JP2012041850A - Control apparatus for purifying internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control apparatus for purifying an internal combustion engine that can properly eliminate deterioration of a catalyst by properly removing a sulfur component adsorbed or occluded in the catalyst.SOLUTION: When a degree of deterioration of the catalyst is a predetermined threshold or more, if a downstream oxygen concentration is the same as a reference oxygen concentration, which is an oxygen concentration of a gas generated when an air and a fuel are combusted in a theoretical air fuel ratio, or an oxygen concentration closer to a lean side than the reference oxygen concentration, a rich operation that makes an upstream oxygen concentration of the catalyst the oxygen concentration the oxygen concentration closer to the rich side than the reference oxygen concentration is operated until the downstream oxygen concentration becomes the oxygen concentration closer to the rich side than the reference oxygen concentration and subsequently, the lean operation that makes the upstream oxygen concentration the oxygen concentration closer to the lean side than the reference oxygen concentration is operated. A control apparatus operates the lean operation if the downstream oxygen concentration is closer to the oxygen concentration of the rich side than the reference oxygen concentration.

Description

  The present invention relates to a control device for an internal combustion engine provided with a catalyst for purifying gas (exhaust gas) discharged from a combustion chamber of the internal combustion engine.

  High temperature exhaust gas containing various components is introduced into a catalyst applied to an internal combustion engine. Therefore, when the catalyst is used for a long period of time, the exhaust gas purification performance of the catalyst may deteriorate (hereinafter, the deterioration of the exhaust gas purification performance of the catalyst is also referred to as “catalyst deterioration”).

  Therefore, one of the conventional control devices for an internal combustion engine (hereinafter referred to as “conventional device”) is used when a predetermined operating condition including that the temperature of the catalyst is equal to or lower than a predetermined threshold is not satisfied. The fuel cut operation is prohibited. Thereby, the conventional apparatus avoids that a large amount of oxygen is introduced into a high temperature catalyst, and suppresses that a catalyst deteriorates (for example, refer patent document 1). Thus, conventionally, it is desired to suppress deterioration of the catalyst.

JP 2006-112289 A

  Examples of the catalyst applied to the internal combustion engine include a three-way catalyst and a NOx storage reduction catalyst. In these catalysts, the temperature of the catalyst is equal to or higher than a predetermined activation temperature, and the oxygen concentration of the exhaust gas introduced into the catalyst is a predetermined oxygen concentration (the oxygen concentration of the exhaust gas generated when the stoichiometric air-fuel mixture burns) In this case, the oxidation reaction of unburned substances (HC and the like) contained in the exhaust gas and the reduction reaction of nitrogen oxides (NOx) can be promoted, and these can be simultaneously purified at a high purification rate. Hereinafter, for convenience, the three-way catalyst, the NOx occlusion reduction catalyst, and the like are simply referred to as “catalyst”.

  The catalyst generally has a support (such as Al2O3) containing an oxygen storage material (such as CeO2-ZrO2) and a catalyst component (noble metal such as Pt and Rh) supported on the support. At the active point (catalytic active point) constituted by the catalyst component, the oxidation-reduction reaction (that is, purification of exhaust gas) between the unburned matter and the nitrogen oxide is promoted. On the other hand, the oxygen storage material occludes excess oxygen contained in the exhaust gas when the oxygen concentration of the exhaust gas is higher than the predetermined oxygen concentration (that is, the oxygen concentration on the lean side). When the oxygen concentration is lower than the predetermined oxygen concentration (that is, when the oxygen concentration is on the rich side), the stored oxygen is released for the oxidation reaction. In this way, the oxygen storage material assists in purification of exhaust gas by adjusting the oxygen concentration in the catalyst component.

  However, the oxygen storage material may store not only oxygen but also sulfur components (SOx and the like) contained in the exhaust gas. Furthermore, sulfur components (S and the like) may be adsorbed on the catalyst component due to various causes. When a sulfur component is stored in the oxygen storage material, oxygen that should be stored by the sulfur component is prevented from being stored, so that the amount of oxygen that can be stored by the catalyst is reduced. Further, when the sulfur component is adsorbed on the catalyst component, the catalyst active point is covered with the sulfur component, so that the number of catalyst active points capable of promoting the purification of exhaust gas is reduced. As a result, the exhaust gas purification performance of the catalyst decreases. Thus, there exists a problem that a catalyst may deteriorate by a sulfur component being adsorbed / occluded in the catalyst.

  In view of the above problems, an object of the present invention is to provide a control device for an internal combustion engine that can appropriately eliminate the deterioration of the catalyst by appropriately removing the sulfur component adsorbed and stored in the catalyst. .

A control device according to the present invention for solving the above-described problems is as follows.
The present invention is applied to an internal combustion engine including a catalyst and a downstream oxygen concentration acquisition unit that acquires the oxygen concentration of gas discharged from the catalyst.

  More specifically, the catalyst is a catalyst through which gas (exhaust gas) discharged from the combustion chamber of the internal combustion engine passes, and purifies the gas introduced from the upstream side of the catalyst and removes the gas. It discharges from the downstream side of the catalyst. Furthermore, the catalyst has a catalyst component and an oxygen storage material.

  The catalyst is not particularly limited as long as it is a catalyst capable of purifying exhaust gas as described above. As said catalyst, the well-known three-way catalyst which has a catalyst component and the support | carrier containing an oxygen storage substance can be employ | adopted, for example. Furthermore, as the catalyst, for example, a known NOx occlusion reduction catalyst having a catalyst component and a carrier containing an oxygen occlusion substance and a NOx occlusion substance can be employed. The catalyst can be provided, for example, in an exhaust passage of an internal combustion engine.

  The catalyst component is not particularly limited as long as it is a component capable of promoting purification of exhaust gas (accelerating the reaction rate of the oxidation-reduction reaction between unburned matter and nitrogen oxides). As the catalyst component, for example, a noble metal such as platinum (Pt) and rhodium (Rh) may be employed. Furthermore, the oxygen storage material is not particularly limited as long as it is a material capable of storing oxygen. As the oxygen storage material, for example, cerium oxide (ceria, CeO2), zirconium oxide (ZrO2), and the like can be employed.

  The above-mentioned “purifying gas” means removing at least a part of the purification target substance such as unburned matter and nitrogen oxide contained in the gas from the gas. It does not mean removing from the gas.

Further, the downstream oxygen concentration acquisition means includes:
The “downstream oxygen concentration”, which is the oxygen concentration of the gas discharged from the catalyst, is acquired.

  The method for obtaining the “downstream oxygen concentration” is not particularly limited. The downstream oxygen concentration can be acquired by, for example, a sensor that can measure the actual value of the oxygen concentration of the gas. Further, the downstream oxygen concentration can be acquired by an estimation unit that can estimate an estimated value of the oxygen concentration of the gas based on the operating state of the internal combustion engine, for example.

  The control device of the present invention applied to the internal combustion engine having the above-described configuration includes a catalyst deterioration degree acquisition unit and a catalyst deterioration degree reduction unit.

  More specifically, the catalyst deterioration degree acquisition means acquires the deterioration degree of the catalyst.

  The “degradation degree of the catalyst” may be an index that can represent the degree of deterioration of the exhaust gas purification performance based on the exhaust gas purification performance that the catalyst originally has (for example, a new (unused) catalyst), There is no particular limitation. The degree of deterioration of the catalyst is, for example, by comparing the maximum amount of oxygen that can be stored by a new catalyst with the maximum amount of oxygen that can be stored by the catalyst at the time when the degree of deterioration is acquired. Can be acquired. Furthermore, the deterioration degree of the catalyst can be acquired based on the amount of unnecessary components (for example, sulfur component) stored in the catalyst at the time of acquiring the deterioration degree, for example. In the present invention, the value of the degree of deterioration indicates that the greater the value, the greater the degree of deterioration of the catalyst.

  As one of the causes of catalyst deterioration, as described above, the sulfur component (SOx, etc.) contained in the exhaust gas is occluded by the oxygen storage material, and the sulfur component (S, etc.) is adsorbed by the catalyst component. .

  Therefore, the catalyst deterioration degree reducing means operates as shown in (A) below or as shown in (B) below depending on the downstream oxygen concentration when the deterioration degree of the catalyst is equal to or greater than a predetermined threshold. Is supposed to do. By these operations, the sulfur component adsorbed and stored in the catalyst is removed, and the degree of deterioration of the catalyst is reduced.

(A) The downstream oxygen concentration is “same as a reference oxygen concentration that is an oxygen concentration of a gas generated when air and fuel burn at a stoichiometric air-fuel ratio” or “an oxygen concentration leaner than the reference oxygen concentration” "Rich operation" in which the upstream oxygen concentration, which is the oxygen concentration of the gas introduced into the catalyst, is set to be richer than the reference oxygen concentration, and the upstream oxygen concentration is the reference oxygen concentration. “Lean operation” in which the oxygen concentration is leaner than the oxygen concentration.
This lean operation is performed after the above operation is performed until the downstream oxygen concentration becomes richer than the reference oxygen concentration.
(B) When the downstream oxygen concentration is “an oxygen concentration richer than the reference oxygen concentration”, the lean operation is performed.

  The “oxygen concentration leaner than the reference oxygen concentration” means an oxygen concentration higher than the reference oxygen concentration. On the other hand, the “oxygen concentration richer than the reference oxygen concentration” means an oxygen concentration lower than the reference oxygen concentration. Hereinafter, the oxygen concentration leaner than the reference oxygen concentration is also simply referred to as “lean oxygen concentration”, and the oxygen concentration richer than the reference oxygen concentration is also simply referred to as “rich oxygen concentration”.

  The “rich operation” is not particularly limited as long as the upstream oxygen concentration is an operation having a rich oxygen concentration. As the rich operation, for example, an operation in which the air-fuel ratio of the air-fuel mixture of the internal combustion engine is set to an air-fuel ratio richer than the stoichiometric air-fuel ratio (so-called fuel increase operation) can be employed. Further, as the rich operation, for example, an operation in which fuel is injected again into the gas discharged from the combustion chamber (so-called exhaust addition) can be employed. On the other hand, the “lean operation” is not particularly limited as long as it is an operation in which the upstream oxygen concentration is the lean oxygen concentration. As the lean operation, for example, an operation in which fuel is not supplied to the combustion chamber (so-called fuel cut operation) can be employed.

The reason why the deterioration degree of the catalyst is reduced by the operations shown in the above (A) and (B) will be described below.
As described above, when the sulfur component is adsorbed and occluded in the catalyst, the catalyst deteriorates. According to various considerations and experiments by the inventors, it has been confirmed that there is a close relationship between “the behavior of the sulfur component adsorbed and occluded by the catalyst” and “the oxygen concentration of the exhaust gas”.

  Specifically, first, the sulfur component stored in the oxygen storage material moves toward the catalyst component when the oxygen concentration of the exhaust gas is the “rich side oxygen concentration”, and the oxygen concentration of the exhaust gas becomes “lean”. It was confirmed that when the “side oxygen concentration” was reached, the catalyst component was released into the exhaust gas. That is, it was confirmed that the sulfur component stored in the oxygen storage material is not released directly into the exhaust gas from the oxygen storage material, but is released into the exhaust gas via the catalyst component. On the other hand, it was confirmed that the sulfur component adsorbed on the catalyst component is released from the catalyst component into the exhaust gas when the oxygen concentration of the exhaust gas is the above-described “lean side oxygen concentration”.

  Therefore, the catalyst deterioration degree reducing means of the present invention is such that when the sulfur component adsorbed and stored in the catalyst is removed from the catalyst, the oxygen concentration (downstream oxygen concentration) of the gas discharged from the catalyst is “lean side oxygen concentration”. First, a rich operation is performed in which the oxygen concentration (upstream oxygen concentration) of the gas introduced into the catalyst is set to the “rich oxygen concentration”. The catalyst deterioration degree reducing means continues this rich operation until the downstream oxygen concentration becomes the “rich oxygen concentration” ((A) above). Thereby, in the whole catalyst, the sulfur component stored in the oxygen storage material is moved toward the catalyst component.

  Next, the catalyst deterioration degree reducing means performs a lean operation in which the upstream oxygen concentration is “lean oxygen concentration” (above (A)). Thereby, both the sulfur component moved toward the catalyst component by the rich operation and the sulfur component adsorbed on the catalyst component are released from the catalyst component into the exhaust gas in the entire catalyst.

  On the other hand, when removing the sulfur component adsorbed and occluded in the catalyst from the catalyst, if the downstream oxygen concentration is the “rich oxygen concentration”, the sulfur component occluded in the oxygen occlusion material is already present in the catalyst. It is thought that it is moving toward the ingredient. Therefore, in this case, the catalyst deterioration degree reducing means performs the lean operation without performing the rich operation (above (B)). As a result, as described above, the sulfur component is released from the catalyst component into the exhaust gas in the entire catalyst.

  Thus, the control device of the present invention can remove the sulfur component adsorbed and occluded by the catalyst in the entire catalyst. As a result, the control device of the present invention can appropriately recover the exhaust gas purification performance of the catalyst (that is, appropriately eliminate the deterioration of the catalyst).

  As described above, the control device of the present invention pays attention to the relationship between “the behavior of the sulfur component adsorbed and occluded by the catalyst” and “the oxygen concentration of the exhaust gas”, and the sulfur component adsorbed and occluded by the catalyst is catalyzed. Is supposed to be removed from. According to various further considerations and experiments by the inventors, it was confirmed that the behavior of the sulfur component adsorbed and occluded by the catalyst is influenced not only by the oxygen concentration of the exhaust gas but also by the “catalyst temperature”.

  Specifically, when the temperature of the catalyst is “in a specific temperature range (for example, not less than the first temperature and not more than the second temperature)”, when the oxygen concentration of the exhaust gas is the “rich oxygen concentration”, It was confirmed that the sulfur component occluded in the oxygen occlusion material efficiently migrates toward the catalyst component. Further, when the catalyst temperature is “above a specific temperature within the above specific temperature range (for example, over a third temperature between the first temperature and the second temperature)”, the oxygen concentration of the exhaust gas is “lean”. In the case of “side oxygen concentration”, it was confirmed that the sulfur component present on the catalyst component was efficiently released into the exhaust gas.

Therefore, as one aspect of the control device of the present invention,
When the catalyst is a catalyst having the characteristics shown in the following (C-1) and (C-2),
The catalyst deterioration degree reducing means is:
When the temperature of the catalyst is “below the first temperature below and lower than the third temperature below”, the rich operation may be “not performed”.

(C-1) If the upstream oxygen concentration is “richer” than the reference oxygen concentration when the temperature of the catalyst is “first temperature or more and second temperature or less”, the oxygen storage The sulfur component occluded by the substance moves toward the catalyst component.
(C-2) When the temperature of the catalyst is “the third temperature or higher” between the first temperature and the second temperature, the upstream oxygen concentration is “lean side” oxygen than the reference oxygen concentration. In the case of a concentration, the sulfur component present on the catalyst component is released into the gas.

  The first temperature, the second temperature, and the third temperature are values that are determined according to the substance that constitutes the catalyst, and can be obtained in advance through experiments or the like.

  In addition, the characteristic of (C-1) is when the temperature of the catalyst is included in the temperature range (first temperature or higher and lower than or equal to the second temperature) indicated by the characteristic, and the temperature of the catalyst is not included in the same temperature range. This means that the sulfur component stored in the oxygen storage material is moved toward the catalyst component more efficiently. That is, the characteristic (C-1) does not mean that the sulfur component stored in the oxygen storage material does not move toward the catalyst component at all when the temperature of the catalyst is not included in the same temperature range. .

  Similarly to the above, the characteristic (C-2) is more efficient when the temperature of the catalyst is included in the temperature range (the third temperature or higher) indicated by the same characteristic than when the temperature of the catalyst is not included in the same temperature range. It means that the sulfur component that is well present on the catalyst component is released into the exhaust gas. That is, the above characteristic (C-2) does not mean that the sulfur component present on the catalyst component is not released into the exhaust gas when the temperature of the catalyst is not included in the same temperature range.

  As described above, the catalyst deterioration degree reducing means of the present invention moves the sulfur component stored in the oxygen storage material toward the catalyst component when removing the sulfur component absorbed and stored in the catalyst from the catalyst. Later, the sulfur component on the catalyst component is released into the exhaust gas (see (A2) and (B) above). However, when the catalyst has the above characteristics (C-1) and (C-2), the temperature range of the catalyst in which the sulfur component stored in the oxygen storage material is efficiently transferred to the catalyst component (the first temperature or higher 2 temperature or lower) and the temperature range (third temperature or higher) of the catalyst in which the sulfur component present on the catalyst component is efficiently released into the exhaust gas may not match.

  Therefore, when the temperature of the catalyst is “above the first temperature and lower than the third temperature”, even if the sulfur component stored in the oxygen storage material by the rich operation is moved toward the catalyst component, the lean operation The sulfur component present on the catalyst component is not efficiently released into the exhaust gas (see FIG. 5).

  Therefore, the catalyst deterioration degree reducing means of this aspect does not perform the rich operation when the temperature of the catalyst is equal to or higher than the first temperature and lower than the third temperature. In other words, the catalyst deterioration degree reducing means of the present invention can efficiently remove the sulfur component adsorbed and occluded by the catalyst (that is, the catalyst temperature is “the first temperature or higher and the third temperature). When it is not included in the “lower temperature range”, an operation (see (A) and (B) above) for removing the sulfur component adsorbed and occluded by the catalyst is performed. Thereby, the sulfur component adsorbed and occluded by the catalyst can be efficiently removed.

Furthermore, as another aspect of the control device of the present invention,
The catalyst deterioration degree reducing means may be configured to adjust the “upstream oxygen concentration when performing the rich operation” according to the degree of deterioration of the catalyst.

For example, the catalyst deterioration degree reducing means is:
When the rich operation is performed when the deterioration level is the “first value”, the “first upstream oxygen concentration”, which is the upstream oxygen concentration when the rich operation is performed, is less than the first value. “The same as the second upstream oxygen concentration” or “richer oxygen concentration than the second upstream oxygen concentration” which is the upstream oxygen concentration when the rich operation is performed when the value is “small second value” Can be configured.

  Thus, by setting the “upstream oxygen concentration at the time of rich operation” to an oxygen concentration that moves away from the reference oxygen concentration to the rich side as the degree of deterioration increases (that is, the first upstream oxygen concentration is set to the second oxygen concentration). By making the oxygen concentration richer than the upstream oxygen concentration), the sulfur component adsorbed and occluded by the catalyst can be more efficiently removed. On the other hand, by not changing the upstream oxygen concentration during the rich operation regardless of the degree of deterioration (that is, by making the first upstream oxygen concentration the same as the second upstream oxygen concentration). Further, the treatment for removing the sulfur component adsorbed and occluded by the catalyst can be performed more simply.

Furthermore, as still another aspect of the control device of the present invention,
The catalyst deterioration degree reducing means may be configured to adjust the “upstream oxygen concentration when performing the lean operation” in accordance with the degree of deterioration of the catalyst.

For example, the catalyst deterioration degree reducing means is:
The “third upstream oxygen concentration”, which is the upstream oxygen concentration when the lean operation is performed when the deterioration level is the “third value”, is greater than the third value. “The same as the fourth upstream oxygen concentration” or “the oxygen concentration on the lean side with respect to the fourth upstream oxygen concentration” which is the upstream oxygen concentration when the lean operation is performed when the value is “small fourth value” Can be configured.

  In this way, by setting the “upstream oxygen concentration when performing lean operation” to an oxygen concentration that deviates from the reference oxygen concentration to the lean side as the degree of deterioration increases (that is, the third upstream oxygen concentration is the fourth oxygen concentration). By making the oxygen concentration leaner than the upstream oxygen concentration), the sulfur component adsorbed and occluded by the catalyst can be more efficiently removed. On the other hand, by not changing the upstream oxygen concentration during lean operation regardless of the degree of deterioration (that is, by making the third upstream oxygen concentration the same as the fourth upstream oxygen concentration) In addition, it is possible to easily perform the treatment for removing the sulfur component adsorbed and occluded by the catalyst.

As described above, in the control device of the present invention, the method for obtaining the degree of deterioration of the catalyst is not particularly limited. For example, as still another aspect of the control device of the present invention,
The catalyst deterioration degree acquisition means includes
The deterioration degree may be acquired based on a maximum amount of oxygen that can be stored in the catalyst.

  As described above, when the sulfur component is stored in the oxygen storage material of the catalyst, the “maximum amount of oxygen that can be stored by the catalyst” decreases. Therefore, as described above, the degree of deterioration of the catalyst can be acquired based on this “maximum amount”.

1 is a schematic view of an internal combustion engine to which a control device according to a first embodiment of the present invention is applied. 2 is a graph showing a relationship between an output value of an upstream oxygen concentration sensor shown in FIG. 1 and an air-fuel ratio. 2 is a graph showing a relationship between an output value of a downstream oxygen concentration sensor shown in FIG. 1 and an air-fuel ratio. 6 is a time chart showing the relationship between the catalyst upstream air-fuel ratio, the output value of the downstream oxygen concentration sensor, and the oxygen storage amount when obtaining the maximum value of the oxygen storage amount of the catalyst. It is the schematic which shows the relationship between the temperature of a catalyst, the air fuel ratio (oxygen concentration) of waste gas, and the main behavior of the sulfur component adsorbed / occluded by the catalyst. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 2nd Embodiment of this invention performs.

  Embodiments of an internal combustion engine control apparatus according to the present invention will be described below with reference to the drawings.

(First embodiment)
<Outline of device>
FIG. 1 shows a schematic configuration of a system in which a control device (hereinafter also referred to as “first device”) according to a first embodiment of the present invention is applied to an internal combustion engine 10. The internal combustion engine 10 is a four-cycle spark ignition multi-cylinder (four-cylinder) engine. FIG. 1 shows only a cross section of one of a plurality of cylinders. The other cylinders have the same configuration as this one cylinder. Hereinafter, for convenience, the “internal combustion engine 10” is also simply referred to as “engine 10”.

  The engine 10 includes a cylinder block portion 20, a cylinder head portion 30 fixed to the upper portion of the cylinder block portion 20, an intake system 40 for introducing an air / fuel mixture into the cylinder block portion 20, and a cylinder block. An exhaust system 50 for releasing gas (exhaust gas) discharged from the section 20 to the outside of the engine 10 is provided.

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 through the connecting rod 23, whereby the crankshaft 24 rotates. The inner wall surface of the cylinder 21, the upper surface of the piston 22, and the lower surface of the cylinder head portion 30 define a combustion chamber 25.

  The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake cam shaft that drives the intake valve 32, and a phase angle and lift amount of the intake cam shaft are continuously provided. Variable intake timing device 33 to be changed, actuator 33a of variable intake timing device 33, injector 34 for injecting fuel into intake port 31, exhaust port 35 communicating with combustion chamber 25, and exhaust valve 36 for opening and closing exhaust port 35 And an exhaust camshaft 37 for driving the exhaust valve 36, an ignition plug 38, and an igniter 39 including an ignition coil for generating a high voltage to be applied to the ignition plug 38.

  The engine 10 may be configured to include an in-cylinder injector (not shown) that injects fuel directly into the combustion chamber 25 instead of the injector 34 or separately from the injector 34.

  The intake system 40 includes an intake manifold 41 that communicates with each cylinder via an intake port 31, an intake pipe 42 that is connected to a collective portion on the upstream side of the intake manifold 41, and an air cleaner that is provided at the end of the intake pipe 42. 43, a throttle valve (intake throttle valve) 44 that can change the opening area (opening cross-sectional area) of the intake pipe 42, and a throttle valve actuator 44a that rotates the throttle valve 44 in response to an instruction signal. ing. The intake port 31, the intake manifold 41, and the intake pipe 42 constitute an intake passage.

  The exhaust system 50 includes an exhaust manifold 51 connected to each cylinder via an exhaust port 35, an exhaust pipe 52 connected to a downstream portion of the exhaust manifold 51, and exhaust gas purification provided in the exhaust pipe 52. Catalyst 53. The exhaust port 35, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage. Hereinafter, the exhaust gas-purifying catalyst 53 is also simply referred to as “catalyst 53”.

  The catalyst 53 is a three-way catalyst composed of ceramics such as alumina as a support containing ceria / zirconia cocatalyst (CeO2-ZrO2) as an oxygen storage material, and noble metals such as platinum and rhodium as catalyst components. is there. In this catalyst 53, the temperature of the catalyst is equal to or higher than its activation temperature, and the oxygen concentration of the exhaust gas introduced into the catalyst 53 is “the oxygen concentration of the exhaust gas generated when the stoichiometric air-fuel mixture is burned”. The redox reaction between unburned substances (HC, etc.) and nitrogen oxides (NOx) in the exhaust gas can be promoted, and these can be simultaneously purified with a high purification rate.

  An accelerator pedal 61 for inputting an acceleration request and a required torque to the engine 10 is provided outside the engine 10. The accelerator pedal 61 is operated by an operator of the engine 10.

Further, the engine 10 includes a plurality of sensors.
Specifically, the first device includes an intake air amount sensor 71, a throttle valve opening sensor 72, a cam position sensor 73, a crank position sensor 74, a water temperature sensor 75, an upstream oxygen concentration sensor 76, and a downstream oxygen concentration sensor. 77, and an accelerator opening sensor 78.

  The intake air amount sensor 71 is provided in the intake passage (intake pipe 42). The intake air amount sensor 71 outputs a signal corresponding to an intake air amount that is a mass flow rate of air flowing through the intake pipe 42 (that is, a mass of air sucked into the engine 10). Based on this signal, a measured value of the intake air amount Ga is acquired.

  The throttle valve opening sensor 72 is provided in the vicinity of the throttle valve 44. The throttle valve opening sensor 72 outputs a signal corresponding to the opening of the throttle valve 44. Based on this signal, the throttle valve opening degree TA is acquired.

  The cam position sensor 73 is provided in the vicinity of the variable intake timing device 33. The cam position sensor 73 is configured to output a signal having one pulse every time the intake camshaft rotates 90 ° (that is, every time the crankshaft 24 rotates 180 °). Based on this signal, a measured value of the rotational position (cam position) of the intake camshaft is obtained.

  The crank position sensor 74 is provided in the vicinity of the crankshaft 24. The crank position sensor 74 outputs a signal having a narrow pulse every time the crankshaft 24 rotates 10 °, and outputs a signal having a wide pulse every time the crankshaft 24 rotates 360 °. It has become. Based on these signals, a measured value of the number of revolutions of the crankshaft 24 per unit time (hereinafter, simply referred to as “engine speed NE”) is acquired.

  The water temperature sensor 75 is provided in the cooling water passage provided in the cylinder 21. The water temperature sensor 75 outputs a signal corresponding to the temperature of the cooling water. Based on this signal, the measured value of the coolant temperature THW is obtained.

  The upstream oxygen concentration sensor 76 is provided in the exhaust passage on the upstream side of the catalyst 53 (in the vicinity of the collecting portion of the exhaust manifold 51 or on the downstream side of the collecting portion). The upstream oxygen concentration sensor 76 is a known limiting current type oxygen concentration sensor. The upstream oxygen concentration sensor 76 outputs a signal corresponding to the oxygen concentration of the exhaust gas introduced into the catalyst 53.

  Hereinafter, the oxygen concentration of the exhaust gas is referred to as “the exhaust gas air-fuel ratio” and the exhaust gas oxygen concentration is the oxygen concentration of the exhaust gas generated when the mixture of the stoichiometric air-fuel ratio burns. It is also called “Yes”. Further, hereinafter, the air-fuel ratio richer than the stoichiometric air-fuel ratio is also referred to as “rich air-fuel ratio”, and the air-fuel ratio leaner than the stoichiometric air-fuel ratio is also referred to as “lean air-fuel ratio”.

  More specifically, the air-fuel ratio of the exhaust gas is “rich air-fuel ratio” means that the exhaust gas contains “a smaller amount of oxygen than is necessary to oxidize all unburned substances contained in the exhaust gas”. It represents the state that has been. On the other hand, the air-fuel ratio of the exhaust gas is “lean air-fuel ratio” means that the exhaust gas contains “a larger amount of oxygen than is necessary to oxidize all unburned substances contained in the exhaust gas”. To express. Further, the fact that the air-fuel ratio of the exhaust gas is “theoretical air-fuel ratio” represents a state where the exhaust gas contains “a quantity of oxygen necessary for oxidizing all unburned substances contained in the exhaust gas”.

  As shown in FIG. 2, the upstream oxygen concentration sensor 76 outputs Vabyfs that is a voltage corresponding to the air-fuel ratio of the gas to be measured. The output value Vabyfs matches the value Vstoich when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio. Further, the output value Vabyfs increases as the air-fuel ratio of the exhaust gas increases (that is, as the air-fuel ratio becomes a leaner air-fuel ratio from the stoichiometric air-fuel ratio). Based on this output value Vabyfs, the air-fuel ratio of the exhaust gas introduced into the catalyst 53 is acquired. Hereinafter, the air-fuel ratio of the exhaust gas introduced into the catalyst 53 is also referred to as “catalyst upstream air-fuel ratio abyfs”. Further, hereinafter, the relationship between the output value Vabyfs and the air-fuel ratio A / F shown in FIG. 2 is also referred to as “table Mapabyfs”.

  Referring to FIG. 1 again, the downstream oxygen concentration sensor 77 is provided in the exhaust passage on the downstream side of the catalyst 53. The downstream oxygen concentration sensor 77 is a known electromotive force type (concentration cell type) oxygen concentration sensor. The downstream oxygen concentration sensor 77 outputs a signal corresponding to the oxygen concentration (air-fuel ratio) of the exhaust gas discharged from the catalyst 53.

  As shown in FIG. 3, the downstream oxygen concentration sensor 77 outputs Voxs that is a voltage corresponding to the air-fuel ratio of the gas to be measured. The output value Voxs has a maximum value (for example, about 0.9 V) when the air-fuel ratio of the exhaust gas is a rich air-fuel ratio, and a minimum value (for example, about 0.1 V when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio. When the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio, the voltage is approximately halfway between the maximum value and the minimum value (for example, about 0.5 V). Further, the output value Voxs changes suddenly from the maximum value to the minimum value when the exhaust gas air-fuel ratio changes from the rich air-fuel ratio to the lean air-fuel ratio, and when the exhaust gas air-fuel ratio changes from the lean air-fuel ratio to the rich air-fuel ratio. It changes suddenly from the minimum value to the maximum value. Based on this output value Voxs, the air-fuel ratio of the exhaust gas discharged from the catalyst 53 is acquired. Hereinafter, the air-fuel ratio of the exhaust gas discharged from the catalyst 53 is also referred to as “catalyst downstream air-fuel ratio oxs”.

  Referring again to FIG. 1, the accelerator opening sensor 78 is provided on the accelerator pedal 61. The accelerator opening sensor 78 outputs a signal corresponding to the opening of the accelerator pedal 61. Based on this signal, the accelerator pedal opening degree Accp is acquired.

Further, the engine 10 includes an electronic control device 80.
The electronic control unit 80 includes a CPU 81, a ROM 82 in which programs executed by the CPU 81, tables (maps), constants, and the like are stored in advance, a RAM 83 in which the CPU 81 temporarily stores data as necessary, and data in a state where power is turned on. And a backup RAM 84 that holds the stored data while the power is shut off, and an interface 85 including an AD converter. The CPU 81, ROM 82, RAM 83, RAM 84, and interface 85 are connected to each other via a bus.

  The interface 85 is connected to each of the above sensors, and transmits signals output from the sensors to the CPU 81. Further, the interface 85 is connected to the actuator 33a, the injector 34, the igniter 39, the throttle valve actuator 44a and the like of the variable intake timing device 33, and sends an instruction signal to them in response to an instruction from the CPU 81.

<Outline of device operation>
Hereinafter, an outline of the operation of the first device applied to the engine 10 will be described.
When the "normal operation" is performed in which the first device matches the stoichiometric air-fuel ratio stoich with the air-fuel ratio of the exhaust gas introduced into the catalyst 53 (the catalyst upstream air-fuel ratio abyfs), the "degradation degree Ke" of the catalyst 53 To get. When the deterioration degree Ke at a predetermined time is equal to or greater than the threshold deterioration degree Keth, the first device responds to “the exhaust gas air-fuel ratio (catalyst downstream air-fuel ratio oxs)” discharged from the catalyst 53 at that time. Then, perform “operation to reduce the degree of degradation Ke”.

  Specifically, when the catalyst downstream air-fuel ratio oxs at the predetermined time is “theoretical air-fuel ratio stoich” or “lean air-fuel ratio lean”, the first device converts the catalyst upstream air-fuel ratio abyfs to the rich air-fuel ratio. After performing “rich operation” with rich until the downstream air-fuel ratio oxs of the catalyst reaches the rich air-fuel ratio rich, “lean operation” with the air-fuel ratio abyfs upstream of the catalyst as the lean air-fuel ratio lean is performed. On the other hand, if the catalyst downstream air-fuel ratio oxs at the predetermined time point is the rich air-fuel ratio rich, the first device performs the lean operation without performing the rich operation.

  Furthermore, the first device stops the lean operation when the integrated amount Galsum of the intake air amount Ga in the period during which the lean operation is performed becomes equal to or greater than the threshold integrated amount Galsumth. Thereafter, the first device resumes normal operation. The above is the outline of the operation of the first device.

<Acquisition method of catalyst degradation degree>
The first device acquires the maximum oxygen storage amount Cmax of the catalyst 53, and acquires the deterioration degree Ke of the catalyst based on the maximum oxygen storage amount Cmax. Hereinafter, acquisition of the maximum oxygen storage amount Cmax and acquisition of the deterioration degree Ke will be described in more detail.

1. Acquisition of Maximum Oxygen Storage Amount Cmax The first device performs control for acquiring the deterioration degree Ke of the catalyst 53 (hereinafter referred to as "the deterioration degree acquisition condition" described later) when a normal operation is performed. Also referred to as “deterioration acquisition control”).

The “deterioration degree acquisition control” will be described with reference to the time chart shown in FIG.
In the period before time t1 in this time chart, “normal operation” is performed. That is, during this period, the catalyst upstream air-fuel ratio abyfs is controlled to coincide with the stoichiometric air-fuel ratio stoich. In the example shown in FIG. 4, for the sake of convenience, the output value Voxs of the downstream oxygen concentration sensor 77 is a value indicating the rich air-fuel ratio rich, and the oxygen storage amount OSA of the catalyst 53 is a predetermined value near zero in this period. It is assumed that there is. The predetermined value is a value determined according to the operation performed before time t1.

  When the “deterioration degree acquisition condition” is satisfied at time t1, “deterioration degree acquisition control” is started. More specifically, the first device controls the engine 10 so that the catalyst upstream air-fuel ratio abyfs becomes the lean air-fuel ratio lean at time t1. For example, the first device causes the engine 10 to perform a fuel cut operation at time t1.

  As a result, the catalyst upstream air-fuel ratio abyfs becomes the lean air-fuel ratio lean at time t1. At this time, exhaust gas having a lean air-fuel ratio lean (that is, exhaust gas having a higher oxygen concentration than exhaust gas having a stoichiometric air-fuel ratio stoich) is introduced into the catalyst 53, so that the catalyst 53 occludes oxygen contained in the exhaust gas. Therefore, the oxygen storage amount OSA of the catalyst 53 increases as time elapses after time t1. On the other hand, since the catalyst 53 occludes oxygen contained in the exhaust gas at this time, the exhaust gas discharged from the catalyst 53 does not substantially contain oxygen. Therefore, even after time t1, the output value Voxs of the downstream oxygen concentration sensor 77 is maintained at a value indicating the rich air-fuel ratio rich.

  Actually, a predetermined time length is required from when the control of the catalyst upstream air-fuel ratio abyfs to the lean air-fuel ratio lean is started until the exhaust gas having the lean air-fuel ratio lean reaches the upstream oxygen concentration sensor 76. It takes a long time. Therefore, in practice, the upstream oxygen concentration abyfs becomes the lean air-fuel ratio lean at the time after the predetermined time length has elapsed from time t1. However, in this description, it is assumed that the upstream oxygen concentration abyfs becomes the lean air-fuel ratio lean at time t1 so as to facilitate understanding. Hereinafter, similarly, it is assumed that the time length from the start of the control for changing the catalyst upstream air-fuel ratio abyfs until the exhaust gas of the air-fuel ratio reaches the upstream oxygen concentration sensor 76 is zero. Continue.

  Thereafter, at time t2, the oxygen storage amount OSA of the catalyst 53 reaches the maximum oxygen storage amount Cmax. At this time, since the catalyst 53 cannot occlude oxygen contained in the exhaust gas, the exhaust gas discharged from the catalyst 53 begins to contain oxygen. Therefore, at time t2, the output value Voxs of the downstream oxygen concentration sensor 77 becomes a value representing the lean air-fuel ratio lean.

  At time t2, the first device controls the engine 10 so that the catalyst upstream air-fuel ratio abyfs becomes the rich air-fuel ratio rich. For example, the first device causes the engine 10 to perform an operation for increasing the fuel injection amount higher than the fuel injection amount when the normal operation is performed at time t2.

  Thereby, at the time t2, the catalyst upstream air-fuel ratio abyfs becomes the rich air-fuel ratio rich. At this time, exhaust gas having a rich air-fuel ratio rich (that is, exhaust gas having a lower oxygen concentration than exhaust gas having the stoichiometric air-fuel ratio stoich) is introduced into the catalyst 53, so that the catalyst 53 converts the stored oxygen into the oxidation-reduction reaction of the exhaust gas. To release. Therefore, the oxygen storage amount OSA of the catalyst 53 decreases as time elapses after time t2. On the other hand, since the redox reaction of the exhaust gas is performed by the oxygen stored in the catalyst 53 at this time, oxygen (unburned oxygen) contained in the exhaust gas is not consumed in the redox reaction of the exhaust gas. Therefore, oxygen (unburned oxygen) contained in the exhaust gas remains in the exhaust gas discharged from the catalyst 53. Therefore, even after time t2, the output value Voxs of the downstream oxygen concentration sensor 77 is maintained at a value indicating the lean air-fuel ratio lean.

  Thereafter, at time t3, the oxygen storage amount OSA of the catalyst 53 reaches zero. At this time, since oxygen is not occluded in the catalyst 53, oxygen (unburned oxygen) contained in the exhaust gas is consumed in the oxidation-reduction reaction of the exhaust gas. For this reason, oxygen (unburned oxygen) contained in the exhaust gas does not exist in the exhaust gas discharged from the catalyst 53. Therefore, the exhaust gas discharged from the catalyst 53 is substantially free of oxygen. Therefore, at time t3, the air-fuel ratio of the exhaust gas becomes a value representing the rich air-fuel ratio rich.

  After time t3, the first device resumes “normal operation”. Thus, after time t3, the catalyst upstream side air-fuel ratio abyfs is controlled to coincide with the stoichiometric air-fuel ratio stoich. Note that the output value Voxs of the downstream oxygen concentration sensor 77 and the oxygen storage amount OSA of the catalyst 53 after the time t3 are values according to the operating state of the engine 10.

After each of the above operations, the first device calculates the maximum oxygen storage amount Cmax of the catalyst 53 according to the following formula (1) and the following formula (2). In the following equation (1), the numerical value 0.23 is the oxygen concentration (weight percent concentration) in the standard state, Fsum is the integrated value of the fuel injection amount F within the unit time Δt, and abyfsave is the catalyst upstream air-fuel ratio abyfs. Of the unit time Δt, and stoich represents the stoichiometric air-fuel ratio. In the following equation (2), the right side of the equation represents the absolute value of the value obtained by integrating ΔO2 with respect to time t in the range from time t2 to time t3. As is well known, the standard state means a state where the temperature is zero ° C. (273.15 K) and the pressure is 1 bar (10 ⁵ Pa).

ΔO2 = 0.23 × Fsum × (abyfsave−stoich) (1)
Cmax = | Σ [t = t2, t3] (ΔO2) | (2)

  As is apparent from the right side of the above equation (1), according to the above equation (1), “the amount of oxygen ΔO2 contained in the exhaust gas introduced into the catalyst 53 per unit time is represented by the amount of oxygen contained in the exhaust gas having the stoichiometric air / fuel ratio”. A value expressed with reference to “is calculated. In brief, ΔO2 is a value representing an excess or deficiency of oxygen based on the amount of oxygen contained in the stoichiometric air-fuel ratio exhaust gas. If the amount of oxygen is excessive, ΔO2 is a positive value, and if the amount of oxygen is insufficient, ΔO2 is a negative value. In other words, if ΔO2 is a positive value, ΔO2 represents the amount of oxygen “occluded” by the catalyst 53 per unit time, and if ΔO2 is a negative value, ΔO2 “releases” from the catalyst 53 per unit time. Represents the amount of oxygen (consumed in the oxidation-reduction reaction of exhaust gas).

  Therefore, as shown in the above equation (2), ΔO2 is integrated over time t in the range from time t2 (at the time when the oxygen storage amount OSA is the maximum value) to time t3 (at the time when the oxygen storage amount OSA is zero). As a result, the maximum oxygen storage amount Cmax of the catalyst 53 is calculated.

  As is clear from the above description, the catalyst can also be obtained by integrating ΔO2 with respect to time t in the range from “the time when the oxygen storage amount OSA is zero” to “the time when the oxygen storage amount OSA is the maximum”. A maximum oxygen storage amount Cmax of 53 can be calculated.

2. Acquisition of catalyst deterioration degree Ke The first device acquires the deterioration degree Ke of the catalyst 53 based on the maximum oxygen storage amount Cmax of the catalyst 53 acquired as described above. Specifically, the first device calculates the deterioration degree Ke of the catalyst 53 according to the following equation (3). In the following equation (3), Cmaxnew represents the maximum oxygen storage amount when the catalyst 53 is in a new state. This Cmaxnew can be acquired in advance by experiments or the like.

      Ke = 1− (Cmax / Cmaxnew) (3)

  As is apparent from the right side of the above equation (3), if the catalyst 53 is not deteriorated at all (that is, if Cmax and Cmaxnew match), the deterioration degree Ke is zero. On the other hand, the degree of deterioration Ke increases as the degree of deterioration of the catalyst 53 increases (that is, as the difference between Cmax and Cmaxnew increases). As is clear from the right side of the above equation (3), the maximum value of the deterioration degree Ke is 1. The above is the method for obtaining the deterioration degree Ke of the catalyst 53 in the first device.

<Method for reducing the degree of catalyst degradation>
When the deterioration degree Ke of the catalyst 53 acquired as described above is equal to or greater than the predetermined threshold deterioration degree Keth, the first device performs “operation for reducing the deterioration degree” based on the characteristics of the catalyst 53. Hereinafter, the operation for reducing the characteristics and the degree of deterioration of the catalyst 53 will be described in more detail.

1. Characteristics of the Catalyst As described above, the sulfur component (SOx and the like) contained in the exhaust gas is stored in the oxygen storage material of the catalyst 53, and the sulfur component (S and the like) is adsorbed on the catalyst component of the catalyst 53. 53 may deteriorate. According to various considerations and experiments by the inventors, there is a close relationship between “the air-fuel ratio of exhaust gas”, “the temperature of the catalyst”, and “the behavior of the sulfur component adsorbed and stored in the catalyst”. It was confirmed. This relationship will be described in more detail with reference to FIG.

  FIG. 5 is a schematic diagram showing the relationship between the air-fuel ratio of exhaust gas, the temperature of the catalyst, and the main behavior of the sulfur component adsorbed and stored in the catalyst. As shown in FIG. 5, it was confirmed that the catalyst 53 has the characteristics shown in the following (1) to (4). In the following characteristics (1) to (4), the activation temperature T0, the first temperature T1, the second temperature T2, and the third temperature T3 are values determined according to the materials constituting the catalyst 53, and are previously tested. Can be obtained by

(1) When the temperature TempC of the catalyst 53 is the activation temperature T0 or more and the first temperature T1 or less and the air-fuel ratio A / F of the exhaust gas is the lean air-fuel ratio lean, the sulfur component contained in the gas introduced into the catalyst 53 Is significantly occluded in the oxygen storage substance OSM.
(2) When the temperature TempC of the catalyst 53 is not less than the first temperature T1 and not more than the second temperature T2, when the air-fuel ratio A / F of the exhaust gas is rich, the sulfur component stored in the oxygen storage material OSM is It moves efficiently toward the catalyst component CC. At this time, the sulfur component exists on the catalyst component CC in a sulfur atom (S) state (that is, a state adsorbed on the catalyst component CC).
(3) When the temperature TempC of the catalyst 53 is equal to or higher than the third temperature T3 between the first temperature T1 and the second temperature T2, the air-fuel ratio A / F of the exhaust gas is lean on the catalyst component CC. Is efficiently released into the exhaust gas. At this time, the sulfur component is released into the exhaust gas in the form of sulfur oxide (SOx).
(4) When the temperature TempC of the catalyst 53 is higher than the second temperature T2, if the air-fuel ratio A / F of the exhaust gas is rich, the sulfur component present on the catalyst component CC is efficiently released into the exhaust gas. Is done. At this time, the sulfur component is released into the exhaust gas in the form of hydrogen sulfide (H2S).

  Note that when the conditions shown in characteristics (3) and (4) (conditions in which the sulfur component is released from the catalyst component CC into the exhaust gas) are not satisfied, the sulfur component in the exhaust gas has a sulfur atom (S) in the catalyst component CC. It is thought that it can adsorb | suck in the state of this. The sulfur component adsorbed on the catalyst component CC, like the sulfur component moved from the oxygen storage material OSM to the catalyst component CC, enters the exhaust gas from the catalyst component CC when the conditions shown in the characteristics (3) and (4) are satisfied. Expected to be released.

  By the way, in the characteristic (1), when the temperature TempC of the catalyst 53 is included in the temperature range (the activation temperature T0 or more and the first temperature T1 or less) indicated in the same relationship, the temperature TempC of the catalyst 53 is not included in the same temperature range. This means that the sulfur component is stored in the oxygen storage material OSM significantly more than the case. That is, the characteristic (1) does not mean that the sulfur component is not stored in the oxygen storage material OSM at all when the temperature TempC of the catalyst 53 is not included in the same temperature range.

  Further, in the characteristic (2), when the temperature TempC of the catalyst 53 is included in the temperature range (the first temperature T1 or more and the second temperature T2 or less) indicated in the same relationship, the temperature TempC of the catalyst 53 is included in the same temperature range. This means that the sulfur component stored in the oxygen storage material OSM is moved toward the catalyst component CC more efficiently than in the case where there is no catalyst. That is, the characteristic (2) does not mean that the sulfur component stored in the oxygen storage material OSM does not move toward the catalyst component CC at all when the temperature TempC of the catalyst 53 is not included in the same temperature range. . Similarly, the characteristic (3) and the characteristic (4) are more efficient when the temperature TempC of the catalyst 53 is included in the temperature ranges indicated in the respective relationships than when the temperature TempC of the catalyst 53 is not included in those temperature ranges. It means that the sulfur component that is well present on the catalyst component CC is released into the exhaust gas. That is, the characteristics (3) and (4) do not mean that no sulfur component is released from the catalyst component CC when the temperature TempC of the catalyst 53 is not included in these temperature ranges.

2. Operation for Reducing Degradation As described above, when the sulfur component stored in the oxygen storage material OSM included in the support of the catalyst 53 satisfies a predetermined condition (see the above characteristic (2)), Efficiently moves from the oxygen storage material OSM toward the catalyst component CC. The sulfur component present on the catalyst component CC is efficiently released into the exhaust gas when a predetermined condition (see the above characteristic (3) and the above characteristic (4)) is established. That is, the sulfur component stored in the oxygen storage material OSM is not released directly into the gas from the oxygen storage material OSM, but is released into the exhaust gas via the catalyst component CC.

  Therefore, the first device pays attention to the relationship between “the exhaust gas air-fuel ratio” and “the behavior of the sulfur component” among the above characteristics (1) to (4), in order to reduce the deterioration degree Ke of the catalyst 53. Do the operation.

  Specifically, when the deterioration degree Ke of the catalyst 53 is equal to or higher than a predetermined threshold deterioration degree Keth, the first device performs the following operation (a) or (b) according to the catalyst downstream air-fuel ratio oxs. Do.

(A) When the catalyst downstream air-fuel ratio oxs is “theoretical air-fuel ratio stoich” or “lean air-fuel ratio lean”, the first device first performs “rich operation with the catalyst upstream-side air-fuel ratio abyfs as the rich air-fuel ratio rich. "I do. The first device continues this rich operation until the downstream air-fuel ratio oxs of the catalyst becomes the rich air-fuel ratio rich. Next, after the catalyst downstream air-fuel ratio oxs becomes rich air-fuel ratio rich, the first device performs “lean operation” in which the catalyst upstream-side air-fuel ratio abyfs is set to the lean air-fuel ratio lean.
(B) When the catalyst downstream air-fuel ratio oxs is the rich air-fuel ratio rich, the first device performs the lean operation without performing the rich operation.

  In the operation (a), when the rich operation is started, the sulfur component stored in the oxygen storage material OSM starts to move toward the catalyst component CC. However, since the catalyst 53 has a predetermined size, it takes a predetermined time until the sulfur component moves toward the catalyst component CC in the entire catalyst 53 after the rich operation is started. Therefore, in the operation (a), the rich operation is continued “until the catalyst downstream air-fuel ratio oxs becomes rich air-fuel ratio rich”. Thereby, in the “entire” of the catalyst 53, the sulfur component stored in the oxygen storage material OSM can be moved toward the catalyst component CC.

As shown in the above operation (a), the rich operation is also performed when the catalyst downstream air-fuel ratio oxs is “same as the stoichiometric air-fuel ratio stoich”. The reason for this will be described below.
As described above, since the catalyst 53 has an oxygen storage capacity, the catalyst downstream air-fuel ratio oxs may become the stoichiometric air-fuel ratio stoich regardless of the value of the catalyst upstream air-fuel ratio abyfs. Therefore, even if the catalyst upstream side air-fuel ratio abyfs becomes the rich air-fuel ratio rich for some reason before the rich operation of operation (a) is performed, the catalyst downstream-side air-fuel ratio oxs may become the stoichiometric air-fuel ratio stoich. . In this case, the sulfur component stored in the oxygen storage material OSM moves toward the catalyst component CC without performing the rich operation of operation (a). However, the first device performs the rich operation even in this case in order to move the sulfur component stored in the oxygen storage material OSM in the entire catalyst 53 more reliably toward the catalyst component CC.

  Further, in the operation (a), the lean operation is performed after the sulfur component is moved toward the catalyst component CC in the entire catalyst 53 as described above. Thereby, the sulfur component on the catalyst component CC is released into the exhaust gas. At this time, the sulfur component adsorbed on the catalyst component CC is also released into the exhaust gas. As a result, the sulfur component adsorbed and stored in the catalyst 53 is removed in the entire catalyst 53.

  On the other hand, in the operation (b), if the catalyst downstream air-fuel ratio oxs is the rich air-fuel ratio rich, the sulfur component stored in the oxygen storage material OSM in the entire catalyst 53 has already moved toward the catalyst component CC. It is thought that. Therefore, in the operation (b), the lean operation is performed without the rich operation. As a result, the sulfur component adsorbed and stored in the catalyst 53 is removed in the entire catalyst 53.

  The first device integrates the intake air amount Ga during the period during which the lean operation in the operation (a) and the operation (b) is performed (that is, the period during which the sulfur component is released into the exhaust gas). To do. The first device continues the lean operation until the accumulated amount Galsum becomes equal to or greater than a predetermined threshold accumulated amount Galsumth. Then, after the integrated amount Galsum becomes equal to or greater than the threshold integrated amount Galsumth, the first device stops the lean operation and resumes the normal operation. Here, the integrated amount Galsum can be set to an appropriate value at which it can be determined that the sulfur component adsorbed and stored in the catalyst 53 has been sufficiently removed. The above is the method for reducing the deterioration degree Ke of the catalyst 53 in the first device.

<Air-fuel ratio control>
Next, the air-fuel ratio control for performing the above-described normal operation, rich operation, and lean operation will be described before the actual operation of the first device is described.

  The air-fuel ratio control in the first device includes “main feedback control” for matching the upstream air-fuel ratio abyfs obtained based on the output value Vabyfs of the upstream oxygen concentration sensor 76 with the upstream target air-fuel ratio abyfr, and downstream It comprises “sub-feedback control” for making the output value Voxs of the side oxygen concentration sensor 77 coincide with the downstream target output value Voxsref.

  More specifically, first, the output value Vabyfs of the upstream oxygen concentration sensor 76 is “the output deviation amount DVoxs which is the difference between the output value Voxs of the downstream oxygen concentration sensor 77 and the downstream target output value Voxsref is reduced. The sub-feedback amount Vafsfb calculated so as to be corrected. Next, the “feedback control output value Vabyfc” obtained by this correction is applied to the table Mapabyfs (see FIG. 2), whereby “feedback control air-fuel ratio (corrected detected air-fuel ratio) abyfsc” is calculated. The Then, the fuel injection amount Fi is controlled such that the feedback control air-fuel ratio abyfsc matches the “upstream target air-fuel ratio abyfr”. Hereinafter, this air-fuel ratio control will be described in more detail.

  In this air-fuel ratio control, the value of a predetermined parameter at the present time (time point k) and the value of a predetermined parameter at a time point before the current time (time point k−N) are used. Hereinafter, when the values of the parameters are described without any particular annotation, the values represent the values at the present time (time k).

1. Main feedback control First, main feedback control performed by the first device will be described.
The first device calculates the feedback control output value Vabyfc according to the following equation (4). In the following equation (4), Vabyfs represents the output value of the upstream oxygen concentration sensor 76, and Vafsfb represents the sub-feedback amount calculated based on the output value Voxs of the downstream oxygen concentration sensor 77. A method of calculating the sub feedback amount Vafsfb will be described later.

      Vabyfc = Vabyfs + Vafsfb (4)

  Next, the first device determines the feedback control air-fuel ratio abyfsc by applying the feedback control output value Vabyfc to the table Mapabyfs (see FIG. 2) according to the following equation (5).

      abyfsc = Mapabyfs (Vabyfc) (5)

  Next, according to the following equation (6), the first device sets the cylinder intake air amount Mc (k), which is the amount of air sucked into the cylinder at the current time (time k), to the upstream side at the current time (time k). A basic fuel injection amount Fbase is calculated by dividing by the target air-fuel ratio abyfr (k). A method for calculating the upstream target air-fuel ratio abyfr (k) will be described later.

      Fbase = Mc (k) / abyfr (k) (6)

  The in-cylinder intake air amount Mc is calculated based on the intake air amount Ga and the engine rotational speed NE at that time each time an intake stroke is performed in each cylinder. For example, the in-cylinder intake air amount Mc is calculated by dividing a value obtained by subjecting the intake air amount Ga to the first-order lag processing by the engine speed NE. This in-cylinder intake air amount Mc is stored in the RAM 83 as data associated with each time point (time point k−N,..., Time point k−1, time point k, time point k + 1,...) When the intake stroke is performed. Stored in The in-cylinder intake air amount Mc may be calculated by a known intake air amount model (a model constructed by imitating the behavior of air in the intake passage).

  Next, the first device corrects the basic fuel injection amount Fbase by the main feedback amount DFi according to the following equation (7) (adds the main feedback amount DFi to the basic fuel injection amount Fbase), thereby obtaining the final fuel injection amount Fi. Is calculated. Then, the first device injects fuel of the final fuel injection amount Fi from the injector 34 of the cylinder in which the intake stroke is performed. A method of calculating the main feedback amount DFi will be described later.

      Fi = Fbase + DFi (7)

The main feedback amount DFi in the above equation (7) is calculated as follows.
First, according to the following equation (8), the first device calculates the in-cylinder intake air amount Mc (k−N) at the time point N cycles before the current time point (time point k−N) as the feedback control air-fuel ratio (correction detection). By dividing by (air-fuel ratio) abyfsc, an “in-cylinder fuel supply amount Fc (k−N)”, which is the amount of fuel supplied to the combustion chamber 25 at a time N cycles before the current time, is calculated.

      Fc (k−N) = Mc (k−N) / abyfsc (8)

  In the above equation (8), the in-cylinder intake air amount Mc (k−N) N cycles before the present time is divided by the (current) feedback control air-fuel ratio abyfsc, so that N cycles before the current time The in-cylinder fuel supply amount Fc (k−N) is calculated. This is because it takes time corresponding to N cycles until the air-fuel mixture burned in the combustion chamber 25 reaches the upstream oxygen concentration sensor 76.

  Next, the first device calculates the in-cylinder intake air amount Mc (k−N) N cycles before the current time at the upstream target air-fuel ratio abyfr (k−N) N cycles before the current time according to the following equation (9). By dividing, “target in-cylinder fuel supply amount Fcr (k−N)” N cycles before the present time is calculated.

      Fcr (k−N) = Mc (k−N) / abyfr (k−N) (9)

  Next, the first device subtracts the in-cylinder fuel supply amount Fc (k−N) from the target in-cylinder fuel supply amount Fcr (k−N) N cycles before the current time according to the following equation (10). The “in-cylinder fuel supply amount deviation DFc” is calculated. This in-cylinder fuel supply amount deviation DFc represents “the excess or deficiency of the fuel supplied into the cylinder at the time point before N cycles”.

      DFc = Fcr (k−N) −Fc (k−N) (10)

  Next, the first device calculates the main feedback amount DFi according to the following equation (11). In the following equation (11), Gp represents a preset proportional gain, Gi represents a preset integral gain, KFB represents a predetermined coefficient, and SDFc represents an integral value of the in-cylinder fuel supply amount deviation DFc.

      DFi = (Gp · DFc + Gi · SDFc) · KFB (11)

  As shown in the above equations (10) and (11), the first device calculates the main feedback amount DFi by proportional-integral control based on the feedback control air-fuel ratio abyfsc and the upstream target air-fuel ratio abyfr. The main feedback amount DFi is added to the basic fuel injection amount Fbase as shown in the above equation (7). Thereby, the final fuel injection amount Fi is calculated. The above is the main feedback control performed by the first device.

2. Sub Feedback Control Next, sub feedback control performed by the first device will be described.
The first device calculates the output deviation amount DVoxs by subtracting the current output value Voxs of the downstream oxygen concentration sensor 77 from the downstream target output value Voxsref according to the following equation (12). In the first device, in consideration of the exhaust gas purification performance of the catalyst 53, “a value corresponding to an air-fuel ratio slightly richer than the theoretical air-fuel ratio” is adopted as the downstream target output value Voxsref.

      DVoxs = Voxsref−Voxs (12)

  Next, the first device calculates the sub feedback amount Vafsfb according to the following equation (13). In the following equation (13), Kp represents a preset proportional gain (proportional constant), Ki represents a preset integral gain (integral constant), and SDVoxs represents an integral value of the output deviation amount DVoxs.

      Vafsfb ＝ Kp ・ DVoxs ＋ Ki ・ SDVoxs (13)

  As shown in the above equations (12) and (13), the first device calculates the sub feedback amount Vafsfb by proportional-integral control based on the output value Voxs of the downstream oxygen concentration sensor 77 and the downstream target output value Voxsref. calculate. The sub feedback amount Vafsfb is added to the output value Vabyfs of the upstream oxygen concentration sensor 76 as shown in the above equation (4). Thereby, the feedback control output value Vabyfc is calculated. The above is the sub feedback control performed by the first device.

3. Summary of Air-Fuel Ratio Control As described above, the first device corrects the output value Vabyfs by adding the sub feedback amount Vafsfb to the output value Vabyfs of the upstream oxygen concentration sensor 76, and the feedback control obtained by this correction The feedback control air-fuel ratio abyfsc is calculated based on the output value Vabyfc (= Vabyfs + Vafsfb). Then, the first device calculates the fuel injection amount Fi so that the calculated feedback control air-fuel ratio abyfsc matches the upstream target air-fuel ratio abyfr.

  As a result, the upstream air-fuel ratio abyfs approaches the upstream target air-fuel ratio abyfr, and the output value Voxs of the downstream oxygen concentration sensor 77 approaches the downstream target output value Voxsref. In other words, both the upstream air-fuel ratio and the downstream air-fuel ratio of the catalyst 53 are brought close to their target values. The above is the air-fuel ratio control performed by the first device.

<Actual operation>
Hereinafter, the actual operation of the first device will be described.
In the first device, the CPU 81 is configured to repeatedly execute each routine shown in the flowcharts in FIGS. 6 to 11 at predetermined timings. In these routines, the CPU 81 uses the catalyst deterioration flag XCD and the deterioration degree reduction operation switching flag XREC.

  When the value of the catalyst deterioration flag XCD is “0”, it indicates that the deterioration degree Ke of the catalyst 53 is smaller than the threshold deterioration degree Keth and it is not necessary to perform an operation for reducing the deterioration degree Ke. On the other hand, when the value of the catalyst deterioration flag XCD is “1”, the deterioration degree Ke of the catalyst 53 is equal to or greater than the threshold deterioration degree Keth, and it is necessary to perform an operation for reducing the deterioration degree Ke.

  When the value of the deterioration degree reduction operation switching flag XREC is “0”, the state of the catalyst 53 is “an operation that moves the sulfur component stored in the oxygen storage material OSM to the catalyst component CC (that is, the rich operation). Is in a state where it can be performed. On the other hand, when the value of the deterioration degree reduction operation switching flag XREC is “1”, the state of the catalyst 53 is “the operation in which the sulfur component is released from the catalyst component CC into the exhaust gas (that is, the above lean operation). It means that it is a “getting state”.

  The value of the catalyst deterioration flag XCD and the value of the deterioration degree reduction operation switching flag XREC are electronically controlled when there is no abnormality in the catalyst 53 at the time of factory shipment or service inspection of a vehicle equipped with the engine 10. When a predetermined operation is performed on the device 80, the initial value is set to “0”.

Hereinafter, each routine executed by the CPU 81 will be described.
First, it is assumed that both the value of the catalyst deterioration flag XCD and the value of the deterioration degree reduction operation switching flag XREC are currently set to “0”. Hereinafter, for the sake of convenience, this assumption is also referred to as “initial setting assumption”.

  When the engine 10 is started, the CPU 81 repeatedly executes the “catalyst temperature estimation routine” shown by the flowchart in FIG. 6 every time a predetermined time elapses. The CPU 81 obtains the temperature TempC of the catalyst by this routine.

  Specifically, the CPU 81 starts processing from step 600 in FIG. 6 at a predetermined timing and proceeds to step 610 to determine whether or not the current time is immediately after the start of the engine 10. If the current time is immediately after the engine 10 is started, the CPU 81 makes a “Yes” determination at step 610 to proceed to step 620. On the other hand, if the current time is not immediately after the engine 10 is started, the CPU 81 makes a “No” determination at step 610 to proceed to step 630. Here, the description will be continued assuming that “the present time is immediately after the start of the engine 10”.

  According to the above assumption, the CPU 81 proceeds to step 620. In step 620, the CPU 81 applies the current cooling water temperature THWS to the starting catalyst temperature estimation function f (THWS) that predetermines the “relation between the starting cooling water temperature THWS and the catalyst temperature TempC”. Obtain (estimate) the current temperature TempC of the catalyst.

  In the startup catalyst temperature estimation function f (TWS), the catalyst temperature TempC is determined to increase as the startup cooling water temperature THWS increases.

  Next, the CPU 81 proceeds to step 630. In step 630, the CPU 81 stores the in-cylinder intake at the present time in an exhaust temperature table MapTex (Mc, NE) that predetermines the “relationship between the in-cylinder intake air amount Mc, the engine speed NE, and the exhaust temperature Tex”. The exhaust gas temperature Tex at the present time is acquired (estimated) by applying the air amount Mc and the engine rotational speed NE.

  Next, the CPU 81 proceeds to step 640. In step 640, the CPU 81 updates and acquires the catalyst temperature TempC according to the following equation (14). In the following equation (14), α is a constant larger than 0 and smaller than 1, TempC (k) is the temperature TempC of the catalyst before being updated, and TempC (k + 1) is the catalyst after being updated. Represents the temperature TempC.

      TempC (k + 1) = α · TempC (k) + (1−α) · Tex (14)

  After executing the processing of step 640, the CPU 81 proceeds to step 695 to end the present routine tentatively.

  Further, the CPU 81 repeatedly executes the “first deterioration degree acquisition routine” shown by the flowchart in FIG. 7 every time a predetermined time elapses. The CPU 81 acquires the deterioration degree Ke of the catalyst 53 by this routine.

  Specifically, the CPU 81 starts the process from step 700 of FIG. 7 at a predetermined timing, proceeds to step 710, and determines whether or not the value of the catalyst deterioration flag XCD is “0”. If the initial setting assumption is followed, the current value of the catalyst deterioration flag XCD is “0”, so the CPU 81 determines “Yes” in step 710 and proceeds to step 720.

  In step 720, the CPU 81 determines whether or not “a condition for determining the deterioration degree Ke of the catalyst 53 (deterioration degree determination condition)” is satisfied. More specifically, in step 720, the CPU 81 determines that the deterioration degree determination condition is satisfied when all of the following conditions a-1 to a-3 are satisfied. In other words, the CPU 81 determines that the deterioration degree determination condition is not satisfied when at least one of the conditions a-1 to a-3 is not satisfied.

(Condition a-1) The temperature THW of the cooling water is equal to or higher than a predetermined threshold value.
(Condition a-2) The amount of change per unit time of the throttle valve opening TA is not more than a predetermined threshold value.
(Condition a-3) The change amount per unit time of the vehicle speed acquired by a vehicle speed sensor (not shown) is not more than a predetermined threshold value.

  The predetermined threshold value related to the condition a-1 is set to an appropriate value at which it can be determined that the engine 10 has been warmed up. The predetermined threshold value related to condition a-2 and condition a-3 is set to an appropriate value that allows the engine 10 to be determined to be in steady operation.

  When the deterioration degree determination condition is “not satisfied”, the CPU 81 makes a “No” determination at step 720 to directly proceed to step 795 to end the present routine tentatively. Therefore, when the deterioration degree determination condition is not satisfied, the deterioration degree Ke of the catalyst 53 is not acquired. In contrast, when the deterioration degree determination condition is “satisfied”, the CPU 81 determines “Yes” in step 720 and proceeds to step 730. Hereinafter, the description will be continued on the assumption that the deterioration degree determination condition is “established” at the present time.

  According to the above assumption, the CPU 81 proceeds to step 730. In step 730, the CPU 81 obtains the maximum oxygen storage amount Cmax of the catalyst 53 at the present time according to the above equations (1) and (2).

  Next, the CPU 81 proceeds to step 740. In step 740, the CPU 81 determines the deterioration of the catalyst 53 based on the current maximum oxygen storage amount Cmax of the catalyst 53 and the maximum oxygen storage amount Cmaxnew when the catalyst 53 is in a new state according to the above equation (3). Get degree Ke.

  Next, the CPU 81 proceeds to step 750. In step 750, the CPU 81 determines whether or not the deterioration degree Ke of the catalyst 53 is equal to or higher than the threshold deterioration degree Keth. The threshold deterioration degree Keth is set to an appropriate value that can be determined to require operation for reducing the deterioration degree of the catalyst 53.

Here, the operation performed by the first device will be described separately in the following two cases.
(Case 1) When the deterioration degree Ke of the catalyst 53 at the present time is smaller than the threshold deterioration degree Keth (Case 2) When the deterioration degree Ke of the catalyst 53 at the current time is equal to or more than the threshold deterioration degree Keth Hereinafter, the description will be continued.

(Case 1) When the degree of deterioration Ke of the catalyst 53 is smaller than the threshold degree of deterioration Keth In this case, the CPU 81 makes a “No” determination at step 750 to proceed to step 795 to end the present routine tentatively.

  Further, the CPU 81 repeatedly executes the “deterioration degree reduction routine” shown by the flowchart in FIG. 8 every time a predetermined time elapses. With this routine, the CPU 81 determines what operation is to be executed in order to reduce the deterioration degree Ke of the catalyst 53 (that is, which of the lean operation and the rich operation is to be executed).

  Specifically, when the CPU 81 starts the process from step 800 in FIG. 8 at a predetermined timing, the CPU 81 proceeds to step 810. In step 810, the CPU 81 determines whether or not the value of the catalyst deterioration flag XCD is “1”. Since the current value of the catalyst deterioration flag XCD is “0”, the CPU 81 makes a “No” determination at step 810 to proceed to step 895 to end the present routine tentatively.

  As described above, when the value of the catalyst deterioration flag XCD is “0”, it is not determined whether any operation is performed in order to reduce the deterioration degree Ke of the catalyst 53. This is because when the value of the catalyst deterioration flag XCD is “0”, it is not necessary to perform an operation for reducing the deterioration degree Ke of the catalyst 53.

  Further, every time the crank angle of an arbitrary cylinder coincides with a predetermined crank angle before the intake stroke (for example, 90 ° crank angle before exhaust top dead center) θf, the CPU 81 “fuel injection control” shown in the flowchart of FIG. Routine "is executed repeatedly. The CPU 81 determines the final fuel injection amount Fi by this routine, and causes the injector 34 to inject the fuel corresponding to the final fuel injection amount Fi. Hereinafter, for convenience, the cylinder before the intake stroke whose crank angle coincides with the predetermined crank angle θf is also referred to as “fuel injection cylinder”.

  Specifically, the CPU 81 starts the process from step 900 in FIG. 9 at a predetermined timing, proceeds to step 910, and determines whether or not the value of the catalyst deterioration flag XCD is “0”. Since the current value of the catalyst deterioration flag XCD is “0”, the CPU 81 makes a “Yes” determination at step 910 to proceed to step 920.

  In step 920, the CPU 81 stores “theoretical air / fuel ratio stoich” in the upstream target air / fuel ratio abyfr (k). Next, the CPU 81 sequentially executes processing of step 930 to step 960 following step 920. The processing executed in steps 930 to 960 is as follows.

Step 930: The CPU 81 acquires an in-cylinder intake air amount Mc (k), which is the amount of air taken into the fuel injection cylinder, based on the intake air amount Ga and the engine speed NE.
Step 940: The CPU 81 calculates the basic fuel injection amount Fbase according to the above equation (6).
Step 950: The CPU 81 calculates the final fuel injection amount Fi by correcting the basic fuel injection amount Fbase with the main feedback amount DFi according to the above equation (7).
Step 960: The CPU 81 gives an instruction to the injector 34 provided in the fuel injection cylinder so as to inject the fuel of the final fuel injection amount Fi.

  After executing the processing of step 960, the CPU 81 proceeds to step 995 to end the present routine tentatively.

  The final fuel injection amount Fi is calculated by the above-described processes, and fuel corresponding to the final fuel injection amount Fi is injected into the fuel injection cylinder. As a result, the “normal operation” in which the upstream target air-fuel ratio abyfr is set to the stoichiometric air-fuel ratio stoich is executed.

  Further, the CPU 81 repeatedly executes the “main feedback amount calculation routine” shown by the flowchart in FIG. 10 every time the crank angle of an arbitrary cylinder matches the predetermined crank angle θg before the intake stroke. The CPU 81 calculates the main feedback amount DFi by this routine.

  More specifically, the CPU 81 starts processing from step 1000 in FIG. 10 at a predetermined timing and proceeds to step 1005, where “feedback control for matching the catalyst upstream air-fuel ratio abyfs with the upstream target air-fuel ratio abyfr is performed. It is determined whether or not “conditions that can be performed (main feedback control conditions)” are satisfied. More specifically, the CPU 81 determines in step 1005 that the main feedback control condition is satisfied when all of the following conditions b-1 to b-5 are satisfied. In other words, the CPU 81 determines that the main feedback control condition is not satisfied when at least one of the following conditions b-1 to b-5 is not satisfied.

(Condition b-1) The temperature TempC of the catalyst is equal to or higher than a predetermined threshold value.
(Condition b-2) The coolant temperature THW is equal to or higher than a predetermined threshold value.
(Condition b-3) The intake air amount Ga is equal to or less than a predetermined threshold value.
(Condition b-4) The upstream oxygen concentration sensor 76 is activated.
(Condition b-5) An operation (fuel cut operation) in which the final fuel injection amount Fi is zero is not being executed.

  The predetermined threshold value related to the condition b-1 is set to an appropriate value at which it can be determined that the catalyst 53 is activated. The predetermined threshold value related to condition b-2 is set to an appropriate value with which it can be determined that the engine 10 has been warmed up. The predetermined threshold value related to the condition b-3 is set to an appropriate value that can be determined that the load on the engine 10 is not excessive. Condition b-4 is a condition that is provided because the output value Vabyfs of the upstream oxygen concentration sensor 76 is used in the main feedback control. Condition b-5 is a condition that is provided because the fuel injection amount cannot be changed during the fuel cut operation. Therefore, for example, the main feedback control condition is not satisfied during a period in which the engine 10 is warming up and a period in which the fuel cut operation is being performed.

  If the main feedback control condition is “not met” at the present time, the CPU 81 makes a “No” determination at step 1005 to proceed to step 1010. In step 1010, the CPU 81 stores zero in the main feedback amount DFi.

  Next, the CPU 81 proceeds to step 1015. In step 1015, the CPU 81 stores zero in the integral value SDFc of the in-cylinder fuel supply amount deviation DFc. Thereafter, the CPU 81 proceeds to step 1095 to end the present routine tentatively.

  Thus, when the main feedback control condition is not satisfied, the main feedback amount DFi is set to zero. Therefore, in this case, the “correction of the basic fuel injection amount Fbase by the main feedback amount DFi” described above is not performed (see step 950 in FIG. 9).

  Next, the CPU 81 repeatedly executes the “sub feedback amount calculation routine” shown by the flowchart in FIG. 11 every time the crank angle of an arbitrary cylinder matches the predetermined crank angle θh before the intake stroke. The CPU 81 calculates the sub feedback amount Vafsfb by this routine.

  More specifically, the CPU 81 starts processing from step 1100 in FIG. 11 at a predetermined timing and proceeds to step 1110. “The output value Voxs of the downstream oxygen concentration sensor 77 matches the downstream target output value Voxsref. It is determined whether or not a “condition for performing sub-feedback control to be performed (sub-feedback control condition)” is satisfied. More specifically, in step 1110, the CPU 81 determines that the sub feedback control condition is satisfied when all of the following conditions c-1 to c-3 are satisfied. In other words, the CPU 81 determines that the sub feedback control condition is not satisfied when at least one of the following conditions c-1 to c-3 is not satisfied.

(Condition c-1) The main feedback condition is satisfied.
(Condition c-2) The upstream target air-fuel ratio abyfr is set to the stoichiometric air-fuel ratio stoich.
(Condition c-3) The downstream oxygen concentration sensor 77 is activated.

  The conditions c-1 and c-2 are conditions that are provided because the sub feedback control is a control that is executed in parallel with the main feedback control when the normal operation is being executed. Condition c-3 is a condition that is provided because the output value Voxs of the downstream oxygen concentration sensor 77 is used in the sub-feedback control. Therefore, for example, during the period in which the engine 10 is warming up, the period in which the fuel cut operation is being performed, and the period in which the rich operation and the lean operation are being performed, the sub feedback control condition Does not hold.

  As described above, since the main feedback control condition is not satisfied at the present time, the sub feedback control condition is not satisfied (see condition c-1). For this reason, the CPU 81 makes a “No” determination at step 1110 to proceed to step 1120. In step 1120, the CPU 81 stores zero in the sub feedback amount Vafsfb.

  Next, the CPU 81 proceeds to step 1020. In step 1020, the CPU 81 stores zero in the integral value SDVoxs of the output deviation amount DVoxs. Thereafter, the CPU 81 proceeds to step 1195 to end the present routine tentatively.

  Thus, when the sub feedback control condition is not satisfied, the sub feedback amount Vafsfb is set to zero. Therefore, in this case, “correction of the output value Vabyfs of the upstream oxygen concentration sensor 76 by the sub feedback amount Vafsfb” described later is not performed (see step 1020 in FIG. 10).

  Therefore, when the main feedback control condition is not satisfied at the present time, the main feedback amount DFi is set to zero and the sub feedback amount Vafsfb is set to zero. Therefore, the fuel of the basic fuel injection amount Fbase determined based on the intake air amount Ga, the engine speed NE, and the upstream target air-fuel ratio abyfr is injected into the fuel injection cylinder (see step 930 to step 960 in FIG. 9). .)

  On the other hand, when the main feedback control condition is “satisfied” at the present time, the CPU 81 starts the process from step 1000 in FIG. Next, the CPU 81 sequentially executes the processing of step 1020 to step 1050 following step 1005. The processing executed in steps 1020 to 1050 is as follows.

Step 1020: The CPU 81 calculates the feedback control output value Vabyfc according to the above equation (4). As described above, the current sub-feedback amount Vafsfb is zero.
Step 1025: The CPU 81 determines the feedback control air-fuel ratio abyfsc according to the above equation (5).
Step 1030: The CPU 81 calculates the in-cylinder fuel supply amount Fc (k−N) at a time point N cycles before the current time according to the above equation (8).
Step 1035: The CPU 81 calculates a target in-cylinder fuel supply amount Fcr (k−N) at a time point N cycles before the current time according to the above equation (9).
Step 1040: The CPU 81 calculates the in-cylinder fuel supply amount deviation DFc in accordance with the above equation (10).
Step 1045: The CPU 81 calculates the main feedback amount DFi according to the above equation (11). In the first device, “1” is adopted as the coefficient KFB. The integral value SDFc of the in-cylinder fuel supply amount deviation DFc is a value obtained by integrating the values of the in-cylinder fuel supply amount deviation DFc up to the present time (see step 1050 below).
Step 1050: The CPU 81 adds the in-cylinder fuel supply amount deviation DFc acquired in step 1040 to the integral value SDFc of the in-cylinder fuel supply amount deviation DFc at the current time point, so that a new in-cylinder fuel supply amount deviation is obtained. Calculate (update) the integral value SDFc.

  After executing the processing of step 1050, the CPU 81 proceeds to step 1095 to end the present routine tentatively.

  By each process described above, the main feedback amount DFi is calculated by proportional integral control (see step 1045). Then, the final fuel injection amount Fi is corrected using the main feedback amount DFi (see step 950 in FIG. 9).

  Furthermore, when the CPU 81 starts processing from step 1100 in FIG. 11 at a predetermined timing, the CPU 81 proceeds to step 1110. If the sub-feedback control condition is not satisfied at this time, the CPU 81 makes a “No” determination at step 1110 to proceed to step 1195 via step 1120 and step 1130 to end the present routine tentatively. In this case, as described above, the sub feedback amount Vafsfb is not calculated.

  On the other hand, if the sub-feedback control condition is satisfied at the present time, the CPU 81 makes a “Yes” determination at step 1110 and proceeds to step 1140. Hereinafter, the description will be continued assuming that the sub-feedback control condition is “established” at the present time.

  According to the above assumption, the CPU 81 sequentially executes the processing of step 1140 to step 1160 following step 1110. The processing executed in steps 1140 to 1160 is as follows.

Step 1140: The CPU 81 calculates the output deviation amount DVoxs according to the above equation (12). In the first device, considering the exhaust gas purification performance of the catalyst 53, a value corresponding to the air-fuel ratio slightly richer than the stoichiometric air-fuel ratio is adopted as the downstream target output value Voxsref.
Step 1150: The CPU 81 calculates the sub feedback amount Vafsfb according to the above equation (13). In the first apparatus, predetermined appropriate values are adopted as the proportional gain Kp and the integral gain Ki.
Step 1160: The CPU 81 calculates (updates) a new output deviation amount integrated value SDVoxs by adding the output deviation amount DVoxs acquired in step 1140 to the integrated value SDVoxs of the current output deviation amount.

  After executing the processing of step 1160, the CPU 81 proceeds to step 1195 to end the present routine tentatively.

  By each process described above, the sub feedback amount Vafsfb is calculated by proportional integral control (see step 1150). Then, the output value Vabyfs of the upstream oxygen concentration sensor 76 is corrected using the sub feedback amount Vafsfb (see step 1020 in FIG. 10). Further, the main feedback amount DFi is calculated based on the corrected feedback control output value Vabyfc (see step 1045 in FIG. 10), and the final fuel injection amount Fi is corrected using the main feedback amount DFi. (See step 950 in FIG. 9).

  As described above, when the degree of deterioration Ke of the catalyst 53 is smaller than the threshold degree of deterioration Keth, “normal operation” is performed in which the catalyst upstream air-fuel ratio abyfs matches the stoichiometric air-fuel ratio stoich.

(Case 2) When the deterioration degree Ke of the catalyst 53 is greater than or equal to the threshold deterioration degree Keth In this case, the CPU 81 starts processing from step 700 in FIG. 7 at a predetermined timing, and goes through steps 710 to 740. When the process proceeds to step 750, “Yes” is determined at step 750 and the process proceeds to step 760. In step 760, the CPU 81 stores “1” as the value of the catalyst deterioration flag XCD. Thereafter, the CPU 81 proceeds to step 795 to end the present routine tentatively.

  At this time, when the CPU 81 starts the process from step 800 in FIG. 8 and proceeds to step 810 at a predetermined timing, the current value of the catalyst deterioration flag XCD is “1”. It is determined as “Yes”, and the process proceeds to Step 820. In step 820, the CPU 81 determines whether or not the value of the deterioration level reduction operation switching flag XREC is “0”. If the initial setting assumption is followed, the current value of the deterioration level reduction operation switching flag XREC is “0”, so the CPU 81 determines “Yes” in step 820 and proceeds to step 830.

  In step 830, the CPU 81 determines whether or not the output value Voxs of the downstream oxygen concentration sensor 77 is equal to or less than “the output value Voxsstoich of the downstream oxygen concentration sensor 77 when the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio stoich”. Determine. That is, in step 830, the CPU 81 determines “whether the catalyst downstream air-fuel ratio oxs is the same as the stoichiometric air-fuel ratio stoich or is an air-fuel ratio leaner than the stoichiometric air-fuel ratio stoich”.

Here, the operation performed by the first device will be described separately in the following two cases.
(Case 2-1) When the current output value Voxs is less than or equal to the output value Voxsstoich (Case 2-2) When the current output value Voxs is larger than the output value Voxsstoich The description will be continued below.

(Case 2-1) When the output value Voxs is equal to or less than the output value Voxsstoich In this case, the CPU 81 determines “Yes” at step 830 and proceeds to step 840. In step 840, the CPU 81 stores “0” as the value of the deterioration level reduction operation switching flag XREC. Thereafter, the CPU 81 proceeds to step 895 to end the present routine tentatively.

  At this time, when the CPU 81 starts processing from step 900 in FIG. 9 at a predetermined timing, the CPU 81 proceeds to step 910. Since the current value of the catalyst deterioration flag XCD is “1”, the CPU 81 makes a “No” determination at step 910 to proceed to step 970.

  Since the value of the deterioration level reduction operation switching flag XREC at present is “0”, the CPU 81 determines “Yes” in step 970 and proceeds to step 980. In step 980, the CPU 81 stores the rich air-fuel ratio rich in the upstream target air-fuel ratio abyfr (k).

  Next, the CPU 81 sequentially executes the processing of step 930 to step 960 following step 980, proceeds to step 995, and once ends this routine. By these processes, the fuel of the final fuel injection amount Fi is injected into the fuel injection cylinder. As a result, the “rich operation” in which the upstream target air-fuel ratio abyfr is set to the rich air-fuel ratio rich is started.

  Further, the CPU 81 executes the routine shown in FIG. 10 and the routine shown in FIG. 11 to perform air-fuel ratio feedback control. However, at this time, the sub-feedback control condition is not satisfied (see condition c-2), so the sub-feedback amount Vafsfb is set to zero (see step 1110 to step 1130 in FIG. 11). Then, the final fuel injection amount Fi is corrected by the main feedback amount DFi calculated by the routine shown in FIG. 10 (see step 950 in FIG. 9). As a result, the catalyst upstream air-fuel ratio abyfs coincides with the rich air-fuel ratio rich. That is, the rich operation is continued.

  When the rich operation is continued, the oxygen stored in the oxygen storage material OSM of the catalyst 53 is consumed over time (the stored oxygen is used for the oxidation-reduction reaction), and the oxygen storage material OSM. The sulfur component occluded in the catalyst moves toward the catalyst component CC as time elapses. Note that, during the period when the oxygen stored in the oxygen storage material OSM is consumed, even if the catalyst upstream air-fuel ratio abyfs is the rich air-fuel ratio rich, the catalyst downstream air-fuel ratio oxs is substantially equal to the stoichiometric air-fuel ratio stoich. Become.

  Thereafter, when substantially all of the oxygen stored in the oxygen storage material OSM is consumed, exhaust gas having a rich air-fuel ratio rich starts to be discharged from the downstream side of the catalyst 53. As a result, the catalyst downstream air-fuel ratio oxs becomes a richer air-fuel ratio than the stoichiometric air-fuel ratio stoich. As described above, at this time, it is considered that substantially all of the sulfur component stored in the oxygen storage material OSM moves toward the catalyst component CC.

  At this time, when the CPU 81 starts processing from step 800 in FIG. 8 at a predetermined timing, the process proceeds to step 830 via step 810 and step 820. Since the catalyst downstream air-fuel ratio oxs at the present time is the rich air-fuel ratio rich, the output value Voxs is larger than the output value Voxsstoich (see FIG. 3). Therefore, the CPU 81 determines “No” in step 830. Proceed to step 850.

  In step 850, the CPU 81 determines whether or not the integrated amount Galsum of the intake air amount Ga introduced into the engine 10 from the time when “lean operation” described later is started to the present time is smaller than a predetermined threshold integrated amount Galsumth. Determine whether.

  The integrated amount Galsum is set to zero as an initial value when the engine 10 is started. Further, the integrated amount Galsum is set to an appropriate value at which it can be determined that substantially all of the sulfur component present on the catalyst component CC has been released into the exhaust gas by the lean operation.

  Since the lean operation has not been performed yet, the accumulated amount Galsum is the initial value (zero). Therefore, the CPU 81 determines “Yes” in step 850 and proceeds to step 860.

  In step 860, the CPU 81 stores “1” as the value of the deterioration level reduction operation switching flag XREC. Thereafter, the CPU 81 proceeds to step 895 to end the present routine tentatively.

  At this time, when the CPU 81 starts the process from step 900 in FIG. 9 and proceeds to step 910 at a predetermined timing, the current value of the catalyst deterioration flag XCD is “1”. It is determined as “No” and the process proceeds to Step 970.

  Then, since the value of the deterioration level reduction operation switching flag XREC at the present time is “1”, the CPU 81 makes a “No” determination at step 970 to proceed to step 990. In step 990, the CPU 81 stores the lean air-fuel ratio lean in the upstream target air-fuel ratio abyfr (k).

  Next, the CPU 81 sequentially executes the processing of step 930 to step 960 following step 990, proceeds to step 995, and once ends this routine. By these processes, the fuel of the final fuel injection amount Fi is injected into the fuel injection cylinder. As a result, the “lean operation” in which the upstream target air-fuel ratio abyfr is set to the lean air-fuel ratio lean is started.

  Further, the CPU 81 executes the routine shown in FIG. 10 and the routine shown in FIG. As a result, the catalyst upstream air-fuel ratio abyfs coincides with the lean air-fuel ratio lean as in the case where the rich operation is performed. That is, the lean operation is continued.

  When the lean operation is continued, the sulfur component present on the catalyst component CC of the catalyst 53 is released into the exhaust gas as time passes. Note that oxygen contained in the exhaust gas is stored in the oxygen storage material OSM of the catalyst 53 as time elapses while the lean operation is being performed. During the period in which oxygen is stored in the oxygen storage material OSM, even if the catalyst upstream air-fuel ratio abyfs is the lean air-fuel ratio lean, the catalyst downstream air-fuel ratio oxs is substantially the stoichiometric air-fuel ratio stoich.

  Further, during the period in which the lean operation is being executed, the CPU 81 executes an “intake air amount integration routine” (not shown) to thereby introduce the intake air amount Ga introduced into the engine 10 from the time when the lean operation is started to the present time. Is accumulated. Thereby, the CPU 81 obtains the integrated amount Galsum of the intake air amount Ga.

  When the CPU 81 starts the process from step 800 in FIG. 8 at a predetermined timing during the period in which the lean operation is being executed, the process proceeds to step 820 after step 810. Since the value of the deterioration level reduction operation switching flag XREC at present is “1”, the CPU 81 makes a “No” determination at step 820 to proceed to step 850.

  At this time, if the current integrated amount Galsum is smaller than the threshold integrated amount Galsumth (that is, if it is not determined that substantially all of the sulfur component present on the catalyst component CC has been released into the exhaust gas), the CPU 81 In step 850, it is determined as “Yes”, the process proceeds to step 895 via step 860, and this routine is temporarily ended. As a result, as described above, the processes shown in the routines of FIGS. 9 to 11 are executed, so that the lean operation is continued.

  On the other hand, if the current integrated amount Galsum is equal to or greater than the threshold integrated amount Galsumth (that is, if it is determined that substantially all of the sulfur component present on the catalyst component CC has been released into the exhaust gas), the CPU 81 In step 850 of FIG.

  In step 870, the CPU 81 stores “0” in the value of the catalyst deterioration flag XCD and proceeds to step 880.

  Next, in step 880, the CPU 81 stores “0” in the value of the deterioration level reduction operation switching flag XREC, and proceeds to step 890.

  Next, in step 890, the CPU 81 sets (resets) the value of the integrated amount Galsum to zero. Thereafter, the CPU 81 proceeds to step 895 to end the present routine tentatively.

  As a result, when the CPU 81 starts the process from step 900 in FIG. 9 at a predetermined timing and proceeds to step 910, the value of the catalyst deterioration flag XCD at the present time is “0”. And go to step 920. In step 920, the CPU 81 sets the theoretical air-fuel ratio stoich to the upstream target air-fuel ratio abyfr (k). Next, the CPU 81 executes the processes of Step 930 to Step 960 in order. As a result, the lean operation is stopped and the “normal operation” is resumed.

  Thus, when the deterioration degree Ke of the catalyst 53 is equal to or greater than the threshold deterioration degree Keth when the normal operation is being performed, if the output value Voxs of the downstream oxygen concentration sensor 77 is equal to or less than the output value Voxsstoich (that is, If the catalyst downstream air-fuel ratio oxs is a lean air-fuel ratio lean), the rich operation is started. Further, the rich operation is continued until the catalyst downstream air-fuel ratio oxs becomes the rich air-fuel ratio rich. Then, when the catalyst downstream air-fuel ratio oxs becomes the rich air-fuel ratio rich (that is, when the output value Voxs becomes larger than the output value Voxsstoich), the lean operation is started. Thereafter, when exhaust gas having a threshold integrated amount Galsumth flows into the catalyst 53, the lean operation is stopped and the normal operation is resumed. As a result, the degree of deterioration Ke of the catalyst 53 is reduced.

(Case 2-2) When the output value Voxs is larger than the output value Voxsstoich In this case, after the catalyst deterioration flag XCD is set to “1” by the routine of FIG. When the process is started from step 800 in FIG. 8, the process proceeds to step 830 via step 810 and step 820. In this case, the CPU 81 makes a “No” determination at step 830 to proceed to step 850.

  Since the value of the integrated amount Galsum at the present time is an initial value (zero), the CPU 81 determines “Yes” in step 850 and proceeds to step 860. In step 860, the CPU 81 stores “1” in the value of the deterioration level reduction operation switching flag XREC, proceeds to step 895, and once ends this routine.

  At this time, when the CPU 81 starts the processing from step 900 in FIG. 9 at a predetermined timing and proceeds to step 910, the value of the catalyst deterioration flag XCD at the present time is “1”. ”And the process proceeds to Step 970. Further, since the value of the deterioration level reduction operation switching flag XREC at the present time is “1”, the CPU 81 makes a “No” determination at step 970 to proceed to step 990.

  In step 990, the CPU 81 stores the lean air-fuel ratio lean in the upstream target air-fuel ratio abyfr (k), and then executes steps 930 to 960 in order. Thereby, as described above, the “lean operation” is started.

  Then, as described above, the CPU 81 continues the lean operation until the integrated amount Galsum of the intake air amount becomes equal to or greater than the threshold integrated amount Galsumth. Furthermore, when the integrated amount Galsum becomes equal to or greater than the threshold integrated amount Galsumth, the CPU 81 stops the lean operation and restarts the “normal operation”.

  Thus, when the deterioration degree Ke of the catalyst 53 is equal to or greater than the threshold deterioration degree Keth during normal operation, if the output value Voxs of the downstream oxygen concentration sensor 77 is greater than the output value Voxsstoich (that is, the catalyst If the downstream air-fuel ratio oxs is rich), the lean operation is started without performing the rich operation. Thereafter, when exhaust gas having a threshold integrated amount Galsumth flows into the catalyst 53, the lean operation is stopped and the normal operation is resumed. As a result, the degree of deterioration Ke of the catalyst 53 is reduced.

  As described above, the first device performs normal operation when the deterioration degree Ke of the catalyst 53 is smaller than the threshold deterioration degree Keth, as described in case 1 and case 2 separately. On the other hand, when the deterioration degree Ke of the catalyst 53 is equal to or higher than the threshold deterioration degree Keth, the first device performs “operation for reducing the deterioration degree Ke”. Specifically, if the output value Voxs of the downstream oxygen concentration sensor 77 is equal to or lower than the output value Voxsstoich, the first device performs the lean operation “after” the rich operation. On the other hand, if the output value Voxs of the downstream oxygen concentration sensor 77 is larger than the output value Voxsstoich, the first device performs the lean operation without performing rich operation. Thereby, the first device can discharge the sulfur component occluded in the oxygen occlusion material OSM and the sulfur component adsorbed in the catalyst component CC into the exhaust gas in “the entire catalyst 53”. As a result, the deterioration degree Ke of the catalyst 53 is appropriately reduced.

(Second Embodiment)
Next, a control device (hereinafter also referred to as “second device”) according to a second embodiment of the present invention will be described.

<Outline of device>
The second device is applied to an engine having the same configuration as the engine 10 to which the first device is applied (see FIG. 1, hereinafter referred to as “the engine 10” for convenience). Therefore, the description of the outline of the device to which the second device is applied is omitted.

<Outline of device operation>
Hereinafter, an outline of the operation of the second device applied to the engine 10 will be described.
Similar to the first device, the second device acquires the deterioration degree Ke of the catalyst 53 during normal operation. When the deterioration degree Ke at a predetermined time point is equal to or higher than the predetermined threshold deterioration degree Keth, the second device determines the deterioration degree according to the “catalyst downstream air-fuel ratio oxs” and the “catalyst temperature TempC” at that time point. Operate to reduce Ke. That is, the second device is different from the first device in that it performs an operation for reducing the deterioration degree Ke in consideration of not only “catalyst downstream air-fuel ratio oxs” but also “catalyst temperature TempC”.

  More specifically, the second device reduces the deterioration degree Ke similar to that of the first device only when the temperature TempC of the catalyst is “not included” in a predetermined temperature range (T1 ≦ TempC <T3). Control for. That is, in the second apparatus, the temperature TempC of the catalyst is a temperature outside the above temperature range (in this example, the temperature included in T3 ≦ TempC ≦ T2 is adopted), and the catalyst at the predetermined time point is used. When the downstream air-fuel ratio oxs is “theoretical air-fuel ratio stoich” or “lean air-fuel ratio lean”, the catalyst downstream air-fuel ratio oxs is set to “rich operation” where the catalyst upstream air-fuel ratio abyfs is set to “rich air-fuel ratio rich”. After the operation is performed until the air-fuel ratio becomes rich, a “lean operation” is performed in which the air-fuel ratio abyfs upstream of the catalyst is set to the lean air-fuel ratio lean. On the other hand, when the temperature TempC of the catalyst is outside the temperature range, the second device performs the rich operation if the catalyst downstream air-fuel ratio oxs at the predetermined time is the rich air-fuel ratio rich. The lean operation is performed without performing the above operation.

  Further, as with the first device, the second device stops the lean operation when the integrated amount Galsum of the intake air amount Ga during the period in which the lean operation is performed becomes equal to or greater than a predetermined threshold integrated amount Galsumth. Thereafter, the second device resumes normal operation. The above is the outline of the operation of the second device.

<Acquisition method of catalyst degradation degree>
The second device acquires the deterioration degree Ke of the catalyst 53 by the same method as the first device. Therefore, the description of the method for obtaining the deterioration degree Ke of the catalyst 53 in the second device is omitted.

<Method for reducing the degree of catalyst degradation>
Based on the same idea as the first device, the second device reduces the deterioration degree Ke of the catalyst 53 by “performing lean operation after performing rich operation” or “performing lean operation”. However, as shown in the characteristics (2) and (3) of the catalyst 53 described above, the temperature at which the sulfur component stored in the oxygen storage material OSM is efficiently moved toward the catalyst component CC (the first temperature T1 or higher). The temperature at which the second temperature T2 or lower) and the sulfur component present on the catalyst component CC are efficiently released into the exhaust gas (third temperature T3 or higher) may not match.

  Specifically, when the temperature TempC of the catalyst is included in “a temperature range that is equal to or higher than the first temperature T1 and lower than the third temperature T3”, the sulfur component stored in the oxygen storage material OSM by the rich operation is the catalyst. Even if moved toward the component CC, the sulfur component present on the catalyst component CC by lean operation (including both the sulfur component transferred from the oxygen storage material and the sulfur component adsorbed on the catalyst component) .) Is not efficiently released into the exhaust gas (see FIG. 5). Therefore, the second device pays attention to the relationship between the “air-fuel ratio of exhaust gas”, the “temperature of the catalyst”, and the “behavior of the sulfur component” among the characteristics (1) to (4) of the catalyst 53 described above. Operation for reducing the degree of deterioration Ke of 53 is performed.

  Specifically, in the second device, when the deterioration degree Ke of the catalyst 53 is equal to or higher than a predetermined threshold deterioration degree Keth, the temperature TempC of the catalyst is “the first temperature T1 or higher and lower than the third temperature T3. If it is not included in the “temperature range (T1 ≦ TempC <T3)”, the following operation (a) or (b) is performed according to the catalyst downstream air-fuel ratio oxs. The following operation (a) is the same as the operation (a) in the first device, and the following operation (b) is the same as the operation (b) in the first device.

(A) When the catalyst downstream air-fuel ratio oxs is “theoretical air-fuel ratio stoich” or “lean air-fuel ratio lean”, the second device first sets the catalyst upstream air-fuel ratio abyfs to “rich air-fuel ratio rich”. Perform “rich operation”. The second device continues this rich operation until the downstream air-fuel ratio oxs of the catalyst becomes the rich air-fuel ratio rich. Next, after the catalyst downstream air-fuel ratio oxs becomes rich air-fuel ratio rich, the second device performs “lean operation” in which the catalyst upstream air-fuel ratio abyfs is set to the lean air-fuel ratio lean.
(B) When the catalyst downstream air-fuel ratio oxs is the rich air-fuel ratio rich, the second device performs the lean operation without performing the rich operation.

  In this example, from the viewpoint of efficiently removing the sulfur component adsorbed and stored in the catalyst 53, the temperature of the catalyst not included in the temperature range (T1 ≦ TempC <T3) is “the third temperature T3 or more and A temperature included in a temperature range (T3 ≦ TempC ≦ T2) that is equal to or lower than the second temperature T2 ”is employed. When the temperature TempC of the catalyst 53 is included in this temperature range (T3 ≦ TempC ≦ T2), the sulfur component stored in the oxygen storage material OSM can be efficiently moved toward the catalyst component CC, and the catalyst component This is because the sulfur component on the CC can be efficiently released into the exhaust gas (see FIG. 5).

  Furthermore, as with the first device, the second device continues the lean operation until the integrated amount Galsum of the intake air amount Ga during the lean operation is equal to or greater than a predetermined threshold integrated amount Galsumth. Then, after the integrated amount Galsum becomes equal to or greater than the threshold integrated amount Galsumth, the second device stops the lean operation and resumes the normal operation. The above is the method for reducing the deterioration degree Ke of the catalyst 53 in the second device.

<Air-fuel ratio control>
The second device controls the air-fuel ratio of the exhaust gas by the same method as the first device, and performs normal operation, rich operation, and lean operation. Therefore, the description of the air-fuel ratio control in the second device is omitted.

<Actual operation>
Hereinafter, the actual operation of the second device will be described.
In the second device, the CPU 81 is configured to repeatedly execute each routine shown in the flowcharts of FIGS. 6 and 8 to 12 at predetermined timings. In these routines, the CPU 81 uses the catalyst deterioration flag XCD and the deterioration degree reduction operation switching flag XREC similar to those in the first device.

Hereinafter, each routine executed by the CPU 81 will be described.
The second device is different from the first device only in that the CPU 81 executes the flowchart shown in FIG. 12 instead of the flowchart shown in FIG. Therefore, the following description will be added focusing on this difference.

  Similar to the first device, the CPU 81 repeatedly executes the routine of FIG. 6 every time a predetermined time elapses. That is, the second device acquires (estimates) the temperature of the catalyst temperature TempC based on the exhaust gas temperature Tex.

  Further, the CPU 81 repeatedly executes the “second deterioration degree acquisition routine” shown by the flowchart in FIG. 12 every time a predetermined time elapses. The CPU 81 acquires the deterioration degree Ke of the catalyst 53 by this routine. The routine shown in FIG. 12 is different from the routine shown in FIG. 7 only in that step 1210 and step 1220 are included. Therefore, in FIG. 12, steps for performing the same processing as the steps shown in FIG. 7 are denoted by the same reference numerals as those given to such steps in FIG. 7. Detailed description of these steps will be omitted as appropriate.

  The routine of FIG. 12 will be specifically described. When the CPU 81 starts processing from step 1200 of FIG. 12 at a predetermined timing, the CPU 81 proceeds to step 710. If the current value of the catalyst deterioration flag XCD is “0”, the CPU 81 determines “Yes” in step 710 and proceeds to step 720.

  If the “deterioration degree determination condition” described above is satisfied at this point, the CPU 81 makes a “Yes” determination at step 720, sequentially executes the processing of step 730 and step 740, and determines the deterioration degree Ke of the catalyst 53. To get. Next, the CPU 81 proceeds to step 750.

  If the current deterioration degree Ke is equal to or greater than the threshold deterioration degree Keth, the CPU 81 determines “Yes” in step 750 and proceeds to step 1210. In step 1210, the CPU 81 determines whether or not the temperature TempC of the catalyst 53 is equal to or higher than the first temperature T1 and is included in a temperature range lower than the third temperature T3. If the current temperature TempC of the catalyst is “included” in this temperature range, the CPU 81 makes a “Yes” determination at step 1210 to proceed to step 1295 to end the present routine tentatively.

  At this time, when the CPU 81 starts the process from step 800 in FIG. 8 at a predetermined timing, the value of the catalyst deterioration flag XCD at the present time is “0”, so that “No” is determined in step 810 and the step is performed. Proceed to step 895 to end the present routine tentatively.

  Further, when the CPU 81 starts processing from step 900 in FIG. 9 at a predetermined timing, it determines “Yes” in step 910 and proceeds to step 920 to set the stoichiometric air-fuel ratio to the upstream target air-fuel ratio abyfr (k). Set stoich. Thereafter, the CPU 81 sequentially executes the processing of step 930 to step 960 following step 920. Thereby, “normal operation” is performed. That is, the operation (rich operation or lean operation) for reducing the deterioration degree Ke of the catalyst 53 is not performed.

  As described above, even when the deterioration degree Ke of the catalyst 53 is equal to or higher than the threshold deterioration degree Keth, when the catalyst temperature TempC is “included” in the temperature range (T1 ≦ TempC <T3), the deterioration degree Ke of the catalyst 53 is determined. There is no driving to reduce.

  On the other hand, when the current temperature TempC of the catalyst is “not included” in the temperature range (T1 ≦ TempC <T3), the CPU 81 starts the process from step 1200 in FIG. 12 and goes through steps 710 to 750. In step 1210, “No” is determined in step 1210, and the process proceeds to step 1220.

  In step 1220, the CPU 81 determines whether or not the temperature TempC of the catalyst 53 is within a temperature range that is equal to or higher than the third temperature T3 and equal to or lower than the second temperature T2. If the current temperature TempC of the catalyst is “not included” in this temperature range, the CPU 81 makes a “No” determination at step 1220 to proceed to step 1295 to end the present routine tentatively. In this case, as described above, the operation for reducing the deterioration degree Ke of the catalyst 53 is not executed. On the other hand, if the current temperature TempC of the catalyst is “included” in this temperature range, the CPU 81 makes a “Yes” determination at step 1220 to proceed to step 760. In step 760, the CPU 81 sets “1” as the value of the catalyst deterioration flag XCD, proceeds to step 1295, and once ends this routine. Hereinafter, the description will be continued assuming that the current temperature TempC of the catalyst is “included” in this temperature range.

  According to the above assumption, when the CPU 81 starts processing from step 800 in FIG. 8 at a predetermined timing and proceeds to step 810, it determines “Yes” at step 810. And CPU81 performs the process of step 820-step 890 similarly to a 1st apparatus. Furthermore, when the CPU 81 starts processing from step 900 in FIG. 9 at a predetermined timing and proceeds to step 910, the CPU 81 determines “Yes” in step 910. And CPU81 performs the process of step 920-step 990 similarly to a 1st apparatus. In addition, the second device executes the routines of FIGS. 10 and 11 in the same manner as the first device. As a result, an operation (rich operation or lean operation) for reducing the deterioration degree Ke of the catalyst 53 is executed in accordance with the catalyst downstream air-fuel ratio oxs.

  As described above, the second device performs “normal operation” when the deterioration degree Ke of the catalyst 53 is smaller than the threshold deterioration degree Keth. On the other hand, if the deterioration degree Ke of the catalyst 53 is equal to or higher than the threshold deterioration degree Keth, the second device deteriorates if the catalyst temperature TempC is “included” in a predetermined temperature range (T1 ≦ TempC <T3). Do not operate to reduce the degree Ke. On the other hand, when the deterioration degree Ke of the catalyst 53 is equal to or higher than the threshold deterioration degree Keth, the second device has the temperature TempC of the catalyst “not included in the temperature range” (in this example, T3 If the temperature is within the temperature range of ≦ TempC ≦ T2, “rich operation” or “lean operation”, which is an operation for reducing the degree of deterioration Ke, is performed.

  Specifically, if the output value Voxs of the downstream oxygen concentration sensor 77 is equal to or lower than the output value Voxsstoich, the second device performs the lean operation “after” the rich operation. On the other hand, if the output value Voxs of the downstream oxygen concentration sensor 77 is larger than the output value Voxsstoich, the second device performs the lean operation without performing the rich operation. Thereby, the second device can discharge the sulfur component occluded in the oxygen occlusion material OSM and the sulfur component adsorbed in the catalyst component CC in the “whole catalyst 53” into the exhaust gas. As a result, the deterioration degree Ke of the catalyst 53 is appropriately reduced.

  By the way, as is apparent from the description of the first device and the second device described above, the catalyst deterioration flag XCD is maintained during the period when the operation (rich operation or lean operation) for reducing the deterioration degree Ke of the catalyst 53 is performed. The value is maintained at “1”. Therefore, in both the first device and the second device, when the CPU 81 starts processing from step 700 in FIG. 7 and proceeds to step 710 during that period, it determines “No” in step 710, and step Proceed directly to 795 to end the present routine tentatively. That is, it is prohibited to acquire the deterioration degree Ke of the catalyst 53 during this period.

  This is because the air-fuel ratio of the exhaust gas is changed when the deterioration degree Ke is acquired (see FIG. 4), and therefore the operation for reducing the deterioration degree Ke by the air-fuel ratio control for acquiring the deterioration degree Ke ( This is to avoid hindering (rich operation or lean operation).

  When the operation for reducing the deterioration degree Ke of the catalyst 53 is completed, the value of the catalyst deterioration flag XCD is set to “0” again (see step 870 in FIG. 8), so the deterioration degree Ke is set. Acquisition (step 730 in FIG. 7) is again possible.

<Summary of Embodiment>
As described above, the control devices (first device and second device) according to each embodiment of the present invention are:
Catalyst 53 having catalyst 53 component CC and oxygen storage material OSM;
Downstream oxygen concentration acquisition means 77 for acquiring a downstream oxygen concentration oxs which is the oxygen concentration of the gas discharged from the catalyst 53;
It is applied to the internal combustion engine 10 having

This controller is
Catalyst deterioration degree acquisition means (see FIGS. 7 and 12) for acquiring the deterioration degree Ke of the catalyst 53, and catalyst deterioration degree reduction means (see FIGS. 8 to 11) for reducing the deterioration degree Ke of the catalyst 53. And).

This catalyst deterioration degree reducing means is:
When the deterioration degree Ke of the catalyst 53 is equal to or greater than a predetermined threshold value Keth (when it is determined “Yes” in step 750 of FIG. 7),
(A) The downstream oxygen concentration oxs is “a reference oxygen concentration (corresponding to the stoichiometric air-fuel ratio stoich in each of the above embodiments) that is an oxygen concentration of a gas generated when air and fuel burn at a stoichiometric air-fuel ratio. If it is “same” or “an oxygen concentration lean on the lean side of the reference oxygen concentration stoich” (if it is determined “Yes” in step 830 in FIG. 8), the oxygen concentration of the gas introduced into the catalyst 53 In the rich operation in which the upstream oxygen concentration abyfs is richer than the reference oxygen concentration stoich (see step 980 in FIG. 9), the downstream oxygen concentration is richer than the reference oxygen concentration stoich. 8 until the oxygen concentration rich on the side is reached (until “No” is determined in step 830 in FIG. 8), the upstream oxygen concentration abyfs is set to the lean oxygen concentration lean relative to the reference oxygen concentration stoich. Lean to Rolling performed (see step 990 of FIG. 9.), And,
(B) If the downstream oxygen concentration oxs is richer than the reference oxygen concentration stoich, the lean operation is performed.
It is like that.

Furthermore, in the control device (second device) according to the second embodiment of the present invention,
The catalyst 53 includes
When the temperature of the catalyst 53 is “the first temperature T1 or more and the second temperature T2 or less”, and the upstream oxygen concentration abyfs is richer than the reference oxygen concentration stoich, the oxygen storage material The sulfur component occluded in the OSM moves toward the catalyst component CC (see the above characteristic (2)), and
When the temperature of the catalyst 53 is “second temperature T3 or more” between the first temperature T1 and the second temperature T2, the upstream oxygen concentration abyfs is leaner than the reference oxygen concentration stoich. In the case of lean, the sulfur component present on the catalyst component CC is released into the gas (see the above characteristic (3)), which is the catalyst 53.

At this time, the catalyst deterioration degree reducing means is
The rich operation is performed when the temperature of the catalyst 53 is “above the first temperature T1 and lower than the second temperature T3” (when it is determined “Yes” in step 1210 of FIG. 12). Not like that.

Furthermore, in the control device (first device and second device) of each of the above embodiments,
The catalyst deterioration degree acquisition means includes
The deterioration degree Ke is acquired based on the maximum amount Cmax of oxygen that can be stored in the catalyst 53 (see step 730 and step 740 in FIG. 7).

  The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention.

  For example, in the control device of the present invention, the catalyst deterioration degree reducing means may be configured to adjust the rich air-fuel ratio rich and the lean air-fuel ratio lean in accordance with the magnitude of the deterioration degree Ke.

  For example, the catalyst deterioration degree reducing means reduces the rich air-fuel ratio rich so that the rich air-fuel ratio rich moves away from the stoichiometric air-fuel ratio stoich toward the rich side as the deterioration degree Ke increases (that is, the air-fuel ratio of the exhaust gas decreases). Can be configured to adjust.

Specifically, the catalyst deterioration degree reducing means is:
The first upstream oxygen concentration, which is the upstream oxygen concentration abyfs when the rich operation is performed when the deterioration degree Ke is the “first value”, is that the deterioration degree Ke is “from the first value”. Is the same as the second upstream oxygen concentration, which is the upstream oxygen concentration abyfs, or the richer oxygen concentration than the second upstream oxygen concentration when the rich operation is performed. It can be configured to be.

  Further, for example, the catalyst deterioration degree reducing means is configured so that the lean air-fuel ratio lean is separated from the stoichiometric air-fuel ratio stoich toward the lean side as the deterioration degree Ke is increased (that is, the air-fuel ratio of the exhaust gas is increased). Can be configured to adjust lean.

Specifically, the catalyst deterioration degree reducing means is:
The third upstream oxygen concentration, which is the upstream oxygen concentration abyfs when the lean operation is performed when the deterioration degree Ke is the “third value”, is that the deterioration degree Ke is “from the third value”. Is the same as the fourth upstream oxygen concentration or the leaner oxygen concentration than the fourth upstream oxygen concentration, which is the upstream oxygen concentration abyfs when the lean operation is performed. It can be configured to be.

  As described above, by adjusting the rich air-fuel ratio rich or the lean air-fuel ratio lean, the sulfur component adsorbed and stored in the catalyst 53 can be more efficiently removed.

  Furthermore, the control device of the present invention can be configured not to perform (inhibit) the rich operation when the temperature TempC of the catalyst 53 is lower than the activation temperature T0. This is because when the temperature TempC of the catalyst 53 is lower than the activation temperature T0, the exhaust gas purification rate is smaller than when the temperature TempC of the catalyst 53 is equal to or higher than the activation temperature T0.

  Furthermore, the control device of the present invention can be configured to decrease the throttle valve opening TA when executing the rich operation and to increase the throttle valve opening TA when performing the lean operation. Thereby, when the rich operation or the lean operation is executed, the output torque is prevented from greatly fluctuating, and the drivability is prevented from being lowered.

  Further, the first device and the second device are configured to continue the lean operation until the cumulative amount Galsum of the intake air amount during the period during which the lean operation is being performed becomes equal to or greater than the threshold cumulative amount Galsumth. However, the control device of the present invention can be configured to stop the lean operation according to the operating state of the engine 10 regardless of the magnitude of the integrated amount Galsum. For example, the lean operation can be stopped when the temperature TempC of the catalyst 53 is lower than a predetermined temperature, or when the temperature THW of the cooling water is lower than the predetermined temperature.

  In addition, as described above, the control device of the present invention determines whether or not the sulfur component has been sufficiently removed from the catalyst 53 based on the integrated amount Galsum of the intake air amount during the period in which the lean operation is being performed. is doing. However, the control device of the present invention is configured to determine whether or not the sulfur component has been sufficiently removed from the catalyst 53 based on a predetermined parameter related to the amount of the sulfur component adsorbed and stored in the catalyst 53. obtain.

  Further, the first device and the second device are applied to an engine (spark ignition type engine) provided with a three-way catalyst. However, the control device of the present invention can be applied to an engine (for example, a diesel engine) provided with a NOx storage reduction catalyst.

  Furthermore, the first device and the second device comprise only one catalyst. However, the control device of the present invention can be applied to an engine including a plurality of catalysts.

  Further, the first device and the second device perform the lean operation by setting the upstream target air-fuel ratio abyfr to the lean air-fuel ratio lean. Here, the control device of the present invention may be configured to execute a “fuel cut operation” as the lean operation.

  Further, the first device and the second device calculate the deterioration degree Ke of the catalyst 53 based on the maximum oxygen storage amount obtained according to the above formulas (1) to (3) (see FIG. 4). . However, the method by which the control device of the present invention acquires the degree of deterioration of the catalyst is not limited to this method. For example, the control device of the present invention can be configured to calculate the degree of deterioration of the catalyst based on the amount of sulfur component adsorbed and stored in the catalyst.

  Further, the second device performs an operation for reducing the deterioration degree Ke of the catalyst 53 when the temperature TempC of the catalyst is included in a predetermined temperature range (T3 ≦ TempC ≦ T2) (FIG. (See 12 step 1220). However, in the control device of the present invention, even when the temperature TempC of the catalyst is not included in this temperature range (T3 ≦ TempC ≦ T2), the operation for reducing the deterioration degree Ke of the catalyst 53 is executed. May be. For example, the control device of the present invention can be configured to execute a routine in which step 1220 is deleted from the routine of FIG. 12 instead of the routine of FIG.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 34 ... Injector, 52 ... Intake pipe, 53 ... Catalyst, 76 ... Upstream oxygen concentration sensor, 77 ... Downstream oxygen concentration sensor, 80 ... Electronic control unit

Claims (5)

A catalyst through which a gas discharged from a combustion chamber of an internal combustion engine passes, having a catalyst component and an oxygen storage material, purifying the gas introduced from the upstream side of the catalyst, and removing the gas downstream of the catalyst A catalyst discharged from the side,
Downstream oxygen concentration acquisition means for acquiring a downstream oxygen concentration that is an oxygen concentration of gas discharged from the catalyst;
Applied to an internal combustion engine with
A catalyst deterioration degree acquisition means for acquiring a deterioration degree of the catalyst;
A catalyst deterioration degree reducing means for reducing the deterioration degree of the catalyst, wherein the deterioration degree of the catalyst is a predetermined threshold value or more;
If the downstream oxygen concentration is the same as the reference oxygen concentration which is the oxygen concentration of the gas generated when air and fuel are burned at the stoichiometric air-fuel ratio, or if the oxygen concentration is leaner than the reference oxygen concentration, the catalyst In the rich operation in which the upstream oxygen concentration that is the oxygen concentration of the gas introduced into the gas is richer than the reference oxygen concentration, the downstream oxygen concentration is richer than the reference oxygen concentration. And performing a lean operation in which the upstream oxygen concentration is set to an oxygen concentration leaner than the reference oxygen concentration, and
If the downstream oxygen concentration is richer than the reference oxygen concentration, the catalyst deterioration degree reducing means for performing the lean operation;
A control device for purifying exhaust gas of an internal combustion engine comprising: The control device according to claim 1,
The catalyst is
When the upstream oxygen concentration is an oxygen concentration richer than the reference oxygen concentration when the temperature of the catalyst is not lower than the first temperature and not higher than the second temperature, the sulfur component stored in the oxygen storage material is Moving towards the catalyst component, and
When the temperature of the catalyst is equal to or higher than a third temperature between the first temperature and the second temperature, the upstream oxygen concentration is an oxygen concentration leaner than the reference oxygen concentration. When the sulfur component present in the catalyst is released into the gas,
The catalyst deterioration degree reducing means is:
A control device for purifying exhaust gas of an internal combustion engine, wherein the rich operation is not performed when the temperature of the catalyst is equal to or higher than the first temperature and lower than the third temperature. In the control device according to claim 1 or 2,
The catalyst deterioration degree reducing means is:
The first upstream oxygen concentration, which is the upstream oxygen concentration when the rich operation is performed when the deterioration level is the first value, is a second value in which the deterioration level is smaller than the first value. The internal combustion engine is configured to be the same as the second upstream oxygen concentration that is the upstream oxygen concentration when the rich operation is performed or the richer oxygen concentration than the second upstream oxygen concentration. Control device for engine exhaust purification. In the control device according to any one of claims 1 to 3,
The catalyst deterioration degree reducing means is:
The fourth upstream oxygen concentration, which is the upstream oxygen concentration when the lean operation is performed when the deterioration level is the third value, is a fourth value in which the deterioration level is smaller than the third value. When the lean operation is performed, the internal combustion engine is configured to be the same as the fourth upstream oxygen concentration that is the upstream oxygen concentration or a leaner oxygen concentration than the fourth upstream oxygen concentration. Control device for engine exhaust purification. In the control device according to any one of claims 1 to 4,
The catalyst deterioration degree acquisition means includes
A control device for purifying exhaust gas of an internal combustion engine, which acquires the degree of deterioration based on a maximum amount of oxygen that can be stored in the catalyst.

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