JP2013002374A - Apparatus for estimating maximum oxygen occlusion amount of catalyst - Google Patents

Abstract

A method for obtaining a maximum oxygen storage amount with high accuracy in determining deterioration of a catalyst.
The provisional maximum stored oxygen amount is calculated by accumulating the excess oxygen amount in a predetermined first period within the lean control period, and the excess unburned matter is determined in the predetermined second period within the rich control period. The provisional maximum released oxygen amount is calculated by integrating the amount of oxygen corresponding to the amount. This device calculates the provisional maximum oxygen storage amount based on the provisional maximum stored oxygen amount and the provisional maximum released oxygen amount, and the corrected provisional maximum oxygen storage amount obtained by correcting based on the provisional maximum oxygen storage amount is maximized. Acquired as oxygen storage amount. At this time, the present apparatus corrects the provisional maximum oxygen storage amount so that the corrected provisional maximum oxygen storage amount decreases as the provisional maximum oxygen storage amount decreases.
[Selection] Figure 7

Description

  The present invention relates to a maximum oxygen storage amount estimation device for a catalyst that estimates a maximum oxygen storage amount corresponding to a maximum amount of oxygen that can be stored by a catalyst disposed in an exhaust passage of an internal combustion engine.

  Conventionally, in order to purify exhaust gas discharged from an internal combustion engine, a three-way catalyst (catalyst unit for exhaust gas purification, catalytic converter) is disposed in the exhaust passage of the engine. As is well known, the three-way catalyst has an “oxygen storage function” for storing oxygen flowing into the three-way catalyst and releasing the stored oxygen.

  Hereinafter, the three-way catalyst is simply referred to as “catalyst”, the exhaust gas flowing into the catalyst is referred to as “catalyst inflow gas”, and the exhaust gas flowing out from the catalyst is also referred to as “catalyst outflow gas”. Further, an air-fuel ratio smaller than the stoichiometric air-fuel ratio is called “rich air-fuel ratio”, an air-fuel ratio larger than the stoichiometric air-fuel ratio is called “lean air-fuel ratio”, and the air-fuel ratio of the air-fuel mixture supplied to the engine is “ It is also called “engine air-fuel ratio”.

  When the catalyst deteriorates, the maximum value of the amount of oxygen that can be stored by the catalyst (that is, the maximum oxygen storage amount) decreases. Therefore, a conventional catalyst maximum oxygen storage amount estimation device (hereinafter referred to as “conventional device”) estimates the maximum oxygen storage amount, and the catalyst deteriorates when the maximum oxygen storage amount is equal to or less than a threshold value. It is determined. The conventional apparatus estimates the maximum oxygen storage amount by the method described below.

  In the conventional apparatus, a period from when the output value of the downstream air-fuel ratio sensor disposed downstream of the catalyst becomes a value corresponding to the rich air-fuel ratio until the output value becomes a value corresponding to the lean air-fuel ratio ( In the catalyst rich period), the upstream target air-fuel ratio that is the target value of the air-fuel ratio of the catalyst inflow gas is set to a target lean air-fuel ratio that is larger than the stoichiometric air-fuel ratio. During this catalyst rich period, the conventional apparatus is configured to detect the amount of excess oxygen (oxidation) contained in the catalyst inflow gas based on the upstream air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor disposed upstream of the catalyst. Gas amount) is estimated, and the estimated amount of oxygen is integrated to estimate the maximum stored oxygen amount of the catalyst (total amount of oxygen stored by the catalyst).

  Further, the conventional apparatus has a period from when the output value of the downstream air-fuel ratio sensor disposed downstream of the catalyst becomes a value corresponding to the lean air-fuel ratio until the output value becomes a value corresponding to the rich air-fuel ratio. In the period (catalyst lean period), the upstream target air-fuel ratio is set to a target rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio. In this catalyst lean period, the conventional apparatus corresponds to the amount of excess unburned matter (reducing gas amount) contained in the catalyst inflow gas based on the upstream air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor. The amount of oxygen is estimated, and the maximum amount of oxygen released from the catalyst (total amount of oxygen released by the catalyst) is estimated by integrating the amount of oxygen corresponding to the estimated amount of unburned matter.

  The conventional apparatus estimates a provisional value of the maximum oxygen storage amount based on the maximum stored oxygen amount and the maximum released oxygen amount. Further, the conventional apparatus pays attention to the fact that when the actual upstream air-fuel ratio deviates from the upstream target air-fuel ratio, the provisional value of the maximum oxygen storage amount changes according to the deviation, and the maximum stored oxygen amount and the maximum released oxygen The provisional value is corrected according to the deviation between the actual upstream air-fuel ratio (the air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor) and the upstream target air-fuel ratio at the time of calculating the amount, and the correction The provisional value thus obtained is acquired as the maximum oxygen storage amount used for catalyst deterioration determination (see, for example, Patent Document 1). The control for alternately setting the upstream target air-fuel ratio to the target rich air-fuel ratio and the target lean air-fuel ratio in order to obtain the maximum oxygen storage amount is also referred to as “active control” for convenience.

JP 2010-159701 A

  However, the inventor stated that “the maximum oxygen storage amount calculated as described above (hereinafter referred to as“ provisional maximum oxygen storage amount ”for convenience) is smaller than the predetermined maximum oxygen storage amount. The provisional maximum oxygen storage amount is calculated as a relatively large value (excessive value) as compared with the case where the provisional maximum oxygen storage amount is larger than the predetermined value. " This is because, as the catalyst deteriorates, the amount of oxygen that the catalyst can actually store becomes smaller when a predetermined amount of oxygen flows into the catalyst, and the catalyst actually moves when a predetermined amount of unburned material flows into the catalyst. It is presumed that the amount of oxygen that can be released is also small. The present invention has been made to address the above-described problems. That is, one of the objects of the present invention is to provide a “maximum oxygen storage amount estimation device for a catalyst” capable of estimating the “maximum oxygen storage amount of a catalyst” more accurately.

One of the apparatuses for estimating the maximum oxygen storage amount of a catalyst according to the present invention (hereinafter also referred to as “first invention apparatus”) is the maximum oxygen that can be stored by the catalyst disposed in the exhaust passage of the internal combustion engine. A device for estimating the maximum oxygen storage amount of a catalyst for estimating a maximum oxygen storage amount corresponding to a large amount,
An upstream air-fuel ratio sensor disposed upstream of the catalyst in the exhaust passage;
A downstream air-fuel ratio sensor disposed in the exhaust passage and downstream of the catalyst;
Air-fuel ratio control means;
A provisional maximum oxygen storage amount calculating means;
Means for obtaining the maximum oxygen storage amount;
Is provided.

The air-fuel ratio control means includes
From “when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio” from “when the output value of the downstream air-fuel ratio sensor is larger than the stoichiometric air-fuel ratio” In the “catalyst rich period” up to the time point corresponding to “the time point corresponding to”, the upstream target air-fuel ratio that is the “target value of the air-fuel ratio” of the “catalyst inflow gas that is exhaust gas flowing into the catalyst” Is set to a target lean air-fuel ratio which is a larger air-fuel ratio.
Further, the air-fuel ratio control means includes:
From “when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to the lean air-fuel ratio” to “when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to the rich air-fuel ratio” In the “catalyst lean period”, the upstream target air-fuel ratio is set to “a target rich air-fuel ratio that is an air-fuel ratio smaller than the theoretical air-fuel ratio”.
In addition, the air-fuel ratio control means
The air-fuel ratio of the air-fuel mixture supplied to the engine is controlled so that the air-fuel ratio of the catalyst inflow gas matches the upstream target air-fuel ratio.
That is, the air-fuel ratio control means performs so-called active control.

The provisional maximum oxygen storage amount calculating means includes:
In a predetermined first period in which the upstream target air-fuel ratio is set to the target lean air-fuel ratio, at least the amount of excess oxygen contained in the catalyst inflow gas per predetermined time is at least the upstream air-fuel ratio. Calculated based on the output value of the fuel ratio sensor, and by calculating the amount of oxygen stored in the catalyst as the provisional maximum stored oxygen amount by integrating the calculated amount of excess oxygen,
In the predetermined second period within the period in which the upstream target air-fuel ratio is set to the target rich air-fuel ratio, “the amount of oxygen corresponding to the amount of excess unburned matter contained in the catalyst inflow gas per predetermined time” By calculating at least the output amount of the upstream air-fuel ratio sensor and integrating the calculated amount of oxygen corresponding to the excess amount of unburned matter. Calculating the amount of oxygen released from the catalyst as a provisional maximum amount of released oxygen; and
Based on the calculated provisional maximum stored oxygen amount and the calculated provisional maximum released oxygen amount, a provisional maximum oxygen storage amount corresponding to a provisional maximum value of the amount of oxygen that can be stored by the catalyst is calculated.

  The maximum oxygen storage amount acquisition means acquires the corrected provisional maximum oxygen storage amount by correcting the provisional maximum oxygen storage amount based on the provisional maximum oxygen storage amount, and sets the corrected provisional maximum oxygen storage amount to the provisional maximum oxygen storage amount. Based on this, the maximum oxygen storage amount of the catalyst is obtained. At this time, the maximum oxygen storage amount acquisition means corrects the provisional maximum oxygen storage amount so that the corrected provisional maximum oxygen storage amount becomes smaller as the provisional maximum oxygen storage amount becomes smaller.

  It can be determined that the oxygen storage amount of the catalyst is substantially “0” when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to the rich air-fuel ratio. Further, when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to the lean air-fuel ratio, it can be determined that the oxygen storage amount of the catalyst has substantially reached the maximum oxygen storage amount. . Therefore, according to the first invention apparatus, the provisional value of the amount of oxygen that can be stored by the catalyst (provisional maximum stored amount of oxygen) and the provisional value of the amount of oxygen that can be released by the catalyst (provisional maximum amount of released oxygen) ) Can be obtained. Further, the first invention apparatus obtains the provisional maximum oxygen storage amount based on the provisional maximum stored oxygen amount and the provisional maximum released oxygen amount, and corrects the provisional maximum oxygen storage amount based on the provisional maximum oxygen storage amount. The corrected provisional maximum oxygen storage amount is acquired, and the maximum oxygen storage amount of the catalyst is acquired based on the corrected provisional maximum oxygen storage amount. At this time, the first invention apparatus corrects the provisional maximum oxygen storage amount so that the corrected provisional maximum oxygen storage amount decreases as the provisional maximum oxygen storage amount decreases. As a result, the maximum oxygen storage amount that accurately represents the degree of deterioration of the catalyst can be obtained regardless of the degree of deterioration of the catalyst (the amount of provisional maximum stored oxygen amount).

  The first period is, for example, “when the actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor changes from an air fuel ratio smaller than the stoichiometric air fuel ratio to a larger air fuel ratio”. To “a time point at which the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio” (see FIG. 4). Furthermore, the first period may coincide with the catalyst rich period.

  Further, the second period is, for example, “when the actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor changes from an air fuel ratio larger than the stoichiometric air fuel ratio to a smaller air fuel ratio”. To “a time point when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a rich air-fuel ratio smaller than the theoretical air-fuel ratio” (see FIG. 4). Further, the second period may coincide with the catalyst lean period.

  By the way, as shown in FIG. 5, even with one catalyst, the larger the actual air-fuel ratio of the catalyst inflow gas during the period when the provisional maximum stored oxygen amount is calculated (the farther away from the theoretical air-fuel ratio), The calculated provisional maximum stored oxygen amount increases. Similarly, as shown in FIG. 5, as the actual air-fuel ratio of the catalyst inflow gas in the period for calculating the provisional maximum released oxygen amount becomes smaller (away from the theoretical air-fuel ratio), the calculated provisional maximum released oxygen amount becomes growing. Further, the actual air-fuel ratio of the catalyst inflow gas (actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor) fluctuates and does not always coincide with the upstream target air-fuel ratio. .

Therefore, in one aspect of the first invention device,
The maximum oxygen storage amount acquisition means is
The average value of the actual upstream air-fuel ratio acquired based on the output value of the upstream-side air-fuel ratio sensor in a predetermined third period within the period in which the amount of excess oxygen is integrated is calculated as the mean air during lean control. Calculated as the fuel ratio,
The actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor in a predetermined fourth period within the period in which the amount of oxygen corresponding to the amount of excess unburned matter is integrated. Calculate the average value as the average air-fuel ratio during rich control,
The corrected provisional maximum oxygen storage amount is calculated so that the corrected provisional maximum oxygen storage amount decreases as the air-fuel ratio difference that is the difference between the lean control average air-fuel ratio and the rich control average air-fuel ratio increases. Configured as follows.

  The third period is, for example, “a certain time or a time that is variable according to the intake air amount and / or the engine speed” from the time when the upstream target air-fuel ratio is set to the target lean air-fuel ratio. It may be a period from the time when elapses until "the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a lean air-fuel ratio larger than the theoretical air-fuel ratio" (see FIG. 4). Further, the third period is “after the time point when the actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor is set to the target lean air-fuel ratio. A period from “when a threshold value that is smaller than the target lean air-fuel ratio by a predetermined value” to “when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a lean air-fuel ratio that is larger than the theoretical air-fuel ratio” It may be.

  Further, the fourth period is, for example, “a fixed time and a time that is variable depending on the intake air amount and / or the engine speed” from the time when the upstream target air-fuel ratio is set to the target rich air-fuel ratio. It may be a period from the time when elapses until “the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio” (see FIG. 4). Further, the fourth period is “after the time point when the actual upstream air-fuel ratio acquired based on the output value of the upstream-side air-fuel ratio sensor is set to the target rich air-fuel ratio. A period from “when a threshold value that is larger than the target rich air-fuel ratio by a predetermined value” to “when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a rich air-fuel ratio that is smaller than the theoretical air-fuel ratio” It may be.

  According to this, since the influence of the average air-fuel ratio during lean control and the average air-fuel ratio during rich control on the maximum oxygen storage amount can be reduced, the maximum oxygen storage amount that more accurately represents the degree of catalyst deterioration can be obtained. can do.

Another device for estimating the maximum oxygen storage amount of the catalyst according to the present invention (hereinafter also referred to as “second invention device”) is an oxygen that can be stored by the catalyst disposed in the exhaust passage of the internal combustion engine. A device for estimating the maximum oxygen storage amount of a catalyst for estimating the maximum oxygen storage amount corresponding to the maximum amount of
An upstream air-fuel ratio sensor disposed upstream of the catalyst in the exhaust passage;
A downstream air-fuel ratio sensor disposed in the exhaust passage and downstream of the catalyst;
Air-fuel ratio control means;
Provisional maximum stored oxygen amount calculating means;
Means for obtaining the maximum oxygen storage amount;
Is provided.

The air-fuel ratio control means includes
From the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, the output value of the downstream air-fuel ratio sensor corresponds to a lean air-fuel ratio greater than the stoichiometric air-fuel ratio. The target lean air-fuel ratio, which is an air-fuel ratio larger than the stoichiometric air-fuel ratio, is the upstream target air-fuel ratio that is the target value of the air-fuel ratio of the catalyst inflow gas that is the exhaust gas flowing into the catalyst in the catalyst rich period up to the point of time And the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled so that the air-fuel ratio of the catalyst inflow gas matches the upstream target air-fuel ratio.

The provisional maximum stored oxygen amount calculating means includes:
At least the upstream air-fuel ratio sensor detects the amount of excess oxygen contained in the catalyst inflow gas per predetermined time in a predetermined first period within a period in which the upstream target air-fuel ratio is set to the target lean air-fuel ratio. And the amount of oxygen stored in the catalyst is calculated as the provisional maximum stored oxygen amount by integrating the calculated excess oxygen amount.

The maximum oxygen storage amount acquisition means is
The corrected provisional maximum stored oxygen amount is obtained by correcting the provisional maximum stored oxygen amount based on the provisional maximum stored oxygen amount, and the maximum oxygen storage amount of the catalyst is determined based on the corrected provisional maximum stored oxygen amount. A means for obtaining, wherein the provisional maximum stored oxygen amount is corrected such that the corrected provisional maximum stored oxygen amount decreases as the provisional maximum stored oxygen amount decreases.

  The first period is as described above. Therefore, according to this aspect, the provisional maximum stored oxygen amount is calculated, and the provisional maximum stored oxygen amount is corrected based on the provisional maximum stored oxygen amount. As a result, the maximum oxygen storage amount of the catalyst can be accurately estimated regardless of the degree of deterioration of the catalyst (the temporary maximum storage oxygen amount).

Furthermore, in one aspect of the second invention device,
The oxygen storage amount acquisition means includes
The average value of the actual upstream air-fuel ratio acquired based on the output value of the upstream-side air-fuel ratio sensor in a predetermined third period within the period in which the amount of excess oxygen is integrated is calculated as the mean air during lean control. Calculated as the fuel ratio,
The corrected provisional maximum stored oxygen amount is calculated such that the corrected provisional maximum stored oxygen amount becomes smaller as the difference between the average air-fuel ratio during lean control and the theoretical air-fuel ratio increases.

  The third period is as described above. Therefore, according to this aspect, since the influence of the average air-fuel ratio during lean control on the maximum oxygen storage amount can be reduced, the maximum oxygen storage amount that more accurately represents the degree of deterioration of the catalyst can be acquired. .

Another device for estimating the maximum oxygen storage amount of the catalyst according to the present invention (hereinafter also referred to as “third invention device”) is an oxygen that can be stored by the catalyst disposed in the exhaust passage of the internal combustion engine. A device for estimating the maximum oxygen storage amount of a catalyst for estimating the maximum oxygen storage amount corresponding to the maximum amount of
An upstream air-fuel ratio sensor disposed upstream of the catalyst in the exhaust passage;
A downstream air-fuel ratio sensor disposed in the exhaust passage and downstream of the catalyst;
Air-fuel ratio control means;
A provisional maximum released oxygen amount calculating means;
Means for obtaining the maximum oxygen storage amount;
Is provided.

The air-fuel ratio control means includes
The output value of the downstream air-fuel ratio sensor corresponds to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio from the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio. The target rich air-fuel ratio, which is an air-fuel ratio smaller than the stoichiometric air-fuel ratio, is the upstream target air-fuel ratio that is the target value of the air-fuel ratio of the catalyst inflow gas that is the exhaust gas flowing into the catalyst in the catalyst lean period until the point of time And the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled so that the air-fuel ratio of the catalyst inflow gas matches the upstream target air-fuel ratio.

The provisional maximum released oxygen amount calculating means includes:
An amount of oxygen corresponding to the amount of excess unburned matter contained in the catalyst inflow gas per predetermined time in a predetermined second period within a period in which the upstream target air-fuel ratio is set to the target rich air-fuel ratio Is calculated based on at least the output value of the upstream air-fuel ratio sensor, and the amount of oxygen corresponding to the amount of excess unburned matter calculated is integrated to calculate the amount of oxygen released from the catalyst as the provisional maximum released oxygen. Calculate as a quantity.

The maximum oxygen storage amount acquisition means is
A corrected provisional maximum released oxygen amount is obtained by correcting the provisional maximum released oxygen amount based on the provisional maximum released oxygen amount, and a maximum oxygen storage amount of the catalyst is obtained based on the corrected provisional maximum released oxygen amount. A means for obtaining, wherein the provisional maximum released oxygen amount is corrected so that the corrected provisional maximum released oxygen amount decreases as the provisional maximum released oxygen amount decreases.

  The second period is as described above. Therefore, according to this aspect, the provisional maximum released oxygen amount is calculated, and the provisional maximum released oxygen amount is corrected based on the provisional maximum released oxygen amount. As a result, the maximum oxygen storage amount of the catalyst can be accurately estimated regardless of the degree of deterioration of the catalyst (the magnitude of the provisional maximum released oxygen amount).

Furthermore, in one aspect of the third invention device,
The oxygen storage amount acquisition means includes
The actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor in a predetermined fourth period within the period in which the amount of oxygen corresponding to the amount of excess unburned matter is integrated. Calculate the average value as the average air-fuel ratio during rich control,
The corrected provisional maximum released oxygen amount is calculated so that the corrected provisional maximum released oxygen amount decreases as the difference between the rich control average air-fuel ratio and the stoichiometric air-fuel ratio increases.

  The fourth period is as described above. Therefore, according to this aspect, since the influence of the average air-fuel ratio during rich control on the maximum oxygen storage amount can be reduced, the maximum oxygen storage amount that more accurately represents the degree of catalyst deterioration can be acquired. .

  Other objects, other features and attendant advantages of the inventive device will be readily understood from the description of each embodiment of the inventive device described with reference to the following drawings.

FIG. 1 is a schematic view of an internal combustion engine to which a maximum oxygen storage amount estimation device (first estimation device) for a catalyst according to a first embodiment of the present invention is applied. FIG. 2 is a graph showing the relationship between the output value of the upstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. FIG. 3 is a graph showing the relationship between the output value of the downstream air-fuel ratio sensor shown in FIG. 1 and the air-fuel ratio. FIG. 4 is a time chart for explaining the operation of the first estimation device. FIG. 5 is a graph showing the relationship between the upstream air-fuel ratio during active control and the “temporary maximum stored oxygen amount and provisional maximum released oxygen amount”. FIG. 6 is a flowchart showing a routine executed by the CPU of the first estimation device. FIG. 7 is a flowchart showing a routine executed by the CPU of the first estimation device. FIG. 8 is a correction coefficient table referred to by the CPU of the first estimation device.

  Embodiments of a catalyst maximum oxygen storage amount estimation apparatus according to the present invention will be described below with reference to the drawings.

<First Embodiment>
(Constitution)
FIG. 1 shows a schematic configuration of an internal combustion engine 10 to which a maximum oxygen storage amount estimation device for a catalyst according to a first embodiment of the present invention (hereinafter also referred to as “first estimation device”) is applied. The engine 10 is a four-cycle / spark ignition type / multi-cylinder (four cylinders in this example) / gasoline fuel engine. The engine 10 includes a main body 20, an intake system 30, and an exhaust system 40.

  The main body portion 20 includes a cylinder block portion and a cylinder head portion. The main body portion 20 includes a plurality (four) of combustion chambers (first cylinder # 1 to fourth cylinder # 4) 21 including a piston top surface, a cylinder wall surface, and a lower surface of the cylinder head portion.

  A plurality of intake ports 22 and a plurality of exhaust ports 23 are formed in the cylinder head portion. Each intake port 22 is connected to each combustion chamber 21 so as to supply “a mixture of air and fuel” to each combustion chamber (each cylinder) 21. The intake port 22 is opened and closed by an intake valve (not shown). Each exhaust port 23 is connected to each combustion chamber 21 so as to discharge exhaust gas (burned gas) from each combustion chamber 21. The exhaust port 23 is opened and closed by an exhaust valve (not shown).

  A plurality (four) of spark plugs 24 are fixed to the cylinder head portion. Each spark plug 24 is disposed such that its spark generating part is exposed at the center of each combustion chamber 21 and in the vicinity of the lower surface of the cylinder head part. Each spark plug 24 generates an ignition spark from the spark generating portion in response to the ignition signal.

  A plurality (four) of fuel injection valves (injectors) 25 are further fixed to the cylinder head portion. One fuel injection valve 25 is provided for each intake port 22 (that is, one for each cylinder). In response to the injection instruction signal, the fuel injection valve 25 injects “the fuel of the indicated fuel injection amount Fi included in the injection instruction signal” into the corresponding intake port 22.

  Further, an intake valve control device 26 is provided in the cylinder head portion. The intake valve control device 26 has a known configuration that adjusts and controls the relative rotation angle (phase angle) between an intake camshaft (not shown) and an intake cam (not shown) by hydraulic pressure. The intake valve control device 26 operates based on an instruction signal (drive signal), and can change the valve opening timing (intake valve opening timing) of the intake valve.

  The intake system 30 includes an intake manifold 31, an intake pipe 32, an air filter 33, a throttle valve 34, and a throttle valve actuator 34a.

  The intake manifold 31 includes a plurality of branch portions connected to each intake port 22 and a surge tank portion in which the branch portions are gathered. The intake pipe 32 is connected to the surge tank portion. The intake manifold 31, the intake pipe 32, and the plurality of intake ports 22 constitute an intake passage. The air filter 33 is provided at the end of the intake pipe 32. The throttle valve 34 is rotatably attached to the intake pipe 32 at a position between the air filter 33 and the intake manifold 31. The throttle valve 34 changes the opening cross-sectional area of the intake passage formed by the intake pipe 32 by rotating. The throttle valve actuator 34a is formed of a DC motor, and rotates the throttle valve 34 in response to an instruction signal (drive signal).

  The exhaust system 40 includes an exhaust manifold 41, an exhaust pipe (exhaust pipe) 42, an upstream catalyst 43, and a downstream catalyst 44.

  The exhaust manifold 41 includes a plurality of branch portions 41a connected to the exhaust ports 23, and a collection portion (exhaust collection portion) 41b in which the branch portions 41a are gathered. The exhaust pipe 42 is connected to a collective portion 41 b of the exhaust manifold 41. The exhaust manifold 41, the exhaust pipe 42, and the plurality of exhaust ports 23 constitute a passage through which exhaust gas passes. In the present specification, a passage formed by the collecting portion 41b of the exhaust manifold 41 and the exhaust pipe 42 is referred to as an “exhaust passage” for convenience.

The upstream side catalyst (catalyst device for exhaust purification, catalytic converter) 43 carries “noble metal as a catalytic substance” and “ceria (CeO ₂ ) as an oxygen storage substance” on a carrier containing ceramic, and oxygen It is a three-way catalyst having a storage / release function (oxygen storage function). The upstream catalyst 43 is disposed (intervened) in the exhaust pipe 42. When the upstream catalyst 43 reaches a predetermined activation temperature, the upstream catalyst 43 exhibits a catalytic function and an oxygen storage function. The upstream catalyst 43 is also referred to as a start catalytic converter (SC) or a first catalyst.

The catalytic function is a function for simultaneously purifying unburned substances (HC, CO, H _{2 and the} like) and nitrogen oxides (NOx).
The oxygen storage function stores oxygen in the catalyst when the catalyst inflow gas contains excess oxygen (oxidant remaining in the gas after oxidation equilibrium) and purifies NOx (reduction). When the catalyst inflow gas contains excessive unburned material (reducing agent remaining in the gas after oxidation equilibrium), the oxygen stored in the catalyst is released and the unburned material in the gas is released. It is a function to purify (oxidize). This oxygen storage function is lowered when the catalyst is deteriorated due to “poisoning and heat deterioration”. As a result, the maximum oxygen storage amount corresponding to the maximum amount of oxygen that can be stored (and therefore released) by the catalyst becomes smaller as the deterioration of the catalyst proceeds.

  The downstream catalyst 44 is a three-way catalyst similar to the upstream catalyst 43. The downstream catalyst 44 is disposed (intervened) in the exhaust pipe 42 downstream of the upstream catalyst 43. Since the downstream side catalyst 44 is disposed below the floor of the vehicle, it is also referred to as an under-floor catalytic converter (UFC) or a second catalyst. In the present specification, when the term “catalyst” is simply used, the “catalyst” means the upstream catalyst 43.

  The first estimation device includes a hot-wire air flow meter 51, a throttle position sensor 52, an engine speed sensor 53, a water temperature sensor 54, an upstream air-fuel ratio sensor 55, a downstream air-fuel ratio sensor 56, and an accelerator opening sensor 57. .

  The hot-wire air flow meter 51 detects the mass flow rate of the intake air flowing through the intake pipe 32 and outputs a signal representing the mass flow rate (intake air amount per unit time of the engine 10) Ga.

  The throttle position sensor 52 detects the opening degree of the throttle valve 34 and outputs a signal representing the throttle valve opening degree TA.

  The engine rotational speed sensor 53 outputs a signal having a narrow pulse every time the intake camshaft rotates 5 ° and a wide pulse every time the intake camshaft rotates 360 °. A signal output from the engine rotational speed sensor 53 is converted into a signal representing the engine rotational speed NE by an electric control device 60 described later. Further, the electric control device 60 acquires the crank angle (absolute crank angle) of the engine 10 based on signals from the engine rotation speed sensor 53 and a cam position sensor (not shown).

  The water temperature sensor 54 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW.

  The upstream air-fuel ratio sensor 55 is disposed in either the exhaust manifold 41 or the exhaust pipe 42 (that is, the exhaust passage) at a position between the collecting portion 41 b of the exhaust manifold 41 and the upstream catalyst 43. The upstream air-fuel ratio sensor 55 is disclosed in, for example, “limit current type wide area air-fuel ratio including a diffusion resistance layer” disclosed in JP-A-11-72473, JP-A-2000-65782, JP-A-2004-69547, and the like. Sensor ".

  As shown in FIG. 2, the upstream air-fuel ratio sensor 55 outputs an output value Vabyfs corresponding to the air-fuel ratio of the exhaust gas (catalyst inflow gas) flowing through the position where the upstream air-fuel ratio sensor 55 is disposed. The air-fuel ratio of the catalyst inflow gas is also referred to as “upstream air-fuel ratio abyfs”. The output value Vabyfs increases as the air-fuel ratio of the catalyst inflow gas increases (that is, as the air-fuel ratio of the catalyst inflow gas becomes leaner).

  The electric control device 60 stores the air-fuel ratio conversion table (map) Mapabyfs shown in FIG. The electric control device 60 detects the actual upstream air-fuel ratio abyfs (obtains the upstream air-fuel ratio abyfs) by applying the output value Vabyfs to the air-fuel ratio conversion table Mapabyfs.

Referring again to FIG. 1, the downstream air-fuel ratio sensor 56 is disposed in the exhaust pipe 42 (that is, the exhaust passage) at a position between the upstream catalyst 43 and the downstream catalyst 44. The downstream air-fuel ratio sensor 56 is a well-known “concentration cell type oxygen concentration sensor (O ₂ sensor)” that generates an electromotive force according to the difference between the oxygen partial pressure in the exhaust gas and the oxygen partial pressure in the atmosphere as an output value. It is.

  More specifically, as shown in FIG. 3, the output value Voxs of the downstream air-fuel ratio sensor 56 indicates that the air-fuel ratio of the gas (catalyst outflow gas) reaching the downstream air-fuel ratio sensor 56 is the theoretical sky. When the oxygen partial pressure of the gas after the oxidation equilibrium (oxygen equilibrium) of the gas having a rich air-fuel ratio smaller than the fuel ratio and reaching the downstream air-fuel ratio sensor 56 is small, the maximum output value Max (for example, about 0. 0). 9V or 1.0V). That is, the downstream air-fuel ratio sensor 56 has a maximum output value Max when the catalyst outflow gas does not contain any excess oxygen (in other words, when the catalyst outflow gas contains unburned substances as a reducing agent). Is output.

  Further, the output value Voxs of the downstream air-fuel ratio sensor 56 is a lean air-fuel ratio in which the air-fuel ratio of the gas (catalyst outflow gas) reaching the downstream air-fuel ratio sensor 56 is larger than the stoichiometric air-fuel ratio, When the oxygen partial pressure of the gas after oxidation equilibrium of the gas reaching the air-fuel ratio sensor 56 is large, it becomes a value near the minimum output value Min (for example, about 0.1 V or 0 V). That is, the downstream air-fuel ratio sensor 56 reduces the minimum output value Min when the catalyst outflow gas contains “excess oxygen” (in other words, when the catalyst outflow gas contains oxygen which is an oxidant). Output.

  This output value Voxs rapidly decreases from a value near the maximum output value Max to a value near the minimum output value Min when the air-fuel ratio of the catalyst outflow gas changes from the rich air-fuel ratio to the lean air-fuel ratio. Conversely, when the air-fuel ratio of the catalyst outflow gas changes from the lean air-fuel ratio to the rich air-fuel ratio, the output value Voxs increases rapidly from the minimum output value Min vicinity value to the maximum output value Max vicinity value. The output value Voxs corresponds to the maximum output value Max and the minimum of the downstream air-fuel ratio sensor 56 when the oxygen partial pressure of the catalyst outflow gas is “the oxygen partial pressure when the air-fuel ratio of the catalyst outflow gas is the stoichiometric air-fuel ratio”. The output value Min substantially matches the center value Vmid (median value Vmid = (Max + Min) / 2). The median value Vmid is also referred to as a stoichiometric air-fuel ratio equivalent voltage Vst for convenience.

  The accelerator opening sensor 57 shown in FIG. 1 detects the operation amount of the accelerator pedal AP operated by the driver, and outputs a signal indicating the operation amount Accp of the accelerator pedal AP.

  The electric control device 60 is an electric circuit including a “well-known microcomputer” including “a CPU, a ROM, a RAM, a backup RAM, an interface including an AD converter, and the like”.

  The backup RAM included in the electric control device 60 is a battery mounted on the vehicle regardless of the position of an ignition key switch (not shown) of the vehicle on which the engine 10 is mounted (any one of an off position, a start position, an on position, etc.). It is supposed to receive power supply from. When receiving power from the battery, the backup RAM stores data according to an instruction from the CPU (data is written) and holds (stores) the data so that the data can be read. The backup RAM cannot retain data when the power supply from the battery is interrupted, for example, when the battery is removed from the vehicle. In other words, the data held so far is lost (destroyed).

  The interface of the electric control device 60 is connected to the sensors 51 to 57 so as to supply signals from the sensors 51 to 57 to the CPU. Further, the interface sends an instruction signal (drive signal) or the like to the ignition plug 24 of each cylinder, the fuel injection valve 25 of each cylinder, the intake valve control device 26, the throttle valve actuator 34a, etc. in accordance with an instruction from the CPU. It is like that. The electric control device 60 sends an instruction signal to the throttle valve actuator 34a so that the throttle valve opening TA increases as the acquired accelerator pedal operation amount Accp increases.

(Outline of operation of first estimation device)
Next, an outline of a method for estimating the maximum oxygen storage amount by the first estimation device will be described. The first estimation device obtains the maximum oxygen storage amount of the catalyst based on the “maximum stored oxygen amount and maximum released oxygen amount”. The maximum oxygen storage amount is, for example, an average value of the maximum stored oxygen amount and the maximum released oxygen amount. When the condition for obtaining the maximum oxygen storage amount of the catalyst is satisfied, the first estimation device estimates the maximum oxygen storage amount as follows. The maximum oxygen storage amount is acquired using “active air-fuel ratio control”. The active air-fuel ratio control itself is described in, for example, the above-mentioned Patent Document 1 and Japanese Patent Laid-Open No. 5-133264.

  Incidentally, when the air-fuel ratio of the catalyst inflow gas is a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, the output value Voxs of the downstream air-fuel ratio sensor 56 is smaller than a predetermined threshold value Voxsref (for example, the stoichiometric air-fuel ratio equivalent voltage Vst). When the value changes from a large value to a large value (see time t1, time t3, and time t5 in FIG. 4), it is estimated that the oxygen storage amount of the catalyst 43 is substantially “0”. That is, when the air-fuel ratio of the catalyst inflow gas is a rich air-fuel ratio, the output value Voxs of the downstream air-fuel ratio sensor 56 becomes a value corresponding to a rich air-fuel ratio smaller than the theoretical air-fuel ratio (hereinafter referred to as “rich inversion”). The time point is referred to as “time point”.) Is a time point when the oxygen that can be released by the catalyst 43 (oxygen that has been occluded) has been consumed.

  On the other hand, when the air-fuel ratio of the catalyst inflow gas is a lean air-fuel ratio larger than the stoichiometric air-fuel ratio, when the output value Voxs of the downstream air-fuel ratio sensor 56 changes from a value larger than a predetermined threshold value Voxsref to a smaller value ( (See time t2 and time t4 in FIG. 4), and it is estimated that the oxygen storage amount of the catalyst 43 has substantially reached the maximum value (maximum oxygen storage amount). That is, when the air-fuel ratio of the catalyst inflow gas is a lean air-fuel ratio, the time point when the output value Voxs of the downstream air-fuel ratio sensor 56 becomes a value corresponding to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio (hereinafter referred to as “lean inversion”). The time point is referred to as “time point”.) Is the time point when the catalyst 43 has fully occluded oxygen.

  Therefore, the first estimation device performs a period from rich inversion to lean inversion (hereinafter referred to as “catalyst rich period”), a target value of the air-fuel ratio of the catalyst inflow gas (that is, the upstream target air-fuel ratio abyfr). ) Is set to “a target lean air-fuel ratio afLean that is an air-fuel ratio larger than the stoichiometric air-fuel ratio” (see time t1 to time t2 in FIG. 4).

  The first estimation device feedback-controls the fuel injection amount so that the upstream air-fuel ratio abyfs represented by the output value Vabyfs of the upstream air-fuel ratio sensor 55 coincides with the upstream target air-fuel ratio abyfr. Feedback control of the air-fuel ratio.

In the catalyst rich period (the period in which the upstream target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean, hereinafter also referred to as the “set air-fuel ratio lean period”), the catalyst inflow gas contains excessive oxygen. . Therefore, the first estimation device is occluded by the three-way catalyst 43 per unit time (predetermined time) Ts in the first period (see time t1a-time t2 in FIG. 4) within the catalyst rich period. The amount of wax oxygen (that is, the amount of change in stored oxygen ΔOSAkz) is calculated according to the following equation (1). In the equation (1), SFi is the amount of fuel per unit time Ts (total amount of fuel injection amount), and 0.23 is the weight ratio of oxygen in the atmosphere. stoich is the stoichiometric air-fuel ratio (for example, 14.6). In the first period, after the upstream target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean, the upstream lean air-fuel ratio abyfs first crosses the stoichiometric air-fuel ratio stoich (time t1a) and the next lean reversal ( This is the period until time t2).

ΔOSAkz = SFi · 0.23 · (abyfs-stoich) (1)

Furthermore, as shown in the following equation (2), the first estimation device calculates the temporary stored oxygen amount ZOSakz by integrating the calculated stored oxygen change amount ΔOSAkz over the first period. In the formula (2), ZOSakz (n) is the provisional stored oxygen amount after update (current time), and ZOSakz (n-1) is the provisional stored oxygen amount at a time point Ts before the current time. The provisional maximum stored oxygen amount ZOSakzMAX is the provisional stored oxygen amount ZOSakz at the time of lean reversal (time t2). The provisional stored oxygen amount ZOSakz is set to “0” immediately after the lean inversion.

ZOSAkz (n) = ZOSAkz (n−1) + ΔOSAkz (2)

  On the other hand, the first estimation device sets the upstream target air-fuel ratio abyfr to “the air-fuel ratio smaller than the stoichiometric air-fuel ratio” during the period from the lean inversion to the rich inversion (hereinafter referred to as “catalyst lean period”). To the target rich air-fuel ratio afRich ”(see time t2−time t3 in FIG. 4).

  During the catalyst lean period (the period in which the upstream target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich, hereinafter also referred to as the “set air-fuel ratio rich period”), the catalyst inflow gas contains excessive unburned substances. It is out. As described above, the catalyst 43 releases the stored oxygen and purifies the unburned matter with this oxygen.

Therefore, the first estimation device will release the three-way catalyst 43 per unit time (predetermined time) Ts in the second period within the catalyst lean period (see time t2a-time t3 in FIG. 4). The amount of oxygen (that is, the amount of oxygen corresponding to the amount of excess unburned material contained in the catalyst inflow gas (necessary to oxidize excess unburnt material, the amount of change in released oxygen) ΔOSAhs is expressed as ( 3) Calculate according to the equation. In other words, the released oxygen change amount ΔOSAhs is the amount of oxygen corresponding to the amount of excess unburned matter flowing into the catalyst 43 per unit time Ts in the second period. In the second period, after the upstream target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich, from the time (time t2a) when the upstream air-fuel ratio abyfs first crosses the stoichiometric air-fuel ratio stoich, This is the period until time t3).

ΔOSAhs = SFi · 0.23 · (stoich-abyfs) (3)

Furthermore, as shown in the following equation (4), the first estimation device calculates the provisional released oxygen amount ZOSahs by integrating the calculated released oxygen change amount ΔOSAhs over the second period. In the equation (4), ZOSahs (n) is the provisional released oxygen amount after update (current time), and ZOSahs (n-1) is the provisional released oxygen amount at a time point Ts before the current time. The provisional maximum released oxygen amount ZOSahsMAX is the provisional released oxygen amount ZOSahs at the time of rich inversion (time t3). The provisional released oxygen amount ZOSahs is set to “0” immediately after the rich inversion.

ZOSAhs (n) = ZOSAhs (n−1) + ΔOSAhs (4)

  By the way, as shown in FIG. 5, even with one catalyst, it is calculated as the average value of the upstream air-fuel ratio abyfs during the period for calculating the provisional maximum stored oxygen amount ZOSakzMAX increases (as the distance from the theoretical air-fuel ratio increases). The tentative maximum stored oxygen amount ZOSakzMAX increases, and as the average value of the upstream air-fuel ratio abyfs in the period for calculating the tentative maximum released oxygen amount ZOSahsMAX becomes smaller (away from the theoretical air-fuel ratio), the calculated provisional maximum released oxygen amount ZOSAhsMAX gets bigger.

  Further, since the actual air-fuel ratio (upstream air-fuel ratio abyfs) of the catalyst inflow gas varies, it does not always coincide with the upstream target air-fuel ratio abyfr. Therefore, when the maximum oxygen storage amount Cmax is calculated based on the provisional maximum stored oxygen amount ZOSakzMAX and the provisional maximum released oxygen amount ZOSahsMAX, the maximum oxygen storage amount Cmax may not accurately represent the degree of deterioration of the catalyst.

  Therefore, the first estimation device uses the average value of the upstream air-fuel ratio abyfs in the third period within the catalyst rich period (set air-fuel ratio lean period) (hereinafter also referred to as “lean control average air-fuel ratio AveLean”). get. In the third period, from the time when the upstream target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean to the next lean reversal (time t2) from the time when the predetermined time Td has elapsed (time t1b in FIG. 4). Period (PLean). The predetermined time Td is a time considering the gas transport delay and the responsiveness of the upstream air-fuel ratio sensor 55, and may be a fixed time or a time varying according to the intake air amount Ga and / or the engine rotational speed NE. May be.

  Further, the first estimation device uses the average value of the upstream air-fuel ratio abyfs in the fourth period within the catalyst lean period (set air-fuel ratio rich period) (hereinafter also referred to as “rich control average air-fuel ratio AveRich”). get. In the fourth period, from the time when the upstream target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich to the next rich inversion (time t3) from the time when the predetermined time Td has elapsed (time t2b in FIG. 4). Period (PRich).

  Thereafter, the first estimation device acquires the average value of the provisional maximum stored oxygen amount ZOSakzMAX and the provisional maximum released oxygen amount ZOSahsMAX as the provisional maximum oxygen storage amount ZCmax. Then, the first estimation device corrects the provisional maximum oxygen storage amount ZCmax based on the air-fuel ratio difference ΔAF that is the difference between the lean control average air-fuel ratio AveLean and the rich control average air-fuel ratio AveRich. The maximum oxygen storage amount ZCmaxh is acquired, and the corrected provisional maximum oxygen storage amount ZCmaxh is acquired as the maximum oxygen storage amount Cmax.

  More specifically, the first estimation device corrects the provisional maximum oxygen storage amount ZCmax so that the corrected provisional maximum oxygen storage amount ZCmaxh decreases as the air-fuel ratio difference ΔAF increases, and the provisional maximum oxygen after the correction. The storage amount ZCmaxh is acquired as the final maximum oxygen storage amount Cmax (used for determining the deterioration of the catalyst 43).

  In addition, even if the catalyst is one catalyst and the air-fuel ratio difference ΔAF is constant (actually, the average air-fuel ratio AveLean during lean control is a constant value and the average air-fuel ratio AveRich during rich control is a constant value. However, the corrected provisional maximum oxygen storage amount ZCmaxh is a relatively large value when the provisional maximum oxygen storage amount is smaller than the predetermined value as compared with the case where the provisional maximum oxygen storage amount is larger than the predetermined value ( It is calculated as an excessively large value).

  Therefore, when the provisional maximum oxygen storage amount ZCmax is obtained, the first estimation device corrects the provisional maximum oxygen storage amount ZCmax in accordance with the magnitude of the provisional maximum oxygen storage amount ZCmax. That is, the first estimation device corrects the provisional maximum oxygen storage amount ZCmax so that the corrected provisional maximum oxygen storage amount ZCmaxh decreases as the provisional maximum oxygen storage amount ZCmax decreases. The first estimating apparatus acquires and employs the corrected provisional maximum oxygen storage amount ZCmaxh corrected based on the “air-fuel ratio difference ΔAF and provisional maximum oxygen storage amount ZCmax” as the maximum oxygen storage amount Cmax.

Actually, the first estimation device stores in the ROM the correction coefficient table Mapkh shown in FIG. 8 that defines the relationship between “the air-fuel ratio difference ΔAF and the provisional maximum oxygen storage amount ZCmax and the correction coefficient kh”. The correction coefficient kh is determined by applying the calculated ΔAF and the calculated provisional maximum oxygen storage amount ZCmax to the correction coefficient table Mapkh. Then, as shown in the following equation (5), the first estimation device corrects the provisional maximum oxygen storage amount ZCmaxh (ie, the maximum oxygen storage amount Cmax after correction) by multiplying the provisional maximum oxygen storage amount ZCmax by the correction coefficient kh. ) Get as.

Cmax = ZCmaxh = kh · ZCmax (5)

(Actual operation)
Next, the actual operation of the first estimation device will be described. Hereinafter, for convenience of explanation, “MapX (a1, a2,...)” Is “a table having arguments a1, a2,...” And represents “a table for obtaining a value X”.

<Fuel injection control>
The CPU of the first estimation device repeatedly executes the fuel injection control routine shown in FIG. 6 for each cylinder every time the crank angle of any cylinder reaches a predetermined crank angle before the intake top dead center. It has become. The predetermined crank angle is, for example, BTDC 90 ° CA (90 ° crank angle before intake top dead center). A cylinder whose crank angle coincides with the predetermined crank angle is also referred to as a “fuel injection cylinder”. The CPU calculates the commanded fuel injection amount (final fuel injection amount) Fi and instructs fuel injection by this fuel injection control routine.

  When the crank angle of an arbitrary cylinder coincides with the predetermined crank angle before the intake top dead center, the CPU starts the process from step 600 and proceeds to step 610 to “the intake air amount Ga measured by the air flow meter 51, the engine rotation speed”. Based on the engine rotational speed NE acquired based on the signal from the speed sensor 53 and the lookup table MapMc (Ga, NE), “the amount of air sucked into the fuel injection cylinder (ie, the amount of intake air in the cylinder)” Mc) ". The in-cylinder intake air amount Mc may be calculated by a well-known air model (a model constructed according to a physical law simulating the behavior of air in the intake passage).

Next, the CPU proceeds to step 620 to determine whether or not the value of the active control flag Xactive is “1”. The value of the active control flag Xactive is set to “1” when the “active control precondition” that is a condition for calculating the maximum oxygen storage amount Cmax of the catalyst 43 is satisfied, and the condition is not satisfied. Is set to “0”. The active control flag control precondition is satisfied, for example, when all the following conditions are satisfied.
(A1) The upstream air-fuel ratio sensor 55 is activated.
(A2) The downstream air-fuel ratio sensor 56 is activated.
(A3) The engine load KL is less than or equal to the threshold KLth.
(A4) The catalyst 43 is activated (for example, the coolant temperature THW is equal to or higher than the threshold coolant temperature THWth).
(A5) The deterioration determination of the catalyst 43 is not performed after the start of the operation of the engine 10 this time.

  Assume that the value of the active control flag Xactive is “0”. In this case, the CPU makes a “No” determination at step 620 to proceed to step 630 to set the upstream target air-fuel ratio abyfr to the stoichiometric air-fuel ratio stoich. That is, the CPU sets the upstream target air-fuel ratio abyfr to a value for normal control.

  Next, the CPU sequentially performs the processing from step 640 to step 670 described below, proceeds to step 695, and once ends this routine.

  Step 640: The CPU calculates the basic fuel injection amount Fbase by dividing the in-cylinder intake air amount Mc by the upstream target air-fuel ratio abyfr. The basic fuel injection amount Fbase is a feed-forward amount of the fuel injection amount necessary for making the air-fuel ratio of the engine coincide with the upstream target air-fuel ratio abyfr.

  Step 650: The CPU reads a main feedback amount KFmain separately calculated by a routine not shown. The main feedback amount KFmain is calculated based on known PID control so that the upstream air-fuel ratio abyfs matches the upstream target air-fuel ratio abyfr. Briefly, the main feedback amount KFmain is decreased when the upstream air-fuel ratio abyfs is smaller than the upstream target air-fuel ratio abyfr, and is increased when the upstream air-fuel ratio abyfs is larger than the upstream target air-fuel ratio abyfr. .

  Step 660: The CPU calculates the command fuel injection amount Fi by correcting the basic fuel injection amount Fbase with the main feedback amount KFmain. More specifically, the CPU calculates the command fuel injection amount Fi by multiplying the basic fuel injection amount Fbase by the main feedback amount KFmain.

  Step 670: The CPU sends an injection instruction signal for injecting “the fuel of the indicated fuel injection amount Fi” from the “fuel injection valve 25 provided corresponding to the fuel injection cylinder” to the fuel injection valve 25. To do.

  As a result, an amount of fuel necessary for making the air-fuel ratio of the engine coincide with the upstream air-fuel ratio abyfs is injected from the fuel injection valve 25 of the fuel injection cylinder. That is, Steps 640 to 670 constitute command fuel injection amount control means (air-fuel ratio control means) that “controls the command fuel injection amount Fi so that the air-fuel ratio of the engine matches the upstream target air-fuel ratio abyfr”. ing.

  On the other hand, if the value of the active control flag Xactive is “1” at the time when the CPU performs the process of step 620, the CPU makes a “Yes” determination at step 620 to proceed to step 680 and perform upstream target empty. The fuel ratio abyfr is set to a value for active control (any one of the target lean air-fuel ratio afLean and the target rich air-fuel ratio afRich). Thereafter, the CPU executes the processes of steps 640 to 670 described above.

Here, the processing of the CPU in step 680 will be described more specifically.
When the CPU proceeds to step 680 immediately after the value of the active control flag Xactive has changed from “0” to “1”, the CPU first sets the upstream target air-fuel ratio abyfr to a constant target larger than the stoichiometric air-fuel ratio stoich. Set to lean air-fuel ratio afLean. In this state, the CPU monitors whether or not the output value Voxs is smaller than a predetermined threshold value Voxsref (for example, the theoretical air-fuel ratio equivalent voltage Vst).

  At this time, when the output value Voxs is smaller than the threshold value Voxsref (that is, when the output value Voxs is a value corresponding to the lean air-fuel ratio), the CPU sets the upstream target air-fuel ratio abyfr to the target rich air-fuel ratio afRich. . On the other hand, when the output value Voxs is larger than the threshold value Voxsref at this time (that is, when the output value Voxs is a value corresponding to the rich air-fuel ratio), the CPU sets the upstream target air-fuel ratio abyfr to the target lean air-fuel ratio afLean. Continue to maintain. When the output value Voxs becomes smaller than the threshold value Voxsref, the CPU sets the upstream target air-fuel ratio abyfr to a constant target rich air-fuel ratio afRich that is smaller than the stoichiometric air-fuel ratio stoich.

  Next, the CPU monitors whether or not the rich inversion time point (first time point, time t1 in FIG. 4) has been reached. When the rich inversion time is detected, the CPU sets the upstream target air-fuel ratio abyfr to the target lean air-fuel ratio afLean. After this rich inversion time point, the next lean inversion time point (second time point, FIG. 4) from the time point (time t1a in FIG. 4) when the upstream air-fuel ratio abyfs becomes larger (lean) than the stoichiometric air fuel ratio stoich. Until the time t2), the provisional maximum stored oxygen amount ZOSakzMAX is calculated by calculating the provisional stored oxygen amount ZOSakz.

  Thereafter, when the CPU detects the lean inversion time (second time point, time t2 in FIG. 4), the CPU sets the upstream target air-fuel ratio abyfr to the target rich air-fuel ratio afRich. After the lean inversion time, the CPU performs the next rich inversion time (third time point) from the time when the upstream air-fuel ratio abyfs becomes smaller (rich) than the stoichiometric air-fuel ratio stoich (time t2a in FIG. 4). Until the time t3) in FIG. 4, the provisional maximum released oxygen amount ZOSahsMAX is calculated by calculating the provisional released oxygen amount ZOSahs.

<Acquisition of catalyst deterioration judgment data (catalyst deterioration judgment)>
The CPU repeatedly executes the “catalyst deterioration determination data acquisition routine (maximum oxygen storage amount acquisition routine)” shown in the flowchart of FIG. 7 every elapse of a predetermined time Ts (unit time). Accordingly, when the predetermined timing comes, the CPU starts the process from step 700 and proceeds to step 705 to determine whether or not the above-mentioned active control precondition (maximum oxygen storage amount acquisition control condition) is satisfied (the above-mentioned (See (A1) to (A5).)

  If the active control precondition is not satisfied, the CPU makes a “No” determination at step 705 to proceed to step 710 to set the value of the active control flag Xactive to “0” and store various data described below. Reset (set to “0”). Thereafter, the CPU proceeds directly to 795 to end the present routine tentatively. As a result, control (normal control) is performed in which the upstream target air-fuel ratio abyfr is set to the stoichiometric air-fuel ratio stoich.

  On the other hand, if the active control precondition is satisfied, the CPU makes a “Yes” determination at step 705 to proceed to step 715 to set the value of the active control flag Xactive to “1”. Next, the CPU proceeds to step 720 and performs the processing described below.

The CPU determines that the current lean time is “the upstream side air-fuel ratio abyfs is higher than the stoichiometric air-fuel ratio stoich (time t1a in FIG. 4) to the next lean reversal time (second time point, time t2 in FIG. 4). In the first period until the provisional stored oxygen amount ZOSakz is calculated according to the above formulas (1) and (2). At the time of lean reversal, the CPU stores the provisional stored oxygen amount ZOSakz as the provisional maximum stored oxygen amount ZOSakzMAX.
The CPU determines that the current time point “the upstream air-fuel ratio abyfs becomes the air-fuel ratio smaller than the stoichiometric air-fuel ratio stoich (time t2a in FIG. 4) to the next rich inversion time (third time, time t3 in FIG. 4). In the second period until the provisional release oxygen amount ZOSahs is calculated according to the above formulas (3) and (4). The CPU stores the provisional released oxygen amount ZOSahs as the provisional maximum released oxygen amount ZOSahsMAX at the rich inversion time (third time point).

The CPU determines that the current lean time is “from the time when the upstream target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean (a time t1b in FIG. 4) to the next lean reversal (time t2). In the period until (the third period) ", the set air-fuel ratio lean period air-fuel ratio integrated value SLaf is calculated by integrating the upstream air-fuel ratio abyfs according to the following equation (6). In the equation (6), SLaf (n) is the updated integrated value SLaf, and SLaf (n−1) is the integrated value SLaf at a time point before the current time by the unit time Ts.

SLaf (n) = SLaf (n−1) + abyfs (6)

When the current time is in the “third period”, the CPU updates the integrated value SLaf integrated counter CL by increasing the integrated value SLaf integrated counter CL by “1” according to the following equation (7). In equation (7), CL (n) is the updated integrated value SLaf integrated counter CL, and CL (n−1) is the integrated value SLaf integrated counter CL at a time point before the current time by the unit time Ts.

CL (n) = CL (n−1) +1 (7)

The CPU determines that the current time “from the time when the upstream target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich has passed the predetermined time Td (time t2b in FIG. 4) and the next rich inversion (time t3). In the period up to (fourth period), the set air-fuel ratio rich period air-fuel ratio SRaf is calculated by integrating the upstream air-fuel ratio abyfs according to the following equation (8). In the equation (8), SRaf (n) is the updated integrated value SRaf, and SRaf (n−1) is the integrated value SRaf at the time before the unit time Ts before the current time.

SRaf (n) = SRaf (n−1) + abyfs (8)

When the current time is in the “fourth period”, the CPU updates the integrated value SRaf integrated counter CR by increasing the integrated value SRaf integrated counter CR by “1” according to the following equation (9). In equation (9), CR (n) is an updated integrated value SRaf integrated counter CR, and CR (n−1) is an integrated value SRaf integrated counter CR at a time point before unit time Ts from the present time.

CR (n) = CR (n−1) +1 (9)

  Next, the CPU proceeds to step 725 to determine whether or not the acquisition of the provisional maximum oxygen storage amount ZCmax calculation data has been completed. More specifically, the CPU determines whether or not a period from the first time point to the third time point has elapsed. At this time, if acquisition of the provisional maximum oxygen storage amount ZCmax calculation data has not been completed, the CPU makes a “No” determination at step 725 to directly proceed to step 795 to end the present routine tentatively.

  On the other hand, when acquisition of the provisional maximum oxygen storage amount ZCmax calculation data has been completed, the CPU makes a “Yes” determination at step 725 to sequentially perform the processing from step 730 to step 755 described below. Proceed to 760.

Step 730: The CPU sets the value of the active control flag Xactive to “0”.
Step 735: The CPU calculates the lean control average air-fuel ratio AveLean (= SLaf / CL) by dividing the set air-fuel ratio lean period air-fuel ratio accumulated value SLaf by the accumulated value SLaf accumulated counter CL.
Step 740: The CPU calculates the rich control average air-fuel ratio AveRich (= SRaf / CR) by dividing the set air-fuel ratio rich period air-fuel ratio accumulated value SRaf by the accumulated value SRaf accumulated counter CR.

Step 745: The CPU calculates the air-fuel ratio difference ΔAF (= AveLean−AveRich) by subtracting the average air-fuel ratio AveRich during rich control from the average air-fuel ratio AveLean during lean control.
Step 750: The CPU calculates the average value of the provisional maximum stored oxygen amount ZOSakzMAX and the provisional maximum released oxygen amount ZOSahsMAX as the provisional maximum oxygen storage amount ZCmax (= (ZOSAkzMAX + ZOSAhsMAX) / 2).

  Step 755: First, the CPU applies the air-fuel ratio difference ΔAF calculated in step 745 and the provisional maximum oxygen storage amount ZCmax calculated in step 750 to the correction coefficient table Mapkh (ΔAF, ZCmax) shown in FIG. Thus, the correction coefficient (correction amount) kh is determined. Next, the CPU obtains a value obtained by correcting the provisional maximum oxygen storage amount ZCmax by multiplying the provisional maximum oxygen storage amount ZCmax by the correction coefficient kh (that is, the corrected provisional maximum oxygen storage amount ZCmaxh). Then, the CPU acquires the corrected provisional maximum oxygen storage amount ZCmaxh as the maximum oxygen storage amount Cmax (= kh · ZCmax).

  According to the correction coefficient table Mapkh (ΔAF, ZCmax) shown in FIG. 8, the correction coefficient kh is determined to be smaller as the air-fuel ratio difference ΔAF is larger and to be smaller as the provisional maximum oxygen storage amount ZCmax is smaller. The Therefore, the provisional maximum oxygen storage amount ZCmax is corrected by the processing of step 745 so that the corrected provisional maximum oxygen storage amount ZCmaxh becomes smaller as the provisional maximum oxygen storage amount ZCmax is smaller.

  Next, the CPU proceeds to step 760 to determine whether or not the maximum oxygen storage amount Cmax is equal to or greater than the abnormality determination threshold (deterioration determination threshold) Ijoth. At this time, if the maximum oxygen storage amount Cmax is equal to or greater than the abnormality determination threshold value Ijoth, it can be determined that the catalyst 43 has not deteriorated. Therefore, in this case, the CPU makes a “Yes” determination at step 760 to proceed to step 765 to set “2” to the diagnosis flag Xijo. When the value of the diagnosis flag Xijo is “2”, it is determined whether or not the catalyst 43 has deteriorated as a result of determining whether or not the catalyst 43 has deteriorated (the catalyst 43 is normal). Show.

  On the other hand, when the maximum oxygen storage amount Cmax is smaller than the abnormality determination threshold value Ijoth, it can be determined that the catalyst 43 has deteriorated. Therefore, in this case, the CPU makes a “No” determination at step 760 to proceed to step 770 to set “1” to the diagnosis flag Xijo. At this time, the CPU may turn on a warning lamp (not shown). The value of the diagnosis flag Xijo being “1” indicates that it is determined that the catalyst 43 has deteriorated as a result of determining whether or not the catalyst 43 has deteriorated (the catalyst 43 is abnormal). Show. The value of the diagnosis flag Xijo is stored in the backup RAM.

As described above, the first estimation device is
The upstream target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean in the catalyst rich period, the upstream target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich in the catalyst lean period, and the air-fuel ratio (upstream) of the catalyst inflow gas is set. Air-fuel ratio control means (step 680 in FIG. 6, and steps 640 to 670) for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine so that the side air-fuel ratio abyfs) matches the upstream target air-fuel ratio abyfr; ,
At least the amount of excess oxygen (occluded oxygen change amount ΔOSAkz) contained in the catalyst inflow gas per predetermined time in a predetermined first period within a period in which the upstream target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean A calculation is made based on the upstream air-fuel ratio abyfs, and the amount of oxygen stored in the catalyst 43 is calculated as the provisional maximum stored oxygen amount ZOSakzMAX by integrating the calculated excess oxygen amount (step 720 in FIG. 7, ( 1) Formula and (2) Formula),
The amount of oxygen corresponding to the amount of excess unburned matter contained in the catalyst inflow gas per predetermined time in the predetermined second period within the period in which the upstream target air-fuel ratio abyfr is set to the target rich air-fuel ratio afRich (That is, the amount of change in released oxygen ΔOSAhs) is calculated based on at least the upstream air-fuel ratio abyfs, and the amount of oxygen corresponding to the amount of excess unburned matter calculated is integrated to release oxygen released from the catalyst 43. The amount is calculated as the provisional maximum released oxygen amount ZOSahsMAX (step 720 in FIG. 7, equations (3) and (4)),
Further, based on the calculated provisional maximum stored oxygen amount ZOSakzMAX and the calculated provisional maximum released oxygen amount ZOSahsMAX, the provisional maximum oxygen storage amount ZCmax that is “the provisional maximum value of the amount of oxygen that can be stored by the catalyst 43” is obtained. A provisional maximum oxygen storage amount calculating means for calculating (step 750);
The corrected provisional maximum oxygen storage amount ZCmaxh is obtained by correcting the provisional maximum oxygen storage amount ZCmax based on the provisional maximum oxygen storage amount ZCmax, and the maximum oxygen storage amount of the catalyst 43 based on the corrected provisional maximum oxygen storage amount ZCmaxh. Cmax is a means for acquiring the maximum oxygen storage amount ZCmax so that the corrected temporary maximum oxygen storage amount ZCmaxh becomes smaller as the provisional maximum oxygen storage amount ZCmax is smaller (step 755 and Table in FIG. 8)
Is provided.

  Therefore, the first estimation device can obtain the maximum oxygen storage amount Cmax that accurately represents the degree of deterioration of the catalyst regardless of the degree of deterioration of the catalyst (the magnitude of the provisional maximum oxygen storage amount ZCmax).

Further, the maximum oxygen storage amount acquisition means includes:
An average value of the upstream air-fuel ratio abyfs is calculated as a lean control average air-fuel ratio AveLean in a predetermined third period within the period in which the amount of excess oxygen is integrated (steps 720 and 735),
An average value of the upstream air-fuel ratio abyfs is calculated as a rich control average air-fuel ratio AveRich in a predetermined fourth period within the period in which the amount of oxygen corresponding to the amount of excess unburned matter is integrated (step 720). , Step 740),
The corrected provisional maximum oxygen storage amount ZCmaxh is calculated so that the corrected provisional maximum oxygen storage amount ZCmaxh decreases as the air-fuel ratio difference ΔAF, which is the difference between the lean control average air-fuel ratio AveLean and the rich control average air-fuel ratio AveRich, increases. (Step 755 and the table of FIG. 8).

  According to this, regardless of the air-fuel ratio difference ΔAF at the time of calculating the temporary maximum oxygen storage amount ZCmax that is the original data for calculating the maximum oxygen storage amount Cmax, the maximum oxygen storage amount Cmax that represents the degree of deterioration of the catalyst 43 more accurately. Can be obtained.

  Note that the first estimation device repeats “a control for alternately setting the upstream target air-fuel ratio abyfr to the target rich air-fuel ratio afRich and the target lean air-fuel ratio afLean” a plurality of times, thereby a plurality of provisional maximum stored oxygen amounts. Obtain ZOSAkzMAX and a plurality of provisional maximum released oxygen amounts ZOSahsMAX, obtain the average value of the plurality of provisional maximum stored oxygen amounts ZOSakzMAX as the final provisional maximum stored oxygen amount ZOSakzMAX, and obtain the plurality of provisional maximum The average value of the maximum released oxygen amount ZOSahsMAX may be obtained as the final provisional maximum released oxygen amount ZOSahsMAX.

Second Embodiment
Next, a maximum oxygen storage amount estimation device for a catalyst according to a second embodiment of the present invention (hereinafter simply referred to as “second estimation device”) will be described. The second estimator obtains the corrected provisional maximum stored oxygen amount ZOSakzMAXh by correcting the provisional maximum stored oxygen amount ZOSakzMAX based on the provisional maximum stored oxygen amount ZOSakzMAX, and based on the corrected provisional maximum stored oxygen amount ZOSakzMAXh. The maximum oxygen storage amount Cmax of the catalyst 43 is acquired. At this time, the second estimation device is configured so that the corrected provisional maximum stored oxygen amount ZOSakzMAXh decreases as the provisional maximum stored oxygen amount ZOSakzMAX decreases, and the difference between the average air-fuel ratio AveLean during lean control and the stoichiometric air-fuel ratio stoich is reduced. The provisional maximum stored oxygen amount ZOSakzMAX is corrected so that the corrected maximum provisional stored oxygen amount ZOSakzMAXh decreases as the size increases. Then, the second estimation device acquires the maximum oxygen storage amount Cmax based on the corrected provisional maximum stored oxygen amount ZOSakzMAXh. For example, the second estimation device employs the corrected provisional maximum stored oxygen amount ZOSakzMAXh as the maximum oxygen storage amount Cmax.

  Therefore, the CPU of the second estimation device does not calculate “temporary released oxygen amount ZOSAhs and integrated value SRaf integrated counter CR” in step 720 of FIG. Furthermore, the CPU of the second estimation device can omit the process of step 740. In addition, in step 745, the CPU of the second estimation device obtains a difference ΔLS between the average air-fuel ratio AveLean during lean control and the stoichiometric air-fuel ratio stoich, and corrects the difference ΔLS by applying it to the same table as in FIG. The coefficient kL is determined. This correction coefficient kL has the same tendency as the correction coefficient kh obtained when the air-fuel ratio difference ΔAF in FIG. 8 is replaced with the difference ΔLS and the provisional maximum oxygen storage amount ZCmax in FIG. 8 is replaced with the provisional maximum storage oxygen amount ZOSakzMAX. Is required to have Then, the second estimation device multiplies the provisional maximum stored oxygen amount ZOSakzMAX by the correction coefficient kL to obtain the corrected provisional maximum stored oxygen amount ZOSakzMAXh (thus, the maximum oxygen storage amount Cmax).

  This second estimation device can also reduce the “effect of the average air-fuel ratio AveLean during lean control and the degree of deterioration of the catalyst on the maximum oxygen storage amount Cmax”. Therefore, the degree of deterioration of the catalyst 43 can be accurately indicated. The maximum oxygen storage amount Cmax can be acquired.

<Third Embodiment>
Next, a maximum oxygen storage amount estimation device for a catalyst according to a third embodiment of the present invention (hereinafter simply referred to as “third estimation device”) will be described. The third estimating apparatus obtains the corrected provisional maximum released oxygen amount ZOSahsMAXh by correcting the provisional maximum released oxygen amount ZOSAhsMAX based on the provisional maximum released oxygen amount ZOSahsMAX, and based on the corrected provisional maximum released oxygen amount ZOSahsMAXh. The maximum oxygen storage amount Cmax of the catalyst 43 is acquired. At this time, the third estimation device makes the corrected provisional maximum released oxygen amount ZOSahsMAXh smaller as the provisional maximum released oxygen amount ZOSahsMAX is smaller, and the difference between the rich control average air-fuel ratio AveRich and the stoichiometric air-fuel ratio stoich The provisional maximum released oxygen amount ZOSahsMAX is corrected so that the corrected provisional maximum released oxygen amount ZOSahsMAXh decreases as the size increases. Then, the third estimation device acquires the maximum oxygen storage amount Cmax based on the corrected provisional maximum released oxygen amount ZOSahsMAXh. For example, the third estimation device employs the corrected provisional maximum released oxygen amount ZOSahsMAXh as the maximum oxygen storage amount Cmax.

  Therefore, the CPU of the third estimation device does not calculate “temporary stored oxygen amount ZOSakz and integrated value SLaf integrated counter CL” in step 720 of FIG. Furthermore, the CPU of the third estimation device can omit the process of step 735. In addition, in step 745, the CPU of the third estimation device obtains a difference ΔRS between the average air-fuel ratio AveRich during rich control and the stoichiometric air-fuel ratio stoich, and corrects the difference ΔRS by applying it to the same table as in FIG. The coefficient kR is determined. The correction coefficient kR has the same tendency as the correction coefficient kh obtained when the air-fuel ratio difference ΔAF in FIG. 8 is replaced with the difference ΔRS and the temporary maximum oxygen storage amount ZCmax in FIG. 8 is replaced with the temporary maximum released oxygen amount ZOSahsMAX. Is required to have Then, the third estimating apparatus obtains the corrected provisional maximum released oxygen amount ZOSahsMAXh (and hence the maximum oxygen storage amount Cmax) by multiplying the provisional maximum released oxygen amount ZOSahsMAX by the correction coefficient kR.

  This third estimation device can also reduce the “effect of the rich air-conditioning average air-fuel ratio AveRich and the degree of deterioration of the catalyst on the maximum oxygen storage amount Cmax”. Therefore, the degree of deterioration of the catalyst 43 can be accurately indicated. The maximum oxygen storage amount Cmax can be acquired.

  As described above, according to the “maximum oxygen storage amount estimation device of the catalyst” according to each embodiment of the present invention, the upstream side empty space during the period when the data for calculating the maximum oxygen storage amount is acquired. Regardless of the degree of the fuel ratio abyfs and the degree of deterioration of the catalyst 43, the maximum oxygen storage amount Cmax that accurately represents the degree of deterioration of the catalyst 43 can be acquired.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention. For example, the first period may coincide with the catalyst rich period. The second period may coincide with the catalyst lean period. The third period starts from “when the upstream air-fuel ratio abyfs reaches a threshold value that is smaller than the target lean air-fuel ratio afLean by a predetermined value after the upstream target air-fuel ratio abyfr is set to the target lean air-fuel ratio afLean”. It may be a period until the subsequent lean reversal. In the fourth period, from the time “the upstream target air-fuel ratio abyfr reaches a threshold value that is larger than the target rich air-fuel ratio afRich by a predetermined value even after the time when the target rich air-fuel ratio afRich is set”, the subsequent rich It may be a period until the reversal time.

  Further, the first estimation device simultaneously performs “correction based on the provisional maximum oxygen storage amount ZCmax and the air-fuel ratio difference ΔAF of the provisional maximum oxygen storage amount ZCmax” by using the correction coefficient kh. After the ZCmax is corrected based on the air-fuel ratio difference ΔAF, the corrected temporary maximum oxygen storage amount ZCmax may be further corrected based on the temporary maximum oxygen storage amount ZCmax before or after correction. The first estimating device corrects the temporary maximum oxygen storage amount ZCmax based on the temporary maximum oxygen storage amount ZCmax, and corrects the temporary maximum oxygen storage amount ZCmax after the correction based on the air-fuel ratio difference ΔAF. The post-provisional maximum oxygen storage amount ZCmaxh (that is, the maximum oxygen storage amount Cmax) may be obtained. Further, the first estimation device corrects a value obtained by correcting the provisional maximum oxygen storage amount ZCmax based on the provisional maximum oxygen storage amount ZCmax (that is, without performing correction based on the air-fuel ratio difference ΔAF). ZCmaxh (that is, the maximum oxygen storage amount Cmax) may be adopted.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Fuel injection valve, 41 ... Exhaust manifold, 42 ... Exhaust pipe, 43 ... Upstream catalyst (catalyst), 44 ... Downstream catalyst, 55 ... Upstream air-fuel ratio sensor, 56 ... Downstream air-fuel ratio Sensor.

Claims (6)

A maximum oxygen storage amount estimation device for a catalyst for estimating a maximum oxygen storage amount corresponding to a maximum amount of oxygen that can be stored by a catalyst disposed in an exhaust passage of an internal combustion engine,
An upstream air-fuel ratio sensor disposed upstream of the catalyst in the exhaust passage;
A downstream air-fuel ratio sensor disposed in the exhaust passage and downstream of the catalyst;
From the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, the output value of the downstream air-fuel ratio sensor corresponds to a lean air-fuel ratio greater than the stoichiometric air-fuel ratio. The target lean air-fuel ratio, which is an air-fuel ratio larger than the stoichiometric air-fuel ratio, is the upstream target air-fuel ratio that is the target value of the air-fuel ratio of the catalyst inflow gas that is the exhaust gas flowing into the catalyst in the catalyst rich period up to the point of time From the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to the lean air-fuel ratio to the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to the rich air-fuel ratio. In the catalyst lean period, the upstream target air-fuel ratio is set to a target rich air-fuel ratio that is an air-fuel ratio smaller than the stoichiometric air-fuel ratio, and the air-fuel ratio of the catalyst inflow gas is set to the upstream target air-fuel ratio. And air-fuel ratio control means for controlling the air-fuel ratio of the mixture supplied to the engine matches the labels,
At least the upstream air-fuel ratio sensor detects the amount of excess oxygen contained in the catalyst inflow gas per predetermined time in a predetermined first period within a period in which the upstream target air-fuel ratio is set to the target lean air-fuel ratio. And calculating the stored oxygen amount of the catalyst as the provisional maximum stored oxygen amount by integrating the calculated excess oxygen amount, and the upstream target air-fuel ratio is calculated as the target rich air amount. The amount of oxygen corresponding to the amount of excess unburned matter contained in the catalyst inflow gas per predetermined time in a predetermined second period within the period set to the fuel ratio is at least the output value of the upstream air-fuel ratio sensor. And calculating the amount of oxygen released from the catalyst as the provisional maximum amount of released oxygen by integrating the amount of oxygen corresponding to the amount of excess unburned matter calculated based on Based on the calculated provisional maximum stored oxygen amount and the calculated provisional maximum released oxygen amount, a provisional maximum oxygen storage amount corresponding to a provisional maximum value of the amount of oxygen that can be stored by the catalyst is calculated. A provisional maximum oxygen storage amount calculating means;
A corrected provisional maximum oxygen storage amount is obtained by correcting the provisional maximum oxygen storage amount based on the provisional maximum oxygen storage amount, and a maximum oxygen storage amount of the catalyst is determined based on the corrected provisional maximum oxygen storage amount. A means for acquiring, a maximum oxygen storage amount acquisition means for correcting the temporary maximum oxygen storage amount so that the corrected temporary maximum oxygen storage amount decreases as the temporary maximum oxygen storage amount decreases;
A device for estimating the maximum oxygen storage amount of a catalyst comprising: An apparatus for estimating the maximum oxygen storage amount of a catalyst according to claim 1,
The maximum oxygen storage amount acquisition means is
The average value of the actual upstream air-fuel ratio acquired based on the output value of the upstream-side air-fuel ratio sensor in a predetermined third period within the period in which the amount of excess oxygen is integrated is calculated as the mean air during lean control. Calculated as the fuel ratio,
The actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor in a predetermined fourth period within the period in which the amount of oxygen corresponding to the amount of excess unburned matter is integrated. Calculate the average value as the average air-fuel ratio during rich control,
The corrected provisional maximum oxygen storage amount is calculated so that the corrected provisional maximum oxygen storage amount decreases as the air-fuel ratio difference that is the difference between the lean control average air-fuel ratio and the rich control average air-fuel ratio increases. Configured as
A device for estimating the maximum oxygen storage amount of a catalyst. A maximum oxygen storage amount estimation device for a catalyst for estimating a maximum oxygen storage amount corresponding to a maximum amount of oxygen that can be stored by a catalyst disposed in an exhaust passage of an internal combustion engine,
An upstream air-fuel ratio sensor disposed upstream of the catalyst in the exhaust passage;
A downstream air-fuel ratio sensor disposed in the exhaust passage and downstream of the catalyst;
From the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, the output value of the downstream air-fuel ratio sensor corresponds to a lean air-fuel ratio greater than the stoichiometric air-fuel ratio. The target lean air-fuel ratio, which is an air-fuel ratio larger than the stoichiometric air-fuel ratio, is the upstream target air-fuel ratio that is the target value of the air-fuel ratio of the catalyst inflow gas that is the exhaust gas flowing into the catalyst in the catalyst rich period up to the point of time Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine so that the air-fuel ratio of the catalyst inflow gas matches the upstream target air-fuel ratio,
At least the upstream air-fuel ratio sensor detects the amount of excess oxygen contained in the catalyst inflow gas per predetermined time in a predetermined first period within a period in which the upstream target air-fuel ratio is set to the target lean air-fuel ratio. A temporary maximum stored oxygen amount calculating means for calculating the stored oxygen amount of the catalyst as a provisional maximum stored oxygen amount by calculating based on the output value and integrating the calculated excess oxygen amount;
The corrected provisional maximum stored oxygen amount is obtained by correcting the provisional maximum stored oxygen amount based on the provisional maximum stored oxygen amount, and the maximum oxygen storage amount of the catalyst is determined based on the corrected provisional maximum stored oxygen amount. A means for obtaining, a maximum oxygen storage amount acquisition means for correcting the provisional maximum stored oxygen amount so that the corrected provisional maximum stored oxygen amount decreases as the provisional maximum stored oxygen amount decreases;
A device for estimating the maximum oxygen storage amount of a catalyst comprising: In the apparatus for estimating the maximum oxygen storage amount of the catalyst according to claim 3,
The oxygen storage amount acquisition means includes
The average value of the actual upstream air-fuel ratio acquired based on the output value of the upstream-side air-fuel ratio sensor in a predetermined third period within the period in which the amount of excess oxygen is integrated is calculated as the mean air during lean control. Calculated as the fuel ratio,
The corrected provisional maximum stored oxygen amount is calculated so that the corrected provisional maximum stored oxygen amount becomes smaller as the difference between the average air-fuel ratio during lean control and the theoretical air-fuel ratio increases.
A device for estimating the maximum oxygen storage amount of a catalyst. A maximum oxygen storage amount estimation device for a catalyst for estimating a maximum oxygen storage amount corresponding to a maximum amount of oxygen that can be stored by a catalyst disposed in an exhaust passage of an internal combustion engine,
An upstream air-fuel ratio sensor disposed upstream of the catalyst in the exhaust passage;
A downstream air-fuel ratio sensor disposed in the exhaust passage and downstream of the catalyst;
The output value of the downstream air-fuel ratio sensor corresponds to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio from the time when the output value of the downstream air-fuel ratio sensor becomes a value corresponding to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio. The target rich air-fuel ratio, which is an air-fuel ratio smaller than the stoichiometric air-fuel ratio, is the upstream target air-fuel ratio that is the target value of the air-fuel ratio of the catalyst inflow gas that is the exhaust gas flowing into the catalyst in the catalyst lean period until the point of time Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine so that the air-fuel ratio of the catalyst inflow gas matches the upstream target air-fuel ratio,
An amount of oxygen corresponding to the amount of excess unburned matter contained in the catalyst inflow gas per predetermined time in a predetermined second period within a period in which the upstream target air-fuel ratio is set to the target rich air-fuel ratio Is calculated based on at least the output value of the upstream air-fuel ratio sensor, and the amount of oxygen corresponding to the amount of excess unburned matter calculated is integrated to calculate the amount of oxygen released from the catalyst as the provisional maximum released oxygen. A provisional maximum released oxygen amount calculating means for calculating the amount;
A corrected provisional maximum released oxygen amount is obtained by correcting the provisional maximum released oxygen amount based on the provisional maximum released oxygen amount, and a maximum oxygen storage amount of the catalyst is obtained based on the corrected provisional maximum released oxygen amount. A means for obtaining, a maximum oxygen storage amount obtaining means for correcting the provisional maximum released oxygen amount so that the corrected provisional maximum released oxygen amount decreases as the provisional maximum released oxygen amount decreases;
A device for estimating the maximum oxygen storage amount of a catalyst comprising: In the catalyst maximum oxygen storage amount estimation apparatus according to claim 5,
The oxygen storage amount acquisition means includes
The actual upstream air-fuel ratio acquired based on the output value of the upstream air-fuel ratio sensor in a predetermined fourth period within the period in which the amount of oxygen corresponding to the amount of excess unburned matter is integrated. Calculate the average value as the average air-fuel ratio during rich control,
Configured to calculate the corrected provisional maximum released oxygen amount so that the corrected provisional maximum released oxygen amount decreases as the difference between the rich control average air-fuel ratio and the theoretical air-fuel ratio increases.
A device for estimating the maximum oxygen storage amount of a catalyst.

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