JP2003035189A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system, capable of reducing the use amount of a noble metal three-way catalyst to reduce manufacturing cost, keeping emission control rate high and sufficiently performing an exhaust emission control from the point of time immediately after engine start. SOLUTION: In an exhaust emission control system 1, a trapping device 7 for trapping at least one of HC and NOx, a first emission control implement 81 , having a noble metal three-way catalyst and an oxygen storage agent and a second emission control implement 82 provided with a three-way catalyst having a perovskite type double oxide, are arranged sequentially from the upstream side on the downstream side of an exhaust pipe 3 in an internal combustion engine 2. The oxygen storage agent has the function for regulating the air/fuel ratio of an exhaust gas introduced into the second emission control implement 82 , so as to be within the A/F Window in the three-way catalyst having the perovskite-type double oxide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purification system for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, Pt,
A three-way catalyst made of a noble metal such as Rh and Pd, that is, one using a noble metal three-way catalyst is known.

[0003]

In the noble metal three-way catalyst, the width of the air-fuel ratio that can obtain a high exhaust gas purification rate,
In other words, the A / F window is wide, and therefore, in the exhaust gas purification system using the noble metal three-way catalyst, there is an advantage that the air-fuel ratio control for improving the exhaust gas purification rate becomes relatively easy, while the noble metal three-way catalyst is used. There is a problem that the manufacturing cost is high due to the use of the catalyst. Another problem is that the noble metal three-way catalyst has a low exhaust gas purification performance until the temperature rises to the activation temperature after the engine is started.

[0004]

According to the present invention, the amount of precious metal three-way catalyst used can be reduced to reduce the manufacturing cost, and the exhaust gas purification rate can be maintained high. It is an object of the present invention to provide the exhaust gas purification system capable of sufficiently purifying the exhaust gas.

According to the present invention to achieve the above object,
A trap device for sequentially capturing at least one of HC and NOx from the upstream side to the downstream side of an exhaust system in an internal combustion engine, a first purifier having a noble metal three-way catalyst and an oxygen storage agent, and a perovskite-type mixed oxide A second purifier equipped with a three-way catalyst is provided, and the oxygen storage agent determines the air-fuel ratio of the exhaust gas introduced into the second purifier as A / in the three-way catalyst having the perovskite type double oxide. Provided is an exhaust gas purification system for an internal combustion engine, which has a function of adjusting so as to fit within F Window.

The three-way catalyst having a perovskite type double oxide has a catalytic ability almost equal to that of a noble metal three-way catalyst. Therefore, by arranging the two three-way catalysts in two stages, it is possible to reduce the amount of expensive precious metal three-way catalysts used, and thereby reduce the manufacturing cost of the exhaust gas purification system.

When the exhaust air-fuel ratio of the internal combustion engine is controlled to be the stoichiometric air-fuel ratio, the exhaust air-fuel ratio at the inlet of the first purifier equipped with the noble metal three-way catalyst shows a relatively large variation due to various external factors. A precious metal three-way catalyst has a wide A
Since it has / F Window, the exhaust gas purifying ability is exhibited despite the variation. At the same time, the oxygen storage agent exerts an oxygen storage effect, so that the exhaust air-fuel ratio at the outlet of the first purifier is converged in a substantially straight line shape so that its variation is small.

The A / F window in a three-way catalyst having a perovskite type double oxide is significantly narrower than that of a noble metal three-way catalyst, but the exhaust air-fuel ratio is reduced by the convergence of the exhaust air-fuel ratio by the oxygen storage agent. It can be accommodated in a narrow A / F window, so that the three-way catalyst provided with the perovskite type complex oxide exhibits excellent exhaust gas purification ability.

It is economical to use a perovskite type complex oxide containing a lanthanoid mixture extracted from the ore bastnasite. Because the lanthanoid simple substance has a lot of man-hours to extract the lanthanoid simple substance from the bastnasite, the production cost of the lanthanoid simple substance is high, but the production cost of the lanthanoid mixture is smaller than that of the lanthanoid simple substance. This is because it is significantly cheaper than that of the lanthanoid alone.

Further, the trap device traps HC and / or NOx immediately after the internal combustion engine is started, whereby the exhaust gas is purified. As the temperature of the exhaust gas rises, the trap device becomes H
Although C and NOx are released, the HC and NOx are oxidized and reduced by the first and second purifiers whose temperature is raised to the activation temperature. Further, by using the trap device, it is not necessary to dispose the first and second purifiers in the vicinity of the engine for early activation, which increases the degree of freedom in system layout and increases the number of cells for early activation. Since there is no need to do so, there will be no reduction in engine output.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the first embodiment shown in FIG.
The exhaust purification system 1 is an exhaust system of an internal combustion engine 2, a purification facility 4 arranged in an exhaust pipe 3 in this example, and an air-fuel ratio for controlling an air-fuel ratio (A / F) of an air-fuel mixture supplied to the internal combustion engine 2. And a control device 5. The fuel injection device 6 injects an amount of fuel into the internal combustion engine 2 based on the control signal from the air-fuel ratio control device 5.

The purification equipment 4 comprises a trap device 7, which is sequentially arranged from the upstream side to the downstream side of the exhaust pipe 3, a first purifier 8 ₁ having an oxygen storage agent together with a noble metal three-way catalyst, and a perovskite type double oxidation. Three-way catalyst having a substance (hereinafter referred to as a perovskite type three-way catalyst in this column)
It comprises a second purifier 8 ₂ equipped with. The oxygen storage agent has a function of adjusting the air-fuel ratio of the exhaust gas introduced into the second purifier 8 ₂ so that it falls within the narrow A / F window of the perovskite type three-way catalyst. The trap device 7 is a well-known device, and the HC and NO
One of x, and in the embodiment, has a function of trapping both.

In the exhaust pipe 3, an air-fuel ratio sensor (O ₂ sensor) 9 is arranged upstream of the purification equipment 4, and the air-fuel ratio sensor 9 is discharged from the internal combustion engine 2 and introduced into the purification equipment 4. Of the air-fuel ratio of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 2 is detected as the oxygen concentration. The air-fuel ratio control device 5, based on the signal from the air-fuel ratio sensor 9,
The air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 2 becomes the stoichiometric air-fuel ratio (A / F = 14.7) at the upstream of the purification equipment 4 of the exhaust pipe 3, that is, at the upstream of the first purifier 8 _1. To control.

In the above structure, when the air-fuel ratio sensor 9 detects the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 2, the detection signal is fed back to the air-fuel ratio controller 5. In the air-fuel ratio control device 5, the fuel injection amount is calculated based on the detection signal so that the target air-fuel ratio, that is, the exhaust air-fuel ratio upstream of the purification equipment 4, becomes the stoichiometric air-fuel ratio, and the amount of fuel is the fuel injection device. 6 is injected into the internal combustion engine 2.

When the exhaust air-fuel ratio of the internal combustion engine 2 is controlled so as to be the stoichiometric air-fuel ratio, the exhaust air-fuel ratio at the inlet of the first purifier 8 ₁ causes a relatively large variation due to various external factors, etc. Three-way catalyst has a wide A / F window
Since it has w, the exhaust gas purification performance is exhibited despite the variation. At the same time, since the oxygen storage agent exerts an oxygen storage effect, the exhaust air-fuel ratio at the outlet of the first purifier 8 ₁ is converged in a substantially linear shape so that its variation is small.

A / F of the perovskite type three-way catalyst
Although the window is significantly narrower than that of the noble metal three-way catalyst, the exhaust air-fuel ratio is converged by the oxygen storage agent, so that the exhaust air-fuel ratio is narrowed.
w, which allows the perovskite type three-way catalyst to exhibit excellent exhaust gas purification performance.

Further, the trap device 7 captures HC and / or NOx immediately after the start of the internal combustion engine 2, whereby the exhaust gas is purified. Trap device 7 with temperature rise of exhaust gas
Releases HC and NOx, and the HC and NOx are oxidized and reduced by the first and second purifiers 8 ₁ and 8 ₂ whose temperature has risen to the activation temperature. Furthermore, the trap device 7
By using, it is not necessary to dispose the first and second purifiers 8 ₁ and 8 ₂ in the vicinity of the engine 2 for early activation, the degree of freedom in system layout is increased, and the number of cells for early activation is increased. Since it is not necessary to increase the output of the engine 2, the output of the engine 2 is not reduced.

CeZr known as an oxygen storage agent
O, CeO ₂ or the like is used.

A perovskite type complex oxide containing a lanthanoid mixture extracted from bastnasite is represented by the general formula: A _ax B _x MO _b , where A is a lanthanoid mixture extracted from bastnasite. B is a divalent or monovalent cation, M is at least one element selected from the group of elements having atomic numbers 22 to 30, 40 to 51 and 73 to 80, and a is 1 or 2 Yes, b is 3, when a is 1, or 4 when a is 2, and x is 0 ≦ x <0.7.

The perovskite type complex oxide is, for example, L
n_0.6Ca_0.4CoO₃(Ln is a lanthanoid, L
a, Ce, Pr, Nd, etc. are included. The same shall apply hereinafter), Ln_0.83
Sr_{0. 17}MnO₃, Ln_0.7Sr_0.3CrO₃, Ln
_0.6Ca_0.4Fe_0.8Mn_0.2O ₃, Ln_0.8Sr_0.2
Mn_0.9Ni_0.04Ru_0.06O₃, Ln_0.8K_0.2Mn
_0.95Ru_0.05O₃, Ln_0.7Sr_0.3Cr_0.95Ru_0.05
O₃, LnNiO₃, Ln₂(Cu_0.6Co_0.2Ni
_0.2) O_Four, Ln_0.8K_0.2Mn_0.95Ru_0.05O₃Etc.
Applicable

Such a perovskite type complex oxide is
International Publication No. WO97 / 37760 (Special Table 2000-5
No. 15057) disclosed in the specification and drawings, and those disclosed herein can be used in the present invention. Further, the air-fuel ratio control device 5 as described above is disclosed in Japanese Patent Application Laid-Open No. 60-1342 filed by the present applicant, and the electronic control unit 5 disclosed therein is disclosed.
Are used in the present invention.

A specific example will be described below. As a conventional purifier corresponding to [I] first cleaner _81, Honda a 1999-type exhaust purifier used in the Accord Ltd., Pd and Rh and the CeZrO gamma-Al ₂ Supported on O ₃ and added to 0.7
What was hold | maintained at the honeycomb support body of L was prepared.

The second purifier 8₂As an international publication WO
97/37760, obtained on the basis of Example 5
In addition, Ln, which is a perovskite complex oxide_0.83Sr_0.17
MnO₃BET specific surface area on 0.7 L honeycomb support
Is 9.3m²Prepare the one held so that it becomes / g
It was [II] A conventional purifier with a 1.5L gas
Exhaust purification bench test by incorporating it into the exhaust pipe of the engine
went. As in the case of Fig. 1, the conventional cleaning of the exhaust pipe
An air-fuel ratio sensor was placed upstream of the carburetor. Also similar
Second purifier 8 by law ₂Exhaust purification bench test
It was

FIG. 2 shows the relationship between the exhaust air-fuel ratio and the exhaust purification rate of the conventional purifier, and FIG. 3 shows the second purifier 8 ₂
Shows the relationship between the exhaust air-fuel ratio and the exhaust purification rate (theoretical air-fuel ratio A / F = 14.7). Comparing FIGS. 2 and 3, the A / F window in the perovskite type three-way catalyst is shown.
Is less than that of the noble metal three-way catalyst, which is about 18% of the A / F window of the noble metal three-way catalyst.

Next, the conventional purifier was incorporated into the exhaust pipe of an automobile equipped with a 1.5 L gasoline engine, and in the exhaust pipe, the first and second air-fuel ratios were provided above and below the conventional purifier, respectively. A sensor was placed to measure the change over time in the exhaust air-fuel ratio at the inlet and outlet of the conventional purifier.
The detection signal of the second air-fuel ratio sensor on the downstream side is used to correct the fuel injection amount calculated by the first air-fuel ratio sensor.

FIG. 4 shows the change over time in the exhaust air-fuel ratio at the inlet of the conventional purifier. It can be seen from FIG. 4 that the exhaust air-fuel ratio at the inlet has a relatively large variation as described above.

FIG. 5 shows changes with time in the exhaust air-fuel ratio at the outlet of the conventional purifier. It can be seen from FIG. 5 that the exhaust air-fuel ratio at the outlet converges in a substantially linear shape as described above due to the oxygen storage effect of CeZrO.

The exhaust air-fuel ratio thus converged is shown in FIG.
A / FW in the perovskite-type three-way catalyst shown in
If it falls within the window, the second purifier 8 ₂ will exhibit a high exhaust purification rate.

Therefore, as the first purifier 8 ₁ , Pt, P
d and Rh and CeZrO were carried on γ-Al ₂ O ₃ and held on a 0.7 L honeycomb support, and the first purifier 8 _{1 was} subjected to the same actual vehicle test as described above. The change with time of the exhaust air-fuel ratio at the outlet of the first purifier 8 ₁ was measured. The first purifier 8 ₁ thus configured has a relatively high exhaust gas purification capacity.

FIG. 6 shows changes with time in the exhaust air-fuel ratio at the outlet of the first purifier 8 ₁ . As is clear from FIG. 6, C
Due to the oxygen storage effect of eZrO, the exhaust air-fuel ratio at the outlet converges in a substantially straight line as described above,
Moreover, the converged exhaust air-fuel ratio is equal to the A / F Windo in the perovskite type three-way catalyst shown in FIG.
It was found that the width was within w, that is, 14.73 ≦ A / F ≦ 14.76.

Such a first purifier 8 ₁ and a second purifier 8
_When combined with ₂ , the relatively high exhaust purification capacity of the first purifier 8 ₁ is added to the high exhaust purification capacity of the second purifier 8 _2, so that the exhaust purification rate of the exhaust purification system 1 is increased. It can be greatly increased.

FIG. 7 shows a second embodiment. In this case, the first
The purifier 8 ₁ is mainly used for adjusting the air-fuel ratio of the exhaust gas introduced into the second purifier 8 ₂ , and the exhaust gas is mainly purified by the second purifier 8 ₂ . In this case, it is possible to reduce the amount of the precious metal three-way catalyst used by configuring the first purifier 8 ₁ in a small size.

In order to expand the A / F window in the perovskite type three-way catalyst to some extent, it is an effective means to add a small amount of a noble metal such as Pd, Rh, Pt or the like to the complex oxide.

[0034]

According to the first aspect of the present invention, the construction as described above reduces the amount of the noble metal three-way catalyst used to reduce the manufacturing cost and keeps the exhaust gas purification rate high. Moreover, it is possible to provide an exhaust gas purification system for an internal combustion engine, which is capable of sufficiently purifying exhaust gas immediately after the engine is started.

According to the second aspect of the present invention, in addition to the above effects, the production cost of the perovskite type complex oxide is reduced,
Consequently, the manufacturing cost of the exhaust gas purification system can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2 is a graph showing a relationship between an exhaust air-fuel ratio and an exhaust purification rate regarding a noble metal three-way catalyst.

FIG. 3 is a graph showing a relationship between an exhaust air-fuel ratio and an exhaust purification rate regarding a perovskite type three-way catalyst.

FIG. 4 is a graph showing changes over time in the exhaust air-fuel ratio at the inlet of a conventional purifier.

FIG. 5 is a graph showing changes over time in the exhaust air-fuel ratio at the outlet of a conventional purifier.

FIG. 6 is a graph showing changes over time in the exhaust air-fuel ratio at the outlet of the first purifier.

FIG. 7 is a block diagram of a second embodiment.

[Explanation of symbols]

1 Exhaust Purification System 2 Internal Combustion Engine 3 Exhaust Pipe (Exhaust System) 7 Trap Device 8 ₁ First Purifier 8 ₂ Second Purifier

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 F02D 41/14 310A F02D 41/14 310 B01D 53/36 103B F term (reference) 3G084 BA09 BA13 BA24 DA10 EB11 FA26 FA29 3G091 AA17 AB03 AB09 AB10 BA02 BA03 BA14 BA15 BA27 DC01 FA02 FA04 FB02 FB11 FC04 GA06 GB05W GB10W HA08 HA20 HA36 3G301 HA01 JA25 JA26 KA01 KA05 MA01 ND01 NE14 PD02Z 4D048 AA06 BA15X30BA13 BA30 BA30BA30 BA33X BA36Y BA37X BA38Y BA41X BA42X BB02 CC32 CC46 CD01 CD08 DA01 DA08 DA20 EA04

Claims (2)

[Claims] 1. A trap device (7) for sequentially capturing at least one of HC and NOx from an upstream side to a downstream side of an exhaust system (3) in an internal combustion engine (2), an oxygen storage agent together with a precious metal three-way catalyst. A first purifier (8)
₁ ) and a second purifier (8 ₂ ) equipped with a three-way catalyst having a perovskite-type mixed oxide, and the oxygen storage agent is used for the exhaust gas introduced into the second purifier (8 ₂ ). An exhaust gas purification system for an internal combustion engine having a function of adjusting an air-fuel ratio so as to be within an A / F window of a three-way catalyst having the perovskite type double oxide. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the perovskite-type mixed oxide contains a lanthanoid mixture extracted from bastnasite.