JPH08144750A - Exhaust emission control device - Google Patents

Abstract

PURPOSE: To improve adsorbing efficiency of an HC adsorber to extend the holding time of the HC so as to prevent the HC which is not purified from being discharged, in an exhaust emission control device. CONSTITUTION: An adsorbing maternal 3 for adsorbing unburnt component included in exhaust gas is fixed on a wall surface 21 opposing to an exhaust port 11, in an exhaust manifold 2 communicated with the exhaust port 11 in an internal combustion engine 1, and a catalyst 5 for purifying exhaust gas is arranged in an exhaust passage 4 downstream of the exhaust manifold 2. An end surface 31 opposing to the exhaust port 11 of the adsorbing material 3 is recessed in a curved shape, and collision force of exhaust gas in averaged so as to improve heat radiating performance.

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 for detoxifying a relatively large amount of hydrocarbons (HC) discharged during cold start of an internal combustion engine such as a gasoline engine.

[0002]

2. Description of the Related Art Conventionally, unburned components such as hydrocarbons (HC) contained in the exhaust gas of an engine are oxidatively decomposed by an oxidation catalyst arranged in the exhaust passage and discharged. However, there is a problem that the oxidation catalyst does not function sufficiently at the time of starting the engine until it reaches a certain purification temperature, and during that time, HC is discharged without being purified. For this reason, an HC adsorbent is provided along the wall surface of the exhaust manifold facing the exhaust port of the engine, and immediately after the engine is started, the HC is collided with the adsorbent and captured, and is desorbed from the adsorbent as the exhaust gas temperature rises. HC coming
There is an exhaust gas purification device that purifies the exhaust gas by an oxidation catalyst arranged in the exhaust passage further downstream (Japanese Patent Laid-Open No. 6-2129).
No. 51).

[0003]

However, in the above-mentioned conventional exhaust gas purifying apparatus, as shown in FIG. 12, the HC particles discharged from the exhaust port 11 of the engine spread radially and spread on the surface of the HC adsorbent 3. A difference occurs in the collision force of the exhaust gas G. Therefore, the amount of adsorbed HC is large where the collision force of the exhaust gas G is large (A portion in the figure), and the amount of adsorbed HC is small where the collision force is small (B portion in the figure). Then, when the collision force of the exhaust gas G is large, the saturated adsorption amount is reached quickly, and thereafter, HC is desorbed without adsorbing, resulting in a problem that a high adsorption rate cannot be obtained. Moreover, when the collision force of the exhaust gas G is large, the temperature rising rate is also fast, so that the desorption temperature is reached quickly, and the desorption of the downstream oxidation catalyst starts before reaching the purification temperature. HC may be discharged.

Therefore, an object of the present invention is to improve the adsorption efficiency of the HC adsorbent in the exhaust gas purifying apparatus provided with the HC adsorbent, extend the holding time of the HC, and discharge unpurified HC. To prevent.

[0005]

The present invention has been made in view of the above circumstances, and as shown in FIG. 1, it faces the exhaust port 11 of the exhaust manifold 2 communicating with the exhaust port 11 of the internal combustion engine 1. An exhaust gas purifying apparatus in which an adsorbent 3 for adsorbing unburned components contained in exhaust gas is fixed to a wall surface 21 and an exhaust gas purifying catalyst 5 is arranged in an exhaust passage 4 downstream of the exhaust manifold 2. In the above, the end surface 31 of the adsorbent 3 facing the exhaust port 11 is recessed in a curved shape (claim 1).

The adsorbent 3 is formed, for example, by recessing one side surface of a rectangular honeycomb structure in an arc shape (FIG. 3, claim 2) or by recessing one end surface of a circular honeycomb structure in a spherical shape. (FIG. 7, claim 3).

[0007]

In FIG. 4, when the engine is started, unburned HC
The exhaust gas G containing fine particles is spread radially from the center of the exhaust port 11 and is discharged. In the present invention, since the end surface 31 of the HC adsorbent 3 with which the exhaust gas G collides is curved according to the spread of the exhaust gas G, the collision force of the exhaust gas is averaged. In addition, since the end face 31 is formed into a curved surface, the adsorption area is expanded, and the adsorption efficiency is further improved.

In the process of raising the temperature of the HC adsorbent 3 after the engine is started, since the end face 31 is curved, the closer to the front position of the exhaust port 11 which is most easily heated, that is, the closer to the concave bottom of the end face 31, the closer. , The distance d between the end surface 31, which is the HC collision surface, and the outer wall surface 21 of the exhaust manifold 2 is short, and heat is quickly dissipated. That is, since the heat transfer distance is changed according to the temperature distribution of the exhaust gas, the heat dissipation is good and the temperature rising rate of the HC adsorbent 3 can be slowed down. Therefore, the HC holding time becomes long, and the downstream oxidation catalyst 5 has reached the purification temperature by the time when HC starts to be desorbed, so that the desorbed HC from the HC adsorbent 3 can be reliably purified, and Prevent it from being discharged as it is.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2, a four-cylinder gasoline engine 1 has four exhaust ports 11 and these exhaust ports 1
Exhaust gas discharged from the engine 1 is collected by an exhaust manifold 2 connected to the side surface of the engine 1 and discharged from a plurality of exhaust pipes 4 connected to the lower surface thereof. The exhaust pipe 4 is provided with a large diameter part in the middle thereof, and H
An oxidation catalyst 5 for purifying C is provided.

The exhaust manifold 2 is a container body in which the four exhaust ports 11 are connected to one side surface, and the HC adsorbent 3 is fixed on the entire wall surface 21 facing the exhaust ports 11. The adsorbent 3 is formed by coating an adsorbent such as zeolite on a carrier having a honeycomb structure formed of ceramics such as alumina or a metal foil. As shown in FIG. The end face 3 is formed by recessing in an arc shape and forming a groove shape as a whole.
1, and the end face 31 is arranged in the exhaust manifold 2 so as to face the exhaust port 11. The end face 31 is processed by electric discharge machining or wire cutting if the carrier is made of metal, and by cutting if it is made of ceramics.

Next, the operation of this apparatus will be described. FIG.
At the time of engine start (during cranking), the exhaust gas containing a large amount of HC is radially discharged from the exhaust port 11. In the present invention, since the end surface 31 of the HC adsorbent 3 facing the exhaust port 11 is a curved surface along the spread of the exhaust gas, the collision force of the exhaust gas can be averaged. Moreover, since the exhaust collision area can be expanded by using the curved surface, HC can be adsorbed efficiently. FIG. 5 shows a comparison of the specific adsorption efficiencies of the product of the present invention and the conventional product. Compared to the conventional product in which the end surface 31 of the HC adsorbent 3 is a flat surface,
It can be seen that the C adsorption efficiency is greatly improved.

After the engine is started (after the complete explosion), the exhaust gas is exhausted from the exhaust port 11 in a more linear manner, so that the HC
The adsorbent 3 is more likely to be heated toward the central portion of the end face 31 which is the exhaust collision surface. In the present invention, the end surface 31 of the HC adsorbent 3 is
Is curved, the distance between the end surface 31 and the exhaust manifold outer wall surface 21 becomes shorter toward the central portion. Therefore, the heat is rapidly dissipated even in the central portion that is easily heated, so that the heat dissipation is improved and the temperature rising rate of the adsorbent can be slowed.

FIG. 6 shows the temperature rise characteristics of the product of the present invention in comparison with the conventional product. Comparing the time required to start HC desorption of the adsorbent in the product of the present invention and the conventional product with reference to the time required to start the purification of the oxidation catalyst, the conventional product shows that the HC desorption before the start of catalyst purification On the other hand, since the product of the present invention has a slow temperature rising rate of the adsorbent, HC desorption starts after the start of purification of the catalyst. Thus, the HC desorbed from the HC adsorbent 3 can be reliably purified by the downstream oxidation catalyst 5.

FIG. 7 shows another example of the shape of the HC adsorbent 3. In this way, the HC adsorbent 3 may be a circular honeycomb structure, and the end surface 31 facing the exhaust port 11 may be recessed into a spherical shape. In order to manufacture the HC adsorbent 3 having such a shape, a spherical concave portion can be formed by cutting if it is made of ceramics and by electric discharge machining if it is made of metal. Alternatively, as shown in FIG.
It can also be formed by using a plurality of strip-shaped metal pieces 6 in which a flat plate and a corrugated plate that gradually widen are overlapped and spirally winding the ends of the minimum width as a center.

When the HC adsorbent 3 having the shape shown in FIG. 7 is applied to this apparatus, as shown in FIG. 9, the end portions of the exhaust port 11 are gathered at one point, and the HC adsorbent 3 is gathered at this gathering portion. Attach so that they face each other. Alternatively, as shown in FIG. 10, a plurality of HC adsorbents 3 are provided, and the HC adsorbents 3 are arranged so as to face each other at a position where two exhaust ports 11 are gathered. The adsorbents 3 may be arranged to face each other (FIG. 11).

[0016]

As described above, according to the present invention, it is possible to improve the adsorption rate of the HC adsorbent and to suppress the temperature rising rate, and
It is possible to prevent early desorption. Therefore, the HC discharged before the temperature of the oxidation catalyst reaches the purification temperature is surely captured and retained, and the H discharged to the outside of the system at the cold start is retained.
C can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional side view of an exhaust gas purification device of the present invention.

FIG. 2 is a partial cross-sectional plan view of the exhaust gas purification device of the present invention.

FIG. 3 is a perspective view of an HC adsorbent.

FIG. 4 is a partial enlarged cross-sectional view of an exhaust gas purification device for explaining the operation of the present invention.

FIG. 5 is a diagram comparing the HC adsorption efficiency between the device of the present invention and the conventional device.

FIG. 6 is a diagram showing temperature rising characteristics of the HC adsorbent in the device of the present invention and the conventional device.

7 shows another example of the shape of the HC adsorbent, FIG. 7 (A) is a perspective view of the HC adsorbent, and FIG. 7 (B) is BB of FIG. 7 (A).
It is a line sectional view. It is a top view.

FIG. 8 is a diagram showing a method for producing the HC adsorbent of FIG.
FIG. 8A is a front view of a metal piece constituting the HC adsorbent, FIG.
(B) is an exploded perspective view of the HC adsorbent.

9 is a plan view showing an example of an exhaust gas purifying device in which the HC adsorbent of FIG. 7 is arranged.

FIG. 10 is a plan view showing another example of the exhaust gas purifying apparatus in which the HC adsorbent of FIG. 7 is arranged.

FIG. 11 is a plan view showing still another example of the exhaust gas purifying apparatus in which the HC adsorbent of FIG. 7 is arranged.

FIG. 12 is a partially enlarged cross-sectional view of a conventional exhaust gas purification device.

[Explanation of symbols]

 1 Engine (Internal Combustion Engine) 11 Exhaust Port 2 Exhaust Manifold 3 HC Adsorbent 31 End Face 4 Exhaust Pipe (Exhaust Passage) 5 Oxidation Catalyst 6 Strip Metal Piece

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Yoshinaga 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Japan Auto Parts Research Institute, Inc.

Claims (3)

[Claims] 1. An adsorbent that adsorbs unburned components contained in exhaust gas is fixed to a wall surface of an exhaust manifold that communicates with an exhaust port of an internal combustion engine, the wall surface facing the exhaust port,
In an exhaust gas purifying apparatus in which a catalyst for purifying exhaust gas is disposed in an exhaust passage downstream of the exhaust manifold, an end face of the adsorbent facing the exhaust port is concavely curved. Gas purification device. 2. The exhaust gas manifold according to claim 1, wherein one side surface of the prismatic honeycomb structure is recessed in an arc shape to form the adsorbent, and the recessed side surface is arranged in the exhaust manifold so as to face the exhaust port. Exhaust gas purification device. 3. The exhaust gas manifold according to claim 1, wherein one end surface of the circular honeycomb structure is recessed into a spherical shape to form the adsorbent, and the recessed end surface is arranged in the exhaust manifold so as to face the exhaust port. Exhaust gas purification device.