JPH11336533A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To delay desorption of an adsorbent more than activity of an exhaust emission controlling catalyst so as to improve exhaust emission by disposing an adsorbent arranged on the upstream from the catalyst disposed in an exhaust passage of an internal combustion engine to adsorb unburnt component in exhaust in the inner wall of a portion of the exhaust passage, which has large heat capacity. SOLUTION: Exhaust discharged from an exhaust port 12 of an internal combustion engine 10 is discharged to an exhaust passage 16 through an exhaust manifold 14. By a catalytic converter rhodium 22 as an exhaust emission controlling catalyst disposed in a downstream passage 20 of the exhaust passage 16, HC(unburnt component) and CO in exhaust are oxidized and NOx is reduced to control emission. In this case, a flexible pipe 26 having a large surface area is connected to the upstream of the three way catalytic converter 22 in the downstream passage 20, and an HC adsorbent as an adsorbing material is disposed in the interior of the pipe 26. Thus, a temperature rise of the HC adsorbing material is restrained to overcome the disadvantage that the HC adsorbing material reaches a desorption temperature before activity of the catalytic converter rhodium 22, thereby inhibiting exhaust emission of HC.

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 apparatus for purifying unburned components discharged during a cold start of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, an unburned component, for example, hydrocarbon (HC) contained in exhaust gas of an internal combustion engine is purified by an exhaust gas purifying catalyst (three-way catalyst) provided in an exhaust passage. I have. However, at the time of starting the internal combustion engine, the catalyst does not function sufficiently until a certain activation temperature is reached, and during that time, there is a problem that HC is exhausted without being purified. In order to solve this problem, an HC adsorbent is provided in an exhaust passage of the internal combustion engine to temporarily adsorb HC in the exhaust gas at a predetermined temperature immediately after a cold start of the engine, and to adsorb the HC at a predetermined temperature or higher. There is known an exhaust gas purifying apparatus that purifies HC desorbed from a fuel by a downstream exhaust gas purifying catalyst. For example, it is known from JP-A-7-139344.

In the above prior art, a bypass passage that bypasses an exhaust passage is provided upstream of an exhaust purification catalyst (oxidation catalyst), and the inner wall of the bypass passage is thinly coated with an HC adsorbent. Immediately after the cold start of the engine, exhaust gas flows through the bypass passage, and the HC in the exhaust gas is adsorbed by the HC adsorbent. When the HC adsorbent reaches a predetermined desorption temperature or higher, the HC desorbs and flows into the exhaust passage, where the activated downstream oxidation catalyst purifies the HC.

[0004]

When the inner wall of the exhaust passage is coated with the HC adsorbent thinly as in the above-mentioned prior art, the exhaust passage coated with the HC adsorbent has a straight single-layer structure that easily radiates heat. Because of the exhaust passage, the HC adsorbent reaches the desorption temperature before the activity of the downstream exhaust purification catalyst under the influence of the gradually rising exhaust temperature after the engine is started. As a result, HC desorbed from the HC adsorbent may be released to the atmosphere without being purified by the exhaust purification catalyst.

[0005] The present invention has been made in view of the above problems, and when the HC adsorbent is provided on the inner wall of the exhaust passage, H
By providing the C adsorbent on the inner wall of the large heat capacity part,
It is an object of the present invention to slow the desorption of the HC adsorbent from the activity of the exhaust purification catalyst and suppress the deterioration of exhaust emissions.

[0006]

The present invention employs the following configuration to solve the above-mentioned problems. That is,
An exhaust gas purifying apparatus according to a first aspect of the present invention includes an exhaust gas purifying catalyst provided in an exhaust passage of an internal combustion engine, and an unburned component in exhaust gas adsorbed at a predetermined temperature or lower upstream of the exhaust gas purifying catalyst. An exhaust purification device comprising: an adsorbent for desorbing adsorbed unburned components; wherein the adsorbent is provided on an inner wall of a portion of the exhaust passage having a large heat capacity.

In the present invention, since the adsorbent for adsorbing unburned components at a predetermined temperature or lower is provided on the inner wall of the portion having a large heat capacity of the exhaust passage, the temperature rise of the adsorbent is delayed even if the exhaust gas temperature rises. Unburned components are prevented from desorbing from the adsorbent before the exhaust purification catalyst is activated.

An exhaust gas purifying apparatus according to a second aspect of the present invention is provided with an exhaust gas purifying catalyst provided in an exhaust passage of an internal combustion engine, and adsorbs unburned components in exhaust gas at a predetermined temperature or lower upstream of the exhaust gas purifying catalyst. An exhaust purification device comprising: an adsorbent that desorbs unburned components adsorbed at a temperature equal to or higher than a temperature, wherein the adsorbent is provided on an inner wall of a portion of the exhaust passage having a large surface area.

According to the present invention, since the adsorbent for adsorbing unburned components at a predetermined temperature or lower is provided on the inner wall of the exhaust passage having a large surface area, the temperature rise of the adsorbent is delayed even if the exhaust gas temperature rises. Unburned components are prevented from desorbing from the adsorbent before the exhaust purification catalyst is activated. In addition, since the surface area of the adsorbent becomes relatively large, the amount of adsorbed unburned components can be increased.

The portion of the exhaust passage having a large heat capacity or a large surface area according to the present invention includes the inner wall of the flexible pipe of the exhaust passage, the inner wall of the inner pipe of the double exhaust pipe comprising the inner pipe and the outer pipe, and A branch portion where the exhaust passage branches into a plurality is exemplified.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an exhaust emission control device according to the present invention will be described with reference to the drawings. FIG. 1 is a first embodiment and is a schematic configuration diagram showing a configuration when the present invention is applied to an exhaust gas purification device for an internal combustion engine.

The internal combustion engine 10 is a gasoline engine, and has an exhaust port 12 on an upper side surface thereof. Exhaust gas discharged from the exhaust port 12 passes through an exhaust manifold 14 connected to the exhaust port 12 to an exhaust passage 16. Is discharged. The exhaust passage 16 includes an upstream passage 18 and a downstream passage 20, and a three-way catalyst 22 as an exhaust purification catalyst is provided in the downstream passage 20. The three-way catalyst 22 oxidizes unburned fuel (HC) and carbon monoxide (CO) in the exhaust gas and reduces and purifies nitrogen oxides (NOx). The exhaust manifold 14 is provided with an air-fuel ratio sensor 24 for detecting an air-fuel ratio of exhaust gas discharged from the exhaust port 12. The fuel injection amount is calculated based on the output of the air-fuel ratio sensor so that the exhaust gas of the internal combustion engine 10 has the stoichiometric air-fuel ratio, and is injected from a fuel injection valve (not shown).

The upstream passage 18 is a double exhaust passage composed of an inner pipe and an outer pipe, and is provided upstream of the downstream passage 20 with respect to the relative displacement, axial bending and vibration of the exhaust passage in the axial direction. A flexible pipe 26 is provided. Further, the exhaust manifold 14 and the upstream passage 18 are connected by a flange 28, and the upstream passage and the downstream passage are connected by a flange 30.

FIG. 2 shows the flexible pipe 26 in the downstream passage.
It is an enlarged view of the principal part of. The flexible pipe 26 includes a wavy bellows 28 connecting the upstream exhaust passage and the downstream exhaust passage. An outer cover 30 is provided so as to cover the outer periphery of the bellows 28. The bellows 28 and the outer cover 30 are welded to the exhaust passage. It is fixed. Also,
A convex inner wall 28a is formed on the inner wall of the bellows 28 in a direction perpendicular to the flow direction of the exhaust passage.

In this embodiment, the inner wall of the bellows is coated with an HC adsorbent 32 as an adsorbent with a predetermined thickness. Further, a convex inner wall 28a which is a part of the inner wall of the bellows 28 is also coated with the HC adsorbent 32.
The HC adsorbent 32 is made of a material containing zeolite as a main component. The HC adsorbent 32 adsorbs unburned fuel (HC) in exhaust gas when the temperature is equal to or lower than a predetermined temperature (for example, 100 ° C.). It has a function of desorbing the adsorbed HC. In consideration of heat resistance, the Si / Al ratio is 500
The above is preferred. When zeolites having different pore diameters are used, the timing of adsorption and desorption can be set widely. Also, the adsorption amount of the HC adsorbent increases when the thickness of the coating is increased.
A thickness of 200 μm is good.

Next, the operation of this embodiment will be described with reference to FIG. When the internal combustion engine 10 is cold started, the start (t =
Time domain (I) from 0) to the first time (t = t1)
In the internal combustion engine, the fuel increase is performed as a warm-up operation. At this time, unburned fuel (HC) is discharged from the exhaust port 12.
Is exhausted, and this exhaust is exhausted by the HC adsorbent 32.
Flows into the downstream passage 20 having If the temperature of the HC adsorbent 32 is equal to or lower than a predetermined temperature, the unburned fuel (HC) in the exhaust gas
Is temporarily adsorbed by the HC adsorbent 32, and the exhaust gas flowing out of the downstream passage 20 passes through the three-way catalyst 22. In the time region (I), the three-way catalyst 22 has not reached the activation temperature, but since the unburned fuel is adsorbed by the HC adsorbent 32, the release to the atmosphere is suppressed.

In the time region (I), the exhaust gas temperature gradually increases. However, since the HC adsorbent 32 in the downstream passage 20 is provided on the inner wall of the exhaust passage having a large heat capacity, the temperature of the three-way catalyst 22 on the downstream side is reduced. Temperature rises more slowly than rises. On the other hand, since the three-way catalyst 22 has the catalyst disposed over the entire cross-sectional area of the exhaust passage, the three-way catalyst 22 directly collides with the exhaust gas, and thus easily receives heat.
The temperature rises quickly even downstream of the HC adsorbent 32. And
At the first time (t = t1), the three-way catalyst 32 reaches the activation temperature (for example, 300 ° C.), and the HC, C
O and NOx are purified. At this time, since the HC adsorbent 32 has not been heated to the desorption temperature, it continues to adsorb HC.

In the time region (II) from the first time (t = t1) to the second time (t = t2), the HC adsorbent 3
The temperature of the two and three way catalysts 22 rises. Then, in the time region (III) after the second time (t = t2), the temperature of the HC adsorbent reaches the desorption temperature, and the HC adsorbed by the HC adsorbent 32 is desorbed. The desorbed HC flows into the downstream three-way catalyst 22 together with the exhaust gas. At this time, since the three-way catalyst 22 has already reached the activation temperature, the HC
Is purified by the three-way catalyst 22.

As described above, in the present embodiment, the HC adsorbent 32 is provided on the inner wall of the bellows 28 having a heat capacity of the exhaust passage larger than that of the conventional straight single exhaust passage.
There is an effect that the temperature rise of the adsorbent is suppressed. Therefore, since the HC adsorbent 32 does not reach the desorption temperature before the activation of the downstream three-way catalyst 22, the HC exhaust emission can be suppressed. Further, since the HC adsorbent 32 is provided on the inner wall of the bellows 28, the exhaust resistance can be suppressed as compared with the conventional HC adsorbent in which the HC adsorbent is provided over the entire cross-sectional area of the exhaust passage, and the power performance of the engine is improved. I do.

Further, when an HC adsorbent is provided on the inner wall of a straight single exhaust passage as in the prior art, the area of contact between the HC adsorbent and the unburned fuel (HC) in the exhaust gas is small.
There is a problem that the adsorption amount of C decreases. In this case, the portion having a relatively large surface area in the exhaust passage, such as the bellows 28, is coated with the HC adsorbent 32.
This has the effect of increasing the amount of C adsorbed.

Next, a second embodiment will be described with reference to FIG. FIG. 4A is a cross-sectional view of the downstream passage 20 of the exhaust passage, and FIG. 4B is a cross-sectional view taken along line bb.
On the inner wall of the downstream passage 20 of the present embodiment, a corrugated corrugated plate 40 is arranged instead of the flexible pipe 26 of the first embodiment. The corrugated sheet 40 is made of metal foil (Fe-20Cr-
5Al) and is fixed to the inner wall of the downstream passage 20 by welding. In the present embodiment, the inner surface of the corrugated plate 40 through which the exhaust gas flows is coated with the HC adsorbent 32.
In this embodiment, the HC adsorbent 32 is coated on the corrugated plate 40 with a uniform thickness. However, as another embodiment, the thickness of the HC adsorbent 32 is reduced in a portion corresponding to the peak of the corrugated plate 40. By increasing the thickness, the amount of adsorption of HC may be increased. Note that the thickness of the corrugated plate 40 is, for example, in the range of 100 μm to 500 μm.

The operation of adsorbing and desorbing the HC adsorbent 32 in such a configuration is the same as that of the above-described embodiment, and the description is omitted. In the present embodiment, since the corrugated plate 40 is provided on the inner wall of the downstream passage 20 and the surface of the corrugated plate 40 is coated with the HC adsorbent 32, the surface area of the HC adsorbent 32 can be increased, and the amount of adsorbed HC is large. Become. In addition, the thickness of the corrugated sheet of the corrugated sheet 40 may be appropriately changed in order to suppress the temperature rise of the HC adsorbent 32. Also, by changing the material composition of the foil of the corrugated sheet 40, the thermal conductivity is changed,
The temperature rise of the adsorbent 32 may be suppressed.

Next, a third embodiment will be described with reference to FIG. FIG. 5 corresponds to an enlarged cross-sectional view of FIG. In the second embodiment described above, the inner surface of the corrugated sheet 40 has H
In contrast to coating the C adsorbent,
The inner surface and the outer surface of the corrugated sheet are coated with the HC adsorbent. Exhaust gas flowing from the exhaust port 12 through the upstream passage 18 flows through the main exhaust passage 42 of the downstream passage 20 and also exhausts to the sub-exhaust passage 44 between the inner wall of the downstream passage 20 and the corrugated plate 40. Exhaust is induced to flow.

As described above, since the HC adsorbent 32 is coated on both surfaces of the corrugated plate 40 and the exhaust gas flows through the main exhaust passage 42 and the sub exhaust passage 44, the amount of adsorbed HC can be increased. Further, since the corrugated plate 40 has a large heat capacity, the temperature rise of the HC adsorbent can be suppressed. The operation is similar to that of the above-described first embodiment, and the description is omitted.

Next, a fourth embodiment will be described with reference to FIG. The downstream passage 20 of the present embodiment branches into two of a first branch passage 60 and a second branch passage 62 in the middle of the downstream passage 20 instead of the flexible pipe 26 of the first embodiment, and merges again downstream. . The HC adsorbent 32 is coated on the inner wall of the passage as in the above-described embodiment.
The upstream end portion 64 of the branch passage is a portion where the temperature rises quickly because the inflowing exhaust gas collides directly. Therefore,
In this embodiment, the upstream end is not coated with the HC adsorbent 32.

Next, the operation of the fourth embodiment, which is different from that of the first embodiment, will be described. During a cold start, the exhaust gas discharged from the exhaust port 12 of the internal combustion engine 10 flows into the downstream passage 20 via the exhaust manifold 14. The exhaust collides with the upstream end portion 64 and is divided into the first branch passage 60 and the second branch passage 62. At this time,
If the HC adsorbent 32 is in a state lower than a predetermined desorption temperature, it adsorbs unburned fuel (HC) in the exhaust gas. In the present embodiment, since the HC adsorbent 32 is provided on the inner walls of both the first branch passage 60 and the second branch passage 62, the exhaust gas and the H
Since the area where C contacts is increased, the amount of adsorption of HC is improved.

Then, as the exhaust gas temperature rises, the temperatures of the HC adsorbent 32 and the downstream three-way catalyst 22 rise. As a result of the three-way catalyst 22 colliding with the exhaust gas directly in the exhaust passage, the temperature of the three-way catalyst 22 rapidly rises to the activation temperature. On the other hand, since the HC adsorbent 32 is provided on the inner wall of the exhaust passage, the amount of directly colliding exhaust gas is smaller than that of the three-way catalyst 22. Further, the downstream passage 20 itself is branched, and the heat capacity as a whole is larger than that of a normal straight exhaust passage. Therefore, H
The temperature rise of the C adsorbent 32 is lower than that of the three-way catalyst 22.
As a result, the HC adsorbent 32 reaches the desorption temperature after the activation of the three-way catalyst 22, so that the adsorbed HC becomes
Purified by.

Next, a fifth embodiment will be described with reference to FIG. The downstream passage 20 is a double exhaust pipe including an inner pipe 70 and an outer pipe 72 instead of the flexible pipe 26 of the first embodiment, and the inner pipe 70 is inserted downstream of the outer pipe 72. The downstream end 74 of the inner pipe is closed and the inner pipe 7 is closed.
The 0 tube wall is provided with a plurality of through holes 76 for discharging exhaust gas into the outer tube. The through hole 76 is provided so that the exhaust gas can be uniformly spread inside the outer tube 72. Outer tube 72
Is coated with an HC adsorbent 32.

Next, the operation of the fifth embodiment different from that of the first embodiment will be described. During a cold start, the exhaust gas discharged from the exhaust port 12 of the internal combustion engine 10 flows into the downstream passage 20 via the exhaust manifold 14. Exhaust gas passes through each through hole 76 of the inner pipe 70 through the outer pipe 72.
Is radially discharged into the inside of the outer tube 72 and uniformly diffuses inside the outer tube 72. At this time, if the HC adsorbent 32 provided on the inner wall of the outer pipe 72 is in a state lower than a predetermined desorption temperature, it adsorbs unburned fuel (HC) in the exhaust gas discharged from the through hole 76. In addition, since the exhaust gas is sufficiently diffused in the outer tube 72, the contact area with the HC in the exhaust gas increases, and the amount of adsorbed HC also increases.

Then, as the exhaust gas temperature rises, the temperatures of the HC adsorbent 32 and the downstream three-way catalyst 22 rise. At this time, the three-way catalyst 22 rapidly rises to the activation temperature,
Since the HC adsorbent 32 in the downstream passage 20 has a double pipe structure of the inner pipe 70 and the outer pipe 72, it has a large heat capacity. Therefore, the temperature rise is suppressed even when the exhaust heat is received, so that the temperature rise of the HC adsorbent 32 becomes slower than that of the downstream three-way catalyst 22. As a result, the HC adsorbent 32 reaches the desorption temperature after the activation of the three-way catalyst 22, so that the adsorbed HC is purified by the three-way catalyst 22.

Next, a sixth embodiment will be described with reference to FIG. The downstream passage 20 of this embodiment is a straight single exhaust passage instead of the flexible pipe 26 of the first embodiment, but has a thick exhaust pipe wall in order to increase the heat capacity. This pipe wall is made of stainless steel (S
US), the thickness of which ranges, for example, from 1 mm to 2 mm. The inner wall of the downstream passage 20 is coated with an HC adsorbent 32 with a uniform thickness. In addition, downstream passage 2
A plurality of exhaust gas rectifying plates 80 each having a triangular prism shape are provided at 0.
° The phases are shifted. The current plate 80 is provided so as to be uniformly diffused in the passage.

Next, the operation of the sixth embodiment different from that of the first embodiment will be described. During a cold start, the exhaust gas discharged from the exhaust port 12 of the internal combustion engine 10 flows into the downstream passage 20 via the exhaust manifold 14. The exhaust gas is uniformly diffused inside the passage by the flow regulating plate 80. At this time, if the HC adsorbent 32 provided on the inner wall is in a state lower than a predetermined desorption temperature, unburned fuel (HC) in the exhaust gas is adsorbed.

Then, as the exhaust gas temperature rises, the temperatures of the HC adsorbent 32 and the downstream three-way catalyst 22 rise. At this time, the three-way catalyst 22 rapidly rises to the activation temperature,
The HC adsorbent 32 in the downstream passage 20 has a large heat capacity because the pipe wall of the downstream passage 20 is thick. Therefore, the temperature rise is suppressed even when the exhaust heat is received, so that the temperature rise of the HC adsorbent 32 becomes slower than that of the downstream three-way catalyst 22. As a result, HC
Since the adsorbent 32 reaches the desorption temperature after the activation of the three-way catalyst 22, the adsorbed HC is purified by the three-way catalyst 22.

In each of the above embodiments, the flexible pipe, the double exhaust pipe, the branch passage, and the exhaust passage provided with the corrugated plate are coated with the HC adsorbent. However, the present invention is not limited to this. In addition, for example, it may be provided in the vicinity of the flange 30 which is a connection portion between the upstream passage and the downstream passage, or may be coated with the HC adsorbent by combining the above various exhaust passage portions.

[0035]

According to the exhaust purifying apparatus of the present invention, when the HC adsorbent is provided on the inner wall of the exhaust passage, the HC adsorbent is provided on the inner wall of the portion where the heat capacity of the exhaust passage is large. The rise of the adsorbent to the desorption temperature is suppressed. Therefore, since the desorbed unburned components are purified by the activated exhaust purification catalyst, deterioration of exhaust emissions is suppressed.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an exhaust gas purifying apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the overall structure of an exhaust passage provided with an adsorbent;

FIG. 3 is a diagram illustrating a temperature change according to the first embodiment of the present invention.

FIG. 4 is a view for explaining a second embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 5 is a diagram illustrating a third embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 6 is a diagram illustrating a fourth embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 7 is a view for explaining a fifth embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 8 is a diagram for explaining a sixth embodiment of the exhaust gas purification apparatus according to the present invention.

[Explanation of symbols]

 10. Internal combustion engine 12 Exhaust port 14 Exhaust manifold 18 Upstream passage 20 Downstream passage 22 Three-way catalyst 26 Flexible pipe 28 Bellows 32 HC adsorbent 40 Corrugated plate 60 First branch passage 62 Second branch passage 70 Inner tube 72 Outer tube 76 Through hole 80 Rectifier plate

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 7/08 ZAB F01N 7/08 ZABA

Claims (5)

[Claims] An exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, adsorbs unburned components in exhaust at a predetermined temperature or less upstream of the exhaust purification catalyst, and removes unburned components adsorbed at a predetermined temperature or more. An exhaust purification device comprising: an adsorbent that is desorbed; and wherein the adsorbent is provided on an inner wall of a portion of the exhaust passage having a large heat capacity. 2. An exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, and an unburned component adsorbed at a predetermined temperature or lower upstream of the exhaust purification catalyst and adsorbed at a predetermined temperature or higher. An exhaust purification device comprising: an adsorbent that is desorbed; wherein the adsorbent is provided on an inner wall of a portion of the exhaust passage having a large surface area. 3. The exhaust gas purification apparatus according to claim 1, wherein a portion of the exhaust passage having a large heat capacity is a flexible pipe of the exhaust passage. 4. The exhaust gas purification apparatus according to claim 1, wherein a portion of the exhaust passage having a large heat capacity is a double exhaust pipe including an inner pipe and an outer pipe. 5. The exhaust gas purifying apparatus according to claim 1, wherein a portion of the exhaust passage having a large heat capacity is a branch portion where the exhaust passage is branched into a plurality.