JPH09222010A - Engine exhaust purification device - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To maximize the early warm-up effect of the first catalyst. SOLUTION: The determining means 21 determines whether or not a first catalyst provided in an exhaust pipe has been activated, and based on the determination result, before the first catalyst is activated, the exhaust air-fuel ratio is rich or lean. The air-fuel ratio control means 22 controls the air-fuel ratio so that it alternates between and. In this case, the setting means 23 sets the magnitude of the amplitude of the exhaust air-fuel ratio which alternates between the rich side and the lean side, according to the oxygen storage capacity of the first catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust purification system.

[0002]

2. Description of the Related Art The fuel injection amount is increased / decreased for each combustion in order to perform early warm-up of a three-way catalyst provided in an exhaust pipe (that is, the exhaust air-fuel ratio is alternately changed to a rich side and a lean side with respect to a theoretical air-fuel ratio. ) Operation repeats rich combustion and lean combustion,
A device has been proposed in which carbon monoxide CO is produced by rich combustion and oxygen O ₂ is produced by lean combustion, and the exhaust gas temperature is raised by the heat generated by the oxidation reaction of both (JP-A-5-33705). See the bulletin).

[0003]

However, if the amplitude of the exhaust air-fuel ratio, which fluctuates alternately between the rich side and the lean side, is set to a constant value, if the air-fuel ratio is limited by the oxygen storage capacity of the catalyst, Even given the amplitude,
When the oxygen storage capacity of the catalyst decreases and exceeds the oxygen storage capacity of the catalyst due to deterioration over time, the conversion rate decreases and exhaust emission deteriorates. On the other hand, if the air-fuel ratio amplitude is set small from the beginning, the catalyst warm-up promotion effect will be small.

In view of this, the present invention maximizes the early warm-up effect of the catalyst by setting the magnitude of the amplitude of the exhaust air-fuel ratio, which alternates between the rich side and the lean side, according to the oxygen storage capacity of the catalyst. The purpose is to withdraw.

[0005]

In the first invention, FIG.
As shown in FIG. 3, means 21 for determining whether the first catalyst provided in the exhaust pipe has been activated, and
Means for controlling the air-fuel ratio so that the exhaust air-fuel ratio fluctuates alternately between the rich side and the lean side before the catalyst is activated.
And means 23 for setting the magnitude of the amplitude of the exhaust air-fuel ratio, which alternates between the rich side and the lean side, according to the oxygen storage capacity of the first catalyst.

In the second invention, the second catalyst is provided on the downstream side of the first catalyst in the first invention.

According to a third aspect of the present invention, means is provided for keeping the average air-fuel ratio of the exhaust gas near the stoichiometric air-fuel ratio while the exhaust air-fuel ratio in the first or second aspect of the invention is alternately swung between the rich side and the lean side.

According to a fourth aspect of the invention, in any one of the first to third aspects of the invention, a sensor is provided before and after the first catalyst, which produces an output according to the oxygen concentration in the exhaust gas.
The oxygen storage capacity of the first catalyst is estimated based on the inversion frequency ratio or the inversion period ratio of the two sensor outputs.

According to a fifth aspect of the present invention, in any one of the first to third aspects of the present invention, a sensor is provided which outputs according to the oxygen concentration in the exhaust gas on the downstream side of the first catalyst, and the amplitude of this sensor output is provided. Based on the above, the oxygen storage capacity of the first catalyst is estimated.

In a sixth invention, the air-fuel ratio amplitude setting means 23 in any one of the first to third inventions.
However, as shown in FIG. 26, a sensor 41 that outputs according to the oxygen concentration in the exhaust gas on the upstream side of the first catalyst and an output according to the oxygen concentration in the exhaust gas on the downstream side of the first catalyst are output. Sensor 42, means 43 for measuring the inversion frequency ratio or inversion period ratio of these two sensor outputs, and this inversion frequency ratio or inversion period ratio becomes a value corresponding to the limit of the oxygen storage capacity of the first catalyst. As described above, the amplitude of the exhaust air-fuel ratio is controlled by feedback-controlling the air-fuel ratio control amount (for example, the increase / decrease amount of the basic injection amount, the increase / decrease amount of the hysteresis width of the slice level for comparison with the downstream sensor output, the proportional increase / decrease amount) Means 44 for setting the size of

In a seventh invention, the air-fuel ratio amplitude setting means 23 in any one of the first to third inventions.
However, as shown in FIG. 27, a sensor 42 that outputs an output according to the oxygen concentration in the exhaust gas on the downstream side of the first catalyst, a unit 51 that measures the amplitude of the output of the downstream side sensor, and the downstream side sensor The air-fuel ratio control amount (for example, the increase / decrease amount of the basic injection amount, the hysteresis width of the slice level for comparison with the downstream sensor output) so that the amplitude of the output becomes a value corresponding to the limit of the oxygen storage capacity of the first catalyst. And a means 52 for setting the magnitude of the amplitude of the exhaust air-fuel ratio by performing feedback control of the increase / decrease amount and the proportional increase / decrease amount.

In the eighth invention, the air-fuel ratio control amount when the oxygen storage capacity of the first catalyst reaches a limit-equivalent value for the first time after starting in the sixth or seventh invention is stored as a learning value. Then, this learned value is used as the initial value of the air-fuel ratio control amount when the exhaust air-fuel ratio is controlled so as to alternate between the rich side and the lean side at the next start.

In a ninth aspect of the present invention, the air-fuel ratio control amount is reset after a predetermined time has elapsed since the first learning of the air-fuel ratio control amount in the eighth aspect.

In a tenth aspect, learning of the air-fuel ratio control amount is prohibited when the air-fuel ratio control amount is reset in the ninth aspect.

In the eleventh invention, the catalyst activation judging means 2 in any one of the first to tenth inventions is used.
Reference numeral 1 denotes a sensor that outputs according to the oxygen concentration in the exhaust gas on the upstream side of the first catalyst, and a sensor that outputs according to the oxygen concentration in the exhaust gas on the downstream side of the first catalyst. It comprises means for measuring the inversion frequency ratio or inversion period ratio of the sensor output, and means for determining whether or not the first catalyst has been activated based on this inversion frequency ratio or inversion period ratio.

In a twelfth aspect of the invention, the catalyst activation determining means 2 in any one of the first to tenth aspects of the invention is used.
1 comprises a sensor for detecting the temperature of the first catalyst, and means for judging whether or not the first catalyst has been activated based on the output of the temperature sensor.

In a thirteenth invention, the catalyst activation judging means 2 in any one of the first to tenth inventions is used.
1 comprises a sensor for detecting the temperature of the cooling water of the engine and a means for judging whether or not the first catalyst has been activated based on the output of the temperature sensor.

In a fourteenth invention, the air-fuel ratio control means 22 is provided in any one of the first to thirteenth inventions.
However, as shown in FIG. 28, a means 61 for calculating a basic injection amount for obtaining a substantially theoretical air-fuel ratio according to operating conditions, and a variable increase of this basic injection amount for some cylinders, and for the remaining cylinders From the means 62 for variably decreasing, and the means 63 for supplying the increased injection amount of fuel to the intake pipes of the partial cylinders and the decreased injection amount of fuel to the intake pipes of the remaining cylinders. Become.

In a fifteenth invention, the air-fuel ratio control means 22 is provided in any one of the first to thirteenth inventions.
However, as shown in FIG. 29, a means 61 for calculating a basic injection amount that provides a stoichiometric air-fuel ratio according to operating conditions and an output according to the oxygen concentration in the exhaust gas on the upstream side of the first catalyst are output. The sensor 41, means 71 for variably setting the hysteresis width of the slice level for comparison with the output of the upstream side sensor 41, and the comparison result of the slice level with the hysteresis width set and the output of the upstream side sensor 41 Means 72 for calculating the air-fuel ratio feedback correction amount based on
And means 73 for calculating the fuel injection amount by correcting the basic injection amount with the air-fuel ratio feedback correction amount, and means 74 for supplying the injection amount of fuel to the intake pipe.

In a sixteenth invention, the air-fuel ratio control means 22 is provided in any one of the first to thirteenth inventions.
However, as shown in FIG. 30, a means 61 for calculating a basic injection amount that provides a theoretical air-fuel ratio according to operating conditions and an output according to the oxygen concentration in the exhaust gas on the upstream side of the first catalyst are output. A sensor 41, a means 81 for variably setting a feedback constant (at least one of a proportional component and an integral component) based on the output of the upstream sensor 41, and a means for calculating an air-fuel ratio feedback correction amount using this feedback constant. 82, a unit 73 for calculating the fuel injection amount by correcting the basic injection amount with the air-fuel ratio feedback correction amount, and a unit 74 for supplying the injection amount of fuel to the intake pipe.

In the seventeenth invention, the means for keeping the average air-fuel ratio of the exhaust gas near the stoichiometric air-fuel ratio in the third invention operates as shown in FIG. A means 61 for calculating according to the conditions, a sensor 41 for providing an output according to the oxygen concentration in the exhaust gas on the upstream side of the first catalyst, and a feedback constant (for example, a proportional portion, an integral portion) based on the output of the upstream side sensor 41. And a sensor 91 for setting a slice level or the like for comparison with the upstream sensor output, a sensor 42 for outputting according to the oxygen concentration in the exhaust gas on the downstream side of the first catalyst, and the downstream sensor 42. Means 92 for modifying the feedback constant so that the average air-fuel ratio of the exhaust gas approaches the stoichiometric air-fuel ratio based on the output, and air-fuel ratio feedback using the modified feedback constant. It comprises means 93 for calculating a positive amount, means 73 for calculating the fuel injection amount by correcting the basic injection amount with this air-fuel ratio feedback correction amount, and means 74 for supplying this injection amount of fuel to the intake pipe. .

[0022]

In the first aspect of the present invention, when the air-fuel ratio is controlled so that the exhaust air-fuel ratio fluctuates alternately between the rich side and the lean side for early warm-up of the first catalyst, the present oxygen of the first catalyst is changed. Since the air-fuel ratio amplitude is set according to the storage capacity, the amplitude of the exhaust air-fuel ratio corresponds to the deterioration of the first catalyst over time and the change in the oxygen storage capacity that accompanies the replacement of the first catalyst with a new one. Even when the first catalyst deteriorates with time or the first catalyst is replaced with a new one, the early warm-up effect of the first catalyst can be maximized.

When the exhaust air-fuel ratio is alternately varied between the rich side and the lean side, the rich / lean determination by the air-fuel ratio feedback control is delayed by that much, and the feedback control period becomes long, so that the average exhaust air-fuel ratio is increased. The fuel ratio may deviate from the stoichiometric air-fuel ratio, but in the third invention, the average air-fuel ratio of the exhaust gas does not deviate more than the stoichiometric air-fuel ratio while the exhaust air-fuel ratio is alternately swung to the rich side and the lean side. .

In the eighth aspect of the invention, the first
The air-fuel ratio control amount when the value corresponding to the limit of the oxygen storage capacity of the catalyst is stored as a learning value, and this learning value fluctuates alternately between the rich side and the lean side at the next start. Since it is used as the initial value of the air-fuel ratio control amount when performing control as described above, compared with the case where the air-fuel ratio control amount is feedback-controlled so that it becomes a value equivalent to the limit of the oxygen storage capacity of the first catalyst at each start. , The maximum air-fuel ratio amplitude that does not exceed the current oxygen storage capacity limit of the first catalyst can be set earlier.

In the ninth aspect of the invention, the air-fuel ratio control amount is reset after a lapse of a predetermined time from the first learning of the air-fuel ratio control amount. Therefore, when the warm-up progresses, the oxygen storage capacity of the first catalyst increases. However, the early warm-up effect of the catalyst can be maximized.

In the tenth aspect of the invention, since the learning is not performed when the air-fuel ratio control amount is reset, it is possible to avoid erroneous learning due to learning the change in the oxygen storage capacity of the first catalyst during the warm-up process. .

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 is an engine body, an intake passage 8 of which is provided with a fuel injection valve 7 located downstream of an intake throttle valve 5, and a control unit (C / U in the figure). (Abbreviation) 2 fuel is injected and supplied into the intake air by the injection signal from 2. The flow rate of fuel supplied to the engine is controlled by volume flow rate, and the flow rate is adjusted by the valve opening time of the injection valve.

On the other hand, the cylinder head is provided with an electrode of an ignition plug facing the combustion chamber, and the control unit 2
When the primary current of the ignition coil is cut off at a predetermined timing by the ignition signal from the spark plug, sparks fly to the electrodes of the spark plug, and the air-fuel mixture in the cylinder is ignited. The gas burned by this ignition is purified by the catalysts (three-way catalysts) 10 and 15 provided in series in the exhaust passage 9.

The control unit 2 has a Ref signal from the crank angle sensor 4 (in every four cylinders, every 180 °, 6
(Generated every 120 ° in the cylinder) and 1 ° signal, intake air amount signal from the air flow meter 6, air-fuel ratio (oxygen concentration) signal from the O ₂ sensor 3 installed upstream of the three-way catalyst 10 in the exhaust passage 9. The engine cooling water temperature signal and the like from the water temperature sensor 11 are input, and the control unit 2 controls the fuel injection amount (air-fuel ratio) based on these signals. Further, the O ₂ sensor 13 is provided not only on the upstream side of the catalyst 10 but also on the downstream side, and the control unit 2 compares the downstream O ₂ sensor output with the upstream O ₂ sensor output to deteriorate the catalyst 10. To diagnose.

Now, in order to warm up the catalyst 10 early, the operation of alternately swinging the exhaust air-fuel ratio to the rich side and the lean side with respect to the theoretical air-fuel ratio (this operation is hereinafter referred to as "air-fuel ratio perturbation operation"). ) Repeats rich combustion and lean combustion to produce a large amount of carbon monoxide CO by rich combustion and a large amount of oxygen O ₂ by lean combustion, and raises the exhaust temperature by the heat generated by the oxidation reaction of both, and at the same time, air-fuel ratio perturbation When the operation is performed during the air-fuel ratio feedback control using the upstream O ₂ sensor output of the catalyst 10, the air-fuel ratio fluctuates, and the air-fuel ratio feedback cycle is lengthened by the increase / decrease of the fuel and the average air-fuel ratio of the exhaust gas is increased. air off but since coming deviates from the stoichiometric air-fuel ratio, based on the upstream O ₂ sensor output by the downstream O ₂ sensor output of the catalyst 10 Readback control apparatus so as to converge the average air-fuel ratio of the exhaust gas in the vicinity of the stoichiometric air-fuel ratio by correcting slowly proportional amount is controlled constant has been proposed (see Japanese Patent Laid-Open No. 5-33705).

This apparatus is equipped with a catalyst 10 as shown in FIG.
When applied to a structure in which another catalyst 15 is provided on the downstream side of the exhaust gas, the average air-fuel ratio of the exhaust gas is theoretically adjusted so that the conversion rate of the catalyst 10 does not decrease after activation or partial activation of the catalyst 10. It is conceivable to perform early warm-up of the upstream and downstream catalysts by performing the air-fuel ratio perturbation operation to raise the exhaust gas temperature in the catalyst 10 while maintaining it near the air-fuel ratio.

In this case, if the amplitude of the exhaust air-fuel ratio by the air-fuel ratio perturbation operation is set to a constant value, even if the air-fuel ratio amplitude is given by the limit of the oxygen storage capacity of the catalyst 10, it will be deteriorated with time. When the oxygen storage capacity of the catalyst 10 is lower than the oxygen storage capacity of the catalyst 10, the conversion rate is decreased and the exhaust emission is deteriorated. To cope with this, in the present invention, the output of the downstream O ₂ sensor is adjusted. By monitoring, the air-fuel ratio amplitude is gradually increased until the output of the downstream side O ₂ sensor largely fluctuates, and when the output of the downstream side O ₂ sensor exceeds the reference value, the oxygen storage capacity of the catalyst 10 is reduced. that is determined to have become the air-fuel ratio amplitude, sets the maximum air-fuel ratio amplitude downstream O ₂ sensor output is not Desa deflection than the reference value exceeding , Maximize the early warm-up effect of the catalyst by the air-fuel ratio perturbation operation.

The contents of this control executed by the control unit 2 will be described with reference to the following flow chart.

First, FIG. 2 is for determining the activation of the upstream side catalyst 10, which is executed at a constant cycle.

In step 1, it is checked whether the engine operating condition is in the activation judgment area. If it is in the activation judgment area, the reversal frequencies F1 and F2 of the two O ₂ sensor outputs are read in steps 2, 3 and 4. Then, the ratio (reversal frequency ratio) Fr (= F2 / F1) of both is calculated, and the table shown in FIG. 3 is searched from the value to obtain the catalyst activity K.
The catalyst activity K has a value that increases as the reversal frequency ratio Fr decreases toward 0 in FIG. 3 (the catalyst is activated).

Looking at the movement of the air-fuel ratio before and after the catalyst 10, as shown in FIG. 4, when the catalyst 10 is not activated, the air-fuel ratio downstream of the catalyst 10 (abbreviated as A / F in the figure) is shown. While the air-fuel ratio upstream of the catalyst 10 moves almost in the same manner, when the catalyst 10 is activated, the air-fuel ratio downstream of the catalyst 10 hardly moves because the catalyst 10 purifies exhaust gas. That is, since the catalyst 10 is activated as the reversal frequency ratio Fr approaches 0, the table value is set so that the value of the catalyst activity K increases as the catalyst 10 activates. is there. There is a correlation shown in FIG. 5 between the reversal frequency ratio Fr and the catalyst conversion rate.

At step 6, the catalyst activity K is compared with a predetermined value. When the catalyst activity K is less than the predetermined value, the catalyst 10 is in an inactive state, so the routine proceeds to step 7 to set the catalyst activation flag Fkf to "0". When the catalyst activity K becomes equal to or higher than a predetermined value, it is determined that the catalyst 10 has been activated to some extent, the process proceeds to step 8 and the catalyst activation flag Fkf is set to "1", and then the flow of FIG. 2 is ended. To do. The catalyst activation flag Fkf is stored in the RAM together with another catalyst activation flag Fkr described next.

The flow chart of FIG. 6 is for determining the activation of the downstream side catalyst 15, which is also executed in a fixed cycle.

In step 11, the internal temperature of the catalyst 15 detected by the temperature sensor 16 (see FIG. 1) is read,
This is compared with a predetermined value in step 12, and when the catalyst internal temperature is lower than the predetermined value, the catalyst activation flag Fkr is set to "0" in step 13, and the catalyst 15 is activated when the catalyst internal temperature is equal to or higher than the predetermined value. Step 1
4, the catalyst activation flag Fkr is set to "1", and then the flow of FIG. 6 is terminated.

The flow chart of FIG. 7 is for determining whether to permit the air-fuel ratio perturbation operation, and is executed after the activation determination of each catalyst shown in FIGS. 2 and 6 is completed.

At steps 21 and 22, two catalyst activation flags Fkf and Fkr are checked. When Fkf = 0, the routine proceeds from step 21 to 23, at which the air-fuel ratio perturbation permission flag Fst is reset to "0", and Fkf = 1 and F
When Kr = 0, the routine proceeds to step 24, where the air-fuel ratio perturbation permission flag Fst is set to "1", and Fkf
= 1 and FKr = 1, the routine proceeds to step 25, where the air-fuel ratio perturbation end flag Fend (initially set to "0" at start-up) is set to "1". Fst, F
Looking at what happens to each flag of end concretely at the cold start, the upstream side catalyst 10 is initially inactive (Fkf =
0), the air-fuel ratio perturbation permission flag F
st is a “0” state, and when the upstream catalyst 10 is activated to some extent but the downstream catalyst 15 is inactive (Fkf = 1 and Fkr), the air-fuel ratio perturbation permission flag Fst is set to “1”. When the downstream side catalyst 15 is activated after that, the perturbation end flag Fend (initially set to "0" at the time of starting) is set to "1".

The flowchart of FIG. 8 is for calculating the fuel injection pulse width given to the fuel injection valve 7 of each cylinder, and is executed in synchronization with the Ref signal.

In step 31, from the intake air amount Qa from the air flow meter 6 and the engine speed Ne detected by the crank angle sensor 4, Tp = (Qa / Ne) × K (1) where K: constant The basic injection pulse width Tp that yields the air-fuel mixture having almost the stoichiometric air-fuel ratio is calculated by the equation,
Look at the two flags Fend and Fst. When Fend = 1 and when Fend = 0 and Fst = 0, there is no air-fuel ratio perturbation permission condition, so the routine proceeds to step 34, where Ti (n) = Tp × α × 2 + Ts (2) where α: empty Fuel ratio feedback correction coefficient Ts: Fuel injection pulse width Ti (n) common to all cylinders according to the formula of invalid pulse width according to battery voltage
(However, n is the cylinder number) is calculated, and this is calculated in step 35.
At the output register.

Here, the fuel injection is a sequential injection system (once every two revolutions of the engine, a system in which the injection timing is immediately before the intake valve is opened in each cylinder), so that it is a four-cylinder engine (the ignition order is # 1). -# 3- # 4- #
2) as an example, 1 is input by inputting the Ref signal this time.
If Ti (1) fuel is supplied to the # 3 cylinder, the Ref signal will be input next time (that is, once) to the # 3 cylinder.
After inputting the Ref signal after 3 times, the Ref.
By inputting a signal, Ti (3) and Ti will be supplied to the 2nd cylinder respectively.
(4), Ti (2) fuel is supplied. Such a sequential injection method is performed in all operating ranges, including when the engine is started.

On the other hand, when Fend = 0 and Fst = 1 (when the air-fuel ratio perturbation permission condition is satisfied), the routine proceeds to step 36 and thereafter, where every other cylinder in the ignition order (for example, the first cylinder and the fourth cylinder). The air-fuel ratio perturbation operation is performed by increasing the air-fuel ratio of (4) and leaning the cylinders (the third cylinder and the second cylinder) in between. That is, in the case of the rich cylinder (cylinder in which the air-fuel ratio is enriched), in step 37, Ti (n) = (Tp + t) × α × 2 + Ts (3) where t: fuel increase / decrease amount (positive value) The fuel injection pulse width, and in the case of a lean cylinder (a cylinder whose air-fuel ratio is lean), in step 38 Ti (n) = (Tp-t) × α × 2 + Ts (4) Step 3 after calculating
5 is executed.

The fuel increase / decrease amount t in the equations (3) and (4) is a value that determines the amplitude of the exhaust air-fuel ratio, and the calculation of this value will be described with reference to the flow charts of FIGS. 9 and 10. In addition,
Since the fuel injection is Ref signal synchronization, R is
It is executed in synchronization with the ef signal.

Here, while the fuel increase / decrease amount t has been a constant value in the past, the fuel increase / decrease amount t of the present invention is a variable value and a learning value, and the learning value is used as the initial value of t. ing.

In steps 41 and 42, two flags Fe
nd and Fst, when the air-fuel ratio perturbation permission condition is satisfied (Fend = 0 and Fst = 1), the learning end flag Fg for the fuel increase / decrease amount is determined in step 43.
Look at end (set to "0" at startup) before learning (Fg
If end = 0), the process proceeds to step 44 and thereafter.

Steps 44 and 45 are portions for setting an initial value to the fuel increase / decrease amount t. If the process has proceeded to step 44 for the first time after starting, the learning value stored in the backup memory in step 45 is put in t, Otherwise, the process of step 45 is skipped.

In step 46, the inversion frequency ratio Fr of the two O ₂ sensor outputs is calculated, and steps 47, 48 and 49 are calculated.
In this case, using the result of comparing this value with the reference value (corresponding to the limit of the oxygen storage capacity of the catalyst) St and the result of the previous comparison, if Fr <St, this time, the catalyst 1
It is determined that the air-fuel ratio amplitude is within the oxygen storage capacity of 0, and in step 50, the fuel increase / decrease amount t is increased by the predetermined value Kt. When Fr ≧ St is continued this time, it is determined that the air-fuel ratio amplitude exceeds the oxygen storage capacity of the catalyst 10 and the catalyst conversion rate decreases, and the fuel increase / decrease amount t is decreased by only the predetermined value Kt in step 51. In this way, the air-fuel ratio amplitude is set by feedback-controlling the fuel increase / decrease amount t such that the reversal frequency ratio Fr corresponds to the limit of the oxygen storage capacity of the catalyst.

Here, the relationship between the inversion frequency ratio Fr and the oxygen storage of the catalyst 10 will be described. When there is an air-fuel ratio amplitude exceeding the oxygen storage capacity, the inversion frequency ratio Fr shows a large value (approaching 1) because the air-fuel ratio around the catalyst 10 moves almost the same, but it does not exceed the oxygen storage capacity. In the case of the air-fuel ratio amplitude, the air-fuel ratio downstream of the catalyst 10 hardly moves, and the reversal frequency ratio Fr shows a small value (close to 0). In other words, the oxygen storage capacity can be estimated from the inversion frequency ratio,
When the reversal frequency ratio Fr is smaller than the reference value St, it can be determined that there is oxygen storage capacity corresponding to the air-fuel ratio amplitude during the air-fuel ratio perturbation operation, and the reversal frequency ratio Fr is larger than the reference value St. If so, it can be determined that the air-fuel ratio amplitude exceeds the oxygen storage capacity. Therefore, when Fr is less than St, it is determined that the oxygen storage capacity has a margin, and t is increased so as to increase the air-fuel ratio amplitude.
In the above case, it is judged that the oxygen storage capacity is exceeded and the catalyst conversion rate is reduced, and t is reduced so that the air-fuel ratio amplitude becomes smaller.

On the other hand, when Fr ≧ St last time, but this time Fr <St, it is judged that the air-fuel ratio amplitude has reached the limit of the oxygen storage capacity, and the routine proceeds from step 47, 48 to step 52, and again. When Fr <St was used the last time, but when Fr ≧ St was used this time, it is determined that the air-fuel ratio amplitude has reached the limit of the oxygen storage capacity.
The process proceeds from step 49 to step 52. In step 52, see if it is the first time to proceed to this step after the start.
Only when it is the first time after starting, in step 53, t at that time is added to the learning value and stored in the backup memory.

The learned value thus stored is used as the initial value of t when the air-fuel ratio perturbation operation is performed at the next start (steps 44 and 4 in FIG. 9).
5) Even if the oxygen storage capacity of the catalyst 10 decreases due to deterioration over time or the catalyst 10 is replaced with a new one, the maximum air-fuel ratio amplitude can be set earlier within the range of the oxygen storage capacity at that time. That is why.

In step 54, since the learning is completed only once, the learning end flag Fgend is set to "1" and the timer TM is reset to 0. This timer TM is for measuring the time from the end of learning.
Configured using the clock in U.

Learning end flag Fgen in step 54
When d is set to "1", the flow from the step 43 of FIG. 9 to the step 55 of FIG. 10 is started from the next time, and the timer TM is compared with a predetermined value (for example, 20 seconds). Before that, the value of t is held in step 56, and after 20 seconds have passed from the end of learning, step 57 is executed.
After that, the inversion frequency ratio Fr and the reference value St are compared again, and t is reset according to the comparison result. However, learning is not performed at this time. The oxygen storage capacity changes not only when it deteriorates over time or when it is replaced with a new one, but also changes depending on the activity (warming process) of the catalyst 10, and the oxygen storage capacity increases as the catalyst 10 warms up. Therefore, by performing the learning only the first time, erroneous learning due to learning the change in the catalyst warm-up process is avoided.

Next, the calculation of the air-fuel ratio feedback correction coefficient α in the equations (2) to (4) will be described with reference to the flow chart of FIG. Since the fuel injection is in synchronization with the Ref signal, α is also executed in synchronization with the Ref signal.

At step 71, it is determined whether or not the air-fuel ratio feedback condition based on the upstream O ₂ sensor output is satisfied, and if the condition is not satisfied, at step 72 the air-fuel ratio feedback correction coefficient α is fixed to 1.0 (clamp).
I do.

When the condition is satisfied, step 73
At step 74, the upstream O ₂ sensor output OSR1 is read, and this is compared with the upper limit SLFH of the slice level at step 74. When OSR1> SLFH, it is judged to be rich, and the routine proceeds to step 75, where it is checked if it was rich last time. As a result, when the previous lean is rich this time, the routine proceeds to steps 76 and 77, where the air-fuel ratio feedback correction coefficient α is reduced by the proportional amount PR, and when it is rich both last time and this time, the routine proceeds to step 78 and the integral IR is obtained from α. Just lose weight. When OSR1 ≦ SLFH, the routine proceeds from step 74 to step 79, where OSR1 is compared with the lower limit SLFL of the slice level. OSR1 ≤ SLFL
If it is, it is judged to be lean, and if it was lean this time at the previous rich in step 80, if it was lean this time at the previous rich, proceed to steps 81 and 82 to increase α by the proportional amount PL, and both at the previous time and this time. When it is lean, the routine proceeds to step 83, where α is increased by the integral amount IL.

If SLFH ≧ OSR1> SLFL (that is, OSR1 is within the hysteresis width of the slice level), the process proceeds from step 74 and 79 to step 84. If it is rich last time, if it is rich, at step 85 α From IR by the integrated amount,
If lean, at step 86 α is increased by the integral amount IL. Hysteresis is provided for the slice level for comparison with the upstream O ₂ sensor output OSR1 (see FIG. 12), and when OSR1 is on the rich side when it increases across the slice level upper limit SLFH, the slice level lower limit When it crosses the SLFL and becomes smaller, it is determined to be on the lean side.

The flow chart of FIG. 13 is a subroutine for performing the processing of step 76 of FIG. 11, each time the upstream O ₂ sensor output OSR1 is reversed to the rich side, and FIG.
11 is a subroutine for performing the processing of step 81 in FIG. 11, and is executed each time the upstream O ₂ sensor output OSR1 is inverted to the lean side.

Since the control contents of the respective subroutines are the same, mainly in FIG. 13, in step 91, a proportional basic value PR0 is read. This basic value PR0
Is the value of the proportional PR when the upstream O ₂ sensor 3 and the catalyst 10 are matched without deterioration, and is a map with the rotation speed Ne and the basic injection pulse width Tp as parameters as shown in FIG. Allocations are made by searching this map.

In steps 92 and 93, two flags Fen are set.
d and Fst, when the air-fuel ratio perturbation permission condition is not satisfied (when Fend = 1 and Fend = 0 and Fs
(when t = 0), the routine proceeds to step 94, where the basic value PR0
Is directly added to the proportional portion PR and the subroutine of FIG. 13 is ended.

When the air-fuel ratio perturbation permission condition is satisfied (Fend = 0 and Fst = 1), step 9
In step 5, the downstream side O ₂ sensor output OSR2 is read, and this is compared with the slice level SLR in step 96. As a result of the comparison, when OSR2> SLR (the air-fuel ratio is tilted to the rich side due to the air-fuel ratio perturbation operation), in steps 97 and 99 LP ← LP-DLP (5) where DLP: Proportional to the predetermined value Corrected value for minutes (initially set to 0 at startup) L
The air-fuel ratio is returned to the lean side by reducing P by DLP and setting the value obtained by subtracting the correction value LP from the basic value PR0 as the proportional portion PR (that is, correcting the proportional portion). When OSR2 ≤ SLR (the air-fuel ratio is leaning toward the lean side due to the air-fuel ratio perturbation operation), the routine proceeds from step 96 to step 98, where the proportional correction value LP is calculated by the formula of LP ← LP + DLP (6) After that, the air-fuel ratio is returned to the rich side by executing the operation of step 99.

Similarly, for the other proportional portion PL, as shown in FIG. 14, when the air-fuel ratio perturbation permission condition is not satisfied, the basic value PL0 (see FIG. 16) of the proportional portion PL is left unchanged in step 104. When the air-fuel ratio perturbation permission condition is satisfied, the proportional value PL is set, and the correction value LP is increased / decreased by looking at OSR2 after step 105, and the value obtained by adding the correction value LP to the basic value PL0 is set as the proportional value PL. , Return the air-fuel ratio to the stoichiometric air-fuel ratio.

When the fuel amount is increased or decreased by the air-fuel ratio perturbation operation, the feedback control cycle becomes long because the rich or lean judgment is delayed by the air-fuel ratio feedback and the feedback control period becomes longer by the amount of the fuel increase or decrease. since there is a possibility to come deviated from an air-fuel ratio, the downstream O ₂ proportional portion PR is a control constant of the air-fuel ratio feedback control based on the upstream O ₂ sensor output based on the sensor output OSR2, gradually the PL avoid this The average air-fuel ratio of the exhaust gas is made to converge near the stoichiometric air-fuel ratio by modifying the above.

The operation of the present invention will now be described.

In the present invention, when performing the air-fuel ratio perturbation operation, the reversal frequency ratio Fr, which is a value by which the oxygen storage capacity of the catalyst 10 can be estimated, is measured, and the measured reversal frequency ratio Fr is the oxygen storage ratio of the catalyst 10. Since the fuel increase / decrease amount (air-fuel ratio control amount) t is feedback-controlled so as to match the reference value St as the limit equivalent to the capacity, the amplitude of the exhaust air-fuel ratio is deteriorated with time and the catalyst 10 is replaced with a new one. The change in oxygen storage capacity accompanying it is dealt with, and even if the catalyst 10 deteriorates with time or is replaced with a new one, the early warm-up effect of the catalyst 10 by the air-fuel ratio perturbation operation can be maximized.

Further, the fuel increase / decrease amount t when the reversal frequency ratio Fr reaches the reference value St for the first time after the start is stored in the backup memory as a learning value, and this is used when performing the air-fuel ratio perturbation operation at the next start. Since the learning value is used as the initial value of the fuel increase / decrease amount t, compared with the case where the fuel increase / decrease amount t is feedback-controlled so that the reversal frequency ratio Fr reaches the limit of the oxygen storage capacity of the catalyst 10 at each start. It can be set faster with a maximum air-fuel ratio amplitude that does not exceed the current oxygen storage capacity limit of 10.

Further, since the fuel increase / decrease amount t is reset after the elapse of a predetermined time from the first learning of the fuel increase / decrease amount t, even when the oxygen storage capacity of the catalyst 10 increases as the warming-up progresses, The effect of early warm-up of the catalyst 10 by the air-fuel ratio perturbation operation can be maximized. Further, at this time (when resetting the fuel increase / decrease amount t), learning is not performed.
It is possible to avoid erroneous learning due to learning the change in the oxygen storage capacity of.

When the fuel is increased or decreased by the air-fuel ratio perturbation operation, the feedback control cycle becomes longer because the rich or lean determination by the air-fuel ratio feedback control is delayed by the amount of the increase or decrease of the fuel, and the exhaust control there is a possibility that the average air-fuel ratio comes deviates from the stoichiometric air-fuel ratio, the present invention is a control constant of the air-fuel ratio feedback control based on the upstream O ₂ sensor output based on the downstream O ₂ sensor output OSR2 proportional amount PR , PL is gradually corrected, so that the average air-fuel ratio of the exhaust gas can be converged to near the stoichiometric air-fuel ratio even during the air-fuel ratio perturbation operation.

The flowcharts of FIGS. 18, 19, and 20 are the second embodiment, and the flowcharts of FIGS. 22, 23, and 24 are the third embodiment, of which FIGS. 18, 19 and 22, 23 are 20 and 24 in FIGS. 9 and 10.
Corresponds to FIG. 11, respectively. The flowchart of FIG. 17 common to the second and third embodiments corresponds to FIG. 8. In the second and third embodiments, the same parts as those in the first embodiment have the same step numbers.

As shown in FIG. 17, even when the fuel injection pulse width given to the fuel injection valve of each cylinder is calculated by the above equation (2), comparison with the upstream side O ₂ sensor output OSR1 is made. When the hysteresis width of the slice level for increasing is increased, the air-fuel ratio when judged to be rich shifts to the rich side, and the air-fuel ratio when judged to be lean shifts to the lean side (see FIG. 21). The amplitude of the exhaust air-fuel ratio during fuel ratio feedback control increases.
That is, the air-fuel ratio perturbation operation can be performed also by changing the hysteresis width of the slice level for comparison with the output of the upstream O ₂ sensor.
In the second embodiment, this hysteresis width is set according to the inversion frequency ratio Fr which is a value for estimating the oxygen storage capacity.

In the air-fuel ratio feedback control (PI control), α is increased by a proportional amount PL when the upstream O ₂ sensor output is inverted to the lean side, and α is increased when the output is changed to the rich side.
Is reduced by the proportional amount PR, the proportional amounts PL, P
By adding both R by a predetermined value to make a large value, the amplitude of the exhaust air-fuel ratio at the time of air-fuel ratio feedback control becomes large. That is, since the air-fuel ratio perturbation operation can be performed by changing the proportional parts PL and PR, the proportional parts PL and PR are set according to the inversion frequency ratio Fr in the third embodiment. In addition,
At this time, not only proportional parts PL and PR but also integral parts IR and IL
May be increased, or in addition to this, the width of the hysteresis of the slice level for comparison with the upstream O ₂ sensor may be increased.

First, the flowcharts of FIGS. 18 and 19 are for calculating the increase / decrease amount s of the hysteresis width for comparison with the output of the upstream O ₂ sensor, and FIGS. 22 and 23 are the increase / decrease of proportional parts PR and PL. This is for calculating the quantity p, and is different from FIG. 9 and FIG. 10 in steps 111, 112, 113 and 11
4, 115, 116, 117 (above FIGS. 18 and 19),
Steps 131, 132, 133, 134, 135, 1
36 and 137 (above FIGS. 22 and 23) are different, but the contents are the same as in the first embodiment.

Here, only for the second embodiment, the first
Explaining mainly the parts different from the embodiment, the learning value is set to the hysteresis value in step 111 only when the air-fuel ratio perturbation permission condition is satisfied in FIG. Put in width s.

Further, this time, Fr <St continuously from the previous time.
If so, it is determined that the air-fuel ratio amplitude is within the oxygen storage capacity of the catalyst 10, and the increase / decrease amount s is increased by a predetermined value Ks in step 112. If this time, Fr ≧ St, the air-fuel ratio amplitude is determined to be the catalyst. It is determined that the oxygen storage capacity of 10 is exceeded, and in step 113, the increase / decrease amount s is decreased by the predetermined value Ks. The last time Fr ≧ St was Fr <St this time, and the last time Fr <St was Fr ≧ St this time, the empty space of the oxygen storage capacity of the catalyst 10 was reached. When it is determined that the fuel ratio amplitude has been reached, the routine proceeds to step 52, where only when it is the first time that the routine has proceeded to this step after start-up, at step 114 the increase / decrease amount s at that time is put into the learning value and stored in the backup memory. After the learning is completed, the timer TM is compared with a predetermined value (for example, 20 seconds), and the value of the increase / decrease amount s is held in step 115 of FIG. After that, step 5 in FIG.
After 7, the inversion frequency ratio Fr and the reference value St are compared again,
The increase / decrease amount s is reset according to the comparison result. However, learning is not performed at this time.

Next, in the flowchart of FIG. 20, when the air-fuel ratio feedback condition is satisfied, step 12
The increase / decrease amount s of the hysteresis width is read at 1 and 122, and the increase / decrease amount s is used to set the slice level upper limit SLFH and the slice level lower limit SLFL SLFH = SLF0 + s / 2 (7) SLFL = SLF0-s / 2 (8) However, SLF0: median of slice level is set by the formula.

Next, in the third embodiment, FIGS.
The proportional increase / decrease amount p is calculated by using the proportional increase / decrease amount p, and in the step 141 which is performed when reversing to the rich side in the flowchart of FIG. 24, α ← α− (PR + p) (9) , Step 1 to proceed when leaning back
At 42, α is updated by the equation α ← α + (PL + p) (10).

[0079] While the embodiments have been described in the case of guessing the oxygen storage capacity of the catalyst 10 by the inversion frequency ratio Fr of the two O ₂ sensor output before and after the catalyst 10, the downstream side O to the inverting each of the downstream O ₂ sensor output the difference between the minimum output and maximum output of the _second sensor measures the amplitude of the downstream O ₂ sensor output,
Based on the measured amplitude of the downstream O ₂ sensor output, the catalyst 1
The oxygen storage capacity of 0 can be estimated (the smaller the amplitude of the downstream O ₂ sensor output, the larger the oxygen storage capacity). In this case, it is preferable to monitor the measured values while performing some weighted averaging. The weighted averaging is performed in order to avoid an error in the air-fuel ratio other than the air-fuel ratio perturbation operation, which may be output from the downstream O ₂ sensor as the air-fuel ratio perturbation operation.

Although the inversion frequency ratio has been described in the embodiment, the inversion period ratio may be used.

In the embodiment, the structure in which another catalyst 15 is provided on the downstream side of the catalyst 10 has been described, but the present invention can be applied to a structure including only the catalyst 10 as in the conventional example. However, in this case, when the catalyst 10 is partially activated is the time when the air-fuel ratio perturbation permission condition is satisfied. Further, different activation determination methods for the two catalysts 10 and 15 have been described, but the present invention is not limited to this, and various known activation determination methods can be used.

[0082]

According to the first invention, when the air-fuel ratio is controlled so that the exhaust air-fuel ratio fluctuates alternately between the rich side and the lean side for early warm-up of the first catalyst, the present catalyst of the first catalyst is used. Since the air-fuel ratio amplitude is set according to the oxygen storage capacity of the exhaust gas, the amplitude of the exhaust air-fuel ratio corresponds to the deterioration of the first catalyst over time and changes in the oxygen storage capacity due to replacement of the first catalyst with a new one. Even if the first catalyst deteriorates with time or the first catalyst is replaced with a new one, the early warm-up effect of the first catalyst can be maximized.

When the exhaust air-fuel ratio is alternately oscillated between the rich side and the lean side, the feedback control cycle becomes longer because a delay is made in the rich and lean determinations by the air-fuel ratio feedback control, and the exhaust control average becomes longer. Although the air-fuel ratio may deviate from the stoichiometric air-fuel ratio, in the third invention, the average air-fuel ratio of the exhaust gas deviates more than the stoichiometric air-fuel ratio even while the exhaust air-fuel ratio is alternately swung to the rich side and the lean side. Never.

In the eighth invention, the first
The air-fuel ratio control amount when the value corresponding to the limit of the oxygen storage capacity of the catalyst is stored as a learning value, and this learning value fluctuates alternately between the rich side and the lean side at the next start. Since it is used as the initial value of the air-fuel ratio control amount when performing control as described above, compared with the case where the air-fuel ratio control amount is feedback-controlled so that it becomes a value equivalent to the limit of the oxygen storage capacity of the first catalyst at each start. , The maximum air-fuel ratio amplitude that does not exceed the current oxygen storage capacity limit of the first catalyst can be set earlier.

In the ninth aspect of the present invention, the air-fuel ratio control amount is reset after a lapse of a predetermined time from the first learning of the air-fuel ratio control amount. Therefore, when the warm-up progresses, the oxygen storage capacity of the first catalyst increases. However, the early warm-up effect of the first catalyst can be maximized.

In the tenth aspect of the invention, since the learning is not performed when the air-fuel ratio control amount is reset, it is possible to avoid erroneous learning due to learning the change in the oxygen storage capacity of the first catalyst during the warm-up process. .

[Brief description of drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining determination of activation of an upstream side catalyst.

FIG. 3 is a diagram showing a table of catalyst activity K.

FIG. 4 is a schematic diagram of an air-fuel ratio waveform before and after an upstream side catalyst.

FIG. 5 is a characteristic diagram showing the relationship between the inversion frequency ratio and the catalyst conversion rate.

FIG. 6 is a flowchart for explaining determination of activation of a downstream side catalyst.

FIG. 7 is a flow chart for explaining determination of an air-fuel ratio perturbation permission condition.

FIG. 8 is a flow chart for explaining calculation of a fuel injection pulse width given to the fuel injection valve of each cylinder.

FIG. 9 is a flowchart for explaining calculation of an increase / decrease amount t of the basic injection pulse width Tp.

FIG. 10 is a flowchart for explaining calculation of an increase / decrease amount t of the basic injection pulse width Tp.

FIG. 11 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α.

FIG. 12 is a change waveform diagram of an air-fuel ratio feedback correction coefficient α.

FIG. 13 is a flowchart for explaining calculation of a proportional portion PR.

FIG. 14 is a flowchart for explaining calculation of a proportional PL.

FIG. 15 is a diagram showing a map of a proportional basic value PR0.

FIG. 16 is a diagram showing a map of a proportional basic value PL0.

FIG. 17 is a flowchart for explaining calculation of the increase / decrease amount t of the basic injection pulse width Tp in the second embodiment and the third embodiment.

FIG. 18 is a flowchart for explaining calculation of an increase / decrease amount s of a hysteresis width according to the second embodiment.

FIG. 19 is a flow chart for explaining calculation of the increase / decrease amount s of the hysteresis width according to the second embodiment.

FIG. 20 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α according to the second embodiment.

FIG. 21 is an operation explanatory view of the second embodiment.

FIG. 22 is a flowchart for explaining calculation of a proportional increase / decrease amount p in the third embodiment.

FIG. 23 is a flowchart for explaining calculation of a proportional increase / decrease amount p in the third embodiment.

FIG. 24 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α according to the third embodiment.

FIG. 25 is a diagram corresponding to the claims of the first invention.

FIG. 26 is a diagram corresponding to the claim of the sixth invention.

FIG. 27 is a diagram corresponding to the claim of the seventh invention.

FIG. 28 is a diagram corresponding to the claim of the fourteenth invention.

FIG. 29 is a diagram corresponding to the claim of the fifteenth invention.

FIG. 30 is a diagram corresponding to the claim of the sixteenth invention.

FIG. 31 is a diagram corresponding to the claim of the seventeenth invention.

[Explanation of symbols]

1 Engine Main Body 2 Control Unit 3 Upstream O ₂ Sensor 4 Crank Angle Sensor 6 Air Flow Meter 7 Fuel Injection Valve 10 Three-Way Catalyst (First Catalyst) 13 Downstream O ₂ Sensor 15 Three-Way Catalyst (Second Catalyst)

Claims (17)

[Claims] 1. A means for determining whether or not a first catalyst provided in an exhaust pipe has been activated, and based on the result of the determination, before the first catalyst is activated, the exhaust air-fuel ratio is on the rich side and the lean side. Means for controlling the air-fuel ratio so that the air-fuel ratio fluctuates alternately, and means for setting the magnitude of the amplitude of the exhaust air-fuel ratio, which fluctuates alternately between the rich side and the lean side, according to the oxygen storage capacity of the first catalyst. An exhaust gas purifying device for an engine, characterized by being provided with. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein a second catalyst is provided on the downstream side of the first catalyst. 3. A means for maintaining an average air-fuel ratio of exhaust gas near a stoichiometric air-fuel ratio while alternately changing the exhaust air-fuel ratio to a rich side and a lean side, according to claim 1 or 2. Engine exhaust purification device. 4. A sensor that outputs an output according to the oxygen concentration in the exhaust gas is provided before and after the first catalyst, and the first catalyst of the first catalyst is output based on the inversion frequency ratio or the inversion period ratio of the outputs of these two sensors. The exhaust gas purification device for an engine according to any one of claims 1 to 3, wherein the oxygen storage capacity is estimated. 5. A sensor for outputting an output according to the oxygen concentration in the exhaust gas on the downstream side of the first catalyst is provided, and the oxygen storage capacity of the first catalyst is estimated based on the amplitude of the sensor output. The exhaust emission control device for an engine according to any one of claims 1 to 3, which is characterized in that. 6. The air-fuel ratio amplitude setting means outputs a sensor according to the oxygen concentration in the exhaust gas on the upstream side of the first catalyst and a sensor for outputting the oxygen concentration in the exhaust gas on the downstream side of the first catalyst. And a means for measuring the inversion frequency ratio or the inversion period ratio of these two sensor outputs, and the inversion frequency ratio or the inversion period ratio is a value corresponding to the limit of the oxygen storage capacity of the first catalyst. 4. The engine exhaust according to claim 1, further comprising means for setting the magnitude of the amplitude of the exhaust air-fuel ratio by feedback-controlling the air-fuel ratio control amount so that Purification device. 7. The air-fuel ratio amplitude setting means, a sensor that outputs according to the oxygen concentration in the exhaust gas on the downstream side of the first catalyst, a means for measuring the amplitude of the downstream side sensor output, and the downstream side thereof. And means for setting the amplitude of the exhaust air-fuel ratio by feedback-controlling the air-fuel ratio control amount so that the amplitude of the side sensor output becomes a value corresponding to the limit of the oxygen storage capacity of the first catalyst. Claim 1 characterized by the above-mentioned.
The exhaust emission control device for an engine according to any one of 1 to 3. 8. An air-fuel ratio control amount when the oxygen storage capacity of the first catalyst reaches a limit-equivalent value for the first time after start-up is stored as a learning value, and this learned value is exhausted at the next start-up. The exhaust gas purifying apparatus for an engine according to claim 6 or 7, wherein is used as an initial value of the air-fuel ratio control amount when controlling so as to alternately swing to the rich side and the lean side. 9. The exhaust purification system for an engine according to claim 8, wherein the air-fuel ratio control amount is reset after a predetermined time has elapsed since the first learning of the air-fuel ratio control amount. 10. The engine exhaust gas purification apparatus according to claim 9, wherein learning of the air-fuel ratio control amount is prohibited when the air-fuel ratio control amount is reset. 11. The catalyst activation determination means outputs a sensor according to the oxygen concentration in the exhaust gas on the upstream side of the first catalyst and a sensor for outputting the oxygen concentration in the exhaust gas on the downstream side of the first catalyst. And a means for measuring the inversion frequency ratio or the inversion period ratio of these two sensor outputs, and determining whether or not the first catalyst is activated based on the inversion frequency ratio or the inversion period ratio. The exhaust gas purification device for an engine according to any one of claims 1 to 10, further comprising: 12. The catalyst activation determination means includes a sensor for detecting the temperature of the first catalyst, and means for determining whether or not the first catalyst has been activated based on the output of the temperature sensor. 11. The method according to claim 1, wherein
The engine exhaust gas purification device according to any one of items 1 to 3. 13. The catalyst activation judging means comprises a sensor for detecting a cooling water temperature of an engine and a means for judging whether or not the first catalyst is activated based on an output of the temperature sensor. The exhaust emission control device for an engine according to any one of claims 1 to 10, characterized in that. 14. The air-fuel ratio control means calculates means for calculating a basic injection amount that substantially obtains a theoretical air-fuel ratio according to operating conditions, and variably increases the basic injection amount for some cylinders, and The means for variably decreasing the cylinder, and the means for supplying the increased injection amount of fuel to the intake pipes of the partial cylinders and the means of supplying the decreased injection amount of fuel to the intake pipes of the remaining cylinders. The exhaust gas purification device for an engine according to any one of claims 1 to 13, wherein 15. The air-fuel ratio control means calculates means for calculating a basic injection amount to obtain a theoretical air-fuel ratio according to operating conditions, and output according to oxygen concentration in exhaust gas on the upstream side of the first catalyst. A sensor, means for variably setting the hysteresis width of the slice level for comparison with the upstream sensor output, and based on the comparison result of the set slice level of the hysteresis width and the upstream sensor output. It comprises means for calculating the air-fuel ratio feedback correction amount, means for calculating the fuel injection amount by correcting the basic injection amount with this air-fuel ratio feedback correction amount, and means for supplying this injection amount of fuel to the intake pipe. The exhaust emission control device for an engine according to any one of claims 1 to 13, characterized in that. 16. The air-fuel ratio control means calculates means for calculating a basic injection amount that substantially obtains a theoretical air-fuel ratio according to operating conditions, and output according to oxygen concentration in exhaust gas on the upstream side of the first catalyst. Sensor, means for variably setting the feedback constant based on the output of the upstream side sensor, means for calculating the air-fuel ratio feedback correction amount using this feedback constant, and the basic injection with this air-fuel ratio feedback correction amount. Means for correcting the amount and calculating the fuel injection amount,
The exhaust gas purification device for an engine according to any one of claims 1 to 13, characterized in that it comprises means for supplying the fuel of this injection amount to the intake pipe. 17. Means for keeping the average air-fuel ratio of the exhaust gas near the stoichiometric air-fuel ratio is a means for calculating a basic injection amount that provides a theoretical air-fuel ratio according to operating conditions, and a first catalyst upstream side. Of the sensor, which outputs according to the oxygen concentration in the exhaust gas, a means for setting a feedback constant based on the output of the upstream side sensor, and an output according to the oxygen concentration in the exhaust gas of the first catalyst downstream side. A sensor, and means for correcting the feedback constant so that the average air-fuel ratio of the exhaust gas comes close to the stoichiometric air-fuel ratio based on the output of the downstream side sensor,
A means for calculating the air-fuel ratio feedback correction amount using the corrected feedback constant, a means for calculating the fuel injection amount by correcting the basic injection amount with the air-fuel ratio feedback correction amount, and a fuel of this injection amount The exhaust gas purification device for an engine according to claim 3, characterized in that it comprises means for supplying the intake pipe.