JPH05240034A - Exhaust purifying device of internal combustion engine - Google Patents

Abstract

PURPOSE:To guard a catalyst from thermal impact so as to improve its durability by providing a second catalyst body for purifying NOx in exhaust staying in lean condition, and providing a first catalyst for purifying exhaust staying in rich condition upstream of the second catalyst. CONSTITUTION:In an internal combustion engine 2, a first catalyst 10, a second catalyst 22, and a third catalyst 24 are provided in this order from the upperstream side on the way of an exhaust passage 6. The first catalyst 20 is provided for such purpose that unburnt gas is forced to react when a large amount of unburnt gas is generated during accelerating operation or decelerating operation of the internal combustion engine 2, and then exhaust gas in rich condition is purified so as to prevent the second catalyst 22 from raising a temperature highly. The second catalyst 22 is set in a large capacity in it lean condition so as to purify most of NOx passing the first catalyst 20. The third catalyst 24 is provided in order to purify non-purified components in exhaust gas passing the first catalyst 20 and the second catalyst 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly, it can protect a second catalyst body for purifying NOx in exhaust gas in a lean state from thermal shock and improve durability. The present invention relates to an exhaust gas purification device for an internal combustion engine, which can sufficiently purify components other than NOx in exhaust gas in a lean state and can purify exhaust gas even in an operating state in a feedback region.

[0002]

2. Description of the Related Art In an internal combustion engine mounted on a vehicle or the like, an exhaust gas purification device is provided to purify harmful components in exhaust gas discharged. An exhaust gas purification apparatus for an internal combustion engine purifies HC, CO, and NOx in exhaust gas by the oxidizing action and reducing action of a catalyst body provided in the middle of an exhaust passage.

The catalyst body includes an oxidation catalyst body that oxidizes unburned components such as HC and CO to convert it to H ₂ O and CO ₂ , and a reducing catalyst that decomposes NOx and converts it to N ₂ and O _2. There are a medium and a three-way catalyst body that performs both functions at the same time.

As such an exhaust gas purifying device for an internal combustion engine, Japanese Patent Laid-Open Nos. 1-171625 and 3-172 are known.
There is one disclosed in Japanese Patent No. 527.

The one disclosed in Japanese Patent Laid-Open No. 1-171625 has two parallel exhaust passages through which exhaust gas is switched and distributed by a switching valve provided with a catalyst body made of copper and zeolite and a three-way catalyst body, respectively. When the exhaust gas temperature is low, the exhaust gas is purified by the catalyst body made of copper and zeolite, and when the exhaust gas temperature is high, the exhaust passage is switched by the switching valve in order to purify the exhaust gas by the three-way catalytic body.

The one disclosed in JP-A-3-172527 discloses two parallel exhaust passages in which exhaust gas is switched and distributed by a bypass valve to an internal combustion engine supplied with alcohol / gasoline fuel having different mixing ratios. Is provided with a catalyst body for purifying NOx in the exhaust gas, the main component of which is zeolite, in one of the two parallel exhaust passages, and the exhaust passage is provided with the catalyst body depending on the mixing ratio of alcohol / gasoline. The exhaust passage is switched by the bypass valve in order to switch the exhaust gas to and from the exhaust passage.

[0007]

The internal combustion engine includes a so-called lean burn internal combustion engine (lean air-fuel ratio fuel internal combustion engine) in which an air-fuel mixture having a lean air-fuel ratio is supplied and burned. In this internal combustion engine, the air-fuel ratio of exhaust gas is O.
₂ Rich, that is, the atmosphere has a lean air-fuel ratio, so that the conventional three-way catalyst can hardly purify NOx. Therefore, in such an internal combustion engine, as disclosed in the above publication, a catalyst body (for example, a Cu-zeolite catalyst body) that purifies NOx in the exhaust gas in a lean atmosphere is provided.

However, N in the exhaust gas in the lean state
A catalyst body that purifies Ox has the disadvantages of insufficient heat resistance and reduced durability due to thermal shock, and also loses its activity in an atmosphere with a high exhaust gas temperature and a rich air-fuel ratio, and can purify exhaust gas. In addition, there is an inconvenience that NOx can be purified while HC and CO are insufficiently purified.

Therefore, as disclosed in the above publication, when the exhaust temperature is low, the exhaust gas is purified by the NOx-purifying catalyst body, and when the exhaust temperature is high, the three-way catalyst body is used to purify the exhaust gas. A device that switches the exhaust passage has been proposed.

However, the switching valve for switching the exhaust passage must be equipped with an expensive heat-resistant valve mechanism in order to avoid deterioration of function due to high temperature and ensure operability by being exposed to high temperature of exhaust gas. There is an inconvenience. In addition, the switching valve is required to have a function of withstanding high temperature and ensuring the sealing property in order to switch the exhaust passage, which causes a problem in the sealing property. Moreover, since it is necessary to provide a plurality of exhaust passages, a switching valve, and a control means for controlling the switching valve, the structure becomes complicated, which is disadvantageous in terms of layout and cost. Further, when the exhaust gas is switched and passed through the catalyst body for purifying NOx, there is a disadvantage that purification of HC and CO is insufficient while NOx can be purified.

[0011]

Therefore, in order to eliminate the above-mentioned inconvenience, the present invention provides a second catalyst body for purifying NOx in exhaust gas in a lean state in the middle of an exhaust passage of an internal combustion engine. A first catalyst body for purifying exhaust gas in a rich state is provided in the exhaust passage upstream of the two catalyst bodies,
A third catalyst body that purifies unpurified components in the exhaust gas that has passed through the first catalyst body and the second catalyst body is provided in the exhaust passage downstream of the second catalyst body.

[0012]

According to the structure of the present invention, the exhaust gas in the lean state is purified of NOx by the second catalyst body. Further, the exhaust gas in the rich state where the temperature becomes high is purified by the first catalyst body, so that the second catalyst body can be prevented from becoming high temperature. Further, the first catalyst body and the second
Unpurified components in the exhaust gas that have passed through the catalyst body, such as HC and CO in the lean state and HC and CO containing NOx in the feedback region, are purified by the third catalyst body.

[0013]

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

FIG. 1 shows an embodiment of the present invention. In FIG. 1, 2 is an internal combustion engine, 4 is an intake passage, and 6 is an exhaust passage. The internal combustion engine 2 forms a lean air-fuel mixture with fuel supplied from a fuel system (not shown), and the lean air-fuel mixture having this air-fuel ratio is supplied to the air-fuel mixture for combustion. Air-fuel ratio fuel internal combustion engine).

The internal combustion engine 2 has an intake passage 4 formed by an air cleaner 8, an intake pipe 10 and an intake manifold 12 in communication with a combustion chamber (not shown), and an exhaust manifold 14 and an exhaust pipe. An exhaust passage 6 formed by 16 and 16 communicates with a combustion chamber (not shown). An intake throttle valve 18 is provided in the middle of the intake passage 4.

The internal combustion engine 2 is provided with a first catalyst body 20, a second catalyst body 22 and a third catalyst body 24 in the middle of the exhaust passage 6 sequentially from the upstream side. In the first to third catalyst bodies 20 to 24, when the capacity of the second catalyst body 22 is "1", the capacity of the first catalyst body 20 is about "1/5", and the third catalyst body 24 is Capacity is about "1/2".

The first catalyst body 20 is composed of a three-way catalyst body or an oxidation catalyst body, and when a large amount of unburned gas is generated, for example, during acceleration operation or deceleration operation of the internal combustion engine 2, this uncatalyzed gas is generated. The exhaust gas in the rich state is purified by reacting the fuel gas, and the second
It prevents the catalyst body 22 from reaching a high temperature. Therefore,
The first catalyst body 20 purifies the exhaust gas in the rich state to an extent sufficient to protect the second catalyst body 22 when a large amount of unburned gas is generated, and in the lean state when the exhaust gas is in the lean state. The catalyst capacity and the amount of precious metal supported are set so that the exhaust gas in the lean state is purified to the extent that the NOx in the exhaust gas can pass through and be purified by the second catalyst body 22.

The second catalyst body 22 is made of a zeolitic catalyst body containing Cu and is set to a large capacity enough to purify most of NOx that has passed through the first catalyst body 20 in a lean state.

The third catalyst body 24 is composed of a three-way catalyst body or an oxidation catalyst body, and is an unpurified component in the exhaust gas that has passed through the first catalyst body 20 and the second catalyst body 22, such as HC or C.
O is mainly purified, and HC and CO containing NOx in the feedback region of the internal combustion engine 2 are also purified. The third catalyst body 24 is advantageous for the reaction of HC and CO in the exhaust gas when the internal combustion engine 2 is supplied with a lean air-fuel mixture, and to some extent by the first catalyst body 20 and the second catalyst body 22. Since it has been purified, the capacity is about "1/2" of the second catalyst body 22.

As described above, NOx in the exhaust gas in the lean state composed of the zeolite-based catalyst body containing a large amount of Cu.
The second catalyst body 22 for purifying the
A small capacity first catalyst body 20 for purifying rich exhaust gas to protect the second catalyst body 22 from thermal shocks is provided in the exhaust passageway 6 on the upstream side of the exhaust passageway on the downstream side of the second catalyst body 22. 6 is provided with a medium capacity third catalyst body 24 for purifying unpurified components.

As a result, in the middle of the exhaust passage 6 of the internal combustion engine 2, the NOx in the exhaust gas in the lean state is purified.
A catalyst body 22 is provided, an exhaust passage 6 upstream of the second catalyst body 22 is provided with a first catalyst body 20 for purifying exhaust gas in a rich state, and an exhaust passage 6 downstream of the second catalyst body 22 is provided.
Further, a third catalyst body 24 for purifying the unpurified component in the exhaust gas that has passed through the first catalyst body 20 and the second catalyst body 22 is provided.

Next, the operation will be described.

The internal combustion engine 2 forms a lean air-fuel mixture with fuel supplied from a fuel system (not shown), and the lean air-fuel mixture is supplied from the intake passage 4 and burned. The internal combustion engine 2 discharges the lean exhaust gas to the exhaust passage 6 by burning the lean air-fuel mixture.

The lean exhaust gas in the exhaust passage 6 is generated by a small capacity first catalyst body 2 composed of a three-way catalyst body or an oxidation catalyst body.
The NOx passes through without being purified by 0, and the NOx is purified by the second catalyst body 24.

Exhaust gas in a rich state in which the temperature becomes high when a large amount of unburned gas is generated, such as during acceleration operation or deceleration operation, is purified by the first catalyst body 20. It is possible to prevent the second catalyst body 22 from reaching a high temperature.

Furthermore, the first catalyst body 20 and the second catalyst body 2
The unpurified component in the exhaust gas that has passed 0 is purified by the third catalyst body 24. For example, the third catalyst body 24 includes HC and CO when the internal combustion engine 2 is supplied with a lean air-fuel mixture, and HC and CO containing NOx when the internal combustion engine 2 is operating in the feedback region.
Purify.

As described above, the exhaust gas purifying apparatus can purify NOx in the exhaust gas in the lean state by the second catalyst body 22, and the second catalyst body 22 becomes high in temperature.
It can be prevented by the catalyst body 20. As a result, the second catalyst body 22 can be protected from thermal shock and durability can be improved.

Further, the third catalyst body 24 can sufficiently purify components other than NOx in the exhaust gas in the lean state, and can sufficiently purify the exhaust gas even in the operating state in the feedback region.

Further, since it is not necessary to provide a switching valve as in the conventional case, no problem occurs in the sealing property,
Further, since it is not necessary to provide a plurality of exhaust passages, a switching valve, a control means for controlling the switching valve, and the like, the structure can be simplified, and a disadvantage that is disadvantageous in terms of layout and cost is eliminated. be able to.

[0030]

As described in detail above, according to the present invention, the NOx in the exhaust gas in the lean state can be purified by the second catalyst body, and the second catalyst body is heated to a high temperature. Since it can be prevented by the above, the second catalyst body can be protected from thermal shock and durability can be improved. In addition, the third catalyst body can sufficiently purify components other than NOx in the exhaust gas in the lean state, and can sufficiently purify the exhaust gas even in the operating state in the feedback region. Further, since there is no need to provide a switching valve as in the conventional case, there is no problem in sealing performance, and there is no need to provide a plurality of exhaust passages, switching valves, control means for controlling these switching valves, and the like. With this, the structure can be simplified, disadvantages that are disadvantageous in terms of layout and cost can be eliminated, and it can be practically implemented.

[Brief description of drawings]

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

[Explanation of symbols]

 2 internal combustion engine 4 intake passage 6 exhaust passage 20 first catalyst body 22 second catalyst body 24 third catalyst body

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[Procedure amendment]

[Submission date] May 19, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

Claims (1)

[Claims] 1. A second catalyst body for purifying NOx in exhaust gas in a lean state is provided in the middle of an exhaust passage of an internal combustion engine,
A first catalyst body for purifying exhaust gas in a rich state is provided in the exhaust passage upstream of the second catalyst body, and the first catalyst body and the second catalyst body are provided in the exhaust passage downstream of the second catalyst body. An exhaust gas purification device for an internal combustion engine, comprising a third catalyst body for purifying unpurified components in the exhaust gas that has passed through.