JPS6128809B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust gas purification device using a catalyst device.

[Conventional technology]

When a catalyst is used to react and purify harmful exhaust gas components, oxygen is necessary for the oxidation of carbon monoxide and hydrocarbons, but for the reduction of nitrogen oxides, the reduction reaction does not proceed if oxygen is present. However, a three-way catalyst has already been proposed that can simultaneously reduce the three harmful components of exhaust gas: hydrocarbons, carbon monoxide, and nitrogen oxides. The purification rate of harmful components of this catalyst is as shown in Figure 3 when the air-fuel ratio is around 14.7.
It simultaneously purifies the three harmful components most efficiently, and when the air-fuel ratio becomes richer than 14.7, the purification rate of nitrogen oxides improves, and when it becomes lean, the purification rate of hydrocarbons and carbon monoxide improves.

By the way, changes in the purification rate of these harmful components are
The proportion of oxygen in the exhaust gas is closely related.
That is, if oxygen is contained in the exhaust gas in excess of a certain value, the oxidation reaction will proceed, but the reduction reaction will be difficult to proceed, and if the amount of oxygen is low, the reduction reaction will be advantageous, but the oxidation reaction will not proceed. The ratio of these four components is most appropriate and the three harmful components can be purified most effectively at an air-fuel ratio of approximately 14.7.

However, the generation of harmful components in exhaust gas also differs depending on the operating conditions. For example, when the load is low, the concentration of nitrogen oxides is low, and the concentration of hydrocarbons and carbon monoxide is high; on the other hand, when the load is high, the concentration of nitrogen oxides is high. The concentration of hydrocarbons and carbon monoxide is decreasing.

Therefore, it is necessary to adopt a configuration that utilizes the characteristics of the three-way catalyst described above in accordance with the proportions of oxygen, hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas, which change with changes in operating conditions.

By the way, Japanese Patent Application Laid-open No. 1983-42220, which is an example of prior art for an exhaust gas purification device that takes into consideration the role of oxygen in purifying exhaust gas, discloses a method in which a gap is formed between the inner surface and the center of the sealed outer housing. A catalyst bed for reducing nitrogen oxides from the exhaust gas introduced from one end is provided at the same time, and a catalyst bed for oxidizing carbon monoxide and hydrocarbons is formed in the above-mentioned gap on the outer periphery via an air layer or a casing. , communicated at the other end of the reduction catalyst bed, and into the exhaust gas that reverses from this communication part and flows in the opposite direction to the above-mentioned oxidation catalyst bed, 2 is dispersed by colliding with a shielding plate facing the above-mentioned communication part.
An exhaust gas purification device is disclosed in which secondary air is introduced.

In addition, Japanese Patent Application Laid-open No. 114379/1983, which is an example of prior art, discloses an exhaust system in which a first catalyst bed and a second catalyst bed made of a three-way catalyst are arranged in a straight line while coating an exhaust pipe. A gas purification device is described.

[Problem that the invention seeks to solve]

By the way, in the above-described exhaust gas purification device, the introduction of secondary air into the oxidation catalyst bed is performed by a pump, so the amount of the introduced air changes as described above with changes in the operating state of the engine. It is difficult to adapt to the generation rate of carbon monoxide and hydrocarbons in the gas, and if a pump is used, the structure is complicated and it is a sterile agent, and the exhaust gas is purified inside the external housing. Since the flow is reversed and flows in the opposite direction, there are problems such as large resistance.

The object of the present invention is to provide an exhaust gas purification device that eliminates these problems.

[Means for solving problems]

In order to achieve the above object, the present invention has the following configuration. That is, a first catalyst bed and a second catalyst bed made of a three-way catalyst are provided in the middle of the exhaust pipe so as to be positioned in a straight line with a mixing section in between, and an inner cylinder is provided in the exhaust passage to the first catalyst bed. The exhaust passage is concentrically divided, and the outer passage that guides the exhaust gas to the outer catalyst part is divided into two parts by the exhaust pulsation in the exhaust pipe.
A device for introducing secondary air is installed to form an oxidizing atmosphere, carbon monoxide and hydrocarbons are oxidized in the outer catalyst section, nitrogen oxides are reduced in the center, and the mixed exhaust gas is Oxidation with 2 catalyst beds,
It is designed to provide a return.

The amount of secondary air introduced is determined to create an atmosphere for efficiently performing oxidation and reduction in the second catalyst bed.

[Effect]

The present invention provides a first catalyst bed and a second catalyst bed made of a three-way catalyst in the middle of an exhaust pipe so as to be positioned on a straight line with a mixing part sandwiched between them, and an inner cylinder is connected to an exhaust passage to the first catalyst bed. A device is installed to introduce secondary air into the outer passage that guides exhaust gas to the outer catalyst section using exhaust pulsation in the exhaust pipe to form an oxidizing atmosphere. It is configured to oxidize carbon monoxide and hydrocarbons, and reduce nitrogen oxides in the center.

Therefore, the exhaust gas flowing in the exhaust pipe is divided into the outer catalytic part and the central catalytic part of the first catalyst bed, which is composed of a three-way catalyst. During low load, secondary air is introduced into the outer catalyst section by exhaust pulsation, creating an oxidizing atmosphere that mainly performs oxidation, oxidizing carbon monoxide and hydrocarbons. Since the temperature is maintained at a high temperature due to the heat of reaction and no secondary air is introduced,
The atmosphere becomes a reducing atmosphere that mainly carries out reduction, and nitrogen oxides are reduced.

Exhaust gas flowing out from the outer catalyst section and the center catalyst section of the first catalyst bed is mixed in the mixing section and flows into the second catalyst bed composed of a three-way catalyst, so that the amount of oxygen in the exhaust gas is adjusted to match the amount of oxygen in the exhaust gas. Oxidation and reduction are carried out respectively,
The three components of carbon monoxide, hydrocarbons and nitrogen oxides are purified.

On the other hand, under high loads, high concentrations of nitrogen oxides,
Exhaust gas consisting of carbon monoxide and hydrocarbons with a low concentration flows into a first catalyst bed composed of a trimorphic catalyst. Even though the exhaust pulsation effect is lowered and the intake rate of secondary air is reduced, an appropriate amount of secondary air is introduced, and a high concentration is generated at the center catalyst without reducing the oxidation reaction at the outer catalyst. Reduces nitrogen oxides. The three components in the exhaust gas that have flowed into the second catalyst bed via the mixing section are oxidized and reduced again to achieve purification.

Moreover, since the first catalyst bed, the mixing section, and the second catalyst bed are arranged in a straight line, there is little resistance to the exhaust gas, and the power loss of the engine is small.

According to the present invention, secondary air is introduced by exhaust pulsation, and the suction rate of secondary air changes depending on the engine operating condition, so three-component purification by the three-way catalyst is effectively performed. Therefore, there is little possibility that nitrogen oxides will combine with atmospheric moisture to produce harmful nitric acid. Further, since the secondary air introduction device does not require a pump, the structure is simplified.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. In the figure, reference numeral 1 denotes an exhaust pipe, and an expanded part 4 connected by tapered parts 2 and 3 is provided in the middle of the exhaust pipe. An inner cylinder 5 having a concentric and similar shape is supported by radial stays 6 and 7 inside the cylinder. Inside the expansion section 4, a first catalyst bed 8 and a second catalyst bed 9 made of a three-way catalyst are provided so as to be located on a straight line, and a mixing section 10 is provided in the middle thereof.
is formed. Note that the first catalyst bed 8 preferably has, for example, a honeycomb structure in which gases do not mix with each other in the radial direction.

Further, an annular chamber 11 is formed around the outer circumference of the end of the exhaust pipe 1a, and a large number of secondary air inlets 12 are provided in the exhaust pipe 1a.
The annular chamber 11 passes through a pipe 13 and communicates with the atmosphere via a check valve 14 and an air cleaner 16, and the exhaust pulsation in the exhaust pipe directs secondary air into the passage 15 between the exhaust pipe and the inner cylinder 5. We are planning to introduce it to

The exhaust gas flowing through the exhaust pipe is passed through a passage 1 between the exhaust pipe and the inner cylinder 5 before entering the catalytic converter.
There are two types: one that passes through the inner cylinder 5 and one that passes through the inner cylinder 5.

When the load is low, the pulsating effect of the exhaust gas passing through the passage 15 causes secondary air to pulsate through the check valve 14, pipe 13, etc.
2 and mixed well, the first catalyst bed 8
Here, carbon monoxide and hydrocarbons in the exhaust gas are oxidized by the oxygen in the secondary air, and nitrogen oxides are also reduced to some extent. The excess oxygen then flows into the downstream mixing section 10 along with oxides and other components. On the other hand, the inner cylinder 5
The exhaust gas flowing through the interior flows into the center 8b of the first catalyst bed 8 and is not supplied with secondary air, so that nitrogen oxides are reduced by carbon monoxide and hydrocarbons, and carbon monoxide is , hydrocarbons are also oxidized to some extent. The excess carbon monoxide and hydrocarbons then flow into the mixing section 10.

That is, in the first catalyst bed 8, the outer circumferential portion 8a becomes an oxidizing atmosphere that mainly performs oxidation, and the central portion 8b becomes a reducing atmosphere that mainly performs reduction, so that all three components in the exhaust gas can be reduced. At this time, the center portion 8b can be maintained at a high temperature due to the heat of oxidation reaction in the outer peripheral portion 8a, so that the reactivity of the catalyst in the center portion 8b can be increased.

Then, from the outer peripheral part 8a and the center part 8b, the mixing part 1
The exhaust gases that have flowed into the exhaust gas are mixed in the mixing section 10 and flow further downstream into the second catalyst bed 9 that is comprised of a three-way catalyst. Here, oxidation and reduction are carried out, and depending on the amount of oxygen present, either oxidation or reduction is carried out primarily, and the three components of carbon monoxide, hydrocarbons, or nitrogen oxides are purified, respectively. And a first catalyst bed 8 composed of a three-way catalyst
Since the exhaust gas and the second catalyst bed 9 react each of the three components in stages when the exhaust gas passes through, a sufficient purification effect can be achieved.

Therefore, as described above, each component in the exhaust gas flowing into the catalyst device changes depending on the operating state of the engine. That is, at low loads, the concentrations of hydrocarbons and carbon monoxide are high, and the concentrations of nitrogen oxides are low. However, at low loads, the exhaust pulsation effect in the exhaust pipe becomes large.
The intake rate of secondary air (secondary air amount/intake air amount) increases, and therefore, it is possible to sufficiently oxidize hydrocarbons and carbon monoxide generated in high concentrations in exhaust gas, and furthermore, the excess oxygen The hydrocarbons and carbon monoxide that have not been oxidized can be mixed as a mixture and further oxidized in the second catalyst bed 9 in an atmosphere with good purification efficiency of the three-way catalyst.

On the other hand, under high load, the exhaust gas has a high concentration of nitrogen oxides and a low concentration of hydrocarbons and carbon monoxide, but the exhaust pulsation effect also decreases and the intake rate of secondary air decreases, causing carbonization. Even if oxygen reaches the outer circumference 8a of the first catalyst bed 8, highly concentrated nitrogen oxides can be sufficiently reduced in the outer circumference 8a without reducing the reduction reaction. At the same time, low concentrations of hydrocarbons and carbon monoxide are oxidized. Further, reduction and oxidation are also performed in the central portion 8b. Furthermore, the hydrocarbons, carbon monoxide, and nitrogen oxides that have not been reduced yet in the first catalyst bed are mixed in the mixing section 10, and are mixed again in the second catalyst bed 9 in an atmosphere with good purification efficiency of the three-way catalyst. It can be purified by performing oxidation and reduction reactions.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, secondary air is transferred to the exhaust gas in the exhaust pipe to the outer catalytic portion of the first catalyst bed consisting of the three-way catalyst on the upstream side depending on the operating state of the engine. Since the air is introduced in a pulsating manner due to the pulsation effect, there is no need for a pump to introduce secondary air, which simplifies the structure and mixes well with the exhaust gas, reducing carbon monoxide and carbonization in the exhaust gas. Since hydrogen is effectively removed by the catalyst in the outer periphery, and nitrogen oxides are reduced in the center where secondary air is not introduced, all three components can be reduced together, and the reduction reaction in the center can be reduced. This is further promoted by the reaction heat of the oxidation reaction zone on the outer periphery, and secondary effects occur depending on the concentration of hydrocarbons and carbon monoxide in the exhaust gas caused by changes in operating conditions, as well as the concentration of nitrogen oxides. Since the air supply rate also increases or decreases, these three harmful components in the exhaust gas can be effectively purified in conjunction with the three-way catalyst.

Moreover, excess hydrocarbons, carbon monoxide, and nitrogen oxides in the first catalyst bed are oxidized and reduced again in the second catalyst bed, so purification of exhaust gas is further promoted, and nitrogen oxide There is less risk that the substance will combine with moisture in the atmosphere and produce harmful nitric acid. The exhaust gas is purified while flowing through the first catalyst bed and the second catalyst bed, which are located in a straight line, without making any bends such as flowing backwards, so the resistance experienced during this time and the power loss of the engine are small. It is possible to achieve the intended purpose.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG.
The figure is a sectional view taken along the line AA in FIG. 1, and FIG. 3 is a graph showing the relationship between the harmful component purification rate and the air-fuel ratio. 1... Exhaust pipe, 2, 3... Tapered part, 4... Expansion part,
5... Inner cylinder, 6, 7... Stay, 8... First catalyst bed, 9
...Second catalyst bed, 10...Mixing section, 11...Recirculation chamber, 1
2... Secondary air inlet, 13... Pipe, 14... Check valve, 15... Passage, 16... Air cleaner.

Claims (1)

[Claims] 1. During the coating of the exhaust pipe, a first catalyst bed and a second catalyst bed made of a three-way catalyst are provided so as to be located in a straight line with a mixing part sandwiched between them, and an inner cylinder is provided in the exhaust passage to the first catalyst bed. The exhaust passage is concentrically divided, and a device is installed that introduces secondary air by exhaust pulsation in the exhaust pipe into the outer passage that guides exhaust gas to the outer catalyst part to form an oxidizing atmosphere. Oxidizes carbon and hydrocarbons, reduces nitrogen oxides in the center,
Furthermore, the exhaust gas purification device for an internal combustion engine is characterized in that the exhaust gas mixed in the mixing section is oxidized and reduced in a second catalyst bed.