JPH05272334A - Engine exhaust device - Google Patents

Abstract

PURPOSE:To protect an NOx purifying catalyst from high temperature exhaust gas flowed into a confluent part from the second exhaust passage in an engine exhaust device provided with the first exhaust passage having the NOx purifying catalyst and the second exhaust passage having a three-way catalyst. CONSTITUTION:A contraflow preventive member 8, which allows flow of exhaust gas flowed in the first exhaust passage 3 and prevents the exhaust gas flowed into from the second exhaust passage 6 from flowing backward upstream of the first exhaust passage 3, is provided in a confluent part between the first exhaust passage 3 and the second exhaust passage 6. Instead of the contraflow preventive member 8, a three-way catalyst is provided to intercept thermally both the passages provided between the NOx purifying catalyst 2 in the first exhaust passage 3 and the confluent part 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system for an engine, and more particularly to a first exhaust passage provided with a NOx purification catalyst and a second exhaust passage branched from the first exhaust passage and provided with a three-way catalyst. And an exhaust passage of the engine.

[0002]

2. Description of the Related Art Exhaust gas from an automobile is released into the atmosphere after CO, HC and NOx contained in the exhaust gas are purified by an exhaust gas purifying catalyst. In this case, the temperature of exhaust gas and CO,
A NOx purification catalyst and a three-way catalyst having purification characteristics corresponding to the content ratios of HC and NOx, etc. are used separately or used together.

The three-way catalyst is NO when the oxygen concentration is high.
It is known that the x purification function is low, and that the NOx purification catalyst has low resistance to heat.

Therefore, when the engine has a high oxygen concentration and a large amount of NOx in the exhaust gas, such as when the engine is operated in a lean burn mode in which the oxygen content is higher than the stoichiometric air-fuel ratio, the exhaust gas is purified with NOx. While passing through the catalyst for exhaust gas, the three-way catalyst is passed when oxygen in the exhaust gas is not rich and the temperature of the exhaust gas is high, as when the engine is operating near the stoichiometric air-fuel ratio. ..

In this way, the NO
As described in Japanese Patent Laid-Open No. 1-171625, it is possible to selectively use a purification catalyst and a three-way catalyst, and the exhaust gas temperature is detected based on the detected temperature of the exhaust gas of the engine. When the temperature is low, exhaust gas is NOx
There is known a technique for purifying exhaust gas, which is introduced into a copper-zeolite catalyst having a large purification function and is introduced into a three-way catalyst when the exhaust gas temperature is high.

Further, as shown in FIG. 8, a NOx purifying catalyst c and a three-way catalyst d are sequentially arranged from an upstream side to a downstream side in a first exhaust passage b provided so as to be connected to an exhaust portion of an engine a. The first exhaust passage b is provided in a branch portion from the vicinity of the engine of the first exhaust passage b, and at the merging portion e on the downstream side of the NOx purification catalyst c and on the upstream side of the three-way catalyst d.
A second exhaust passage f is provided so as to join the
A three-way catalyst h is provided in the exhaust passage f of the exhaust gas, and the flow path of the exhaust gas is from the first exhaust passage b to the second exhaust passage f.
By switching the valve g provided in the part where
There is known an exhaust gas purification device in which the first exhaust passage b or the second exhaust passage f is selected as described below. That is, when the exhaust gas has a low temperature and a high oxygen concentration, the NOx purifying catalyst c purifies NOx after passing through the first exhaust passage b, and then the three-way catalyst d purifies CO and HC, Second when the gas is hot
Of the three-way catalyst h provided in the second exhaust passage f by flowing through the exhaust passage f of the NOx purifying catalyst c and flowing into the first exhaust passage b from the merging portion e on the downstream side of the NOx purification catalyst c. CO is generated by the three-way catalyst d provided in the first exhaust passage b.
And HC and NOx are purified.

[0007]

However, if exhaust gas is to be purified by the purification technique described in Japanese Patent Laid-Open No. 1-171625, the exhaust gas will be ternary when the exhaust gas is at a high temperature. Since the copper-zeolite catalyst is not introduced into the catalyst and is not introduced into the catalyst, the copper-zeolite catalyst having low heat resistance can be protected from heat and deterioration can be prevented, while exhaust gas is exhausted when the temperature is low. Since the gas is introduced into the copper-zeolite catalyst and not into the three-way catalyst, there is a problem that NOx in the exhaust gas is sufficiently purified but HC and CO are not sufficiently purified.

Further, in the conventional exhaust gas purifying apparatus shown in FIG. 8, when the exhaust gas is at a high temperature, it flows through the second exhaust passage and at the confluence of the first exhaust passage and the second exhaust passage. The exhaust gas that has flowed into the first exhaust passage causes a difference in gas pressure between the upstream side and the downstream side of the merging portion in the first exhaust passage, so that the high-temperature exhaust gas merges into the merging portion. It is inevitable that a partial reverse flow from the portion to the upstream side of the first exhaust passage will occur. As a result, there is a problem that the NOx purification catalyst provided in the first exhaust passage on the upstream side of the merging portion is deteriorated by the heat of the high-temperature exhaust gas.

In view of the above, according to the present invention, the high temperature exhaust gas flowing through the second exhaust passage flowing into the confluence portion of the first exhaust passage and the second exhaust passage is provided upstream of the confluence portion. It is an object of the present invention to protect the NOx purification catalyst from the influence of the heat of the high-temperature exhaust gas by preventing the NOx purification catalyst provided in the first exhaust passage from reaching the NOx purification catalyst.

[0010]

In order to achieve the above-mentioned object, the invention of claim 1 provides a first exhaust passage and a second exhaust passage.
The exhaust gas flowing through the second exhaust passage and flowing into the first exhaust passage at the merging portion with the exhaust passage is prevented from flowing backward to the first exhaust passage on the upstream side of the merging portion. is there.

Specifically, the means for solving the problems of the first aspect of the invention is to provide a first exhaust passage through which exhaust gas flows, a NOx purification catalyst provided in the first exhaust passage, and the first exhaust passage. A second exhaust passage that branches from the upstream side of the NOx purification catalyst in the exhaust passage of the NOx and that joins on the downstream side of the NOx purification catalyst and through which the exhaust gas flows, and the three exhaust passages provided in the second exhaust passage. On the premise of an engine exhaust system including an original catalyst, the exhaust gas flowing through the second exhaust passage is at the confluence of the first exhaust passage and the second exhaust passage. A backflow prevention member for preventing backflow is provided on the upstream side of the passage.

According to the second aspect of the present invention, the exhaust gas flowing through the first exhaust passage can flow to the downstream side of the merging portion, while flowing from the second exhaust passage into the first exhaust passage. The exhaust gas to be circulated is surely circulated toward the downstream side of the merging portion in the first exhaust passage, and specifically, in the configuration of claim 1, the backflow preventing member is the first The exhaust gas flowing through the exhaust passage is allowed to flow from the joining portion to the downstream side, while the exhaust gas flowing through the second exhaust passage is passed from the joining portion to the upstream side of the first exhaust passage. It adds a configuration that is a check valve that blocks distribution.

Further, according to the invention of claim 3, only when the exhaust gas flows through the first exhaust passage, the exhaust gas flows through the first exhaust passage on the downstream side of the merging portion due to the gas pressure of the exhaust gas. And a flow passage through which exhaust gas circulates from the second exhaust passage to the first exhaust passage on the downstream side of the merging portion is always formed. Specifically, in the structure of claim 2, the check valve is
Between the valve seat provided inside the first exhaust passage and the valve seat by the gas pressure of the exhaust gas flowing through the first exhaust passage while being urged so as to be in close contact with the valve seat. A configuration in which a valve body that forms a flow passage for exhaust gas is formed therebetween is added.

Further, according to the invention of claim 4, when the exhaust gas flows through the second exhaust passage and flows into the merging portion in the first exhaust passage, the merging portion is formed in the merging portion by the gas pressure of the exhaust gas. A flow passage through which the exhaust gas flows is formed in a first exhaust passage on the downstream side of the portion. Specifically, in the configuration of claim 2, the check valve includes: Exhaust gas that flows from the first exhaust passage into the merging portion due to the gas pressure of the exhaust gas flowing into the merging portion, and has its downstream end turned toward the second exhaust passage side. A configuration is added in which the downstream end is a rotating plate that is pivotally supported so as to rotate toward the first exhaust passage side by the gas pressure of the gas.

Further, the invention of claim 5 guides the flow direction of the exhaust gas flowing from the second exhaust passage to the merging portion toward the downstream side of the merging portion in the first exhaust passage. Specifically, in the structure of claim 1, in the backflow prevention member, the exhaust gas flowing from the second exhaust passage into the merging portion is downstream from the merging portion in the first exhaust passage. The structure is a guide plate that guides the material to be distributed to the.

Further, in the invention of claim 6, the exhaust gas flowing through the second exhaust passage and flowing into the first exhaust passage from the merging portion is further guided by the guide plate so as to be further purified by the three-way catalyst. And specifically,
The structure according to claim 5, wherein the first portion on the downstream side of the merging portion
The configuration in which the three-way catalyst is provided in the exhaust passage of is added.

Further, according to the invention of claim 7, the exhaust gas flowing through the first exhaust passage is allowed to flow downstream of the confluence of the first exhaust passage and the second exhaust passage. ,
The high-temperature exhaust gas flowing through the second exhaust passage and flowing into the first exhaust passage from the confluence portion and the NOx purification catalyst provided upstream of the confluence portion are thermally provided. It is about to shut off.

[0018] Specifically, the solution means taken by the invention of claim 7 is a first exhaust passage through which exhaust gas flows, a NOx purification catalyst provided in the first exhaust passage, and the first exhaust passage. A second exhaust passage that branches from the upstream side of the NOx purification catalyst in the exhaust passage of the NOx and that joins on the downstream side of the NOx purification catalyst and through which the exhaust gas flows, and the three exhaust passages provided in the second exhaust passage. On the premise of an engine exhaust system including a source catalyst, the NOx purification catalyst of the first exhaust passage upstream of the confluence of the first exhaust passage and the second exhaust passage The three-way catalyst on the downstream side is the NOx
It is configured to be provided integrally with the purification catalyst.

[0019]

According to the structure of claim 1, the first exhaust passage and the second exhaust passage
Since a backflow preventing member for preventing backflow of exhaust gas is provided upstream of the first exhaust passage at a confluence portion with the exhaust passage, the second exhaust passage flows into the first exhaust passage. The exhaust gas that flows circulates in the first exhaust passage on the downstream side of the merging portion.

Further, according to the second aspect of the invention, the backflow prevention member is a check valve that forms a flow passage from the upstream side to the downstream side of the first exhaust passage, and therefore flows through the first exhaust passage. The exhaust gas circulates downstream from the merging portion without any hindrance, while the exhaust gas flowing from the second exhaust passage to the downstream side of the check valve in the first exhaust passage passes from the merging portion in the first exhaust passage. Is also distributed downstream.

According to a third aspect of the present invention, the check valve comprises a valve seat provided inside the first exhaust passage and a valve element biased so as to come into close contact with the valve seat. Since it is a check valve in which the flow passage to the downstream side is formed only by the gas pressure of the exhaust gas flowing through the first exhaust passage,
Exhaust gas flowing through the exhaust passage always flows only to the downstream side of the merging portion in the first exhaust passage.

According to the structure of claim 4, the check valve forms a flow passage through which the exhaust gas flows by the gas pressure of the exhaust gas flowing through the first exhaust passage or the second exhaust passage. Since the downstream plate body is a rotating plate that is pivotally supported so as to rotate, when the exhaust gas flowing through the second exhaust passage flows into the merging portion, the rotating plate causes the rotating plate to move. Since the first exhaust passage is rotated to the side of the first exhaust passage and the first exhaust passage is almost closed, a flow passage is formed from the second exhaust passage to the first exhaust passage downstream of the merging portion.

According to a fifth aspect of the present invention, the backflow preventing member allows the exhaust gas flowing from the second exhaust passage to the merging portion to flow to the first exhaust passage downstream of the merging portion. Since the guide plate guides the flow direction of the exhaust gas, the exhaust gas flowing from the second exhaust passage to the merging portion is guided so as to flow toward the downstream side of the merging portion in the first exhaust passage. ..

Further, according to the sixth aspect of the present invention, since the three-way catalyst is provided on the downstream side of the merging portion in the first exhaust passage, the three-way catalyst flows through the second exhaust passage, and the first exhaust gas flows from the merging portion. The exhaust gas flowing into the passage is guided in the flow direction toward the three-way catalyst provided on the downstream side of the merging portion.

According to the seventh aspect of the invention, the three-way catalyst is integrated with the NOx purification catalyst on the upstream side of the confluence portion in the first exhaust passage and on the downstream side of the NOx purification catalyst. Since it is provided, the high-temperature exhaust gas flowing through the second exhaust passage and flowing into the first exhaust passage from the joining portion of the first exhaust passage and the second exhaust passage is upstream of the joining portion. Provided in the first exhaust passage on the side
The NOx purification catalyst is thermally shielded from the x-purification catalyst, and the NOx purification catalyst is shielded from the influence of heat.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) As shown in FIG. 1, an engine exhaust system A according to the present invention includes a first exhaust passage 3 connected to an exhaust portion of an engine 1 and provided with a NOx purification catalyst 2. The low temperature exhaust gas flows through the first exhaust passage 3. The NOx purifying catalyst 2 is switched and branched by a switching valve 4 provided on the upstream side of the NOx purifying catalyst 2 arranged in the first exhaust passage 3 so that high-temperature exhaust gas flows through the inside of the NOx purifying catalyst 2. Has a second exhaust passage 6 which merges with the first exhaust passage 3 in the downstream side of the merging portion 5, and the three-way catalyst 7 is provided in the second exhaust passage 6.
Is provided. Further, the high temperature exhaust gas flowing from the second exhaust passage 6 flows back to the upstream side of the first exhaust passage 3 at the confluence portion 5 of the first exhaust passage 3 and the second exhaust passage 6. A backflow prevention member 8 for preventing the above is provided.
Further, a downstream three-way catalyst 9 is provided in the first exhaust passage 3 downstream of the confluence portion 5.

The engine exhaust system A according to the first embodiment
The backflow prevention member 8 provided in the above allows the exhaust gas flowing through the first exhaust passage 3 to flow downstream from the joining portion 5, while the exhaust gas flowing through the second exhaust passage 6 joins. It is a check valve that prevents reverse flow from the portion 5 to the upstream side of the first exhaust passage 3.

That is, as shown in FIG. 2, the check valve 10A provided at the confluence portion 5 of the first exhaust passage 3 and the second exhaust passage 6 is a check valve having a movable valve body. The inner wall surface of the first exhaust passage 3 is formed in the valve seat 11, and the main valve body 13 biased by the main spring 12 is provided so as to closely contact the valve seat 11 from the downstream side. Further, cut out the vicinity of the axis of the main valve body 13 to cut the center hole 1
4a is provided and the sub-valve body 1 is biased by the sub-spring 14b which is weaker than the main spring 12 so as to closely contact the periphery of the center hole 14a from the downstream side.
4c is provided, and these form the sub check valve 14.

As a result, the check valve 10A has the sub check valve 14, and when the gas pressure of the exhaust gas flowing through the first exhaust passage 3 is not applied, the sub valve body 14c is the main valve. Since the main valve body 13 is in close contact with the body 13 and the main valve body 13 is in close contact with the valve seat 11, the check valve 10 </ b> A is connected to the first exhaust passage 3 at the merging portion 5.
Since the exhaust gas flowing from the second exhaust passage 6 into the confluence portion 5 flows to the first exhaust passage 3 downstream of the check valve 10A, the exhaust gas flowing from the second exhaust passage 6 to the first exhaust passage 3 upstream of the confluence portion 5 is closed. There is no reverse flow to the exhaust passage 3.

In the check valve 10A according to the first embodiment, the auxiliary check valve 14 is first opened by the gas pressure of the exhaust gas flowing through the first exhaust passage 3 so that the exhaust gas flows downstream and the exhaust gas If the gas pressure increases, a flow passage that allows exhaust gas to flow downstream can be formed in the entire check valve 10A, and appropriate multi-stage flow passages can be formed according to the amount of exhaust gas flowing.

A circulation hole 16 is provided in the cylindrical wall portion 15 of the plate that supports the base portion of the main spring 12, and a flow passage through which the exhaust gas flowing through the first exhaust passage 3 flows to the downstream side. Has become a part of.

(Second Embodiment) As shown in FIG. 3, a check valve 10B as a backflow preventing member 8 in the second embodiment is provided at a confluence portion 5 of a first exhaust passage 3 and a second exhaust passage 6. It is a rotating plate 17 provided.

The rotating plate 17 is the first member in the merging section 5.
Is supported by the shaft 17a on the inner wall surface of the exhaust passage 3, and its downstream end 17b is rotatable toward either the first exhaust passage 3 side or the second exhaust passage 6 side. It is provided.

Therefore, in the check valve 10B including the rotating plate 17 according to the second embodiment, the rotating plate 1 is driven by the gas pressure of the exhaust gas flowing from the first exhaust passage 3 into the merging portion 5.
7 is rotated toward the second exhaust passage 6 side,
On the other hand, the downstream side end portion 17b of the rotating plate 17 rotates toward the first exhaust passage 3 side by the gas pressure of the exhaust gas flowing from the second exhaust passage 6 into the confluence portion 5. As a result, when the exhaust gas flows from the second exhaust passage 6 into the confluence portion 5, the downstream end 17b of the rotating plate 17 is rotated toward the first exhaust passage 3 side. First exhaust passage 3 on the downstream side of
A flow passage is formed in which the exhaust gas flows, and the exhaust gas flows through the flow passage. At the same time, the first exhaust passage 3 is almost closed by the downstream end portion 17b of the rotating rotary plate 17, so that the exhaust gas flows backward to the upstream side of the confluence portion 5 of the first exhaust passage 3. Is blocked.

(Embodiment 3) In the backflow prevention member 8 provided in the exhaust system A of the engine according to Embodiment 3, the exhaust gas flowing from the second exhaust passage 6 into the confluence portion 5 has the first exhaust passage. 3 is a guide plate that guides the fluid to flow downstream of the confluence portion 5.

That is, as shown in FIG. 4, the guide plate 1
Reference numeral 8 denotes a guide plate body 18a, which is provided in the guide plate body 18a so as to project from the surface of the guide plate body 18a, and a guide portion 18b which guides the flow of exhaust gas, and which flows through the first exhaust passage 3. A circulation permitting portion 18c that permits the exhaust gas to flow downstream of the confluence portion 5 is provided. The guide plate 18 in the third embodiment is formed by a guide plate main body 18a made of a plate-shaped body that can be inserted into the first exhaust passage 3 and a so-called cut-and-raised shape from the guide plate main body 18a. Multiple guide parts 1
8b and a flow permitting portion 18c formed by a hole formed by cutting and raising the guide portion 18b.

As shown in FIG. 5, such a guide plate 18 is attached so that one end portion 18d of the guide plate 18 is joined to the inner wall surface of the first exhaust passage 3 on the upstream side of the merging portion 5. As a result, the guide plate 18 is provided so as to cross the first exhaust passage 3 at the confluence portion 5.

As a result, the exhaust gas flowing through the second exhaust passage 6 and flowing into the merging portion 5 is guided to flow by the guide portion 18b of the guide plate 18, and is downstream of the merging portion 5 in the first exhaust passage 3. Distribute to the side. At the same time, the flow permitting portion 18c formed on the guide plate 18 is connected to the guide portion 18b.
As a result, the exhaust gas flowing from the second exhaust passage 6 is shielded from the exhaust gas flowing in from the second exhaust passage 6, so that the exhaust gas flowing from the second exhaust passage 6 into the merging portion 5 is located upstream of the merging portion 5. There is no backflow to 3.

On the other hand, the exhaust gas flowing through the first exhaust passage 3 flows through the flow permitting portion 18c provided on the guide plate 18 at the joining portion 5, and flows downstream from the joining portion 5 without any trouble.

(Embodiment 4) In the engine exhaust system A according to Embodiment 4, a guide plate is used as the backflow prevention member 8 provided at the confluence portion. That is, as shown in FIG. 6, a guide plate 18 similar to the guide plate 18 in the third embodiment is similarly provided in the confluence portion 5 of the first exhaust passage 3 and the second exhaust passage 6.

NOx located upstream of the guide plate 18 provided in the first exhaust passage 3 is intended to make the entire exhaust system of the engine compact.
The purification catalyst 2 and the downstream three-way catalyst 9 located downstream of the guide plate 18 are coaxially provided.

Therefore, also in the fourth embodiment, the guide plate main body 18 is provided in the first exhaust passage 3 in the merging portion 5.
Since the guide plate 18 in which the guide portion 18b and the flow permitting portion 18c are formed is provided in a, the exhaust gas flowing from the second exhaust passage 6 into the confluence portion 5 as in the third embodiment. The flow is guided to the downstream side of the merging portion 5 in the first exhaust passage 3, and does not flow back to the upstream side of the merging portion 5.

On the other hand, the exhaust gas flowing through the first exhaust passage 3 flows from the upstream side of the guide plate 18 to the downstream side without any trouble.

(Embodiment 5) The engine exhaust system according to the fifth embodiment is replaced with the first backflow preventing member 8 provided at the confluence portion 5 of the engine exhaust system A according to the first to fourth embodiments. By providing a three-way catalyst having high heat resistance as a heat insulating member on the upstream side of the confluence portion 5 in the exhaust passage 3 and on the downstream side of the NOx purification catalyst 2, the second exhaust passage 6 moves to the confluence portion 5. Inflowing hot exhaust gas and NO
The x-purifying catalyst 2 is thermally isolated.

That is, as shown in FIG. 7, in the first exhaust passage 3 in which the NOx purification catalyst is provided, the first
An adiabatic three-way catalyst 19 is provided upstream of the confluence 5 of the exhaust passage 3 and the second exhaust passage 6 and downstream of the NOx purification catalyst 2.

The adiabatic three-way catalyst 19 may be a separately obtained three-way catalyst and may be disposed between the NOx purification catalyst 2 and the merging portion 5. In the fifth embodiment, for example, A NOx purification catalyst 2 is formed by coating a NOx purification component on the upstream side within a range of about 3/4 of the entire length of a catalyst carrier made of cordierite or the like, and the uncoated portion 20
Both of the catalysts are integrally provided by coating the downstream side of the catalyst carrier with CO, HC and NOx purifying components through the to form the adiabatic three-way catalyst 19. As a result, the NOx purification catalyst 2 and the heat insulating three-way catalyst 19 provided on the downstream side thereof are formed in a compact form.

In the engine exhaust system A according to the fifth embodiment, the second exhaust passage 6 circulates through the second exhaust passage 6 to reach the first part from the merging part 5.
The high temperature exhaust gas flowing into the exhaust passage 3 of the
A part of the gas flows backward to the first exhaust passage 3 on the upstream side of
The exhaust gas flowing back from the merging portion 5 first comes into contact with the adiabatic three-way catalyst 19 provided on the downstream side of the NOx purification catalyst 2. However, since the three-way catalyst is originally highly heat resistant and is not deteriorated by heat of about 900 ° C., the adiabatic three-way catalyst 19 is not affected by the heat of the exhaust gas that flows back and contacts. Furthermore, since the exhaust gas that has flowed back and contacted with the adiabatic three-way catalyst 19 has a reduced gas pressure, the rate of reverse flow inside the adiabatic three-way catalyst 19 to the upstream side becomes minute,
The amount of exhaust gas flowing back inside is small, and its temperature drops significantly.

Therefore, the NOx purification catalyst 2 is protected from the heat of the exhaust gas flowing back from the confluence portion 5 to the upstream side and is not deteriorated. At the same time, most of the exhaust gas flowing from the second exhaust passage 6 into the merging portion 5 flows back to the upstream side of the merging portion 5 and then returns to the downstream side of the merging portion 5 along with a part of the exhaust gas that has recirculated. Distribute to the side.

On the other hand, the exhaust gas flowing through the first exhaust passage 3 successively passes through the NOx purifying catalyst 2 and the adiabatic three-way catalyst 19 provided in the first exhaust passage 3, and the confluent portion 5 Can be distributed downstream.

[0051]

As described above, according to the exhaust system for an engine of the first aspect of the present invention, the backflow prevention member is provided at the confluence of the first exhaust passage and the second exhaust passage. As a result, the exhaust gas flowing from the second exhaust passage into the first exhaust passage flows to the downstream side of the first exhaust passage without flowing backward to the upstream side of the merging portion. When the exhaust gas flowing from the exhaust passage to the merging portion is at a high temperature, the heat-sensitive NOx purification catalyst provided upstream of the merging portion in the first exhaust passage due to the backflow of the hot exhaust gas. Thermal deterioration is prevented.

Further, according to the second aspect of the present invention, since the backflow prevention member is a check valve that forms only a flow passage from the upstream side to the downstream side of the first exhaust passage, it flows through the first exhaust passage. Exhaust gas flowing through the second exhaust passage and the exhaust gas flowing into the first exhaust passage on the downstream side of the check valve flows on the downstream side of the merging portion of the first exhaust passage. Therefore, the backflow of the exhaust gas to the first exhaust passage on the upstream side of the merging portion is prevented.

According to the third aspect of the present invention, the check valve is a check valve in which the flow passage to the downstream side is formed only by the gas pressure of the exhaust gas flowing through the first exhaust passage. Since the exhaust gas flowing through the second exhaust passage always flows only to the downstream side of the joining portion in the first exhaust passage, the reverse flow of the exhaust gas to the first exhaust passage upstream of the joining portion is surely performed. Be blocked.

Further, according to the invention of claim 4, the check valve is configured such that the check valve forms a passage for each exhaust gas by the gas pressure of the exhaust gas flowing through the first exhaust passage or the second exhaust passage. When the exhaust gas flowing through the second exhaust passage flows into the merging portion, the rotating plate is supported by the first exhaust gas on the downstream side of the merging portion from the second exhaust passage due to the gas pressure thereof. Since the flow passage is formed toward the passage, the reverse flow of the exhaust gas to the first exhaust passage on the upstream side of the merging portion is reliably prevented.

According to the fifth aspect of the present invention, the backflow prevention member guides the exhaust gas flowing from the second exhaust passage to the merging portion so as to flow to the first exhaust passage downstream of the merging portion. Since it is a guide plate, the exhaust gas flowing from the second exhaust passage to the merging portion is guided so as to flow toward the downstream side of the merging portion in the first exhaust passage. As a result, backflow of the exhaust gas to the first exhaust passage on the upstream side of the merging portion is prevented.

Further, since the guide plate has no moving parts, a maintenance-free effect can be obtained together.

Further, according to the invention of claim 6, a three-way catalyst is provided on the downstream side of the confluent portion in the first exhaust passage, and further, the three-way catalyst is circulated in the second exhaust passage to reach from the confluent portion to the first portion. Since the exhaust gas flowing into the exhaust passage of the first exhaust gas is guided so as to flow toward the three-way catalyst, the exhaust gas flowing from the second exhaust passage into the merging portion is the first exhaust gas on the upstream side of the merging portion. There is no backflow into the passage.

Further, in such a structure, NOx located on the upstream side of the guide plate in the first exhaust passage.
Since it becomes easy to provide the purification catalyst and the three-way catalyst located on the downstream side coaxially, it becomes possible to make the exhaust system of the engine compact.

According to the engine exhaust system of the seventh aspect of the present invention, the three-way catalyst is the N-type catalyst which is upstream of the confluence portion in the first exhaust passage and downstream of the NOx purification catalyst.
Since it is provided integrally with the Ox purification catalyst, it is between the high temperature exhaust gas flowing from the second exhaust passage to the confluence and the NOx purification catalyst due to the heat-resistant characteristic of the three-way catalyst. Is thermally shut off. This prevents the NOx purification catalyst from thermally deteriorating due to the backflow of high-temperature exhaust gas.

Further, the above-mentioned three-way catalyst used for blocking heat can also have a function of purifying exhaust gas.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an exhaust system for an engine according to the present invention.

FIG. 2 is a sectional view showing a check valve according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a rotating plate according to a second embodiment of the present invention.

FIG. 4 is a perspective view of a guide plate used in Examples 3 and 4 of the present invention.

FIG. 5 is a sectional view showing a guide plate according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing a guide plate in Example 4 of the present invention.

FIG. 7 is a sectional view showing a three-way catalyst for heat insulation in Example 5 of the present invention.

FIG. 8 is a cross-sectional view showing a conventional example.

[Explanation of symbols]

 2 NOx purification catalyst 3 First exhaust passage 4 Switching valve 5 Merging part 6 Second exhaust passage 7 Three-way catalyst 8 Backflow prevention member 9 Downstream three-way catalyst 10A, 10B Check valve 11 Valve seat 13 Main valve body 14 Sub check valve 17 Rotating plate 17a Downstream side of rotating plate 18 Guide plate 18b Guide portion 18c Flow permitting portion 19 Insulation three-way catalyst 20 Uncoated portion

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomotaka Hirota 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation

Claims (7)

[Claims] 1. A first exhaust passage through which exhaust gas flows,
The NOx purifying catalyst provided in the first exhaust passage and the NOx purifying catalyst in the first exhaust passage branch from the upstream side of the NOx purifying catalyst, and merge with the downstream side of the NOx purifying catalyst so that the exhaust gas flows. In an exhaust system of an engine including a second exhaust passage and a three-way catalyst provided in the second exhaust passage, in a confluence portion of the first exhaust passage and the second exhaust passage, An exhaust system for an engine, comprising: a backflow prevention member for preventing exhaust gas flowing through the second exhaust passage from flowing back to the upstream side of the first exhaust passage. 2. The backflow prevention member allows the exhaust gas flowing through the first exhaust passage to flow downstream from the merging portion, while the exhaust gas flowing through the second exhaust passage passes through the second exhaust passage. The exhaust device for an engine according to claim 1, wherein the check device is a check valve that blocks the flow from the merging portion to the upstream side of the first exhaust passage. 3. The check valve is urged so as to come into close contact with a valve seat provided inside the first exhaust passage and the valve seat, and flows through the first exhaust passage. The exhaust system for an engine according to claim 2, further comprising: a valve body that forms a flow passage for the exhaust gas between the valve seat and the valve seat by the gas pressure of the exhaust gas. 4. The check valve has a downstream end turned to the second exhaust passage side by a gas pressure of exhaust gas flowing into the merging portion from the first exhaust passage, and the second end is rotated toward the second exhaust passage side. 7. The rotating plate pivotally supported so that the downstream end thereof is rotated toward the side of the first exhaust passage by the gas pressure of the exhaust gas flowing from the exhaust passage into the merging portion. 2. The engine exhaust system according to 2. 5. The backflow prevention member is a guide plate that guides exhaust gas flowing from the second exhaust passage into the confluence portion so as to flow from the confluence portion to a downstream side of the first exhaust passage. The exhaust system for an engine according to claim 1, wherein the exhaust system is provided. 6. The exhaust system for an engine according to claim 5, wherein a three-way catalyst is provided in the first exhaust passage downstream of the merging portion. 7. A first exhaust passage through which exhaust gas flows,
The NOx purifying catalyst provided in the first exhaust passage and the NOx purifying catalyst in the first exhaust passage branch from the upstream side of the NOx purifying catalyst, and merge with the downstream side of the NOx purifying catalyst so that the exhaust gas flows. An exhaust system for an engine, comprising: a second exhaust passage for controlling the exhaust gas; and a three-way catalyst provided in the second exhaust passage, the first exhaust passage and the second exhaust passage in the first exhaust passage. An exhaust system for an engine, wherein a three-way catalyst is provided integrally with the NOx purification catalyst on the upstream side of the confluence with the passage and on the downstream side of the NOx purification catalyst.