JP2001020722A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

An object of the present invention is to provide a technique capable of efficiently performing an SOx release process without wasting energy during an SOx release process of a storage reduction type NOx catalyst. SOx absorbent 31 disposed in an exhaust passage of an internal combustion engine 1 for absorbing SOx when the exhaust air-fuel ratio is lean and releasing the absorbed SOx when the oxygen concentration decreases, and for absorbing SOx When the exhaust gas is passed through the absorbent in the first direction, and when the SOx is released, the exhaust gas is passed through the absorbent in a second direction opposite to the first direction. And control means 100 for controlling a part of the cylinders 1 and 3 of the internal combustion engine to be rich and the other cylinders 2 and 3 to be lean when flowing the fuel in the second direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an exhaust gas purifying apparatus for an internal combustion engine capable of switching a flow direction of exhaust gas flowing through exhaust gas purifying means as required. is there.

[0002]

2. Description of the Related Art Generally, an exhaust gas purification device is provided in an exhaust passage of an internal combustion engine to purify exhaust gas discharged from the internal combustion engine. When the exhaust gas of the internal combustion engine is flowing through the exhaust gas purification device, deposits gradually adhere from the upstream side of the exhaust gas purification device. What this sediment is
It varies depending on the composition of the exhaust gas or the configuration of the exhaust gas purification device and the mechanism of the exhaust gas purification, and examples thereof include oxides, sulfides, nitrates, and sulfates. These deposits may reduce the purification performance of the exhaust gas purification device or increase the exhaust resistance, and need to be removed at a predetermined timing.

[0003] For example, as an exhaust gas purifying device for purifying NOx of exhaust gas discharged from an internal combustion engine that performs combustion at a lean air-fuel ratio, there is an NOx storage reduction catalyst. This storage reduction type NOx catalyst is a catalyst that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases, and reduces it to N2. A NOx storage-reduction catalyst is disposed in the exhaust passage, and nitrogen oxides (NOx) are produced from exhaust gas having a lean air-fuel ratio.
By enriching the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst by, for example, increasing the amount of fuel supplied to the internal combustion engine after NOx absorption, the NOx absorbed from the NOx storage reduction catalyst is reduced. At the same time, the released NOx is reduced and purified into N2 by reducing components such as unburned HC and CO in the exhaust gas.

[0004] In general, the fuel of the internal combustion engine contains sulfur, and when the fuel is burned in the internal combustion engine, the sulfur in the fuel burns to generate sulfur oxides (SOx). Since the NOx storage reduction catalyst absorbs SOx in exhaust gas by the same mechanism as that of absorbing NOx, when the NOx storage reduction catalyst is disposed in the exhaust passage of the internal combustion engine, the NOx storage reduction catalyst Absorbs not only NOx but also SOx.

However, since SOx absorbed by the NOx storage reduction catalyst forms stable sulfate over time, the release and reduction purification of NOx from the NOx storage reduction catalyst (hereinafter referred to as NOx release / reduction processing). Under the conditions of (1), there is a tendency that decomposition and release are difficult to occur and are easily accumulated in the NOx storage reduction catalyst. SOx in NOx storage reduction catalyst
When the accumulated amount increases, the NOx absorption capacity of the NOx storage reduction catalyst decreases, so that it is not possible to sufficiently remove NOx in the exhaust gas, so that NOx purification efficiency is reduced, that is, SOx poisoning occurs. Therefore, in order to maintain the NOx purification performance of the NOx storage reduction catalyst high over a long period of time, it is necessary to release SOx absorbed by the catalyst at an appropriate timing.

To release SOx absorbed by the NOx storage reduction catalyst, the air-fuel ratio of the inflowing exhaust gas is made rich,
In addition, it is known that the temperature of the NOx storage reduction catalyst needs to be higher than that during the NOx release / reduction processing.

[0007] By the way, SOx in the NOx storage reduction catalyst
Is larger in the NOx storage reduction catalyst as it is closer to the exhaust gas inlet side.
If the exhaust gas with a rich air-fuel ratio is caused to flow in the same direction as the exhaust gas at the time of NOx absorption when releasing the SOx absorbed by the NOx storage-reduction catalyst,
Even if the SOx absorbed in the inlet side of the x-catalyst is released, the released SOx simply moves to the outlet side of the exhaust gas through the NOx storage-reduction catalyst, and the NOx storage-reduction type
There is a problem that the catalyst is re-absorbed and cannot be efficiently exhausted from the NOx storage reduction catalyst.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 7-259542, when the SOx absorbed by the NOx storage reduction catalyst is released, the exhaust gas with a rich air-fuel ratio is discharged in the opposite direction to that during NOx absorption. There has been proposed a technique of flowing the NOx storage-reduction catalyst. With the backflow function of releasing the SOx by reversing the flow of the exhaust gas, the SOx released from the NOx storage reduction catalyst has a small moving distance in the NOx storage reduction catalyst and is immediately stored. Since the SOx is discharged outside the reduced NOx catalyst, the released SOx can be prevented from being re-absorbed by the NOx storage reduction catalyst.

The exhaust gas purifying apparatus for an internal combustion engine with a backflow function disclosed in the above publication is configured as follows. An upstream exhaust passage connected to the inlet of the NOx storage reduction catalyst and a downstream exhaust passage connected to the outlet of the NOx storage reduction catalyst are connected by a bypass passage that bypasses the NOx storage reduction catalyst. A first exhaust flow switching valve is provided at a junction of the side exhaust passage and the bypass passage, and a second exhaust flow switching valve is provided at a junction of the downstream exhaust passage and the bypass passage. The first exhaust flow switching valve is capable of switching exhaust gas flowing from an upstream thereof to either the storage-reduction type NOx catalyst or to the bypass passage. The flow switching valve causes the exhaust gas that has passed through the NOx storage reduction catalyst to flow to a downstream exhaust passage downstream of the second exhaust flow switching valve, or the exhaust gas that has passed through the bypass passage to the second exhaust gas passage. The flow can be switched to either one of flowing to a downstream exhaust passage downstream of the exhaust flow switching valve. Further, a suction exhaust passage is branched from an upstream exhaust passage between the storage reduction type NOx catalyst and the first exhaust flow switching valve, and the suction exhaust passage is connected to a suction port of an exhaust pump, and the exhaust gas is exhausted. The discharge port of the pump is connected to the bypass passage. In addition, a reducing agent supply device that supplies a reducing agent to a downstream exhaust passage between the storage reduction type NOx catalyst and the second exhaust flow switching valve is provided.

During the NOx absorption processing, the first and second exhaust flow switching valves are switched so as to close the bypass passage, and the entire amount of exhaust gas of the internal combustion engine is transferred from the inlet to the outlet of the NOx storage reduction catalyst. Let go through. On the other hand, when releasing SOx from the NOx storage reduction catalyst, the first and second exhaust flow switching valves are switched so that substantially all of the exhaust gas of the internal combustion engine flows into the bypass passage, and at the same time, the exhaust pump is turned on. By operating and sucking exhaust gas in the upstream exhaust passage between the storage reduction NOx catalyst and the first exhaust flow switching valve and discharging the exhaust gas to the bypass passage, the storage reduction NOx catalyst enters the storage reduction NOx catalyst from its outlet side through the inlet. A flow of the exhaust gas flowing in the opposite direction to the side is generated, and the reducing agent supply device is operated to supply the reducing agent to the downstream side exhaust passage. As a result, exhaust gas having a rich air-fuel ratio is caused to flow back through the NOx storage reduction catalyst, and the NOx storage reduction
SOx is being released from the catalyst.

[0011]

In the conventional exhaust gas purifying apparatus for an internal combustion engine with a backflow function, it is possible to effectively prevent SOx poisoning of the NOx storage reduction catalyst. However, as a result of intensive studies focusing on the SOx poisoning removal effect of the NOx storage reduction catalyst due to the addition of the backflow function, the following was found.

The above SOx release processing involving backflow in the NOx storage reduction catalyst is a processing method that focuses on avoiding reabsorption of SOx by shortening the moving distance of SOx at the time of SOx release. On the other hand, if this treatment method is adopted, the exhaust gas is stored and reduced NOx
Since the distance to the catalyst becomes longer, the temperature of the exhaust gas decreases greatly while flowing through the long path, and SOx
From the viewpoint of the temperature conditions at the time of release, there is a case where it is not always the best method for releasing SOx.

Regarding this point, a countermeasure for raising the catalyst temperature at the time of releasing SOx is considered. As one of measures to increase the catalyst temperature at the time of SOx release, a method of controlling the exhaust air-fuel ratio to stoichiometric or rich can be considered. However, the storage reduction type N
The SOx poisoning region of the Ox catalyst is deposited on one side of the NOx storage reduction catalyst, and raising the temperature of the entire catalyst is a waste of energy.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to eliminate waste of energy at the time of SOx release processing of an NOx storage reduction catalyst. An object of the present invention is to provide a technology capable of performing an SOx release process efficiently.

[0015]

The present invention has the following features to attain the object mentioned above. According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, which is disposed in an exhaust passage of the internal combustion engine when the exhaust air-fuel ratio is lean.
SOx that absorbed x and absorbed when the oxygen concentration decreased
And SOx absorbent for releasing SOx, exhaust gas is passed through the absorbent in a first direction when absorbing SOx, and exhaust gas is passed through the absorbent in a second direction opposite to the first direction when SOx is released. It is characterized by comprising backflow means for allowing passage, and control means for controlling a part of the cylinders of the internal combustion engine to be rich and other cylinders to be lean when the exhaust gas is caused to flow in the second direction by the backflow means.

At the time of backflow, SOx is deposited on the exhaust gas downstream side of the absorbent. By increasing the temperature of the absorbent by controlling some cylinders to be rich and other cylinders to be lean, SOx deposited on the exhaust downstream side of the SOx absorbent can be efficiently removed. In other words, when control is performed to make some cylinders rich and other cylinders lean, the fuel and air rise due to the catalytic reaction, and the temperature of the SOx absorbent corresponding to the exhaust gas flowing backward from the center to the outlet of the SOx absorbent is reduced. Reach the highest. In this region, the oxygen concentration also decreases. Therefore, an SOx emission atmosphere is completed. If all the cylinders are made rich, energy is wasted, so control is performed to make some cylinders rich. Thus, waste of energy, that is, waste of fuel and the like can be eliminated.

[0017] In the second means of the present invention, the position of the SOx absorbent in the exhaust passage is such that the first exhaust gas is longer than the length of the exhaust passage formed when the exhaust gas flows in the second direction. It is arranged at a position where the length of the exhaust passage formed when flowing in the direction is shortened.

As described above, the SOx absorbent and the exhaust gas are
The position of the exhaust passage formed when the exhaust gas flows in the first direction is shorter than the length of the exhaust passage formed when the exhaust gas flows in the first direction. Temperature of the SOx absorbent (catalyst temperature) can be secured.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a schematic diagram of an embodiment in which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a gasoline engine capable of burning at a lean air-fuel ratio (so-called lean burn gasoline engine). FIG. 3 is a diagram illustrating a configuration.

In FIG. 1, an engine 1 is an in-line four-cylinder, and intake air is supplied to each cylinder via an intake pipe 2 and an intake manifold 3. The intake pipe 2 is provided with a throttle valve 4 that opens and closes an intake passage in the intake pipe 2 in conjunction with an accelerator pedal (not shown). The throttle valve 4 outputs an output signal corresponding to the opening of the throttle valve 4. A throttle position sensor 5 that outputs to an electronic control unit (ECU) 100 for engine control is attached.

An air flow meter 6 that outputs an output signal corresponding to an amount of intake air (mass of intake air) Q flowing through the intake pipe 2 to the ECU 100 is provided upstream of the throttle valve 4 in the intake pipe 2. .

Fuel (gasoline) is injected from a fuel injection valve 7 into each intake passage connected to each cylinder of the engine 1. The valve opening timing and valve opening period of the fuel injection valve 7 are controlled by the ECU 100 according to the operating state of the engine 1.

Exhaust gas exhausted from each cylinder of the engine 1 is exhausted through an exhaust manifold 8 and an exhaust pipe 9. The exhaust pipe 9 is connected to a first port of an exhaust switching valve (flow direction switching means) 20 having four ports.
A second port of the exhaust switching valve 20 is connected to an exhaust pipe 10 that exhausts exhaust gas to the atmosphere, and a third port of the exhaust switching valve 20 is connected via a exhaust pipe 11 to a catalytic converter (exhaust gas purifying means).
30 is connected to an inlet 30a of the catalytic converter 30 via the exhaust pipe 12 and a fourth port of the exhaust switching valve 20.
0b. The catalytic converter 30 contains a NOx storage reduction catalyst (hereinafter abbreviated as NOx catalyst) 31. The NOx catalyst 31 will be described later in detail.

The exhaust switching valve 20 is a valve that can change the flow direction of exhaust gas flowing through the catalytic converter 30 by switching its valve body between a forward flow position shown in FIG. 1 and a reverse flow position shown in FIG. When the valve body is located at the forward flow position, the exhaust switching valve 20 connects the exhaust pipe 9 and the exhaust pipe 11 and simultaneously connects the exhaust pipe 10 and the exhaust pipe 12.
And at this time, the exhaust gas flows from the exhaust pipe 9 to the exhaust pipe 1
It flows in the order of 1 → catalytic converter 30 → exhaust pipe 12 → exhaust pipe 10 and is released to the atmosphere. The flow of the exhaust gas flowing from the inlet 30a to the outlet 30b of the catalytic converter 30 in this manner is referred to as "forward flow" in the following description.

When the valve body of the exhaust gas switching valve 20 is located at the reverse flow position shown in FIG. 2, the exhaust gas switching valve 20 connects the exhaust pipe 9 and the exhaust pipe 12, and connects the exhaust pipe 10 and the exhaust pipe. 11 and at this time, the exhaust gas is changed to the exhaust pipe 9 →
The gas flows in the order of the exhaust pipe 12 → the catalytic converter 30 → the exhaust pipe 11 → the exhaust pipe 10 and is released to the atmosphere. The flow of the exhaust gas flowing from the outlet 30b to the inlet 30a of the catalytic converter 30 in this manner is referred to as "backflow" in the following description.

The exhaust switching valve 20 is connected to an actuator 21
The actuator 21 is controlled by the ECU 100 to switch the valve body position. In this embodiment, the actuator 21 and E
The CU 100 constitutes control means. The switching control of the valve body position of the exhaust switching valve 20 will be described later in detail.

An exhaust temperature sensor 13 for outputting an output signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 11 to the ECU 100 is mounted near the inlet 30a of the catalytic converter 30 in the exhaust pipe 11.

The ECU 100 is composed of a digital computer and includes a ROM (Read-On-Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, and an output port interconnected by a bidirectional bus. In addition to performing the basic control such as the air-fuel ratio control of No. 1, in this embodiment, the SOx release processing control of the catalytic converter 30 and the like are performed.

For these controls, an input signal from the air flow meter 6, an input signal from the exhaust temperature sensor 13, and an input signal from the rotation speed sensor 14 are input to the input ports of the ECU 100. You. The rotation speed sensor 14 outputs an output signal corresponding to the rotation speed of the engine 1 to the ECU.
The ECU 100 calculates the engine speed N from the output signal. The ECU 100 calculates the intake air amount Q from the output signal of the air flow meter 6 and calculates the engine load Q / N (intake air amount Q / engine speed N). The ECU 100 calculates the engine speed N
And the engine load Q / N to determine the operating state of the engine 1 and control the amount of fuel injected from the fuel injection valve in accordance with the operating state, to control the lean air-fuel ratio and the stoichiometric or rich state for all cylinders simultaneously or for each cylinder. The air-fuel ratio control for switching to the air-fuel ratio is performed. As an example of the air-fuel ratio control, there is a control method in which a stoichiometric or rich air-fuel ratio is set in a warm-up operation and a high load operation range, and a lean air-fuel ratio is set in a low-medium load operation range.

NO stored in catalytic converter 30
The x-catalyst 31, that is, the storage-reduction NOx catalyst uses, for example, alumina as a carrier, and on the carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, or cesium Cs, or an alkaline earth such as barium Ba or calcium Ca. And at least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt.

When the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as the exhaust air-fuel ratio) is lean, the NOx catalyst 31
When the oxygen concentration in the inflowing exhaust gas decreases, the absorbed NOx is released and reduced to N2. Here, the exhaust air-fuel ratio means the ratio of the sum of the amount of air supplied to the exhaust passage, the engine combustion chamber, the intake passage, and the like upstream of the NOx catalyst 31 to the sum of the fuel (hydrocarbon). And Therefore, when no fuel, reducing agent or air is supplied into the exhaust passage upstream of the NOx catalyst 31,
The exhaust air-fuel ratio matches the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber.

In this embodiment, a so-called lean-burn gasoline engine capable of burning at a lean air-fuel ratio is used as the internal combustion engine, and the air-fuel ratio of the air-fuel mixture is controlled according to the operating state of the engine 1. . Therefore, Engine 1
When the vehicle is operated at a lean air-fuel ratio, the exhaust air-fuel ratio becomes lean and the oxygen concentration becomes high. On the other hand, when the engine 1 is operated at the stoichiometric or rich air-fuel ratio, the exhaust air-fuel ratio becomes stoichiometric or rich, the oxygen concentration in the exhaust gas is greatly reduced, and the unburned HC, CO And other components increase.

Although the mechanism of the NOx absorption / release operation of the NOx catalyst 31 is not clear, it is thought that the mechanism is performed by the mechanism shown in FIG. For this mechanism, platinum Pt and barium Ba
The following description will be made with reference to an example in which is carried, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.

First, the incoming exhaust gas is considerably lean
And the oxygen concentration in the inflowing exhaust gas greatly increases.
As shown in FIG._TwoIs O_Two ^-Or O^2-White in the form of
It adheres to the surface of gold Pt. Next, the N contained in the exhaust gas
O is O on the surface of platinum Pt. _Two ^-Or O^2-Reacts with NO
_Two(2NO + O_Two→ 2NO_Two).

Thereafter, the generated NO ₂ is supplied to the NOx catalyst 3
As long as the first NOx absorption capacity is not saturated, while being oxidized on the platinum Pt and is absorbed in the NOx catalyst 31 bonding with the barium oxide BaO, 3 nitrate as shown in (A) ions NO ₃ ^- NOx in the form of It diffuses into the catalyst 31. In this way, NOx is absorbed in the NOx catalyst 31.

On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases, the amount of NO ₂ produced decreases, and the NOx catalyst 3 reacts in a reverse manner (NO ₃ ⁻ → NO ₂ ) to the above reaction.
Nitrate ions NO ₃ in 1 ^- is, N in the form of NO ₂ or NO
It is released from the Ox catalyst 31.

On the other hand, if reducing components such as HC and CO are present in the inflowing exhaust gas, these components are oxidized by reacting with oxygen O ₂ ^- or O ^2- on platinum Pt, and oxygen in the exhaust gas is reduced. Consumption reduces the oxygen concentration in the exhaust gas. Further, NO ₂ or NO released from the NOx catalyst 31 due to a decrease in the oxygen concentration in the exhaust gas is, as shown in FIG.
It is reduced by reacting with HC and CO. When NO ₂ or NO on the platinum Pt disappears in this way, NOx
NO ₂ or NO is released from the catalyst 31 one after another.

[0038] That is, HC in the inflowing exhaust gas, CO, first oxygen O ₂ on the platinum Pt ^- or O ^2- immediately be reacted with oxidized, then the platinum Pt on the oxygen O ₂ ^- or O ^2- If HC and CO still remain after consumption, this H
C, NOx discharged from the released NOx, the engine from the NOx catalyst 31 by the CO is made to reduction to N _2.

[0039] Thus, NOx when the exhaust air-fuel ratio becomes lean is absorbed in the NOx catalyst 31, NOx when the exhaust air-fuel ratio to the stoichiometric or rich is released in a short time from the NOx catalyst 31, reduced to N ₂ Is done. Therefore, emission of NOx into the atmosphere can be prevented.

Next, the mechanism of SOx poisoning of the NOx catalyst 31 will be described. Sulfur oxide (SO
When x) is included, the NOx catalyst 31 absorbs SOx in the exhaust gas by the same mechanism as the above-described NOx absorption. That is, when the exhaust air-fuel ratio is lean, oxygen O ₂ adheres to the surface of the platinum Pt of the NOx catalyst 31 in the form of O ₂ ⁻ or O ²⁻ , and SOx (eg, SO ₂ ) in the inflowing exhaust gas
Is oxidized on the surface of platinum Pt to SO ₃ .

After that, the generated SO ₂ is further oxidized on the surface of the platinum Pt and is absorbed in the NOx catalyst 31 to be combined with barium oxide BaO, and then enters the NOx catalyst 31 in the form of sulfate ion SO ₄ ^2−. diffused to form the sulfate BaSO _4. Since BaSO ₄ has a crystal that tends to be coarse and relatively stable, it is difficult to be decomposed and released once it is formed. For this reason, when the amount of BaSO ₄ generated in the NOx catalyst 31 increases with the passage of time, the amount of BaO that can participate in the absorption of the NOx catalyst 31 decreases, and the NOx absorption capacity decreases. This is SOx poisoning. Therefore, in order to keep the NOx absorption capacity of the NOx catalyst 31 high, it is necessary to release the SOx absorbed by the NOx catalyst 31 at an appropriate timing.

It is known that SOx can be released from the NOx catalyst 31 by lowering the oxygen concentration of the exhaust gas as in the case of releasing NOx.
It is known that the higher the temperature of the x catalyst 31, the easier it is to release.

According to the research conducted by the present applicant, in order to release SOx absorbed by the NOx catalyst 31, normal NOx release / reduction in which the inflow exhaust air-fuel ratio is made stoichiometric or rich and NOx is released from the NOx catalyst 31 is performed. It has been found that the temperature of the NOx catalyst 31 needs to be higher than during the treatment.

The SOx in the catalytic converter 30
The NOx catalyst 31 located closer to the inlet 30a of the catalytic converter 30 has a larger SOx absorption amount than the NOx catalyst 31 located farther from the inlet 30a. When releasing SOx, high-temperature exhaust gas having a stoichiometric or rich exhaust air-fuel ratio is supplied from the outlet 30b side of the catalytic converter 30 to the inlet 3b.
When flowing toward the 0a side, SOx can be released in a short time.

Therefore, in this embodiment, the exhaust switching valve 2
0, the flow direction of the exhaust gas in the catalytic converter 30 is switched and controlled, so that the flow of the exhaust gas in the catalytic converter 30 is made to flow forward when NOx and SOx are absorbed, and the exhaust gas in the catalytic converter 30 is released when NOx and SOx are released. The gas flow was reversed.
Further, when the flow of the exhaust gas is reversed, the bank control is performed. The bank control changes the exhaust air-fuel ratio of each cylinder, for example, by controlling some cylinders of the engine 1 to a rich air-fuel ratio and other cylinders to a lean air-fuel ratio, thereby supplying a reducing agent and oxygen to a catalyst, The exhaust gas was made stoichiometric or rich while the temperature was raised by the catalytic reaction, and the catalyst was reduced and regenerated in a high temperature range.

As shown in FIG. 1, the catalytic converter 30 is disposed in the exhaust passage at an inlet 30a of the catalytic converter 30 in order to secure the NOx catalyst bed temperature when the exhaust gas flows forward. The arrangement is located near the valve 20. That is, in the catalytic converter 30, the length of the exhaust passage formed when the flow of the exhaust gas is set to the forward flow (first direction) is such that the exhaust gas flows backward (second direction).
It is arranged at a position that is shorter than the length of the exhaust passage formed when.

Next, the operation of the exhaust gas purifying apparatus according to this embodiment will be described. As described above, the engine 1
Is a lean burn gasoline engine. The air-fuel ratio is controlled by the ECU 100 in accordance with the operating state of the engine 1. When the engine 1 is operated at the lean air-fuel ratio, the exhaust air-fuel ratio becomes lean and the oxygen concentration increases. When the engine 1 is operated at the stoichiometric or rich air-fuel ratio, the exhaust air-fuel ratio becomes stoichiometric or rich, the oxygen concentration in the exhaust gas is significantly reduced, and unburned HC, CO, etc. Component increases.

Therefore, when the engine 1 is operating at a lean air-fuel ratio, the operation of the actuator 21 is controlled by the ECU 100 so that the valve body of the exhaust switching valve 20 is maintained at the forward flow position shown in FIG. Thereby, the exhaust gas of the engine 1 flows in the order of the exhaust pipe 9 → the exhaust pipe 11 → the catalytic converter 30 → the exhaust pipe 12 → the exhaust pipe 10;
It is released to the atmosphere, and the catalytic converter 30 has a forward flow flowing from the inlet 30a to the outlet 30b. At this time, NOx and SOx in the exhaust gas are absorbed by the NOx catalyst 31 of the catalytic converter 30.

When the engine 1 is operated at the stoichiometric or rich air-fuel ratio, the ECU is set so that the valve body of the exhaust switching valve 20 is maintained at the reverse flow position shown in FIG.
100 controls the operation of the actuator 21.
Thus, the exhaust gas of the engine 1 is discharged from the exhaust pipe 9 → the exhaust pipe 12 → the catalytic converter 30 → the exhaust pipe 11 → the exhaust pipe 10.
, And is released to the atmosphere. In the catalytic converter 30, a reverse flow flows from the outlet 30b toward the inlet 30a. Further, when the engine 1 is operated at the stoichiometric or rich air-fuel ratio, the exhaust gas temperature is set so that the exhaust gas temperature at which SOx is easily released from the NOx catalyst 31 is maintained.
The operation of the engine 1 is controlled by U100.

Thus, high-temperature exhaust gas having a stoichiometric or rich air-fuel ratio flows through the catalytic converter 30 with NOx,
As it passes in the opposite direction to that during SOx absorption, NOx
NOx is released from the catalyst 31, and is further reduced and purified to N2 by unburned HC, CO and the like in the exhaust gas. Also, the exhaust gas flows back through the catalytic converter 30,
SOx absorbed by the NOx catalyst 31 can be released from the NOx catalyst 31 in a short time.

Further, when the lean air-fuel ratio operation is continued for a long time depending on the operating conditions of the engine 1, the cylinder 1 of the engine 1 is forcibly controlled to operate at a rich air-fuel ratio and other cylinders at a lean air-fuel ratio. Then, by making the exhaust gas flowing through the exhaust pipe stoichiometric or rich, the NOx and SOx release processing is performed, and the catalytic converter 30 is not saturated with NOx and SOx. In the following description, such an air-fuel ratio control method for the engine 1 will be referred to as cylinder-specific lean / rich spike control.

The cylinder-specific lean / rich spike control will be specifically described with numerical values. The "lean air-fuel ratio operation" of all cylinders of the engine 1 takes several tens of seconds (for example, 40 to 40 seconds).
(For 60 seconds), the "rich air-fuel ratio operation" for enriching some cylinders lasts for several seconds (for example, 2 to 3 seconds), and the "lean air-fuel ratio operation" and the "rich air-fuel ratio operation" are executed alternately. And so on. Regarding the control for each cylinder during the "rich air-fuel ratio operation", when the engine 1 is a four-cylinder engine, for example, the first and fourth cylinders are controlled to be rich and the second and third cylinders are controlled to be lean. Of course, the 1st and 4th cylinders are lean,
The second and third cylinders can be controlled richly.

As described above, the exhaust air-fuel ratio (A / A
By changing F), the reducing agent and oxygen are supplied to the NOx catalyst 31, and while the temperature is raised by the catalytic reaction, the exhaust gas is made stoichiometric or rich, and the NOx catalyst 31 is reduced and regenerated in a high temperature range. According to this control method, the fuel and the air rise by the catalytic reaction, and the catalyst temperature reaches a maximum from the center of the NOx catalyst 31 corresponding to the backflow to the outlet (the inlet 30a). In this region, since the oxygen concentration is also reduced, SOx
The release atmosphere is completed and the NOx catalyst 3
The outlet portion 1 is more easily regenerated. In addition, by adopting a method of controlling a part of the cylinders to a rich air-fuel ratio in order to raise the temperature of the region where the NOx catalyst 31 is highly poisoned with SOx, waste of energy (waste of fuel) is achieved.
Can be eliminated. Therefore, when the SOx poisoning of the NOx catalyst 31 is the forward flow of the exhaust gas, the NOx catalyst 31
The problem of more poisoning can be effectively dealt with with less energy at the entrance portion.

In this embodiment, the lean burn gasoline engine constitutes an internal combustion engine, and the NOx catalyst 31
x absorbent, and SOx is an SOx absorbent (NOx catalyst 3
This constitutes the deposit to be removed from 1). Also, the direction in which the exhaust gas flows in the forward direction is the first direction, and the direction in which the exhaust gas flows in the reverse direction is the second direction. In addition, the exhaust pipe 9, the exhaust pipe 11, the exhaust pipe 12, the exhaust pipe 10, the exhaust switching valve 20, the actuator 21, the ECU 100, and the like constitute exhaust gas backflow means. Further, since the air-fuel ratio (lean or rich) of each exhaust gas required for SOx removal and the exhaust gas temperature (high temperature) are obtained by the operation control of the engine 1, the operation control of the engine 1 is performed in this embodiment. The ECU 100 including the sensors for performing the operation forms a control unit.

In this embodiment, a reducing agent is added to the exhaust passage (ie, the exhaust passage 12 or the exhaust passage 9) located upstream of the catalytic converter 30 when the exhaust gas flowing through the catalytic converter 30 is made to flow backward. When a reducing agent adding device is provided to perform a NOx and SOx release process, a reducing agent is added to the exhaust gas from the reducing agent adding device,
NOx release, reduction, and SOx release may be promoted. In this case, the control means also controls the operation of the reducing agent addition device in addition to the operation control of the engine 1.

In the above-described embodiment, the process of releasing NOx and SOx from the NOx catalyst 31 is performed simultaneously. However, the amount of SOx contained in the exhaust gas of the engine, particularly, the exhaust gas of the gasoline engine is extremely small. NOx
It is not necessary to perform the SOx release process at the same frequency as the SOx release process. Therefore, when performing the NOx release process, even when the engine 1 is in the operating state where the exhaust gas temperature is relatively low even in the stoichiometric or rich air-fuel ratio operating range, the exhaust gas is supplied to the catalytic converter 30 when the NOx is absorbed. NOx is released and reduced from the NOx catalyst 31 while the engine 1 is in the stoichiometric or rich air-fuel ratio operating range and the exhaust gas temperature rises to a high temperature (acceleration). Only when the exhaust gas condition becomes stoichiometric or rich air-fuel ratio favorable for SOx release and at high temperature.
0 is switched to the reverse flow position, and the catalytic converter 30
May be controlled so that the flow of the exhaust gas flowing through the SOFC is reversed, and the SOx release processing is performed.

The NOx catalyst 3 is controlled by the ECU 100.
It is determined whether the SOx release processing is necessary or not. If it is determined that the SOx release processing is not necessary, the flow of the exhaust gas flowing through the catalytic converter 30 is maintained by holding the valve body of the exhaust switching valve 20 at the forward flow position. When it is determined that it is necessary, the valve body of the exhaust switching valve 20 is switched to the reverse flow position, the flow of the exhaust gas flowing through the catalytic converter 30 is reversed, and the ECU 100 sets the optimal target air space for SOx release. Calculate the fuel ratio and the target catalyst temperature, further calculate the target reducing agent amount when the above-described reducing agent adding device is provided, and control the engine 1 and the reducing agent adding device and the like so that these target values are obtained. SOx release processing may be performed. As a method of determining the necessity of the SOx release process, the ECU 100 integrates the operation time of the engine 1 and determines that the SOx release process is necessary when the integrated value reaches a predetermined time.
For example, 0 is integrated with the SOx amount absorbed by the NOx catalyst 31, and when the integrated value reaches a predetermined amount, it is determined that the SOx release process is necessary.

As described above, when the ECU 100 determines that the SOx release process is necessary, the valve position of the exhaust switching valve 20 is switched to reverse the flow of the exhaust gas flowing through the catalytic converter 30. When a part of the cylinders is set to the rich air-fuel ratio operation to release SOx, it is preferable to set the lean air-fuel ratio during the switching operation of the valve body position of the exhaust switching valve 20. This is for the following reason. When switching the valve body from the forward flow position to the reverse flow position, or when switching the reverse, the exhaust switching valve 20 always connects the exhaust pipe 9 and the exhaust pipe 10 during the switching operation as shown in FIG. There is a state of communication. In the state where the exhaust pipe 9 and the exhaust pipe 10 communicate with each other, the exhaust gas may be short-passed from the exhaust pipe 9 to the exhaust pipe 10 due to the flow resistance, and HC and CO in the exhaust may be discharged to the atmosphere. There is. Therefore, in order to minimize HC and CO discharged to the atmosphere during the operation of switching the valve body position of the exhaust switching valve 20, the exhaust air-fuel ratio of all the cylinders is changed during the operation of switching the valve body position of the exhaust switching valve 20. Control to be lean.

[Second Embodiment] Next, a second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIG.
This will be described with reference to FIGS.

FIG. 5 is a diagram showing a schematic configuration of an exhaust gas purifying apparatus for an internal combustion engine according to the second embodiment. The example shown in FIG. 1 shows an example in which the present invention is applied to an exhaust gas purification device for an internal combustion engine in which S traps 40 and 50 are installed upstream of the exhaust gas switching valve 20. In this case, the exhaust manifold
An exhaust manifold 81 corresponding to No. 1 and No. 4 of each cylinder of the engine 1 and an exhaust manifold 82 corresponding to No. 2 and No. 3 are provided.
Exhaust pipes 91 and 92 extend from the exhaust pipes 1 and 82 and join the exhaust pipe 9. Then, in the middle of the exhaust pipe 91, the S trap 40
Is installed, and the S trap 50 is installed in the middle of the exhaust pipe 92. Other configurations are basically the same as those of the first embodiment.

That is, the engine 1 is an in-line four-cylinder lean-burn gasoline engine, in which intake air is supplied to each cylinder through an intake pipe 2 and an intake manifold 3, and the first to fourth cylinders
The fuel is injected from the fuel injection valve 7 into each intake passage connected to each of the cylinders up to the number, and the exhaust gas discharged from each cylinder is exhaust manifolds 81 and 82, exhaust pipes 91 and 92, S traps 40 and 50, and exhaust pipes. Exhaust gas through the intake pipe 2
Is provided with a throttle valve 4 having a throttle position sensor 5 and an air flow meter 6, an exhaust pipe 11 is provided with an exhaust gas temperature sensor 13, the engine 1 is provided with a rotation speed sensor 14, and the throttle position sensor 5, Air flow meter 6, exhaust temperature sensor 13, rotation speed sensor 14
Are output to the ECU 100 and the ECU 100
The operation of the fuel injection valve 7 is controlled based on the output signal from the ECU.

The exhaust pipe 9 is connected to a first port of an exhaust switching valve (flow direction switching means) 20 having four ports, and a second port of the exhaust switching valve 20 is connected to the atmosphere via the exhaust pipe 10. The third port of the exhaust switching valve 20 is connected to the inlet 30a of the catalytic converter 30 via the exhaust pipe 11, and the fourth port of the exhaust switching valve 20 is connected to the outlet 30b of the catalytic converter 30 via the exhaust pipe 12. It is connected.

The reason why the two S traps 40 and 50 are provided is to take into consideration the fact that the present invention employs the concept of changing the exhaust air-fuel ratio for each cylinder. Will be described later.

The S traps 40, 50 contain SOx absorbents 40a, 50a. SOx absorbent 4
0a and 50a are S when the air-fuel ratio of the inflow gas is lean.
It absorbs Ox and releases the absorbed SOx when the oxygen concentration of the inflowing gas is low. This SOx absorbent 40
Examples of the a and 50a include a three-way catalyst, a NOx catalyst having a high SOx absorption ability among storage-reduction NOx catalysts, and a catalyst in which platinum is supported on zeolite.

When the S traps 40 and 50 are provided as described above, when the valve body of the exhaust gas switching valve 20 is set at the forward flow position as shown in FIG.
Since 0,50 is located upstream of the catalytic converter 30, SOx in the exhaust gas is reduced by the S trap 40,
The SOx absorbents 50a and 50a are adsorbed by the SOx absorbents 50 and can prevent the SOx from flowing into the catalytic converter 30.
SOx poisoning of the NOx catalyst 31 of the catalytic converter 30 can be prevented.

In this embodiment, usually,
In the rich spike operation, the flow of the exhaust gas flows forward as shown in FIG. At this time, SOx is absorbed by the SOx absorbents 40a and 50a of the S traps 40 and 50, and SOx is not supplied to the NOx catalyst 31.

However, if the above operation is continued and it is determined that the SOx absorbents 40a and 50a cannot absorb SOx, the operation is switched to the stoichiometric operation and the SOx absorbents 40a and 50a are switched to the stoichiometric operation.
50a is reproduced. At this time, the S traps 40 and 50
Of the NOx catalyst 31 by the SOx discharged from the
In order to prevent poisoning, the valve body of the exhaust switching valve 20 is located at the center as shown in FIG. When it is determined that the vehicle is in the stoichiometric state during acceleration or the like, the operation is similarly bypassed.

When the S traps 40 and 50 are regenerated in this manner, there is almost no flow of exhaust gas to the NOx catalyst 31, but local SOx poisoning proceeds at the inlet of the NOx catalyst 31. Need to be removed.

Therefore, also in this embodiment, the first
As in the case of the embodiment, by operating the exhaust switching valve 20, the flow direction of the exhaust gas in the catalytic converter 30 is switched and controlled, and when NOx and SOx are absorbed, the flow of the exhaust gas in the catalytic converter 30 flows forward. When the S traps 40 and 50 are regenerated, the catalytic converter 30 is bypassed, and when NOx and SOx are released, the flow of the exhaust gas in the catalytic converter 30 is reversed. Further, when the flow of the exhaust gas is reversed, the bank control is performed. The bank control changes the exhaust air-fuel ratio of each cylinder, for example, by controlling some cylinders of the engine 1 to a rich air-fuel ratio and other cylinders to a lean air-fuel ratio, thereby supplying a reducing agent and oxygen to a catalyst, While raising the temperature by the catalytic reaction, the exhaust is stoichiometric or rich,
The NOx catalyst is reduced and regenerated in a high temperature range so that SOx poisoning can be removed.

That is, when the NOx catalyst is subjected to reduction and regeneration in a high temperature range, the operation of the actuator 21 is controlled by the ECU 100 so that the valve body of the exhaust switching valve 20 is maintained at the reverse flow position shown in FIG. Thereby, the engine 1
Exhaust gas from exhaust pipes 91 and 92 → S traps 40 and 5
0 → exhaust pipe 9 → exhaust pipe 12 → catalyst converter 30 → exhaust pipe 11 → exhaust pipe 10 so as to be released to the atmosphere. In the catalytic converter 30, a reverse flow flows from the outlet 30b toward the inlet 30a. Become. Also, Engine 1
NOx and S are controlled by forcibly controlling some of the cylinders to operate at a rich air-fuel ratio and the other cylinders to operate at a lean air-fuel ratio to make the exhaust gas flowing through the exhaust pipe stoichiometric or rich.
Ox release processing is performed, and the catalytic converter 30
Avoid saturation with Ox.

The cylinder-specific lean / rich spike control in the second embodiment will be specifically described with numerical values. The "lean air-fuel ratio operation" of all the cylinders of the engine 1 takes several tens of seconds (for example, 40 to 40 seconds). (For 60 seconds), the "rich air-fuel ratio operation" for enriching some cylinders lasts for several seconds (for example, 2 to 3 seconds), and the "lean air-fuel ratio operation" and the "rich air-fuel ratio operation" are executed alternately. And so on.
Regarding the control for each cylinder during the "rich air-fuel ratio operation", when the engine 1 is a four-cylinder engine, for example, the first and fourth cylinders are controlled to be rich and the second and third cylinders are controlled to be lean.

Here, the two S traps 4
The reason why 0 and 50 are provided is that the present invention adopts a concept of changing the exhaust air-fuel ratio for each cylinder. That is, the exhaust gas of the rich air-fuel ratio from the first and fourth cylinders and the exhaust gas of the lean air-fuel ratio from the second and third cylinders are prevented from mixing on the upstream side of the S traps 40 and 50. In this way, a few
The SOx in the exhaust gas from the No. 2 cylinder is absorbed by the S trap 50, so that the SOx is not supplied from the No. 2 and No. 3 cylinders to the catalytic converter 30.
Oxygen in the lean air-fuel ratio can be supplied to the catalytic converter 30. Further, the reducing components such as HC and CO in the rich air-fuel ratio exhaust gas from the first and fourth cylinders can be supplied to the catalytic converter 30 through the S trap.

As described above, the exhaust air-fuel ratio (A /
By changing F), the reducing agent and oxygen are supplied to the NOx catalyst 31, and while the temperature is raised by the catalytic reaction, the exhaust gas is made stoichiometric or rich, and the NOx catalyst 31 is reduced and regenerated in a high temperature range. According to this control method, the fuel and the air rise by the catalytic reaction, and the catalyst temperature reaches a maximum from the center of the NOx catalyst 31 corresponding to the backflow to the outlet (the inlet 30a). In this region, since the oxygen concentration is also reduced, SOx
The release atmosphere is completed and the NOx catalyst 3
The outlet portion 1 is more easily regenerated. In addition, by adopting a method of controlling a part of the cylinders to a rich air-fuel ratio in order to raise the temperature of a region (local region) where SOx poisoning of the NOx catalyst 31 is large, waste of energy (fuel Waste) can be eliminated. Therefore,
The problem that SOx poisoning of the NOx catalyst 31 becomes more poisonous toward the inlet of the NOx catalyst 31 when exhaust gas flows forward can be effectively dealt with with less energy.

The timing of switching the valve body position of the exhaust switching valve 20, that is, the timing of switching the flow of the exhaust gas flowing through the exhaust gas purifying means between the forward flow and the reverse flow, will be described in the first and second embodiments. The timing is not limited to this.

For example, when the exhaust gas purifying means is the NOx catalyst 31, the NOx catalyst 31
x and SOx are easily absorbed and released when the temperature of the exhaust gas rises. Therefore, when the temperature of the exhaust gas falls, the position of the exhaust switching valve 20 is set to the forward flow position and the exhaust gas is supplied to the NOx catalyst 31. Even when the exhaust gas is heated and the exhaust gas is heated, the valve position of the exhaust switching valve 20 is set to the reverse flow position so that the exhaust gas flows backward to the NOx catalyst 31. Good.

Depending on the type of deposit to be removed from the exhaust gas purifying means, for example, the deposit to be removed may be H2SO
In the case where the floor temperature of the exhaust gas purifying means is decomposed and desorbed when the floor temperature exceeds a predetermined temperature (for example, 400 ° C.) as shown in FIG. 4, the valve position of the exhaust switching valve 20 when the floor temperature is lower than the predetermined temperature. Is set to the forward flow position so that the exhaust gas flows forward in the purifying means, and when the floor temperature becomes equal to or higher than the predetermined temperature, the valve body position of the exhaust switching valve 20 is switched to the reverse flow position so that the exhaust gas is supplied to the exhaust purifying means. The position of the valve body of the exhaust switching valve 20 may be switched and controlled so as to flow in the reverse flow.

[0077]

According to the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect of the present invention, the exhaust gas is caused to flow backward by the exhaust gas backflow means to remove the SOx poisoning of the SOx absorbent disposed in the exhaust passage. In addition, by controlling a part of the cylinders to be rich and the other cylinders to be lean, it is possible to efficiently perform the SOx releasing process without wasting energy at the time of the SOx releasing process of the SOx absorbent.

According to the second means of the present invention, regarding the position of the SOx absorbent in the exhaust passage, the length of the exhaust passage formed when the exhaust gas flows in the first direction moves the exhaust gas in the second direction. By arranging at a position shorter than the length of the exhaust passage formed when flowing, SOx when flowing in the first direction
The temperature of the absorbent (catalyst temperature) can be secured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to a first embodiment of the present invention, showing a state in which an exhaust switching valve is located at a forward flow position.

FIG. 2 is a diagram illustrating main parts when an exhaust gas switching valve is located at a reverse flow position in the exhaust gas purification apparatus according to the first embodiment;

FIG. 3 is a diagram illustrating the NOx absorption / release / reduction action of a storage reduction type NOx catalyst.

FIG. 4 is a diagram illustrating a main part when the exhaust gas switching valve is located at a neutral position between a forward flow position and a reverse flow position in the exhaust gas purification apparatus according to the first embodiment;

FIG. 5 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to a second embodiment of the present invention, showing a state where an exhaust gas switching valve is located at a forward flow position.

FIG. 6 is a diagram illustrating a main part when an exhaust gas switching valve is located at a reverse flow position in the exhaust gas purification apparatus according to the second embodiment.

FIG. 7 is a diagram illustrating a main part when an exhaust gas switching valve is located at a neutral position between a forward flow position and a reverse flow position in the exhaust gas purification apparatus according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lean burn gasoline engine (internal combustion engine) 2 Intake pipe (intake passage) 6 Air flow meter 7 Fuel injection valve 9 Exhaust pipe 10 Exhaust pipe 11 Exhaust pipe 12 Exhaust pipe 13 Exhaust temperature sensor 14 Rotation speed sensor 20 Exhaust switching valve (Flow direction) Switching means) 21 actuator (control means) 30 catalytic converter 31 NOx catalyst (SOx absorbent) 30a inlet 30b outlet 81, 82 exhaust port 91, 92 exhaust pipe 40, 50 S trap 40a, 50a SOx absorbent 100 ECU (control means) )

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/02 325 F02D 41/02 325H 41/04 305 41/04 305A F-term (Reference) 3G091 AA12 AA13 AA17 AA23 AA28 AB03 AB06 AB08 AB09 AB11 AB13 BA04 BA11 BA14 BA15 BA19 BA20 BA33 BA36 CA12 CA13 CA18 CA26 CB02 CB03 CB06 DA01 DA02 DA03 DB06 DB10 EA01 EA05 EA07 EA17 EA18 EA30 EA31 FA04 FA12 FA13 FA04 FB11 FC03 GB02W GB03W GB04W GB05W GB06W GB09X GB09Y GB10X GB16X HA07 HA08 HA11 HA18 HA20 HA21 HA36 HA37 HA38 HB02 HB03 3G301 HA01 HA06 HA15 HA18 JA15 JA25 JA33 JB09 LA01 LB02 MA01 MA11 MA18 NA08 NE01 NE06 NE13 NE11 NE11 PA11 PDB PAB PE01B PE01Z PE03B PE03Z PE05B PE05Z

Claims (2)

[Claims] 1. An SOx absorbent disposed in an exhaust passage of an internal combustion engine that absorbs SOx when the exhaust air-fuel ratio is lean, and releases the absorbed SOx when the oxygen concentration decreases, and absorbs SOx. Sometimes, the exhaust gas passes through the absorbent in the first direction, and when the SOx is released, the exhaust gas passes through the absorbent in a second direction opposite to the first direction. An exhaust purification device for an internal combustion engine, comprising: control means for controlling a part of a cylinder of the internal combustion engine to be rich and another cylinder to be lean when flowing in the second direction. 2. An arrangement position of the SOx absorbent in the exhaust passage is such that a length of an exhaust passage formed when exhaust gas flows in a first direction is formed when exhaust gas flows in a second direction. The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the exhaust gas purifying device is disposed at a position shorter than a length of the exhaust passage.