WO2013118173A1 - Control device for internal combustion engine - Google Patents

Abstract

This control device for an internal combustion engine acquires the temperature of a catalyst having an oxidation function and provided within the exhaust passage, and acquires the amount of oxidation agent in the exhaust air flowing into the catalyst. The amount of oxidation product formed in the catalyst is estimated on the basis of the acquired temperature and the acquired amount of oxidation agent. When the estimated amount of the oxidation product exceeds a prescribed upper limit value, a recovery control is executed in order to remove the oxidation product. Preferably the oxidation agent is NO₂, and the oxidation product is a noble metal oxide formed by oxidation of a noble metal in the catalyst.

Description

Control device for internal combustion engine

The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine in which a catalyst having an oxidation function is provided in an exhaust passage.

For example, in a compression ignition type internal combustion engine for automobiles, that is, a diesel engine, it is known to install an oxidation catalyst in the exhaust passage for oxidizing and removing HC and CO in the exhaust. This oxidation catalyst not only removes HC and CO, but also raises the temperature of the exhaust gas using reaction heat when reacting with them, and sends higher temperature exhaust gas to another catalyst (such as a NOx catalyst) in the subsequent stage. Also used for.

On the other hand, the noble metal in the oxidation catalyst is oxidized by an oxidant such as NO ₂ contained in the exhaust to form an oxide, and the formation of this oxide reduces the activity of the oxidation catalyst. However, this decrease in activity can be recovered by exposing the catalyst to high temperature or a reducing atmosphere. Such a decrease in activity is apparently reversible deterioration, and should be distinguished from permanent irreversible deterioration such as thermal deterioration.

In connection with this, Patent Document 1 discloses that the oxidation performance of the oxidation catalyst decreases due to contact with SOx contained in the exhaust gas.

By the way, when the performance of the oxidation catalyst is deteriorated due to the oxidant contained in the exhaust gas, it is necessary to execute processing for recovering the performance at an early stage in order to prevent the deterioration of the exhaust emission thereafter.

However, in the past, it was difficult to accurately grasp the time when the performance of the oxidation catalyst deteriorated, and therefore it was difficult to determine an appropriate start timing for the recovery process.

Therefore, an object of the present invention is to provide a control device for an internal combustion engine that can accurately grasp the performance deterioration timing of the oxidation catalyst and optimally determine the start timing of the recovery process.

JP 2010-031697 A

According to one aspect of the invention,
A catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine;
First acquisition means for acquiring the temperature of the catalyst;
Second acquisition means for acquiring the amount of oxidant in the exhaust gas flowing into the catalyst;
Estimating means for estimating the amount of oxide formed on the catalyst based on the catalyst temperature obtained by the first obtaining means and the oxidant amount obtained by the second obtaining means;
Recovery control means for executing recovery control for eliminating the oxide when the amount of oxide estimated by the estimation means exceeds a predetermined upper limit;
A control device for an internal combustion engine is provided.

Preferably, the oxidizing agent is NO _2, wherein the oxide, the noble metal in said catalyst is a noble metal oxide formed by oxidation.

Preferably, the estimating means calculates the formation rate of the oxide based on the catalyst temperature and the amount of the oxidant, calculates the thermal decomposition rate of the oxide based on the catalyst temperature, and the formation rate and the The amount of oxide is estimated based on the thermal decomposition rate.

Preferably, the estimation unit calculates the disappearance rate of the oxide during the execution of the recovery control by the recovery control unit, and based on the disappearance rate in addition to the formation rate and the thermal decomposition rate, Estimate the amount of oxide.

Preferably, the control device further includes calculation means for calculating a minimum activation temperature of the catalyst based on the amount of oxide estimated by the estimation means,
The recovery control means executes the recovery control when the minimum activation temperature calculated by the calculation means exceeds an upper limit corresponding value corresponding to the upper limit value,
The recovery control means executes the recovery control during deceleration of the internal combustion engine when the minimum activation temperature calculated by the calculation means is not more than the upper limit corresponding value and exceeds a predetermined threshold value.

Preferably, the recovery control means is such that the minimum activation temperature calculated by the calculation means is not more than the upper limit corresponding value and exceeds the threshold value, and the internal combustion engine is not decelerating and the first acquisition temperature The recovery control is executed when the catalyst temperature acquired by the means falls below a value that is higher than the minimum activation temperature calculated by the calculating means by a predetermined minute value.

Preferably, the control device further includes a temperature increase control means for executing temperature increase control for increasing the temperature of the catalyst,
The temperature increase control means performs the temperature increase control until the catalyst temperature acquired by the first acquisition means exceeds the minimum activation temperature calculated by the calculation means.

Preferably, the recovery control means includes an addition valve for adding a reducing agent containing HC into the exhaust passage, and a glow ignition device for igniting the reducing agent added from the addition valve,
The recovery control means supplies the reducing agent from the addition valve so that HC is adsorbed to the catalyst at the initial stage of the recovery control.

Preferably, the recovery control means operates the glow ignition device simultaneously with the start of the recovery control, and starts supplying the reducing agent from the addition valve before the glow ignition device reaches a predetermined operating temperature.

Preferably, the recovery control means controls the reducing agent from the addition valve so that the air-fuel ratio of the gas flowing into the catalyst becomes richer than the stoichiometry until a predetermined time elapses from the start of operation of the addition valve. Then, the reducing agent is supplied from the addition valve so that the air-fuel ratio of the gas becomes leaner than the stoichiometric ratio.

Preferably, the recovery control means supplies a reducing agent containing HC into the exhaust passage during the execution of the recovery control, and supplies the reducing agent according to the oxide formation rate calculated by the estimating means. Change the amount.

Preferably, the recovery control means supplies a reducing agent containing HC into the exhaust passage during the execution of the recovery control, and the reduction control is performed according to the amount of oxidant in the exhaust obtained by the second acquisition means. The supply amount of the agent is changed.

Preferably, the recovery control means includes an addition valve for adding a reducing agent containing HC into the exhaust passage, and a glow ignition device for igniting the reducing agent added from the addition valve,
The recovery control means ignites the reducing agent added from the addition valve by the glow ignition device during execution of the recovery control and supplies the reducing agent addition amount from the addition valve to the glow ignition device. The lower the exhaust gas temperature is, the more it increases.

Preferably, the control device further includes suppression control means for executing suppression control for suppressing the amount of the oxidant discharged from the cylinder during execution of the recovery control by the recovery control means.

Preferably, the control device further includes diagnostic means for diagnosing whether or not the catalyst has deteriorated irreversibly,
The diagnosis means performs diagnosis immediately after the recovery control is completed.

According to the present invention, it is possible to accurately grasp the time when the performance of the oxidation catalyst is deteriorated and to exhibit the excellent effect of being able to optimally determine the start timing of the recovery process.

It is the schematic of the internal combustion engine which concerns on this embodiment. It is the schematic which shows the formation and disappearance mechanism of a noble metal oxide. It is a time chart which shows the time transition of the amount of noble metal oxides. It is a flowchart which shows the control routine of this embodiment. Engine speed, showing a map representing the in-cylinder injection amount and the NO ₂ content of the relationship. NO ₂ amount shows a map representing the relationship between the catalyst temperature and deposition rate. The map showing the relationship between catalyst temperature and thermal decomposition rate is shown. The map showing the relationship between oxide amount and minimum active temperature is shown. The map showing the relationship between the amount of reducing agents, catalyst temperature, and disappearance rate is shown. It is a figure for demonstrating the calculation method of the amount of reducing agents. Engine speed, a catalyst temperature, is a time chart showing changes in the exhaust NO ₂ amount and a noble metal oxide content. It is a time chart which shows transition of the catalyst temperature in engine operation in another example. It is a flowchart which shows the control routine in 1st other embodiment. The map showing the relationship between the oxide amount in 1st other embodiment and minimum active temperature is shown. It is a time chart of 3rd other embodiment. It is a time chart of the 1st example of 3rd other embodiments. It is a time chart of the 2nd example of 3rd other embodiments. It is a time chart which shows the control method of the fuel addition valve suitable for the 2nd example of 3rd other embodiment. The map showing the relationship between the formation speed and fuel addition amount in 4th other embodiment is shown. It shows a map representing _two amount and the exhaust NO fuel addition amount of the relationship in the fifth alternative embodiment. It is a graph which shows the relationship between the air fuel ratio in 6th other embodiment, CO, and the amount of smoke. It is a graph which shows the relationship between the air fuel ratio in 6th other embodiment, and exhaust temperature.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, it should be noted that the embodiments of the present invention are not limited to the following aspects, and the present invention includes all modifications and applications included in the concept of the present invention defined by the claims. . The dimensions, materials, shapes, relative arrangements, and the like of the constituent elements described in the embodiments are not intended to limit the technical scope of the invention only to those unless otherwise specified.

In the following description, the upstream side is also referred to as “front” and the downstream side is also referred to as “rear”.

FIG. 1 shows a schematic configuration of an internal combustion engine according to the present embodiment. The internal combustion engine (engine) E of the present embodiment is a multi-cylinder compression ignition internal combustion engine, that is, a diesel engine mounted on an automobile. An intake passage 2 and an exhaust passage 3 are connected to an engine body 1 including a cylinder block, a cylinder head, a piston, and the like. An air flow meter 4 is provided upstream of the intake passage 2, and the amount of intake air per unit time is detected by the air flow meter 4.

The engine body 1 has a plurality of cylinders (not shown), and each cylinder is provided with a fuel injection valve for directly injecting fuel into the cylinder, that is, an in-cylinder injection valve 6. Each cylinder is provided with an intake valve and an exhaust valve.

In the middle of the exhaust passage 3, a variable capacity turbocharger 5 is provided. The turbocharger 5 includes a turbine 5T that is driven by exhaust gas and a compressor 5C that is driven by the turbine 5T to increase the intake pressure. A plurality of variable vanes (not shown) for making the flow rate of exhaust gas flowing into the turbine 5T variable and a vane actuator 5A for opening and closing these variable vanes simultaneously are provided at the inlet of the turbine 5T. Yes. An electronically controlled throttle valve 8 is provided in the intake passage 2 on the downstream side of the compressor 5C.

The engine E is also provided with an EGR device 9. The EGR device 9 is for executing EGR (external EGR) for circulating the exhaust gas in the exhaust passage 3 to the intake passage 2. The EGR device 9 includes an EGR passage 9A that connects the exhaust passage 3 and the intake passage 2, and an EGR cooler 9B and an EGR valve 9C that are sequentially provided in the EGR passage 9A from the upstream side.

In the exhaust passage 3 on the downstream side of the turbine 5T, an oxidation catalyst 10 and a NOx catalyst 11 are installed in series in this order from the upstream side. The outlet of the exhaust passage 3 further downstream from the NOx catalyst 11 is opened to the atmosphere via a silencer (not shown).

The oxidation catalyst 10 is a catalyst having an oxidation function that oxidizes and removes hydrocarbons (HC), carbon monoxide (CO), and the like contained in inflowing exhaust gas. The oxidation catalyst 10 is configured by providing a coat layer made of cerium oxide (CeO ₂ ) or the like on the surface of a honeycomb carrier made of ceramic or the like, and dispersing and supporting a large number of noble metal fine particles on the coat layer. Platinum (Pt), palladium (Pd), rhodium (Rh) or the like is used as the noble metal.

The NOx catalyst 11 is composed of, for example, an NOx storage reduction (NSR) catalyst. The NOx catalyst 11 occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust gas is higher than the stoichiometric (theoretical air-fuel ratio, for example, 14.6), and stores the NOx occluded when the air-fuel ratio of the inflowing exhaust gas is less than the stoichiometric. It has the function of releasing and reducing. The NOx catalyst 11 is configured by supporting a noble metal such as platinum Pt as a catalyst component and a NOx absorbing component on the surface of a base material made of an oxide such as alumina Al ₂ O ₃ . The NOx absorbing component is at least one selected from, for example, an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, and a rare earth such as lanthanum La and yttrium Y. It consists of one. The NOx catalyst 11 may be a selective reduction type NOx catalyst (SCR: Selective Catalytic Reduction) capable of continuously reducing NOx in exhaust gas when supplying a reducing agent such as urea.

In addition to the oxidation catalyst 10 and the NOx catalyst 11, a particulate filter (DPF) for collecting fine particles (PM, particulates) such as soot in the exhaust gas may be provided. Preferably, the DPF is of a continuous regeneration type in which a catalyst containing a noble metal is supported and the collected fine particles are continuously burned and removed. Preferably, the DPF is disposed at least downstream of the oxidation catalyst 10. The engine may be a spark ignition type internal combustion engine, that is, a gasoline engine. In this case, it is preferable that a three-way catalyst is provided in the exhaust passage. These DPF catalysts and three-way catalysts also correspond to catalysts having an oxidation function.

In the exhaust passage 3, a burner device 20 is installed on the downstream side of the turbine 5T and the upstream side of the oxidation catalyst 10. The main purpose of the burner device 20 is to raise the temperature of exhaust gas supplied to the oxidation catalyst 10 and the NOx catalyst 11 (particularly, the oxidation catalyst 10 at the most upstream position) on the downstream side. The burner device 20 includes a fuel addition valve 21 and a glow plug 22 as a glow ignition device.

The fuel addition valve 21 injects, supplies or adds liquid fuel F into the exhaust passage 3. As the fuel F, diesel oil, which is a fuel for the engine, is shared, but another type of fuel may be used. The fuel addition valve 21 generally injects the fuel F toward the glow plug 22, and the glow plug 22 ignites or burns the fuel F injected from the fuel addition valve 21 or a mixture of the fuel F and the exhaust gas. The glow plug 22 is disposed at a position downstream of the fuel addition valve 21.

The burner device 20 may include a small oxidation catalyst (not shown) installed in the exhaust passage 3 at a position immediately after the glow plug 22.

Here, the fuel F also functions as a reducing agent containing HC, and the fuel addition valve 21 also functions as an addition valve for adding the reducing agent into the exhaust passage 3. Although details will be described later, when the recovery process of the oxidation catalyst 10 is performed, the fuel F as the reducing agent may be added from the fuel addition valve 21 in some cases.

The engine E is comprehensively controlled by an electronic control unit (hereinafter referred to as ECU) 100 mounted on the vehicle. The ECU 100 inputs and outputs signals to and from a CPU that executes various arithmetic processes related to engine control, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores CPU calculation results, and the like. The input / output port is configured.

In addition to the air flow meter 4 described above, the ECU 100 is connected to a crank angle sensor 31 for detecting the crank angle of the engine and an accelerator opening sensor 32 for detecting the accelerator opening.

ECU100 calculates engine speed (engine speed) Ne based on the output of the crank angle sensor 31. Further, the ECU 100 calculates the intake air amount Ga based on the output of the air flow meter 4. Then, the ECU 100 calculates an engine load (engine load) based on the calculated intake air amount Ga.

In the exhaust passage 3, an upstream exhaust temperature sensor 33 is provided at a position downstream of the turbine 5T and upstream of the burner device 20, and a downstream exhaust temperature sensor 34 is positioned downstream of the burner device 20 and upstream of the oxidation catalyst 10. And an air-fuel ratio sensor 35 is provided. These sensors 33 to 35 are also connected to the ECU 100. In particular, the downstream exhaust temperature sensor 34 and the air-fuel ratio sensor 35 are sensors for detecting the temperature of the gas flowing into the oxidation catalyst 10 and the air-fuel ratio, respectively.

The ECU 100 controls the in-cylinder injection valve 6, the throttle valve 8, the vane actuator 5A, the EGR valve 9C, and the burner device 20 (the fuel addition valve 21 and the glow plug 22) based on the detection values of the sensors.

Here, the basic operation of the burner device 20 will be described. The burner device 20 is used or operated to activate the oxidation catalyst 10 at the most upstream position as soon as possible, mainly during warm-up after a cold start of the engine. On the other hand, even when not warming up, when the temperature of the oxidation catalyst 10 falls below the minimum activation temperature and the oxidation catalyst 10 becomes inactive, the burner device 20 is activated to activate it.

When the burner device 20 is operated, the fuel addition valve 21 and the glow plug 22 are activated (turned on), and the fuel F added from the fuel addition valve 21 or a mixture of this and the exhaust gas is ignited and burned by the glow plug 22. Be made. As a result, a heated gas containing a flame is generated, and the temperature of the exhaust gas is raised by the heated gas. The exhaust gas whose temperature has been raised is supplied to the oxidation catalyst 10 to promote the activation of the oxidation catalyst 10. The burner device 20 can be stopped (turned off) at the same time that the oxidation catalyst 10 is activated.

In addition, when the small oxidation catalyst is provided in the burner device 20, the small oxidation catalyst receives supply of the added fuel F, generates heat, and assists in raising the exhaust gas temperature. The small-sized oxidation catalyst also has a function of reforming the added fuel F and sending the reformed added fuel to the oxidation catalyst 10 to assist the activation of the oxidation catalyst 10.

As described above, the exhaust gas discharged from the cylinder of the engine contains an oxidant. This oxidizing agent includes nitrogen dioxide (NO ₂ ), nitrogen trioxide (NO ₃ ) and oxygen (O ₂ ), of which the oxidizing action of NO ₂ is the most dominant. Therefore oxidizing agent proceed to the following described as a NO _2.

The NO ₂ contained in the exhaust gas oxidizes the noble metal of the oxidation catalyst 10 to form an oxide, and the activity or performance of the oxidation catalyst 10 decreases due to the formation of this oxide.

FIG. 2 schematically shows the mechanism of oxide formation and disappearance when the noble metal is Pt. (A) shows non-oxidized Pt, and a plurality of arms 41 extend from Pt. The tip of the arm 41 is called a site 42, and all the sites 42 are vacant in the illustrated example. This state is represented by Pt_ ^* .

From this state, as shown in (B), when NO ₂ as an oxidant is present in the atmosphere of Pt, oxygen atoms (O) adhere to the tip of the arm 41 and the site 42 is buried. To refer to this state in Pt_O _x. This means that x O is attached to one Pt. As a result, Pt is oxidized, and this oxidized Pt is a Pt oxide, that is, a noble metal oxide.

It is assumed that the Pt atmosphere changes from this state to a reducing atmosphere as shown in (C1) of (C). In the illustrated example, CO as a reducing agent exists around Pt. Then, O attached to the tip of the arm 41 is desorbed and removed and reacts with CO in the atmosphere. As shown in (C2) of (C), the site 42 is emptied, and carbon dioxide (CO ₂ ) is generated in the Pt atmosphere. As a result, Pt is reduced and the oxidation state of Pt is eliminated, and Pt is restored to the original unoxidized state. And Pt oxide disappears.

The mechanism of formation and disappearance of such Pt oxide is expressed by the following reaction formula. First, the formation of Pt oxide is represented by the following reaction formula (1).

Further, the disappearance of Pt oxide due to thermal decomposition is represented by the following reaction formula (2). Here, the thermal decomposition of the Pt oxide refers to a reaction in which O is desorbed from the Pt oxide by the heat applied to the Pt oxide.

Further, the disappearance due to the reduction of the Pt oxide is represented by the following reaction formula (3).

As a result of intensive studies, the present inventor has determined that the amount of noble metal oxide in the oxidation catalyst 10 is the catalyst temperature (bed temperature) of the oxidation catalyst 10 and the amount or concentration of NO _{2 in} the exhaust gas flowing into the oxidation catalyst 10. New knowledge that it depends heavily on

The above three reactions, that is, the formation reaction represented by the reaction formula (1), the thermal decomposition reaction represented by the reaction formula (2), and the reduction reaction represented by the reaction formula (3) all occur simultaneously. The reaction rate of each reaction varies depending on the catalyst temperature and the atmosphere of the noble metal. The balance of these reaction rates determines the amount of noble metal oxide when the final saturation state is reached.

FIG. 3 shows a temporal transition of the amount of noble metal oxide formed in the oxidation catalyst 10 when exhaust gas having a constant NO ₂ concentration is circulated through the oxidation catalyst 10 in which the noble metal is not oxidized in the initial state. Line a is when the catalyst temperature is 300 ° C, line b is when the catalyst temperature is 400 ° C, and line c is when the catalyst temperature is 500 ° C. Here, only the formation reaction and the thermal decomposition reaction occur, and the reduction reaction does not need to be considered.

As shown by the line a, when the catalyst temperature is 300 ° C., the amount of noble metal oxide increases gradually with time and reaches a relatively large amount and saturates.

As shown by the line b, when the catalyst temperature is 400 ° C., the amount of noble metal oxide increases more rapidly with time and reaches a relatively large amount and saturates.

As shown by the line c, when the catalyst temperature is 500 ° C., the amount of the noble metal oxide is saturated in an extremely short time at the beginning of the exhaust circulation, but the saturation amount itself is relatively small.

The reason why the amount of noble metal oxide is saturated in a short time when the catalyst temperature is 400 ° C. is that the rate of the formation reaction and the pyrolysis reaction increases because the catalyst temperature is higher than when the catalyst temperature is 300 ° C. is there. The reason why the amount of noble metal oxide saturates in a shorter time when the catalyst temperature is 500 ° C. is the same as in the case of 400 ° C.

Also, the reason why the saturation amount of the noble metal oxide is smaller when the catalyst temperature is 500 ° C. than when the catalyst temperature is 400 ° C. is that the thermal decomposition reaction rate is relatively dominant over the formation reaction rate.

Based on these results and other test results, the present inventor has obtained the following knowledge.
(1) The formation reaction rate increases as the NO ₂ concentration in the exhaust gas increases.
(2) When the catalyst temperature is 300 ° C. or higher and the oxidation catalyst 10 is exposed to NO ₂ , the formation of noble metal oxide becomes significant.
(3) When the catalyst temperature is 600 ° C. or higher, the thermal decomposition reaction becomes dominant.
(4) If the oxidation catalyst is active, that is, if the catalyst temperature is above the minimum activation temperature, a reduction reaction is possible. In the case of a normal catalyst in which the noble metal is not oxidized and has a low degree of irreversible deterioration, the minimum active temperature is, for example, about 150 ° C.

As described above, when the performance of the oxidation catalyst is deteriorated due to the formation of the noble metal oxide, it is necessary to execute processing for recovering the performance at an early stage in order to prevent the deterioration of the exhaust emission thereafter.

However, in the past, it was difficult to accurately grasp when the performance of the oxidation catalyst deteriorated, and therefore it was difficult to determine an appropriate start timing for the recovery process.

Therefore, in this embodiment, in order to solve this problem, the amount of the noble metal oxide formed on the oxidation catalyst 10 is estimated, and the noble metal oxide disappears when the estimated amount of oxide exceeds a predetermined upper limit value. Execute recovery control. The upper limit value corresponds to the maximum value of the amount of noble metal oxide within which the performance of the oxidation catalyst 10 is within an allowable range. Therefore, by grasping the time when the estimated oxide amount exceeds the upper limit value, it is possible to accurately grasp the performance deterioration time of the oxidation catalyst. It is possible to optimally determine the start timing of recovery processing, that is, recovery control.

In particular, in the present embodiment, based on the above knowledge, the amount of noble metal oxide formed on the oxidation catalyst 10 is estimated based on the catalyst temperature of the oxidation catalyst 10 and the amount of NO _{2 in} the exhaust gas flowing into the oxidation catalyst 10. To do. As a result, the amount of the noble metal oxide can be accurately estimated, the performance deterioration timing of the oxidation catalyst 10 can be accurately grasped, and the recovery control start timing can be accurately determined.

It can be said that the greater the amount of the noble metal oxide in the oxidation catalyst 10, the greater the degree of reversible degradation of the oxidation catalyst 10. Therefore, it can be said that the amount of noble metal oxide is an index value representing the degree of reversible deterioration of the oxidation catalyst 10.

Hereinafter, the control of this embodiment will be described in more detail. FIG. 4 shows a control routine of the present embodiment, which is repeatedly executed by the ECU 100 at every predetermined calculation cycle.

In step S101, the formation rate A, which is the reaction rate of the above-described noble metal oxide formation reaction, is calculated. Here, first, the catalyst temperature Tc of the oxidation catalyst 10 is acquired. The catalyst temperature Tc may be directly detected by a temperature sensor provided in the oxidation catalyst 10, but in the present embodiment, the catalyst temperature Tc is estimated based on the temperature detected by the downstream exhaust temperature sensor 34, the engine operating state, and the like. Thus, the catalyst temperature Tc is acquired by detection or estimation.

Next, the amount M of NO _{2 in} the exhaust gas flowing into the oxidation catalyst 10 is acquired. Here, the detected value of the engine speed Ne is determined according to a map (a function, which may be a function) in which the relationship among the engine speed Ne, the in-cylinder injection amount Q, and the NO ₂ amount M as shown in FIG. Based on the in-cylinder injection amount Q as an instruction value to the in-cylinder injection valve 6, the NO ₂ amount M per calculation cycle is estimated. As described above, the NO ₂ amount is acquired by estimation, but the NO ₂ amount may be detected and acquired by a sensor provided in the exhaust passage, for example.

The in-cylinder injection amount Q as the instruction value is determined according to a predetermined map (not shown) based on the detected value of the engine speed Ne and the detected value of the accelerator opening degree Ac.

Next, according to a map in which the relationship between the NO ₂ amount M, the catalyst temperature Tc and the formation rate A as shown in FIG. 6 is defined in advance, the formation rate is determined based on the acquired catalyst temperature Tc and the estimated NO ₂ amount M. A is calculated. The formation rate A tends to increase as the catalyst temperature Tc increases and as the NO ₂ amount M increases.

Thus, when the calculation of the formation speed A is completed, the process proceeds to step S102. In step S102, a thermal decomposition rate B, which is a reaction rate of the above-described thermal decomposition reaction of the noble metal oxide, is calculated. Here, the pyrolysis rate B is calculated based on the acquired catalyst temperature Tc according to a map that preliminarily defines the relationship between the catalyst temperature Tc and the pyrolysis rate B as shown in FIG. The thermal decomposition rate B tends to increase as the catalyst temperature Tc increases.

Next, in step S103, it is determined whether or not the recovery flag is on. The recovery flag is a flag that is turned on when executing recovery control, which will be described in detail later, and turned off when stopped. If the recovery flag is ON, the disappearance speed C is calculated in step S104, and the process proceeds to step S106. This disappearance speed C will be described later. On the other hand, when the recovery flag is off, the disappearing speed C is set to zero in step S105, and the process proceeds to step S106.

In step S106, based on the calculated formation rate A, thermal decomposition rate B, and disappearance rate C, respectively, the amount of noble metal oxide formed on the oxidation catalyst 10, that is, the oxide amount R is based on the following equation (4). Presumed.

Dt is a calculation cycle. According to this equation, (ABC) is multiplied by the calculation cycle dt to obtain the oxide formation amount per calculation cycle, and the oxide formation amount per calculation cycle is calculated for each calculation cycle (routine execution). The amount of oxide R is calculated every time. If (ABC) is a positive value, an oxide is newly formed in the current calculation cycle, and the oxide amount R increases. On the other hand, if (ABC) is a negative value, the oxide is somewhat lost in the current calculation cycle, and the oxide amount R decreases.

Next, in step S107, the minimum activation temperature T of the oxidation catalyst 10 is calculated or estimated. The minimum activation temperature T refers to the minimum value of the temperatures at which the oxidation catalyst 10 becomes active, in other words, the activation start temperature of the oxidation catalyst 10 in the process of increasing the catalyst temperature. Here, the minimum active temperature T is calculated based on the estimated oxide amount R according to a map that preliminarily defines the relationship between the oxide amount R and the minimum active temperature T as shown in FIG. The minimum active temperature T tends to increase as the amount of oxide R increases. This is because the catalyst activity decreases as the amount of oxide R increases. Thus, there is a correlation between the minimum active temperature T and the oxide amount R.

Next, in step S108, the estimated minimum activation temperature T is compared with a predetermined upper limit value Tmax. This is synonymous with the fact that the oxide amount R corresponding to the minimum active temperature T is compared with the upper limit oxide amount Rmax corresponding to the upper limit value Tmax. As described above, the upper limit oxide amount Rmax corresponds to the maximum value of the noble metal oxide amounts within which the performance of the oxidation catalyst 10 is within the allowable range. The upper limit value Tmax is set to 180 ° C., for example.

When the minimum activation temperature T exceeds the upper limit value Tmax (T> Tmax), recovery control for eliminating the noble metal oxide of the oxidation catalyst 10 is executed in step S109. Specific contents of this recovery control will be described later. In step S110, the recovery flag is turned on, and the routine is terminated.

On the other hand, when the minimum activation temperature T does not exceed the upper limit value Tmax (T ≦ Tmax), it is determined in step S111 whether the recovery flag is on. If the recovery flag is not on (if off), the routine is terminated.

On the other hand, if the recovery flag is ON, the minimum activation temperature T is compared with a predetermined reference value T0 in step S112. As shown in FIG. 8, the reference value T0 corresponds to the minimum activation temperature when the noble metal of the oxidation catalyst 10 is not substantially oxidized. T0 <Tmax and R0 <Rmax. The reference value T0 is set to 150 ° C., for example.

When the minimum activation temperature T is equal to or higher than the reference value T0, the process proceeds to step S109 and recovery control is executed. On the other hand, when the minimum activation temperature T is lower than the reference value T0, the recovery control is stopped in step S113, the recovery flag is turned off in step S114, and the routine is ended.

According to this control routine, the recovery control is immediately started as soon as the minimum activation temperature T exceeds the upper limit value Tmax. Since the recovery flag is turned on, the oxide amount R and the minimum activation temperature T are calculated in consideration of the reduction rate C. Since the recovery control is in progress, the oxide amount R and the minimum activation temperature T gradually decrease. In this lowering process, the recovery flag is still on, and the minimum activation temperature T is equal to or higher than the reference value T0. Therefore, the recovery control is continued and the recovery flag remains on.

When the minimum activation temperature T falls below the reference value T0, the recovery control is stopped and the recovery flag is turned off. That is, once the recovery control is started, the recovery control is continued until the minimum active temperature T falls below the reference value T0, that is, until the oxide amount R decreases below the reference amount R0 corresponding to the reference value T0. Thereby, the noble metal oxide of the oxidation catalyst 10 is almost completely lost simultaneously with the end of the recovery control, and the oxidation catalyst 10 can be recovered or regenerated to the original state before the oxidation.

Here, recovery control is explained. The recovery control is control for disappearing the noble metal oxide of the oxidation catalyst 10, and there are roughly two ways to eliminate this. One is a method in which a gas richer than stoichiometric gas is supplied to the oxidation catalyst 10 to eliminate the noble metal oxide mainly by a reduction reaction. The other is a method in which a high-temperature gas that is leaner than stoichiometric but close to stoichiometric (weakly lean) is supplied to the oxidation catalyst 10 to eliminate the noble metal oxide mainly by a thermal decomposition reaction. The former is called a reduction method and the latter is called a thermal decomposition method. The disappearance due to the reduction method and the disappearance due to the thermal decomposition method are sometimes collectively referred to as disappearance.

First, the reduction method will be described. The first mode is a method using the burner device 20 and is a method employed in the present embodiment.

During execution of the recovery control, the fuel addition valve 21 is turned on, and the fuel F as a reducing agent is added from the fuel addition valve 21 into the exhaust passage 2. At this time, the fuel addition valve 21 is preferably turned on intermittently and the fuel F is intermittently added. The glow plug 22 is continuously turned on, and the added fuel F is ignited and burned by the glow plug 22. The high-temperature heated gas thus generated is mixed with the surrounding exhaust gas and supplied to the oxidation catalyst 10. Since the heated gas contains unburned HC and CO having a stronger reducing action, the noble metal oxide of the oxidation catalyst 10 is suitably reduced. Further, since the high-temperature gas is supplied to the oxidation catalyst 10, the oxidation catalyst 10 is actively heated, and the noble metal oxide is also thermally decomposed. In addition, thermal decomposition by heat of reduction reaction is also expected. The noble metal oxide is preferably eliminated (or removed) by the cooperative action of the reduction reaction and the thermal decomposition reaction.

In this case, the disappearance speed C in step S103 is calculated as follows. That is, based on the acquired catalyst temperature Tc and the separately calculated reducing agent amount F according to a map that predefines the relationship between the reducing agent amount F, the catalyst temperature Tc, and the disappearance rate C as shown in FIG. The disappearance speed C is calculated. The disappearance rate C tends to increase as the catalyst temperature Tc increases and the amount F of the reducing agent increases.

As shown in FIG. 10, the reducing agent amount F is calculated as a value equal to the product of the difference ΔA / F between the exhaust air / fuel ratio A / F detected by the air / fuel ratio sensor 35 and the calculation cycle. In addition, the area of the hatched portion in the figure represents the total amount of supplied reducing agent. The exhaust air-fuel ratio A / F can also be estimated or calculated based on the in-cylinder injection amount Q, the fuel addition amount Z, and the intake air amount Ga that is a substitute value for the exhaust gas flow rate.

As a modification of the first mode, it is possible to create a richer gas than stoichiometric by only adding fuel from the fuel addition valve 21 with the glow plug 22 turned off. In this case, only HC having a reducing power lower than that of CO can be supplied, and there is a concern that the reducing power is reduced particularly when the catalyst temperature is low. However, the reduction itself is possible. Since the glow plug 22 is not used, it can be omitted. At this time, the burner device 20 is not configured.

This first aspect is advantageous in that the reducing agent can be supplied independently of the in-cylinder combustion, but there is a risk of overheating of the oxidation catalyst 10 or the like, there is an upper temperature limit, and there is a risk of occurrence of smoke. There is a drawback.

Next, the second aspect of the reduction method will be described. In this second aspect, instead of supplying the added fuel as the reducing agent into the exhaust passage by the burner device 20, the additional fuel as the reducing agent is supplied into the cylinder by the in-cylinder injection valve 6, and the principle This is similar to the first embodiment.

In this case, additional fuel is injected during the expansion stroke in the cylinder, and the additional fuel is burnt incompletely. This is so-called after injection. According to this, the noble metal oxide of the oxidation catalyst 10 can be eliminated on the same principle as in the first embodiment using the burner device 20. The calculation method of the reduction rate C is the same.

As a modified example of the second aspect, there is a method in which additional fuel is injected in the exhaust stroke in the cylinder and discharged without burning the additional fuel. This is so-called post injection. This is in principle the same as the modification of the first aspect.

The advantages of the second aspect are that an additional device such as the fuel addition valve 21 and the glow plug 22 (or the burner device 20) is not necessary, and that CO having a high reducing power can be supplied. On the other hand, the disadvantages of the second aspect are that the exhaust manifold, the oxidation catalyst 10 and the like may overheat and have an upper temperature limit, that oil dilution may occur due to additional fuel, and that smoke may be generated. There is a point.

As a third aspect of the reduction method, there is a method of supplying reformed fuel into the exhaust passage from a fuel reformer (reformer). This has the advantage that hydrogen (H ₂ ), which has a stronger reducing action than CO, can be supplied, but has the disadvantage that the installation cost of the fuel reformer is high.

Next, the thermal decomposition method will be described. The 1st aspect is a method of using the burner apparatus 20 similarly to the 1st aspect of a reduction method.

In this case as well, during the execution of the recovery control, the fuel addition valve 21 is turned on, and the fuel F as a reducing agent is added from the fuel addition valve 21 into the exhaust passage 2. However, the amount of fuel added is less than in the first embodiment, and the gas flowing into the oxidation catalyst 10 is leaner than stoichiometric and in a weak lean range close to stoichiometric. Then, although a reduction reaction cannot be expected, the temperature of the oxidation catalyst 10 can be raised by the heated gas, and the noble metal oxide can be thermally decomposed. As a result, the noble metal oxide disappears.

In this case, steps S103, S104, and S105 in the control routine of FIG. 4 are omitted. This is because the thermal decomposition rate due to the increase in the catalyst temperature Tc by the recovery control is also calculated in step S102.

As a modification of the first mode, it is possible to add fuel only from the fuel addition valve 21 while the glow plug 22 is off. In this case, HC contained in the added fuel reacts and burns in the oxidation catalyst 10, and the temperature of the oxidation catalyst 10 rises due to the reaction heat, thereby promoting the thermal decomposition of the noble metal oxide. The glow plug 22 can be omitted.

The advantages and disadvantages of this first aspect are the same as in the first aspect of the reduction method.

Next, the second aspect of the thermal decomposition method will be described. In the second aspect, similar to the second aspect of the reduction method, the in-cylinder injection valve 6 supplies additional fuel as a reducing agent into the cylinder. In this case, it is preferable to perform the after-injection, and post-injection can be performed as a modified example. The advantages and disadvantages of the second aspect are the same as those of the second aspect of the reduction method.

As described above, according to the control of this embodiment, the performance deterioration timing of the oxidation catalyst 10 due to the formation of the noble metal oxide is accurately grasped, and the recovery control is started at an appropriate timing to surely eliminate the noble metal oxide. The performance of the oxidation catalyst 10 can be recovered.

Note that the following modification is possible in the control routine of FIG. For example, in the estimation of the formation speed A in step S101, the formation speed A may be calculated based only on the acquired catalyst temperature Tc. In this case, there is a possibility that the calculation accuracy is somewhat lowered, but there is a possibility that it can be adopted under the condition that the NO ₂ amount M can be regarded as constant. Further, in the estimation of the formation rate A in step S101, the formation rate A may be calculated based on the NO ₂ amount M, the catalyst temperature Tc, and the number of sites in accordance with the Arrhenius reaction model constructed in advance. Also in the estimation of the thermal decomposition rate B in step S102, the thermal decomposition rate B may be calculated based on the catalyst temperature Tc and the number of sites according to the Arrhenius reaction equation model.

Next, another embodiment will be described. The description of the same parts as the above-described embodiment (referred to as the basic embodiment) will be omitted, and the differences will be mainly described below.

[First Other Embodiment]
In the control according to the basic embodiment, when the minimum activation temperature T exceeds the upper limit value Tmax (the oxide amount R exceeds the upper limit oxide amount Rmax), the recovery control is executed immediately. On the other hand, even if the minimum active temperature T exceeds the upper limit value Tmax, if a certain amount of noble metal oxide is formed, it is desirable to perform recovery control to eliminate the noble metal oxide. This is to keep the oxidation catalyst 10 in an active state as high as possible. When the recovery control is performed before such an upper limit, there is still a margin until the oxide amount R exceeds the upper limit oxide amount Rmax. Therefore, it is preferable to select a timing suitable for the recovery control and implement it.

FIG. 11 shows changes in the engine speed Ne, the catalyst temperature Tc, the NO ₂ amount M in the exhaust gas, and the noble metal oxide amount R during vehicle travel. At time t0, the accelerator pedal is fully returned to start engine deceleration and fuel cut, and thereafter the engine speed Ne gradually decreases. Along with this, the catalyst temperature Tc gradually decreases, and the NO ₂ amount M in the exhaust gas decreases rapidly with fuel cut and eventually becomes zero.

Further, before the time t0, the engine is operated at a constant speed at a predetermined speed and load, and both the catalyst temperature Tc and the NO ₂ amount M are relatively high. For example, the catalyst temperature Tc is about 300 to 400 ° C. where the formation rate A is relatively fast.

If recovery control is performed at a timing during constant speed operation such as time t1, the formation rate A is significantly faster than the thermal decomposition rate B at this timing. It is difficult to make recovery control efficiently because the disappearance of the battery does not progress easily. As a result, the required amount of reducing agent increases and fuel consumption deteriorates.

However, the timing of decelerating operation, such as after time t2 in the figure since the exhaust NO ₂ amount M is very small or zero, formation speed A is reduced, it is possible to perform recovery control efficiently. Therefore, it is suitable as a timing for performing recovery control during engine deceleration.

Meanwhile, the transition of the catalyst temperature Tc during engine operation in another example is shown in FIG. From time t0, the catalyst temperature Tc gradually decreases with engine deceleration or the like, and before time t0, the catalyst temperature Tc is a relatively high constant value Tc1. As described above, the time t1 when the catalyst temperature Tc is the constant value Tc1 is not suitable for the recovery control.

The time t2 when the catalyst temperature Tc becomes Tc2 while the catalyst temperature is decreasing is not optimal. This is because the catalyst temperature Tc is higher than Tc3 lower than Tc2. Tc3 is a value slightly higher than the minimum activation temperature T corresponding to the amount of noble metal oxide R at the present time. That is, the oxidation catalyst 10 is active as long as the catalyst temperature Tc is equal to or higher than Tc3. Conversely, when the catalyst temperature Tc falls below Tc3, the catalyst temperature Tc falls below the minimum activation temperature T immediately after that, and the oxidation catalyst 10 is deactivated. There is a high possibility of doing.

At time t2 when the catalyst temperature is Tc2, there is still a margin before the catalyst temperature reaches Tc3. Even if the recovery control is executed at time t2, the catalyst temperature may be increased due to engine acceleration or the like as indicated by the broken line in the figure, and the recovery control may be wasted. On the other hand, since the catalyst is active at this time, there is no need to urgently perform recovery control.

Therefore, in this embodiment, the recovery control is performed after waiting until the catalyst temperature drops to Tc3. If it carries out like this, the active state of a catalyst can be maintained as long as possible, and recovery control can be performed at the timing just before deactivation. At this timing, since the catalyst temperature is sufficiently lowered, the formation speed A is slow, which is convenient for recovery control. Therefore, by performing the recovery control at the timing when the catalyst temperature Tc becomes Tc3, it is possible to prevent unnecessary recovery control and efficiently perform the recovery control. In addition, useless consumption of reducing agent can be eliminated and fuel consumption can be prevented from deteriorating.

FIG. 13 shows a control routine of this embodiment. FIG. 14 shows a map in which the relationship between the oxide amount R and the minimum active temperature T similar to that in FIG. 8 is defined in advance.

Steps S201 to S214 are the same as steps S101 to S114 described above. In this embodiment, steps S215 to S217 are newly added.

In step S208, when the minimum activation temperature T does not exceed the upper limit value Tmax (T ≦ Tmax), the minimum activation temperature T is compared with a predetermined threshold value T1 in step S215. As shown in FIG. 14, the threshold value T1 is a value lower than the upper limit value Tmax and higher than the reference value T0, and is set to 170 ° C., for example.

If the minimum activation temperature T is higher than the threshold value T1, it is determined in step S216 whether or not the engine is decelerating, that is, whether or not the detected value of the engine speed Ne is decreasing.
When the engine is decelerating, the process proceeds to step S209 and recovery control is executed. In this case, although it corresponds to the case where a certain amount of noble metal oxide is formed which is smaller than the upper limit oxide amount Rmax, recovery control is performed after waiting for the opportunity of engine deceleration.

On the other hand, if the engine is not decelerating, the process proceeds to step S217, where the acquired catalyst temperature Tc is compared with a value (ie, T + α) that is higher than the calculated minimum activation temperature T by a predetermined minute value α. This T + α corresponds to Tc3 as described with reference to FIG.

When Tc <T + α, there is no room until the minimum activation temperature T, so the process proceeds to step S209 and recovery control is executed.

On the other hand, if the minimum activation temperature T is equal to or lower than the threshold value T1 in step S215, and if Tc ≧ T + α in step S217, the process proceeds to step S211 to determine whether or not the recovery flag is on.

[Second Other Embodiment]
In the present embodiment, temperature increase control for increasing the temperature of the oxidation catalyst 10 is executed. The temperature increase control can be the same as each aspect of the recovery control, and preferably can be the same as either of the first and second aspects of the thermal decomposition method advantageous for increasing the temperature of the oxidation catalyst 10. . This temperature increase control is executed until the acquired (estimated or detected) catalyst temperature Tc exceeds the minimum activation temperature T calculated in step S107 of the control routine of FIG. 4, for example.

Conventionally, the temperature increase control is performed without considering the amount of noble metal oxide in the oxidation catalyst 10, and the minimum activation temperature is fixed at, for example, the above-described upper limit value Tmax in anticipation of the worst condition. However, in this case, for example, when temperature increase control is performed during engine warm-up, the catalyst temperature must be increased to the uniform upper limit value Tmax even when the amount of noble metal oxide is small, and fuel is consumed more than necessary. .

However, according to the present embodiment, the temperature increase control is executed only up to the minimum activation temperature T calculated in step S107. As shown in FIG. 8, the amount R of the noble metal oxide and the minimum active temperature T are approximately proportional to each other. When the amount R of the noble metal oxide R is small, the calculated minimum activity temperature T is also low. Therefore, when the noble metal oxide amount R is smaller than the upper limit oxide amount Rmax, the catalyst temperature only needs to be raised to the minimum activation temperature T lower than the upper limit value Tmax. Therefore, it is possible to prevent the temperature increase control from being performed more than necessary and to prevent wasteful fuel consumption. In other words, it is possible to execute appropriate temperature increase control according to the amount R of the noble metal oxide.

[Third other embodiment]
The present embodiment relates to a reduction method for recovery control, and more particularly to a method for eliminating noble metal oxide by reduction using the burner device 20.

In general, when a gas richer than stoichiometric gas is supplied to the oxidation catalyst 10 using the burner device 20, the atmosphere of the entire catalyst becomes richer than stoichiometric gas, and there is a risk that HC and CO are not treated with the oxidation catalyst 10 and pass through (HC, CO slip). This is because the oxidation catalyst 10 cannot treat HC and CO unless the atmosphere is leaner than stoichiometric.

In order to solve such problems in exhaust emission, in the present embodiment, fuel is added from the fuel addition valve 21 so that HC is adsorbed to the oxidation catalyst 10 in the initial stage of recovery control.

Specifically, the glow plug 22 is turned on simultaneously with the start of the recovery control, and fuel addition from the fuel addition valve 21 is started when the glow plug 22 reaches a predetermined operating temperature. At this time, the fuel is not ignited at the initial stage of fuel addition, and the added fuel is supplied to the oxidation catalyst 10 without being burned. At this time, HC in the fuel is locally adsorbed on the oxidation catalyst 10, particularly the front end portion thereof (local rich state). However, when the fuel is continuously added, the added fuel is ignited, the high temperature gas is supplied to the oxidation catalyst 10, the catalyst temperature rises rapidly, and the adsorbed HC burns at a stretch. The noble metal oxide is reduced in the combustion or oxidation reaction process of the adsorbed HC.

Here, the catalyst is in a lean atmosphere on the rear side from the HC adsorption site, and the catalyst is on average in a lean atmosphere when viewed as a whole of the catalyst. Accordingly, surplus HC and CO are purified in the catalyst to prevent HC and CO slip. Thereby, exhaust emission deterioration can be prevented.

Thus, the advantage of this embodiment is that the noble metal oxide can be reduced and disappeared while suppressing HC and CO slip. In addition, since the noble metal oxide can be reduced in the desorption process of HC trapped in the pores in the catalyst, it is also an advantage of this embodiment that the noble metal oxide in the pores can be reduced.

FIG. 15 schematically shows the above operation. When the fuel addition valve 21 is turned on at time t1, the added fuel does not ignite immediately after that, so the HC concentration of the gas flowing into the catalyst temporarily increases. At this time, HC in the gas is locally adsorbed on the front end of the catalyst. However, when the added fuel is ignited, the catalyst temperature gradually rises, and the combustion rate of the added fuel increases to finally reach 100%.

By the way, when performing the reduction process using such adsorbed HC, in order to enhance the effect, it is effective to perform the following control.

In the first example, the glow plug 22 is turned on simultaneously with the start of the recovery control, and the fuel addition from the fuel addition valve 21 is started before the glow plug 22 reaches a predetermined operating temperature.

As shown in FIG. 16, when the glow plug 22 is turned on at time t1, the temperature of the glow plug 22 increases from this point. In the above example, as shown in (C), the fuel addition valve 21 is turned on simultaneously with the temperature of the glow plug 22 reaching the predetermined operating temperature TG1. However, here, as shown in (D), before the temperature of the glow plug 22 reaches the operating temperature TG1, the fuel addition valve 21 is turned on, particularly at the same time as the glow plug 22 is turned on.

In this way, it is possible to increase the amount of fuel that has not been ignited in the initial stage of fuel addition and increase the adsorbed HC. And the reduction action by adsorption HC can be heightened.

In the second example, the fuel addition valve 21 is configured so that the air-fuel ratio of the gas flowing into the oxidation catalyst 10 becomes richer than the stoichiometry during an initial period from the start of operation of the fuel addition valve 21 until a predetermined time elapses. In this control, fuel is added, and then the fuel is added from the fuel addition valve 21 so that the air-fuel ratio of the gas becomes leaner than the stoichiometric ratio.

As shown in FIG. 17, the fuel addition valve 21 is turned on at time t1. In general, as shown in (B), fuel is added from the fuel addition valve 21 so that the air-fuel ratio of the gas (referred to as catalyst-containing gas) that flows into the oxidation catalyst 10 thereafter becomes richer than stoichiometric. Is done. However, here, as shown in (C), the air-fuel ratio of the catalyst-filled gas is made rich only during the initial period from time t1 to time t2 when a predetermined time elapses, and after time t2, the catalyst enters Fuel is added from the fuel addition valve 21 so that the air-fuel ratio of the gas becomes leaner than the stoichiometric ratio.

In the general example shown in (B), there is concern about HC and CO slip because it is always rich. On the other hand, in the second example shown in (C), since only the initial period t1 to t2 is made rich, HC adsorption can be performed in this period, and in the subsequent period after t2, it is made lean. Reduction of CO can suppress HC and CO slip.

FIG. 18 shows a control method of the fuel addition valve 21 suitable for the second example. As shown, the fuel addition valve 21 is duty controlled. In the example shown in (A), in the initial period t1 to t2, the duty cycle is shorter than the subsequent period, the duty ratio (the ratio of the on time to the duty cycle) is increased, and the fuel is added more densely. It has become.

In the example shown in (B), in the initial period t1 to t2, the duty cycle is made longer than the subsequent period, the duty ratio is increased, and the fuel addition amount per addition is further increased.

Note that this second example can also be executed in combination with the first example. Such air-fuel ratio control of the gas containing the catalyst can also be performed by controlling the throttle valve 8, that is, controlling the intake air amount, instead of or in addition to the fuel addition amount control. Specifically, the throttle valve opening is decreased during the initial period to reduce the intake air amount and thus the exhaust flow rate, and thereafter the throttle valve opening is increased to increase the intake air amount and thus the exhaust flow rate.

By the way, although the reduction method of recovery control has been described above, similar control can be applied to the thermal decomposition method of recovery control, and this point will be described below.

In this recovery control thermal decomposition method, the air-fuel ratio of the catalyst-containing gas is maintained at a low lean level in the initial stage of warming-up of the engine, and thus the oxidation catalyst 10, and the temperature of the catalyst-containing gas is changed to the thermal decomposition of the noble metal oxide. It is kept at a high temperature (for example, 600 ° C. or higher) so as to be dominant. As a result, the noble metal oxide disappears at the early stage of warm-up, the activity of the oxidation catalyst 10 is recovered during the warm-up, and HC and CO slip can be suppressed because the atmosphere of the entire catalyst is leaner than stoichiometric.

In this case, for example, the fuel addition valve 21 can be controlled as shown in FIG. That is, as shown in (A), in the warm-up initial period t1 to t2, the duty cycle is made shorter and the duty ratio is increased than the subsequent period. Alternatively, as shown in (B), in the warm-up initial period t1 to t2, the duty cycle is made longer and the duty ratio is increased than the subsequent period. In any case, the fuel addition is performed after the temperature of the glow plug 22 reaches the operating temperature TG1 to ensure that the added fuel is ignited.

In this way, the temperature of the gas containing the catalyst can be increased in the initial warm-up period than in the subsequent period, and thermal decomposition can be promoted.

Also, as described above, it is possible to perform control to reduce the throttle valve opening in the initial warm-up period than in the subsequent period. Furthermore, the operating temperature TG1 of the glow plug 22 may be increased so that the added fuel is more reliably ignited in the initial warm-up period than in the subsequent period.

It should be noted that the recovery control of the present embodiment described above can also be executed by in-cylinder combustion using after injection.

[Fourth Embodiment]
The present embodiment relates to a reduction method for recovery control, and more particularly to a method for eliminating noble metal oxide by reduction using the burner device 20.

For example, in a catalyst temperature range of 300 to 400 ° C., the formation rate A of the noble metal oxide is relatively fast, and particularly when the amount of NO _{2 in the} exhaust gas is large, continuous recovery control may be required, resulting in deterioration of fuel consumption. Is concerned.

Therefore, in the present embodiment, during the execution of the recovery control, for example, the fuel addition amount (reducing agent amount) Z is changed according to the formation speed A estimated in step S101 of FIG.

That is, the fuel addition amount Z is determined based on the formation speed A estimated in step S101 according to a map that preliminarily defines the relationship between the formation speed A and the fuel addition amount Z as shown in FIG. The fuel addition amount Z increases as the formation speed A increases, and the fuel addition amount Z decreases as the formation speed A decreases.

Thereby, the fuel addition amount Z can be controlled to the minimum necessary amount according to the formation speed A, and deterioration of fuel consumption can be suppressed.

It should be noted that such control of the amount of reducing agent can also be applied to cases where only fuel addition is performed using the fuel addition valve 21, after-injection, and post-injection.

[Fifth other embodiment]
The present embodiment relates to a reduction method for recovery control, and more particularly to a method for eliminating noble metal oxide by reduction using the burner device 20.

In the fourth other embodiment, fuel consumption deterioration is suppressed by changing the fuel addition amount Z according to the formation speed A. On the other hand, the fuel addition amount Z necessary for eliminating the noble metal oxide also varies depending on the NO ₂ amount M in the exhaust.

Therefore, in the present embodiment, during the execution of the recovery control, for example, the fuel addition amount (reducing agent amount) Z is changed in accordance with the NO ₂ amount M in exhaust estimated in step S101 of FIG.

That is, the fuel addition amount Z is determined on the basis of the NO ₂ amount M in exhaust estimated in step S101 according to a map that predefines the relationship between the exhaust NO ₂ amount M and the fuel addition amount Z as shown in FIG. Is done. Fuel addition amount Z larger the exhaust NO ₂ amount M is increased, the fuel addition amount Z smaller the exhaust NO ₂ amount M is reduced.

Thus, it is possible to control the fuel addition amount Z on the amount of the minimum necessary in accordance with the exhaust NO ₂ amount M, the fuel economy can be suppressed.

It may be changed according to the present embodiment fourth combined with other embodiments, in the exhaust and forming speed A fuel addition amount Z NO ₂ amount M. Such control of the amount of the reducing agent is also applicable to the case where only fuel addition is performed using the fuel addition valve 21, the case where after injection is performed, and the case where post injection is performed.

[Sixth other embodiment]
The present embodiment relates to a reduction method for recovery control, and more particularly, to a method for solving the problem when only fuel addition is performed using only the fuel addition valve 21 of the burner device 20 in the fifth other embodiment.

When only such fuel addition is performed, the oxides already formed on the noble metal are reduced and eliminated, and NO ₂ in the exhaust is directly reduced with HC in the fuel before being supplied to the oxidation catalyst 10 to oxidize. It is possible to suppress the formation itself.

However, HC has a relatively low reducing power, and when the exhaust temperature is low, direct reduction of NO ₂ cannot be expected so much.

Therefore, in this embodiment, during the execution of the recovery control, the fuel added from the fuel addition valve 21 is first ignited by the glow plug 22 to generate CO having a stronger reducing power. Then, the fuel addition amount Z from the fuel addition valve 21 increases as the temperature of the exhaust gas supplied to the glow plug 22 decreases. Here, the temperature of the exhaust gas can be the exhaust temperature detected by the upstream exhaust temperature sensor 33.

FIG. 21 shows the relationship between the air-fuel ratio A / F of the mixture of added fuel and exhaust gas, and the amount of CO and smoke produced when the mixture is ignited. As shown in the figure, the air-fuel ratio A / F at which the CO amount reaches its maximum peak is AF1 richer than stoichiometric. Ideally, the fuel addition is performed so that the air-fuel ratio AF1 is obtained. However, when the air-fuel ratio AF1 is used, the amount of smoke is remarkably increased. Therefore, in the present embodiment, the fuel addition amount Z is changed within the range leaner than AF2 that is the smoke limit. AF2 is slightly leaner than stoichiometric.

In the present embodiment, the relationship between the air-fuel ratio A / F of the mixture of added fuel and exhaust gas and the exhaust temperature of the exhaust gas supplied to the glow plug 22 is as shown in FIG. The fuel addition amount Z is controlled. That is, the fuel addition amount Z is increased as the exhaust gas temperature is lowered, and as a result, the air-fuel ratio A / F of the air-fuel mixture is also changed to the rich side as the exhaust gas temperature is lowered, and approaches the stoichiometry. The fuel addition amount Z is a value at which the air-fuel ratio A / F of the air-fuel mixture becomes AF2 at the maximum.

Thereby, NO ₂ in the exhaust can be directly reduced efficiently with CO, and even when the exhaust temperature is particularly low, the amount of CO can be increased to reliably reduce NO ₂ directly. When the exhaust temperature is high, the fuel addition amount Z can be reduced, so that unnecessary fuel consumption can be avoided and fuel consumption can be suppressed.

In addition, this embodiment is applicable also when performing post injection.

[Seventh Embodiment]
The present embodiment relates to both the reduction method and the thermal decomposition method of recovery control, and more particularly to additional suppression control that is executed together with the execution of recovery control.

This suppression control is control for suppressing the amount of NO ₂ discharged from the cylinder. Preferably, the suppression control includes control for increasing the EGR gas flow rate by at least one of increasing the opening of the EGR valve 9C and decreasing the opening of the throttle valve 8.

When this suppression control is executed, the amount of NO ₂ discharged from the cylinder is suppressed or reduced, so that the formation of noble metal oxide during the recovery control can be suppressed and the efficiency of the recovery control can be increased. And the amount of reducing agents required for recovery control can be reduced and fuel consumption deterioration can be suppressed.

Note that it is also conceivable to perform only suppression control instead of recovery control and wait for its natural disappearance while suppressing new formation of the noble metal oxide.

[Eighth other embodiment]
The present embodiment relates to a diagnostic process for diagnosing whether or not the oxidation catalyst 10 has been irreversibly deteriorated due to thermal deterioration or the like. In this case, any method including a known method can be adopted as a diagnostic method. For example, the amount of increase in the catalyst temperature when a predetermined amount of fuel is added is detected, and this amount of increase is compared with a predetermined deterioration determination value to diagnose whether the oxidation catalyst 10 has deteriorated irreversibly. It is possible.

At the time of this diagnosis, if a noble metal oxide is formed on the oxidation catalyst 10, the reversible deterioration due to this is added to the irreversible deterioration, and an accurate diagnosis cannot be performed. That is, the reversible deterioration due to the noble metal oxide is temporary that can be recovered. Therefore, irreversible deterioration should be diagnosed except for this amount, and if this amount is added, there is a possibility of erroneously diagnosing deterioration even though it is normally normal.

Therefore, in order to increase the accuracy of irreversible deterioration diagnosis and prevent erroneous diagnosis, in this embodiment, deterioration diagnosis is performed immediately after the end of recovery control. As a result, the deterioration diagnosis can be performed immediately after the noble metal oxide disappears and the influence is removed, and the diagnosis accuracy can be improved and the erroneous diagnosis can be prevented.

Specifically, for example, in the control routine of FIG. 4 (or FIG. 13), after the recovery control is stopped or terminated in step S113 (or step S213), the recovery flag is turned off in step S114 (or step S214). At the same time, deterioration diagnosis is executed.

The preferred embodiment of the present invention has been described above, but various other embodiments of the present invention are conceivable. For example, the present invention can be applied to a spark ignition type internal combustion engine, that is, a gasoline engine, and particularly applicable to a lean burn gasoline engine that operates at an air-fuel ratio leaner than stoichiometric. Further, the fuel injection method is not limited to the direct injection method, and may be a port injection method for injecting into the intake port. The above numerical values are examples and can be changed to other values. The above embodiments and their respective components can be combined as much as possible.

Claims (15)

A catalyst having an oxidation function provided in an exhaust passage of the internal combustion engine;
First acquisition means for acquiring the temperature of the catalyst;
Second acquisition means for acquiring the amount of oxidant in the exhaust gas flowing into the catalyst;
Estimating means for estimating the amount of oxide formed on the catalyst based on the catalyst temperature obtained by the first obtaining means and the oxidant amount obtained by the second obtaining means;
Recovery control means for executing recovery control for eliminating the oxide when the amount of oxide estimated by the estimation means exceeds a predetermined upper limit;
A control apparatus for an internal combustion engine, comprising: _2. The control device for an internal combustion engine according to claim 1, wherein the oxidant is NO ₂ , and the oxide is a noble metal oxide obtained by oxidizing a noble metal in the catalyst. The estimation means calculates the formation rate of the oxide based on the catalyst temperature and the amount of the oxidant, calculates the thermal decomposition rate of the oxide based on the catalyst temperature, and the formation rate and the thermal decomposition rate. The control apparatus for an internal combustion engine according to claim 1, wherein the amount of oxide is estimated based on The estimation means calculates the disappearance rate of the oxide during the execution of the recovery control by the recovery control means, and calculates the amount of the oxide based on the disappearance rate in addition to the formation rate and the thermal decomposition rate. The control device for an internal combustion engine according to claim 3, wherein the control device is estimated. A calculation means for calculating a minimum activation temperature of the catalyst based on the amount of oxide estimated by the estimation means;
The recovery control means executes the recovery control when the minimum activation temperature calculated by the calculation means exceeds an upper limit corresponding value corresponding to the upper limit value,
The recovery control means executes the recovery control during deceleration of the internal combustion engine when the minimum activation temperature calculated by the calculation means is not more than the upper limit corresponding value and exceeds a predetermined threshold value. The control apparatus for an internal combustion engine according to any one of claims 1 to 4. The recovery control means is such that the minimum active temperature calculated by the calculation means is not more than the upper limit corresponding value and exceeds the threshold value, and is not being decelerated of the internal combustion engine but acquired by the first acquisition means. 6. The internal combustion engine according to claim 5, wherein the recovery control is executed when the determined catalyst temperature falls below a value that is higher by a predetermined minute value than the minimum activation temperature calculated by the calculation means. Control device. Further comprising a temperature increase control means for performing temperature increase control for increasing the temperature of the catalyst;
The temperature increase control means performs the temperature increase control until the catalyst temperature acquired by the first acquisition means exceeds the minimum activation temperature calculated by the calculation means. 6. The control apparatus for an internal combustion engine according to 6. The recovery control means includes an addition valve for adding a reducing agent containing HC into the exhaust passage, and a glow ignition device for igniting the reducing agent added from the addition valve,
The internal combustion engine according to any one of claims 1 to 7, wherein the recovery control means supplies the reducing agent from the addition valve so that HC is adsorbed to the catalyst at an initial stage of the recovery control. Engine control device. The recovery control means operates the glow ignition device simultaneously with the start of the recovery control, and starts supplying a reducing agent from the addition valve before the glow ignition device reaches a predetermined operating temperature. The control apparatus for an internal combustion engine according to claim 8. The recovery control means supplies the reducing agent from the addition valve so that the air-fuel ratio of the gas flowing into the catalyst becomes richer than the stoichiometry until a predetermined time elapses from the start of operation of the addition valve. Then, after that, the reducing agent is supplied from the addition valve so that the air-fuel ratio of the gas becomes leaner than the stoichiometric ratio. The control apparatus for an internal combustion engine according to claim 8 or 9, The recovery control means supplies the reducing agent containing HC into the exhaust passage during the execution of the recovery control, and changes the supply amount of the reducing agent according to the oxide formation rate calculated by the estimation means. The control device for an internal combustion engine according to claim 3 or 4, characterized in that: The recovery control means supplies a reducing agent containing HC into the exhaust passage during the execution of the recovery control, and supplies the reducing agent according to the amount of oxidant in the exhaust gas acquired by the second acquisition means. The control device for an internal combustion engine according to any one of claims 1 to 11, wherein the amount is changed. The recovery control means includes an addition valve for adding a reducing agent containing HC into the exhaust passage, and a glow ignition device for igniting the reducing agent added from the addition valve,
The recovery control means ignites the reducing agent added from the addition valve by the glow ignition device during execution of the recovery control and supplies the reducing agent addition amount from the addition valve to the glow ignition device. The control apparatus for an internal combustion engine according to any one of claims 1 to 12, wherein the temperature of the exhaust gas to be increased increases as the temperature of the exhaust gas decreases. 14. A suppression control means for executing suppression control for suppressing the amount of the oxidant discharged from the cylinder during execution of the recovery control by the recovery control means. The control apparatus for an internal combustion engine according to any one of the above. A diagnostic means for diagnosing whether or not the catalyst is irreversibly deteriorated;
The control apparatus for an internal combustion engine according to any one of claims 1 to 14, wherein the diagnosis means performs a diagnosis immediately after completion of the recovery control.

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