JPH0988686A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively apply the deterioration recovery process to a catalyst metal without deteriorating the operating property of an engine. SOLUTION: This exhaust emission control device for an engine is provided with an exhaust emission control catalyst 101 installed on the exhaust system of the engine, a deterioration recovery process operating area judging means 102 judging the deterioration recovery process operating area where the exhaust temperature exceeds a prescribed value, an air-fuel ratio detecting means 103 detecting the air-fuel ratio of the engine, and a deterioration recovery processing means 104 applying the proportional integration control to approximate the air-fuel ratio of the air-fuel mixture fed to the engine to a target value on the rich side from the theoretical air-fuel ratio in the deterioration recovery process operating area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an exhaust gas purification device for an internal combustion engine using a catalyst.

[0002]

2. Description of the Related Art In an automobile internal combustion engine or the like, in order to purify exhaust gas, feedback control is performed so that an air-fuel ratio becomes a stoichiometric air-fuel ratio, and HC and CO are oxidized and NO is reduced in an exhaust passage. A system equipped with a three-way catalyst that simultaneously performs the above is widely put into practical use.

Rhodium (Rh) and platinum (Pt), which are general catalytic metals used in this three-way catalyst, exert a catalytic action in a metal state, but at a high temperature which is an air-fuel ratio leaner than the theoretical air-fuel ratio. When exposed to a lean exhaust atmosphere, it oxidizes, causing a so-called temporary deterioration in which catalytic performance is temporarily reduced. This temporary deterioration progresses when exposed to a high-temperature lean exhaust atmosphere, but it has a characteristic that it is reduced and recovered when exposed to a high-temperature rich exhaust atmosphere.

Utilizing such characteristics, there is a conventional apparatus for performing deterioration recovery processing for enriching the air-fuel ratio when the degree of deterioration of the catalyst exceeds a predetermined value (for example, Japanese Patent Laid-Open No. 5-80).
7363, Japanese Patent Application Laid-Open No. 5-808383).

[0005]

However, in the deterioration recovery process performed by such a conventional device, the air-fuel ratio is open-controlled to be considerably richer than the stoichiometric air-fuel ratio, but not only the drivability of the engine is deteriorated, but also FIG. As shown in, it was found that the open control of the air-fuel ratio to the rich side delays the recovery of the catalyst conversion rate compared to the case where the air-fuel ratio is feedback-controlled to the rich side.

The present invention focuses on the above points, and an object thereof is to effectively carry out the deterioration recovery process of the catalyst metal without deteriorating the drivability of the engine.

[0007]

As shown in FIG. 10, an exhaust gas purification apparatus for an internal combustion engine according to claim 1 has an exhaust gas purification catalyst 101 installed in an exhaust system of the engine and an exhaust gas temperature of a predetermined value. Deterioration recovery processing operation range determining means 102 for determining a deterioration recovery processing operation range, an air-fuel ratio detecting means 103 for detecting an air-fuel ratio of the engine, and a mixture supplied to the engine when in the deterioration recovery processing operation range. Deterioration recovery processing means 104 for performing proportional-plus-integral control so that the air-fuel ratio of air becomes closer to the target value on the rich side of the theoretical air-fuel ratio.

[0008]

In the exhaust gas purification device for an internal combustion engine according to claim 1, in the deterioration recovery processing operation range in which the exhaust gas temperature exceeds a predetermined value,
Performing proportional-plus-integral control to bring the air-fuel ratio of the air-fuel mixture supplied to the engine closer to the target value on the rich side of the theoretical air-fuel ratio, and varying the air-fuel ratio of the exhaust gas guided to the catalyst around the target value at a certain frequency. As a result, the exhaust gas temperature is lowered, and the temporary deterioration recovery of the catalyst metal whose permanent deterioration has not progressed is effectively performed. As a result, deterioration of fuel consumption and deterioration of exhaust emission can be suppressed, and the life of the catalyst can be extended.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, a fuel injection valve 5 is attached to an intake passage 8 of an engine 7 and injects fuel in response to a signal from a controller 4.

The exhaust passage 9 is provided with a three-way catalyst 1 that simultaneously oxidizes HC and CO in the exhaust gas and reduces NOx. The three-way catalyst 1 is configured by supporting rhodium (Rh), platinum (Pt), palladium (Pd) as a catalyst metal on a carrier made of alumina or the like, and also supporting ceria or the like.

An O ₂ sensor 2 is installed upstream of the three-way catalyst 1. The O ₂ sensor 2 outputs a signal corresponding to the oxygen concentration in the exhaust gas.

The controller 4 inputs a detection signal from the water temperature sensor 12 for detecting the engine cooling water temperature, a signal from an idle switch (not shown), a detection signal of the intake air amount Q, a detection signal of the rotational speed N, etc. The fuel injection amount Tp is calculated, and the detection signal of the O ₂ sensor 2 is input so that the fuel injection amount is the theoretical air-fuel ratio (1
Feedback control is performed so that it falls within a narrow range around 4.6).

Fuel injection control is performed by detecting the detected intake air amount Q.
And the engine speed N, the basic injection amount Tp is calculated as follows: Tp = K · Q / N (1) where K; constant, and then the basic injection amount Tp is detected. , The throttle opening TVO, the oxygen concentration in the exhaust gas, etc.
Is calculated.

Ti = Tp × (1 + K _TW + K _AS + K _AI + K _MR ) × K _FC + T _S (2) However, K _TW ; water temperature increase correction coefficient K _AS ; start and post-start increase correction coefficient K _AI ; idle Post-increase correction coefficient K _MR ; increase correction coefficient at high load K _FC ; fuel cut correction coefficient T _S ; battery voltage correction amount A pulse signal corresponding to the calculated fuel injection amount Ti is output to each fuel injection valve 5. , Fuel injection control is performed.

An exhaust gas recirculation passage 14 for recirculating a part of the exhaust gas from the exhaust passage 9 is connected to the intake passage 8, and an exhaust gas recirculation control valve 15 via a controller 4 controls the exhaust gas recirculation amount according to operating conditions. To reduce NOx in the exhaust gas.

By the way, the deterioration form of the catalyst metal includes temporary deterioration caused by the oxidation reaction or reduction reaction of the catalyst metal.
In addition to such temporary deterioration, there is permanent deterioration in which the catalyst conversion rate decreases due to physical factors such as a decrease in specific surface area due to thermal deformation of the washcoat and a decrease in dispersity of the catalyst metal.

Rhodium (Rh) and platinum (Pt) exert a catalytic action in a metal state, but when exposed to a high temperature lean exhaust atmosphere at an air-fuel ratio leaner than the theoretical air-fuel ratio, rhodium or platinum is oxidized. As a result, the catalyst performance temporarily deteriorates, so-called temporary deterioration occurs.

FIG. 4 shows an operation in which proportional-integral control is performed so that the air-fuel ratio approaches a target value on the rich side of the stoichiometric air-fuel ratio.
It shows the result of measuring the conversion rate η of CO in the exhaust gas when the operation was continued for a minute. As a result, there is a characteristic that the exhaust temperature on the upstream side of the three-way catalyst 1 recovers in a rich region where the exhaust gas temperature is 650 to 700 ° C. or higher and the air-fuel ratio A / F is 14.6 or lower.

FIG. 5 shows the results of measuring the catalyst conversion rate while operating with the exhaust temperature kept constant, in each of the case where the air-fuel ratio is open-controlled to the rich side and the case where the air-fuel ratio is feedback-controlled to the rich side. Indicates. Thus, it can be seen that the catalyst conversion rate is recovered more quickly when the air-fuel ratio is feedback-controlled to the rich side than when the air-fuel ratio is open-controlled to the rich side.

Paying attention to the above experimental results, the fuel injection amount is theoretically empty based on the detection signal of the O ₂ sensor 2 in the deterioration processing operation range where the exhaust gas temperature is high and the load is high. Feedback control is performed so as to be within a narrow range centered on a predetermined value on the rich side of the fuel ratio.

The flowchart of FIG. 2 shows a routine for performing deterioration recovery processing, which is executed by the controller 4 at regular intervals.

First, in step A1, it is determined whether the idle switch is off or the operation is other than idle.

Next, at step A2, it is judged if the intake air amount Oa is at a high exhaust temperature higher than a predetermined value Q _HTMP .

Subsequently, the routine proceeds to step A3, where it is judged whether or not the increase correction coefficient K _MR under high load is larger than 1.0.

When it is determined that the increase correction coefficient K _MR at high load is smaller than 1.0, after a predetermined delay time D _YHTMP (for example, 4 seconds) has elapsed in step A4, the process proceeds to step A5, As the deterioration recovery process for the three-way catalyst 1, proportional-integral control is performed so that the air-fuel ratio approaches the target value on the rich side.

When it is determined that the increase correction coefficient K _{MR under} high load is 1.0 or more, the process proceeds to step A6, in which the air-fuel ratio is open-controlled using the increase correction coefficient K _MR under high load,
When it is determined in step A7 that the increase correction coefficient K _MR at high load is 1.0 or less, the process immediately proceeds to step A5, and the deterioration recovery process of the three-way catalyst 1 is performed.

The flowchart of FIG. 3 shows a program for air-fuel ratio feedback control executed by the controller 4, which is executed at regular intervals.

First, in step S1, engine speed N, throttle opening TVO, cooling water temperature TW, intake air amount Q
Read in.

In step S2, the basic fuel injection amount Tp is calculated based on these detected values.

In step S3, it is determined whether or not the current operating condition is within the preset air-fuel ratio feedback control region. If it is within the region, the process proceeds to step S4, and if it is outside the region, the process proceeds to step S20. Then, the air-fuel ratio correction coefficient α is set to 100%, the process then proceeds to step S21, the flag FlagV is reset, and the current basic fuel injection amount Tp is stored in BTp in step S11.

In step S4, the O ₂ sensor output VO ₂ is read, and in step S5 VO ₂ is compared with a predetermined value VSL to determine whether the air-fuel ratio of the exhaust gas is richer or leaner than the theoretical air-fuel ratio.

When VO ₂ is judged to be leaner than the predetermined value VSL, the routine proceeds to step S6, where the flag FlagVO
Referring to, the lean air-fuel ratio when the exhaust air-fuel ratio is inverted from rich to lean is detected. When this reversal is detected, the process proceeds to step S7, and the air-fuel ratio correction control coefficient to be described later is calculated.

During lean reversal, the routine proceeds to step S8, where the proportional control amount Pl during rich reversal is set based on a map preset according to the engine speed N and the basic fuel injection amount Tp.
Is searched for, and the proportional control amount Pl is added to the air-fuel ratio correction coefficient α in step S9.

If it is not lean inversion, step S12.
To the lean-time integral control component I of the air-fuel ratio correction control coefficient I.
1 is read, and the routine proceeds to step S13, where the air-fuel ratio correction coefficient α
Is added to the integral control component Il.

After the air-fuel ratio correction coefficient α is determined in this way, the routine proceeds to step S10, where the rich / lean determination result of this time is stored in the flag FlagVO, and the basic fuel injection amount Tp of this time is BTp in step S11. Store in.

On the other hand, when VO ₂ is richer than the predetermined value VSL, the routine proceeds to step S14, where the flag Fl is set.
With reference to ugVO, a rich inversion time when the exhaust air-fuel ratio is inverted from lean to rich is detected.

At the time of rich inversion, the process proceeds to step S15,
The proportional control amount P at the time of lean reversal based on a map preset according to the engine speed N and the basic fuel injection amount Tp
r is searched, and the routine proceeds to step S16, where the air-fuel ratio correction coefficient α
This proportional control amount Pr is subtracted from.

When it is not the time of rich inversion, step S18
To the rich-time integral control component I of the air-fuel ratio correction control coefficient I.
r is read, and the routine proceeds to step S19, where the air-fuel ratio correction coefficient α
This integral control component Ir is subtracted from.

After the air-fuel ratio correction coefficient α is determined in this way, the lean / rich determination result of this time is stored in the flag FlagVO in step S17, and step S11
Then, the basic fuel injection amount Tp of this time is stored in BTp.

The controller 4 calculates the fuel injection amount by the equation (2) based on the air-fuel ratio correction coefficient α calculated in the above routine.

As shown in FIG. 8, during normal operation,
When the air-fuel ratio becomes leaner and the output of the O ₂ sensor 2 becomes smaller than the slice level at which λ = 1, the air-fuel ratio correction coefficient α is first lowered stepwise by the proportional control amount Pl, and then the integral control is performed. It is controlled so that the air-fuel ratio is made thicker by gradually lowering it with the inclination of the minute Il. Thus, when the air-fuel ratio is on the rich side and the output of the O ₂ sensor 2 becomes larger than the slice level corresponding to the theoretical air-fuel ratio, the air-fuel ratio correction coefficient α is first lowered by the proportional control amount Pr in a stepwise manner.
Then, the air-fuel ratio is controlled to be gradually reduced by gradually lowering the slope of the integral control amount Ir. By repeating this control, the actual air-fuel ratio can be maintained near the stoichiometric air-fuel ratio.

On the other hand, during the deterioration recovery process of the three-way catalyst 1, the slice level is shifted to the rich side, and the air-fuel ratio is changed at a predetermined frequency with the slice level on the rich side as the center.

In this way, the air-fuel ratio A in the predetermined deterioration treatment operation range (see FIG. 6) where the exhaust gas can reach a high temperature to some extent.
/ F is controlled to approach the target value (14, 4) on the rich side of the theoretical air-fuel ratio, and the operating state is continuously maintained for a certain period of time, for example, 10 to 30 minutes, so that the deterioration of the three-way catalyst 1 is prevented. It effectively recovers and lowers the exhaust temperature.

As a result, it is possible to suppress deterioration of fuel consumption and deterioration of exhaust emission, and to properly perform temporary deterioration recovery of the catalyst metal that has not deteriorated permanently. As shown in FIGS. 8 and 9, the three-way catalyst is used. The life of 1 can be extended.

[0046]

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect, the stoichiometric air-fuel ratio of the air-fuel mixture supplied to the engine is set in the deterioration recovery operation region where the exhaust temperature exceeds a predetermined value. Temporary deterioration of the catalyst metal that has not progressed permanently due to the configuration in which the proportional-integral control is performed so that it approaches the target value on the rich side of the fuel ratio, and the air-fuel ratio of the exhaust gas guided to the catalyst is changed at a certain frequency centered on the target value. Recovery is effectively performed, fuel consumption deterioration and exhaust emission deterioration can be suppressed, and the life of the catalyst can be extended.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing the control contents of the catalyst deterioration recovery process.

FIG. 3 is a flow chart showing control contents for similarly performing catalyst deterioration recovery processing.

FIG. 4 is a characteristic diagram showing a relationship of catalyst conversion performance with respect to exhaust temperature and air-fuel ratio.

FIG. 5 is a characteristic diagram showing catalyst conversion performance in rich feedback control and rich open control.

FIG. 6 is a setting diagram showing a deterioration recovery processing operation range.

FIG. 7 is a timing chart showing an example of air-fuel ratio control.

FIG. 8 is a characteristic diagram showing the relationship between catalyst conversion performance and vehicle mileage.

FIG. 9 is a characteristic diagram showing a relationship between catalyst conversion performance and traveling distance of a vehicle.

FIG. 10 is a diagram corresponding to a ram of the invention according to claim 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Three-way catalyst 2 O ₂ sensor 4 Controller 5 Fuel injection valve 7 Engine 9 Exhaust passage 101 Catalyst 102 Deterioration recovery processing operation range determination means 103 Air-fuel ratio detection means 104 Deterioration recovery processing means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location F02D 45/00 ZAB F02D 45/00 ZAB 314 314R (72) Inventor Yukinori Mojima Shima, Yokohama 2 Takaracho, Kanagawa-ku Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. A catalyst for purifying exhaust gas, which is installed in an exhaust system of an engine, deterioration recovery processing operation range determining means for determining a deterioration recovery processing operation range in which an exhaust temperature exceeds a predetermined value, and an air-fuel ratio of the engine is detected. Air-fuel ratio detection means and deterioration recovery processing means for performing proportional-integral control so that the air-fuel ratio of the air-fuel mixture supplied to the engine is closer to the target value on the rich side than the theoretical air-fuel ratio when in the deterioration recovery processing operation range. An exhaust emission control device for an internal combustion engine, comprising: