JP2000008841A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the purification ratio of both catalysts in an exhaust emission control device in which a first catalyst, and a second catalyst lower in activation temperature than the first catalyst are disposed. SOLUTION: A second catalyst 5 lower in activation temperature than a first catalyst 2 is arranged on the upstream side of the first catalyst 2 provided in the middle of an exhaust system of an internal combustion engine. A bypass passage 6 to bypass the second catalyst 5 and directly introduce the exhaust emission to the first catalyst 2 is provided. An opening/closing valve 8 is provided on the bypass passage 6. The second catalyst 5 is concentric with the bypass passage 6. A passage to the second catalyst 5 is formed on an outer circumference of the bypass passage 6. A cooling means 14 is provided on a passage to the second catalyst 5.

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 device, and more particularly, to a device for purifying exhaust gas from an internal combustion engine of an automobile or the like with a catalyst.

[0002]

2. Description of the Related Art In recent years, in order to improve the purification of exhaust gas discharged from an internal combustion engine, a second catalyst having an active temperature lower than the three-way catalyst in the exhaust system and a three-way catalyst upstream of the three-way catalyst has been used.
(NOx catalyst or HC adsorbing catalyst) is provided, and when the internal combustion engine is in a lean operation or when the engine is started, the exhaust gas is supplied to the second engine.
An exhaust gas purifying apparatus has been developed in which exhaust gas is allowed to flow through the three-way catalyst during stoichiometric operation (operation in which combustion is performed while maintaining a stoichiometric air-fuel ratio) around the catalyst.

For example, as shown in FIGS. 7 and 8, a NOx catalyst 101 is disposed on the upstream side, and a three-way catalyst 10 is disposed on the downstream side.
2, a bypass passage 103 is provided in the center of the NOx catalyst 101, and an on-off valve 104 is provided in the bypass passage 103.
During the lean operation of the internal combustion engine, the on-off valve 104 is closed to allow the exhaust gas to flow through the NOx catalyst 101, and then flow through the three-way catalyst 101. Japanese Patent Application Laid-Open No. 7-279654 discloses a configuration in which most of the exhaust gas flows directly through the three-way catalyst 102. This is referred to as a first conventional technique.

Since the activation temperature of the NOx catalyst is lower than that of the three-way catalyst, it is necessary to provide a cooling means for cooling the exhaust gas upstream of the NOx catalyst in order to make the NOx catalyst work effectively. There is.

[0005] However, in the first prior art,
When exhaust gas is cooled by providing a cooling means on the upstream side of the purification device, the exhaust gas is cooled even during the stoichiometric operation, the exhaust gas temperature becomes lower than the activation temperature of the three-way catalyst, and the purification rate of the exhaust gas is reduced. There is a problem of decline.

To solve this problem, for example, as shown in FIG. 9, a bypass valve 203 is provided in a bypass passage 202 from the internal combustion engine E to the three-way catalyst 201, and HC is adsorbed so as to bypass the bypass valve 203. Catalyst passage 20
The HC adsorption passage 2 is provided in the HC catalyst passage 204.
And a cooling means 206 for introducing secondary air for cooling is provided upstream of the HC adsorbing catalyst 205, and when the internal combustion engine is started, the bypass valve 203 is closed so that the exhaust gas is discharged from the HC adsorbing catalyst 205. Japanese Patent No. 2662633 discloses a device that is introduced into the use passage 204 and operates the cooling means 206. This is the second
Conventional technology.

[0007]

The first conventional technique has the above-described problem and has a structure in which both sides of the bypass passage 103 are in contact with the converter housing 105 as shown in FIG. Therefore, the heat of the exhaust gas guided to the three-way catalyst 101 is easily radiated to the outside air from the converter housing 105 exposed to the outside air. Therefore, there is a problem that the three-way catalyst 101 does not easily reach the activation temperature early, and a high purification rate cannot be obtained.

[0008] In the second prior art,
The cooling means can increase the purification rate of the HC adsorption catalyst.
07 and control means for controlling the opening and closing of the valve are required, so that the cooling means 206 becomes complicated and the entire purification device becomes large.

Accordingly, an object of the present invention is to solve the above problems and to provide a more effective exhaust gas purifying apparatus.

[0010]

In order to solve the above-mentioned problems, a first aspect of the present invention is directed to a first aspect of the present invention, wherein the first catalyst is provided upstream of a first catalyst provided in the exhaust system of an internal combustion engine. A second catalyst having an activation temperature lower than that of the first catalyst, a bypass passage for bypassing the second catalyst and directly introducing exhaust gas to the first catalyst, and an openable and closable opening and closing port for the bypass passage In the exhaust gas purifying apparatus provided with a valve, the second catalyst and the bypass passage are provided concentrically to form a passage to the second catalyst on the outer periphery of the bypass passage. A cooling means is provided in the passage.

In the present invention, the bypass passage for directly leading the exhaust gas to the first catalyst does not directly contact the outside air,
Since the outer periphery is surrounded by the passage to the second catalyst and the second catalyst, the bypass passage is kept warm by these. Therefore, the cooling of the exhaust gas in the bypass passage is suppressed, the first catalyst quickly reaches the activation temperature, and the purification rate of the first catalyst can be increased.

Further, since the exhaust gas guided to the second catalyst is cooled by the cooling means, the second purification rate can be increased. According to a second aspect of the present invention, in the first aspect, the first catalyst, the second catalyst, the bypass passage, and the cooling unit are housed in one container. It is assumed that.

In the present invention, since both of the catalyst, the bypass passage, and the cooling means are housed in one container, the size of the apparatus is reduced and the mountability on a vehicle is improved.
According to a third aspect of the present invention, in the first or second aspect, the cooling means comprises a heat radiating means.

According to the present invention, the cooling means can be configured simply, and the apparatus can be made compact and inexpensive as compared with the above-described conventional air-cooling type having an air supply mechanism or the like or other water-cooling type. Can be formed.

According to a fourth aspect of the present invention, in the first, second, or third aspect, a muffler is provided at an upstream portion of the bypass passage. In the present invention, by forming a silencer using the above-mentioned bypass passage, a device having both the exhaust gas purifying function and the silencing function is provided, and the mountability of both functions to a vehicle is improved.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the first catalyst is a three-way catalyst and the second catalyst is a NOx catalyst. It is characterized by the following.

In the present invention, the exhaust gas is guided from the exhaust passage having the cooling means to the NOx catalyst as the second catalyst by closing the on-off valve during the lean operation. Thus, the purification rate of the NOx catalyst activated at a low temperature can be increased by the above-described operation. Further, the purifying rate of the three-way catalyst activated at a high temperature by opening the opening / closing valve during the stoichiometric operation to guide the high-temperature exhaust gas to the three-way catalyst can be increased by the above-described action.

According to a sixth aspect of the present invention, in any one of the first to fourth aspects, the first catalyst is a three-way catalyst and the second catalyst is an HC adsorption catalyst. It is characterized by being.

In the present invention, at the time of starting the internal combustion engine in which a large amount of HC is discharged, the on-off valve is closed, and the exhaust gas is led from the exhaust passage provided with the cooling means to the HC adsorption catalyst as the second catalyst. This makes it possible to increase the HC purification rate of the HC adsorption catalyst, which increases the HC adsorption at a low temperature, by the above-described action. In addition, by opening the on-off valve when the amount of HC emission decreases, most of the exhaust gas is guided to the three-way catalyst, and the above-described operation can increase the purification rate of the three-way catalyst.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described based on an embodiment shown in FIGS. 1 shows a side cross section of the exhaust gas purifying device, FIG. 2 shows a cross section taken along line XX of FIG. 1, and FIG. 3 shows a cross section taken along line YY of FIG.

The catalyst container 1 constituting the exhaust system of the internal combustion engine and the exhaust gas purifying device is formed in a cylindrical shape, and the upstream end 1a is reduced in diameter and connected to the upstream exhaust pipe of the internal combustion engine. The downstream end 1b is reduced in diameter and connected to a downstream exhaust pipe.

The first catalyst 2 is located downstream of the catalyst container 1.
However, a second catalyst 5 is provided on the outer periphery of the first catalyst 2 via a heat insulating material 3 and a space 4 upstream of the first catalyst 2. The first catalyst 2 is a three-way catalyst, and the second catalyst 5 is a NOx catalyst or an HC adsorption catalyst.

A cylindrical bypass passage 6 is provided at the center of the second catalyst 5 so as to pass therethrough concentrically, and the entire outer periphery of the bypass passage 6 is surrounded by the second catalyst 5. Thereby, the outer periphery of the bypass passage 6 is arranged so as not to directly contact the outside air, and the second catalyst 5 also serves as a heat insulating material.

Further, a heat insulating material 7 is interposed between the bypass passage 6 and the second catalyst 5 to suppress the heating of the second catalyst 5 due to the exhaust heat of the bypass passage 6 and to flow through the bypass passage 6. The exhaust gas is kept warm.

The downstream end of the bypass passage 6 opens into the space 4, and the upstream side extends to extend to the upstream end 1 a of the catalyst container 1.
It is open to a nearby exhaust inlet 13. Further, an opening / closing valve 8 is provided in an upstream side portion of the bypass passage 6.
When the NOx catalyst is used as the second catalyst 5, the opening / closing valve 8 is used when the internal combustion engine is operating in a lean state.
When an HC adsorption catalyst is used as the catalyst 5, the control means (not shown) is controlled so as to be closed when the internal combustion engine is started and opened when the stoichiometric operation is performed.

A cylindrical guide 9 is arranged on the outer periphery of the bypass passage 6 on the upstream side of the second catalyst 5 with a space between the bypass passage 6 and the catalyst container 1. Both ends of 9 are hermetically fixed to the bypass passage 6.

Further, a plurality of small holes 10 are formed in the bypass passage 6.
Is formed, and the small hole 10 and the space 11 formed by the bypass passage 6 and the guide 9 form a sound deadening means.

A space formed by the guide 9 and the catalyst container 1 forms an annular exhaust passage 12 concentric with the bypass passage 6. The upstream side of the exhaust passage 12 is in open communication with an exhaust inlet 13 upstream of the on-off valve 8, and the downstream side is in open communication with the second catalyst 5.

Further, as shown in FIG. 3, fins 14 which are corrugated in the circumferential direction are arranged in the exhaust passage 12 all around and long in the axial direction. The fin 14 is connected to the exhaust passage 12.
Absorbs the heat of the exhaust gas flowing inside the
Heat radiating means for transferring heat from the contact portion between the catalyst container 1 and the catalyst container 1 to the catalyst container 1 and radiating heat from the catalyst container 1 to the outside air constitutes a cooling means for exhaust gas flowing through the exhaust passage 12.

Next, the operation of the above embodiment will be described. When a NOx catalyst is used as the second catalyst 5, the on-off valve 8 is closed during the lean operation. As a result, the exhaust gas flows through the exhaust passage 12 from the inflow port 13, and the NOx
The catalyst flows through the second catalyst 5 serving as a catalyst, flows through the three-way catalyst of the first catalyst 2 from the space 4, and is discharged to an exhaust pipe (not shown) connected downstream of the catalyst container 1.

In this circulation, the exhaust gas flows through the exhaust passage 1
2, the heat of the exhaust gas is absorbed by the fins 14 having a large surface area, the heat is radiated from the catalyst container 1 to the outside air, and the cooled exhaust gas is introduced to the second catalyst 5, which is a NOx catalyst. I will

During the stoichiometric operation, the on-off valve 8 is opened, and most of the exhaust gas flows through the bypass passage 6 and flows into the first catalyst 2, which is a three-way catalyst. here,
As shown by the curve A in FIG. 4, the purification rate of the NOx catalyst has a characteristic that the activity is high and the purification rate is high when the temperature is low, but the activity is low and the purification rate is low when the temperature is high. Also, as shown by the curve B in FIG. 4, the three-way catalyst has a characteristic that the activity is low and the purification rate is low when the temperature is low, and the activity is high and the purification rate is high when the temperature is high.

As shown in FIG. 5, the degree of deterioration of the NOx catalyst and the three-way catalyst with respect to the exhaust gas temperature is lower at the lower temperature in the NOx catalyst shown by the curve D than in the three-way catalyst shown by the curve C. .

Therefore, as described above, a high NOx purification rate can be achieved by cooling the exhaust gas and guiding it to the NOx catalyst 5 during the lean operation. In addition, during the stoichiometric operation, a high purification rate can be achieved by guiding the exhaust gas to the three-way catalyst 2 through the bypass passage 6. At this time, a part of the exhaust gas also flows into the exhaust passage 12 side,
The exhaust gas that has flowed in is cooled by the fins 14 and flows into the NOx catalyst 5, so that deterioration of the NOx catalyst is suppressed.

Next, a case where an HC adsorption catalyst is used as the second catalyst 5 will be described. The HC adsorption catalyst adsorbs HC at a low temperature and desorbs the HC at a high temperature. The amount of adsorption shows the characteristic of curve E in FIG. 6, and the amount of desorption shows the characteristic of curve F in FIG. The characteristic B in FIG. 6 indicates the purification rate of the three-way catalyst as in FIG.

Therefore, by opening and closing the on-off valve 8 at the start of the internal combustion engine where a large amount of HC is discharged, the exhaust gas passes through the fins 12 serving as the cooling means, and the cooled exhaust gas flows to the HC adsorption catalyst 5. Be guided. Therefore,
A high HC purification rate can be achieved.

Thereafter, by opening the on-off valve 8 when the amount of HC emission decreases, most of the exhaust gas is directly led to the three-way catalyst 2, so that the temperature of the three-way catalyst 2 rises and Exhaust gas starts to be purified by the catalyst 2. At this time, the exhaust gas slightly flows to the HC adsorption catalyst 5, but the exhaust gas is sufficiently cooled by the fins 14 as cooling means. Further, the temperature rise is suppressed by heat conduction from the surroundings of the HC adsorption catalyst 5 to the outside air. Therefore, it is possible to prevent the HC from being desorbed from the HC adsorption catalyst before the three-way catalyst is sufficiently activated to be led to the three-way catalyst. As the activity of the three-way catalyst 2 increases, the temperature of the HC adsorption catalyst 5 gradually increases, and the adsorbed HC is desorbed and purified by the three-way catalyst 2.

[0038]

As described above, according to the first aspect of the present invention, the bypass passage to the first catalyst which is activated at a high temperature is kept warm, and the first exhaust gas flowing through the bypass passage is kept warm. The temperature rise of the first catalyst can be accelerated, and the purification rate of the first catalyst can be increased. Further, the exhaust gas to the second catalyst which is activated at a low temperature is cooled, and the purification rate of the second catalyst can be increased.

Therefore, a high purification rate can be achieved in all operating states. According to the second aspect of the present invention, since the two catalysts, the bypass passage, and the cooling means are housed in one container, the size of the device can be reduced and the mountability on a vehicle can be improved. .

According to the third aspect of the present invention, the cooling means can be formed simply, compactly and inexpensively. According to the fourth aspect of the invention, the purifying device and the muffler can be more easily mounted on a vehicle.

According to the fifth aspect of the present invention, NOx
In the case of using a catalyst and a three-way catalyst, the purification rates of these two catalysts can be increased, and a high purification rate can be achieved in all operating states. According to the sixth aspect of the present invention, HC
In the case of using an adsorption catalyst and a three-way catalyst, the purification rates of these two catalysts can be increased, and a high purification rate in all operating states can be achieved.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX in FIG.

FIG. 3 is a sectional view taken along line YY in FIG. 1;

FIG. 4 is a characteristic diagram showing a purification rate with respect to a temperature of a NOx catalyst and a three-way catalyst.

FIG. 5 is a characteristic diagram showing the degree of deterioration of a NOx catalyst and a three-way catalyst with respect to temperature.

FIG. 6 is a characteristic diagram showing the amount of adsorption and desorption with respect to the temperature of the HC adsorption catalyst and the purification rate with respect to the temperature of the three-way catalyst.

FIG. 7 is a side sectional view of an exhaust gas purification apparatus showing a first conventional technique.

FIG. 8 is a sectional view taken along line ZZ of FIG. 7;

FIG. 9 is a side sectional view of an exhaust gas purification apparatus showing a second conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Container 2 ... Three-way catalyst which is 1st catalyst 5 ... NOx catalyst or HC adsorption catalyst which is 2nd catalyst 6 ... Bypass passage 8 ... Opening / closing valve 10, 11 ... Small hole and space 12 which comprise a silencer 12 ... exhaust passage 14 ... fins constituting cooling means (radiation means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/20 F01N 3/20 A 3/28 301 3/28 301B

Claims (6)

[Claims] 1. A second catalyst having an active temperature lower than that of the first catalyst is disposed upstream of the first catalyst provided in the exhaust system of the internal combustion engine, and the second catalyst is provided. An exhaust gas purifying apparatus provided with a bypass passage that bypasses the gas and directly introduces exhaust gas into the first catalyst, and an open / close valve that can be opened and closed in the bypass passage, wherein the second catalyst and the bypass passage are provided concentrically. An exhaust gas purifying apparatus, wherein a passage to the second catalyst is formed on the outer periphery of the bypass passage, and cooling means is provided in the passage to the second catalyst. 2. The exhaust gas purifying apparatus according to claim 1, wherein the first catalyst, the second catalyst, the bypass passage, and the cooling unit are housed in one container. 3. The exhaust gas purifying apparatus according to claim 1, wherein said cooling means comprises a heat radiating means. 4. The exhaust gas purifying apparatus according to claim 1, wherein a silencer is provided in an upstream portion of the bypass passage. 5. The exhaust gas purifying apparatus according to claim 1, wherein the first catalyst is a three-way catalyst, and the second catalyst is a NOx catalyst. 6. The exhaust gas purifying apparatus according to claim 1, wherein the first catalyst is a three-way catalyst, and the second catalyst is an HC adsorption catalyst.