JPH11229864A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the amount of NOx emission accurately and surely by accurately detecting the deterioration of the NOx catalyst. SOLUTION: The device includes three way catalyst 20 for reducing at least NOx in the exhaust in the atmosphere in the neighborhood of stoichiometric air fuel ratio, and NOx catalyst 19, having weaker reduction function than three way catalyst 20, which is disposed upstream of three way catalyst 20 and which occludes NOx in the exhaust in an excessive oxygen atmosphere and discharges the occluded NOx in a decreased oxygen concentration atmosphere. A NOx sensor 22 for detecting the NOx concentration in the exhaust is provided between three way catalyst 20 and NO. catalyst 19. Further, The NOx concentration of exhaust which has been discharged by NOx catalyst 19 in the decreased oxygen concentration atmosphere and the NOx content of which has not been reduced is detected by a sensor 19. Accordingly, the deterioration of NOx catalyst 19 is accurately understood, as well as decreasing the amount of NOx emission by reducing NOx by three way catalyst 20 and accurately detecting the deterioration of NOx catalyst 19.

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 in which an air-fuel ratio of an air-fuel mixture is controlled to be leaner than a stoichiometric air-fuel ratio to improve fuel efficiency.

[0002]

2. Description of the Related Art As the NO _x catalyst to sufficiently purify NO _x in the exhaust, the NO _x in an oxygen-rich atmosphere to purify NO _x in the exhaust by occluding on the catalyst, the oxygen concentration is reduced it is known that has a function to release the adhered NO _x. That, the NO _x catalyst, in an oxygen concentration excess atmosphere, the NO _x in the exhaust is oxidized to produce nitrate, thereby while occluding NO _x in the atmosphere in which the oxygen concentration is lowered, and occluded in the NO _x catalyst reacting the CO in the exhaust nitrates to produce a carbonate, thereby so as to release NO _x. After operation at a predetermined time oxygen-rich atmosphere is executed, and so as to release the air-fuel ratio of the exhaust oxygen concentration lowering atmosphere (introduction of fuel) NO _x (rich spike).

[0003] Incidentally, a sulfur component (S component) is contained in fuel and lubricating oil, and such a sulfur component is also contained in exhaust gas. In the NO _x catalyst, an oxygen concentration excess atmosphere, sulfur components together with storage of the NO _x is also occluded. That is, the sulfur component burns and is further oxidized on the NO _x catalyst to SO ₃ . Then, a part of the SO ₃ reacts with the NO _x storage agent on the NO _x catalyst to form a sulfate, which is stored in the NO _x catalyst.

[0004] Therefore, nitrate and sulfate adhere to the NO _x catalyst. Sulfate has higher stability as a salt than nitrate, and even in an atmosphere where the oxygen concentration is reduced, the sulfate is one of them. since part only degraded, the amount of sulfate remaining in the nO _x catalyst is increased with time. This results in NO _x
Storage capacity of the catalyst decreases with time, the performance of the the NO _x catalyst will worsen (S poisoning).

[0005] sulfate reducing the _the NO _x storage capacity of the NO _x catalyst has decomposed properties at higher temperatures. Therefore, when a certain amount or more of a sulfur component (SO _x ) adheres to the NO _x catalyst, the air-fuel ratio of the exhaust gas is changed to an atmosphere with a low oxygen concentration (fuel injection) to generate a large amount of HC and CO, and NO _x by the catalyst to a high temperature, so that to release the sO _x (S purge operation).

In order to determine the necessity of performing the S purge operation, NO_x
NO to determine the degree of catalyst deterioration _xNO on the downstream side of the catalyst
_xNO in exhaust after rich spike with sensor attached_xDark
NO degree_xNO by detecting with sensor_xDeterioration of catalyst
Is determined (Japanese Patent Laid-Open No. 7-208151).

However, the oxygen excess after the rich spike
NO for detection in excess atmosphere _xFrom catalyst to atmosphere
NO released_xThe concentration is NO_xUntil the catalyst is near saturation
Is small and the change is small.
NO_xMisjudgment when deterioration is judged based on concentration change over time
There is a high possibility of being determined. Conversely, NO_xThe difference in concentration is clear
When it changes, it is already NO_xThe catalyst is near saturation
It is time, and in this state NO_xLarge amount of NO from catalyst to atmosphere
_xMay have been released.

Therefore, when the NO _x sensor detects the NO _x concentration in the exhaust gas, a method of detecting the NO _x concentration in an atmosphere having a reduced oxygen concentration is considered. That is, the difference of the NO _x concentration before and after the deterioration of the NO _x catalyst when performing the detection in an oxygen concentration reduction atmosphere is greater than the case of detecting in an oxygen-rich atmosphere, the easy detection of the deteriorated state in NO _x sensor I can do it.

[0009]

However [0007], there are the following problems in the case of detecting the concentration of NO _x in the exhaust at an oxygen concentration reduction atmosphere by NO _x sensor. That is, since the NO _x catalyst provided in an internal combustion engine has a normal three-way function, the three-way performance is strong of the NO _x catalyst, NO _x released by comprising an oxygen concentration lowering atmosphere NO _x It is immediately reduced on the catalyst. For this reason, the value detected by the NO _x sensor is the NO _x concentration of the exhaust gas after most of the NO _x has been reduced, and the deterioration state of the NO _x catalyst could not be accurately detected. Therefore, it has been difficult to reliably reduce NO _x emissions.

[0010] The present invention has been made in view of the above circumstances, to provide an exhaust purification system of an internal combustion engine capable of reliably reducing the NO _x emissions to accurately detect the deterioration state of the NO _x catalyst With the goal.

[0011]

In the present invention for achieving the above object, according to an aspect of the reduction catalyst for reducing NO _x at least in the exhaust in an oxygen concentration reduction atmosphere and in an atmosphere of near stoichiometric air-fuel ratio upstream of the reduction catalyst oxygen concentration lowered to release the occluded NO _x in an atmosphere reducing catalytic reduction features than weak NO _x with occludes NO _x in the exhaust in an oxygen-rich atmosphere provided
Consists of a catalyst, a NO _x sensor which detects the concentration of NO _x in the exhaust is provided between the reduction catalyst and the NO _x catalyst, by detecting the concentration of the NO _x by NO _x sensor at an oxygen concentration reduction atmosphere,
NO in exhaust gas discharged from the NO _x catalyst NO _x is not reduced
_x concentration deterioration of the NO _x catalyst is detected by the NO _x sensor is accurately grasped, NO _x is NO _x emitted to the atmosphere is reduced with a reducing catalyst is reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. This embodiment is a multi-cylinder in-cylinder injection in which fuel is directly injected into a combustion chamber as an internal combustion engine in which the air-fuel ratio of an air-fuel mixture is controlled to be leaner than the stoichiometric air-fuel ratio to improve fuel economy characteristics. The internal combustion engine is described as an example. FIG. 1 shows a schematic configuration of an internal combustion engine provided with an exhaust gas purification device according to an embodiment of the present invention, and FIG. 2 shows a fuel injection control map.

As the multi-cylinder in-cylinder injection internal combustion engine, for example, an in-cylinder in-line 4-cylinder gasoline engine (in-cylinder injection engine) 1 for injecting fuel directly into a combustion chamber is applied. In the direct injection engine 1, a combustion chamber, an intake device, an exhaust gas recirculation device (EGR device), and the like are designed exclusively for direct injection.

The cylinder head 2 of the in-cylinder injection engine 1 is provided with an ignition plug 3 for each cylinder and an electromagnetic fuel injection valve 4 for each cylinder.
An injection port of the fuel injection valve 4 is opened in the combustion chamber 5, and fuel injected from the fuel injection valve 4 is directly injected into the combustion chamber 5. Cylinder 6 of in-cylinder injection engine 1
A piston 7 is slidably supported in the up-down direction, and a hemispherically concave cavity 8 is formed on the top surface of the piston 7. The cavity 8 generates a reverse tumble flow in the intake flow, which is opposite to a normal tumble flow.

An intake port 9 and an exhaust port 10 facing the combustion chamber 5 are formed in the cylinder head 2.
Is opened and closed by the drive of the intake valve 11, and the exhaust port 10
Is opened and closed by driving the exhaust valve 12. Exhaust port 1
0 is a large-diameter exhaust gas recirculation port (EGR port) 1
3 branches.

An intake pipe 14 is connected to the intake port 9.
A surge tank, an air cleaner, a throttle body, and the like (not shown) are connected to the intake pipe 14. On the other hand, an exhaust pipe 15 is connected to the exhaust port 10, and the exhaust pipe 15 is provided with a catalyst 16 as an exhaust purification device and a muffler (not shown). The EGR port 13 has a large diameter E
The EG is connected to the intake pipe 14 side via a GR pipe 17.
The R pipe 17 is provided with a stepper motor type EGR valve 18.

The vehicle has an electronic control unit (ECU) 23
The ECU 23 is provided with an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, and a timer and counters. EC
Comprehensive control of the direct injection engine 1 is performed by U23. The detection information of the various sensors is input to the ECU 23. The ECU 23 determines the ignition timing, the amount of the EGR gas introduced, etc., including the fuel injection mode and the fuel injection amount, based on the detection information of the various sensors. 4, the spark plug 3, the EGR valve 18 and the like are drive-controlled.

In the above-described in-cylinder injection engine 1, the intake air flowing into the combustion chamber 5 from the intake port 9 forms a reverse tumble flow, injects fuel in the latter half of the compression stroke, and performs combustion while utilizing the reverse tumble flow. A small amount of fuel is collected only in the vicinity of the spark plug 3 arranged at the center of the top of the chamber 5, and an extremely lean air-fuel ratio state is formed in a portion separated from the spark plug 3. 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 3
While suppressing fuel consumption.

In order to obtain a high output from the engine, fuel from the injector 8 is injected in the intake stroke to homogenize the entire combustion chamber 1 and perform premix combustion. Of course, higher output can be obtained with the stoichiometric air-fuel ratio or rich air-fuel ratio than with the lean air-fuel ratio,
Also at this time, the fuel is injected at a timing such that the fuel is sufficiently atomized and vaporized, so that a high output is efficiently obtained.

The ECU 23 searches the current fuel injection region from the fuel injection map of FIG. 2 based on the load Pe during operation and the engine speed Ne according to the opening of the throttle valve to determine the fuel injection mode. . Thereby, the fuel injection amount according to the target air-fuel ratio in each fuel injection mode is determined, and the drive of the fuel injection valve 4 and the drive control of the ignition plug 3 are controlled according to the fuel injection amount. At the same time, EG
Open / close control of the R valve 18 is also performed.

In a low load region such as an idling operation or a low-speed traveling, the late injection lean mode (compression lean mode) in FIG. 2 is selected as the fuel injection region. In the compression lean mode, fuel injection is performed during the compression stroke (particularly in the latter half of the compression stroke) in order to achieve lean operation by stratified super-lean combustion and improve fuel efficiency.

In the middle load region such as at the time of constant speed running, the fuel injection region is selected from the pre-injection lean mode (intake lean mode) and the stoichiometric feedback mode in FIG. In the intake lean mode, fuel injection is performed during the intake stroke (particularly in the first half of the intake stroke) in order to achieve lean operation by premixed combustion and obtain output by gentle acceleration. In the stoichiometric feedback mode, fuel injection is performed during the intake stroke in order to realize stoichiometric operation (stoichiometric air-fuel ratio operation) by premixed combustion and to improve the output over the intake lean mode.

In a high load region such as during rapid acceleration or high speed running, the open loop mode in FIG. 2 is selected for the fuel injection region. In the open loop mode, rich operation by premixed combustion is realized, and the output is improved compared to the stoichiometric feedback mode. Further, in a region where the throttle valve is substantially fully closed in the course of shifting to coasting or stopping,
The fuel injection region is in the fuel cut mode in FIG. 2 and the supply of fuel into the combustion chamber 5 is stopped.

Next, the structure of the catalyst 16 as an exhaust gas purifying apparatus according to one embodiment of the present invention will be described with reference to FIG. FIG. 3 shows a schematic configuration of the catalyst 16.

As shown in the figure, the catalyst 16 has a function of the NO _x in an oxygen-rich atmosphere to purify NO _x in the exhaust by occluding on the catalyst, the oxygen concentration emits NO _x adhering to decrease and the NO _x catalyst 19 having a includes an atmosphere of the stoichiometric air-fuel ratio CO, and a three-way catalyst 20 as a reducing catalyst having a HC and NO _x possible purifying three way function. The NO _x catalyst 19 is disposed in the exhaust pipe 15 upstream of the three-way catalyst 20, it has little reduction performance.

NO_xNO between the catalyst 19 and the three-way catalyst 20
_xA sensor 22 is provided and NO_xOxygen concentration by catalyst 19
NO in a reduced atmosphere_xNO in exhaust gas on the downstream side of the catalyst 19
_xIs detected. Catalyst when operating in lean mode
When exhaust gas flows into NO.16, NO _xIs NO_xOccluded by catalyst 19
Then, the three-way catalyst 20 purifies HC, CO, and the like and discharges them.
If the operation in the lean mode continues for a predetermined time, another predetermined
The air-fuel ratio of the time exhaust is set to an atmosphere with reduced oxygen concentration (Richs
Pike), NO attached_xNO_xReleased from catalyst 19
NO released with_xIs reduced by the three-way catalyst 20 and purified
Is done. NO during this rich spike_xWith the sensor 22
NO_xNO in exhaust gas on the downstream side of the catalyst 19_xConcentration detected
NO_xNO based on the detection value of the sensor 22_xCatalyst 19
It is determined whether the occlusion capacity has been reduced (deteriorated).

That is, the NO _x catalyst 19 oxidizes NO _{x in} the exhaust gas to produce nitrate in an atmosphere having an excessive oxygen concentration, such as during stratified super-lean combustion operation in the compression lean mode or the intake lean mode. NO _x is absorbed,
Exhaust gas purification is performed.

On the other hand, in an atmosphere having a reduced oxygen concentration, NO
and CO and the reaction of the exhaust and nitrates occluded _x catalyst 19 is generated carbonates, thereby NO _x is released. Therefore, NO if occlusion of the NO _x to _x catalyst 19 progresses, and reduced with additional to such the fuel is injected to reduce the oxygen concentration in NO _x from the catalyst 19 to release the NO _x three-way catalyst 20, NO _x catalyst 1
9 functions are maintained.

By the way, the sulfur components contained in fuel and lubrication in oil (SO _x) is also present in the exhaust, in the NO _x catalyst 19,
In an oxygen-rich atmosphere, SO _x is also stored together with NO _x . That is, the sulfur component is burned, further the NO _x catalyst 19
Is oxidized above becomes SO _3. And part of this SO ₃
Reacts with occluding agent for the NO _x catalyst 19 on an additional NO _x occluding the the NO _x catalyst 19 becomes sulfate.

The NO _x catalyst 19 has a function of releasing the attached SO _x when the oxygen concentration decreases. In other words, the oxygen concentration in the atmosphere decreases, NO _x partially CO and carbonates react in the exhaust gas of the occluded sulfate in the catalyst 19 is produced SO ₃ is released.

[0031] However, sulfates have high stability as salts than nitrates, since the oxygen concentration is not decomposed only a part thereof even if the atmosphere is reduced, time is the amount of sulfate remaining in the NO _x catalyst 19 Increase with. This results in NO _x
Storage capacity of the catalyst 19 decreases with time, the catalyst 1 can not be reduced in _the amount of NO _x which is not occluded is increased three-way catalyst 20
The amount of NO _x emitted from 6 increases.

[0032] Therefore, to understand that the NO _x catalyst 19 adheres more than a certain amount of sulfur components (SO _x) is the the NO _x catalyst 19 has deteriorated, when the NO _x catalyst 19 is deteriorated, the fuel input such as Accordingly, the air-fuel ratio of the exhaust gas in the oxygen concentration lowering atmosphere to generate a large amount of HC and CO, and the the NO _x catalyst 19 to a high temperature,
The stored SO _x is released.

That is, apart from the driving of the fuel injection valve 4 in the main fuel injection for the normal combustion in the combustion chamber 5 (fuel injection in the compression stroke and the intake stroke), it is difficult to affect the output of the engine ( At the end of the expansion stroke), the fuel injection valve 4 is driven to inject additional fuel, and by burning this additional fuel, a large amount of HC and CO is supplied to the NO _x catalyst 19, so that SO ₃ is reduced and NO _x is reduced. by the catalyst 19 to a high temperature, to release the occluded SO _x.

[0034] NO _x because the catalyst 19 to grasp that it has deteriorated, NO is provided between of the NO _x catalyst 19 and the three-way catalyst 20 _x
The sensor 22 detects NO _x in an atmosphere with a reduced oxygen concentration.
And detects the concentration of the NO _x discharged from the catalyst 19. In the atmosphere of oxygen concentration is lowered, greatly change the concentration before and after of the NO _x which the NO _x catalyst 19 is deteriorated. Moreover, since no the NO _x catalyst 19 in the released NO _x is reduced, NO _x in the sensor 22 can reliably determine the deterioration of the NO _x catalyst 19 by detecting the concentration of the NO _x, the degradation state of the NO _x catalyst can be accurately detected. NO _x NO _x discharged from the catalyst 19 is purified by reduction by the three-way catalyst 20, NO _x is reduced is discharged to the atmosphere.

NO_xNO based on the detection information of the sensor 22_x
When the deterioration of the catalyst 19 is determined, NO _xAnd SO_xRelease treatment
And execute NO_xThe regeneration of the catalyst 19 is performed. NO_xTouch
By accurately determining the deterioration of the medium 19, the NO_xAnd SO
_xRelease process, NO_xMaintains the storage capacity of catalyst 19
And always exactly no_xReduce emissions.

By using the catalyst 16 having the above structure,
Without the oxygen concentration is reduced by the NO _x catalyst 19 mostly released NO _x in an atmosphere with a reduced, the NO _x catalyst 19
Flow NO _x sensor can 22 accurately detect the concentration of the NO _x by after, NO _x it is possible to reliably determine the deterioration of the catalyst 19, NO _x is the three-way catalyst 20 is discharged from the NO _x catalyst 19 in which purified it can reduce the emission of NO _x.

Therefore, the storage capacity of the NO _x catalyst 19 can be maintained by reliably determining the deterioration of the NO _x catalyst 19 by the above-described catalyst 16, and the catalyst 16 is always accurate with the purification by the three-way catalyst 20. it is possible to reduce the emissions of the NO _x to.

Incidentally, depending on the catalyst, NO may be used in a reducing atmosphere._xcatalyst
NO released from_xIs partially converted to NH by the reaction on the catalyst._Three
In that case, NO_xSensor is NO_xIn addition to the concentration
Eh NH _ThreeIf the concentration is also to be detected, the
NO output as total_xDeterioration judgment based on sensor output value
May be performed.

The above-described catalyst 16 can be applied to various types of internal combustion engines such as a diesel engine in addition to the direct injection engine 1.

[0040]

Purification system of an internal combustion engine of the present invention exhibits, the concentration of the exhaust of the NO _x which is not reduced is discharged from the NO _x catalyst
It is detected by the NO _x sensor. As a result, NO _x and NO _x with catalyst deterioration can be accurately grasped can be reduced with a reducing catalyst, accurately and reliably emissions of the NO _x to accurately detect the deterioration state of the NO _x catalyst Can be reduced to

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine including a purification device according to an embodiment of the present invention.

FIG. 2 is a fuel injection control map.

FIG. 3 is a schematic configuration diagram of a catalyst.

[Explanation of symbols]

1 cylinder injection engine 19 NO _x catalyst 20 three-way catalyst 22 NO _x sensor 23 Electronic control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 45/00 368 F02D 45/00 368F

Claims (1)

[Claims] And 1. A reduction catalyst for reducing NO _x at least in the exhaust in an oxygen concentration reduction atmosphere is provided in an exhaust passage of the engine and atmosphere near the stoichiometric air-fuel ratio, provided in the exhaust passage upstream of the reduction catalyst Exhausted in an oxygen-rich atmosphere
Absorbed NO _x and stored in an atmosphere with low oxygen concentration
Reduction capacity than the reducing catalyst releases NO _x and weak the NO _x catalyst, it has a NO _x sensor which detects the concentration of NO _x in the exhaust is provided between the the NO _x catalyst and the reduction catalyst An exhaust gas purifying apparatus for an internal combustion engine, comprising: