JP4138277B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification system for an internal combustion engine.
[0002]
[Prior art]
Conventionally, as this type of system, a three-way catalyst made of a noble metal such as Pt, Rh, or Pd, that is, one using a noble metal three-way catalyst is known.
[0003]
[Problems to be solved by the invention]
In the precious metal three-way catalyst, the range of the air-fuel ratio that can obtain a high exhaust purification rate, that is, the A / F Window is wide. Therefore, in the exhaust purification system using the precious metal three-way catalyst, the exhaust purification rate is improved. However, there is a problem that the manufacturing cost is high due to the use of the noble metal three-way catalyst. In addition, the noble metal three-way catalyst has a problem that the exhaust purification ability is low until the temperature is raised to the activation temperature after the engine is started.
[0004]
[Means for Solving the Problems]
The present invention aims to reduce the production cost by reducing the amount of precious metal three-way catalyst used, and to keep the exhaust purification rate high, and to sufficiently perform exhaust purification immediately after the engine is started. An object of the present invention is to provide the exhaust purification system.
[0005]
In order to achieve the above-described object, according to the present invention , exhaust purification performance is achieved by a trap device that captures at least one of HC and NOx sequentially from the upstream side to the downstream side of an exhaust system in an internal combustion engine, and a noble metal three-way catalyst. a first cleaner which exhibits, perovskite type complex oxide was closed and the noble metal does not have a second purifying the a / F Window than precious metal three-way catalyst exhibits exhaust purifying performance in a narrow perovskite type three-way catalyst arranged and vessels in series, the first purifier, the air-fuel ratio of the exhaust gas introduced into the second purifier, a function of adjusting to fit a / F Window in the perovskite-type three-way catalyst An exhaust gas purification system for an internal combustion engine comprising an oxygen storage agent is provided .
[0006]
Perovskite type complex oxide chromatic was and precious metals have no perovskite type three-way catalyst has a catalytic activity substantially equivalent to the precious metal three-way catalyst. Therefore, if both the three-way catalysts are arranged in two stages, it is possible to reduce the amount of expensive noble metal three-way catalyst used, thereby reducing the manufacturing cost of the exhaust purification system.
[0007]
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 varies relatively greatly due to various external factors, Since the noble metal three-way catalyst has a wide A / F window, the exhaust purification ability 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 converges substantially linearly so that the variation is small.
[0008]
Perovskite type complex oxides Yu was and noble A / F Window in no perovskite type three-way catalyst is significantly narrower than that of the noble metal three-way catalyst, wherein the convergence of the exhaust air-fuel ratio by the oxygen storage material, The exhaust air-fuel ratio can be stored in a narrow A / F window, and the perovskite type three-way catalyst exhibits an excellent exhaust purification ability.
[0009]
As the perovskite type double oxide, it is economical to use one containing a lanthanoid mixture extracted from bastonite as an ore. This is because the production cost of lanthanoids alone is high because it takes a lot of man-hours to extract lanthanoids alone from bust nesite, but the lanthanoid mixture can be obtained with less man-hours than lanthanoids alone. This is because it is much cheaper than that of lanthanoid alone.
[0010]
The trap device captures HC and / or NOx immediately after starting the internal combustion engine, thereby purifying exhaust gas. The trap device releases HC and NOx as the exhaust gas is heated, and the HC and NOx are oxidized and reduced by the first and second purifiers that have been heated to the activation temperature. In addition, by using a trap device, it is not necessary to place the first and second purifiers near the engine for early activation, increasing the degree of freedom in system layout and increasing the number of cells for early activation. There is no need to do so, so there is no reduction in engine output.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the first embodiment shown in FIG. 1, the exhaust purification system 1 includes an exhaust system of an internal combustion engine 2, in this example, purification equipment 4 disposed in an exhaust pipe 3, and an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine 2. And an air-fuel ratio control device 5 for controlling (A / F). 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.
[0012]
Purifying equipment 4, have a first purifier 8 ₁ and perovskite type complex oxides trap device 7 from the upstream side of the exhaust pipe 3 are sequentially disposed toward the downstream side, with a noble metal three-way catalyst having an oxygen storage agent and and precious metals do not have perovskite type three-way catalyst (hereinafter, simply referred to as the perovskite-type three-way catalyst.) made of the second purifier 8 ₂ with. The oxygen storage agent has a function of adjusting the air-fuel ratio of the exhaust gas is introduced into the second clarifier ₈₂ to fit in a narrow A / F Window with perovskite type three-way catalyst. The trap device 7 is known and has a function of trapping one of HC and NOx, in the embodiment, both immediately after the engine is started.
[0013]
In the exhaust pipe 3, an air-fuel ratio sensor (O ₂ sensor) 9 is disposed on the upstream side of the purification facility 4, and the air-fuel ratio sensor 9 is the air-fuel ratio of the exhaust discharged from the internal combustion engine 2 and introduced into the purification facility 4. Therefore, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 2 is detected as the oxygen concentration. Based on the signal from the air-fuel ratio sensor 9, the air-fuel ratio control device 5 converts the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 2 upstream of the purification equipment 4 of the exhaust pipe 3, that is, upstream of the first purifier 8 ₁ . Control is performed so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio (A / F = 14.7).
[0014]
In the above configuration, when the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 2 is detected by the air-fuel ratio sensor 9, the detection signal is fed back to the air-fuel ratio control device 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. 6 is injected into the internal combustion engine 2.
[0015]
If it controlled to exhaust air-fuel ratio of the internal combustion engine 2 becomes the stoichiometric air-fuel ratio, the exhaust gas air-fuel ratio of the first cleaner ₈₁ inlet is caused to relatively large variations by various external factors such as a noble metal three-way catalyst Has a wide A / F Window, and thus exhibits exhaust purification ability despite the above-mentioned variation. At the same time, the oxygen storage agent so exhibits an oxygen storage effect, the exhaust air-fuel ratio of the first cleaner ₈₁ outlet is focused substantially linearly as the variation is insignificant.
[0016]
The A / F Window possessed by the perovskite type three-way catalyst is significantly narrower than that of the noble metal three-way catalyst, but the exhaust air / fuel ratio is narrowed by the convergence of the exhaust air / fuel ratio by the oxygen storage agent. As a result, the perovskite type three-way catalyst exhibits excellent exhaust purification ability.
[0017]
The trap device 7 captures HC and / or NOx immediately after the internal combustion engine 2 is started, thereby purifying the exhaust gas. The trap device 7 releases HC and NOx as the exhaust gas is heated, and the HC and NOx are oxidized and reduced by the first and second purifiers 8 ₁ and 8 ₂ that have been heated to the activation temperature. . Further, by using the trap device 7, it is not necessary to arrange the first and second purifiers 8 ₁ and 8 ₂ in the vicinity of the engine 2 for early activation, and the degree of freedom in system layout is increased and early activation is achieved. For this reason, it is not necessary to increase the number of cells, so that the output of the engine 2 is not reduced.
[0018]
As the oxygen storage agent, known CeZrO, CeO ₂ or the like is used.
[0019]
The perovskite-type double oxide containing a lanthanoid mixture extracted from bust nesite is represented by the general formula: A _ax B _x MO _b , A is a lanthanoid mixture extracted from bust nesite, and B is 2 Is a valent 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, a is 1 or 2, b Is 3 when a is 1 or 4 when a is 2, and x is 0 ≦ x <0.7.
[0020]
Perovskite type double oxides include, for example, Ln _0.6 Ca _0.4 CoO ₃ (Ln is a lanthanoid, including La, Ce, Pr, Nd, etc., the same shall apply hereinafter), Ln _0.83 Sr _0.17 MnO ₃ , Ln _0.7 Sr _0.3 CrO ₃ , Ln _0.6 Ca _0.4 Fe _0.8 Mn _0.2 O ₃ , Ln _0.8 Sr _0.2 Mn _0.9 Ni _0.04 Ru _0.06 O ₃ , Ln _0.8 K _0.2 Mn _0.95 Ru _0.05 O ₃ , Ln _0.7 Sr _0.3 Cr _0.95 Ru _0.05 O ₃ , LnNiO ₃ , Ln ₂ (Cu _0.6 Co _0.2 Ni _0.2 ) O ₄ , Ln _0.8 K _0.2 Mn _0.95 Ru _0.05 O _{3 and the} like are applicable.
[0021]
Such perovskite type double oxides are disclosed in the specification and drawings of International Publication No. WO97 / 37760 (Japanese translations of PCT publication No. 2000-515057), and those disclosed herein can be used in the present invention. is there. The air-fuel ratio control apparatus 5 as described above is disclosed in Japanese Patent Application Laid-Open No. 60-1342, which is filed by the present applicant, and the electronic control unit 5 disclosed herein is used in the present invention.
[0022]
Hereinafter, specific examples will be described.
[I] As a conventional purifier corresponding to the first purifier 8 ₁ , an exhaust purifier used in a 99-year accord manufactured by Honda Motor Co., Ltd., which uses Pd, Rh and CeZrO as γ-Al ₂ An O ₃ supported on a 0.7 L honeycomb support was prepared.
[0023]
Further, as the second purifier 8 ₂ , Ln _0.83 Sr _0.17 MnO ₃ , which is a perovskite type double oxide obtained based on the specification of International Publication WO 97/37760, Example 5, was used as a 0.7 L honeycomb support. What was hold | maintained so that a BET specific surface area might be 9.3 m < ² > / g was prepared.
[II] An exhaust purification bench test was conducted by incorporating a conventional purifier into the exhaust pipe of a 1.5 L gasoline engine, which is an internal combustion engine. As in the case of FIG. 1, an air-fuel ratio sensor is disposed upstream of the conventional purifier in the exhaust pipe. Also conducted an exhaust purification bench test relates second cleaner ₈₂ in a similar manner.
[0024]
Figure 2 shows the relationship between the exhaust air-fuel ratio for a conventional type purifier exhaust purification rate, and FIG. 3 shows the relationship between the exhaust air-fuel ratio and the exhaust gas purification rate for the second cleaner 8 ₂ (stoichiometric air-fuel ratio A / F = 14.7). 2 and 3, the A / F window in the perovskite type three-way catalyst is narrower than that of the noble metal three-way catalyst, and is about 18% of the A / F window of the noble metal three-way catalyst.
[0025]
Next, the conventional purifier is installed in the exhaust pipe of an automobile equipped with a 1.5 L gasoline engine, and the first and second air-fuel ratio sensors are arranged on the exhaust pipe on the upstream side and the downstream side, respectively. Then, the change with time of the exhaust air-fuel ratio at the inlet and outlet of the conventional purifier was measured. 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.
[0026]
FIG. 4 shows the change with time of the exhaust air-fuel ratio at the inlet of the conventional purifier. As can be seen from FIG. 4, the exhaust air-fuel ratio at the inlet has a relatively large variation as described above.
[0027]
FIG. 5 shows the change over time of the exhaust air-fuel ratio at the outlet of the conventional purifier. FIG. 5 shows that the exhaust air-fuel ratio at the outlet converges substantially linearly as described above due to the oxygen storage effect of CeZrO.
[0028]
Thus converged exhaust air-fuel ratio is, the second cleaner 8 ₂ if it fits in the A / F Window in the perovskite-type three-way catalyst as shown in Figure 3 will exhibit a high exhaust gas purification rate.
[0029]
Therefore, a first purifier 8 ₁ is manufactured in which Pt, Pd, Rh, and CeZrO are supported on γ-Al ₂ O ₃ and held on a 0.7 L honeycomb support, and the first purifier 8 ₁ is manufactured. vessels 8 ₁ was measured the time course of the exhaust air-fuel ratio in the first purifier 8 _first outlet by performing the same vehicle tested. The first cleaner 8 ₁ configured to have a relatively high exhaust gas purifying ability.
[0030]
Figure 6 shows the time course of the exhaust air-fuel ratio in the first outlet of the purifier 8 _1. As is apparent from FIG. 6, the exhaust air-fuel ratio at the outlet converges substantially linearly as described above due to the oxygen storage effect of CeZrO, and the converged exhaust air-fuel ratio is shown in FIG. In addition, it was found that the perovskite type three-way catalyst was within the range of A / F Window, that is, 14.73 ≦ A / F ≦ 14.76.
[0031]
When such a first purifier 8 ₁ and a second purifier 8 ₂ are combined, the high exhaust purification performance exhibited by the second purifier 8 ₂ has a relatively high exhaust purification capability of the first purifier 8 _1. Therefore, the exhaust gas purification rate of the exhaust gas purification system 1 can be greatly increased.
[0032]
FIG. 7 shows a second embodiment. In this case, the first 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 purification is mainly performed by the second purifier 8 ₂ . In this case, the first purifier 8 ₁ constitutes a compact, it is possible to reduce the amount of the precious metal three-way catalyst.
[0033]
【The invention's effect】
According to the first aspect of the invention, the perovskite type three-way catalyst having a perovskite type double oxide and having no precious metal has substantially the same catalytic ability as the noble metal three-way catalyst. By arranging the precious metal three-way catalyst and the perovskite type three-way catalyst separately in the first and second purifiers arranged in series, it is possible to reduce the amount of expensive precious metal three-way catalyst used in the exhaust purification system. In this way, the manufacturing cost of the exhaust purification system can be reduced. In this case, the exhaust air-fuel ratio at the inlet of the first purifier equipped with the noble metal three-way catalyst varies relatively greatly due to various external factors and the like, but the noble metal three-way catalyst has a wide A / F Window, Exhibits exhaust purification capability despite variations. At the same time, since the oxygen storage agent in the first purifier exerts an oxygen storage effect, the exhaust air / fuel ratio at the outlet of the first purifier is converged substantially linearly so that the variation is small.
[0034]
Thus, the A / F Window in the perovskite type three-way catalyst (second purifier) having a perovskite type double oxide and no precious metal is significantly larger than that of the noble metal three-way catalyst (first purifier). However, since the exhaust air / fuel ratio can be accommodated in a narrow A / F window by the convergence of the exhaust air / fuel ratio by the oxygen storage agent in the first purifier, the perovskite type 3 is greatly reduced in the A / F window. also it is possible to exhibit excellent exhaust gas purification performance based catalyst, the above results, while maintaining the exhaust gas purification rate higher, possible to reduce the manufacturing cost by reducing the amount of precious metal three-way catalyst in the exhaust purification system Can do. Moreover, the use of a trap apparatus, it is possible intends sufficiently rows purification of exhaust immediately after engine startup.
[0035]
According to the second aspect of the invention, in addition to the above effects, the manufacturing cost of the perovskite type double oxide can be reduced, and the manufacturing cost of the exhaust purification system can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram of the first embodiment. FIG. 2 is a graph showing a relationship between an exhaust air-fuel ratio and an exhaust purification rate for a precious metal three-way catalyst. FIG. 3 is a graph showing an exhaust air-fuel ratio and an exhaust purification rate for a perovskite three-way catalyst. Graph showing the relationship [FIG. 4] Graph showing the time-dependent change of the exhaust air-fuel ratio at the inlet of the conventional purifier [FIG. 5] Graph showing the time-dependent change of the exhaust air-fuel ratio at the outlet of the conventional-type purifier [FIG. FIG. 7 is a graph showing the change over time in the exhaust air-fuel ratio at the outlet of the purifier. FIG. 7 is a block diagram of the second embodiment.
DESCRIPTION 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

Claims (2)

A trap device (7) that sequentially captures at least one of HC and NOx from the upstream side to the downstream side of the exhaust system (3) in the internal combustion engine (2) and a precious metal three-way catalyst that exhibits exhaust purification capability . 1 purifier (8 _1), second to exert and precious metals have a perovskite type complex oxide does not have, the exhaust purification performance in a narrow perovskite type three-way catalyst a / F Window than the noble metal three-way catalyst A purifier (8 ₂ ) is placed in series ,
The first purifier (8 ₁ ) has a function of adjusting the air-fuel ratio of the exhaust gas introduced into the second purifier (8 ₂ ) so as to be within the A / F Window in the perovskite type three- way catalyst. An exhaust purification system for an internal combustion engine comprising an oxygen storage agent .   The exhaust purification system for an internal combustion engine according to claim 1, wherein the perovskite type double oxide contains a lanthanoid mixture extracted from bastonite.

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