JP3402132B2 - Engine exhaust purification device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an engine exhaust gas purification apparatus provided with an adsorbent that adsorbs HC (hydrocarbon) contained in exhaust gas.

[0002]

2. Description of the Related Art In an exhaust emission control device provided in an automobile engine or the like, a catalytic converter carrying a catalytic metal such as platinum or rhodium is installed in an exhaust passage to oxidize HC and CO in exhaust gas, NOx is reduced. However, in the catalyst inactive region where the catalyst temperature is lower than the predetermined value, the catalyst hardly purifies HC and the like in the exhaust gas.

For this reason, there is a system in which an adsorbent for adsorbing HC and the like is installed in the exhaust passage. The adsorbent made of zeolite or the like has a characteristic that it adsorbs HC and the like at a low temperature, and the amount of adsorbed HC and the like is desorbed as the temperature rises.

Conventionally, as an exhaust emission control device for a diesel engine, there is one as shown in FIG.
No. 5, gazette).

To explain this, a heat exchanger 92 is installed in the exhaust passage 91 of the engine 90.
The catalytic converter 96 is installed in the second low temperature side passage. The adsorbent 94 is installed downstream of the high temperature side flow path of the heat exchanger 92 and upstream of the catalytic converter 96. This allows
The temperature rise of the catalytic converter 96 due to the heat of the exhaust gas is promoted via the heat exchanger 92, and the temperature rise of the adsorbent 94 is suppressed.

The unburned HC and the like are adsorbed by the adsorbent 94 for a while after the cold start of the engine. Eventually adsorbent 94
When HC and the like are desorbed from the adsorbent 94 as the temperature of the HC rises, the temperature of the catalytic converter 96 also rises via the heat exchanger 92, so the HC and the like oxidize via the catalytic converter 96. Is prompted.

The adsorbent 94 is connected to the high temperature side passage and the low temperature side passage of the heat exchanger 92 via exhaust pipes 93 and 95.

[0008]

However, in such a conventional exhaust emission control device, the heat exchanger 92 is provided in the middle of the exhaust passage 91, and the exhaust gas passing through the heat exchanger 92 is adsorbed. Since the structure is provided with the exhaust pipes 93, 95, etc. leading to 94, the size of the device is increased.

Further, since the heat capacity of the heat exchanger 92 is large, it takes time for the catalytic converter 96 to rise above the catalyst activation temperature after the cold start of the engine, during which time the adsorbent 94 and HC, etc. In order to prevent desorption, it is necessary to increase the capacity of the adsorbent 94, which leads to an increase in size of the device.

The present invention has been made in view of the above problems, and it is an object of the present invention to reduce the size of an exhaust gas purifying apparatus for an engine provided with an adsorbent that adsorbs unburned HC and the like.

[0011]

According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an engine, an exhaust passage for exhausting the exhaust gas of the engine, first and second catalytic converters for promoting oxidation of HC and the like in the exhaust gas, and exhaust gas in the exhaust gas. An adsorbent for adsorbing HC and the like and a metal catalyst container provided in the middle of the exhaust passage are provided, and the adsorbent is installed on the downstream side of the first catalytic converter in the catalyst container for adsorption in the catalyst container. A second catalytic converter is installed on the downstream side of the agent, a space is defined between the first and second catalytic converters and the adsorbent, and each carrier of the first and second catalytic converters is formed of metal to form a catalyst container. On the other hand, each carrier of the first and second catalytic converters is supported by metal contact, and a heat insulating material is interposed between the catalyst container and the adsorbent.

[0013] exhaust gas purifying device for an engine according to claim 2 is the invention according to claim 1, the carrier of said adsorbent
Is made of ceramic.

[0014] exhaust gas purifying device for an engine according to claim 3 is the invention according to claim 1 or 2, wherein the insulation
The material was made of ceramic wool.

According to a fourth aspect of the present invention, there is provided an engine exhaust gas purification device according to any one of the first to third aspects, further comprising a heat insulating layer for suppressing heat radiation from the catalyst container to the outside air.
I was prepared.

According to a fifth aspect of the present invention, in the exhaust gas purification device for an engine according to any one of the first to fourth aspects, the catalyst carrying amount of the first catalytic converter is set to the second catalytic coke.
It is set to be larger than the catalyst loading amount of the inverter.

[0017]

[0018]

[0019]

[0020]

[0021]

In the exhaust gas purifying apparatus for an engine according to claim 1 , when the engine is warmed up, the first catalytic converter located on the most upstream side as exhaust gas temperature rises Absorbs heat and unburned H
The heat of oxidation reaction such as C is absorbed, and the temperature rises before the adsorbent and the second catalytic converter.

Until the first catalytic converter reaches the catalyst activation temperature, unburned HC and the like contained in the exhaust gas pass through the first catalytic converter and are adsorbed by the adsorbent and HC and the like in the catalyst inactive region. Can be prevented from being discharged to the outside.

In the process in which the temperature of the first catalytic converter rises in this way, the heat of the first catalytic converter is transferred to the second catalytic converter via the catalyst container in metal contact, and the temperature rise of the second catalytic converter is promoted.

Since the heat capacity of the catalyst container is smaller than that of the heat exchanger of the conventional device, the time required for the temperatures of the first and second catalytic converters to rise can be shortened and the capacity of the adsorbent can be reduced.

On the other hand, due to the structure in which a heat insulating material having a low thermal conductivity is interposed between the catalyst container and the adsorbent, the heat of the first catalytic converter is difficult to be transferred to the adsorbent through the catalyst container.

As described above, when the engine is warmed up, the amount of heat transferred from the first catalytic converter to the second catalytic converter is larger than the amount of heat transferred to the adsorbent. The desorption of HC and the like from the agent is delayed and the activation of the catalyst of the second catalytic converter is promoted.

HC and the like that are desorbed from the adsorbent as the temperature of the adsorbent rises are led to the second catalytic converter. When the HC desorbed from the adsorbent reaches the second catalytic converter, the catalyst of the second catalytic converter whose temperature has risen before the adsorbent has already been activated, so that the HC desorbed from the adsorbent becomes In the process of passing through the two-catalyst converter, oxidation is promoted via the catalyst, and HC and the like can be suppressed from being discharged to the outside through the second catalytic converter without being oxidized.

Due to the structure in which the first catalytic converter, the adsorbent, and the second catalytic converter are arranged side by side inside the catalyst container, a structure having a heat exchanger and its associated exhaust pipe, etc. is provided as in the conventional device. In comparison, the device can be made compact.

In the engine exhaust gas purification device according to the second aspect , by forming the carrier of the adsorbent from ceramics, the heat retention effect of the adsorbent is enhanced, and the temperature rise of the adsorbent can be delayed more than that of the second catalytic converter. This makes it possible to activate the catalyst of the second catalytic converter in the meantime, and to prevent HC and the like from being discharged to the outside through the second catalytic converter without being oxidized.

In the engine exhaust emission control device according to the third aspect of the present invention, the heat insulation material is formed of fibrous ceramic wool so that the catalyst container and the adsorbent are thermally insulated and the exhaust gas is adsorbed to the catalyst container. Seal between the agents. Also, the impact of the heat insulating material transmitted from the catalyst container to the adsorbent can be mitigated, and the durability of the adsorbent and the like can be secured.

In the engine exhaust gas purification device according to the fourth aspect , since the heat insulating layer for suppressing heat radiation from the catalyst container to the outside air is provided, heat radiation from the catalyst container to the outside is suppressed,
The amount of heat transferred from the catalyst container to the second catalytic converter is increased. Therefore, the catalyst of the second catalytic converter is activated early, and it is possible to prevent HC and the like from being discharged to the outside through the second catalytic converter without being oxidized.

In the exhaust gas purifying apparatus for an engine according to claim 5 , since the catalyst carrying amount of the first catalytic converter is made larger than the catalyst carrying amount of the second catalytic converter, the temperature rise of the first catalytic converter can be accelerated. The temperature rise of the second catalytic converter with respect to the adsorbent can be accelerated through the catalyst container and the like. As a result, it is possible to prevent HC and the like from being discharged to the outside through the second catalytic converter without being oxidized.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the exhaust gas purification device 2 includes a catalyst container 6 installed in the middle of an exhaust passage, a first catalytic converter 11 accommodated in the catalyst container 6, an adsorbent 10, and a first catalyst converter 11. A two-catalyst converter 12 is provided. First catalytic converter 1
1, the adsorbent 10, the second catalytic converter 12 is a catalyst container 6
Are arranged in series. That is, the first catalytic converter 11 is arranged on the most upstream side of the catalyst container 6, and the adsorbent 10 is arranged on the downstream side of the first catalytic converter 11.
The second catalytic converter 12 is arranged on the downstream side of 0.

A space (exhaust passage) 18 is defined between the first catalytic converter 11 and the adsorbent 10, and a space (exhaust passage) 19 is defined between the adsorbent 10 and the second catalytic converter 12. It

The catalyst container 6 is formed in a cylindrical shape from a metal plate having a predetermined thermal conductivity as described later. The inlet 7 of the catalyst container 6 communicates with the exhaust port of the engine through an exhaust pipe (not shown) connected to the inlet 7 so that the exhaust gas discharged from the engine is introduced into the catalyst container 6 as shown by the arrow in the figure. Has become. The outlet 9 of the catalyst container 6 communicates with the outside through a muffler and an exhaust pipe (not shown) connected to the outlet 9, and exhaust gas is exhausted from the inside of the catalyst container 6 as shown by an arrow in the figure.

The first and second catalytic converters 11 and 12 are
Each carrier is a so-called metal catalyst that is formed by alternately stacking and winding corrugated metal thin plates and flat metal thin plates, and has a large number of honeycomb-shaped passages (narrow paths) in the exhaust flow direction. ), The three-way catalyst carried in each passage oxidizes HC and CO in the exhaust gas passing therethrough and reduces NOx. A noble metal such as platinum or rhodium is used as the catalyst.

FIG. 2 is a characteristic diagram showing the relationship between the temperature of the catalyst and the conversion rate for purifying HC and the like by the catalyst. As shown in the figure, when the temperature is lower than the predetermined activation temperature, the H
Almost no purification of C and the like is performed, and as the temperature rises above a certain value, the conversion rate for purifying HC and the like by the catalyst sharply increases. Here, the temperature at which the conversion rate of HC and the like starts to rise sharply due to the catalyst is defined as the catalyst activation temperature.

The carrier of the adsorbent 10 is made of ceramic and has a large number of passages (narrow passages) in the exhaust flow direction.
Zeolite or the like is carried in each passage, and unburned HC or the like in the exhaust gas passing therethrough is adsorbed.

FIG. 3 shows the temperature of the adsorbent 10, the amount of HC adsorbed on the adsorbent 10, and the amount of H desorbed from the adsorbent 10.
It is a characteristic view which shows the relationship of the desorption amount of C etc. As shown in this figure, the adsorbent 10 adsorbs HC and the like in a state where the temperature is low, and as the temperature rises above a certain value, the amount of adsorbed HC and the like desorbs sharply increases. Here, the temperature at which the amount of HC and the like desorbed from the adsorbent 10 starts to increase rapidly is defined as the desorption temperature.

The first and second catalytic converters 11 and 12 are supported in metallic contact with the catalyst container 6. That is,
The outer circumferences of the first and second catalytic converters 11 and 12 are joined to the inner circumferential surface of the catalyst container 6 and fixed by brazing or the like.

The adsorbent 10 is housed in the catalyst container 6 via a cylindrical heat insulating material 16. As the heat insulating material 16, fibrous ceramic wool or the like is used, and the catalyst container 6 and the adsorbent 1 are used.
Insulation is performed between 0 and the exhaust gas seals between the catalyst container 6 and the adsorbent 10. In addition, since the heat insulating material 16 reduces the impact transmitted from the catalyst container 6 to the adsorbent 10,
The durability of the adsorbent 10 made of a brittle material such as ceramic can be ensured.

A heat insulating layer 17 is provided around the catalyst container 6. An outer shell 5 is provided around the catalyst container 6, and a heat insulating layer 17 is defined as a space between the catalyst container 6 and the outer shell 5 to suppress heat radiation from the catalyst container 6 to the outside. There is.

FIG. 4 shows the characteristics that the temperatures of the first catalytic converter 11, the second catalytic converter 12 and the adsorbent 10 rise after the cold start of the engine. As will be described later, these heating rates are determined by the first catalytic converter 11,
The second catalytic converter 12 and the adsorbent 10 are higher in this order. Then, the thermal conductivity of the catalyst container 6 is set so that the time when the second catalytic converter 12 rises above the catalyst activation temperature rises earlier than the time when the adsorbent 10 rises above the desorption temperature. The heat capacity and the like of the catalytic converter 11, the second catalytic converter 12, the adsorbent 10 are set.

The operation of the present invention constructed as above will be described below.

After the cold start of the engine, the first catalytic converter 11 located on the most upstream side absorbs the heat of the exhaust gas as the exhaust gas temperature rises, and the unburned HC
The temperature of the adsorbent 10 and the second catalytic converter 12 rises before the heat of the oxidation reaction such as.

Until the first catalytic converter 11 reaches the catalyst activation temperature, unburned HC contained in the exhaust gas
And the like pass through the first catalytic converter 11 and are adsorbed by the adsorbent 10 to prevent HC and the like from being discharged to the outside in the catalyst inactive region.

In the process in which the temperature of the first catalytic converter 11 rises in this way, the heat of the first catalytic converter 11 is transmitted to the second catalytic converter 12 via the catalyst container 6 in metal contact, and the temperature of the second catalytic converter 12 rises. Is prompted.

The heat capacity of the cylindrical catalyst container 6 is smaller than that of the heat exchanger of the conventional device, so that the time required for the temperatures of the first and second catalytic converters 11 and 12 to rise is shortened, and the adsorbent is reduced. The capacity of can be reduced.

Further, by providing the heat insulating layer 17 surrounding the catalyst container 6, the heat radiation from the catalyst container 6 to the outside is suppressed, and the amount of heat transferred from the catalyst container 6 to the second catalytic converter 12 is increased.

On the other hand, due to the structure in which the heat insulating material 16 having a low thermal conductivity is interposed between the catalyst container 6 and the adsorbent 10, the heat of the first catalytic converter 11 is transferred to the adsorbent 10 via the catalyst container 6. It is hard to convey.

Further, since the carrier of the adsorbent 10 is made of ceramic having a low thermal conductivity, the heat retaining effect of the adsorbent 10 is enhanced and the temperature rise of the adsorbent 10 is delayed.

The carrier of the adsorbent 10 may be made of metal, and in this case as well, a heat insulating material 16 having a low thermal conductivity is interposed between the catalyst container 6 and the adsorbent 10 so that the adsorbent is It is possible to delay the temperature rise of 10 more than the second catalytic converter 12.

As described above, when the engine is warmed up, the amount of heat transferred from the first catalytic converter 11 to the second catalytic converter 12 is larger than the amount of heat transferred to the adsorbent 10, so that the second catalytic converter 12 precedes the adsorbent 10. The temperature rises and delays the desorption of HC and the like from the adsorbent 10, and
Activation of the catalyst of the second catalytic converter 12 is promoted.

HC and the like that are desorbed from the adsorbent 10 as the temperature of the adsorbent 10 rises are guided to the second catalytic converter 12. When HC and the like desorbed from the adsorbent 10 reach the second catalytic converter 12, the catalyst of the second catalytic converter 12 whose temperature has risen earlier than that of the adsorbent 10 has already been activated, and therefore desorbed from the adsorbent 10. The HC and the like are promoted to be oxidized through the catalyst in the process of passing through the second catalytic converter 12, and the HC and the like can be prevented from being discharged to the outside through the second catalytic converter 12 without being oxidized.

Furthermore, the adsorbent 10 is set so that the time when the second catalytic converter 12 rises above the catalyst activation temperature rises earlier than the time when the adsorbent 10 rises above the desorption temperature. The HC and the like desorbed from the catalyst are promoted to be oxidized through the catalyst of the second catalytic converter 12 that has been sufficiently activated, and purification treatment is performed.

The first catalytic converter 1 is provided inside the catalyst container 6.
1. The structure in which the adsorbent 10 and the second catalytic converter 12 are arranged side by side enables the device to be made compact as compared with the structure including the heat exchanger and the exhaust pipe related thereto as in the conventional device. .

As another embodiment, the catalyst carrying amount of the first catalytic converter 11 may be made larger than the catalyst carrying amount of the second catalytic converter 12 at a predetermined ratio.

In this case, activation of the catalyst is promoted by increasing the amount of catalyst supported by the first catalytic converter 11.
Therefore, as shown by the broken line in FIG. 4, the temperature increase of the first catalytic converter 11 can be accelerated and the temperature increase of the second catalytic converter 12 can be accelerated via the catalyst container 6. As a result, the HC and the like desorbed from the adsorbent 10 are promoted to oxidize via the catalyst of the fully activated second catalytic converter 12, and the HC and the like are discharged to the outside through the second catalytic converter 12. Can be effectively suppressed. Further, the temperature rise of the second catalytic converter 12 can be accelerated without increasing the amount of the catalyst (noble metal) carried by the second catalytic converter 12, and the production cost can be suppressed.

The carrier of the adsorbent 10 is not limited to ceramic, but may be formed of metal. Also in this case, the temperature rise of the adsorbent 10 can be delayed more than that of the second catalytic converter 12 by interposing the heat insulating material 16 having a low thermal conductivity between the catalyst container 6 and the adsorbent 10.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an exhaust emission control device showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a catalyst temperature and a conversion rate for purifying HC and the like.

FIG. 3 is a characteristic diagram showing the relationship between the temperature of the adsorbent, the adsorption amount of HC and the like, and the desorption amount of HC and the like desorbed from the adsorbent.

FIG. 4 is a characteristic diagram showing how the temperatures of the first catalytic converter, the second catalytic converter, and the adsorbent respectively rise after cold starting of the engine.

FIG. 5 is a system diagram of an exhaust system showing a conventional example.

[Explanation of symbols]

2 Exhaust gas purification device 6 catalyst container 10 Adsorbent 11 First catalytic converter 12 Second catalytic converter 16 Insulation 17 Thermal insulation layer 18 spaces 19 space

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-8-238420 (JP, A) JP-A-7-42539 (JP, A) JP-A-5-263634 (JP, A) JP-A-64- 7935 (JP, A) Actual Kaihei 2-85815 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/24-3/28 B01D 53/86

Claims (5)

(57) [Claims] 1. An exhaust passage for exhausting engine exhaust gas.
And the first and second catalytic converters that promote the oxidation of HC etc. in the exhaust gas.
Bei and chromatography data, and adsorbent for adsorbing the HC etc. in the exhaust gas, and a metal catalyst container interposed in the middle of the exhaust passage
The adsorbent on the downstream side of the first catalytic converter in the catalyst container.
Install a second catalytic converter downstream from the adsorbent in the catalyst container.
Installed to define a space between the first and second catalytic converter and the adsorbent
And each carrier of the first and second catalytic converter is made of metal
Then, place each carrier of the first and second catalytic converters in the catalyst container.
An engine exhaust purification system characterized in that it is supported by metal contact and a heat insulating material is interposed between the catalyst container and the adsorbent . 2. The adsorbent carrier is formed of ceramics.
The exhaust emission control device for an engine according to claim 1, wherein 3. The heat insulating material is formed of ceramic wool
The exhaust emission control device for an engine according to claim 1 or 2 , wherein the exhaust purification device is an engine. 4. The heat dissipation from the catalyst container to the outside air is suppressed.
4. The heat insulating layer according to claim 1, wherein the heat insulating layer is provided.
The engine exhaust gas purification device described in one of them . 5. The catalyst loading amount of the first catalytic converter is set to
Characterized by making it more than the amount of catalyst supported in the two-catalyst converter
The exhaust emission control device for an engine according to any one of claims 1 to 4 .