JPH11193713A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability of the exhaust emission control system for internal combustion engine by reliably reducing the amount of hydrocarbon in the exhaust emission at the cold start of the engine and by detaching the NOx and SOx from the NOx catalyst while preventing fuel economy from being worsened when the NOx conversion efficiency of the NOx catalyst decreases. SOLUTION: This exhaust emission control system is provided with an exhaust emission controller 13, a light-off catalyst 11, and a control means 20. The exhaust emission controller 13 is arranged to an exhaust passage 3 of the internal combustion engine, and when the exhaust emission is lean in terms of air-fuel ratio, the NOx is adsorbed, while when the concentration of oxygen in the exhaust emission decreases, the absorbed NOx is detached. The light-off catalyst 11 is provided to the exhaust passage 3 in the upstream side of the exhaust emission controllers 13 and 14, with the O2 storage capability lower than that of the exhaust emission converter 14. The control means 20 provides a control such that the concentration of oxygen in the atmosphere in the vicinity of the exhaust emission controller 13 and 14 is lowered if the NOx conversion efficiency of the exhaust emission controller 13 decreases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to a method for efficiently purifying harmful components in exhaust gas, particularly NO _x (nitrogen oxide), even in an internal combustion engine having a lean exhaust air-fuel ratio. The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

At present, have been developed lean-burn internal combustion engine capable to achieve further fuel efficiency (engine), the NO _X in the exhaust gas during lean combustion in such engine conventional three-way catalyst It is difficult to purify using [having a three-way function near stoichiometric air (stoichiometric air-fuel ratio)].

[0003] Therefore, an oxygen-rich atmosphere to adsorb NO _X of (oxidizing atmosphere) in the exhaust gas, the catalyst having an oxygen concentration has a function to desorb NO _X adsorbed to decrease (occlusion-type lean NO _X catalyst, trap type lean NO _X catalyst) have been developed. In other words, a lean NO _X catalyst means that in an atmosphere having an excessive oxygen concentration, NO _X in exhaust gas is oxidized to generate nitrate, thereby adsorbing NO _X , while in an atmosphere having a reduced oxygen concentration (reducing atmosphere), It has a function of reacting nitrate adsorbed on the lean NO _X catalyst with CO in exhaust gas to generate carbonate, thereby desorbing NO _X. Then, the desorbed NO _X is purified by a three-way function of the lean NO _X catalyst, a three-way catalyst provided on the downstream side, or the like.

[0004] by the lean NO _X catalyst having such a function, but also during the lean operation is to reliably purify NO _X in the exhaust gas, such lean NO _X
It is difficult to reliably reduce HC in exhaust gas by using only a catalyst, for example, when the engine is started cold. For this reason,
A light-off catalyst (L / O catalyst, F / F) is disposed immediately downstream of the engine upstream of a normal catalyst so that HC in the exhaust gas can be reliably reduced even when the engine is cold started.
CC: Front Catalytic Converter) has been proposed.

For example, JP-A-8-294618 (first publication) and JP-A-5-187230 (second publication) disclose examples.

[0006]

As disclosed in the first and second publications, a three-way catalyst (TWC: Three Way Catalyst) is used as the light-off catalyst. A three-way catalyst or an oxidation catalyst used as a light-off catalyst is provided with, for example, ceria CeO ₂ as an additive having an O ₂ storage function.

[0007] This is because even in an engine in which stoichiometric feedback operation or lean operation is performed during normal operation, rich operation may be performed in a transient state such as acceleration, and in such a case, O ₂ is contained in exhaust gas. , HC and CO are oxidized by utilizing O ₂ stored in ceria CeO ₂ of the light-off catalyst.
This is to ensure that HC can be reduced even during a transient rich operation.

However, the first and second publications mentioned above disclose
As disclosed, lean NO _XCatalyst and light off
If both the catalyst and the light-off catalyst are provided,_Two S
Lean NO because of the storage function_XAbsorbed by catalyst
NO wearing_XNO to desorb_XNear the catalyst
Lean NO_XCatalyst
NO_XCO required to desorb CO is a light-off catalyst
Is oxidized by CO._XTouch
Medium cannot be supplied, and lean NO_XAdsorbed on the catalyst
NO_XCannot be reliably removed.

That is, the vicinity of the lean NO _X catalyst is set to an atmosphere having a reduced oxygen concentration (for example, a rich air-fuel ratio) to obtain a lean NO _X catalyst.
_Even if a recovery control (rich spike) such as additional fuel injection is performed to release NO _X adsorbed on the _X catalyst and recover the NO _X purification efficiency, the CO supplied by the recovery control is restored. additive added to light-off catalyst (e.g., ceria CeO ₂₎ for is consumed is oxidized by O ₂ stored in, be reliably desorbing NO _X adsorbed in the lean NO _X catalyst As a result, the NO _X purification efficiency of the lean NO _X catalyst cannot be sufficiently restored.

In order to sufficiently restore the NO _X purification efficiency of the lean NO _X catalyst, it is conceivable to set the air-fuel ratio to a richer side. However, this is not preferable because fuel efficiency is deteriorated.

Incidentally, a sulfur component (S component) is contained in fuel and lubricating oil, and such a sulfur component is also contained in exhaust gas. For this reason, the lean NO _X catalyst adsorbs NO _X in an oxygen-rich atmosphere,
Such sulfur components will also be adsorbed. That is,
Sulfur components contained in fuel or lubricating oil burns, further, it becomes SO ₃ is oxidized on the lean NO _X catalyst. Then, the lean NO become sulfates part of the SO ₃ reacts with occluding agent for further NO _X on the lean NO _X catalyst
Adsorb on _X catalyst.

Therefore, nitrate and sulfate are adsorbed on the lean NO _X catalyst, and sulfate has a higher stability as a salt than nitrate, and even in an atmosphere where the oxygen concentration is lowered, the lean NO _x catalyst has a higher stability. since only a part is not degraded, the amount of sulfate remaining in the lean nO _X catalyst is increased with time. As a result, the NO _X adsorption capacity of the lean NO _X catalyst decreases with time, and the purification efficiency of the lean NO _X catalyst decreases (this is referred to as S poisoning).

For this reason, lean NO_XSuch a catalyst
When S poisoning occurs, lean NO_XSulfur from catalyst
Ingredient (SO_X) Must be removed. But
As disclosed in the above first and second publications,
Lean NO _XDeploy both catalyst and light-off catalyst
In some cases, the light-off catalyst has a high O_TwoHas storage capacity
Lean NO_XSO adsorbed on the catalyst_XDetached
I can't let it.

That is, lean NO_XOxygen concentration near the catalyst
Lean NO_XSO adsorbed on the catalyst_X
To remove NO_XExample to regenerate the catalyst
For example, by enriching the air-fuel ratio and reducing the oxygen concentration in exhaust gas
Even if playback control such as
Therefore, the added CO and the additive added to the light-off catalyst
Additives (eg, ceria CeO_Two O stored in)_Two And
Reacts, SO _XCO required for desorption is oxidized
NO because it is consumed_XAdsorbed on catalyst
SO_XCan not be desorbed and lean NO_XCatalyst
You will not be able to play it.

Further, SO ₂ discharged from the engine reacts with O ₂ stored in the additive of the light-off catalyst to cause S 2
Since O ₃ is generated (2SO ₂ + O ₂ → 2SO ₃ ),
Sulfur components to the lean NO _X catalyst disposed downstream of the light-off catalyst is easily adsorbed, S lean NO _X catalyst
It also promotes poisoning. The present invention has been made in view of such a problem, and it is possible to surely reduce HC in exhaust gas at the time of a cold start of an engine, and to adsorb NO _X and SO _X to a NO _X catalyst to improve NO _X purification efficiency. Even if the fuel consumption decreases, the NO
It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, in which NO _X and SO _X can be reliably desorbed from an _X catalyst, and the durability thereof is improved.

[0016]

[SUMMARY OF To this end, the exhaust purification system of an internal combustion engine of the present invention, in an exhaust passage of an internal combustion engine, the exhaust air-fuel ratio is adsorbed NO _x when the lean decrease the oxygen concentration in the exhaust gas exhaust gas purifying means is provided for releasing or reducing the NO _x adsorbed upon. Further, on the upstream side of the exhaust passage of the exhaust gas purification means, O ₂ storage capability provided low light-off catalyst than the exhaust gas purifying means. And
When the NO _X purification efficiency of the exhaust gas purifying means decreases, the control means controls the vicinity of the exhaust gas purifying means so as to have an atmosphere having a reduced oxygen concentration.

[0017] With this, NO is added to the exhaust gas purifying means._XAnd S
O_XIs adsorbed and NO_XPurification efficiency decreases, and exhaust gas purification
For example, add additional fuel so that the atmosphere
Suppose that control was performed to supply CO by performing fuel injection, etc.
Even the CO supplied by the light-off catalyst is oxidized.
And the amount of CO supplied to the exhaust gas purification means is reduced.
Is reduced, and the fuel consumption is reduced without deteriorating fuel economy.
NO from gas purification means _XAnd SO_XTo make sure that
And its durability is enhanced.

Further, the exhaust gas purifying means, and the NO _x catalyst to release or reduce the adsorbed NO _x when the air-fuel ratio of exhaust gas oxygen concentration of the adsorbed in the exhaust gas to NO _x in the exhaust gas when the lean lowered, NO exhaust air-fuel ratio is provided in the exhaust passage downstream of the _x catalyst is preferably composed of a three-way catalyst for purifying harmful components in the exhaust gas to the stoichiometric air-fuel ratio near.

Further, the exhaust gas purification means may be configured as a single catalyst that has combined the functions of a function and a three-way catalyst as the NO _x catalyst. The light-off catalyst provided on the upstream side of the exhaust passage serves as a three-way catalyst and directly purifies SO _X in exhaust gas, or adsorbs SO _X when the exhaust air-fuel ratio is lean, and exhaust SO It may be configured as a single catalyst having a function as an SO _X catalyst for desorbing SO _X adsorbed when the fuel ratio is rich.

The light-off catalyst is configured such that the oxygen adsorption amount per liter of the catalyst capacity is about 150 cc or less as measured by the oxygen pulse method, whereby the O ₂ storage capacity of the light-off catalyst decreases. . Also,
The light-off catalyst is configured such that the oxygen storage component added per liter of catalyst capacity is about 25 g or less;
As a result, the O ₂ storage capacity of the light-off catalyst decreases.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. An exhaust gas purifying apparatus for an internal combustion engine according to one embodiment of the present invention will be described with reference to FIGS. Since the exhaust emission control device according to one embodiment of the present invention is provided in an internal combustion engine, the internal combustion engine will be described first.

This internal combustion engine is configured as shown in FIG. 1, and is an internal combustion engine that performs each of the intake, compression, expansion, and exhaust strokes in one operation cycle, that is, a four-cycle engine, which is a spark ignition type. The engine is configured as a direct injection internal combustion engine (direct injection engine) that directly injects fuel into the combustion chamber. An intake passage 2 and an exhaust passage 3 are connected to the combustion chamber 1 so that they can communicate with each other. The communication between the intake passage 2 and the combustion chamber 1 is controlled by an intake valve 4, and the exhaust passage 3 and the combustion chamber 1 are connected to each other. Is controlled by the exhaust valve 5.

The intake passage 2 is provided with an air cleaner and a throttle valve (not shown).
Is provided with an exhaust purification device 6 and a muffler (muffler) (not shown). The details of the exhaust gas purification device 6 will be described later. Injector (fuel injection valve)
Numeral 8 is arranged so that its opening faces the combustion chamber 1 so as to directly inject fuel toward the combustion chamber 1 in the cylinder. Naturally, the injectors 8 are provided for each cylinder. For example, if the engine of the present embodiment is an in-line four-cylinder engine, four injectors 8 are provided.

With such a configuration, the air sucked through the air cleaner (not shown) in accordance with the opening of the throttle valve (not shown) is drawn into the combustion chamber 1 by opening the intake valve 4, and is drawn into the combustion chamber 1. The air and the fuel directly injected from the injector 8 are mixed based on a signal from an electronic control unit (ECU) 20 as a control means, and the ignition plug 7 is ignited in the combustion chamber 1 at an appropriate timing. After being burned to generate engine torque, the exhaust gas is discharged from the combustion chamber 1 to the exhaust passage 3, and the exhaust gas purifier 6 removes CO, H in the exhaust gas.
From C, it is purified three harmful components NO _x, are muted in the muffler so as to be discharged to the atmosphere side.

The engine is provided with various sensors.
The detection signal from the sensor is sent to the ECU 20.
It is supposed to be. For example, exhaust gas purification of the exhaust passage 3
NO on the upstream side of the gasifier 6_XSensor 9 (hereinafter, upstream
Side NO_XSensor 9) is provided.
Lean NO to prescribe _XNO at the downstream side of the catalyst 13_XC
Sensor 10 (hereinafter, downstream NO_XSensor 10)
Have been killed. And these upstream NO_XSensor 9
And downstream NO_XBased on the detection information from the sensor 10
NO by the exhaust purification device 6_XCalculation of purification efficiency
It has become. Note that NO_XAbout the calculation of purification efficiency
It will be described later.

The engine will be further described. This engine is configured such that the intake air flowing into the combustion chamber 1 from the intake passage 2 forms a vertical vortex (reverse tumble flow). Since the flow forms such a vertical vortex, a small amount of fuel is collected only in the vicinity of the ignition plug 7 disposed at the center of the top of the combustion chamber 1 while utilizing the vertical vortex, and is separated from the ignition plug 7. It is possible to achieve an extremely lean air-fuel ratio in the portion where the air-fuel ratio has been obtained, and achieve a stable stratified combustion (stratified super-lean combustion) by setting only the stoichiometric air-fuel ratio or the rich air-fuel ratio only in the vicinity of the ignition plug 7 The fuel consumption can be suppressed. The optimum fuel injection timing in this case is the latter stage of the compression stroke in which the air flow is weak and fuel is not excessively diffused by the time of ignition.

When a high output is obtained from the engine, the fuel from the injector 8 is homogenized throughout the combustion chamber 1 and the interior of all the combustion chambers 1 is brought to a mixture state with a stoichiometric air-fuel ratio or a lean air-fuel ratio. The stoichiometric air-fuel ratio can provide a higher output than the lean air-fuel ratio. Of course, the timing at which the fuel is sufficiently atomized and vaporized is also used. By performing the fuel injection, a high output can be obtained efficiently. In such a case, the optimal fuel injection timing is set so as to end the fuel injection during the intake stroke so that atomization and vaporization of the fuel can be promoted using the intake air flow.

For this reason, in the present engine, as a mode of fuel injection, operation (extremely lean) in a very lean state of the fuel (that is, the air-fuel ratio is much larger than the stoichiometric air-fuel ratio) by the stratified combustion by the compression stroke fuel injection. Combustion operation), a super-lean operation mode (compression lean operation mode), and a fuel-lean state (that is, less than the super-lean operation mode)
Stoichiometric operation mode the air-fuel ratio is performed and the lean operation mode for performing operation in large) than the stoichiometric air-fuel ratio (intake lean operation mode), the feedback control based on the O ₂ sensor information such as the air-fuel ratio becomes the stoichiometric air-fuel ratio (Stoichiometric feedback operation mode) and an enrichment operation mode (open loop mode) in which operation is performed in a fuel rich state (that is, the air-fuel ratio is smaller than the stoichiometric air-fuel ratio).

Then, one of the various operation modes is selected to control the operation of the engine.
e and the effective pressure Pe indicating the load state. That is, when the engine speed Ne is low and the load Pe is small, the compression lean operation mode (pressure-L) is selected, and the engine speed Ne and the load P are determined.
As e becomes larger than this, the intake lean operation mode (suction-L), the stoichiometric feedback operation mode (S / F), and the open loop mode (O / L) are selected.

The selection and setting of the operation mode will be further described later. Next, the exhaust gas purification device 6 according to the present embodiment will be described. The present exhaust gas purifying apparatus 6 has the structure shown in FIG.
As shown in the figure, light-off catalyst (L / O catalyst, FCC)
11, the lean NO _x catalyst (the NO _x catalyst, NO _x -TR
AP) 13 and three-way catalyst (TWC: Three Way Catalys)
t) 14). It should be noted that the lean NO _x catalyst 13 and the three-way catalyst 14 constitute exhaust gas purifying means.

[0031] Of these, light-off catalyst 11 is composed of a three-way catalyst that functions to purify CO in the exhaust gas, HC and NO _x. The light-off catalyst 11 is disposed in the exhaust passage 3 immediately downstream of the combustion chamber 1 of the engine so as to immediately reach an activation temperature by high-temperature exhaust gas from a cold start of the engine. During the cold start, HC in the exhaust gas is reduced.
Note that the light-off catalyst 11 is provided in the exhaust passage 3 on the upstream side of the lean NO _x catalyst 13.

Further, the O ₂ storage capability of the light-off catalyst 11 is set lower than the O ₂ storage capability of the three-way catalyst 14. That is, the O _{2 of the} light-off catalyst 11
The storage capacity was measured by the oxygen pulse method, and the amount of oxygen adsorbed per liter of catalyst capacity was about 150 cc [ie,
The oxygen adsorption amount is set to 150 cc / liter (L)] or less.

Here, O ₂ by a general oxygen pulse method is used.
A storage capacity measuring device and a measuring method thereof will be described. As shown in FIG. 9, an apparatus for measuring the O ₂ storage capacity by the oxygen pulse method uses a sample (here, ceria Ce).
A sample tube 56 for containing a light-off catalyst comprising O ₂ );
A supply passage 60 for supplying gas [He, air, H ₂ ] to the sample in the sample tube 56, a discharge passage 61 for discharging gas from the sample tube 56, and a heating furnace 57 for heating the sample tube 56 to a predetermined temperature. It is comprised including.

The supply passage 60 has its upstream side connected to the He introduction path 60 a and the Air introduction path 6 via the switching cock 52.
0b, are connected in H ₂ introduction path 60c, the downstream side is connected to the sample tube 56 via a connector 55. By switching the switching cock 52, one of He, air, and H ₂ can be introduced into the supply passage 60 and supplied to the sample in the sample tube 56.

In the supply passage 60 between the switching cock 52 and the sample tube 56, a flow meter 51 is provided in order from the upstream side.
a, an oxygen pulse introduction unit 53 is provided. And
The flow rate of the gas flowing through the supply passage 60 can be detected by the flow meter 51a. Further, oxygen can be introduced in a pulse form by the oxygen pulse introduction unit 53 when measuring the O ₂ storage capacity.

A flow path switching cock 54 is provided so as to connect the supply path 60 and the discharge path 61. The flow path switching cock 54 allows the supply path 60 to be connected to the inside of the supply path 60 when the O ₂ storage capacity is measured. The flow path can be switched between a side that supplies the gas flowing through the sample tube 56 to the sample in the sample tube 56 and a side that bypasses the sample tube 56 so that the gas flowing in the supply passage 60 flows to the discharge passage 61 side. Has become.

In the discharge passage 61 on the downstream side of the flow path switching cock 54, a flow meter 51b and a purge cock 58 are arranged in this order from the upstream side. And the flow meter 51
The flow rate of gas flowing in the discharge passage 61 can be detected by b. Unnecessary gas can be discharged to the atmosphere by the purge cock 58 during the pre-processing of the O ₂ storage capacity measurement.

Further, a thermal conductivity detector 59 for detecting the thermal conductivity of the gas passing through the sample tube 56 is provided. Next, O by an oxygen pulse method using such a measuring device is used.
_{2 A} method for measuring the storage capacity will be described. First,
Before starting the measurement of the O ₂ storage capacity, a pretreatment is performed to remove oxygen already adsorbed on the sample.

In this pretreatment, a sample is put into the sample tube 56, and the sample tube 56 is connected to the measuring device main body side (specifically, the supply passage 60 and the exhaust passage 61) via the connector 55.
Further, the heating furnace 57 is set. And the switching cock 5
2 is switched to the H ₂ introduction path 60c side, H ₂ is introduced into the sample tube 56 through the supply path 60, and the sample is kept at about 450 ° C. for 30 minutes.

In this case, the flow rate of the gas introduced into the sample tube 56 is controlled by the flow meter 51a so as to be a predetermined flow rate. Further, the purge cock 58 is opened, and the gas flowing through the exhaust passage 61 is discharged to the atmosphere. By such a treatment, oxygen adsorbed on the sample is reacted with H ₂ to desorb oxygen from the sample, so that oxygen is not adsorbed on the sample.

Next, the switching cock 52 is connected to the He introduction path 60a.
To the sample tube 56 through the supply passage 60.
And hold it for 30 minutes while cooling the sample to room temperature. By such a treatment, the H ₂ supplied in the above-described treatment to desorb oxygen from the inside of the sample is obtained.
Is purified by He. By performing such a pretreatment, a more accurate O ₂ storage capacity of the sample can be measured.

Next, after completing such pre-processing,
Measure the actual O ₂ storage. When performing the measurement of the O ₂ storage, oxygen is introduced in a pulse form from the oxygen pulse introduction unit 53 into the supply passage 60, and the sample tube 56 is introduced.
Supply oxygen to the sample inside. Thereafter, after the oxygen adsorption to the sample has reached a steady state (that is, a state estimated to be saturated), oxygen is introduced a predetermined number of times (for example, twice) from the oxygen pulse introduction unit 53, and Supply oxygen to the sample and terminate.

When measuring the O ₂ storage, the introduction of gas from the switching cock 52 is stopped, and the purge cock 58 is closed. The thermal conductivity is detected by the thermal conductivity detector 59 every time oxygen is supplied in a pulse form from the oxygen pulse introduction unit 53 into the supply passage 60. In addition, the flow path switching cock 54 is switched to a side that bypasses the sample tube 56 to calibrate the oxygen amount.

In the calibration of the oxygen amount, the relationship between the oxygen amount supplied in a pulse form from the oxygen pulse introduction unit 53 and the area of the peak detection value detected by the thermal conductivity detector 59 with respect to the oxygen amount is obtained. . Then, based on the relationship between the amount of oxygen obtained by the calibration of the amount of oxygen and the area of the peak detection value, the average of the area of the peak detection value detected by the thermal conductivity detector 59 after the sample enters a steady state. The oxygen adsorption adsorbed on the sample is determined from the area difference between the value and the area of the peak detection value detected by the thermal conductivity detector 59 each time oxygen is supplied from the oxygen pulse introduction unit 53 before the sample enters a steady state. The amount is converted, and the oxygen adsorption amount per liter of the sample (cc / liter), that is, the O ₂ storage capacity of the sample can be calculated from the total amount.

Next, the light-off the O ₂ storage capability of the catalyst 11, the O ₂ storage capability of the commonly used underfloor catalyst (e.g. lean NO _x catalyst 13 and the exhaust gas purifying means composed of the three-way catalyst 14.) (200 to 500 cc / liter as measured by the oxygen pulse method),
The reason for setting the pressure to about 150 cc / liter or less in the measurement by the oxygen pulse method will be described with reference to FIG.

Here, FIG. 10 shows the case of the oxygen pulse method.
O of the light-off catalyst 11 to be measured _TwoStorage capacity
When resurrection control (rich spike) is introduced when changed
It shows the experimental results for the interval. The result of this experiment
Is a lean NO with a capacity of about 1.3 liters_Xcatalyst
13 and a three-way catalyst 14 having a capacity of about 1.0 liter
About 0.7 upstream of the exhaust gas purifying means
A light-off catalyst 11 having a capacity of 1 liter is provided and exhausted.
The air purification device is configured to have an air-fuel ratio (A / F) of about 30.
The lean operation is continued for about 60 seconds, and the lean NO_Xcatalyst
NO adsorbed on 13_XRequired to be fully released
Measure live control introduction time (rich spike introduction time)
This is the result obtained in the experiment.

As shown in the experimental results in FIG. 10, when the O ₂ storage capacity of the light-off catalyst 11 is about 150 cc / liter or less as measured by the oxygen pulse method, the rich spike introduction time is relatively short, Catalyst 11
The O ₂ storage capability becomes higher than about 150 cc / liter as measured in an oxygen pulse method, rapidly it can be seen that the rich spike introduction time becomes longer.

[0048] H by the way, if so O ₂ storage capability of the light-off catalyst 11 becomes more than about 150 cc / liter, since the rich spike introduction time is shortened, the O ₂ storage capability of the light-off catalyst 11
It is considered that C and CO have almost no effect on oxidation. Incidentally, the light-off catalyst 11 having an O ₂ storage capacity of about 300 cc / liter as measured by the oxygen pulse method.
To exhaust purification device provided with, in the exhaust purification apparatus to O ₂ storage capacity with a light-off catalyst 11 to about 150 cc / liter as measured in the oxygen pulse method, in terms of fuel consumption rate, consumption of about 60% of the fuel The effect of reducing the rate can be obtained. Therefore, the O ₂ storage capacity of the light-off catalyst 11 was about 1 as measured by the oxygen pulse method.
It is preferred to be 50 cc / liter or less.

Even when the regeneration control for desorbing the sulfur component from the light-off catalyst 11 is taken into consideration, the light-off catalyst 1
Preferably, the O ₂ storage capacity of No. 1 is about 150 cc / liter or less as measured by the oxygen pulse method.

Therefore, the light-off catalyst 11 in the present embodiment is prepared by adding an additive having an O ₂ storage function, such as ceria CeO ₂ , to 25 g per liter of the light-off catalyst 11 (ie, 25 g / addition amount). Liters) or less (including the case where the addition amount is zero), the amount of oxygen that can be stored in the light-off catalyst 11 becomes 150 cc per liter of the light-off catalyst 11 (that is, the oxygen amount). (150 cc / liter) to reduce the O ₂ storage capacity of the light-off catalyst 11 by the above-described oxygen pulse method.

In this case, the ceria C of the light-off catalyst 11
eO_Two As shown in FIG. 2 (a), the amount of
Sea urchin, ceria CeO_Two Of a structure without any addition of
Just do it. Also, as shown in FIG.
The catalyst 11 has a multilayer structure (in FIG.
And B-layer structure).
If only one layer (for example, only layer A or layer B)
Layer only) Ceria CeO _Two With no structure added
Just do it.

As described above, in the present embodiment, by reducing the amount of ceria CeO ₂ added to the light-off catalyst 11, HC and CO supplied to the lean NO _X catalyst 13 at the time of recovery control and regeneration control are oxidized. Therefore, NO _X and SO _X adsorbed on the lean NO _X catalyst 13 can be surely desorbed without deteriorating the fuel efficiency, whereby the lean NO _X catalyst 13 Durability can be increased.

When the addition amount of ceria CeO ₂ is reduced as described above, it is necessary to perform the air-fuel ratio control more accurately so that the rich operation is performed at the time of cold start of the engine and HC and CO are not discharged. . This is because, when the restoration control (rich spike) and the regeneration control are performed, HC and CO supplied to the lean NO _X catalyst by the restoration control and the regeneration control are stored in the ceria CeO ₂ of the light-off catalyst 11. This is because oxidation and consumption by the O ₂ are suppressed.

[0054] three-way catalyst 14 is disposed downstream of the exhaust passage 3 (underfloor side), and is particularly used for purifying CO in the exhaust gas, the HC and NO _x after engine warm-up.

In the stoichiometric feedback operation mode, the three-way catalyst 14 controls CO, HC and N in exhaust gas.
It has a function of purifying O _x and oxidizing CO and HC in the lean operation mode. In the present embodiment, the light-off catalyst 11 which does not comprise a ceria CeO ₂ (or those with reduced amounts of ceria CeO ₂₎ constitutes a, in this case, O ₂ storage ability is decreased, the exhaust gas Since it is considered that the purification efficiency of HC in the interior is reduced, the three-way catalyst 14 is configured to include ceria CeO ₂ having an O ₂ storage function so as to improve the purification efficiency of HC in the exhaust gas.

Further, by increasing the O ₂ storage capacity of the three-way catalyst 14, for example, the lean N
The SO _X desorbed from the O _X catalyst is converted into H 2 present around the catalyst.
Changes to harmful substances that react with C H ₂ S This H ₂
There is an advantage in that S can be oxidized by O ₂ stored in the three-way catalyst 14 to reduce the amount of H ₂ S released.

[0057] lean NO _x catalyst. 6A, the upstream side of the exhaust passage of the three-way catalyst 14 is provided in the 3 (an exhaust passage of underfloor side), engine during perform lean operation saving operation while the air-fuel ratio to the lean and to be able to sufficiently purify the NO _x in the exhaust gas also. This lean NO _x catalyst 6A
It is, N in the exhaust gas by adsorbing the NO _X on the catalyst
Of the type which purifies O _X at (occlusion-type lean NO _X catalyst, trap type lean NO _X catalyst), for example, FIG. 3
As shown in (a), an alumina Al ₂ O ₃ is used as a base material,
On this base material, a metal component M such as barium Ba as an occluding material and platinum Pt as an active metal are respectively supported.

The metal component M carried on the lean NO _X catalyst 13 adsorbs NO _X in the exhaust gas in an oxygen-excess atmosphere, and desorbs the adsorbed NO _X when the oxygen concentration decreases.
O _X adsorption, those having a desorption function, such as barium Ba, sodium Na, may be configured as bearing at least one of the metal component M of potassium K.

The lean NO _X catalyst 13 of the present embodiment
Although the substrate is made of alumina Al ₂ O ₃ , other substrates such as zirconium oxide ZrO ₂ may be used. Further, the lean NO _x catalyst 13 may be configured to have a three-way function. Next, the function of adsorbing and desorbing NO _X in the lean NO _X catalyst 13 configured as described above will be described.

In an oxygen-excess atmosphere (lean atmosphere), as shown in FIG. 3B, first, O ₂ is adsorbed on the surface of platinum Pt, and NO in the exhaust gas reacts with O ₂ on the surface of platinum Pt. The result is NO ₂ (2NO + O ₂ → 2NO ₂ ). On the other hand, as for the storage material, for example, barium Ba supported on the lean NO _X catalyst 13, a part of barium Ba reacts with O ₂ and exists as barium oxide BaO. , C in exhaust gas
Reacts with O and the like to form barium carbonate BaCO ₃ .

Under these circumstances, part of the generated NO ₂ is further converted to barium oxide BaO and CO 2 on platinum Pt.
Reacts with the barium carbonate BaCO ₃ generated from the catalyst to generate barium nitrate Ba (NO ₃ ) _{2, which} is adsorbed by the lean NO _X catalyst 13. When such a reaction is represented by a chemical reaction formula, the following reaction formula (1) is obtained. _{BaCO 3 + 2NO + 3 / 2O} 2 → Ba (NO 3) 2 + CO 2 ··· (1) On the other hand, the atmosphere in which the oxygen concentration is lowered (rich atmosphere), as shown in FIG. 3 (c), the amount of NO ₂ Decreases, the reverse reaction proceeds, and the lean NO _X catalyst 13
O ₂ is eliminated.

That is, barium nitrate Ba (NO ₃ ) ₂ adsorbed on the lean NO _X catalyst 13 reacts with CO in the exhaust gas on the surface of platinum Pt to produce NO ₂ and barium carbonate BaCO ₃ , NO ₂ is a lean NO _X catalyst 13
Is detached from This can be represented by the following reaction formula (2) when expressed by a chemical reaction formula. Ba (NO ₃ ) ₂ + CO → BaCO ₃ + 2NO + O ₂ (2) However, 2NO + O ₂ → 2NO ₂ (a part of NO is discharged as it is.) Then, the desorbed NO ₂ is exhausted. Unburned HC and H inside
₂ , reduced by CO and discharged as N ₂ (NO
+ CO → 1 / 2N ₂ + CO ₂ ), (NO + H ₂ → 1 / 2N
₂ + H ₂ O).

As described above, the lean NO_XIn the catalyst 13,
Barium nitrate Ba (NO_Three )_Two And barium carbonate BaC
O_Three Exists in a state of chemical equilibrium, and lean NO_XCatalyst 13
Reaction in each direction depending on the atmosphere near the
Become. By the way, such a lean NO_xCatalyst 6A is
SO in exhaust gas in oxygen-excess atmosphere_XAdsorbs the predetermined height
Under a warm atmosphere, if the oxygen concentration decreases, the adsorbed SO _X
Also has the property of desorbing a part of it.

That is, this lean NO_XThe catalyst 13
As shown in FIG. 4A, an oxygen-excess atmosphere (lean atmosphere)
Then, O_Two Is adsorbed on the surface of platinum Pt, fuel and lubrication
The sulfur component in the oil is_TwoDischarged as
And the SO contained in this exhaust gas _Two Is on the surface of platinum Pt
In O_Two Reacts with SO_Three (2SO_Two + O_Two → 2S
O _Three ).

Next, the generated SO_Three Part of is platinum P
barium carbonate BaCO using t as a catalyst_Three Reacting with
Barium sulfate BaSO_Four Is generated and lean N
O_XAdsorbed on the catalyst 13. This is shown by the chemical reaction formula
And the following reaction formula (3). BaCO_Three + SO_Three → BaSO_Four + CO_Two ... (3) On the other hand, in an atmosphere in which the oxygen concentration is low (rich atmosphere)
Represents a lean NO, as shown in FIG._XFor catalyst 13
Adsorbed barium sulfate BaSO_Four Part of and in exhaust gas
Of barium carbonate B by the catalytic action of platinum Pt
aCO_Three And SO _Two Is generated and SO_Two Is lean no_X
It is desorbed from the catalyst 13. This is represented by a chemical reaction formula,
The following reaction formula (4) is obtained.

BaSO ₄ + CO → BaCO ₃ + SO ₂ (4) By the way, in such a lean NO _X catalyst 13, NO
_X adsorption, to purify NO _X by an elimination action, NO
_{When X} is adsorbed, it needs to be desorbed appropriately. Further, in the lean NO _X catalyst 13, barium carbonate BaCO ₃ and barium sulfate BaSO ₄ exist in a state of chemical equilibrium, and the reaction in each direction easily proceeds according to the atmosphere near the lean NO _X catalyst 13. That is, as the air-fuel ratio of the exhaust gas (exhaust air-fuel ratio) becomes smaller (that is, as the air-fuel ratio becomes richer), barium sulfate BaSO ₄ is more easily decomposed and barium carbonate BaCO ₃ is more easily generated. Conversely, as the air-fuel ratio of the exhaust gas increases (that is, the air-fuel ratio becomes leaner), barium carbonate BaCO ₃ is more easily decomposed, and barium sulfate BaSO ₄ is more easily generated.

However, in practice, barium sulfate B
Since aSO ₄ is hardly decomposed, barium sulfate Ba is reduced even when the oxygen concentration is reduced (that is, even when the air-fuel ratio becomes rich).
SO ₄ remains without being decomposed. Thus, barium nitrate Ba (NO ₃ ) is used for the amount of barium Ba used.
₂ is no longer generated, N by the lean NO _X catalyst 13
Since the purification ability of O _x is reduced (this is
That poisoning), SO _X adsorbed in the lean NO _X catalyst 13
Also need to be appropriately desorbed.

Further, for example, when the concentration of the sulfur component contained in the fuel or the lubricating oil is high, the lean NO _X catalyst 13 deteriorates before reaching the target life time (for example, about 100,000 km of traveling distance). , there is also a case where nO _X purification efficiency is significantly reduced, also necessary that the concentration of the nO _X discharged into the atmosphere does not exceed the permissible value due to regulations.

For this reason, in the lean burn internal combustion engine according to the present embodiment, when the NO _X purification efficiency of the lean NO _X catalyst 13 is reduced by the adsorption of NO _X , the adsorbed NO _X is desorbed and the NO _X purification efficiency is reduced. the control for reviving (resurrected control), SO _X in the lean NO _X catalyst 13 adsorbs N
A control (regeneration control) for regenerating the lean NO _X catalyst 13 by desorbing the adsorbed SO _X when the O _X purification efficiency is reduced is performed.

Therefore, the lean burn according to the present embodiment
The ECU 20 of the internal combustion engine has a functional block diagram shown in FIG.
NO_XPurification efficiency calculating means 21, NO_Xpurification
Efficiency determining means 22, operation mode setting means 23,
Mode selection means 24 and fuel injection control means 25 are provided.
Have been. Where NO_XPurification efficiency calculating means 21
Upstream NO_XSensor 9 and downstream NO_XFrom sensor 10
NO based on the detection information_XN by catalyst 13
O_XThis is for calculating the purification efficiency. That is, NO_X
The purifying efficiency calculating means 21 is provided with an upstream NO_XBy sensor 9
Detection value A₁ And downstream NO_XA value detected by the sensor 10 _Two 
And no lean_XNO by catalyst 13_XPurification efficiency
(= A_Two / A₁ ) Is calculated.

This NO_XN by the purification efficiency calculating means 21
O_XThe calculation of the purification efficiency is performed when the operation mode is the intake lean operation mode.
Switch to lean operation mode such as load mode or compression lean operation mode.
After a certain period of time
Has become. Therefore, NO _XPurification efficiency calculation means 21
Means that the count value of the timer 29 is read.
When the count value reaches the set value, calculate
Swelling.

The NO _X purification efficiency determining means 22 determines the lean N
When the NO _X purification efficiency of the O _X catalyst 13 decreases due to NO _X adsorption, control for restoring the NO _X purification efficiency (restoration control), the SO _X is adsorbed on the lean NO _X catalyst 13 and the NO _X purification efficiency is reduced. When it is lowered, the lean NO _X catalyst 13
It is determined whether or not it is necessary to perform any one of the controls for reproducing (reproduction control).

For this reason, the NO _X purification efficiency determining means 22 includes a recovery control determining means 22A and a regeneration control determining means 22B. First, the recovery control determining means 22A performs the operation in the lean operation mode such as the intake lean operation mode or the compression lean operation mode for a predetermined time (for example, about 6 hours) in order to determine whether the recovery control needs to be performed.
(0 seconds). For this reason, the count value of the timer 29 is read into the recovery control determination means 22A.

When it is determined by the recovery control determining means 22A that the operation in the lean operation mode has been performed for a predetermined time (for example, about 60 seconds), it is determined that the recovery control needs to be performed. The output is provided to an additional fuel injection control means 27 provided in a fuel injection control means 25 described later. The reproduction control determination means 22B includes:
NO to determine whether or not it is necessary to perform regeneration control
_This is for determining whether or not the NO _X purification efficiency η after the restoration control calculated by the _X purification efficiency calculation means 21 has become smaller than the regeneration control determination value a.

[0075] Then, judged by the reproduction control determining unit 22B, if the NO _X purification efficiency after the resurrection control η is determined to have become smaller than the threshold value a for regeneration control, it is necessary to perform playback control Then, the output is outputted to an additional fuel injection control means 27 provided in the fuel injection control means 25 described later. Note that the reproduction control determination value a is
As shown in FIG. 7, when the concentration of the sulfur component contained in the fuel is 100 ppm, the value is set as a value corresponding to the NO _X purification efficiency of the lean NO _X catalyst 13 when the traveling distance reaches about 10,000 km. Is done.

Incidentally, the fuel injection control means 24 comprises a normal fuel injection control means 25 and an additional fuel injection control means 26. Among these, the additional fuel injection control means 25 performs additional fuel injection as the recovery control when the recovery control determination means 22A determines that the recovery control is necessary, and the regeneration control determination means 22B The fuel injection valve 8 is controlled so that additional fuel injection is performed as regeneration control when it is determined that control is necessary.
This controls the operation of.

The additional fuel injection control means 25 sets the injection start timing T _INJ of the additional fuel injection based on the detection information (for example, the engine speed information and the engine load information) from the various sensors 28. The injection time of the additional fuel in each cycle is set. First,
The setting of the injection start timing T _INJ and the injection time of the additional fuel injection for performing the additional fuel injection as the recovery control will be described.

The injection start timing T _INJ and the injection time for performing the additional fuel injection as the recovery control are shown in FIG.
As shown in (2), the vicinity of the lean NO _X catalyst 13 is set to be a rich atmosphere with a reduced oxygen concentration. For example, to achieve a rich atmosphere, the air-fuel ratio is set to about 13 and the operation is performed for about 2 seconds. In this case, when the additional fuel injection as the recovery control is started, the timer 29 is started.
May start counting, and the additional fuel injection control means 27 may read the count value of the timer 29.

The additional fuel injection as the recovery control is for making the vicinity of the lean NO _X catalyst 13 a rich atmosphere, and is also called a rich spike. When such a control is performed in an operation in a lean operation mode such as an intake lean operation mode or a compression lean operation mode, the vicinity of the lean NO _X catalyst 13 becomes an oxygen-excess atmosphere (lean atmosphere), and Since the reaction represented by the reaction formula (1) proceeds, if these lean operation modes are performed for a predetermined time (for example, about 60 seconds) or more, the lean N
A large amount of NO _X is adsorbed on the O _X catalyst 13 and lean NO
_This is because the NO _X purification efficiency by the _X catalyst 13 gradually decreases.

As a result, the lean NO _X catalyst 13
O also _X adsorption amount is reduced is NO _X purification efficiency by increasing, it is performed the additional fuel injection as resurrected controlled by the additional fuel injection control unit 27, the above-mentioned reaction formula (2)
Since, as shown in the reaction is promoted, it is possible to the NO _X from the lean NO _X catalyst 13 desorbed, as shown in FIG. 6 (b), to improve the NO _X purification efficiency due to lean NO _X catalyst 13 be able to. FIG. 6B is a partially enlarged view of a portion X in FIG.

In the recovery control of the lean NO _X catalyst 13, in this embodiment, since the amount of ceria CeO ₂ added to the light-off catalyst 11 is reduced, the CO supplied by the recovery control becomes light-off. Oxidation and consumption by O ₂ stored in the ceria CeO ₂ provided in the catalyst 11 is suppressed, whereby lean NO
NO _X adsorbed on the _X catalyst 13 can be reliably desorbed, and its durability can be enhanced.

Next, the setting of the injection start timing T _INJ and the injection time of the additional fuel injection for performing the additional fuel injection as the regeneration control will be described. The injection start timing T _INJ and the injection time for performing the additional fuel injection as the regeneration control are set to a rich atmosphere (for example, A / F = about 12) in which the oxygen concentration is reduced in the vicinity of the lean NO _X catalyst 13, and
The temperature is set to be equal to or higher than a predetermined temperature (for example, about 600 ° C.), and is performed for a predetermined time (for example, about 3 minutes).

That is, the additional fuel injection control means 27
Additional fuel injection as regeneration control by
Between the middle stage and the end of the exhaust stroke.
Period during which heat during combustion (main combustion) exists
Injection start time T
_INJIs set. Thus, the injection start timing T_INJSet
Is to determine the fuel injected by the additional fuel injection,
Combustion (hereinafter also referred to as reburning)
Lean NO _XSO adhering to catalyst 13_XShould be removed
No, lean NO_XThe oxygen concentration in the vicinity of the catalyst 13 decreased
Rich atmosphere and high temperature atmosphere (for example, about 60
0 ° C.).

More specifically, the additional fuel injection control means 25
Is to correct the basic fuel injection start timing Tb _INJ, which is the basis for the additional fuel injection after the latter stage of the expansion stroke, by the coolant temperature θ _W , the EGR amount, and the ignition timing T _IG in the main combustion, thereby making the injection start timing T b Set _INJ . Further, the additional fuel injection control means 104 sets the basic drive time t _B which is the basis for additional fuel injection after the expansion stroke,
The injector drive time t _PLUS is set by correcting the injection start timing T _INJ and the catalyst temperature θ _CC .

Such control is performed for a predetermined time.
(E.g., about 60 seconds) lean NO _XResurrection of catalyst 13
Even if you perform a rich spike as a control,
NO_XThe vicinity of the catalyst 13 is in an oxygen-excess atmosphere (lean atmosphere).
), Lean NO_XIn the catalyst 13, the above reaction
Since the reaction represented by equation (3) also proceeds, lean NO_Xcatalyst
SO gradually to 13_XAlso adsorbs, lean NO_XFor catalyst 13
Barium sulfate BaSO_Four Adsorbed as lean NO_XTouch
Even if the oxygen concentration in the vicinity of the medium 13 decreases (that is,
Even when the ratio becomes rich), barium sulfate BaSO_Four Is a minute
Lean NO without understanding_XRemains adsorbed on the catalyst 13
SO_XBa used for the adsorption of water
Barium nitrate Ba (NO_Three )_Two Is no longer generated
This allows for a lean NO_XNO by catalyst 13_Xof
This is because the purification ability is reduced.

In order to measure the predetermined time, the reproduction system
When the additional fuel injection control is started, the timer 29
Starts counting and additional fuel injection
The control unit 25 reads the count value of the timer 29.
It is supposed to be. As a result, lean NO_Xcatalyst
SO to 13_XNO due to increased adsorption_XPurification
Additional fuel injection control as regeneration control even if
The reaction promotes the reaction as shown in the above reaction formula (4).
Advanced, lean no_XCatalyst 13 to SO _XDesorb
As shown by the solid line A in FIG.
NO_XNO by catalyst 13_XImproving purification efficiency
Can be.

In FIG. 7, solid line A represents NO after the restoration control.
_XThe purification efficiency is shown, and the broken line B indicates NO after regeneration control._X
This shows the purification efficiency. Such a lean NO_XCatalyst 1
In the reproduction control of No. 3, the light-off touch
Ceria CeO of medium 11_Two To reduce the amount of
Therefore, the CO supplied by this regeneration control is turned off.
Ceria CeO of catalyst 11_Two O stored in _Two By acid
Can be reduced and consumed.
, Lean NO_XSO adsorbed on catalyst 13_XSurely
Can be separated and its durability can be increased
It is.

The lean burn internal combustion engine according to the present embodiment
Because of the configuration described above, the restoration control and the reproduction control are performed, for example, as shown in the flowchart of FIG. First, in step S10, a restoration control mode (rich spike mode) is executed. In this rich spike mode, although not shown in detail in FIG. 8, the following processing is performed.

That is, when the lean NO _X catalyst 13 is operated in a lean operation mode such as a compression lean operation mode or an intake lean operation mode, the amount of NO _X adsorbed gradually increases. NO _X adsorbed on the _X catalyst 13 is desorbed to remove NO from the lean NO _X catalyst 13.
_It is determined whether or not it is necessary to perform the restoration control to restore the _X purification efficiency.

Whether the recovery control needs to be performed or not is determined by the recovery control determining means 22A for a predetermined time (for example, about 60 seconds) in the lean operation mode such as the intake lean operation mode or the compression lean operation mode. Is determined based on whether or not has elapsed. As a result of this determination, if it is determined that the resurrection control is necessary, the additional fuel injection control means 27
As a result, additional fuel injection (rich spike) is performed as recovery control.

As a result, the vicinity of the lean NO _X catalyst 13 is made rich and the NO _X adsorbed on the lean NO _X catalyst 13 is desorbed, so that the NO _X purification efficiency of the lean NO _X catalyst 13 increases. In this case, since the amount of ceria CeO ₂ added to the light-off catalyst 11 according to the present embodiment is small, CO supplied by the reactivation control is oxidized by O ₂ stored in the ceria CeO ₂ provided in the light-off catalyst 11. the is consumed is suppressed Te, thereby, reliably desorbing NO _X adsorbed in the lean NO _X catalyst 13.

However, the predetermined time (for example,
Even if the resurrection control is performed every 60 seconds),
No_XThe catalyst 13 contains SO_XAlso adsorbed, once adsorbed
SO _XCan not be detached by the above resurrection control
So gradually SO_XAs the amount of adsorption increases, for example, traveling
Lean NO when the distance reaches about 10,000 km_XCatalyst 1
NO by 3_XPurification efficiency will be reduced.

[0093] Therefore, in step S20, after computing the NO _X purification efficiency η with the lean NO _X catalyst 13 after resurrection controlled by NO _X purification efficiency calculating unit 21, at step S30, the playback control determination unit 22B, It is determined whether or not the NO _X purification efficiency η after the recovery control is smaller than the regeneration control determination value a. The result of this determination, if the revived control after of the NO _X purification efficiency η is determined not to be smaller than the determination value a reproduction control is still returns to step S10 for regeneration control is not required after resurrection Control NO _X Purification efficiency η
Are smaller than the reproduction control determination value a, the processing from step S10 to step S30 is repeated.

On the other hand, when it is determined that the NO _X purification efficiency η after the recovery control is smaller than the regeneration control determination value a, SO _X is adsorbed on the lean NO _X catalyst 13 so that N
O _X purification efficiency is degraded and it is considered that it is necessary to playback control, the process proceeds to step S40, the reproduction processing mode is executed. In this regeneration processing mode, the additional fuel injection control means 27 performs additional fuel injection as regeneration control.

As a result, the vicinity of the lean NO _X catalyst 13 is set to a rich atmosphere, and a predetermined temperature (for example, about 6
(00 ° C.) or more, and the SO _X adsorbed on the lean NO _X catalyst 13 is desorbed, so that the NO _X purification efficiency of the lean NO _X catalyst 13 increases. The CO supplied by the regeneration control can be suppressed from being oxidized and consumed by O ₂ stored in the ceria CeO ₂ of the light-off catalyst 11, whereby the SO 2 adsorbed on the lean NO _X catalyst 13 can be suppressed. _X is reliably detached.

In this control, the processing from step S10 to step S40 is repeated. Since the exhaust gas purifying apparatus for an internal combustion engine according to one embodiment of the present invention is configured as described above, it has the following operations and effects. In the exhaust gas purifying apparatus for the internal combustion engine, when the engine is started in a cold state, HC in the exhaust gas is reduced by the light-off catalyst 11 provided immediately downstream of the engine.

In the stoichiometric feedback operation mode after the engine is warmed up, HC, CO, and NO _X in the exhaust gas are purified by the light-off catalyst 11 and the three-way catalyst 14. On the other hand, the lean operation mode after the warm-up of the engine, although NO _X in the exhaust gas by the light-off catalyst 11 and the three way catalyst 14 can not be purified by the purification characteristic, NO in the flue gas by the lean NO _X catalyst 13
_X is adsorbed and emission of NO _{X to} the atmosphere is suppressed.

Since the amount of adsorbed NO _{X that} can be adsorbed by the lean NO _X catalyst 13 is limited, when the NO _X purification efficiency is reduced, the vicinity of the lean NO _X catalyst 13 is set to an atmosphere having a reduced oxygen concentration to obtain a lean NO _X catalyst. _A recovery control (rich spike) is performed in order to desorb NO _X adsorbed on the _X catalyst 13 and recover NO _X purification efficiency. The NO _X desorbed from the lean NO _X catalyst 13 during the resurrection control is
Most of them are purified by the three-way catalyst 14.

In this case, since the light-off catalyst 11 according to the present embodiment has a small amount of ceria CeO ₂ added, the oxidation of CO supplied by the reactivation control by the O ₂ stored in the ceria CeO ₂ of the light-off catalyst 11 is performed. Is suppressed.
Thereby, the N adsorbed on the lean NO _X catalyst 13
O _X is desorbed, NO _X purification efficiency will be resurrected.

If SO _X is adsorbed on the lean NO _X catalyst 13 and the NO _X purification efficiency decreases, the lean NO _X
The vicinity of the _X catalyst 13 is made to have
Regeneration control is performed to desorb SO _X adsorbed on the O _X catalyst 13 and regenerate NO _X purification efficiency. In this case, the light-off catalyst 11 according to the present embodiment is ceria C
Since the addition amount of eO ₂ is small, the oxidation of CO supplied by the regeneration control using O ₂ stored in ceria CeO ₂ of the light-off catalyst 11 is suppressed. As a result, the SO _X adsorbed on the lean NO _X catalyst 13 is surely desorbed, and the lean NO _X catalyst 13 is regenerated.

Therefore, the exhaust gas purifying apparatus of this internal combustion engine is
According to the description, when the engine is cold started, NO _xDischarge upstream of the catalyst
Exhaust gas is emitted by the light-off catalyst 11 provided in the air passage.
While reducing the amount of HC in
Ceria CeO of off catalyst 11 _Two Is low in O_Two 
Lean NO due to low storage capacity_XCatalyst 13 with N
O_XAnd SO_XIs adsorbed and NO_XWhen purification efficiency drops
Even lean NO_XNO from catalyst 13_XAnd SO_X
Can be reliably removed and its durability can be increased.
There is an advantage that can be.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, a three-way catalyst 14 is provided separately from the lean NO _X catalyst 13 in the exhaust passage 3 downstream of the lean NO _X catalyst 13 as exhaust gas purifying means. Although configured as described above, it may be configured as a single catalyst having both the function as a lean NO _X catalyst and the function as a three-way catalyst. In this case, the O ₂ storage capability of the light-off catalyst 11 may be set lower than the O ₂ storage capability of the single catalyst.

Further, in the exhaust gas purifying apparatus of the present internal combustion engine, when the lean NO _X catalyst 13 becomes S-poisoned, the lean burn operation region is controlled so as to be narrow, and the function of the three-way catalyst 14 is effectively utilized. so as to, NO _X in the exhaust gas
The component may not be increased. Further, the lean NO.
The life time of the _X catalyst 13 can be extended, and the NO _X component in the exhaust gas can be prevented from increasing.

Further, in the exhaust gas purifying apparatus of the present internal combustion engine, additional fuel injection is performed by the additional fuel injection control means 27 in the restoration control in order to make the vicinity of the lean NO _X catalyst 13 a rich atmosphere. The method of making the vicinity of the lean NO _X catalyst 13 a rich atmosphere as the restoration control is not limited to this, and may be a method of switching the operation mode to the rich side.

Further, in the exhaust gas purifying apparatus of the present internal combustion engine, in the regeneration control, additional fuel injection is performed by the additional fuel injection control means 27 in order to make the vicinity of the lean NO _X catalyst 13 a rich atmosphere and raise the exhaust gas temperature. Do,
Although the exhaust gas temperature is raised, the method is not limited to this. For example, rich operation, retarded ignition timing, or another device (electrically heated catalyst) may be used. .

In the exhaust gas purifying apparatus for an internal combustion engine,
No_XNO of catalyst 13_XTo calculate the purification efficiency, N
O_XLean sensor NO_XUpstream and downstream of the catalyst 13
, But is not limited to this.
O_XNO on the downstream side of the catalyst 13 _XProviding one sensor
NO_XThe exhaust gas discharged from the exhaust gas purification device 6 by the sensor
NO in gas_XThe amount is detected and supplied to the exhaust purification device 6.
NO in exhaust gas_XThe amount is preset according to the operating conditions.
NO_XAmount (value stored in the ECU) and NO_X
Lean NO by comparing the detected value of the sensor with the memory value_X
The deterioration of the catalyst 13 may be estimated.

Further, the exhaust gas purifying apparatus for the internal combustion engine has been described as an in-cylinder injection type internal combustion engine. However, the present invention is not limited to this, and any internal combustion engine capable of lean burn may be used. By the way, in the exhaust gas purification apparatus 6 according to the present embodiment, in order to prevent the lean NO _X catalyst 13 from causing S poisoning, SO _X adsorbed on the lean NO _X catalyst 13 is desorbed by performing regeneration control. However, the method of preventing the lean NO _X catalyst 13 from causing S poisoning is not limited to this, and may be as follows.

That is, lean NO_XS poisoning of catalyst 13
Lean NO to prevent_XExhaust passage on the upstream side of the catalyst 13
3, the sulfur in the exhaust gas as shown by the two-dot chain line in FIG.
Ingredient (SO_xSO adsorbing)_XCatalyst (S-Trap) 12
May be provided. This SO_XThe catalyst 12 is made of SO_XThe catalyst
SO in exhaust gas by adsorbing on _XAlso purify
So alumina alumina_Two O_Three As base material, and as storage material
Metal component M 'such as trontium Sr, white as active metal
Gold Pt is respectively supported and configured. This implementation
SO in form_XIn the catalyst 6B, the base material was alumina Al._Two O_Three 
But zirconium oxide ZrO_Two Other base materials such as
Can also be used.

The metal component M ′ carried on the SO _x catalyst 6B adsorbs SO _x in the exhaust gas in an oxygen-excess atmosphere,
SO _X concentration of oxygen desorbs SO _X adsorbed to decrease
It has a function of adsorbing and desorbing NO, and hardly adsorbs NO _X when the air-fuel ratio is lean, such as strontium Sr, calcium Ca, zinc Zn, and manganese Mn.

Since the SO _X catalyst 12 has a limit in the amount of SO _X adsorbed similarly to the NO _X catalyst, the vicinity of the SO _X catalyst 6B is changed to a rich atmosphere with a reduced oxygen concentration by, for example, injecting additional fuel. sO _X catalyst 6B adsorbed sO _X can be desorbed by, thereby, so that can prevent deterioration of the purifying ability of sO _X by sO _X catalyst 6B. Also in this case, since the O ₂ storage capacity of the light-off catalyst is low, CO in the exhaust gas is not oxidized by the light-off catalyst, so that SO _X can be desorbed without deteriorating fuel efficiency.

It should be noted that SO_XIn the catalyst 6B, S in the exhaust gas
O_XAdsorbs, but NO in exhaust gas _XDoes not adsorb
But NO not adsorbed on strontium Sr_XIs
SO _XLean NO disposed downstream of the catalyst 6B_Xcatalyst
13 will be absorbed.

In this case, the SO 3 is provided separately from the light-off catalyst 11 in the exhaust passage 3 downstream of the light-off catalyst 11.
_{Although the X} catalyst 12 is provided, it may be configured to have both a function as a light-off catalyst (three-way function) and a function as a SO _X catalyst. Again,
Since the amount of ceria CeO ₂ added to the light-off catalyst 11 is small, the trapped SO ₂ reacts on the catalyst with O ₂ stored in ceria CeO ₂ to become SO ₃ , which is adsorbed by the lean NO _X catalyst 13. That can be suppressed.

[0113] Further, as described above, provided with a SO _X catalyst 12, SO _X adsorbed in the lean NO _X catalyst 13
May be performed.

[0114]

As described in detail above, claims 1 to 4 are described.
According to the internal combustion engine exhaust purification apparatus of the present invention,
Exhaust passage upstream of exhaust gas purifying means during cold start of Seki
HC in exhaust gas by light-off catalyst provided in
While it can be surely reduced,
O_Two Due to low storage capacity, NO
_XAnd SO_XIs adsorbed and NO_XWhen purification efficiency drops
Exhaust gas purification means
From NO_XAnd SO_XCan be reliably removed, and
There is an advantage that the durability of the device can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an overall configuration of an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a light-off catalyst of the exhaust gas purification device for an internal combustion engine according to one embodiment of the present invention;
(A) shows the case of a single layer structure, and (b) shows the case of a multilayer structure.

FIG. 3 is a schematic diagram for explaining the principle of NO _X purification of a lean NO _X catalyst in a lean burn internal combustion engine according to one embodiment of the present invention, and FIG. 3 (a) is a diagram showing a configuration of a lean NO _X catalyst; is a diagram showing a (b) is a diagram showing the NO _X adsorbing function of the lean NO _X catalyst, (c) the NO _X desorption function of the lean NO _X catalyst.

FIG. 4 is a schematic diagram for explaining a sulfur component adsorption / desorption function of a lean NO _X catalyst in a lean burn internal combustion engine according to one embodiment of the present invention, and (a) shows a sulfur component adsorption function; FIG. 3B is a diagram showing a sulfur component desorbing function.

FIG. 5 is a functional block diagram schematically showing a main configuration of a control system of an exhaust gas purification device for an internal combustion engine according to an embodiment of the present invention.

FIG. 6 is a view for explaining a rich spike as a resurrection control in the exhaust gas purifying apparatus for an internal combustion engine according to one embodiment of the present invention, wherein (a) shows an exhaust air-fuel ratio;
(B) shows the NO _X purification efficiency by the lean NO _X catalyst.

FIG. 7 is a diagram for explaining regeneration control in the exhaust gas purification device for an internal combustion engine according to one embodiment of the present invention.

FIG. 8 is a flow chart showing resurrection control, regeneration control, and lean burn operation area reduction control in the exhaust gas purification apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 9 is a diagram showing the overall configuration of a measuring device when measuring the O ₂ storage capacity in a general oxygen pulse method.

FIG. 10 is a diagram showing an effect of the exhaust gas purifying apparatus for an internal combustion engine according to one embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 3 exhaust passage 6 exhaust purification device 11 light-off catalyst 12 SO _X catalyst 13 lean NO _X catalyst (exhaust gas purification means) 14 three-way catalyst (exhaust gas purification means) 20 electronic control unit (ECU) as control means 21 NO _X purification efficiency Calculation means 22 NO _X purification efficiency determination means 22A Recovery control determination means 22B Regeneration control determination means 23 Operation mode setting means 24 Operation mode selection means 27 Additional fuel injection control means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 ZAB F01N 3/28 ZAB 3/28 ZAB 301E 301 B01J 23/42 A // B01J 23/42 B01D 53/36 102B 104A (72) Inventor Uniform Iwachido 5-3-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation

Claims (4)

[Claims] An exhaust air passage provided in an exhaust passage of an internal combustion engine.
NO in exhaust gas when fuel ratio is lean_xAdsorbs exhaust gas
Adsorbed when the oxygen concentration in the atmosphere decreased _xRelease
Is disposed in the exhaust passage upstream of the exhaust gas purifying means,
O than exhaust gas purification means_Two Light with low storage capacity
OFF catalyst and NO of the exhaust gas purifying means_xIf the purification efficiency drops,
Ensure that the atmosphere near the exhaust gas purifying means has an atmosphere with reduced oxygen concentration.
Control means for controlling the exhaust air-fuel ratio.
An exhaust purification device for an internal combustion engine. Wherein the exhaust gas purification means, and the NO _x catalyst in which the exhaust air-fuel ratio is the oxygen concentration of the adsorbed in the exhaust gas to NO _x in the exhaust gas when the lean releasing or reducing the NO _x adsorbed when lowered , characterized in that it is composed of a three-way catalyst exhaust air-fuel ratio provided the exhaust passage downstream of the the NO _x catalyst is for purifying harmful components in the exhaust gas to the stoichiometric air-fuel ratio near the claim 2. The exhaust gas purification device for an internal combustion engine according to claim 1. 3. The light-off catalyst has an oxygen adsorption amount of about 1 per liter of catalyst capacity as measured by an oxygen pulse method.
The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is configured to be 50 cc or less. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the light-off catalyst is configured so that an oxygen storage component added per liter of catalyst capacity is about 25 g or less. .