proportional parts are calculated by a calculation means 37. A renewal means 38 renews an air-fuel ratio feedback correction rate alpha by using the proportional parts and reference integration parts IL, IR.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio control system.

[0002]

2. Description of the Related Art In a so-called three-way catalyst system, since the conversion rates of exhaust three components (CO, HC, NOx) are all increased, the air-fuel ratio in the exhaust passing through the catalyst is centered around the theoretical air-fuel ratio. The air-fuel ratio is corrected by feedback so that it falls within a narrow range (see Automotive Engineering, June 1991, page 45 to page 48, issued by Japan Railway Company).

In the feedback correction in this case, the air-fuel ratio is swung by a certain width as the proportional amount and the integral amount as the update amount of the air-fuel ratio feedback correction coefficient α, and the exhaust air-fuel ratio is inverted from the lean side to the rich side, for example. Immediately after that, the proportional amount P _R is subtracted (proportional amount P _L is added immediately after reversing from the rich side to the lean side) so that the air-fuel ratio returns well in the opposite direction and then the air-fuel ratio The control is stabilized by subtracting a small integral value I _R (reverse inversion) (adding an integral part I _L after the proportional amount P _L ).

[0004]

By the way, the air-fuel ratio for obtaining the optimum conversion of the catalyst varies depending on the catalyst temperature.

However, in the above apparatus, since the proportional components P _R and P _L and the integral components I _R and I _L are matched with a certain assumed catalyst temperature, the actual catalyst temperature is deviated from the assumed temperature. If there is a deviation, the conversion rate of the catalyst cannot be optimized.

Therefore, the object of the present invention is to improve the conversion rate of the catalyst by detecting the catalyst temperature and shifting the control average air-fuel ratio to the rich side when the catalyst temperature deviates from a predetermined assumed temperature. And

[0007]

A first invention, as shown in FIG. 20, is a means 31 for detecting the temperature of a catalyst and a sensor 32 for detecting the oxygen concentration in the exhaust gas flowing through the catalyst.
And a means 33 for determining whether the exhaust air-fuel ratio is inverted from one of the rich side and the lean side to the other side or is continuing on the same side based on the sensor detection value, From the judgment result, it is a basic integral amount added when continuing on the same side (for example, I _R when continuing on the rich side and I _L when continuing on the lean side), and optimizes the control average air-fuel ratio and the conversion rate of the catalyst. Means 34 for calculating a basic integral for matching the air-fuel ratio for the predetermined assumed temperature Tso
Based on the judgment result, the basic proportional amount added at the time of reversal (for example, P _R when reversing to the rich side, P _L when reversing to the lean side), and the control average air-fuel ratio and the conversion rate of the catalyst are optimized. Means 35 for calculating a basic proportional portion for making the air-fuel ratio to match the assumed temperature Tso, and shifting the control average air-fuel ratio to the rich side when the detected value of the catalyst temperature deviates from the assumed temperature Tso. A means 36 for calculating a proportional correction amount (for example, FPR for P _{R and} FPL for P _L ) and a proportional correction amount FPR, FPL for correcting the basic proportional amounts P _L , P _R Means 37 for calculating minutes
And a means 38 for updating the air-fuel ratio feedback correction amount α using the proportional component and the basic integral components I _L and I _R, and the basic injection amount Tp corresponding to the operating condition signal with the air-fuel ratio feedback correction amount α. A means 39 for correcting the fuel injection amount and calculating the fuel injection amount, and a device 40 for supplying this fuel to the intake pipe are provided.

As shown in FIG. 21, the second aspect of the present invention is a means 31 for detecting the temperature of the catalyst, a sensor 32 for detecting the oxygen concentration in the exhaust gas flowing through the catalyst, and an exhaust gas based on the sensor detection value. A means 33 for determining whether the air-fuel ratio is inverted from one of the rich side and the lean side to the other side or is continuing the same side, and a basic proportional component added at the time of inversion from this determination result. (For example, P _R when reversing to the rich side, P _L when reversing to the lean side), and the control average air-fuel ratio and the air-fuel ratio for optimizing the conversion rate of the catalyst are set to a predetermined assumed temperature Tso. Means 35 for calculating a basic proportional amount to be matched with each other, and a basic integral amount to be added when the same side is continued from the determination result (for example, I _R when the rich side continues, I _L when the lean side continues). Control average air-fuel ratio and before Means 34 for calculating a basic integral for matching the air-fuel ratio for optimizing the conversion rate of the catalyst at the assumed temperature Tso, and a control average air-fuel ratio when the detected value of the catalyst temperature deviates from the assumed temperature Tso. Correction amount (for example, FIR with respect to I _R ,
Wherein the means 51 for calculating the FIL) against I _L, the integrated amount correction amount FIL, wherein the FIR basic integrated amount I _L, a means 52 for calculating the integrated amount by correcting the I _R, and the integral component Means 53 for updating the air-fuel ratio feedback correction amount α by using the basic proportional components P _L , P _R, and the fuel injection amount by correcting the basic injection amount Tp according to the operating condition signal with this air-fuel ratio feedback correction amount α And a device 40 for supplying this fuel to the intake pipe.

According to a third aspect of the present invention, in the first or second aspect of the invention, the correction is performed so that the shift amount of the control average air-fuel ratio to the rich side increases as the detected value of the catalyst temperature deviates from the assumed temperature Tso. An amount (a proportional correction amount in the first invention, an integral correction amount in the second invention) is calculated according to the detected value of the catalyst temperature.

As shown in FIG. 22, a fourth aspect of the present invention is a means 31 for detecting the temperature of the catalyst, a sensor 32 for detecting the oxygen concentration in the exhaust gas flowing through the catalyst, and an exhaust gas based on this sensor detection value. A means 33 for determining whether the air-fuel ratio is reversed from one of the rich side and the lean side to the other side or is continuing the same side, and a means 33 is added based on this determination result when the same side continues. It is a basic integral amount (for example, I _R when the rich side continues, I _L when the lean side continues), and the control average air-fuel ratio and the air-fuel ratio for optimizing the conversion rate of the catalyst are set to predetermined predetermined temperatures. A means 34 for calculating a basic integral amount to be matched at Tso, and a basic proportional amount P _R added at the time of reversal to the rich side from the determination result for optimizing the control average air-fuel ratio and the conversion rate of the catalyst. Air-fuel ratio and the above A means 61 for delaying a basic proportional amount to be matched at the constant temperature Tso by a predetermined time when the detected value of the catalyst temperature deviates from the assumed temperature Tso, and immediately calculating near the assumed temperature Tso, and the determination. From the result, the basic proportional amount P _L added when reversing to the lean side
And a means 62 for immediately calculating a basic proportional portion for matching the control average air-fuel ratio and the air-fuel ratio for optimizing the conversion rate of the catalyst at the assumed temperature Tso, and the basic proportional portion P _R , A means 63 for updating the air-fuel ratio feedback correction amount α using P _L and the basic integrals I _L , I _R, and the basic injection amount Tp corresponding to the operating condition signal is corrected by this air-fuel ratio feedback correction amount α. Means 3 for calculating the fuel injection amount
9 and a device 40 for supplying this fuel to the intake pipe.

In a fifth aspect based on the fourth aspect, the predetermined time period is set such that the control amount of the control average air-fuel ratio shifts to the rich side as the detected value of the catalyst temperature deviates from the assumed temperature Tso. It is calculated according to the detected value of the catalyst temperature.

A sixth aspect of the invention is the catalyst temperature detecting means 31 according to any one of the first, second, and fourth aspects.
As shown in FIG. 23, is the equilibrium temperature TC of the catalyst in response to an engine operating condition signal (for example, rotation speed and load).
It comprises a means 71 for calculating A and a means 72 for predicting a value that changes with the first-order lag of this equilibrium temperature as the temperature of the catalyst.

[0013]

In the first aspect of the present invention, when the detected value of the catalyst temperature deviates from the predetermined assumed temperature Tso, the proportional correction amount for shifting the control average air-fuel ratio to the rich side is calculated. When P _L and P _R are corrected, the control temperature approaches the air-fuel ratio for obtaining the optimum conversion rate by shifting to the rich side of the control average air-fuel ratio. Therefore, the catalyst temperature becomes the predetermined assumed temperature Tso.
Even when it is out of the range, the conversion rate of the catalyst is improved.

In the second aspect, when the detected value of the catalyst temperature deviates from the assumed temperature Tso, the integral correction amount for shifting the control average air-fuel ratio to the rich side is calculated, and the basic integral I _L is calculated by this integral correction amount. , I _R is corrected, the control average air-fuel ratio shifts to the rich side to approach the air-fuel ratio for obtaining the optimum conversion rate. Therefore, even when the catalyst temperature deviates from the assumed temperature Tso, The conversion rate is improved.

In the third aspect of the present invention, the proportional correction amount and the integral correction amount are detected so that the shift amount of the control average air-fuel ratio to the rich side increases as the detected value of the catalyst temperature deviates from the assumed temperature. When calculated according to the value, the first or second
In addition to the effect of the invention of (1), the proportional correction amount and the integral correction amount can be provided without excess or deficiency at any catalyst temperature.

In the fourth aspect of the invention, the control proportional air-fuel ratio and the air-fuel ratio for optimizing the conversion rate of the catalyst, which is the basic proportional component P _R added at the time of reversal to the rich side, are set to a predetermined assumed temperature Ts.
If the detected value of the catalyst temperature deviates from the assumed temperature Tso, the basic proportional portion to be matched with o is delayed for a predetermined time, and is calculated immediately near the assumed temperature Tso. Shifts to the rich side and approaches the air-fuel ratio for obtaining the optimum conversion rate.

In the fifth aspect of the present invention, the predetermined time is adjusted according to the detected value of the catalyst temperature so that the shift amount of the control average air-fuel ratio to the rich side becomes larger as the detected value of the catalyst temperature deviates from the assumed temperature Tso. When calculated by the above, in addition to the effect of the fourth aspect of the present invention, the predetermined time is given without excess or deficiency at any catalyst temperature.

In the sixth aspect of the invention, when the equilibrium temperature of the catalyst is calculated in response to the engine operating condition signal and the value that changes with the first-order delay of the equilibrium temperature is predicted as the catalyst temperature, the first, second, fourth In addition to the operation of any one of the inventions described above, the catalyst temperature sensor is not necessary, and the cost is reduced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, air sucked from an air cleaner is once stored in a collector section having a constant volume, and then flows into each cylinder through a branch pipe. An injector 4 is provided in the intake port of each cylinder, and fuel is intermittently injected from the injector 4 in synchronization with engine rotation. The air-fuel mixture formed from the injected fuel and air is compressed by the piston in the combustion chamber and burns with the help of sparks emitted from the spark plug.

The longer the injection time from the injector 4, the larger the injection amount, and the shorter the injection time, the smaller the injection amount. The richness of the air-fuel mixture, that is, the air-fuel ratio, shifts to the rich side when the fuel injection amount for a fixed amount of intake air increases, and shifts to the lean side when the fuel injection amount decreases. Therefore, if the control unit 21 including a microcomputer determines the basic injection flow rate of fuel so that the ratio with the intake air flow rate is constant, the same air-fuel ratio can be obtained even under different operating conditions. When the fuel injection is performed once per one revolution of the engine, the basic injection pulse width Tp is obtained from the intake air flow rate and the engine speed at that time with respect to the amount of air sucked in one revolution. Usually, the air-fuel ratio determined by Tp (called the base air-fuel ratio) is close to the theoretical air-fuel ratio.

In the exhaust pipe 5, CO discharged from the combustion chamber,
A catalyst (three-way catalyst) 6 for treating three harmful components such as HC and NOx is provided. The catalyst 6 can efficiently process the harmful three components at the same time only when the exhaust air-fuel ratio is within a narrow range (catalyst window) centered on the stoichiometric air-fuel ratio. In order to keep the air-fuel ratio within this range, the control unit 21 feedback-corrects the fuel injection amount from the injector 4 based on the output of the O ₂ sensor 12 provided upstream of the catalyst 6.

Now, when the catalyst temperature rises, the conversion rate of the catalyst for NOx in the lean region deteriorates, so that H
The air-fuel ratio when the conversion rates of C, CO and NOx are optimally balanced (that is, the air-fuel ratio for obtaining the optimum conversion rate) shifts to the rich side as shown in FIG.
On the other hand, the output of the O ₂ sensor is not constant with respect to all the exhaust temperatures, and when the exhaust temperature becomes low, the output of the O ₂ sensor shifts to the lean side. The lower the temperature, the more it shifts to the lean side.

When these characteristics of both are overlapped, FIG.
As shown in Fig. 5, the deviation between the air-fuel ratio and the control average air-fuel ratio for obtaining the optimum conversion rate becomes larger as the catalyst temperature becomes lower, and conversely, the deviation becomes larger even when the catalyst temperature becomes higher. There is. In FIG. 4, the temperature Tso at which the control average air-fuel ratio and the air-fuel ratio for obtaining the optimum conversion rate are exactly the same is the assumed temperature when the proportional component and the integral component are matched in the conventional device.

Therefore, the actual catalyst temperature is the assumed temperature T.
When it is different from so, the control average air-fuel ratio deviates to the lean side from the air-fuel ratio for obtaining the optimum conversion rate, so that the optimum conversion rate cannot be obtained.

In order to cope with this, the control unit 21 detects the catalyst temperature, and when the detected value of the catalyst temperature deviates from the assumed temperature Tso, the control average air-fuel ratio is shifted to the rich side. In FIG. 4, the control average air-fuel ratio shown by the solid line is shifted in the direction of the arrow so that it approaches the air-fuel ratio (shown by the broken line) for obtaining the optimum conversion rate.

The sensor required for this control is an air flow meter 7 which outputs an output according to the flow rate of air taken in from the air cleaner, a signal for each unit crank angle and R.
A crank angle sensor 10 that outputs an ef signal (a reference position signal of the crank angle), an O ₂ sensor 12 that has a characteristic that the output reacts with the oxygen concentration in the exhaust gas and the value suddenly changes at the stoichiometric air-fuel ratio Yes, these signals are idle switch 9, water temperature sensor 11, knock sensor 1
3. The signal from the vehicle speed sensor 14 is input to the control unit 21.

FIG. 5 shows a base flow, which is executed at a constant cycle (for example, 10 ms).

In step 1, it is judged whether the signal from the starter switch (abbreviated as starter SW in the figure) is switched from ON to OFF. If it is switched, it is judged that the engine is starting, and in steps 2 and 3, it is judged from the start. An initial value of 0 is set in the timer value TIMER indicating the elapsed time, and the predetermined value T1 is obtained from the starting water temperature TWINT by referring to the table having the contents of FIG.

The predetermined value T1 is a value that defines the boundary between the temperature range required for warming up the catalyst (for example, 100 to 300 ° C. at the catalyst temperature) and the warming up completion temperature range, and as shown in FIG. 6, the starting water temperature TWINT. Is higher, the value of the predetermined value T1 is smaller. The higher the starting water temperature is, the smaller the value of the predetermined value T1 is because the higher the starting water temperature is, the faster the completion of catalyst warm-up should be.

In step 4, from the engine speed NRPM and the basic injection pulse width (engine load equivalent amount) Tp,
Equilibrium temperature TCA of the catalyst with reference to the map containing
Ask for.

The equilibrium temperature TCA is a catalyst temperature when the operating conditions of the engine are maintained in a steady state, and as shown in FIG. 7, a value that increases as the basic injection pulse width Tp increases and the rotational speed NRPM increases. Is. The specific value may differ depending on the engine model, so it is set by matching.

In steps 5 and 6, it is determined whether both of the following conditions <1> timer value TIMER> predetermined value T1 and <2> cooling water temperature TW> predetermined value (constant value) TW1 are satisfied. When both conditions are satisfied, it is determined that the catalyst warm-up is completed, and the routine proceeds to step 7, where the predicted value TC of the catalyst temperature is TC = TC × K1 + TCA × (1−K1) (1) where K1 ; Calculated by the formula of weighted average coefficient. Equilibrium temperature TCA calculated this time and variable TC
The weighted average value with (TC on the right side represents the previous catalyst temperature predicted value) is newly added to the variable TC. The weighted average value (that is, the value that changes with the first-order lag of the equilibrium temperature) is predicted to be the catalyst temperature. The temperature of the catalyst can be determined by providing a temperature sensor on the catalyst.

If either of the above conditions <1> and <2> is not satisfied, the equilibrium temperature TCA is directly entered in the variable TC in step 9.

When the predicted value of the catalyst temperature is calculated, the value of the flag F2 is set to "0" in step 8, and when the predicted value is not calculated, the value of the flag F2 is set to "1" in step 10. This flag F2 is a flag for knowing whether the catalyst warm-up has been completed, and is used in steps 31 and 37 of FIG. 8 described later.

In step 11, the process proceeds to the subroutine of FIG. 8 and the air-fuel ratio feedback correction coefficient α is updated. Using this air-fuel ratio feedback correction coefficient α, the fuel injection pulse width Ti given to the injector 4 in step 12 is changed to Ti _{= Tp × C O × α +} Ts ... (2) However, C _O; sum Ts of 1 and various correction coefficient; calculated by equation invalid pulse width, and transfers the calculated value to the output register in step 13.

The equation (2) is a general equation including the injection pulse width under various operating conditions. When the air-fuel ratio feedback condition is entered after the engine is warmed up, Ti = Tp × α + Ts (3) Then, the basic injection pulse width Tp is corrected by the air-fuel ratio feedback correction coefficient α.

The basic injection pulse width Tp of the equation (2) is given by the equation of Tp = (Qa / NRPM) × K (4), where Qa is the air flow meter output K and is a constant that determines the base air-fuel ratio. Needless to say.

In addition, for the judgment at the next step 5,
In step 14, the timer value TIMER is incremented by TIMER = TIMER + DT, where DT is the control cycle of FIG. 5 (5).

FIG. 8 (subroutine A in step 11 of FIG. 5) is a flow chart for updating the air-fuel ratio feedback correction coefficient α, which is executed independently of the base flow of FIG. 5 in synchronization with the Ref signal. Synchronizing with the Ref signal is
The fuel injection is Ref signal synchronization, and the system disturbance is also Ref signal synchronization.

At step 21, whether or not the air-fuel ratio feedback condition (abbreviated as F / B condition in the figure) is checked,
If it is not a feedback condition, α is set to 1 in step 22.
Fix at 00%. The air-fuel ratio feedback stop condition is
At the time of start-up, at low water temperature, at idle, when the O ₂ sensor is abnormal, when the rich and lean inversion cycle of the O ₂ sensor exceeds a predetermined value, and the like, feedback conditions are other than these conditions.

In the case of the feedback condition, step 2
In step 3, the O ₂ sensor output ORS1 is AD-converted (analog-digital converted) and captured.

Steps 24, 25, 26, 27, 28,
Reference numeral 29 is a portion for determining whether the exhaust air-fuel ratio is reversed from the rich side to the lean side or vice versa, or when it is continuously on the same side.

At step 24, the sensor output ORS1 is compared with the slice level SL, and if ORS1 <SL, it is judged that the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and at step 25 the flag F1 is set to "0" and ORS1 is set. If .gtoreq.SL, it is judged to be on the rich side, and the flag F1 is set to "1" at step 26. In step 27, flag F
Whether or not the value of 1 has been inverted between the previous time and this time, and when it is inverted, the process proceeds to step 28 and the value of the flag F1 is checked.

If F1 = 0, it is determined that the lean side has been reversed this time, and step 30 is performed. If F1 = 1, it is determined that the rich side has been reversed this time, and the process proceeds to step 36.

At step 30, engine speed NRPM
And the basic injection pulse width Tp, the basic proportional portion P _L is obtained by referring to the map. Similarly, in step 36, the basic proportional portion P _R is obtained by referring to the map.

The basic proportional components P _L and P _R are the estimated temperature TC0.
Is a proportional amount when the control average air-fuel ratio is matched so as to match the air-fuel ratio for obtaining the optimum conversion rate. The values of the basic proportional parts P _L and P _R may be basically the same,
As shown in FIG. 9, the operating region is divided into almost two, and the value of 3 to 6% is set in the low and medium load region, and is set to 1 to 2 in the high load region.
The small value of% is put. This is because the conversion rate of the catalyst increases when the exhaust air-fuel ratio is fluctuated within a certain range by increasing the proportional amount to a certain degree.On the other hand, when the fluctuation range of the exhaust air-fuel ratio is increased, a surge easily occurs. Become. Therefore, in order to prevent a surge from occurring in a region that is not frequently used (that is, a high load region), the proportion is made smaller than that in a low and medium load region that is frequently used. In addition, there is a region where the surge is felt sensitively (called a surge region) in a part of the low and medium load region, and in this region as well, P _L ,
The value of P _R is 1 to 2%.

At steps 31 and 32, it is checked whether both the following conditions are satisfied. <3> F2 = 0. That is, after the catalyst has been warmed up. <4> P _L > P _L 1 The predetermined value P _L 1 is, for example, 2%, and the region satisfying P _L > P _L 1 is the low to medium load region excluding the surge region. Since the catalyst temperature greatly changes in the low and medium load range, the catalyst temperature greatly deviates from the assumed temperature Tso depending on the operating conditions.

If both conditions <3> and <4> are satisfied,
In step 33, the proportional correction amount FPL is obtained from the predicted value TC of the catalyst temperature by referring to the table containing the solid line in FIG. 10, and the air-fuel ratio feedback correction coefficient α is calculated in step 34 using this correction amount FPL. = Α + (P _L + FPL) (6) is updated.

Similarly, in steps 37 and 38, both of the following conditions <5> F2 = 0, <6> P _R > predetermined value (for example, 2%) P _R 1 are satisfied? If both conditions are satisfied, in step 39, the proportional correction amount FP is calculated from the predicted value TC of the catalyst temperature by referring to the table containing the broken line in FIG.
R is obtained, and the air-fuel ratio feedback correction coefficient α is updated in step 40 using this correction amount FPR by the expression α = α- (P _R + FPR) (7).

The reason why the two correction amounts FPL and FPR are set to the respective characteristics shown in FIG. 10 is as follows. From FIG. 4, the estimated temperature T
In order for the control average air-fuel ratio to match the air-fuel ratio for obtaining the optimum conversion rate even at catalyst temperatures other than so, the control average air-fuel ratio is shifted to the rich side, and the shift amount to the rich side is changed. It is necessary to increase the temperature as the catalyst temperature becomes lower than the assumed temperature Tso (even when it becomes higher than the assumed temperature Tso).

Here, from the above, P _L + FPL> P _R + FPR
(That is, FPL> FPR), and the lower the estimated temperature Tso (the estimated temperature Tso
Since the difference between FPL-FPR must be increased as the temperature becomes higher), the characteristics of the two correction amounts FPL and FPR are as shown in FIG.

The temperature at which the control average air-fuel ratio and the air-fuel ratio for obtaining the optimum conversion rate match (that is, the assumed temperature Tso) is always the center position of the catalyst temperature range as shown in FIG. However, it changes as shown in FIGS. 11 and 12 due to the difference in mode (for example, difference between American mode and European mode) and the difference in catalyst position. Further, since the exhaust temperature varies depending on the type of engine, there are differences due to the difference in the type of engine. Therefore, the characteristics of the correction amounts FPL and FPR must be specifically determined in consideration of the mode to be applied, the position of the catalyst, the type of engine, and the like.

If neither of the above conditions <3> and <4> is satisfied, the air-fuel ratio feedback correction coefficient α is calculated in step 35 by the formula α = α + P _L (8) and the above <5> If any one of the conditions <6> is not satisfied, the air-fuel ratio feedback correction coefficient α is updated in step 41 in the same manner as in the conventional case by the expression α = α-P _R (9).

When the conditions <3> and <5> are not satisfied, it means that the catalyst is being warmed up. It is difficult to predict the temperature difference between the O ₂ sensor and the catalyst while the catalyst is warming up, and if a proportional correction is performed using the correction amounts FPL and FPR, an error may occur. Therefore, the proportional correction is not performed. Further, when the conditions of <4> and <6> are not satisfied, it is in the high load region (also in the surge region of the low and medium load region). In the high load region, the value of the basic proportional amount is originally reduced so that the surge does not occur. Therefore, the proportional amount is not increased by the correction using the correction amounts FPL and FPR.

On the other hand, if it is not reversed in step 27, the value of the flag F1 is checked in step 29, and if F1 = 0, it is continuously judged to be on the lean side, the routine proceeds to step 42, and the air-fuel ratio feedback correction coefficient α is α = α + I _L (10) where I _L ; basic integral (constant value), and when F1 = 1, it is continuously determined that it is on the rich side, and α is set to α in step 43. _{= α-I R ... (11} ) However, I _R; updating the same as that of the conventional formula of the basic integral amount (constant value). The values of the basic integrals I _L and I _R may be basically the same.

The operation of this example will be described below. In this example, when the catalyst temperature deviates from the assumed temperature Tso, the proportional proportional correction amount FPL on one side corresponds to the basic proportional component P
_L and the other proportional amount correction amount FPR, the basic proportional amount P _R is corrected to this, and the corrected proportional amount P _L +
When the air-fuel ratio feedback correction amount α is updated with FPL and P _R + FPR as the update amounts, the control average air-fuel ratio shifts to the rich side and approaches the air-fuel ratio for obtaining the optimum conversion rate, so the catalyst temperature Even when the temperature deviates from the assumed temperature Tso, the conversion rate of the catalyst is improved.

Further, the proportional correction amounts FPL and FPR are calculated according to the catalyst temperature so that the shift amount of the control average air-fuel ratio to the rich side increases as the catalyst temperature deviates from the assumed temperature Tso. The proportional correction amounts FPL and FPR can be given without excess or deficiency at any catalyst temperature.

Further, the catalyst temperature is not directly detected by providing a sensor, but the equilibrium temperature TCA of the catalyst is calculated from the engine speed and the engine load equivalent amount.
Since the value that changes with the first-order lag of A is predicted as the catalyst temperature, the catalyst temperature sensor becomes unnecessary, and the cost can be reduced.

FIG. 13 shows the second embodiment and FIG. 8 of the first embodiment.
Accordingly, in step 11 of FIG. 5, the process jumps to the subroutine B of FIG.

In this example, when the catalyst temperature deviates from the assumed temperature Tso, one integral correction amount FIL corresponds to the basic integral I _L , and the other integral correction amount FIR corresponds to this. By correcting the basic integral I _R , the control average air-fuel ratio is made closer to the air-fuel ratio for obtaining the optimum conversion rate.

In FIG. 13, the same steps as those in FIG. 8 are designated by the same numbers, and steps 51 to 56 are different from those in FIG.

In step 51, if the above condition <3> is satisfied, in step 52 the integral correction amount FIL is obtained from the predicted value TC of the catalyst temperature by referring to the table having the solid line in FIG. Then, the air-fuel ratio feedback correction coefficient α is updated by the equation α = α + (I _L + FIL) (12). Similarly, when the condition of <5> is satisfied in step 54, the integral correction amount FIR is referred to in step 55 with reference to the table having the broken line in FIG.
And this correction value is updated by the equation of the air-fuel ratio feedback correction coefficient _{α α = α- (I R +} FIR) ... (13). By adding the integral correction amount FIL to the corresponding basic integral I _L by the equations (12) and (13) and adding the integral correction amount FIR to the corresponding basic integral I _R , the integral Is being corrected.

Since the basic integrals I _L and I _R are constant values, the above conditions <4> and <6> are unnecessary.

In this example, I _L = I _R and the characteristic of FIG. 14 results in I _L + FIL> I _R + FIR, and as in the first embodiment, the control average air-fuel ratio shifts to the rich side for optimum conversion. Approaches the air-fuel ratio to get the rate.

Further, the shift amount of the control average air-fuel ratio to the rich side is determined according to the difference FIL-FIR between the two correction amounts, and the air-fuel ratio difference (to obtain the control average air-fuel ratio and the optimum conversion rate in FIG. 4). The difference in correction amount F
Since the IL-FIR has the characteristics shown in FIG. 14, the integral correction amounts FIL and FIR can be provided without excess or deficiency at any catalyst temperature.

15 and 17 show the third embodiment, FIG. 15 corresponds to FIG. 5 of the first embodiment, and FIG. 17 corresponds to FIG. 8 of the first embodiment. In this example as well, the same steps as those in the first embodiment are designated by the same numbers.

In this example, when the catalyst temperature deviates from the assumed temperature Tso, the proportional average P _R is delayed from being added at the time of reversal to the rich side, whereby the control average air-fuel ratio is shifted to the rich side.

In FIG. 15, the difference from the first embodiment is steps 61, 62 and 63. In step 61, the delay time DLR is obtained from the predicted value TC of the catalyst temperature by referring to the table having the contents of FIG. .

The delay time DLR is a time for delaying the addition of the proportional P _R at the time of inversion to the rich side.

In FIG. 17 (subroutine C of step 63 of FIG. 15), what is different from the conventional case is <A> lean side to rich side inversion and <B> rich continuation.
The case of DLR> 0 will be described first, followed by the case of DLR = 0.

(1) When DLR> 0 <A> At the time of reversal from the lean side to the rich side This is the case where the process proceeds from step 27, 28 to step 71. Looking at the delay time DLR, since DLR> 0, the routine proceeds to step 72, where the initial value 0 is set to the timer value TIMER2, the flag N1 is set to "0" at step 73, and the routine of FIG. 17 is terminated.

Here, the flag N1 is a flag for determining addition of the proportional portion P _R , and when N1 = 0, it is not permitted to subtract the proportional portion P _R. When N1 = 1, the proportional portion P _R is not permitted. Indicates that _R can be subtracted. That is,
Setting N1 = 0 in step 73 means ending without subtracting the proportional amount P _R from the air-fuel ratio feedback correction coefficient α (keeping the air-fuel ratio feedback correction coefficient α at the previous value).

<B> During rich continuation In the case of proceeding from step 27, 29 to step 77, the timer value TIMER2 is compared with the delay time DLR,
While TIMER2 <DLR, in step 78, the timer value TIMER2 is set to TIMER2 = TIMER2 + DT2 (14) However, DT2; increment by the formula of the control period in FIG. View. Since N1 = 0 in <A> above, the routine proceeds to step 80, where the flag N1 is set to "1", and at step 81 the proportional amount P _R is subtracted from the air-fuel ratio feedback correction coefficient α to reduce the air-fuel ratio. The feedback correction coefficient α is updated.

Specifically, referring to the waveform diagram of FIG. 18, the above <A> is, for example, time t1 (or t3, t6).
Is the timing. From this timing, the proportional amount P _R is not subtracted from α and is held at a constant value,
Timer value TIMER2 and delay time DLR at time t1
Wait until the timing of and the value of
_R is deducted.

Note that, as shown in FIG. 19, it is assumed that the air-fuel ratio is reversed to the lean side for some reason while holding (for example, the timing of time t11 or t12) without subtracting the proportional P _R from α. However, since the proportional amount P _L is immediately added, no inconvenience occurs.

(2) When DLR = 0 In this case, the updating of α must be the same as the conventional one.

<A> At the time of reversal from the lean side to the rich side Proceeding from step 27, 28, 71 to step 74,
A predetermined value T that is a sufficiently large value for the timer value TIMER2
2 (T2> DLR) is set, and flag N1 is set in step 75.
After setting "1" to, in step 76, the proportional amount P _R is subtracted from the air-fuel ratio feedback correction coefficient α.

<B> During rich continuation From step 27, 29 to steps 77, 79, 82, the integral I _R is subtracted from the air-fuel ratio feedback correction coefficient α.

When DLR = 0 is also observed in the waveform diagram of FIG. 18, <A> in this case is the timing at time t5, and the proportional P _R is immediately subtracted from α.

In this example as well, the same operational effects as those of the above-described embodiment are produced.

[0081]

According to the first aspect of the present invention, means for detecting the temperature of the catalyst, a sensor for detecting the oxygen concentration in the exhaust gas flowing through the catalyst, and a lean side and a lean side of the exhaust air-fuel ratio based on the sensor detection value are used. One side of the other side to the other side to determine whether it is reversed or the same side, and from this determination result is the basic integral added when the same side continues, the control average A means for calculating a basic integral part for matching the air-fuel ratio and the air-fuel ratio for optimizing the conversion rate of the catalyst at a predetermined assumed temperature, and a basic proportional part added at the time of reversal from the judgment result and a control average A means for calculating a basic proportional portion for matching the air-fuel ratio and the air-fuel ratio for optimizing the conversion rate of the catalyst at the assumed temperature,
A means for calculating a proportional correction amount for shifting the control average air-fuel ratio to the rich side when the detected value of the catalyst temperature deviates from the assumed temperature, and a proportional portion for correcting the basic proportional amount by this proportional correction amount. And means for updating the air-fuel ratio feedback correction amount by using the proportional component and the basic integral component, and the basic injection amount according to the operating condition signal is corrected by the air-fuel ratio feedback compensation amount. Since the means for calculating the injection amount and the device for supplying this fuel to the intake pipe are provided, the catalyst approaches the air-fuel ratio for obtaining the optimum conversion rate by shifting the control average air-fuel ratio to the rich side. Even when the temperature deviates from the predetermined assumed temperature, the conversion rate of the catalyst is improved.

A second aspect of the present invention is a means for detecting the temperature of the catalyst, a sensor for detecting the oxygen concentration in the exhaust flowing through the catalyst, and the exhaust air-fuel ratio on the rich side and the lean side based on the sensor detection value. A means for determining whether one side has been reversed to the other side or is continuing the same side, and a basic proportional amount added at the time of reversal from this determination result, which is the control average air-fuel ratio and the catalyst. A means for calculating a basic proportional portion for matching the air-fuel ratio for optimizing the conversion rate at a predetermined assumed temperature, and a basic integral portion added during continuation on the same side from the determination result as a control average air-fuel ratio. And means for calculating a basic integral for making the air-fuel ratio for optimizing the conversion rate of the catalyst at the assumed temperature, and a control average air-fuel ratio when the detected value of the catalyst temperature deviates from the assumed temperature. Li Means for calculating the integral correction amount to be shifted to the side, means for correcting the basic integral component with this integral component correction amount, and calculating the integral component, and the air-fuel ratio using this integral component and the basic proportional component. Provided are means for updating the feedback correction amount, means for calculating the fuel injection amount by correcting the basic injection amount according to the operating condition signal with this air-fuel ratio feedback correction amount, and a device for supplying this fuel to the intake pipe. Therefore, since the control average air-fuel ratio is shifted to the rich side to approach the air-fuel ratio for obtaining the optimum conversion rate, the conversion rate of the catalyst is improved even when the catalyst temperature deviates from the assumed temperature.

In a third aspect based on the first or second aspect, the correction is performed so that the shift amount of the control average air-fuel ratio to the rich side increases as the detected value of the catalyst temperature deviates from the assumed temperature. Since the amount is calculated according to the detected value of the catalyst temperature, in addition to the effect of the first or second invention, it is possible to give the proportional correction amount or the integral correction amount without excess or deficiency at any catalyst temperature. it can.

In a fourth aspect of the invention, means for detecting the temperature of the catalyst, a sensor for detecting the oxygen concentration in the exhaust gas flowing through the catalyst, and the exhaust air-fuel ratio on the rich side and the lean side based on the sensor detection value are used. A means for determining whether one side is reversed to the other side or whether the same side is continued, and the control average air-fuel ratio which is the basic integral amount added when the same side continues from this determination result. And a means for calculating a basic integral part for making the air-fuel ratio for optimizing the conversion rate of the catalyst at a predetermined assumed temperature, and a basic proportional part added at the time of reversal to the rich side from the judgment result. When the detected value of the catalyst temperature deviates from the assumed temperature by a predetermined time, the basic proportional amount for matching the control average air-fuel ratio and the air-fuel ratio for optimizing the conversion rate of the catalyst at the assumed temperature is delayed. , A means for immediately calculating near the assumed temperature, and an air-fuel ratio for optimizing the control average air-fuel ratio and the conversion rate of the catalyst, which is the basic proportional amount added at the time of reversal to the lean side from the determination result. And a means for immediately calculating a basic proportional amount for making the estimated temperature coincide with each other, a means for updating the air-fuel ratio feedback correction amount by using the basic proportional amount and the basic integral amount, and the air-fuel ratio feedback correction amount. With the means for calculating the fuel injection amount by correcting the basic injection amount according to the operating condition signal and the device for supplying this fuel to the intake pipe, the control average air-fuel ratio is shifted to the rich side and optimized. Approaching the air-fuel ratio for obtaining a high conversion rate.

In a fifth aspect based on the fourth aspect, the shift amount of the control average air-fuel ratio to the rich side increases as the detected value of the catalyst temperature deviates from the assumed temperature.
Since the predetermined time is calculated according to the detected value of the catalyst temperature, in addition to the effect of the fourth aspect of the invention, the predetermined time can be given at any catalyst temperature without excess or deficiency.

In a sixth aspect based on any one of the first, second and fourth aspects, the catalyst temperature detecting means receives the engine operating condition signal and calculates the equilibrium temperature of the catalyst. And means for predicting a value that changes with the first-order lag of the equilibrium temperature as the temperature of the catalyst, in addition to the effect of any one of the first, second, and fourth inventions,
The catalyst temperature sensor becomes unnecessary, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment.

FIG. 2 is a characteristic diagram of an air-fuel ratio for obtaining an optimum conversion rate with respect to a catalyst temperature.

FIG. 3 is a characteristic diagram of a control average air-fuel ratio with respect to exhaust temperature.

FIG. 4 is a characteristic diagram showing an air-fuel ratio for obtaining an optimum conversion rate and a control average air-fuel ratio in an overlapping manner.

FIG. 5 is a flowchart for explaining the base flow of the first embodiment.

FIG. 6 is a characteristic diagram showing table contents of a predetermined value T1.

FIG. 7 is a characteristic diagram showing map contents of an equilibrium temperature TCA.

FIG. 8 is an air-fuel ratio feedback correction coefficient α according to the first embodiment.
5 is a flowchart for explaining the update of the.

FIG. 9 is a characteristic diagram showing map contents of basic proportional components P _L and P _R.

FIG. 10 is a characteristic diagram showing table contents of proportional correction amounts FPL and FPR.

FIG. 11 is a characteristic diagram of another example in which the air-fuel ratio for obtaining the optimum conversion rate and the control average air-fuel ratio are shown in an overlapping manner.

FIG. 12 is a characteristic diagram of another example in which an air-fuel ratio for obtaining an optimum conversion rate and a control average air-fuel ratio are shown in an overlapping manner.

FIG. 13 is a flow chart for explaining updating of the air-fuel ratio feedback correction coefficient α according to the second embodiment.

FIG. 14 is a characteristic diagram showing table contents of integrated correction amounts FIL and FIR.

FIG. 15 is a flowchart for explaining updating of the air-fuel ratio feedback correction coefficient α according to the third embodiment.

FIG. 16 is a characteristic diagram showing table contents of delay time DLR.

FIG. 17 is a flow chart for explaining updating of the air-fuel ratio feedback correction coefficient α according to the third embodiment.

FIG. 18 is a waveform diagram for explaining the operation of the third embodiment.

FIG. 19 is a waveform diagram for explaining the operation of the third embodiment.

FIG. 20 is a diagram corresponding to claims of the first invention.

FIG. 21 is a diagram corresponding to a claim of the second invention.

FIG. 22 is a diagram corresponding to the claim of the fourth invention.

FIG. 23 is a diagram corresponding to the claim of the sixth invention.

[Explanation of symbols]

3 intake pipe 4 injector (fuel supply device) 6 catalyst 7 air flow meter 10 crank angle sensor 12 O ₂ sensor (oxygen concentration sensor) 21 control unit 31 catalyst temperature detection means 32 oxygen concentration sensor 33 reversal / continuation determination means 34 basic integration Calculation means 35 Basic proportional amount calculation means 36 Proportional amount correction amount calculation means 37 Proportional amount calculation means 38 Air-fuel ratio feedback correction amount calculation means 39 Fuel injection amount calculation means 40 Fuel supply device 51 Integral correction amount calculation means 52 Integral amount calculation means 53 air-fuel ratio feedback correction amount calculation means 61 rich side inversion basic proportional amount calculation means 62 lean side inversion basic proportional amount calculation means 63 air-fuel ratio feedback correction amount calculation means 71 equilibrium temperature calculation means 72 catalyst temperature prediction means

Claims (6)

[Claims] 1. A means for detecting the temperature of a catalyst, a sensor for detecting the oxygen concentration in the exhaust flowing through the catalyst, and an exhaust air-fuel ratio of either the rich side or the lean side based on the sensor detection value. Means for determining whether it has been reversed from one side to the other side or is continuing the same side, and from this determination result is a basic integral amount added when the same side continues, and the control average air-fuel ratio and the catalyst A means for calculating a basic integral amount for matching the air-fuel ratio for optimizing the conversion rate at a predetermined assumed temperature, and a basic proportional amount added at the time of reversal from the determination result, that is, the control average air-fuel ratio and the catalyst A means for calculating a basic proportional portion for matching the air-fuel ratio for optimizing the conversion rate at the assumed temperature, and a control average air-fuel ratio shifts to the rich side when the detected value of the catalyst temperature deviates from the assumed temperature. Means for calculating a proportional correction amount, means for correcting the basic proportional amount with the proportional correction amount, and calculating a proportional amount, and an air-fuel ratio feedback correction amount using the proportional amount and the basic integral amount Means for updating the fuel injection amount, means for calculating the fuel injection amount by correcting the basic injection amount according to the operating condition signal with this air-fuel ratio feedback correction amount, and a device for supplying this fuel to the intake pipe. A characteristic engine air-fuel ratio controller. 2. A means for detecting the temperature of the catalyst, a sensor for detecting the oxygen concentration in the exhaust gas flowing through the catalyst, and an exhaust air-fuel ratio of either the rich side or the lean side based on the sensor detection value. Means for determining whether it is reversed from one side to the other side or whether it is continuing on the same side, and from this judgment result is the basic proportional amount added at the time of reversal and the control average air-fuel ratio and the conversion rate of the catalyst are A means for calculating a basic proportional portion for matching the air-fuel ratio for optimization at a predetermined assumed temperature, and a basic integral portion added during continuation on the same side from the determination result, that is, the control average air-fuel ratio and the catalyst A means for calculating a basic integral for matching the air-fuel ratio for optimizing the conversion rate at the assumed temperature, and a control average air-fuel ratio shifts to the rich side when the detected value of the catalyst temperature deviates from the assumed temperature. Means for calculating an integral correction amount, a means for correcting the basic integral with this integral correction amount to calculate an integral, and an air-fuel ratio feedback correction amount using the integral and the basic proportional component. Means for updating the fuel injection amount, means for calculating the fuel injection amount by correcting the basic injection amount according to the operating condition signal with this air-fuel ratio feedback correction amount, and a device for supplying this fuel to the intake pipe. A characteristic engine air-fuel ratio controller. 3. The correction amount is calculated according to the detected value of the catalyst temperature so that the shift amount of the control average air-fuel ratio to the rich side increases as the detected value of the catalyst temperature deviates from the assumed temperature. The air-fuel ratio control device for the engine according to claim 1 or 2. 4. A means for detecting the temperature of the catalyst, a sensor for detecting the oxygen concentration in the exhaust gas flowing through the catalyst, and an exhaust air-fuel ratio of either the rich side or the lean side based on the sensor detection value. Means for determining whether it is reversed from one side to the other side or is continuing on the same side, and from this determination result is a basic integral amount added when the same side continues, and the control average air-fuel ratio and the catalyst A means for calculating a basic integral amount that matches the air-fuel ratio for optimizing the conversion rate at a predetermined assumed temperature, and a basic proportional amount added at the time of reversal to the rich side from the determination result, which is the control average air-fuel ratio. And the air-fuel ratio for optimizing the conversion of the catalyst at the assumed temperature are delayed by a predetermined time when the detected value of the catalyst temperature deviates from the assumed temperature by a predetermined proportional amount, and the assumed A means for immediately calculating near the temperature, and a control average air-fuel ratio and an air-fuel ratio for optimizing the conversion rate of the catalyst, which is a basic proportional component added when reversing to the lean side from the determination result. A means for immediately calculating a basic proportional portion to be matched at the assumed temperature, a means for updating the air-fuel ratio feedback correction amount using these basic proportional portion and the basic integral portion, and an operating condition with this air-fuel ratio feedback correction amount. An air-fuel ratio control apparatus for an engine, comprising: a unit that corrects a basic injection amount according to a signal to calculate a fuel injection amount; and a device that supplies the fuel to an intake pipe. 5. The predetermined time is calculated according to the detected value of the catalyst temperature so that the shift amount of the control average air-fuel ratio to the rich side becomes larger as the detected value of the catalyst temperature deviates from the assumed temperature. The air-fuel ratio control device for an engine according to claim 4, wherein. 6. The catalyst temperature detecting means receives the engine operating condition signal, calculates the equilibrium temperature of the catalyst, and predicts a value that changes with a first-order lag of the equilibrium temperature as the temperature of the catalyst. The air-fuel ratio control device for an engine according to any one of claims 1, 2 and 4, wherein: