JP2003166414A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine having a catalyst in an exhaust passage which maintains the purifying capacity of the catalyst constantly at an adequate value. <P>SOLUTION: The catalyst is disposed in the exhaust passage of the internal combustion engine. A main O<SB>2</SB>sensor and a sub O<SB>2</SB>sensor are disposed on the upstream side and the downstream side of the catalyst, respectively. The fuel injection is controlled based on the output of the main O<SB>2</SB>sensor so that the air-fuel ratio of the exhaust emission on the upstream side of the catalyst is oscillated across the theoretical air-fuel ratio. The quantity of oxygen flowing into the catalyst after the fuel cut is started and before the output of the sub O<SB>2</SB>sensor reaches a value corresponding to the air (Step 114) is calculated (Step 112). The maximum oxygen occlusion is calculated with the oxygen quantity regarded as 50% of the maximum oxygen occlusion of the catalyst. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine, and more particularly to a control device suitable for controlling an internal combustion engine having a catalyst in an exhaust passage.

[0002]

2. Description of the Related Art Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 8-193537, there is known a system in which a catalyst is arranged in an exhaust passage of an internal combustion engine and exhaust gas discharged from the internal combustion engine is purified by the catalyst. Has been. The catalyst used to purify the exhaust gas can store an appropriate amount of oxygen inside it, and if NOx is contained in the exhaust gas, it reduces the N0x by storing oxygen and also exhausts it. If the gas contains HC and CO, they can be oxidized by releasing oxygen. Therefore, according to the above system, the emission amount of NOx, CH, HC, etc. can be suppressed sufficiently small.

In order for the catalyst arranged in the exhaust passage to exhibit an appropriate purifying ability, a proper amount of oxygen is stored inside the catalyst, and a surplus capacity is left for the oxygen absorbing ability of the catalyst. is necessary. In the normal control of the internal combustion engine, the fuel injection amount is controlled so that the exhaust air-fuel ratio oscillates lean and rich across the stoichiometric air-fuel ratio. That is, the fuel injection amount is controlled so that the exhaust gas containing NOx and the exhaust gas containing HC and CO are alternately discharged. In this case, the oxygen storage state of the catalyst is always maintained in an appropriate state, so that good purification performance is continuously exhibited.

In the vehicle-mounted internal combustion engine, when fuel supply is unnecessary, fuel cut control is performed. Air flows through the exhaust passage during the fuel cut. For this reason, if the fuel cut is continued for a certain period of time, the catalyst will be in a state of fully storing oxygen.

When exhaust gas containing NOx is exhausted while oxygen is fully stored inside the catalyst, the NOx blows through the catalyst without being reduced. Therefore,
In the conventional system, in order to prevent such blow-through, a rich control for forcibly making the air-fuel ratio of the air-fuel mixture rich is executed for a predetermined period immediately after the end of the fuel cut.

During execution of the rich control, exhaust gas containing HC and CO is discharged. Meanwhile, the catalyst releases oxygen to oxidize HC and CO. As a result, when the rich control is performed for an appropriate period, the catalyst returns to a state in which it stores an appropriate amount of oxygen. Then, if the normal fuel injection amount control is restarted after the catalyst returns to that state, it is possible to maintain good exhaust emission characteristics continuously, including immediately after the fuel cut, without emitting HC or CO. You can

In the above conventional system, it is necessary to learn the maximum oxygen storage amount of the catalyst in order to properly control the rich control execution period. In the conventional system, in order to satisfy this request, a process of forcibly fixing the air-fuel ratio of the air-fuel mixture to rich and lean is performed over a predetermined period when a predetermined execution condition is satisfied.

When the air-fuel ratio of the air-fuel mixture is forcibly fixed to be rich, HC and CO do not flow downstream of the catalyst while oxygen remains in the catalyst. On the other hand, when all the stored oxygen in the catalyst is released, the gas containing HC and CO flows out downstream of the catalyst. Therefore, if the air-fuel ratio of the air-fuel mixture is forcibly fixed to rich, then the time at which all the oxygen stored in the catalyst is released can be detected by monitoring the exhaust air-fuel ratio downstream of the catalyst. it can.

When the air-fuel ratio of the air-fuel mixture is forcibly fixed to lean, NOx does not flow downstream of the catalyst while the oxygen storage capacity of the catalyst has a surplus. On the other hand, when the oxygen storage capacity is exhausted and the catalyst is fully stored with oxygen, thereafter, a gas containing NOx flows out to the downstream side of the catalyst.
Therefore, if the air-fuel ratio of the air-fuel mixture is forcibly fixed to lean, then the time when the oxygen storage capacity of the catalyst is exhausted can be detected by monitoring the exhaust air-fuel ratio downstream of the catalyst.

In the conventional system, by forcibly fixing the air-fuel ratio of the air-fuel mixture to rich or lean, a state in which all the oxygen in the catalyst is released and a state in which the catalyst fully stores oxygen are alternated. Will be realized. Then, while these states are switched, the total amount of oxygen that has flowed into the catalyst or the total amount of oxygen that has been released from the catalyst is calculated. In this case, the calculated value corresponds to the amount of oxygen that can be stored from the empty state to the full state of the catalyst, that is, the maximum oxygen storage amount of the catalyst. Thus, according to the conventional system, by forcibly fixing the air-fuel ratio to rich or lean,
The maximum oxygen storage amount can be calculated.

[0011]

However, in an internal combustion engine, forcibly fixing the air-fuel ratio of the air-fuel mixture to rich or lean is allowed only under extremely limited circumstances. Therefore, in the above conventional system, it is difficult to calculate the maximum oxygen storage amount at a desired frequency, and the value stored as the maximum oxygen storage amount easily deviates from the actual maximum oxygen storage amount. Is likely to occur.

Further, in the above-mentioned conventional system, the rich control may be excessively executed after the fuel cut due to the above-mentioned deviation of the maximum oxygen storage amount. If the rich control is excessively executed, the oxygen storage amount in the catalyst becomes too small at the time when the control is ended. In this case, the oxidizing ability of the catalyst for HC and CO becomes insufficient,
A situation may occur in which rich exhaust gas cannot be properly purified.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a control device for an internal combustion engine for always maintaining the purifying ability of a catalyst appropriately.

[0014]

The invention according to claim 1 is
In order to achieve the above object, there is provided a control device for an internal combustion engine having a catalyst in an exhaust passage, the main sensor detecting an exhaust air-fuel ratio upstream of the catalyst, and an exhaust air-fuel ratio downstream of the catalyst. And a fuel injection amount control means for controlling the fuel injection amount so that the exhaust air-fuel ratio upstream of the catalyst oscillates across the stoichiometric air-fuel ratio, and the fuel for cutting fuel injection under predetermined operating conditions. After the fuel cut is started, an increasing oxygen amount calculating means for calculating the amount of oxygen flowing into the catalyst as an increasing oxygen amount until the output of the sub-sensor becomes a value corresponding to air, and the increasing means. A maximum oxygen storage amount calculation means that regards the amount of oxygen as 50% of the maximum oxygen storage amount of the catalyst;
It is characterized by including.

The invention according to claim 2 is the control device for an internal combustion engine according to claim 1, wherein the oxygen storage capacity calculation means is a catalyst temperature acquisition means for acquiring the temperature of the catalyst, and the maximum oxygen storage capacity. Storage amount correction means for correcting the amount to the maximum oxygen storage amount secured when the catalyst is at the standard temperature, based on the temperature.

The invention according to claim 3 is the invention according to claim 1 or 2.
A control device for an internal combustion engine as described above, wherein the injection amount control means includes rich operation realization means for performing fuel increase correction so that the air-fuel ratio of the air-fuel mixture becomes rich under predetermined conditions. When the cut is executed within a predetermined period after the increase correction, the storage amount calculation prohibiting means for prohibiting execution of the process by the maximum oxygen storage amount calculating means is provided.

The invention according to claim 4 is the control device for an internal combustion engine according to any one of claims 1 to 3, wherein the increased oxygen amount or the maximum oxygen calculated based on the increased oxygen amount. It is characterized by comprising catalyst deterioration determination means for determining deterioration of the catalyst when the storage amount is less than a predetermined determination value.

The invention according to claim 5 is the control device for an internal combustion engine according to any one of claims 1 to 4, wherein the first determination time elapses after the fuel cut is started. , When the output of the main sensor does not become a lean output, main sensor abnormality determining means for determining abnormality of the main sensor, and after the fuel cut is started until the second determination time elapses, It is characterized by comprising at least one of a sub sensor abnormality judging means for judging an abnormality of the sub sensor when the output of the sub sensor does not become a lean output.

According to a sixth aspect of the present invention, there is provided a control device for an internal combustion engine having a catalyst in an exhaust passage, the maximum oxygen storage amount acquiring means for acquiring a maximum oxygen storage amount of the catalyst, and a predetermined operating condition. Fuel cut means for cutting fuel injection; inflow oxygen amount calculation means for calculating the inflow oxygen amount flowing into the catalyst during execution of the fuel cut;
Of the inflowing oxygen amount and the deviation guard value, a deviation initial value setting means for setting the smaller one as an initial value of the oxygen storage amount deviation,
A means for realizing rich control that makes the exhaust air-fuel ratio upstream of the catalyst rich, and after the end of the fuel cut,
Rich control executing means for executing the rich control, so that an amount of oxygen corresponding to the initial value of the oxygen storage amount deviation is released from the catalyst, the deviation guard value,
½ or less of the maximum oxygen storage amount of the catalyst, and
It is characterized in that the value is equal to or more than the oxygen storage capacity necessary for giving the catalyst a desired reducing ability.

According to a seventh aspect of the present invention, there is provided a control device for an internal combustion engine according to the sixth aspect, wherein at the time of starting the internal combustion engine, it is determined whether or not the catalyst is in an active state. The deviation initial value setting means includes a forced setting means for substituting the deviation guard value into the initial value of the oxygen storage amount deviation when the catalyst is in an active state at the time of starting the internal combustion engine. It is characterized by

The invention according to claim 8 is the invention according to claim 6 or 7.
In the control device for the internal combustion engine described above, the rich control executing means starts the rich control when the initial value of the oxygen storage amount deviation is larger than 0 at the end of the fuel cut. It is characterized by including.

According to a ninth aspect of the present invention, there is provided the control device for an internal combustion engine according to the eighth aspect, wherein an injection amount calculating means for calculating a fuel injection amount using an air-fuel ratio feedback coefficient and exhaust gas upstream of the catalyst are provided. Feedback coefficient updating means for updating the air-fuel ratio feedback coefficient in a decreasing direction when the air-fuel ratio is rich, and updating the air-fuel ratio feedback coefficient in an increasing direction when the exhaust air-fuel ratio upstream of the catalyst is lean. And a means for realizing the rich control, first realizing means for realizing the rich control by raising the air-fuel ratio feedback coefficient by a predetermined value, and an increasing speed of the air-fuel ratio feedback coefficient,
A second realization unit that realizes the rich control by speeding up the reduction speed, and a selection unit that selects the first realization unit during idling and selects the second realization unit during non-idling. It is characterized by

The invention as defined in claim 10 is defined by claim 6 through claim 9.
The control device for an internal combustion engine according to any one of claims 1 to 4, wherein the catalyst active state determination means determines whether the catalyst is in an active state, and when the catalyst is not in an active state, the rich control of Rich control execution prohibition means for prohibiting execution,
It is characterized by including.

The invention described in claim 11 is the invention according to claims 6 to 1.
The control device for an internal combustion engine according to any one of 0, wherein the released oxygen amount calculation means calculates an amount of released oxygen released from the catalyst in accordance with execution of the rich control, and the oxygen storage amount deviation. Deviation calculation means for calculating the oxygen storage amount deviation by subtracting the released oxygen amount from the initial value, and rich control termination means for terminating the rich control when the oxygen storage amount deviation becomes 0 or less, It is characterized by including.

According to a twelfth aspect of the present invention, there is provided the control device for an internal combustion engine according to the eleventh aspect, wherein a sub-sensor for detecting an exhaust air-fuel ratio downstream of the catalyst and a catalyst for the catalyst during execution of the rich control are provided. When a rich exhaust air-fuel ratio is detected downstream, a deviation reset means for setting the oxygen storage amount deviation to 0 or less at that time is provided.

The invention according to claim 13 is the control device for an internal combustion engine according to claim 11 or 12, wherein a sub-sensor for detecting an exhaust air-fuel ratio downstream of the catalyst, and an output of the sub-sensor for the fuel injection amount Sub-feedback means for reflecting in the calculation, and sub-feedback prohibiting means for prohibiting updating of the coefficient for reflecting the output of the sub-sensor in the calculation of the fuel injection amount when the oxygen storage amount deviation is larger than a predetermined value. And are provided.

According to a fourteenth aspect of the present invention, there is provided a control device for an internal combustion engine according to any one of the eleventh to thirteenth aspects.
When a predetermined correlation is recognized between the main sensor that detects the exhaust air-fuel ratio upstream of the catalyst, the sub-sensor that detects the exhaust air-fuel ratio downstream of the catalyst, and the output of the main sensor and the output of the sub-sensor. Further, a catalyst deterioration determination means for determining deterioration of the catalyst, and a catalyst deterioration determination prohibition means for prohibiting deterioration determination of the catalyst when the oxygen storage amount deviation is a value larger than a predetermined value. Is characterized by.

According to a fifteenth aspect of the present invention, there is provided a control device for an internal combustion engine, comprising a catalyst unit including an upstream catalyst and a downstream catalyst arranged in series in an exhaust passage, the fuel injection being performed under a predetermined operating condition. Fuel cut means to cut,
Of the unit inflowing oxygen amount calculation means for calculating the amount of oxygen flowing into the catalyst unit as the unit inflowing oxygen amount during execution of the fuel cut, the unit inflowing oxygen amount, and the unit deviation guard value, the smaller one is Unit deviation initial value setting means for setting an initial value of oxygen storage amount deviation of the catalyst unit, a sub-sensor for detecting an exhaust air-fuel ratio between the upstream catalyst and the downstream catalyst, and during execution of the fuel cut, the sub-sensor Of the downstream inflow oxygen amount calculation means for calculating the amount of oxygen flowing into the catalyst unit as the downstream inflow oxygen amount after the output of becomes a value corresponding to air, the downstream inflow oxygen amount, and the downstream deviation guard value. , A downstream deviation initial value setting means for setting the smaller one as an initial value of the oxygen storage amount deviation of the downstream catalyst, and upstream of the catalyst unit. A rich control realizing means for making the air-fuel ratio rich, a rich control executing means for executing the rich control after the end of the fuel cut, and an oxygen amount released from the catalyst unit along with the execution of the rich control. Is a unit release oxygen amount calculation means for calculating as a unit release oxygen amount, and subtracts the unit release oxygen amount from the initial value of the oxygen storage amount deviation of the catalyst unit,
A unit deviation calculating means for calculating a unit oxygen storage amount deviation, and a downstream for calculating the amount of oxygen released from the catalyst unit after the output of the sub-sensor changes to a rich output during the execution of the rich control as a downstream released oxygen amount. A released oxygen amount calculation means, a downstream deviation calculation means for calculating the downstream oxygen storage amount deviation by subtracting the downstream released oxygen amount from the initial value of the oxygen storage amount deviation of the downstream catalyst, and the unit oxygen storage amount deviation and Rich control termination means for terminating the rich control when at least one of the downstream oxygen storage amount deviations becomes 0 or less.

The invention according to claim 16 is the control device for an internal combustion engine according to claim 15, comprising unit maximum oxygen storage amount acquisition means for acquiring the maximum oxygen storage amount of the catalyst unit, and the unit deviation guard. The value is equal to or less than 1/2 of the maximum oxygen storage amount of the catalyst unit, and is a value equal to or more than the oxygen storage capacity required to give the catalyst unit a desired reducing ability.

The invention according to claim 17 is the control device for an internal combustion engine according to claim 15 or 16, comprising a downstream maximum oxygen storage amount acquisition means for acquiring the maximum oxygen storage amount of the downstream catalyst, The deviation guard value is equal to or less than a value obtained by subtracting 1/2 of the maximum oxygen storage amount of the catalyst unit from the maximum oxygen storage amount of the downstream catalyst, and the sum of the maximum oxygen storage amount of the upstream catalyst and the catalyst It is characterized in that it is a value which is equal to or more than the oxygen storage capacity necessary for giving the unit a desired reducing ability.

The invention according to claim 18 is the control device for an internal combustion engine according to claim 16 or 17, wherein a main sensor for detecting an exhaust air-fuel ratio upstream of the upstream catalyst, and an exhaust gas upstream of the upstream catalyst. An injection amount control means for controlling the fuel injection amount so that the air-fuel ratio oscillates across the stoichiometric air-fuel ratio, and the unit maximum oxygen storage amount acquisition means,
After the fuel cut is started, the upstream oxygen increase amount calculating means for calculating the amount of oxygen flowing into the catalyst unit as the upstream oxygen increase amount until the output of the sub-sensor reaches a value corresponding to air, and the upstream increase An upstream maximum oxygen storage amount calculation means for calculating the maximum oxygen storage amount of the upstream catalyst by regarding the oxygen amount as 50% of the maximum oxygen storage amount of the upstream catalyst, and a downstream for obtaining the maximum oxygen storage amount of the downstream catalyst. A maximum oxygen storage amount acquisition means, a maximum oxygen storage amount of the upstream catalyst, and an addition means for calculating the unit maximum oxygen storage amount by adding the maximum oxygen storage amount of the downstream catalyst,
It is characterized by including.

The invention according to claim 19 is the control device for an internal combustion engine according to claim 17 or 18, wherein a second sub-sensor for detecting an exhaust air-fuel ratio downstream of the downstream catalyst and an upstream of the upstream catalyst are provided. Injection amount control means for controlling the fuel injection amount so that the exhaust air-fuel ratio oscillates across the stoichiometric air-fuel ratio, the downstream maximum oxygen storage amount acquisition means, during execution of the fuel cut, the output of the sub-sensor Downstream increasing oxygen amount calculating means for calculating, as the downstream increasing oxygen amount, the amount of oxygen that has flowed into the catalyst unit until the output of the second sub-sensor reaches the value corresponding to air. And a downstream maximum oxygen storage amount calculation means for calculating the maximum oxygen storage amount of the downstream catalyst by regarding the downstream increased oxygen amount as 50% of the maximum oxygen storage amount of the downstream catalyst. And wherein the door.

The invention according to claim 20 is the control device for an internal combustion engine according to any one of claims 15 to 19,
At the time of starting the internal combustion engine, it is provided with a start-up active state determining means for determining whether or not the catalyst unit is in an active state, and the unit deviation initial value setting means, when starting the internal combustion engine, the catalyst unit is in an active state. When it is, the first deviation setting means for substituting the unit deviation guard value into the initial value of the oxygen storage amount deviation of the catalyst unit, the downstream deviation initial value setting means, when starting the internal combustion engine, When the catalyst unit is in the active state, the second forced setting means for substituting the downstream deviation guard value into the initial value of the oxygen storage amount deviation of the downstream catalyst is provided.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. It should be noted that elements common to each drawing are denoted by the same reference numerals, and redundant description will be omitted.

First, the configuration of a system that can be used in the embodiment of the present invention will be described. FIG. 1 shows an example of a typical system configuration that can be used in the embodiment of the present invention. The configuration shown in FIG. 1 includes an internal combustion engine 10. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. The intake passage 12 has an air filter 16 at the upstream end.

An air flow meter 20 is arranged downstream of the air filter 16. The air flow meter 20 is a sensor that detects the intake air amount Ga flowing through the intake passage 12. A throttle valve 22 is provided downstream of the air flow meter 20. A throttle sensor 24 for detecting the throttle opening TA is provided near the throttle valve 22.
And an idle switch 26 that is turned on when the throttle valve 22 is fully closed.

A surge tank 28 is provided downstream of the throttle valve 22. Further, a fuel injection valve 30 for injecting fuel into an intake port of the internal combustion engine 10 is arranged further downstream of the surge tank.

A catalyst 32 communicates with the exhaust passage 14. The catalyst 32 can store a certain amount of oxygen, and when unburned components such as HC and CO are contained in the exhaust gas, the stored oxygen is used to oxidize them and the exhaust gas is exhausted. When the gas contains oxidizing components such as NOx, they can be reduced and the released oxygen can be stored. The exhaust gas discharged from the internal combustion engine 10 is purified by being processed in the catalyst 32 as described above.

In the exhaust passage 14, upstream and downstream of the catalyst 32, a main O ₂ sensor 34 and a sub O ₂ sensor 3 are provided.
6 are arranged. Main O ₂ sensor 34 and sub O
Each of the _two sensors 36 is a sensor that changes its output according to the oxygen concentration in the gas to be detected, and when the exhaust air-fuel ratio becomes rich, thereafter, 1 V is applied until the air-fuel ratio becomes lean.
It is a sensor that generates a voltage in the vicinity and, when the exhaust air-fuel ratio becomes lean, subsequently generates a voltage of about 0.1 V until the air-fuel ratio becomes rich.

According to the main O ₂ sensor 34, the catalyst 32
It is possible to detect whether the exhaust air-fuel ratio is rich or lean upstream, that is, whether the exhaust gas discharged from the internal combustion engine 10 is rich or lean. Further, according to the sub O ₂ sensor 36, the exhaust gas (H
It is possible to judge whether the exhaust gas containing C, CO has flowed out, or the exhaust gas with a lean air-fuel ratio (exhaust gas containing NOx) has flowed out.

As shown in FIG. 1, the system of this embodiment includes an ECU (Electronic Control Unit) 40.
The ECU 40 includes various sensors and the fuel injection valve 3 described above.
In addition to 0, a water temperature sensor 42 that detects the cooling water temperature THW of the internal combustion engine 10 is connected.

FIG. 2 is a simplified view of a modification of the configuration that can be used in the embodiment of the present invention.
The system shown in FIG. 1 has the internal combustion engine 10 as described above.
The exhaust passage 14 is provided with one catalyst 32 and two O ₂ sensors 34 and 36. The configuration shown in FIG. 2B represents the configuration of this system. Hereinafter, this configuration will be referred to as a "1 catalyst 2 sensor configuration".

FIG. 2A shows the exhaust passage 1 of the internal combustion engine 10.
4 has one catalyst 32 and one O ₂ sensor 34. This configuration is based on the system configuration shown in FIG.
It is assumed that the O ₂ sensor 36 is removed. Hereinafter, this configuration will be referred to as a “one-catalyst, one-sensor configuration”.

FIG. 2C shows the exhaust passage 1 of the internal combustion engine 10.
4, two catalysts 32,44 and two O ₂ sensors 34,3
6 is provided. This configuration is similar to the system configuration shown in FIG. 1 except that the second catalyst 4 is provided downstream of the sub O ₂ sensor 36.
4 represents the configuration added. Hereinafter, this configuration will be referred to as a “two-catalyst, two-sensor configuration”.

FIG. 2D shows the exhaust passage 1 of the internal combustion engine 10.
4, two catalysts 32,44 and three O ₂ sensors 34,3
It is equipped with 6,48. This configuration represents that in the system configuration shown in FIG. 1, a second catalyst 44 is added downstream of the sub O ₂ sensor 36 and a second sub O ₂ sensor 48 is added further downstream thereof. To do. Hereinafter, this configuration will be referred to as a “two-catalyst, three-sensor configuration”.

In the following description, when the two-catalyst two-sensor configuration shown in FIG. 2C or the two-catalyst three-sensor configuration shown in FIG.
In order to distinguish 2, 44, the upstream side catalyst 32 and the downstream side catalyst 44 will be referred to as "upstream catalyst 32" and "downstream catalyst 44", respectively. Further, the upstream catalyst 32
And the downstream catalyst 44 are collectively referred to as “catalyst unit 46”.

By the way, in the system configuration described above,
An O ₂ sensor that detects whether the exhaust air-fuel ratio is rich or lean is used as the sensor that detects the exhaust air-fuel ratio, but the sensor is not limited to this. That is, O included in the configurations shown in FIGS. 1 and 2.
_{The two} sensors may be replaced with an air-fuel ratio sensor that generates a signal according to the exhaust air-fuel ratio.

Embodiment 1. Next, the first embodiment of the present invention will be described with reference to FIGS. The system of this embodiment can be realized by using the configuration shown in FIGS. 1 and 2B, that is, the one-catalyst two-sensor configuration. FIG. 3 shows the system of the present embodiment.
6 is a flowchart for explaining the flow of main processing executed by the ECU 40.

As shown in FIG. 3, in the system of this embodiment, first, the maximum oxygen storage amount of the catalyst 32 (catalyst oxygen storage capacity) is calculated (S100). ECU40 is
When the engine speed NE is high and the throttle valve 22 is fully closed, the process of stopping the fuel injection from the fuel injection valve 30, that is, the fuel cut is performed.
In this step S100, the maximum oxygen storage amount of the catalyst 32 is calculated by the method described later during the fuel cut.

Next, an initial value of the catalyst oxygen storage amount deviation is calculated (S200). The oxygen storage amount deviation is an average oxygen storage amount of the catalyst 32, or a deviation between an upper limit of the oxygen storage amount for the catalyst 32 to exhibit a desired reducing ability and an estimated value of the actual oxygen storage amount. It is a concept that means. In other words, the oxygen storage amount deviation is a value that means the amount of oxygen to be released from the catalyst 32 in order to give the catalyst 32 a desired reducing ability. In this step S200, the oxygen storage amount deviation is calculated by the method described later at the end of the fuel cut, and the calculated value is recorded as the initial value of the oxygen storage amount deviation.

Next, rich control is executed (S30).
0). The oxygen stored in the catalyst 32 can be released by supplying the exhaust gas with a rich air-fuel ratio to the catalyst 32. In rich control, to reduce the oxygen storage amount deviation,
This is a process executed to supply the exhaust gas with a rich air-fuel ratio to the catalyst 32. The contents of the rich control will be described later in detail.

Next, a process for subtracting the oxygen storage amount deviation of the catalyst 32 is performed (S400). The oxygen storage amount of the catalyst 32 decreases as the rich control is executed. Therefore, the amount of oxygen to be released from the catalyst 32 in order to provide the desired reducing ability, that is, the oxygen storage amount deviation, decreases with the execution of the rich control. In this step S400,
The amount of oxygen released from the catalyst 32 during the rich control process is calculated according to the method described below. Then, by subtracting the released amount from the initial value of the oxygen storage amount deviation, the oxygen storage amount deviation is updated to a value that actually matches.

Next, a process relating to restriction of related control is performed (S500). The system of the present embodiment is a sub O ₂
The output of the sensor 36 is used for some related control. Sub 0 ₂ sensor 36 and are located downstream of the catalyst 32, the output is affected by the oxygen storage state of the catalyst 32. Therefore, when oxygen is excessively stored inside the catalyst 32 due to the execution of fuel cut,
The output of the O ₂ sensor 36 may have a value different from the normal value. In this step S500, a process for limiting the execution of the related control is performed when the catalyst 32 has excessive oxygen so that the related control is not unreasonably advanced under such a situation.

The contents of S100 shown in FIG. 3, that is, a method for the system of the present embodiment to calculate the maximum oxygen storage amount of the catalyst 32 will be described below with reference to FIGS. FIG. 4 shows changes in the output of the main O ₂ sensor 34 before and after the fuel cut (FIG. 4A) (FIG. 4A).
(B)) and changes that occur in the output of the sub O ₂ sensor 36 (FIG. 4C).

FIG. 4A shows that the fuel cut is performed at time t1. Also, FIG. 4 (B)
Until the fuel cut (before time t1)
Indicates that the ECU 40 is executing the air-fuel ratio feedback control based on the output of the main O ₂ sensor 34.

The air-fuel ratio feedback control is a control for correcting the fuel injection time TAU using the air-fuel ratio feedback coefficient FAF. Where A / F feedback coefficient
FAF is a correction coefficient for expanding and contracting the fuel injection time TAU, and for example, while the air-fuel ratio of the air-fuel mixture is rich, that is, while the main O ₂ sensor 34 is producing a rich output (about 1V). , Is gradually updated to a small value in order to shorten the fuel injection time TAU. When the FAF is updated in this way in the shortening direction, the fuel injection time TAU is gradually reduced and the air-fuel ratio of the air-fuel mixture eventually becomes lean, resulting in the main O ₂
The output of the sensor 34 is inverted to the lean output (about 0.1V).

When the output of the main O ₂ sensor 34 is inverted to the lean output, the air-fuel ratio feedback coefficient FAF is largely skipped in the increasing direction at that time. Then, until the output of the main O ₂ sensor 34 is inverted to the rich output,
That is, FAF is gradually updated to a large value until the air-fuel ratio of the air-fuel mixture becomes rich. As a result, fuel injection time
TAU is gradually increased, the air-fuel ratio of the air-fuel mixture becomes rich, and the output of the main O ₂ sensor 34 is inverted to the rich output (about 1V). When the output of the main O ₂ sensor 34 is inverted to the rich output, the air-fuel ratio feedback coefficient FAF is skipped to a large decrease at that time. After that, the air-fuel ratio of the air-fuel mixture is maintained near the stoichiometric air-fuel ratio by repeatedly executing the above-described update processing. as a result,
The output of the main O ₂ sensor 34 is the time t1 in FIG.
As shown previously, the reversal is repeated, and the air-fuel ratio of the air-fuel mixture (exhaust air-fuel ratio upstream of the catalyst 32) repeats increasing and decreasing centering on the theoretical air-fuel ratio.

During the execution of the air-fuel ratio feedback control, while the exhaust air-fuel ratio upstream of the catalyst 32 is rich, HC and CO contained in the exhaust gas are oxidized, so that the stored oxygen in the catalyst 32 is consumed (released). To be done. On the other hand, during execution of the air-fuel ratio feedback control, oxygen generated by NOx reduction is stored in the catalyst 32 while the exhaust air-fuel ratio upstream of the catalyst 32 is lean. Therefore, during the execution of the air-fuel ratio feedback control, the amount of stored oxygen in the catalyst 32 is repeatedly increased and decreased, and as a result, an appropriate amount of oxygen necessary for exhibiting a desired oxidation capacity is obtained. The catalyst 32 is maintained in a state in which it is ensured in the catalyst 32 and the oxygen storage capacity necessary for exhibiting a desired reduction capacity is left in the catalyst 32.

When the fuel cut is executed in the internal combustion engine 10, air then flows through the exhaust passage 14. As a result, as shown in FIG. 4B, after time t1,
The output of the main O ₂ sensor 34 changes to a value according to the oxygen concentration in the air. At this time, the output is specifically reduced to a value (near 0V) sufficiently smaller than the lean output (0.1V) output during the execution of the air-fuel ratio feedback control. Therefore, by monitoring the output of the main O ₂ sensor 34, it is possible to detect the timing (time t2) when the air actually starts flowing into the catalyst 32 after the fuel cut is started.

When air begins to flow through the exhaust passage 14, oxygen in the air is stored in the catalyst 32, and the amount of stored oxygen in the catalyst 32 increases rapidly. When the catalyst 32 stores oxygen to its full capacity, that is, when the oxygen storage amount in the catalyst 32 reaches the maximum oxygen storage amount, air having the same components as the air discharged from the internal combustion engine 10 flows downstream of the catalyst 32. It begins to blow through. As a result, as shown in FIG. 4C, the output of the sub O ₂ sensor 36 changes to a value according to the oxygen concentration in the air. Therefore, if the output of the sub O ₂ sensor 36 is monitored,
It is possible to detect the timing (time t3) when the oxygen having the maximum capacity is stored in the catalyst 32.

By the way, FIG. 4 is a timing chart when the sub-O ₂ sensor 36 outputs a rich output (about 1 V) before execution of the fuel cut. On the other hand, FIG. 5 shows a timing chart when the sub-O ₂ sensor 36 outputs a lean output (about 0.1 V) before execution of the fuel cut. As shown in FIG. 5C, the sub-O
_{2 The} value that the sensor 36 outputs to air (about 0V) is
The sensor 36 has a sufficiently small value as compared with the lean output generated during the execution of the air-fuel ratio feedback control. Therefore, even if the sub-O ₂ sensor 36 outputs a lean output (about 0.1 V) before executing the fuel cut, by monitoring the output, the oxygen storage amount of the catalyst 32 reaches the maximum oxygen storage amount. It is possible to detect the timing (time t3).

As described above, in the system of this embodiment,
By monitoring the output of the main O ₂ sensor 34, the catalyst 3
2 detects the timing when the air reaches the upstream,
By monitoring the output of the sub O ₂ sensor 36, the catalyst 32
It is possible to detect the timing when oxygen is fully stored in oxygen. More specifically, the time (time t2) at which the output of the main O ₂ sensor 34 decreases to a value that does not normally occur (for example, 0.1 V) is detected as the timing at which air reaches the upstream of the catalyst 32, and The time (time t2) when the output of the sub-O ₂ sensor 36 decreases to a value that does not normally occur (for example, 0.1 V) can be detected as the timing when the catalyst 32 has fully stored oxygen. Therefore, in the example shown in FIG. 4 or FIG. 5, the period from time t2 to time t3 can be regarded as the period during which the catalyst 32 newly adsorbs oxygen during the fuel cut process.

FIG. 6 shows the system of this embodiment.
It is a figure for explaining an image of change which occurs in the amount of oxygen occlusion of catalyst 32 before and after fuel cut. Figure 6
(A) is a diagram showing the state of the catalyst 32 before the fuel cut is executed, that is, during the feedback operation. In this figure, the band indicated by the reference numeral represents the average oxygen storage level during the feedback operation. Further, the region indicated by the reference numeral represents the remaining capacity of the oxygen storage capacity that should be ensured inside the catalyst 32 in order to exhibit the desired reduction capacity. Usually, a storage capacity of about 1/3 of the maximum oxygen storage amount is required as the remaining capacity.

During the feedback operation, as described above,
The increase and decrease of the oxygen storage amount are repeated. When this operation is performed for a long period of time (including intermittent cases), the oxygen storage amount stochastically converges to about 50% of the maximum oxygen storage amount.
Therefore, in the normal state, the catalyst 32 satisfies the requirement regarding the remaining capacity.

FIG. 6B is a diagram showing a state in which the catalyst 32 occludes oxygen to its full capacity as the fuel cut is performed. In the example shown in FIG. 4 or FIG. 5 described above, the catalyst 32 is in the state shown in FIG. 6 (A) at time t2. Then, since oxygen is stored in the catalyst 32 from time t2 to time t3, the state shown in FIG. 6B is formed in the catalyst 32 at the time t3.

Here, from time t2 to time t3, the catalyst 3
It can be estimated that the amount of oxygen stored in 2 corresponds to a value obtained by subtracting the oxygen storage amount in the normal time from the maximum oxygen storage amount of the catalyst 32, that is, approximately 50% of the maximum oxygen storage amount of the catalyst 32. Therefore, in the present embodiment, assuming that twice the amount of oxygen stored in the catalyst 32 from the time t2 to the time t3 is the maximum oxygen storage amount of the catalyst 32, the maximum oxygen storage amount is calculated. There is.

In FIG. 6 (C), the rich control is executed so that the remaining capacity related to the oxygen storage capacity of the catalyst 32 is
It shows the condition of being restored to the required amount. As mentioned above, catalyst 3
2 requires a reserve capacity of about 1/3 of the maximum oxygen storage amount. In the present embodiment, the rich control in S300 described above is performed so that the remaining capacity that has been used up due to the execution of the fuel cut is restored to about 1/3 of the maximum oxygen storage amount as shown in FIG. 6 (C). To be executed.

FIG. 7 is a flowchart of the first group of processes executed to implement the step S100 shown in FIG. More specifically, FIG. 7 is a flowchart of a series of processes executed by the ECU 40 to obtain the actual measured value of the maximum oxygen storage amount of the catalyst 32.

In the routine shown in FIG. 7, first, it is judged whether or not the precondition for obtaining the actual measured value of the maximum oxygen storage amount is satisfied. Specifically, the catalyst 32 is in an active state, or the main O ₂ sensor 34 and the sub O _{2
2 It} is determined whether the sensor 36 is in the active state (step 102).

As a result, if it is determined that the precondition is not satisfied, the other processing shown in FIG. 7 is skipped. On the other hand, if it is determined that the precondition is satisfied, then it is determined whether or not the fuel cut is being executed (step 104).

The system of this embodiment acquires the data necessary for calculating the maximum oxygen storage amount during the fuel cut. Therefore, if it is determined that the fuel cut has not been executed, the other processing shown in FIG. 7 is thereafter skipped. On the other hand, if it is determined that the fuel cut is being performed, then it is determined whether or not the rich operation has been performed for a predetermined period before the fuel cut is performed (step 106).

The rich operation is an operation in which the fuel injection amount is increased and corrected so that the air-fuel ratio of the air-fuel mixture becomes rich. For example, when the driver requests acceleration of the vehicle, or when the catalyst 32 is heated (OT: Over Temperatu
This is performed when it is required to make the exhaust air-fuel ratio rich to prevent re) (as a result, the catalyst temperature can be lowered).

During the rich operation, the exhaust gas containing HC and CO flows into the catalyst 32 and the stored oxygen in the catalyst 32 is consumed. Therefore, immediately after the rich operation, the oxygen storage amount of the catalyst 32 becomes smaller than the normal storage amount. The system of the present embodiment calculates the maximum oxygen storage amount on the assumption that the oxygen storage amount of the catalyst 32 is a normal value. Therefore, when the oxygen storage amount of the catalyst 32 is smaller than the normal value, the maximum oxygen storage amount cannot be calculated accurately.

Therefore, when the condition of the above step 106 is not satisfied (when the rich operation is performed), the calculation process of the maximum oxygen storage amount is stopped, and thereafter, as shown in FIG.
The routine shown in is ended. On the other hand, the above step 10
When the condition of 6 is satisfied, the oxygen storage amount is considered to be a normal value, and the process for calculating the maximum oxygen storage amount is continued. Specifically, it is determined whether or not the output of the main O ₂ sensor 34 is below 0.1V (step 108).

When it is determined that the condition of step 108 is not satisfied, the air containing no fuel is still in the catalyst 32.
It can be judged that it has not reached. In the routine shown in FIG. 7, the following processing is jumped in this case. On the other hand, when the condition of step 108 is satisfied, it can be determined that the fuel-free air is flowing into the catalyst 32. In this case, it is then determined whether or not the transfer delay time has elapsed (step 110).

Exhaust gas is the main O_Two
From the position of the sensor 34 to the sub O_TwoFlow to the position of sensor 36
It is the time it takes to be done. Referring to FIG. 4 and FIG.
In the example described, the main O_TwoOutput of sensor 34 is 0.1V
From time t2 when _TwoThe output of the sensor 36
The catalyst 32 adsorbs oxygen until time t3 below 0.1 V.
It has already been described that it can be grasped as a period to do. But Naga
The air remaining inside the catalyst 32 at time t3
Is inside the catalyst 32 after it has fully stored oxygen.
Is the air that has flowed into the. Therefore, the catalyst 32 stores oxygen.
Strictly speaking, the period of time is "Transfer from time t2 to time t3
It is necessary to catch "the delay time is earlier until the time". So
Here, in the routine shown in FIG._TwoOutput of sensor
After the force falls below 0.1V, the transfer delay time elapses.
The time at which the catalyst 32 occludes oxygen
By eliminating the influence of transfer delay time,
There is.

The determination in step 110 is a process for realizing the above function. In the routine shown in FIG. 7, when the condition of step 110 is not satisfied, the following processing is jumped. Then, the above step 110
If the condition of is satisfied, then the integration of the intake air amount Ga is started (step 112). When the processing of the present step 112 is executed, thereafter, the integrated air amount is calculated by integrating the intake air amount Ga detected by the air flow meter 20 by another routine.

In the routine shown in FIG. 7, the sub O ₂
It is determined whether the output of the sensor 36 is lower than 0.1V (step 114).

As a result, when it is determined that the condition of step 114 is not satisfied, it is determined that the catalyst 32 has not yet stored oxygen having the maximum capacity. in this case,
After that, other processing shown in FIG. 7 is jumped. On the other hand, when it is determined that the output of the sub O ₂ sensor 36 is lower than 0.1 V, it is determined that the catalyst 32 has stored oxygen with the maximum capacity. In this case, next, the sub O ₂ sensor 36
The amount of oxygen actually stored during the oxygen storage period by the catalyst 32 is calculated based on the integrated air amount calculated until the output of 1 is below 0.1 V (step 116).

In step 116, specifically, the intake oxygen amount is calculated by multiplying the integrated air amount by the oxygen ratio in the air (0.23). By the way, in the present embodiment, the integrated air amount is calculated by actually integrating the intake air amount Ga detected by the air flow meter, but the method of calculating the integrated air amount is not limited to this. That is, during fuel cut, the throttle valve 22 is fully closed, so the intake air amount Ga generated per unit time during that time is a substantially fixed value.
Therefore, the integrated air amount may be obtained by multiplying the fixed value by the time until the condition of step 114 is satisfied after the condition of step 110 is satisfied.

As described above, according to the series of processes described above, it is estimated that the amount of oxygen newly stored in the catalyst 32 during the fuel cut process, that is, 50% of the maximum stored oxygen amount of the catalyst 32 is estimated. The amount of oxygen can be calculated. By the way, the maximum stored oxygen amount of the catalyst 32 varies depending on the catalyst temperature. Therefore, the above step 116
The oxygen amount calculated in 1 is a value affected by the catalyst temperature.

In the routine shown in FIG. 7, in order to eliminate the influence, the current catalyst temperature is first acquired after the processing of step 116 is completed (step 118).
The catalyst temperature can be predicted by a known method from the operating state of the internal combustion engine 10 before the fuel cut is executed. Further, a bed temperature sensor may be arranged on the catalyst 32 and the catalyst temperature may be acquired by actual measurement.

Next, based on the catalyst temperature obtained in step 118, the oxygen amount calculated in step 116 is converted into the oxygen amount at the standard temperature (step 120). In the present embodiment, the ECU 40 stores a coefficient for converting the oxygen amount obtained at an arbitrary catalyst temperature into the oxygen amount that should be obtained when the catalyst temperature is the standard temperature, in a map format. . This step 1
In 20, the oxygen amount at the standard temperature is calculated by multiplying the oxygen amount calculated in step 116 by the coefficient read from the map.

The oxygen amount at the standard temperature calculated by the series of processes described above is a value that can be regarded as ½ of the maximum oxygen storage amount of the catalyst 32 at the standard temperature. Therefore, if the oxygen amount is doubled, the maximum oxygen storage amount of the catalyst 32 at the standard temperature can be obtained. However, the above oxygen amount is superposed with an error due to the variation in the environment when the value is calculated. Therefore, in the system of the present embodiment, in order to absorb the variation in the oxygen amount, the oxygen amount calculated in step 120 is not directly used to determine the maximum oxygen storage amount, but a plurality of oxygen calculated in the above-described procedure is used. The maximum amount of oxygen is determined based on the average value of the amount of oxygen. Therefore, in the routine shown in FIG. 7, the oxygen amount calculated in step 120 is temporarily stored as the nth data Nn.

FIG. 8 is a flowchart of the second group of processes executed to realize the step S100 shown in FIG. More specifically, FIG. 8 is a flowchart of a series of processes executed by the ECU 40 to calculate the maximum oxygen storage amount of the catalyst 32 based on the individual oxygen amount calculated by the process shown in FIG. 7. is there.

In the routine shown in FIG. 8, first, it is judged whether or not the update processing of the nth data Nn has been performed (step 130).

As a result, if it is determined that the update processing of the data Nn is not performed, then other processing shown in FIG. 8 is jumped. On the other hand, if it is determined that the data Nn has been updated, then the average value from the 0th data N0 to the nth data Nn is calculated (step 13).
2).

Next, twice the average value is calculated as the maximum oxygen storage amount of the catalyst 32 (step 134). According to the above process, the variation in the environment in the process of calculating the individual oxygen amount is leveled, and the maximum oxygen storage amount more suitable for the actual state can be obtained.

When the above process is completed, the oxygen amount data is exchanged, that is, the first data N1 to nth data Nn are replaced with the 0th data N0 to n-1 in preparation for the next process. The process of re-storing to the nth data Nn-1 is executed.

As described above, according to the routines shown in FIGS. 7 and 8, the catalyst 32 is used during the fuel cut process.
It is possible to determine the maximum oxygen storage amount by considering the newly stored oxygen amount as 50% of the maximum oxygen storage amount and taking into consideration variations in catalyst temperature and environment. According to this method, the maximum oxygen storage amount can be obtained at high frequency almost every time the fuel cut is executed without forcibly fixing the air-fuel ratio to rich or lean. Therefore, according to the system of the present embodiment, it is possible to always grasp the maximum oxygen storage amount that accurately matches the actual state.

By the way, in the system of this embodiment, in addition to the main processing shown in FIG. 3, processing for realizing the following functions is executed. (1) The process of determining deterioration of the catalyst 32 based on the maximum oxygen storage amount obtained by the above method, and (2) the phenomenon that occurs after the start of fuel cut is used to utilize the main O ₂ sensor 34 and the sub O ₂ sensor. ₂ Process for determining abnormality of the sensor 36.

FIG. 9 shows E to realize the function of (1) above.
It is a flow chart of a routine which CU40 performs. In the routine shown in FIG. 9, first, it is determined whether or not the maximum oxygen storage amount calculated in step 134 is smaller than a predetermined determination value (step 600).

The maximum oxygen storage amount of the catalyst 32 decreases as the deterioration of the catalyst 32 progresses. The above determination value is a value corresponding to the maximum oxygen storage amount that the catalyst 32 at the standard temperature should have at least. Therefore, when it is determined that the maximum oxygen storage amount <the determination value is not established, it can be determined that the catalyst 32 does not undergo unacceptable deterioration. In this case, the current processing cycle is ended thereafter without executing any processing. On the other hand, if the above conditions are satisfied, the catalyst 32
In addition, it can be determined that unacceptable deterioration has occurred. In this case, the current processing cycle is ended after it is determined that the catalyst 32 has deteriorated (step 602).

As described above, according to the routine shown in FIG. 9, it is determined whether the catalyst 32 is deteriorated based on the maximum oxygen storage amount calculated by the routines shown in FIGS.
It can be performed easily and accurately.

FIG. 10 is a flow chart of a routine executed by the ECU 40 in order to realize the function (2), that is, to determine the abnormality of the main O ₂ sensor 34 and the sub O ₂ sensor. In the routine shown in FIG.
First, it is determined whether the fuel cut is being executed (step 610).

As a result, if it is determined that the fuel cut has not been executed, the determination counter is reset (step 612) and then the current processing cycle is ended. Here, the determination counter is a counter for counting the elapsed time after the fuel cut is started.

On the other hand, if it is determined in step 610 that the fuel cut is being executed, first, the count-up process of the determination counter is performed (step 614).

Next, the output of the main O ₂ sensor 34 is
It is determined whether or not the value has changed to a value smaller than 0.1 V (step 616).

As a result, if the above condition is satisfied,
It can be determined that the output of the main O ₂ sensor 34 is appropriately changing. In this case, the main O ₂ sensor 34
Is determined to be normal, and thereafter, the processing of steps 618 and 620 is jumped. On the other hand, if it is determined that the above conditions are not satisfied, then it is determined whether or not the count value of the determination counter is smaller than the first determination time T1 (step 618).

As shown in FIGS. 4 and 5, after the fuel cut is started, it takes some time for the output of the main O ₂ sensor 34 to change to a value below 0.1V. The first determination time T1 is a time corresponding to that time. Therefore, when the determination counter <T1 is satisfied, it is still not possible to specify whether the output of the main O ₂ sensor 34 is normal or abnormal. Therefore, in such a case, the process of step 620 is skipped. On the other hand, if the above conditions are not met,
That is, when the judgment counter is T1 or more, the main
It can be determined that the output of the O ₂ sensor 34 has not changed normally. In this case, in the routine shown in FIG. 10, it is determined whether the main O ₂ sensor 34 is abnormal (step 620).

When the above-mentioned series of processing is completed, next,
The output of the sub _{O 2} sensor 36, whether or not changed to a value smaller than 0.1V is determined (step 622).

As a result, if the above condition is satisfied,
It can be determined that the output of the sub O ₂ sensor 36 is appropriately changing. In this case, the sub O ₂ sensor 36 is determined to be normal, and thereafter, steps 624 and 62 are performed.
The process of 6 is jumped. On the other hand, if it is determined that the above condition is not satisfied, then it is determined whether or not the count value of the determination counter is smaller than the second determination time T2 (step 624).

As shown in FIGS. 4 and 5, it takes some time for the output of the sub O ₂ sensor 36 to change to a value below 0.1 V after the fuel cut is started. The second determination time T2 is a time corresponding to that time. Therefore, if the judgment counter <T2 is satisfied, is the output of the sub O ₂ sensor 36 still normal?
Alternatively, it is not possible to specify whether it is abnormal. Therefore, in such a case, the process of step 620 is skipped. On the other hand, when the above condition is not satisfied, that is, when the determination counter is T2 or more, it can be determined that the output of the sub O ₂ sensor 36 has not changed normally. In this case, in the routine shown in FIG.
An abnormality determination of the O ₂ sensor 36 is made (step 62).
6).

As described above, according to the routine shown in FIG. 10, after the fuel cut is executed, the output of the main O ₂ sensor 34 is appropriately changed or the sub O ₂ sensor is changed.
Based on whether the output of the sensor 36 changes appropriately, it is possible to easily and accurately determine whether or not an abnormality has occurred in these sensors 34, 36.

Next, with reference to FIGS. 11 and 12, the contents of S200 shown in FIG. 3, that is, the method of the system of this embodiment for calculating the initial value of the oxygen storage amount deviation of the catalyst 32 will be described. . FIG. 11 is a flowchart of the first group of processes executed to realize the step S200 shown in FIG. More specifically, FIG. 11 is a flowchart of a series of processes executed by the ECU 40 to set the initial value of the oxygen storage amount deviation immediately after the end of the fuel cut.

In the routine shown in FIG. 11, first, it is judged if the fuel cut is being executed (step 202).

The system of the present embodiment acquires the data necessary for calculating the initial value of the oxygen storage amount deviation during the fuel cut. Therefore, if it is determined that the fuel cut has not been executed, the routine shown in FIG. 11 is immediately ended thereafter. On the other hand, if it is determined that the fuel cut is being executed, then the integrated value of the intake air amount Ga generated during the fuel cut (from the start to the end), that is, the integrated intake air during the fuel cut is performed. The quantity is calculated (step 204).

The integrated intake air amount can be calculated by integrating the intake air amount Ga detected by the air flow meter 20 from the start to the stop of the fuel cut. However, the method of calculating the cumulative intake air amount is not limited to this. That is, during the fuel cut, the throttle valve 22 is fully closed, so the intake air amount Ga generated per unit time during that time is a substantially fixed value. Therefore, the cumulative intake air amount is
It may be obtained by multiplying the execution time of the fuel cut.

After the integrated intake air amount is calculated, the value is multiplied by the oxygen ratio in air (0.23) to calculate the oxygen amount flowing into the catalyst 32 during the fuel cut (step 206). .

Next, it is judged whether or not the inflowing oxygen amount calculated in step 206 is smaller than the deviation guard value (step 208). Here, the deviation guard value is a value obtained by multiplying the maximum oxygen storage amount (value at standard temperature) calculated by the processing of FIGS. 7 and 8 by a predetermined ratio α. Further, the predetermined ratio α is set to 1/3 in this embodiment. Therefore, in this step 208, specifically, it is determined whether or not the inflowing oxygen amount calculated in step 206 is less than 1/3 of the maximum oxygen storage amount.

In step 208, when it is determined that the inflow oxygen amount <the deviation guard value (maximum oxygen storage amount / 3), the inflow oxygen amount is set to the initial value of the oxygen storage amount deviation ( Step 210). On the other hand, when it is determined that the condition of step 208 is not satisfied,
The deviation guard value (maximum oxygen storage amount / 3) is set to the initial value of the oxygen storage amount deviation (step 212).

As described above, the oxygen storage amount deviation is determined by the catalyst 32.
It is a value that means the amount of oxygen to be released from the catalyst 32 in order to give the desired reducing ability to the. According to the process shown in FIG. 11, the smaller of the amount of oxygen flowing into the catalyst 32 during the fuel cut and the deviation guard value set to 1/3 of the maximum oxygen storage amount at the same time when the fuel cut is finished, Is the initial value of the oxygen storage deviation, that is,
The amount of oxygen to be released from the catalyst 32 can be set by subsequent rich control.

That is, according to the process shown in FIG. 11, when only a small amount of oxygen, which is less than 1/3 of the maximum oxygen storage amount, flows into the catalyst 32 during execution of the fuel cut, the inflowing oxygen The amount of catalyst 32 in the subsequent rich control
It can be set as the amount of oxygen to be released from. In this case, since the increase / decrease in the oxygen storage amount of the catalyst 32 during fuel cut and during rich control is small, the state of the catalyst 32 can be relatively easily changed by performing rich control before performing fuel cut. The state, that is, the oxidizing ability and the reducing ability can be properly returned to the exerted state.

Further, according to the processing shown in FIG. 11, when a large amount of oxygen exceeding 1/3 of the maximum oxygen storage amount flows into the catalyst 32 during execution of the fuel cut, the maximum oxygen storage amount of 1 / 3 can be set as the amount of oxygen to be released from the catalyst 32 in the subsequent rich control. In this case, the rich control causes an unreasonably large amount of oxygen to be generated in the catalyst 3.
It is possible to reliably prevent the release of oxygen from No. 2 and it is possible to surely give the oxygen storage capacity of the catalyst 32 a reserve capacity equivalent to 1/3 of the maximum oxygen storage amount at the end of the rich control.

According to the former effect (excessive oxygen release preventing effect), it is possible to guarantee that the catalyst 32 exhibits an appropriate oxidizing ability at the end of the rich control. The remaining capacity of the oxygen storage capacity (⅓ of the maximum oxygen storage amount) secured by the latter effect is a value sufficient for the catalyst 32 to exhibit the desired reduction capacity. Therefore, according to the routine shown in FIG. 11, when the rich control ends, the catalyst 32
It is possible to regain proper reduction ability.

As described above, according to the routine shown in FIG. 11, the initial value of the oxygen storage amount deviation can be set to an appropriate value at the end of the fuel cut. When the rich control is subsequently executed according to the set value, the catalyst 32 can be appropriately restored to the state in which it exhibits the oxidizing ability and the reducing ability at the end of the control.

By the way, in the above description, the deviation guard value used when setting the initial value of the oxygen storage amount deviation is set to 1/3 of the maximum oxygen storage amount, but the value of the guard value is It is not limited. That is, the deviation guard value is not more than 1/2 of the maximum oxygen storage amount of the catalyst 32, and is a value equal to or more than the remaining oxygen storage capacity to be ensured in order for the catalyst 32 to exhibit a desired reducing capacity. Good. For example, in the configuration of the present embodiment, any value within the range of 1/2 to 1/3 of the maximum oxygen storage amount can be used as the deviation guard value.

FIG. 12 is a flowchart of the second group of processes executed to implement the step S200 shown in FIG. More specifically, FIG. 12 shows that the ECU 4 is used to set the initial value of the oxygen storage amount deviation immediately after the start of the internal combustion engine 10.
3 is a flowchart of a series of processes executed by 0.

In the routine shown in FIG. 12, first, it is determined whether or not the internal combustion engine 10 is being started (step 2).
20). In this step 220, for example, when the ignition switch (not shown) changes from off to on from the time of the previous processing cycle to the time of this processing cycle, the start of the internal combustion engine 10 is determined.

In step 220, the internal combustion engine 1
If it is determined that the start time is 0, the other processing shown in FIG. 12 is skipped. On the other hand, if it is determined that the internal combustion engine 10 is being started, then it is determined whether the catalyst 32 has already been activated (step 22).
2). In addition to this routine, the ECU 40 executes a routine for determining the active state of the catalyst 32 (see FIG. 1).
3). In step 222, the active state of the catalyst 32 is determined according to the execution result of the routine.

When it is determined in step 222 that the catalyst 32 is not in the active state, the processing shown in FIG. 12 is immediately ended thereafter. On the other hand, the above step 22
When it is determined that the catalyst 32 is in the active state in 2, the deviation guard value, that is, 1/3 of the maximum oxygen storage amount is set as the initial value of the oxygen storage amount deviation (step 224). ).

When the internal combustion engine 10 is started, the catalyst 32 is
Air that does not contain fuel circulates. At this time, if the catalyst 32 is already in the active state, the oxygen storage amount of the catalyst 32 increases to near the maximum oxygen storage amount. Further, when the catalyst 32 is already in the active state, execution of the air-fuel ratio feedback control is required immediately after that. Therefore, in such a case, it is necessary to execute rich control to quickly give the catalyst 32 a surplus of oxygen storage capacity required to exert a desired reducing capacity.

According to the routine shown in FIG. 12, if the catalyst 32 is already in the active state when the internal combustion engine 10 is started, 1/3 of the maximum oxygen storage amount at that time is set as the initial value of the oxygen storage amount deviation. , That is, catalyst 3 by rich control
2 can be set as the amount of oxygen to be released. Therefore, according to the routine shown in FIG. 12, when the catalyst 32 is already in the active state when the internal combustion engine 10 is started, the catalyst 32 is promptly brought into a state in which it can properly exhibit the oxidizing ability and the reducing ability. Can be transferred.

If the catalyst 32 is in the inactive state when the internal combustion engine 10 is started, the air-fuel ratio feedback control will not be executed immediately thereafter. Therefore, in such a case, it is not necessary to intentionally execute the rich control at the time of starting. Further, at that time, the catalyst 32 does not exhibit the purifying ability, and therefore the rich control for discharging a large amount of HC and CO should not be executed.

According to the routine shown in FIG. 12, if the catalyst 32 is inactive when the internal combustion engine 10 is started, the oxygen storage amount deviation is not set to a value at that time. That is, in that case, the existence of the oxygen amount to be released by the rich control is not recognized. In this case, since rich control is not executed, the above requirement can be satisfied.

As described above, according to the routine shown in FIG. 12, when the catalyst 32 is already activated when the internal combustion engine 10 is started, the rich control is requested to be executed,
The catalyst 32 can be rapidly moved to an appropriate state. Further, if the catalyst 32 is in an inactive state when the internal combustion engine 10 is started, it is possible to prevent deterioration of exhaust emission by preventing execution of unnecessary rich control. Therefore, according to the routine shown in FIG. 12, the emission characteristic immediately after the internal combustion engine 10 is started can be always kept good.

FIG. 13 shows the ECU 40 in this embodiment.
6 is a flowchart of a routine that is executed to determine the active state of the catalyst 32, separately from the main processing shown in FIG. In the routine shown in FIG. 13, first, it is determined whether or not the internal combustion engine 10 is being started (step 630).

As a result, when it is determined that the internal combustion engine 10 is being started, the cooling water temperature THW at that time, that is, the starting cooling water temperature THWS of the internal combustion engine 10 is read (step 632).

Next, based on the starting cooling water temperature THWS read in step 632, the total predicted value of the intake air amount Ga required until the catalyst 32 reaches the active state (hereinafter referred to as “active intake air”). (Referred to as “quantity”) is calculated (step 634). The ECU 40 stores a map that defines the relationship between the active intake air amount and the starting cooling water temperature THWS.
In step 634, the active intake air amount is calculated with reference to the map.

When the routine is started from the next time onward, it is determined in step 630 that the internal combustion engine 10 is not started. In this case, the processing of steps 632 and 634 is skipped. Therefore, thereafter, until the internal combustion engine 10 is stopped, the active intake air amount calculated in step 634 is maintained as it is.

In the routine shown in FIG. 13, following the series of processes described above, the integrated intake air amount generated after the internal combustion engine 10 is started is read (step 636).

Next, it is judged whether or not the cumulative intake air amount is equal to or larger than the active intake air amount (step 63).
8).

As a result, if it is determined that the condition of cumulative intake air amount ≧ active intake air amount is not satisfied, it is determined that the catalyst 32 is inactive.

On the other hand, if it is determined in step 638 that the condition of cumulative intake air amount ≧ active intake air amount is satisfied, the activity of the catalyst 32 is determined (step 64).
0). When the starting cooling water temperature THWS is sufficiently high, the active intake air amount is set to 0 in step 634. Therefore, in this case, the activity of the catalyst 32 is determined immediately after the start of the internal combustion engine 10.

As described above, according to the routine shown in FIG. 13, the internal combustion engine 1 is based on the starting coolant temperature THWS.
Immediately after the start of 0, it is possible to accurately determine whether or not the catalyst 32 is in the activated state. The method for determining whether the catalyst 32 is in the active state is shown in FIG.
It is not limited to the method shown in. For example, the catalyst 32
It is also possible to provide a bed temperature sensor for detecting the temperature of 1 to measure the catalyst temperature and to directly determine the activation state of the catalyst 32 from the catalyst temperature.

Next, referring to FIGS. 14 to 16, FIG.
The contents of S300 shown in FIG. 3, that is, the contents of the rich control executed in this embodiment will be described. FIG. 14 shows a first process executed to realize the step S300 shown in FIG.
3 is a timing chart for explaining the content of rich control of FIG. More specifically, FIG. 14A shows the air-fuel ratio feedback coefficient FA for realizing the first rich control.
It is the waveform of F. In addition, FIG. 14B is the same as FIG.
3 is an output waveform of the main O ₂ sensor 34 corresponding to FAF shown in FIG.

The first rich control is a control executed when the internal combustion engine 10 is in the idle state (the idle switch 26 is in the on state) at the end of the fuel cut. In FIG. 14, time t1 indicates the end point of the fuel cut. As shown in FIG. 14 (A), the air-fuel ratio feedback coefficient FAF is 0 during execution of fuel cut.
It is said that. The air-fuel ratio feedback coefficient FAF is
As described above, this is a correction coefficient for expanding and contracting the fuel injection time TAU (the larger the FAF, the longer the TAU, and the FA
The smaller the F, the shorter the TAU). The first rich control is realized by adding a predetermined padding value to FAF at the end of fuel cut, and then performing normal air-fuel ratio feedback control.

During fuel cut, main O ₂
The sensor 34 gives a lean output. Further, after the fuel cut is terminated, the period until the fuel injected at the time of termination (time t1) arrives at the main O ₂ sensor 34 (period), the output of the main O ₂ sensor 34 is lean output Maintained. Meanwhile, since the exhaust air-fuel ratio is lean, the ECU 40 uses the FAF to extend the fuel injection time TAU.
Is gradually updated to a large value. As a result, at the end of the period (time t2), exhaust gas with a rich air-fuel ratio
The area around the O ₂ sensor 34 is reached.

At that time (time t2), the ECU 34 reduces the air-fuel ratio feedback coefficient FAF by a normal skip value, and then the output of the main O ₂ sensor 34 is inverted to the lean output (time t3). Reduce FAF gradually (period). Then, after the time t2, the air-fuel ratio feedback control is continued by the usual method.

According to the series of processing described above, FIG.
As shown in (B), it is possible to create a period in which the exhaust air-fuel ratio becomes rich for a long period after the fuel cut is completed. Therefore, according to the first rich control, it is possible to reduce the oxygen storage amount deviation in the catalyst 32, which has increased during the fuel cut.

FIG. 15 is a timing chart for explaining the contents of the second rich control executed to realize step S300 shown in FIG. More specifically,
FIG. 15A is a waveform of the air-fuel ratio feedback coefficient FAF for realizing the second rich control. Also, FIG.
5 (B) is the main O corresponding to the FAF shown in FIG. 15 (A).
₂ is an output waveform of the sensor 34.

The second rich control is a control executed when the internal combustion engine 10 is in the non-idle state (the idle switch 26 is in the off state) after the end of the fuel cut. This control can be realized by setting the skip value of the air-fuel ratio feedback coefficient FAF as follows and performing the air-fuel ratio feedback control. (1) FAF when the output of the main O ₂ sensor 34 changes from lean to rich
The reduction skip value to be applied to is set to a value skipL-α that is smaller than the normal value skipL by a predetermined value α. (2) Main O ₂ sensor 34
The increase skip value applied to the FAF when the output of is inverted from rich to lean is set to a value skipR + α that is larger than the normal value skipR by a predetermined value α.

When the FAF decrease skip value is set to skipL-α, the FAF decrease speed is substantially slowed down, so the main O ₂
After the output of the sensor 34 reverses from lean to rich (time t4, t6), the exhaust air-fuel ratio is maintained rich for a relatively long period (see period in FIG. 15B). On the other hand, when the FAF increase skip value is set to skipR + α, the FAF increase speed becomes substantially faster, and after the output of the main O ₂ sensor 34 reverses from lean to rich (time t5, t7),
Period in which the exhaust air-fuel ratio is maintained lean (Fig. 15 (B))
(See middle and period) becomes relatively short. As described above, according to the second rich control, it is possible to make the rich period and the lean period of the exhaust air-fuel ratio unbalanced and bias the average of the air-fuel ratio toward the rich side. Therefore, according to the second rich control, it is possible to reduce the oxygen storage amount deviation in the catalyst 32, which has increased during the fuel cut.

By the way, in the above-described first rich control, the air-fuel ratio feedback coefficient FAF is greatly changed only once at the end of the fuel cut. Since the output of the internal combustion engine 10 naturally changes at the end of the fuel cut, the above FAF change does not give the driver of the vehicle a feeling of strangeness. In this respect, the first rich control is suitable as a method for enriching the air-fuel ratio in an environment in which the output change of the internal combustion engine 10 greatly affects the fluctuation of the engine speed NE, such as during idle operation.

On the other hand, in the second rich control, every time the exhaust air-fuel ratio is reversed from rich to lean, the air-fuel ratio feedback coefficient FAF is greatly skipped and increased as compared with the normal time. FAF skip increase is due to fuel injection time TAU
Is increased, and as a result, the output of the internal combustion engine 10 is increased in a skip manner. Such an output change causes a change in the engine speed NE during idle operation, and reduces the drivability of the vehicle. In this respect, the second rich control is a suitable method as a method for making the air-fuel ratio rich when not idling.

In the present embodiment, considering the characteristics of the first rich control and the second rich control as described above, if the internal combustion engine 10 is in the idle operation at the end of the fuel cut, then The first rich control is performed only once, and then the second rich control is performed until the desired oxygen amount is released from the catalyst 32 after the internal combustion engine 10 shifts to the non-idle operation.

FIG. 16 is a flowchart of the process executed to realize the step S300 shown in FIG. More specifically, FIG. 16 is a flowchart of a series of processes executed by the ECU 40 to execute the first rich control and the second rich control by the above method after the end of the fuel cut.

In the routine shown in FIG. 16, first, it is judged if the execution condition of the air-fuel ratio feedback control is satisfied (step 302). In this step 302, for example, whether the cooling water temperature THW exceeds a predetermined temperature,
Whether or not the main and sub O ₂ sensors 34 and 36 are activated, and whether or not the fuel cut execution condition is not satisfied is determined.

If it is determined in step 302 that the execution condition of the air-fuel ratio feedback control is not satisfied, then all the processes shown in FIG. 16 are skipped. On the other hand, if it is determined that the execution condition is satisfied, then it is determined whether or not the catalyst 32 is activated (step 304).

If it is determined that the catalyst 32 has not been activated yet, the rich control should not be executed, and hence the routine shown in FIG. 16 is immediately terminated. On the other hand, if it is determined that the catalyst 32 is already activated, then it is determined whether the oxygen storage amount deviation is greater than 0 (step 306).

The oxygen storage amount deviation is the amount of oxygen to be released from the catalyst 32 by the rich control as described above. In the present embodiment, as described above, step S2 shown in FIG.
00, that is, by the series of processes shown in FIG. 11 or FIG. 12, at the end of the fuel cut, or
When the internal combustion engine 10 is started, the initial value of the oxygen storage amount deviation is calculated. Then, the oxygen storage amount deviation is updated to a value smaller by the amount of oxygen released from the catalyst 32 by the process described later.

Therefore, when it is determined in step 306 that the oxygen storage amount deviation> 0 is not established, it can be determined that the oxygen to be released from the catalyst 32 by the rich control does not already exist. In the routine shown in FIG. 16, the following processing is jumped in this case. On the other hand, when it is determined that the condition of step 306 is satisfied, it can be determined that the oxygen to be released from the catalyst 32 by the rich control is still present. In this case, next, whether the internal combustion engine 10 is in the idle state,
More precisely, it is judged whether or not the idle switch 26 is on (step 308).

As a result, when it is determined that the idle switch 26 is in the on state, it is determined whether or not the first rich control should be executed. Therefore, the current processing cycle is the air-fuel ratio feedback control. Is restarted, that is, the cycle executed for the first time after the end of fuel cut is determined (step 31).
0).

As described above, the first rich control is performed by adding the padding value to the air-fuel ratio feedback coefficient FAF only once at the end of the fuel cut under the environment where the normal air-fuel ratio feedback control is executed. Can be realized. In the present embodiment, the processing required for normal air-fuel ratio feedback control is performed in another routine. Therefore, the routine shown in FIG. 16 requires only the function of adding the padding value to the FAF at the end of the fuel cut in order to realize the first rich control.

Therefore, in step 310,
If it is determined that the current processing cycle is not the cycle when the air-fuel ratio feedback control is restarted, the routine shown in FIG. 16 is immediately ended. On the other hand, if it is determined in step 310 that the above condition is satisfied, the padding value to be added to FAF is calculated (step 312).

In step 312, the padding value is calculated based on the initial value of the oxygen storage amount deviation calculated in step S200 (FIG. 11 or 12).
The ECU 40 stores a map that defines the relationship between the initial value of the oxygen storage amount deviation and the padding value. This step 312
At, the ECU 40 calculates the padding value by referring to the map. As a result, the padding value is calculated to be larger as the initial value of the oxygen storage amount deviation is larger.

In the routine shown in FIG. 16, next, the padding value is added to the air-fuel ratio feedback coefficient FAF (step 314). In this step 314, the air-fuel ratio feedback coefficient FAF added to the padding value is the value used before the fuel cut is started or the FAF reference value (for example, 0).

According to the above-described processing, the air-fuel ratio feedback coefficient FAF can be changed with the waveform shown in FIG. 14A after the fuel cut is completed. For this reason,
According to the above processing, it is possible to achieve the intended purpose of biasing the exhaust air-fuel ratio rich.

In the routine shown in FIG. 16, the above step 3
If it is determined in 08 that the idle switch 26 is not in the ON state, then a process for realizing the second rich control is executed thereafter. Specifically, first, it is determined whether or not the output of the main O ₂ sensor 34 is inverted from the previous processing cycle to the current processing cycle (step 316).

As a result, when it is determined that the output of the main O ₂ sensor 34 is inverted, the inversion is further
It is determined whether the increase in the air-fuel ratio feedback coefficient FAF is requested to be skipped, or more specifically, whether the reversal is a reversal from the rich output to the lean output (step 318).

If the condition of step 318 is satisfied, the skip value skip of the air-fuel ratio feedback coefficient FAF is appropriately increased (for example, 1% increase is corrected).
Is performed (step 320). On the other hand, step 3 above
If the condition of 18 is not satisfied, the skip value skip is appropriately reduced (for example, 1% reduction correction) (step 322).

According to the above-described processing, as long as the oxygen storage amount deviation larger than 0 is generated after the fuel cut is completed, the air-fuel ratio feedback coefficient FAF is set in the waveform shown in FIG. Can be changed. Therefore, according to the above processing, it is possible to achieve the intended purpose of biasing the exhaust air-fuel ratio rich.

Next, referring to FIG. 17, S4 shown in FIG.
00, that is, a process of subtracting the oxygen storage amount deviation of the catalyst 32 with the execution of the rich control will be described. FIG. 17 shows a flowchart of a series of processes executed by the ECU 40 to realize the above functions.

In the routine shown in FIG. 17, first, the latest oxygen storage amount deviation, that is, the initial value of the oxygen storage amount deviation set in the current processing cycle, or the oxygen storage amount calculated in the previous processing cycle, Latest deviation is 0
It is determined whether or not it is larger (step 402).

When it is determined that the oxygen storage amount deviation is not greater than 0, it is determined that the process shown in FIG. 17 does not need to be performed, and thereafter this routine is promptly terminated.
On the other hand, if it is determined that the oxygen storage amount deviation> 0 holds, then it is determined whether the internal combustion engine 10 is in the idle state,
That is, it is determined whether or not the idle switch 26 is on (step 404).

As described above, in the system of this embodiment, the air-fuel ratio is made rich by the first rich control (see FIG. 14) when the idle switch 26 is on. Therefore, when it is determined in step 404 that the idle switch 26 is in the on state, the subtraction process of the oxygen storage amount deviation assuming the first rich control is performed thereafter.

Specifically, in this case, first, it is judged whether or not the raising rich by the first rich control is being performed (step 406). In this step 406, after the fuel cut is completed, it is determined that the “bulk raising rich is in progress” until the period shown in FIG. 14 ends. More specifically, after the fuel cut is completed, it is determined that the “bulk-up rich” is being performed until the output of the main O ₂ sensor 34 is first inverted from the rich output to the lean output.

If it is determined in step 406 that the padding rich is not in progress, then steps 408 and 41 are executed.
Processes 2 and 414 are jumped. On the other hand, when it is determined that the raising rich is being performed, the main O ₂
It is determined whether or not the sensor 34 emits a rich output (step 408).

After the fuel cut is completed, the period until the exhaust gas containing the fuel reaches the position of the main O ₂ sensor 34, that is, the period in which the air is flowing into the catalyst 32, is as described above. _{The 2} sensor 34 continues to emit a lean output (FIG. 14, period). During this period, in step 408, it is determined that the output of the main O ₂ sensor 34 is not the rich output. In the routine shown in FIG.
In this case, next, it is determined whether the output of the main O ₂ sensor 34 has been inverted from the rich output to the lean output from the previous processing cycle to the current processing cycle (step 410).

After the fuel cut is completed, the main O is supplied during the period when the air is flowing into the catalyst 32 (period shown in FIG. 14).
_{The 2} sensor 34 continuously produces a lean output. Therefore, in this case, it is determined that the condition of step 410 is not satisfied. Then, thereafter, the processing after step 422 is started without performing the processing for updating the oxygen storage amount deviation. After the fuel cut ends, the oxygen storage amount deviation in the catalyst 32 does not change during the period in which the air flows into the catalyst 32. According to the series of processes described above, in such a case, the oxygen storage amount deviation can be appropriately maintained at the initial value.

In the system of this embodiment, after the fuel cut is completed, the exhaust gas containing fuel is discharged into the main O gas.
_{2 When} the position of the sensor 34 is reached, that is, the catalyst 32
Once the exhaust gas containing fuel begins to flow into the
The O ₂ sensor 34 produces a rich output (FIG. 14, period). Meanwhile, in step 408, it is determined that the condition regarding the output of the main O ₂ sensor 34 is satisfied.

When the condition of step 408 is satisfied,
Next, a multiplication value of the integrated amount of air flowing into the catalyst 32 after the condition is satisfied and a half of the padding value (% conversion value) is calculated. Then, based on the multiplication value, the catalyst 3
The amount of oxygen released from 2 (released oxygen amount) is calculated (step 412).

Next, the oxygen storage amount deviation is calculated by subtracting the released oxygen amount calculated by the processing of step 412 from the initial value of the oxygen storage amount deviation (step 414).

[0174] The processing of steps 412 and 414 described above, the output of the main _{0 2} sensor 34 is repeatedly executed until inverted to lean output. As a result, in step 412, finally, a calculated value obtained by multiplying the average rich degree in the period shown in FIG. 14 by the integrated intake air amount generated in that period can be obtained, and further, the calculation An oxygen release amount corresponding to the value can be obtained. According to such arithmetic processing, the amount of oxygen released from the catalyst 32 during the period can be calculated accurately. Then, according to the process of step 414, the amount of released oxygen calculated accurately is subtracted from the initial value of the oxygen storage amount deviation, so that the catalyst 32 is exhausted at the end of the first rich control.
The oxygen storage amount deviation remaining inside can be accurately obtained.

[0175] During raising rich by the first rich control, the output of the main 0 ₂ sensor 34 is inverted from rich to lean, i.e., when the period shown in FIG. 14 ends, the routine shown in FIG. 17, in step 408 A determination is made that the condition is not satisfied, and then step 410
The condition is discriminated at. In this case, FIG.
In the routine shown in (4), next, it is determined whether the padding rich has ended (step 412). As a result, when the process of step 406 is executed thereafter, the satisfaction of the condition is always denied.

In the routine shown in FIG. 17, the above step 4
When it is determined in 04 that the idle switch 26 is not in the ON state, the subtraction process of the oxygen storage amount deviation that assumes the second rich control is performed thereafter.

Specifically, in this case, first, after the second rich control is started (after the condition of step 404 is satisfied), the integrated amount of air flowing into the catalyst 32 and FAFs
When kip is rich, the multiplication value with A / F is calculated. Then, the amount of oxygen released from the catalyst 32 (the amount of released oxygen) is calculated based on the multiplied value (step 418). here,
“FAFskip rich A / F” is an average exhaust gas realized by executing the second rich control, that is, by making the increase skip value and decrease skip value of FAF imbalanced. It is the air-fuel ratio. The ECU 40 stores the FAFskip rich A / F which is experimentally obtained in advance, and executes the process of step 418 using the stored value.

In the routine shown in FIG. 17, next, the oxygen storage amount deviation is calculated by subtracting the released oxygen amount calculated by the processing of step 418 from the initial value of the oxygen storage amount deviation (step 420). ).

According to the processing of step 418, the second
It is possible to accurately calculate the amount of oxygen released from the catalyst 32 as the rich control is performed. Then, according to the process of step 420, the amount of released oxygen calculated with high precision is subtracted from the initial value of the oxygen storage amount deviation, so that it remains inside the catalyst 32 during the execution of the second rich control. The oxygen storage amount deviation can be accurately obtained.

In the routine shown in FIG. 17, following the series of processes described above, it is judged whether or not the sub O ₂ sensor 36 has detected a rich exhaust air-fuel ratio (step 42).
2). The sub-O ₂ sensor 36 detects the rich exhaust air-fuel ratio when the rich exhaust gas flows downstream of the catalyst 32. Here, the rich exhaust gas flows out to the downstream side of the catalyst 32 when the catalyst 32 cannot oxidize HC and CO, that is, a sufficient oxygen storage amount is secured inside the catalyst 32. Limited to no case. Therefore, when the condition of this step 422 is satisfied, it can be determined that the oxygen amount to be released by the rich control, that is, the oxygen storage amount deviation does not remain inside the catalyst 32.

In the routine shown in FIG. 17, when the condition of step 422 is satisfied, the oxygen storage amount deviation is set to 0 at that time (step 424). On the other hand, if the condition of step 422 is not satisfied, then step 4
24 is jumped, and the oxygen storage amount deviation set by the processing of steps 404 to 420 is maintained as it is.

According to the above processing, although the oxygen storage amount in the catalyst 32 is actually extremely small due to the calculation error of the initial value of the oxygen storage amount deviation and the released oxygen amount,
When the calculated oxygen storage amount deviation is larger than 0, the calculated oxygen storage amount deviation can be quickly set to 0 and the execution of the rich control can be stopped. Therefore, according to the system of the present embodiment, it is possible to reliably prevent unduly continued rich control in an environment where the oxygen storage amount deviation is insufficient.

Next, referring to FIGS. 18 to 21, FIG.
The contents of S500 shown in FIG. 5, that is, the limitation of the related control executed in this embodiment will be described. FIG.
[Fig. 4] is a timing chart for explaining the content of the first related control executed in the system of the present embodiment, specifically, the content of the sub feedback control.

As described above, in the system of this embodiment,
Air-fuel ratio feedback control based on the output of the main O ₂ sensor 34 is being executed. In addition to this, in the system of the present embodiment, sub feedback control using the output of the sub O ₂ sensor 36 is executed.

While the air-fuel ratio feedback control is being executed, the output of the main O ₂ sensor 34 is repeatedly inverted between the rich output and the lean output, as shown in FIG. 4 (A).
As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is maintained near the stoichiometric air-fuel ratio. At this time, the sub O ₂ sensor 3
6 outputs a rich output (FIG. 18 (B) left column),
It can be determined that the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is biased toward rich as a whole. On the other hand, if the sub-O ₂ sensor 36 outputs a lean output (right column in FIG. 18B), it can be determined that the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is lean as a whole.

In the system of this embodiment, as described above with reference to FIG. 15 as the description of the second rich control, the skip value of the air-fuel ratio feedback coefficient FAF is imbalanced between the increasing side and the decreasing side ( (Increase skip value> Decrease skip value)
Thus, the exhaust air-fuel ratio can be made rich. Hereinafter, this setting is referred to as "rich setting". Also,
If the magnitude relationship between the increasing skip value and the decreasing skip value is reversed from the above relationship, the exhaust air-fuel ratio can be biased toward the lean side. Hereinafter, this setting is referred to as "lean setting".

In the present embodiment, in the sub feedback control, when the sub O ₂ sensor 36 outputs a rich output, the FAF skip value is updated to the lean setting side. If the sub-O ₂ sensor 36 outputs a lean output, the FAF skip value is updated to the rich setting side. According to such sub-feedback control, as a result of the air-fuel ratio feedback control based on the output of the main O ₂ sensor 34, the air-fuel ratio biased toward the rich side or the lean side as a whole can be corrected to the stoichiometric air-fuel ratio side. it can.

In the sub-feedback control described above, the air-fuel ratio of the exhaust gas flowing into the catalyst 32 vibrates uniformly on the rich side and the lean side due to the function of the air-fuel ratio feedback control, and the catalyst 32 is It is performed on the premise that it shows an appropriate oxidation / reduction ability. Therefore, in an environment where oxygen is excessively occluded in the catalyst 32 immediately after the fuel cut, if the skip value is continuously updated by the sub-feedback control, the fuel injection time TAU is overcorrected and the air-fuel ratio is increased. There is a possibility that the control accuracy of will rather deteriorate. Therefore, in the system of the present embodiment, in a situation where oxygen is excessively stored in the catalyst 32, updating of the skip value by sub-feedback control is prohibited to avoid problems such as overcorrection of the fuel injection time TAU. I have decided.

In order to realize the above functions, FIG.
4 is a flowchart of a first group of processes executed by the ECU 40 in step S500 shown in FIG. In the routine shown in FIG. 19, first, it is determined whether the oxygen storage amount deviation calculated in step S400, that is, the oxygen storage amount deviation calculated in the routine shown in FIG. 502).

As a result, if the oxygen storage amount deviation> 0 holds, the update of the skip value by the sub feedback control is prohibited (step 504). On the other hand, if the oxygen storage amount deviation> 0 is not satisfied, the update of the skip value by the sub feedback control is permitted (step 50).
6).

As described above, according to the routine shown in FIG. 19, the sub-feedback control can be permitted only when the oxygen storage amount of the catalyst 32 is a normal value. Therefore, according to the system of the present embodiment,
It is possible to effectively avoid a situation in which the control accuracy of the air-fuel ratio rather deteriorates due to the execution of the sub feedback control immediately after the fuel cut or the like.

FIG. 20 shows the contents of the second related control executed in the system of this embodiment, specifically, the main.
6 is a timing chart for explaining the content of a deterioration determination process of the catalyst 32 based on the correlation between the output of the O ₂ sensor 34 and the output of the sub O ₂ sensor 36. Here, in FIG.
The timing chart shown in the left column corresponds to the case where the catalyst 32 has a sufficiently large maximum oxygen storage amount,
On the other hand, the timing chart shown in the right column shows that the catalyst 32
It corresponds to the case where the maximum oxygen storage amount of is small.

When the catalyst 32 has a sufficiently large maximum oxygen storage amount, it exerts a large oxidizing ability and reducing ability. Therefore, in such a case, there is almost no correlation between the output of the main O ₂ sensor 34 and the output of the sub O ₂ sensor 36, and the output of the sub O ₂ sensor 36 is a rich output or a lean output. Stabilizes at.

On the other hand, when the maximum oxygen storage amount of the catalyst 32 is small, the catalyst 32 cannot sufficiently purify the exhaust gas, so the change in the exhaust air-fuel ratio occurring upstream of the catalyst 32 remains unchanged. It is transmitted downstream of the catalyst 32. Therefore, in such a case, a correlation appears between the output of the main O ₂ sensor 34 and the output of the sub O ₂ sensor 36.

As described above, the maximum oxygen storage amount of the catalyst 32 decreases as its deterioration progresses. Therefore, the main
If a correlation shown in the right column in FIG. 20 is recognized between the output of the O ₂ sensor 34 and the output of the sub O ₂ sensor 36, it is determined that the catalyst 32 is unacceptably deteriorated. I can judge. Therefore, in the system of the present embodiment, the deterioration of the catalyst 32 is determined when a predetermined correlation is recognized between the outputs of these two sensors.

The above method for determining the deterioration of the catalyst 32 is premised on that the oxygen storage amount of the catalyst 32 is about 50% of the maximum oxygen storage amount. That is,
Immediately after the fuel cut, if the catalyst 32 is storing oxygen with the maximum capacity, even if the catalyst 32 is deteriorated and the maximum oxygen storage amount is reduced, the main O ₂ sensor 34 No correlation appears between the output and the output of the sub O ₂ sensor 36. In this case, since the apparently appropriate state is maintained, the abnormality of the main O ₂ sensor 34 is overlooked. Further, contrary to the above situation, the catalyst 3
When the rich control is continued in a state where the oxygen storage amount of 2 is very small, the output of the main O ₂ sensor 34 repeats rich and lean (rich on average)
The output of the O ₂ sensor 36 remains rich, and a situation occurs in which no correlation is recognized between the two. Even in this case, since the apparently appropriate state is maintained, the abnormality of the main O ₂ sensor 34 is overlooked. Therefore, the system according to the present embodiment prohibits the determination of the deterioration of the catalyst 32 by the above method under the condition that the catalyst 32 stores excessive oxygen.

In order to realize the above function, FIG.
4 is a flowchart of a second group of processes executed by the ECU 40 in step S500 shown in FIG. In the routine shown in FIG. 21, first, it is determined whether or not the oxygen storage amount deviation calculated in step S400, that is, the oxygen storage amount deviation calculated by the routine shown in FIG. 510).

As a result, when the oxygen storage amount deviation> 0 holds, the deterioration determination of the catalyst 32 based on the correlation with the sensor output is prohibited (step 512). On the other hand, when the oxygen storage amount deviation> 0 is not established, the deterioration determination of the catalyst 32 based on the correlation of the sensor outputs is permitted (step 514).

As described above, according to the routine shown in FIG. 21, it is possible to permit the deterioration determination of the catalyst 32 based on the correlation of the sensor output only when the oxygen storage amount of the catalyst 32 is a normal value. . Therefore, according to the system of the present embodiment, it is possible to effectively prevent the deterioration of the catalyst 32 from being erroneously determined in an environment where an excessive oxygen storage amount is generated, such as immediately after the fuel cut.

By the way, in the first embodiment described above, the one-catalyst, two-sensor configuration shown in FIGS. 1 and 2B is used as the system configuration, but the configuration is not limited to this. is not. That is, in the present embodiment, as the system configuration, the 1-catalyst 1-sensor configuration shown in FIG. 2 (A) or the 2-catalyst 2-sensor configuration shown in FIG. 2 (C) may be adopted.

The process of step S100 shown in FIG.
It is required that the main O ₂ sensor 34 and the sub O ₂ sensor 36 are arranged before and after the number 2. Therefore, when the one-catalyst, one-sensor configuration is used as the system configuration, step S100
Therefore, the maximum oxygen storage amount of the catalyst 32 cannot be calculated. In this case, the maximum oxygen storage amount of the catalyst 32 may be set to a fixed value, and the processes of step S200 and thereafter may be executed.

In the first embodiment described above, the catalyst 3
For 1 catalyst 2 sensor structure using 2 only one is adopted, the sub-O ₂ when the sensor 36 detects a rich exhaust air-fuel ratio is being (the steps and to terminate the rich control at the time 422, 424). However, as the system configuration, the two catalysts 32 and 4 are used.
When a 2-catalyst 2-sensor configuration using 4 is used, even if rich exhaust gas is discharged downstream of the upstream catalyst 32,
The exhaust gas can be purified by the downstream catalyst 44. Therefore, in this case, when the rich exhaust air-fuel ratio is detected by the sub O ₂ sensor 36, the oxygen storage amount deviation is not set to 0 at that time, and thereafter, until the oxygen storage amount deviation becomes 0 in the calculation. The rich control may be continued.

In the first embodiment, the main O ₂ sensor 34 is the "main sensor" of claim 1 and the sub O ₂ sensor 36 is the "sub sensor" of claim 1. Equivalent to ECU 40
However, the "injection amount control means" according to claim 1 executes the air-fuel ratio feedback control, and the "fuel cut means" according to claim 1 performs the fuel cut under predetermined conditions. Step 104 ~
By executing the process of 116, the "increased oxygen amount calculating means" of claim 1 and the "maximum oxygen storage amount calculating means" of claim 1 by executing the process of step 134, respectively. Has been realized.

In the first embodiment described above,
When the ECU 40 executes the process of step 118, the “catalyst temperature acquisition unit” described in claim 2 executes the process of step 120, and the “storage amount correction unit” described in claim 2 operates. , Have been realized respectively.

Further, in the first embodiment described above,
The ECU 40 performs the rich operation, thereby allowing the ECU 40 to perform the rich operation.
The “rich operation realizing means” described is the same as in step 106 above.
The "storage amount calculation prohibition means" according to the third aspect is realized by executing the processing of.

In addition, in the above-described first embodiment,
The "catalyst deterioration determining means" according to claim 4 is realized by the ECU 40 executing the routine shown in FIG.

In addition, in the above-described first embodiment,
The ECU 40 executes the processes of steps 616 to 620, and the "main sensor abnormality determination means" of claim 5 executes the processes of steps 622 to 626, and the "sub-sensor of claim 5". "Abnormality determination means" are realized respectively.

Further, in the above-described first embodiment,
The ECU 40 executes the routines shown in FIGS. 7 and 8 so that the “maximum oxygen storage amount acquisition means” according to claim 6 performs fuel cut under a predetermined condition. "Fuel cut means"
However, by performing the processing of steps 204 and 206, the "inflow oxygen amount calculation means" according to claim 6
However, the "deviation initial value setting means" according to claim 6 by executing the processing of steps 208 to 212,
The "rich control realizing means" according to claim 6 by executing the processes of steps 314, 320, and 322, and the "rich control of claim 6 by performing the processes of steps 306 to 322. “Execution means” are realized.

Further, in the above described first embodiment,
The ECU 40 executes the processing of the steps 220 and 222, and the "start-up active state determining means" according to claim 7 executes the processing of the step 224, and the "forced setting" according to the claim 7. Means ”are realized respectively.

Further, in the above described first embodiment,
The "rich control start means" according to claim 8 is realized by the ECU 40 executing the process of step 306.

Further, in the above described first embodiment,
The ECU 40 calculates TAU using FAF, and the "injection amount calculation means" according to claim 9 updates the FAF based on the output of the main O ₂ sensor 34. The “feedback coefficient updating means” executes the processing of the step 314, and thereby the “first realizing means” of the claim 9 performs the steps 318 to
By executing the processing of 322, the "second realizing means" of claim 9 is realized, and by executing the processing of the step 308, the "selecting means" of claim 9 is realized.

Further, in the above-described first embodiment,
The "catalyst activation state determination means" according to claim 10, wherein the ECU 40 executes the routine shown in FIG.
However, the "rich control execution prohibiting means" according to claim 10 is realized by executing the process of step 304.

In the first embodiment described above,
The ECU 40 executes the processing of the step 412 or 418, whereby the "released oxygen amount calculating means" of claim 11 executes the processing of the steps 414 and 420, and the "deviation of the deviation of claim 11". The "rich means for ending the rich control" according to claim 11 is characterized in that the "calculating means" executes the processing of the step 306.
Each has been realized.

In the first embodiment described above,
The sub-O ₂ sensor 36 corresponds to the “sub-sensor” described in claim 12, and the ECU 40 executes the processes of steps 422 and 424 to implement the “deviation reset means” described in claim 12. Has been done.

In the first embodiment described above,
The sub-O ₂ sensor 36 corresponds to the “sub-sensor” in claim 13, and the ECU 40 executes sub-feedback control based on the output of the sub-O ₂ sensor 36. The "feedback means" executes the routine shown in FIG. 19 to implement the "sub-feedback prohibition means".

Further, in the above-mentioned first embodiment,
The main O ₂ sensor 34 corresponds to the “main sensor” of claim 14 and the sub O ₂ sensor 36 corresponds to the “sub sensor” of claim 14, and the ECU
40 is the output of the main O ₂ sensor 34 and the sub O ₂ sensor 3
The "catalyst deterioration determining means" according to claim 14, wherein the deterioration of the catalyst 32 is determined based on the correlation of the outputs of Nos. 6 and 15.
However, by executing the routine shown in FIG. 21, the "catalyst deterioration determination inhibiting means" according to claim 14 is realized.

Embodiment 2. Next, in addition to the drawings referred to in the description of Embodiment 1, FIGS.
Embodiment 2 of the present invention will be described with reference to FIG.
The system of this embodiment has a two-catalyst, two-sensor configuration shown in FIG. That is, the system of the present embodiment includes the catalyst unit 46 including the upstream catalyst 32 and the downstream catalyst 44 in the exhaust passage 14.

In the configuration in which only one catalyst 32 is arranged in the exhaust passage 14, that is, in the one-catalyst / one-sensor configuration shown in FIG. 2 (A) and the one-catalyst / two-sensor configuration shown in FIG. Later, the catalyst 32 needs to be restored to a proper state. On the other hand, in the system of the present embodiment, the catalyst unit 46 including the two catalysts 32 and 44 is
It is desirable to restore overall proper oxidizing and reducing capacities after fuel cut. Therefore, in the system of the present embodiment, the maximum oxygen storage amount and the oxygen storage amount deviation are calculated for the catalyst unit 46, and rich control is executed so that the catalyst unit 46 returns to the proper state after the fuel cut. I have decided.

In the present embodiment, the main processing by the ECU 40 proceeds in accordance with the flowchart shown in FIG. 3, as in the case of the first embodiment. Hereinafter, the individual steps shown in FIG. 3 will be described focusing on the points different from the case of the first embodiment.

In this embodiment, step S1 shown in FIG.
00 together with the routine shown in FIG. 7 and FIG.
The routine shown in 2 is executed. The routine shown in FIG. 22 is the maximum oxygen storage amount of the upstream catalyst 32 calculated by the routines shown in FIG. 7 and FIG.
It is a routine for calculating the maximum oxygen storage amount of the catalyst unit 46 based on the maximum oxygen storage amount of the downstream catalyst 44 stored in 40.

The routine shown in FIG. 22 is executed subsequent to the routines shown in FIGS. 7 and 8 in the main processing executed by the ECU 40. In this routine, first, the value stored in the ECU 40 as the maximum oxygen storage amount of the downstream catalyst 44, that is, the downstream maximum oxygen storage amount is read (step 140).

Next, the maximum oxygen storage amount of the upstream catalyst 32 calculated by the routines shown in FIGS. 7 and 8 is added to the downstream maximum oxygen storage amount obtained in step 140 to obtain the catalyst unit 46. The maximum oxygen storage amount is calculated (step 142).

As described above, in this embodiment, in step S100, in addition to the maximum oxygen storage amount of the upstream catalyst 32, the maximum oxygen storage amount of the downstream catalyst 44 and the maximum oxygen storage amount of the catalyst unit 46 are acquired. be able to.

In this embodiment, step S2 shown in FIG.
In 00, together with the routines shown in FIGS. 11 and 12,
The routine shown in FIG. 23 is executed. 11 and 1
The routine shown in 2 is a routine for setting the initial value of the oxygen storage amount deviation when the fuel cut is completed or when the internal combustion engine 10 is started. In this embodiment,
These routines are executed to set the initial value of the oxygen storage amount deviation of the catalyst unit 46.

In those routines, the above-mentioned function uses the "maximum oxygen storage amount" used in step 208 or 224 as the maximum oxygen storage amount of the catalyst unit 46, and calculates it in step 210, 212, or 224. This can be realized by storing the “initial value of the oxygen storage amount deviation” as the initial value of the oxygen storage amount deviation of the catalyst unit 46.

The routine shown in FIG. 23 is a routine executed by the ECU 40 for calculating the initial value of the oxygen storage amount deviation of the downstream catalyst 44 at the end of the fuel cut. The routine shown in FIG. 23 is executed subsequently to the routines shown in FIGS. 11 and 12 in the main processing executed by the ECU 40.

In this routine, first, it is judged if the fuel cut is being executed (step 23).
0).

The system of this embodiment acquires the data necessary for calculating the initial value of the oxygen storage amount deviation of the downstream catalyst 46 during the fuel cut. Therefore, when it is determined that the fuel cut is not executed, the routine shown in FIG. 23 is immediately ended thereafter. On the other hand, if it is determined that the fuel cut is being executed, then it is determined whether the sub O ₂ sensor 36 has detected a lean air-fuel ratio (step 232).

While the sub-O ₂ sensor 36 does not detect a lean air-fuel ratio, the oxygen in the air flowing along with the fuel cut is stored by the upstream catalyst 32, and the oxygen storage amount of the downstream catalyst 46 is It can be judged that it has not increased. In this case, thereafter, all the other processes shown in FIG. 23 are jumped.

On the other hand, when it is judged that the sub O ₂ sensor 36 detects the lean air-fuel ratio, the upstream catalyst 32 has already stored oxygen to its full capacity, and the downstream catalyst 46 is
It can be judged that oxygen is flowing in. In this case, in the routine shown in FIG. 23, the integrated value of the intake air amount Ga generated from that time to the end of the fuel cut (hereinafter,
"Downstream integrated intake air amount" is calculated (step 234).

The downstream accumulated intake air amount is measured by the sub O ₂ sensor 3
This can be calculated by integrating the intake air amount Ga detected by the air flow meter 20 until the fuel cut is stopped after 6 detects a lean air-fuel ratio. However, the downstream integrated intake air amount may be obtained by multiplying the reference value (fixed value) of the intake air amount Ga generated during the fuel cut by the duration of the above period.

When the downstream integrated intake air amount is calculated, the calculated value is multiplied by the oxygen ratio in air (0.23) to obtain the amount of oxygen flowing into the downstream catalyst 44 during fuel cut (hereinafter referred to as "downstream"). The amount of inflowing oxygen "is calculated (step 236).

Next, it is judged whether or not the downstream inflowing oxygen amount calculated in the above step 236 is smaller than the downstream deviation guard value (step 238). Here, the downstream deviation guard value is a value obtained by multiplying the downstream maximum oxygen storage amount acquired in step 140 by a predetermined ratio β (for example, 1/5). Therefore, in this step 238, specifically, it is determined whether or not the downstream inflow oxygen amount calculated in step 236 is less than β times the maximum oxygen storage amount of the downstream catalyst 44.

When it is judged in the above step 238 that the downstream inflow oxygen amount <the downstream deviation guard value (downstream maximum oxygen storage amount * β) is satisfied, the downstream inflow oxygen amount is
The initial value of the oxygen storage amount deviation of the downstream catalyst 44, that is, the initial value of the downstream oxygen storage amount deviation is set (step 24).
0). On the other hand, if it is determined that the condition of step 238 is not satisfied, the downstream deviation guard value (downstream maximum oxygen storage amount * β) is set to the initial value of the downstream oxygen storage amount deviation (step 242).

The downstream oxygen storage amount deviation is determined by the catalyst unit 46.
It is a value that means the amount of oxygen to be released from the downstream catalyst 44 in order to impart a desired reducing ability to the. According to the process shown in FIG. 23, at the same time when the fuel cut is completed, the amount of oxygen flowing into the downstream catalyst 44 during the fuel cut and the downstream deviation guard value set to the downstream maximum oxygen storage amount * β are smaller. One can be set to the initial value of the downstream oxygen storage amount deviation, that is, the amount of oxygen to be released from the downstream catalyst 44 in the subsequent rich control.

That is, according to the process shown in FIG. 23, when only a small amount of oxygen, which is less than β times the downstream maximum oxygen storage amount, flows into the downstream catalyst 44 during the execution of the fuel cut, the downstream of the downstream catalyst 44 is reduced. The inflowing oxygen amount can be set as the amount of oxygen to be released from the downstream catalyst 44 in the subsequent rich control. In this case, since the increase / decrease in the oxygen storage amount of the downstream catalyst 44 during fuel cut and during rich control is small, execution of rich control results in
It is possible to relatively easily restore the state of the downstream catalyst 44 to the state before execution of the fuel cut, that is, the state where the oxidizing ability and the reducing ability are properly exhibited.

Further, according to the processing shown in FIG. 23, when a large amount of oxygen exceeding β times the downstream maximum oxygen storage amount flows into the downstream catalyst 44 during execution of the fuel cut, the maximum downstream oxygen storage amount is obtained. Can be set as the amount of oxygen to be released from the downstream catalyst 44 in the subsequent rich control. In this case, it is possible to surely prevent an unreasonably large amount of oxygen from being released from the downstream catalyst 44 by the rich control, and at the end of the rich control, the oxygen storage capacity of the downstream catalyst 44 is set to the maximum oxygen storage amount. It is possible to surely give a reserve power equivalent to β times.

According to the former effect (excessive oxygen release preventing effect), it is possible to guarantee that the catalyst unit 46 exhibits an appropriate oxidizing ability at the end of the rich control.
Further, the remaining capacity of the oxygen storage capacity secured in the downstream catalyst 44 (β times the downstream maximum oxygen storage amount) due to the latter effect is combined with the maximum oxygen storage amount of the upstream catalyst 32, and the catalyst unit 46 has a desired reduction capacity. It is a sufficient value to exert.
Therefore, according to the routine shown in FIG. 23, it is possible to cause the catalyst unit 46 to regain an appropriate reducing ability at the stage when the rich control ends.

As described above, according to the routine shown in FIG. 23, the initial value of the downstream oxygen storage amount deviation can be set to an appropriate value at the end of the fuel cut. Then, if the rich control is subsequently executed in accordance with the set value, at the end of the control, the catalyst unit can be appropriately restored to a state in which the oxidizing ability and the reducing ability are exhibited.

By the way, in the above description, the downstream deviation guard value used when setting the initial value of the downstream oxygen storage amount deviation is β times the downstream maximum oxygen storage amount (for example, 1/5).
However, the guard value is not limited to this. That is, the downstream deviation guard value prevents the oxygen of ½ or more of the maximum oxygen storage amount of the catalyst unit 46 from being released from the catalyst unit 46 in the process of rich control, and at the end of the rich control, Catalyst unit 46
In addition, it may be a value that can give a desired reducing ability.

Specifically, in the present embodiment, the downstream deviation guard value may be any value that satisfies the following requirements. (1) greater than a value obtained by subtracting 1/2 of the maximum oxygen storage amount of the catalyst unit 46 from the downstream maximum oxygen storage amount, and
(2) The sum of the maximum oxygen storage amount of the upstream catalyst 32 is larger than the remaining oxygen storage capacity to be ensured in the catalyst unit 46 in order to have a desired reduction capacity, that is, the desired reduction. Catalytic unit 46 to exert its ability
Must be larger than the value obtained by subtracting the maximum oxygen storage amount of the upstream catalyst 32 from the remaining oxygen storage capacity that should have.

Further, in the above description, the process of setting the initial value of the oxygen storage amount deviation when the internal combustion engine 10 is started (FIG. 12).
The processing shown in FIG. 4) is executed only for the catalyst unit 46, but the configuration of the present embodiment is not limited to this. That is, in the present embodiment, the initial value of the downstream oxygen storage amount deviation may be set when the internal combustion engine 10 is started in the same procedure as the processing shown in FIG.

As described above, in the present embodiment, by the process of step S200, at the end of the fuel cut,
Alternatively, when the internal combustion engine 10 is started, the initial value of the oxygen storage amount deviation of the catalyst unit 46 and the oxygen storage amount deviation of the downstream catalyst 44 can be set to appropriate values.

In this embodiment, step S3 shown in FIG.
At 00, the same processing as in the case of the first embodiment is executed. That is, in step S300, the rich control is executed according to the procedure of the flowchart shown in FIG. 15 until it is determined that the oxygen storage amount deviation> 0 does not hold (see step 306).

In this embodiment, step S4 shown in FIG.
00, instead of the routine shown in FIG.
The routine shown in is executed. FIG. 24 is a flowchart of a routine that the ECU 40 executes to subtract the oxygen storage amount deviation of the catalyst unit 46 and the oxygen storage amount deviation of the downstream catalyst 44 in accordance with the execution of the rich control in the present embodiment. . Incidentally, in FIG.
The same steps as the steps shown in are attached with the same reference numerals, and the description thereof will be omitted or simplified.

In the routine shown in FIG. 24, the processing of steps 402 to 422 is the same as the step shown in FIG. However, in those steps, in steps 414 and 420, the released oxygen amount is subtracted from the initial value of the oxygen storage amount deviation of the catalyst unit 46, and as a result, the oxygen storage amount deviation of the catalyst unit 46 is calculated. .

If it is determined in step 422 that the sub-O ₂ sensor 36 has detected a rich air-fuel ratio, the oxygen in the upstream catalyst 32 has been exhausted, and the downstream catalyst 32 is exhausted.
It can be judged that exhaust gas containing HC and CO is flowing out. Further, when the exhaust gas containing HC and CO is discharged downstream of the upstream catalyst 32, it can be determined that the oxygen of the downstream catalyst 44 is released in order to purify the exhaust gas. Figure 2
In this case, in the routine shown in FIG.
The integrated value of the amount of oxygen released from, that is, the amount of downstream released oxygen is calculated (step 430).

After the rich control is started, the downstream catalyst 44
It is usually after the second rich control is started that the stored oxygen of is started to be released. Therefore, step 4 above
In 30, the amount of oxygen released downstream is calculated by the same method as in step 418. More specifically, the downstream oxygen release amount is calculated by multiplying the integrated amount of air that has flowed into the downstream catalyst 44 after the sub-O ₂ sensor 36 detects a rich air-fuel ratio by the A / F during FAFskip rich. It

In this embodiment, the calculation method of the amount of oxygen released downstream is based on the assumption that the stored oxygen of the downstream catalyst 44 does not start to be released during the execution of the first rich control. As described above, the method corresponding to the second rich control is limited, but the calculation method is not limited to this. That is, when the stored oxygen of the downstream catalyst 44 may be released during the execution of the first rich control, a method corresponding to the first rich control (method similar to the above step 412) is used as the calculation method. ) And a method corresponding to the second rich control may be selectively used.

In the routine shown in FIG. 24, next, the downstream oxygen storage amount deviation is calculated by subtracting the downstream released oxygen amount calculated by the processing of step 430 from the initial value of the downstream oxygen storage amount deviation. (Step 43
2).

Next, it is judged whether or not the downstream oxygen storage amount deviation calculated by the above processing is larger than 0 (step 434).

As a result, when it is determined that the downstream oxygen storage amount deviation> 0 is satisfied, it can be determined that sufficient oxygen is not yet released from the downstream catalyst 44.
In this case, the process of step 436 is jumped and the routine shown in FIG. 24 is promptly ended. When the routine shown in FIG. 24 is terminated in this way, the oxygen storage amount deviation larger than 0 is still recognized, and therefore,
The rich control is continued.

On the other hand, if it is determined in step 434 that the downstream oxygen storage amount deviation> 0 does not hold,
It can be determined that the oxygen for giving the desired reducing ability to the catalyst unit 46 has already been released from the downstream catalyst 44. That is, in this case, it can be determined that the rich control termination condition is already satisfied. In the routine shown in FIG. 24, in this case, a process of setting the oxygen storage amount deviation to 0 is performed (step 436).

The routine shown in FIG.
When the processing is completed after passing through 6, it is determined that the oxygen storage amount deviation> 0 is not satisfied in step S300 in the next processing cycle (see FIG. 11, step 306). Therefore, in this case, the execution of the rich control ends in the current processing cycle.

As described above, according to the routine shown in FIG. 24, the rich control is performed when either the oxygen storage amount deviation of the catalyst unit 46 or the oxygen storage amount deviation of the downstream catalyst 44 becomes 0 or less. Can be terminated.

In this embodiment, step S5 shown in FIG.
At 00, the same processing as in the case of the first embodiment is executed. That is, in step S500, FIG.
When the oxygen storage amount deviation> 0 is satisfied according to the procedure of the flowchart shown in FIG. 5, execution of the sub feedback control and determination of deterioration of the catalyst 32 are prohibited.

As described above, in the system of the present embodiment, the oxygen storage amount deviation of the entire catalyst unit 46 and the oxygen storage amount deviation of the downstream catalyst 44 alone are monitored separately, and either one of them is set to 0. The rich control can be ended when the following occurs. According to such a method, when the two catalysts 32 and 44 are present in the exhaust passage 14, it is possible to reliably prevent the unpurified exhaust gas from flowing out to the downstream side of the downstream catalyst 44, while ensuring that the two catalysts 32 and 44 are not exhausted. Catalyst 3
The oxygen storage capacity of the catalyst unit 46 composed of 2,44 can be efficiently utilized. Therefore, according to the system of the present embodiment, excellent exhaust emission characteristics can be realized under all conditions including immediately after the fuel cut and immediately after the internal combustion engine 10 is started.

By the way, in the above-described second embodiment, in step S100, the maximum oxygen storage amount of the upstream catalyst 32 is calculated, and the calculated value is added to the maximum oxygen storage amount of the downstream catalyst 44 to obtain the catalyst unit. Although the maximum oxygen storage amount of 46 is acquired, the present invention is not limited to this. That is, the maximum oxygen storage amount of the catalyst unit 46 may be stored in the ECU 40 in advance as a fixed value, like the maximum oxygen storage amount of the downstream catalyst 44.

Further, in the above-described second embodiment,
As the system configuration, the 2-catalyst 2-sensor configuration shown in FIG. 2C is used, but the configuration is not limited to this. That is, in the present embodiment, as the system configuration, the 2-catalyst 3-sensor configuration shown in FIG. 2D may be adopted.

When the two-catalyst three-sensor configuration is used, the maximum oxygen storage amount of the upstream catalyst 32 can be calculated using the main O ₂ sensor 34 and the sub-O ₂ sensor as described above, and the main O ₂ sensor 34 can also be used. And the second sub O ₂ sensor 48, the maximum oxygen storage amount of the catalyst unit 46 can be calculated. Further, by using the sub O ₂ sensor 36 and the second sub O ₂ sensor 48, the downstream The maximum oxygen storage amount of the catalyst 44 can be calculated. Therefore, when the two-catalyst three-sensor configuration is used, in step S100, the maximum oxygen storage amount of the catalyst unit 46 and the maximum oxygen storage amount of the downstream catalyst 44 may be obtained by calculation.

In the second embodiment, the sub O ₂ sensor 36 corresponds to the "sub sensor" in claim 15. Further, in the above-described second embodiment, the ECU 40 performs the fuel cut under a predetermined condition, and the "fuel cut means" according to claim 15 executes the processes of the steps 204 and 206. The “unit inflowing oxygen amount calculation means” according to claim 15 is the steps 208 to 212.
The "unit deviation initial value setting means" according to claim 15 by executing the processing of step 234 and 236 by executing the processing of steps 234 and 236.
The "downstream inflowing oxygen amount calculation means" described above is the same as in step 2 above.
The above-mentioned claim 1 by executing the processing of 38 to 242.
The "downstream deviation initial value setting means" described in 5 performs the processing of steps 314, 320, and 322, whereby the "rich control realization means" described in claim 15
The "rich control execution means" according to claim 15 by executing the processing of steps 306 to 322, and the "unit release oxygen amount calculation according to claim 15 by performing the processing of step 412 or 418. The "unit means" performs the processing of steps 414 and 420, and the "unit deviation calculation means" according to claim 15 performs the processing of step 430, and the "downstream released oxygen" according to claim 15 16. The “quantity calculating means” executes the processing of the step 432, and the “downstream deviation calculating means” described in claim 15 executes the processing of the steps 306, 434, and 436. "Rich control termination means" are respectively realized.

Further, in the above-described second embodiment,
The "unit maximum oxygen storage amount acquisition means" according to claim 16 is realized by the ECU 40 executing the process of step 142.

In the second embodiment described above,
The "downstream maximum oxygen storage amount acquisition means" according to claim 17 is realized by the ECU 40 executing the process of step 140.

Further, in the above-described second embodiment,
The main O ₂ sensor 34 corresponds to the “main sensor” according to claim 18, and the ECU 40 executes the air-fuel ratio feedback control to thereby perform the above-mentioned claim 18.
The "injection amount control means" described is the same as in steps 104 to 1 above.
By executing the process of 16, the "upstream increase oxygen amount calculating device" of claim 18 is executed, and by executing the process of step 134, the "upstream maximum oxygen storage amount calculating device" of claim 18 is executed. The "downstream maximum oxygen storage amount acquisition means" according to claim 18 by performing the processing of the step 140, and the "addition means" according to claim 18 by performing the processing of the step 142, Each has been realized.

In addition, in the above-described second embodiment,
The second sub-O ₂ sensor 48 is the “second
The "injection amount control means" according to claim 19 is realized by the ECU 40 performing the air-fuel ratio feedback control while being equivalent to the "sub-sensor". Further, in this embodiment, the ECU 40 uses the sub-O ₂ sensor 36 and the second sub-O ₂ sensor 48, and in the same procedure as steps 104 to 116 described above, the catalyst unit 46.
20. The “downstream increased oxygen amount calculation means” according to claim 19 is calculated by calculating the amount of oxygen flowing into the device, and the maximum oxygen storage amount of the downstream catalyst 44 is calculated by the same procedure as in step 134. Each of the “downstream maximum oxygen storage amount calculation means” described in 19 can be realized.

Further, in the above-described second embodiment,
The ECU 40 executes the processes of steps 220 and 222, and the "start-up active state determining means" according to claim 20 executes the process of step 224. "Forced setting means" are realized. Further, in this embodiment, the ECU 40 is caused to execute the process corresponding to the step 224 for the downstream catalyst 44, whereby the "second compulsory setting means" according to claim 20 can be realized.

[0267]

Since the present invention is constructed as described above, it has the following effects. Claim 1
According to the invention described, after the fuel cut is started, the oxygen amount that has flowed into the catalyst until the sub-sensor emits an output corresponding to the air, the amount of increase in the oxygen storage amount of the catalyst,
That is, it can be calculated as the increased oxygen amount. Then, the increased oxygen amount can be regarded as 50% of the maximum oxygen storage amount. Before starting the fuel cut, oxygen corresponding to about 50% of the oxygen storage amount is stored in the catalyst. Therefore, according to the above-mentioned treatment, the maximum oxygen storage amount can be accurately estimated.

According to the second aspect of the present invention, the maximum oxygen storage amount secured when the catalyst temperature is the standard temperature can be accurately calculated.

According to the third aspect of the present invention, when the fuel cut is executed immediately after the increase correction, the calculation of the maximum oxygen storage amount can be prohibited. During the increase correction, oxygen in the catalyst is consumed and the oxygen storage state is not in a normal state. Therefore, when the maximum oxygen storage amount is calculated in such an environment, an inappropriate value is calculated. According to the present invention, it is possible to effectively prevent such an inappropriate calculation from being executed.

According to the invention as set forth in claim 4, deterioration of the catalyst can be accurately determined.

According to the fifth aspect of the invention, it is possible to accurately determine the abnormality of the main sensor or the abnormality of the sub sensor.

According to the sixth aspect of the present invention, the rich control can be executed so that after the fuel cut, the amount of oxygen corresponding to the initial value of the oxygen storage amount deviation is released from the catalyst. At this time, the initial value of the oxygen storage amount deviation is 1/2 or less of the maximum oxygen storage amount, and is a value equal to or larger than the oxygen storage capacity required to give the catalyst a desired reducing ability (deviation guard value). Be guarded by. Therefore, according to the present invention, by executing the rich control, it is possible to surely impart the desired reducing ability to the catalyst while avoiding the oxygen storage amount of the catalyst becoming too small.

According to the seventh aspect of the present invention, when the catalyst is in the active state at the time of starting the internal combustion engine, the deviation guard value can be substituted for the initial value of the oxygen storage amount deviation.
At the time of starting the internal combustion engine, air flows through the catalyst. Therefore, if the catalyst is already active at that time, a large amount of oxygen is stored in the catalyst. According to the present invention, the situation can be accurately reflected in the initial value of the oxygen storage amount deviation.

According to the invention described in claim 8, the rich control can be started when the initial value of the oxygen storage amount deviation is larger than 0 at the end of the fuel cut.

According to the ninth aspect of the present invention, the rich control can be realized by raising the air-fuel ratio feedback coefficient at the time of idling, and the rich control can be realized by making the increasing speed of the air-fuel ratio feedback coefficient non-target at the time of non-idling. it can. Therefore, according to the present invention, the air-fuel ratio can be enriched without causing a large rotation fluctuation during idling, and the air-fuel ratio can be continuously enriched during non-idling.

According to the tenth aspect of the invention, when the catalyst is inactive, execution of rich control can be prohibited. The catalyst does not exhibit a sufficient oxygen storage capacity in the inactive state. Therefore, if the rich control is executed under such a situation, HC and CO may blow through and the exhaust emission may deteriorate. According to the present invention, such deterioration of exhaust emission can be reliably prevented.

According to the eleventh aspect of the present invention, the oxygen storage amount deviation (oxygen amount to be released) can be updated in response to the oxygen being released from the catalyst in accordance with the rich control. Then, the rich control can be ended at an appropriate timing by ending the rich control when the oxygen storage amount deviation becomes 0 or less.

According to the twelfth aspect of the invention, the oxygen storage amount deviation can be set to 0 or less when the rich exhaust gas flows out to the downstream of the catalyst. Rich exhaust gas flows downstream of the catalyst when oxygen in the catalyst is almost completely released. Therefore, under such circumstances, it is required to end the rich control promptly. According to the present invention, when that situation occurs, the oxygen storage amount deviation is set to 0.
As a result, the above request can be promptly met.

According to the thirteenth aspect of the present invention, when the oxygen storage amount deviation is larger than a predetermined value, it is possible to prohibit the updating of the coefficient for reflecting the output of the sub sensor in the calculation of the fuel injection amount. When the oxygen storage amount deviation is larger than the predetermined value, the catalyst is in an excessive oxygen state. In this case, the output of the sub sensor located downstream of the catalyst tends to show a value different from the normal value. According to the present invention, it is possible to effectively prevent inappropriate control from being executed in such a situation.

According to the fourteenth aspect of the present invention, when the oxygen storage amount deviation is larger than the predetermined value, the catalyst deterioration determination based on the correlation between the output of the sub sensor and the output of the main sensor is prohibited. When the oxygen storage amount deviation is larger than the predetermined value, the catalyst is in an excessive oxygen state. In this case, the output of the sub sensor located downstream of the catalyst tends to show a value different from the normal value. According to the present invention, it is possible to effectively prevent erroneous determination of catalyst deterioration under such circumstances.

According to the fifteenth aspect of the present invention, at the end of the fuel cut, the initial value of the oxygen storage amount deviation of the catalyst unit and the initial value of the oxygen storage amount deviation of the downstream catalyst can be obtained. Further, during the execution of the rich control thereafter, the unit oxygen storage amount deviation is calculated based on the oxygen amount flowing out from the catalyst unit, and further, the downstream oxygen storage amount deviation is calculated based on the oxygen amount flowing out from the downstream catalyst. You can The rich control can be ended when at least one of the unit oxygen storage amount deviation and the downstream oxygen storage amount deviation becomes 0 or less. According to such a procedure, it is possible to reliably prevent the excessive exhaust of oxygen from the catalyst unit, and it is possible to reliably prevent the rich exhaust gas from being blown further downstream of the downstream catalyst.

According to the sixteenth aspect of the present invention, the initial value of the oxygen storage amount deviation of the catalyst unit is 1/2 or less of the maximum oxygen storage amount of the catalyst unit, and the catalyst unit has a desired reduction capacity. It is possible to guard to a value (unit deviation guard value) that is equal to or larger than the oxygen storage capacity required to have it. Therefore, according to the present invention, by executing the rich control, it is possible to surely impart a desired reducing ability to the catalyst unit while avoiding the oxygen storage amount of the catalyst unit becoming too small. .

According to the seventeenth aspect of the present invention, the initial value of the oxygen storage amount deviation of the downstream catalyst is set to prevent excessive release of oxygen from the catalyst unit, and to provide the catalyst unit with a desired reducing ability. It can be any value needed to have it. Therefore, according to the present invention, by executing the rich control, it is possible to surely impart a desired reducing ability to the downstream catalyst while avoiding the oxygen storage amount of the catalyst unit becoming too small. .

According to the eighteenth aspect of the present invention, after the fuel cut is started, the amount of oxygen flowing into the catalyst until the sub-sensor emits an output corresponding to air is calculated by the amount of increase in the oxygen storage amount of the upstream catalyst, That is, it can be calculated as the upstream increased oxygen amount. Then, the maximum oxygen storage amount of the upstream catalyst can be calculated by regarding the upstream increased oxygen amount as 50% of the maximum oxygen storage amount. Before starting the fuel cut, the oxygen storage capacity of 50
Percentage of oxygen is stored. For this reason, according to the above treatment, the maximum oxygen storage amount of the upstream catalyst can be accurately estimated. Furthermore, according to the present invention, by adding the maximum oxygen storage amount of the upstream catalyst calculated as described above to the maximum oxygen storage amount of the downstream catalyst, it is possible to accurately calculate the maximum oxygen storage amount of the catalyst unit. .

According to the nineteenth aspect of the present invention, the amount of oxygen flowing into the catalyst after the subsensor outputs an output corresponding to air and before the second subsensor outputs an output corresponding to air, the oxygen amount of the downstream catalyst is changed. It can be calculated as the increased amount of the stored amount, that is, the downstream increased oxygen amount. The maximum oxygen storage amount of the downstream catalyst can be calculated by regarding the downstream increased oxygen amount as 50% of the maximum oxygen storage amount. Before the fuel cut is started, oxygen equivalent to 50% of the oxygen storage amount is stored in the downstream catalyst. Therefore, according to the above-mentioned treatment, the maximum oxygen storage amount of the downstream catalyst can be accurately estimated.

According to the twentieth aspect of the present invention, when the catalyst unit is in the active state when the internal combustion engine is started,
A unit deviation guard value or a downstream deviation guard value can be substituted for the initial value of the oxygen storage amount deviation of the catalyst unit and the initial value of the oxygen storage amount deviation of the downstream catalyst, respectively. At the time of starting the internal combustion engine, air flows through the catalyst unit. Therefore, if the catalyst unit is already in an active state at that time, a large amount of oxygen is stored in each of the upstream catalyst and the downstream catalyst. According to the present invention, the situation can be accurately reflected in the initial value of the oxygen storage amount deviation.

[Brief description of drawings]

FIG. 1 shows an example of a typical system configuration that can be used in an embodiment of the present invention.

FIG. 2 is a diagram for explaining a modified example of the system configuration that can be used in the embodiment of the present invention.

FIG. 3 is a flowchart for explaining a flow of main processing executed in the first embodiment of the present invention.

FIG. 4 is a timing chart showing an example of changes that occur in the outputs of the main O ₂ sensor and the sub O ₂ sensor before and after the fuel cut in the first embodiment of the present invention.

FIG. 5 is a timing chart showing another example of changes that occur in the outputs of the main O ₂ sensor and the sub O ₂ sensor before and after the fuel cut in the first embodiment of the present invention.

FIG. 6 is a diagram for explaining an image of changes occurring in the oxygen storage amount of the catalyst before and after fuel cut in the first embodiment of the present invention.

FIG. 7 is a flowchart of a first group of processes executed to implement step S100 shown in FIG. 3 in Embodiment 1 of the present invention.

FIG. 8 is a flowchart of a second group of processes executed to implement step S100 shown in FIG. 3 in the first embodiment of the present invention.

FIG. 9 is a flowchart of a routine that is executed to determine catalyst deterioration in the first embodiment of the present invention.

FIG. 10 is a flowchart of a routine that is executed to determine the abnormality of the O ₂ sensor in the first embodiment of the present invention.

FIG. 11 is a flowchart of a first group of processes executed to implement step S200 shown in FIG. 3 in the first embodiment of the present invention.

FIG. 12 is a flowchart of a second group of processes executed to implement step S200 shown in FIG. 3 in the first embodiment of the present invention.

FIG. 13 is a flowchart of a routine that is executed to determine the active state of the catalyst according to the first embodiment of the present invention.

FIG. 14 is a timing chart for explaining the contents of first rich control executed in the first embodiment of the present invention.

FIG. 15 is a timing chart for explaining the content of second rich control executed in the first embodiment of the present invention.

FIG. 16 is a flowchart of processing executed to implement step S300 shown in FIG. 3 in the first embodiment of the present invention.

FIG. 17 is a flowchart of processing executed to implement step S400 shown in FIG. 3 in the first embodiment of the present invention.

FIG. 18 is a timing chart for explaining the content of sub feedback control executed in the first embodiment of the present invention.

FIG. 19 is a flowchart of a first group of processes executed to implement step S500 shown in FIG. 3 in the first embodiment of the present invention.

FIG. 20 is a timing chart for explaining the contents of catalyst deterioration determination processing executed in the first embodiment of the present invention.

FIG. 21 is a flowchart of a second group of processes executed to implement step S500 shown in FIG. 3 in the first embodiment of the present invention.

FIG. 22 is a flowchart of a third group of processes executed together with the processes shown in FIGS. 7 and 8 in order to realize step S100 shown in FIG. 3 in the second embodiment of the present invention.

23 is a plan view of the second embodiment of the present invention in order to realize the step S200 shown in FIG.
11 is a flowchart of a third group of processes executed together with the process shown in FIG.

FIG. 24 is a flowchart of a third group of processes executed to implement step S400 shown in FIG. 3 in the second embodiment of the present invention.

[Explanation of symbols]

10 Internal Combustion Engine 14 Exhaust Passage 32 Catalyst (Upstream Catalyst) 34 Main O ₂ Sensor 36 Sub O ₂ Sensor 40 ECU (Electronic Control Unit 44 Downstream Catalyst 46 Catalyst Unit 48 Second Sub O ₂ Sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 41/04 330 F02D 41/04 330Z 45/00 368 45/00 368G 368H F term (reference) 3G084 AA04 BA09 BA13 BA24 CA06 DA10 DA27 DA30 EB02 EB11 FA07 FA10 FA20 FA29 3G091 AA17 AB03 AB06 AB08 BA01 BA14 BA27 BA33 CA26 CB02 DA02 DC01 EA05 EA07 EA16 EA18 EA34 EA36 FA02 FA05 FA01 FA02 FA05 FA19 FA02 JA25 J01B01 HA01 3B301 HA01 HA01 3B301 HA01 HA02 3G301 HA01 HA01 3B301 BA01 MA11 MA24 ND01 NE01 PA01Z PA11Z PB03A PD09A PD09B PD09Z PD12Z

Claims (20)

[Claims] 1. A control device for an internal combustion engine comprising a catalyst in an exhaust passage, the main sensor detecting an exhaust air-fuel ratio upstream of the catalyst, a sub-sensor detecting an exhaust air-fuel ratio downstream of the catalyst, Injection amount control means for controlling the fuel injection amount so that the exhaust air-fuel ratio upstream of the catalyst oscillates across the stoichiometric air-fuel ratio; fuel cut means for cutting fuel injection under predetermined operating conditions; and the fuel cut After the start, the increased oxygen amount calculation means for calculating the amount of oxygen flowing into the catalyst as the increased oxygen amount until the output of the sub-sensor becomes a value corresponding to air, and the increased oxygen amount of the catalyst. 50% of maximum oxygen storage
A control device for an internal combustion engine, comprising: 2. The oxygen storage capacity calculation means secures the catalyst temperature acquisition means for acquiring the temperature of the catalyst, and the maximum oxygen storage amount when the catalyst is at a standard temperature based on the temperature. The control device for an internal combustion engine according to claim 1, further comprising: a storage amount correction means for correcting the maximum oxygen storage amount. 3. The injection amount control means includes rich operation realization means for performing fuel amount increase correction so that the air-fuel ratio of the air-fuel mixture becomes rich under predetermined conditions, and the fuel cut controls the amount increase correction. The internal combustion engine according to claim 1 or 2, further comprising: an occlusion amount calculation inhibiting means for inhibiting execution of the process by the maximum oxygen occlusion amount calculating means when executed within a predetermined period. Control device. 4. A catalyst deterioration determination means for determining deterioration of the catalyst when the increased oxygen amount or the maximum oxygen storage amount calculated based on the increased oxygen amount is less than a predetermined determination value. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein: 5. After the fuel cut is started,
When the output of the main sensor does not become a lean output by the time the first determination time elapses, a main sensor abnormality determining unit that determines an abnormality of the main sensor, and after the fuel cut is started, The sub-sensor abnormality determining means for determining an abnormality of the sub-sensor when the output of the sub-sensor does not become a lean output by the time when two determination times elapse, and at least one of them is provided. 5. The control device for an internal combustion engine according to claim 4. 6. A control device for an internal combustion engine having a catalyst in an exhaust passage, comprising: a maximum oxygen storage amount acquisition means for acquiring a maximum oxygen storage amount of the catalyst; and a fuel injection cut under a predetermined operating condition. A fuel cut unit, an inflow oxygen amount calculation unit that calculates the inflow oxygen amount that has flown into the catalyst during execution of the fuel cut, the inflow oxygen amount, and the deviation guard value, whichever is smaller is the oxygen storage amount deviation. Deviation initial value setting means to be an initial value of, a realization means of rich control to make the exhaust air-fuel ratio upstream of the catalyst rich, after the end of the fuel cut, the amount corresponding to the initial value of the oxygen storage amount deviation Rich control executing means for executing the rich control so that oxygen is released from the catalyst, wherein the deviation guard value is 1 / maximum of the maximum oxygen storage amount of the catalyst.
A control device for an internal combustion engine, which is 2 or less and is a value which is equal to or more than an oxygen storage capacity necessary for giving the catalyst a desired reducing ability. 7. When the internal combustion engine is started, the starting-time active state determination means for determining whether or not the catalyst is in an active state is provided, and the deviation initial value setting means is configured such that when the internal combustion engine is started, the catalyst is activated. 7. The control device for an internal combustion engine according to claim 6, further comprising a forced setting means for substituting the deviation guard value into the initial value of the oxygen storage amount deviation when the activation state is active. 8. The rich control execution means comprises rich control start means for starting the rich control when the initial value of the oxygen storage amount deviation is greater than 0 at the end of the fuel cut. The control device for an internal combustion engine according to claim 6 or 7. 9. An injection amount calculation means for calculating a fuel injection amount using an air-fuel ratio feedback coefficient, and updating the air-fuel ratio feedback coefficient in a decreasing direction when the exhaust air-fuel ratio upstream of the catalyst is rich,
A feedback coefficient updating means for updating the air-fuel ratio feedback coefficient in an increasing direction when the exhaust air-fuel ratio upstream of the catalyst is lean; and the rich control realizing means sets the air-fuel ratio feedback coefficient to a predetermined value. A first realization unit that realizes the rich control by raising the air-fuel ratio, and a second realization unit that realizes the rich control by increasing the increasing speed of the air-fuel ratio feedback coefficient faster than the decreasing speed thereof. 9. The control device for an internal combustion engine according to claim 8, further comprising: selecting means for selecting the first realizing means at times and selecting the second realizing means for non-idling. 10. A catalyst active state determining means for determining whether or not the catalyst is in an active state, and a rich control execution inhibiting means for inhibiting execution of the rich control when the catalyst is not in an active state, The control device for an internal combustion engine according to any one of claims 6 to 9, further comprising: 11. A release oxygen amount calculation means for calculating the release oxygen amount released from the catalyst in accordance with execution of the rich control, and subtracting the release oxygen amount from an initial value of the oxygen storage amount deviation, 11. A deviation calculation means for calculating an oxygen storage amount deviation, and a rich control termination means for terminating the rich control when the oxygen storage amount deviation becomes 0 or less. One of
A control device for an internal combustion engine according to the item. 12. A sub-sensor for detecting an exhaust air-fuel ratio downstream of the catalyst; and a rich exhaust air-fuel ratio downstream of the catalyst during execution of the rich control, at which time the oxygen storage is performed. The control device for the internal combustion engine according to claim 11, further comprising: a deviation resetting unit that sets the quantity deviation to 0 or less. 13. A sub-sensor for detecting an exhaust air-fuel ratio downstream of the catalyst, a sub-feedback means for reflecting the output of the sub-sensor in the calculation of the fuel injection amount, and the oxygen storage amount deviation is a value larger than a predetermined value. In this case, the control device for the internal combustion engine according to claim 11 or 12, further comprising: a sub-feedback prohibition unit that prohibits update of a coefficient that reflects the output of the sub-sensor in the calculation of the fuel injection amount. 14. A main sensor that detects an exhaust air-fuel ratio upstream of the catalyst, a sub-sensor that detects an exhaust air-fuel ratio downstream of the catalyst, and a predetermined sensor between the output of the main sensor and the output of the sub-sensor. When a correlation is recognized, catalyst deterioration determination means for determining deterioration of the catalyst, and catalyst deterioration determination prohibition means for prohibiting deterioration determination of the catalyst when the oxygen storage amount deviation is a value larger than a predetermined value. The control device for the internal combustion engine according to any one of claims 11 to 13, further comprising: 15. A control device for an internal combustion engine, comprising a catalyst unit including an upstream catalyst and a downstream catalyst, which are arranged in series, in an exhaust passage, and fuel cut means for cutting fuel injection under predetermined operating conditions. The unit inflow oxygen amount calculation means for calculating the amount of oxygen flowing into the catalyst unit during execution of the fuel cut as the unit inflow oxygen amount, the unit inflow oxygen amount, and the unit deviation guard value, whichever is smaller. A unit deviation initial value setting means that is an initial value of the oxygen storage amount deviation of the catalyst unit, a sub-sensor that detects an exhaust air-fuel ratio between the upstream catalyst and the downstream catalyst, and during execution of the fuel cut, The amount of oxygen flowing into the catalyst unit after the output of the sub-sensor reaches a value corresponding to air is calculated as the amount of oxygen flowing in downstream. An inflowing oxygen amount calculating means, a downstream inflowing oxygen amount, and a downstream deviation initial value setting means for setting the smaller one of the downstream deviation guard values as an initial value of the oxygen storage amount deviation of the downstream catalyst, the catalyst A rich control realizing means for making the exhaust air-fuel ratio upstream of the unit rich, a rich control executing means for executing the rich control after the fuel cut is completed, and a rich control execution means for releasing the rich control from the catalyst unit. Unit release oxygen amount calculation means for calculating the oxygen amount as the unit release oxygen amount, and the unit release oxygen amount is subtracted from the initial value of the oxygen storage amount deviation of the catalyst unit to calculate the unit oxygen storage amount deviation. Unit deviation calculation means, and during execution of the rich control, after the output of the sub-sensor changes to a rich output, from the catalyst unit Downstream released oxygen amount calculation means for calculating the amount of released oxygen as the downstream released oxygen amount, and subtracting the downstream released oxygen amount from the initial value of the oxygen storage amount deviation of the downstream catalyst to calculate the downstream oxygen storage amount deviation. And a rich control ending means for ending the rich control when at least one of the unit oxygen storage amount deviation and the downstream oxygen storage amount deviation becomes 0 or less. Control device for internal combustion engine. 16. A unit maximum oxygen storage amount acquisition means for acquiring a maximum oxygen storage amount of the catalyst unit, wherein the unit deviation guard value is ½ or less of the maximum oxygen storage amount of the catalyst unit, and The control device for an internal combustion engine according to claim 15, wherein the control unit has a value equal to or larger than an oxygen storage capacity required for providing the catalyst unit with a desired reducing ability. 17. A downstream maximum oxygen storage amount acquisition means for acquiring the maximum oxygen storage amount of the downstream catalyst, wherein the downstream deviation guard value is from the maximum oxygen storage amount of the downstream catalyst to the maximum oxygen storage amount of the catalyst unit. Is less than or equal to a value obtained by subtracting 1/2 of the above, and is a value such that the sum of the maximum oxygen storage amount of the upstream catalyst is equal to or more than the oxygen storage capacity necessary for providing the catalyst unit with a desired reduction capacity. The control device for an internal combustion engine according to claim 15 or 16, characterized in that. 18. A main sensor for detecting an exhaust air-fuel ratio upstream of the upstream catalyst, and an injection amount control for controlling a fuel injection amount so that the exhaust air-fuel ratio upstream of the upstream catalyst oscillates at a stoichiometric air-fuel ratio. The unit maximum oxygen storage amount acquisition means is configured to increase the amount of oxygen flowing into the catalyst unit upstream until the output of the sub-sensor reaches a value corresponding to air after the fuel cut is started. An upstream increased oxygen amount calculation means for calculating the oxygen amount, and an upstream maximum oxygen storage amount for calculating the maximum oxygen storage amount of the upstream catalyst by regarding the upstream increased oxygen amount as 50% of the maximum oxygen storage amount of the upstream catalyst. Calculating means, downstream maximum oxygen storage amount acquisition means for acquiring the maximum oxygen storage amount of the downstream catalyst, maximum oxygen storage amount of the upstream catalyst, and maximum oxygen storage amount of the downstream catalyst The control device for an internal combustion engine according to claim 16 or 17, further comprising: an addition unit that calculates the unit maximum oxygen storage amount by adding the amount. 19. A second sub-sensor that detects an exhaust air-fuel ratio downstream of the downstream catalyst, and an injection amount that controls the fuel injection amount so that the exhaust air-fuel ratio upstream of the upstream catalyst oscillates across the stoichiometric air-fuel ratio. The downstream maximum oxygen storage amount acquisition means includes a control means, and the output of the second sub sensor corresponds to air after the output of the sub sensor becomes a value corresponding to air during execution of the fuel cut. A downstream increase oxygen amount calculating means for calculating the amount of oxygen flowing into the catalyst unit until it reaches a value as a downstream increase oxygen amount, and the downstream increase oxygen amount is regarded as 50% of the maximum oxygen storage amount of the downstream catalyst. 19. The control device for an internal combustion engine according to claim 17, further comprising: a downstream maximum oxygen storage amount calculation means for calculating a maximum oxygen storage amount of the downstream catalyst. 20. At the time of starting the internal combustion engine, there is provided start-up active state determining means for determining whether or not the catalyst unit is in an active state, and the unit deviation initial value setting means is for starting the internal combustion engine. When the catalyst unit is in the active state, the unit deviation guard value is provided to the initial value of the oxygen storage amount deviation of the catalyst unit is provided with first forcing setting means, the downstream deviation initial value setting means, When the engine starts,
The second forcible setting means for substituting the downstream deviation guard value into the initial value of the oxygen storage amount deviation of the downstream catalyst when the catalyst unit is in an active state is provided. 13. A control device for an internal combustion engine according to claim 1.