JP2000328928A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent SOx poisoning of a NOx catalyst by exhaust gas generated from reclamation of a SOx absorbent. SOLUTION: An exhaust switch valve 28 is provided with 4 ports. An exhaust pipe 19 communicated with an engine 1 is connected to the first port through a SOx absorbent 17. An exhaust pipe 24 for discharging the exhaust gas to atmosphere is connected to the second port. An exhaust pipe 25 communicated with an inlet portion 21a of a casing 21 containing a NOx catalyst 20 therein is connected to the third port. An exhaust pipe 26 communicated with an outlet portion 21b of the casing 21 is connected to the fourth port. When reclaiming the SOx absorbent 17, the exhaust switch valve 28 is used to connect the exhaust pipes 19 and 24, and the exhaust pipes 25 and 26 such that the exhaust gas generated from reclamation of the SOx absorbent 17 flows directly from the exhaust pipe 19 to the exhaust pipe 24 without flowing it to the NOx catalyst 20. The exhaust pipes 25 and 26, and the casing 21 and the exhaust switch valve 28 form a closed loop, thus producing no difference between the pressure to the front of the NOx catalyst 20 and the pressure to the rear thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing nitrogen oxides (NO
The present invention relates to an exhaust gas purification device capable of purifying x).

[0002]

2. Description of the Related Art As an exhaust gas purifying apparatus for purifying NOx from exhaust gas discharged from an internal combustion engine capable of lean combustion, there is a NOx absorbent represented by a NOx storage reduction catalyst. N
The Ox absorbent has an air-fuel ratio of the inflowing exhaust gas that is lean (ie,
NOx is absorbed during an oxygen-excess atmosphere, and the absorbed NOx is released when the oxygen concentration of the inflowing exhaust gas decreases. The NOx storage reduction catalyst, which is a type of NOx absorber, air-fuel ratio of the exhaust gas is lean (i.e., under oxygen-rich atmosphere) to absorb NOx when the oxygen concentration of the inflowing exhaust gas is the catalyst for reducing the absorbed NOx release and N ₂ when dropped.

When this storage-reduction type NOx catalyst (hereinafter sometimes simply referred to as a catalyst or NOx catalyst) is disposed in an exhaust passage of an internal combustion engine capable of lean combustion, when exhaust gas having a lean air-fuel ratio flows, the exhaust gas contains NOx is absorbed by the catalyst, and NO is absorbed by the catalyst when exhaust gas having a stoichiometric (stoichiometric air-fuel ratio) or rich air-fuel ratio flows.
x is released as NO ₂ , and HC and C
It is reduced to N ₂ by a reducing component such as O, that is, NOx is purified.

In general, the fuel of an internal combustion engine contains sulfur, and when the fuel is burned in the internal combustion engine, the sulfur in the fuel burns and sulfur oxides such as SO ₂ and SO ₃ (SOx ) Occurs. The storage reduction type NOx catalyst includes N 2
Since SOx in the exhaust gas is absorbed by the same mechanism as that for absorbing Ox, when this NOx catalyst is arranged in the exhaust passage of the internal combustion engine, not only NOx but also SOx is absorbed by the NOx catalyst.

However, the sulfur absorbed by the NOx catalyst
Ox forms stable sulfate over time,
Under the same conditions as those for releasing and reducing NOx from the NOx catalyst, there is a tendency that the NOx catalyst is hardly decomposed and released and is easily accumulated in the catalyst. When the accumulated amount of SOx in the NOx catalyst increases,
The NOx absorption capacity of the catalyst decreases, so that NOx in the exhaust gas cannot be sufficiently removed, and the NOx purification efficiency decreases. This is so-called SOx poisoning.

Therefore, in order to maintain the NOx purifying performance of the NOx storage reduction catalyst high for a long period of time, an SOx absorbent that mainly absorbs SOx in exhaust gas is disposed upstream of the NOx catalyst, An exhaust gas purifying device has been developed which prevents SOx poisoning by preventing SOx from flowing into the catalyst.

[0007] The SOx absorbent, the air-fuel ratio of the inflow gas absorbs SOx when the lean and the SOx when the air-fuel ratio of the inlet gas is absorbed when the stoichiometric air-fuel ratio or rich as to release as SO ₂ However, since the SOx absorbent has a limited SOx absorption capacity, it is necessary to execute a process of releasing SOx from the SOx absorbent before the SOx absorbent is saturated with SOx, that is, a regeneration process.

[0008] Regarding the SOx absorbent regeneration technology,
For example, it is disclosed in Japanese Patent Publication No. 2605580. According to this publication, it is necessary to set the air-fuel ratio of the inflowing exhaust gas to a stoichiometric air-fuel ratio or a rich air-fuel ratio in order to release the SOx absorbed by the SOx absorbent.
It is said that the higher the temperature of the SOx absorbent, the easier it is to release SOx.

Further, in the regeneration treatment technology disclosed in this publication, when SOx is released from the SOx absorbent, the released SOx is prevented from being absorbed by the NOx catalyst disposed downstream. A bypass passage branched from an exhaust pipe connecting the SOx absorbent and the NOx catalyst to bypass the NOx catalyst, and an exhaust switching valve for selectively switching exhaust gas to either the NOx catalyst or the bypass passage. During the regeneration process for releasing SOx from the SOx absorbent, the exhaust gas is caused to flow to the bypass passage by the exhaust switching valve so as not to flow to the NOx catalyst,
When the regeneration process is not being performed, the exhaust gas is caused to flow to the NOx catalyst by the exhaust switching valve so as not to flow to the bypass passage. In this way, during execution of the regeneration process, the SOx released from the SOx absorbent does not flow into the NOx catalyst, so that the NOx catalyst
Poisoning can be prevented.

[0010]

According to the regeneration technology disclosed in the above publication, as described above, when the SOx absorbent is regenerated, the exhaust gas flows through the bypass passage, but the NOx catalyst does not. The exhaust switching valve is switched so as not to flow.

However, the exhaust gas switching valve used here has an imperfect seal, and when exhaust gas is flowing through the bypass passage, the downstream of the NOx catalyst is connected to the atmosphere. Therefore, a pressure difference occurs between the upstream and downstream of the NOx catalyst, and as a result, NO
A small amount of exhaust gas, which should not flow to the x catalyst, leaked from the exhaust switching valve and flowed to the NOx catalyst, though the amount was small. By the way,
The degree of leakage of the currently used exhaust switching valve is 1 to 10
%.

[0012] Thus, the exhaust gas leaking from the exhaust switching valve at the time of reproduction processing of the SOx absorbing material flows into the NOx catalyst, the exhaust gas is the regenerative pumping of the SOx absorbing material SO ₂
Since the concentration is high, the flow rate of the flowing gas is small.
The Ox catalyst poisons SOx.

The present invention has been made in view of such problems of the prior art, and an object of the present invention is to solve the problem of the SOx absorption of the NOx absorption material caused by the regeneration of the SOx absorption material. To prevent poison.

[0014]

The present invention has the following features to attain the object mentioned above. The exhaust gas purifying apparatus for an internal combustion engine according to the present invention is (a) disposed in an exhaust passage of an internal combustion engine capable of lean combustion, and absorbs SOx when the air-fuel ratio of the inflowing exhaust gas is lean, thereby reducing the oxygen of the exhaust gas flowing in. And (b) disposed in the exhaust passage downstream of the SOx absorbent and absorbing NOx when the inflowing exhaust gas has a lean air-fuel ratio. A NOx absorbent that releases NOx absorbed when the oxygen concentration of the inflowing exhaust gas is low; (c) exhaust path switching means disposed between the SOx absorbent and the NOx absorbent; Exhaust path switching means and the N
A first exhaust passage including an Ox absorber and forming a closed loop; and (e) a second exhaust passage provided downstream of the exhaust passage switching unit, wherein the exhaust passage switching unit includes:
The first exhaust passage has a closed loop and the SO
a first path for causing the exhaust gas flowing out of the x-absorbing material to flow through the second exhaust passage while bypassing the first exhaust passage;
The first exhaust passage can be switched to a second passage in which the exhaust gas flowing out of the SOx absorbent is allowed to pass through the first exhaust passage and then flow to the second exhaust passage after the first exhaust passage is closed. It is characterized by.

In the exhaust gas purifying apparatus for an internal combustion engine,
During the regeneration process for releasing the SOx absorbed by the SOx absorbent from the SOx absorbent, the exhaust path switching means is held in the first path. During the regeneration processing of the SOx absorbent, the SOx concentration of the exhaust gas (regenerated exhaust) flowing out of the SOx absorbent becomes high. However, when the exhaust path switching means is held in the first path, the exhaust gas bypasses the NOx absorbent. And discharged through the second exhaust passage. At this time, since the first exhaust passage forms a closed loop together with the exhaust path switching means and the NOx absorbent, the regenerative exhaust gas flows from the exhaust path switching means to the first exhaust path because the sealing performance of the exhaust path switching means is incomplete. Even if the exhaust gas flows into the exhaust passage, the pressure in the closed loop immediately rises and the state becomes equilibrium, so that the flow of the regenerated exhaust gas stops instantaneously. Then, the pressure inside the closed loop becomes equal in the entire region, and there is no pressure difference between the upstream side and the downstream side of the NOx absorbent. Therefore, the regeneration exhaust gas does not flow to the NOx absorbent during the regeneration of the SOx absorbent, and the NOx absorbent does not poison the SOx absorbent.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, examples of the internal combustion engine capable of lean burn include a direct-injection-type lean-burn gasoline engine and a diesel engine. In the case of a lean burn gasoline engine, the air-fuel ratio control of the exhaust gas can be realized by the air-fuel ratio control of the air-fuel mixture supplied to the combustion chamber. In the case of a diesel engine, the air-fuel ratio of exhaust gas is controlled by performing so-called sub-injection of injecting fuel in an intake stroke, an expansion stroke, or an exhaust stroke, or in an exhaust passage upstream of a SOx absorbent or a NOx absorbent. This can be realized by supplying a reducing agent. Here, the air-fuel ratio of the exhaust gas refers to the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage and the exhaust passage upstream of the SOx absorbent or the NOx absorbent.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a NOx storage reduction catalyst can be exemplified as the NOx absorbent. The storage reduction type NOx catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean,
When the oxygen concentration in the exhaust gas flowing in decreases, the absorbed N
Releasing ox, a catalyst for reducing the N _2. The NOx storage reduction catalyst uses, for example, alumina as a carrier, and, for example, potassium K, sodium Na, lithium L
i, alkali metal such as cesium Cs, barium B
a, alkaline earth such as calcium Ca, lanthanum L
a, at least one selected from rare earth elements such as yttrium Y and a noble metal such as platinum Pt are supported.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a storage reduction type NOx catalyst can be exemplified as the SOx absorbent. Further, a three-way catalyst or a selective reduction type NOx catalyst which adsorbs SOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases it stoichiometrically or richly can also be exemplified as the SOx absorbent.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the exhaust path switching means may be constituted by a switching valve having four ports. In that case, the first of the switching valve
The port is connected to the SOx absorbent, the second port is connected to the second exhaust passage, the third port and the fourth port are connected to the first exhaust passage, and the NOx absorbent is connected in the first exhaust passage. And the valve body of the switching valve is held at the first valve body position, so that the first port communicates with the second port and the third port communicates with the fourth port. By holding at the position, the first port and the third port may be communicated and the second port and the fourth port may be communicated.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the length of the flow path from the exhaust path switching means to the outlet of the NOx absorbent is determined by changing the length of the flow path from the exhaust path switching means to the N.
It is preferable that the length be shorter than the flow path length to the inlet of the Ox absorbent. In this case, the regeneration exhaust gas flows into the first exhaust passage due to imperfect sealing performance of the exhaust path switching means during regeneration of the SOx absorbent, and the NOx absorbent is slightly poisoned by the SOx. In addition, the poisoning site can be specified on the outlet side of the NOx absorbent. SOx poisoning at the outlet side of the NOx absorbent is easier to recover from SOx poisoning (release of SOx) than when SOx poisoning is performed at the inlet side.

Further, as described above, when the flow path length from the exhaust path switching means to the outlet of the NOx absorbent is shortened, the SOx absorbed by the SOx absorbent is released.
During the regeneration process of the absorbent, the exhaust path switching means is held in the first path, and after the regeneration processing of the SOx absorbent, the exhaust path switching means is switched to the second path. For each of the cylinders, cylinder-by-cylinder air-fuel ratio control that burns at a rich air-fuel ratio and burns at a lean air-fuel ratio for other cylinders may be executed. As described above, when the cylinder-by-cylinder air-fuel ratio control is performed, the reducing agent is oxidized in the NOx absorbent, so that the outlet side of the NOx absorbent can be heated to a higher temperature. In addition, recovery from SOx poisoning becomes easier.

[0022]

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 FIGS.

First Embodiment First, a first embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration in a case where the present invention is applied to a gasoline engine for a vehicle capable of lean combustion. In this figure, reference numeral 1 denotes an engine body,
2 is a piston, 3 is a combustion chamber, 4 is a spark plug,
Reference numeral 5 indicates an intake valve, reference numeral 6 indicates an intake port, reference numeral 7 indicates an exhaust valve, and reference numeral 8 indicates an exhaust port.

The intake port 6 is connected to a surge tank 10 via a corresponding branch pipe 9, and each branch pipe 9 is provided with a fuel injection valve 11 for injecting fuel into the intake port 6. The surge tank 10 is connected to an air cleaner 14 via an intake duct 12 and an air flow meter 13, and a throttle valve 15 is arranged in the intake duct 12.

On the other hand, the exhaust port 8 is connected to the exhaust manifold 16.
The exhaust port of the casing 18 is connected to a first port of an exhaust switching valve (exhaust path switching means) 28 having four ports via an exhaust pipe 19. Have been. Exhaust switching valve 2
The second port 8 is connected to an exhaust pipe (second exhaust passage) 24 for discharging exhaust gas to the atmosphere.
The port is connected through an exhaust pipe (first exhaust passage) 25 to an inlet 21a of a casing 21 containing a storage-reduction type NOx catalyst (NOx absorbent) 20, and a fourth port of the exhaust switching valve 28 is connected to an exhaust pipe. The first exhaust passage 26 is connected to the outlet 21 b of the casing 21 via a first exhaust passage 26. Hereinafter, the storage reduction type NOx catalyst 20 is abbreviated as the NOx catalyst 20. SOx
The absorbent 17 and the NOx catalyst 20 will be described later in detail.
In this embodiment, the length of the exhaust pipe 25 (flow path length)
Is set shorter than the length of the exhaust pipe 26 (flow path length).

The valve element of the exhaust switching valve (exhaust flow switching means) 28 is operated by an actuator 27 in accordance with a command from an electronic control unit (hereinafter abbreviated as ECU) 30 for engine control. More specifically, the valve body of the exhaust gas switching valve 28 connects the exhaust pipe 25 and the exhaust pipe 26 to form a closed loop as shown in FIG. An actuator is selected by selecting one of a body position and a second valve body position connecting the exhaust pipe 19 and the exhaust pipe 25 and connecting the exhaust pipe 26 and the exhaust pipe 24 as shown in FIG. 2
7 actuated.

By switching the valve position of the exhaust switching valve 28, the exhaust gas discharge path is determined. First, when the valve body of the exhaust switching valve 28 is at the first valve body position as shown in FIG. 1, a first path through which exhaust gas flows from the exhaust pipe 19 to the exhaust pipe 24 is formed. At this time, since both the exhaust pipe 25 and the exhaust pipe 26 are separated from the exhaust pipes 19 and 24,
Exhaust gas does not flow into these exhaust pipes 25 and 26.
Further, even if some exhaust gas leaks into the exhaust pipes 25 and 26 due to imperfect sealing of the exhaust switching valve 28,
Since the exhaust pipe 25 and the exhaust pipe 26 form a closed loop together with the casing 21 and the exhaust switching valve 28, the pressure inside the exhaust pipe 19 is instantaneously balanced in this closed loop, and the inflow of exhaust gas stops. In addition, since the pressure inside the closed loop is equal and there is no pressure difference between the inlet 21a and the outlet 21b of the casing 21, the exhaust gas does not flow in the NOx catalyst 20.

When the valve body of the exhaust switching valve 28 is located at the second valve body position as shown in FIG. 2, the exhaust gas flows from the exhaust pipe 19 through the exhaust pipe 25 through the NOx catalyst 20 and further to the exhaust pipe 26. A second path which flows from the exhaust pipe 24 to the exhaust pipe 24 is formed.

The ECU 30 is composed of a digital computer, and ROMs connected to each other by a bidirectional bus 31.
(Read Only Memory) 32, RAM (Random Access Memory) 33, CPU (Central Processor Unit) 34, Input Port 35, Output Port 36. The air flow meter 13 generates an output voltage proportional to the amount of intake air, and this output voltage is input to an input port 35 via an AD converter 37.

On the other hand, the exhaust pipe 1 downstream of the SOx absorbent 17
A temperature sensor 23 that generates an output voltage proportional to the temperature of the exhaust gas that has passed through the SOx absorbent 17 is attached to the inside of the A / D converter 9.
Through the input port 35. The input port 35 is connected to a rotation speed sensor 41 that generates an output pulse indicating the engine rotation speed. The output port 36 is connected to the ignition plug 4, the fuel injection valve 11, and the actuator 27 via a corresponding drive circuit 39, respectively.

In this gasoline engine, the fuel injection time TAU is calculated based on, for example, the following equation. TAU = TP · K Here, TP indicates a basic fuel injection time, and K indicates a correction coefficient. The basic fuel injection time TP indicates a fuel injection time required for setting the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder to the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained in advance by an experiment, and the engine load Q / N
As a function of (intake air amount Q / engine speed N) and engine speed N, the ROM 3 is previously stored in the form of a map as shown in FIG.
2 is stored. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder. If K = 1.0, the air-fuel mixture supplied to the engine cylinder becomes the stoichiometric air-fuel ratio. On the other hand, if K <1.0, the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, the air-fuel ratio becomes a lean air-fuel ratio.
If> 1.0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes smaller than the stoichiometric air-fuel ratio, that is, a rich air-fuel ratio.

In the gasoline engine of this embodiment,
In the engine low-medium load operation region, the value of the correction coefficient K is set to a value smaller than 1.0, and the lean air-fuel ratio control is performed, and the engine high load operation region, the warm-up operation when starting the engine, the acceleration,
And at a constant speed operation of 120 km / h or more, the value of the correction coefficient K is set to 1.0 and the stoichiometric air-fuel ratio control is performed. Then, rich air-fuel ratio control is performed.

In an internal combustion engine, low-medium load operation is usually performed most frequently. Therefore, during most of the operation period, the value of the correction coefficient K is made smaller than 1.0, and the lean mixture is burned. become.

FIG. 4 schematically shows the concentration of typical components in the exhaust gas discharged from the combustion chamber 3. As can be seen from this figure, the concentration of unburned HC and CO in the exhaust gas discharged from the combustion chamber 3 increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes richer. The concentration of oxygen O _{2 in} the discharged exhaust gas increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes leaner.

NOx contained in casing 21
The catalyst 20 has, for example, alumina as a carrier, on which potassium K, sodium Na, lithium Li, alkali metal such as cesium Cs, barium Ba, alkaline earth such as calcium Ca, lanthanum La, yttrium Y At least one selected from such rare earths and a noble metal such as platinum Pt are supported. The ratio of air and fuel (hydrocarbon) supplied into the engine intake passage and the exhaust passage upstream of the NOx catalyst 20 is referred to as the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 (hereinafter referred to as the exhaust air-fuel ratio). The NOx catalyst 20 absorbs NOx when the exhaust air-fuel ratio is lean, and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases.
Performs the absorption and release action.

When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NOx catalyst 20, the exhaust air-fuel ratio matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3. Therefore, in this case, the NOx catalyst 2
When the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is lean, 0 absorbs NOx, and releases the absorbed NOx when the oxygen concentration of the air-fuel mixture supplied into the combustion chamber 3 decreases.

The detailed mechanism of the NOx absorption / release operation of the NOx catalyst 20 is not clear in some parts. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking platinum Pt and barium Ba supported on a carrier as an example.
The same mechanism is obtained by using an alkali metal, an alkaline earth, or a rare earth.

That is, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration of the inflowing exhaust gas greatly increases, and the oxygen O ₂ becomes O ₂ ⁻ or O ²⁻ as shown in FIG. On the surface of platinum Pt. On the other hand, NO contained in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ).

Next, a part of the generated NO ₂ is absorbed in the NOx catalyst 20 while being oxidized on the platinum Pt and combined with the barium oxide BaO, and as shown in FIG. NO ₃ ^- diffuses into the NOx catalyst 20 in the form of. In this way, NOx is absorbed in the NOx catalyst 20.

As long as the oxygen concentration of the inflowing exhaust gas is high, platinum P
As long as NO ₂ is generated on the surface of t and the NOx absorption capacity of the NOx catalyst 20 is not saturated, NO ₂ is absorbed in the NOx catalyst 20 and nitrate ions NO ₃ ⁻ are generated.

On the other hand, when the oxygen concentration of the inflowing exhaust gas decreases and the NO ₂ generation amount decreases, the reaction proceeds in the opposite direction (N
O ₃ ⁻ → NO ₂ ), and nitrate ions N in the NOx catalyst 20
O ₃ ^- is released from the main catalyst 20 in the form of NO ₂ or NO. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NOx is released from the NOx catalyst 20.
As shown in FIG. 4, when the degree of leanness of the inflowing exhaust gas decreases, the oxygen concentration of the inflowing exhaust gas decreases. Therefore, when the degree of leanness of the inflowing exhaust gas decreases, NOx decreases.
NOx is released from the catalyst 20.

On the other hand, at this time, when the mixture supplied to the combustion chamber 3 is made stoichiometric or rich and the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, as shown in FIG. Unburned HC and CO are discharged, and these unburned HC and CO are separated from oxygen O ₂ ^- or O ^2- on platinum Pt.
And oxidize.

When the exhaust air-fuel ratio reaches the stoichiometric air-fuel ratio or the rich air-fuel ratio, the oxygen concentration of the inflowing exhaust gas is extremely reduced, so that NO ₂ or NO is released from the NOx catalyst 20, and this NO ₂ or NO As shown in FIG. 5 (B), it reacts with unburned HC and CO to be reduced to N ₂ .

[0044] 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 by CO is made to reduction to N _2.

In this way, NO _{2 is} deposited on the surface of platinum Pt.
Alternatively, when NO is no longer present, NO ₂ or NO is released from the NOx catalyst 20 one after another, and is further reduced to N ₂ . Therefore, if the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio, the NOx catalyst 2
NOx will be released from zero.

As described above, when the exhaust air-fuel ratio becomes lean, NOx is absorbed by the NOx catalyst 20, and when the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio, the NOx becomes NOx catalyst 2.
0 is released in a short time from being reduced to N _2. Therefore, emission of NOx into the atmosphere can be prevented.

In this embodiment, as described above, the mixture supplied to the combustion chamber 3 is set to the rich air-fuel ratio at the time of full load operation, and at the time of high load operation and warm-up operation at engine start. When the vehicle is accelerating, and when operating at a constant speed of 120 km / h or more, the air-fuel mixture is set to the stoichiometric air-fuel ratio. When the engine is operated at low to medium load, the air-fuel mixture is set to the lean air-fuel ratio. The NOx is absorbed by the NOx catalyst 20, and is released and reduced from the NOx catalyst 20 during the full load operation and the high load operation. However, if the frequency of full load operation or high load operation is low, the frequency of low / medium load operation is high, and the operation time is long, NO
x release / reduction cannot be performed in time,
The absorption capacity of Ox is saturated and NOx cannot be absorbed.

Therefore, in this embodiment, when the lean air-fuel mixture is being burned, that is, when the low-to-medium load operation is being performed, the stoichiometric or rich stoichiometric or rich operation is performed in a relatively short cycle. The air-fuel ratio of the air-fuel mixture is controlled so that the air-fuel mixture is burned, and NOx is released and reduced in a short cycle. As described above, the exhaust air-fuel ratio (in this embodiment, the air-fuel ratio of the air-fuel mixture) is used to absorb and release NOx.
In the following description, it is referred to as "lean-rich spike control" in which "lean" and "spike-like stoichiometric air-fuel ratio or rich air-fuel ratio" are alternately repeated in a relatively short cycle. In this application, the lean-rich spike control is included in the lean air-fuel ratio control.

On the other hand, the fuel contains sulfur (S), and when the sulfur in the fuel burns, sulfur oxides (SOx) such as SO ₂ and SO ₃ are generated, and the NOx catalyst 20 These SOx also absorb. It is considered that the SOx absorption mechanism of the NOx catalyst 20 is the same as the NOx absorption mechanism. That is, assuming that platinum Pt and barium Ba are supported on the carrier in the same manner as when the NOx absorption mechanism is described, as described above, when the exhaust air-fuel ratio is lean, oxygen O ₂ is reduced. O ₂ ^- or O ^2-
The SOx (for example, SO ₂ ) in the inflowing exhaust gas becomes platinum Pt in the form of
Is oxidized to SO ₃ on the surface.

[0050] Then, SO ₃ produced while being further oxidized on the surface of the platinum Pt and is absorbed in the NOx catalyst 20 bonding with the barium oxide BaO, the NOx catalyst 20 to the sulfuric acid ion SO ₄ ^2-form Diffuses to produce sulfate BaSO ₄ . The sulfate BaSO ₄ is stable and hard to decompose, and is not decomposed even if the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio for a short time due to the rich spike in the lean-rich spike control described above. NO
x It remains in the catalyst 20. Therefore, if the amount of BaSO ₄ generated in the NOx catalyst 20 increases with the passage of time, the amount of BaO that can participate in the absorption of the NOx catalyst 20 decreases, and the NOx absorption capacity decreases. This is SOx
Poisoning.

In order to prevent SOx from flowing into the NOx catalyst 20, this exhaust purification system absorbs SOx when the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio and changes the air-fuel ratio of the inflowing exhaust gas to the stoichiometric air-fuel ratio. Alternatively, when the oxygen concentration decreases due to the rich air-fuel ratio, the absorbed SOx is released.
The Ox absorbent 17 is disposed upstream of the NOx catalyst 20. This SOx absorbent 17 is the SOx absorbent 1
When the air-fuel ratio of the exhaust gas flowing into the exhaust gas 7 is a lean air-fuel ratio, NOx is absorbed together with SOx, but when the air-fuel ratio of the flowing exhaust gas becomes a stoichiometric air-fuel ratio or a rich air-fuel ratio and the oxygen concentration decreases, the absorbed SOx Not only does it release NOx.

As described above, in the NOx catalyst 20, SOx
Is absorbed to produce stable sulfate BaSO ₄ ,
As a result, even if the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 is set to the stoichiometric air-fuel ratio or rich, the SOx becomes smaller than the NOx catalyst 2.
It is no longer released from zero. Therefore, the SOx absorbent 1
In order to release SOx from the SOx absorbent 17 when the air-fuel ratio of the exhaust gas flowing into the exhaust gas 7 is set to the stoichiometric air-fuel ratio or rich, the absorbed SOx is converted to sulfate ions SO ₄
Or exist in the SOx absorbent 17 in the form of ^2-
Alternatively, even when sulfate BaSO ₄ is generated, it is necessary that the sulfate BaSO ₄ be present in the SOx absorbent 17 in an unstable state. S that makes this possible
As the Ox absorber 17, a transition metal such as copper Cu, iron Fe, manganese Mn and nickel Ni, sodium Na, titanium Ti and lithium L
An SOx absorbent 17 carrying at least one selected from i can be used.

In this SOx absorbent 17, the SOx absorbent 1
Air-fuel ratio of the exhaust gas flowing into the 7 is absorbed while SO ₂ in the exhaust gas is oxidized on the surface of the SOx absorbent 17 in the sulfate ions SO ₄ ^2-form in the SOx absorbent 17 when the lean,
Next, it is diffused into the SOx absorbent 17. In this case, S
Platinum Pt, palladium Pd,
If any of rhodium Rh is supported, SO
₂ platinum Pt in SO ₃ ^2-form, palladium Pd, easily adsorbed on the rhodium Rh, thus SO ₂ is likely to be absorbed in the SOx absorbent 17 in the sulfate ions SO ₄ ^2-form.
Therefore, in order to promote the absorption of SO ₂ , it is preferable that any one of platinum Pt, palladium Pd, and rhodium Rh be carried on the carrier of the SOx absorbent 17.

When the SOx absorbent 17 is arranged upstream of the NOx catalyst 20, when the air-fuel ratio of the exhaust gas flowing into the SOx absorbent 17 becomes lean, the SOx in the exhaust gas is absorbed by the SOx absorbent 17, so that Downstream NOx catalyst 2
At 0, SOx does not flow, and the NOx catalyst 20 absorbs only NOx in the exhaust gas.

On the other hand, the SOx absorbed by the SOx absorbent 17 as described above sulfate ions SO ₄ ^{2 -} a form in either diffuse the SOx absorbing material 17, or sulfate BaSO ₄ in an unstable state ing. Therefore, the SOx absorbent 1
When the air-fuel ratio of the exhaust gas flowing into the exhaust gas 7 becomes the stoichiometric air-fuel ratio or rich and the oxygen concentration decreases, the SOx absorbed by the SOx absorbent 17 is easily released from the SOx absorbent 17.

By the way, according to the research of the present applicant, SOx
The following has been found regarding the absorption / release action of the absorbent 17.
When the amount of SOx absorbed by the SOx absorbent 17 is small, the SOx absorbent 17 has a strong SOx adsorbing power,
If exhaust gas having a stoichiometric or rich air-fuel ratio is allowed to flow through the x absorbent 17 for a short time (for example, 5 seconds or less), SOx is not released from the SOx absorbent 17. Regarding this, the applicant has determined that the rich spike duration during lean / rich spike control performed to release NOx from the NOx catalyst 20 when the SOx amount absorbed in the SOx absorbent 17 is small. It has been confirmed that SOx is not released from the SOx absorbent 17. However, the SOx absorbent 17
Even when the amount of SOx absorbed in
When exhaust gas having a stoichiometric or rich air-fuel ratio flows through the Ox absorbent 17 for a long time, the SOx absorbent 17
Is released.

However, when the amount of SOx absorbed by the SOx absorbent 17 increases, the SOx adsorbing power of the SOx absorbent 17 becomes weak, so that the exhaust gas of the stoichiometric or rich air-fuel ratio is supplied to the SOx absorbent 17 for a short time. Even when flowing, SOx leaks out of the SOx absorbent 17 and the downstream NOx
There is a possibility that the catalyst 20 may be poisoned.

Therefore, in this embodiment, the SOx absorbed by the SOx absorbent 17 is determined from the history of the operating state of the engine.
The amount is estimated, the time when the estimated SOx absorption amount reaches a predetermined amount is determined as the regeneration time of the SOx absorbent 17, and a regeneration process for releasing SOx from the SOx absorbent 17 is executed. SOx
When the regeneration process of the absorbent 17 is performed, the ECU 30
Determines the engine operating state at that time from the engine speed N and the engine load Q / N, and substitutes the exhaust gas temperature at that time detected by the temperature sensor 23 as the temperature of the SOx absorbent 17 to determine the engine operating state. Based on the temperature of the SOx absorbent 17, a stoichiometric or rich condition and a processing time capable of releasing SOx most efficiently with little deterioration in fuel efficiency are selected, and the exhaust gas under the selected air-fuel ratio condition is supplied to the SOx absorbent 17 for the selected processing time. Run by flowing.

It is known that the temperature of the SOx absorbent 17 needs to be higher than a predetermined temperature (for example, 550 ° C.) in order to release the SOx from the SOx absorbent 17, and the ECU 30 During execution of the regeneration process of the SOx absorbent 17, the temperature of the exhaust gas is controlled by appropriate means to control the temperature of the SOx absorbent 17 above the predetermined temperature (hereinafter referred to as the SOx release temperature).

When the SOx absorbent 17 is regenerated, a large amount of SOx released from the SOx absorbent 17 is added to the exhaust gas flowing out of the SOx absorbent 17 (hereinafter referred to as regenerated exhaust).
When the regenerated exhaust gas flows into the NOx catalyst 20, SOx in the regenerated exhaust gas is absorbed by the NOx catalyst 20, and the NOx catalyst 20 is poisoned with SOx.
There is no point in providing the x-absorbing material 17. Therefore, in this exhaust gas purification apparatus, in order to prevent the SOx released from the SOx absorbent 17 from being absorbed by the NOx catalyst 20 at the time of the regeneration processing of the SOx absorbent 17, the exhaust switching is performed at the time of the regeneration processing of the SOx absorbent 17. As shown in FIG. 1, the valve body of the valve 28 is held at the first valve body position so that the exhaust gas flows through the first path, and the regeneration exhaust gas does not flow through the NOx catalyst 20.

If the valve body of the exhaust switching valve 28 is held at the first valve body position during the regeneration processing of the SOx absorbent 17, the regenerated exhaust gas flows from the exhaust pipe 19 to the exhaust pipe 24. The regeneration exhaust does not flow into the exhaust pipes 25 and 26. Further, even if a small amount of regenerated exhaust gas leaks into the exhaust pipes 25 and 26 due to imperfect sealing of the exhaust switching valve 28, the exhaust pipes 25 and 26 form a closed loop together with the casing 21 and the exhaust switching valve 28. Therefore, the inside of the closed loop is instantaneously equilibrated with the pressure in the exhaust pipe 19 and the flow of the regenerated exhaust gas is stopped. In addition, since the pressure inside the closed loop is equal and there is no pressure difference between the inlet 21a and the outlet 21b of the casing 21, the flow of the regeneration exhaust gas does not occur in the NOx catalyst 20. Therefore, SOx poisoning of the NOx catalyst 20 during the regeneration processing of the SOx absorbent 17 can be prevented.

On the other hand, during the non-regeneration process of the SOx absorbent 17, the valve body of the exhaust switching valve 28 is held at the second valve body position as shown in FIG. Run down the path. That is, when the exhaust pipe 19 is connected to the exhaust pipe 25 and the exhaust pipe 26 is connected to the exhaust pipe 24 while the valve body of the exhaust switching valve 28 is located at the second valve body position, the exhaust gas flows from the exhaust pipe 19 to the exhaust pipe 25. Through the NOx catalyst 20, and the exhaust gas passing through the NOx catalyst 20 further flows through the exhaust pipe 26 to the exhaust pipe 24. When the exhaust gas flows in the second path in this way, the exhaust gas becomes SOx
The exhaust gas passes through the absorbent 17 and the NOx catalyst 20 in order. When the lean / rich spike controlled exhaust gas passes through the SOx absorbent 17, SOx in the exhaust gas is absorbed by the SOx absorbent 17, and thereafter, the SOx
When the exhaust gas from which x has been removed flows through the NOx catalyst 20, N
Oxon absorption / release / reduction purification is performed.

[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 FIGS. In the above-described first embodiment, the length of the exhaust pipe 25 is set shorter than the length of the exhaust pipe 26, and the inlet 21a of the casing 21 is disposed closer to the exhaust switching valve 28 than the outlet 21b. But
In the second embodiment, as shown in FIG. 6, the length of the exhaust pipe 26 is set shorter than the length of the exhaust pipe 25, and the outlet 21b of the casing 21 is set to be smaller than the inlet 21a. It is located near 28. This is the only structural difference between the first embodiment and the second embodiment.

The outlet 21b of the casing 21 is connected to the inlet 2
Advantages of the arrangement closer to the exhaust switching valve 28 than 1a will be described below. As described in the first embodiment, the NOx catalyst 21 is regenerated by holding the valve element of the exhaust gas switching valve 28 at the first valve element position shown by the solid line in FIG. 6 during the regeneration processing of the SOx absorbent 17. Even if the exhaust gas does not flow, the regenerated exhaust gas flows from the exhaust gas switching valve 28 to the exhaust pipe 2 due to imperfect sealing of the exhaust gas switching valve 28.
It is conceivable that there is a case where the leakage occurs at 5, 26. However, even if the regenerative exhaust gas leaks into the exhaust pipes 25 and 26, the inside of the closed loop formed by the casing 21, the exhaust pipes 25 and 26, and the exhaust switching valve 28 instantaneously balances the pressure in the exhaust pipe 19. Since the flow of the regeneration exhaust gas stops and no pressure difference occurs between the inlet 21a and the outlet 21b of the casing 21, N
The regeneration exhaust should not flow through the Ox catalyst 20.

However, if the lengths of the exhaust pipes 25 and 26 are absolutely short, the regenerated exhaust may reach the end of the NOx catalyst 20 before the inflow of the regenerated exhaust stops. Even if the regenerated exhaust gas does not directly reach the NOx catalyst 20, the regenerated exhaust gas once entering the exhaust pipes 25 and 26 is discharged during the regeneration of the SOx absorbent 17 by the exhaust switching valve 28.
As long as the valve body of the exhaust pipe 2 is held at the first valve body position.
Exhaust pipes 25 and 2
It is conceivable that the staying regenerated exhaust gas gradually diffuses and reaches the end of the NOx catalyst 20. In this case, the end of the NOx catalyst 20 on the side closer to the exhaust pipe having the shorter pipe length should be susceptible to SOx poisoning. Therefore, the length of the exhaust pipe 25 is
6 is shorter than the length of the exhaust pipe 25, the end of the NOx catalyst 20 closer to the inlet 21a of the casing 21 is susceptible to SOx poisoning. The catalyst 20 is provided at the outlet 21 b of the casing 21.
Is more susceptible to SOx poisoning.

Here, if the end of the NOx catalyst 20 on the side close to the inlet 21a of the casing 21 is poisoned by SOx, after the SOx absorbent 17 is regenerated, the valve body of the exhaust gas switching valve 28 is switched to the second valve. By switching to the valve body position and flowing lean / rich spike controlled exhaust gas through the second path,
The poisoned SOx on the inlet side of the NOx catalyst 20 is decomposed when the rich spike exhaust gas flows, and the decomposed SOx becomes N
The NOx catalyst 20 moves downstream of the Ox catalyst 20 and is adsorbed again by the NOx catalyst 20, so that SOx cannot be released from the NOx catalyst 20 only by being diffused widely throughout the NOx catalyst 20.

On the other hand, when the end of the NOx catalyst 20 near the outlet 21b of the casing 21 is poisoned by SOx, after the regeneration process of the SOx absorbent 17, the valve body of the exhaust switching valve 28 Is switched to the second valve body position (indicated by a broken line in FIG. 6), and when the exhaust gas subjected to the lean / rich spike control flows through the second path, the NOx catalyst 20
SOx was poisoned to the outlet side of decomposed when flowing the exhaust gas of a rich spike, is released from the NOx catalyst 20 becomes SO _2.

Therefore, as in the second embodiment, the length of the exhaust pipe 26 is made shorter than the length of the exhaust pipe 25, and the outlet side of the NOx catalyst 20 is made smaller than the inlet side.
A value closer to 8 is advantageous in that even if the NOx catalyst 20 is poisoned by SOx in the process of regenerating the SOx absorbent 17, it is easy to release the poisoned SOx.

When the length of the exhaust pipe 26 is shorter than the length of the exhaust pipe 25, the valve body of the exhaust switching valve 28 after the regeneration process of the SOx absorbent 17 is indicated by the second broken line in FIG. When the exhaust gas is caused to flow through the second path by switching to the valve body position for a predetermined time immediately after the switching of the exhaust path by the exhaust switching valve 28, the temperature is equal to or higher than the SOx release temperature as in the case of the regeneration of the SOx absorbent 17 It is preferable to control the exhaust gas having a high stoichiometric or rich air-fuel ratio to flow, and to switch the air-fuel ratio control of the exhaust gas to the lean-rich spike control after the predetermined time has elapsed.

In this way, the SOx in the regenerated exhaust gas flowing into the exhaust pipe 25 during the regeneration processing of the SOx absorbent 17 and staying in the exhaust pipe 25 during the regeneration processing is changed by the exhaust switching valve 28. Since the gas passes through the NOx catalyst 20 together with the stoichiometric or rich air-fuel ratio exhaust gas flowing immediately after the switching of the exhaust path, it is possible to prevent the SOx in the regeneration exhaust from poisoning the NOx catalyst 20. Moreover,
Exhaust gas with high temperature and stoichiometric or rich air-fuel ratio is NO
Decompose SOx poisoned on the outlet side of x catalyst 20
discharge.

Further, as described above, when the exhaust gas having the stoichiometric or rich air-fuel ratio flows for a predetermined time immediately after the exhaust path is switched by the exhaust switching valve 28 after the regeneration processing of the SOx absorbent 17, the cylinder-by-cylinder air It is more effective to control the exhaust gas air-fuel ratio by the fuel ratio control. This will be described with reference to FIG.

FIG. 7 shows an example of a four-cylinder engine.
Reference numerals 1A, 1B, 1C, and 1D denote cylinders of the first cylinder, the second cylinder, the third cylinder, and the fourth cylinder, respectively, and the exhaust manifold 16A of the first cylinder and the exhaust manifold 16D of the fourth cylinder are SOx absorbents 17 respectively. Casing 18 with built-in
A, exhaust manifolds 16B and 3 of the second cylinder
The exhaust manifold 16C of the cylinder No. 2 is connected to a casing 18B containing a SOx absorbent 17 therein.
A and the casing 18B are connected to a first port of an exhaust switching valve 28 via an exhaust pipe 19. The configuration downstream of the exhaust switching valve 28 is the same as that shown in FIG.

In this internal combustion engine, the exhaust switching valve 28
7, the regeneration process of the SOx absorbent 17 of the casing 18A and the SOx absorbent 17 of the casing 18B is performed at the same time while maintaining the first valve position shown by the solid line in FIG. 7 is switched to the second valve body position indicated by the broken line in FIG. 7, and at the same time, the first and fourth cylinders are operated at a lean air-fuel ratio, and the second and third cylinders are operated at a rich air-fuel ratio. The air-fuel ratio control for each cylinder is executed to make the air-fuel ratio of the entire exhaust gas stoichiometric or slightly rich (slightly rich).

In this way, both casings 18A,
Since the SOx absorbent 17B of 18B is in a state immediately after the regeneration process and almost no SOx is adsorbed, the rich air-fuel ratio exhaust gas discharged from the cylinder 1B of the second cylinder and the cylinder 1C of the third cylinder is supplied to the casing 18B. SOx absorber 1
Reducing agent (HC, CO, etc.) in exhaust gas when passing through 7
Without exhausting the exhaust pipe 19
Leaked to On the other hand, when the lean air-fuel ratio exhaust gas discharged from the first cylinder 1A and the fourth cylinder 1D passes through the SOx absorbent 17 of the casing 18A, the SOx in the exhaust gas is adsorbed by the SOx absorbent 17. The exhaust gas having a lean air-fuel ratio from which SOx has been removed flows into the exhaust pipe 19. The exhaust gas having the lean air-fuel ratio and the exhaust gas having the rich air-fuel ratio are supplied from the exhaust pipe 19 to the exhaust switching valve 28 and the exhaust pipe 2.
5 flows into the casing 21 through the NOx catalyst 2
At 0, a large amount of oxygen contained in the exhaust gas having a lean air-fuel ratio reacts with a large amount of a reducing agent (such as HC or CO) contained in the exhaust gas having a rich air-fuel ratio to generate reaction heat. Since this reaction involves the flow of exhaust gas, the NOx catalyst 20 tends to have higher heat on the downstream side than on the upstream side. Therefore, if the cylinder-by-cylinder air-fuel ratio control is performed in this manner, NO
Since the outlet side of the x catalyst 20 that is poisoned by SOx can be heated to a high temperature, the poisoned SOx at the outlet side of the NOx catalyst 20 can be more reliably decomposed and released. It should be noted that the above-described cylinder-by-cylinder air-fuel ratio control is not limited to a four-cylinder engine, but is also possible with a six-cylinder engine or the like.

[Other Embodiments] In each of the embodiments described above, the present invention is applied to a gasoline engine. However, it goes without saying that the present invention can be applied to a diesel engine. In the case of a diesel engine, the combustion in the combustion chamber is performed in a much leaner region than the stoichiometric air-fuel ratio.
In addition, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 is very lean, and although SOx and NOx are absorbed, SOx and NOx are hardly released.

In the case of a gasoline engine, the air-fuel mixture supplied to the combustion chamber 3 is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio as described above, so that the exhaust gas flowing into the SOx absorbent 17 and the NOx catalyst 20 is reduced. The air-fuel ratio can be set to the stoichiometric air-fuel ratio or the rich air-fuel ratio to release SOx and NOx absorbed by the SOx absorbent 17 and the NOx catalyst 20, but in the case of a diesel engine,
If the air-fuel mixture supplied to the combustion chamber is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio, there is a problem that soot is generated at the time of combustion and cannot be adopted.

Therefore, when the present invention is applied to a diesel engine, in order to make the air-fuel ratio of the inflowing exhaust gas a stoichiometric air-fuel ratio or a rich air-fuel ratio, separately from burning fuel to obtain engine output. It is necessary to supply a reducing agent (for example, light oil as a fuel) into the exhaust gas. The supply of the reducing agent to the exhaust gas can be performed by sub-injecting the fuel into the cylinder during the intake stroke, the expansion stroke, or the exhaust stroke, or the reducing agent can be supplied into the exhaust passage upstream of the SOx absorbent 17. Is also possible.

When a diesel engine is provided with an exhaust gas recirculation device (so-called EGR device),
By introducing a large amount of exhaust gas recirculation gas into the combustion chamber, it is possible to make the air-fuel ratio of the exhaust gas a stoichiometric air-fuel ratio or a rich air-fuel ratio.

[0079]

According to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, (a) an SOx absorbent disposed in an exhaust passage of an internal combustion engine capable of lean combustion, and (b) a downstream side from the SOx absorbent. A NOx absorbent disposed in the exhaust passage of
(C) exhaust path switching means disposed between the SOx absorbent and the NOx absorbent; and (d) a first loop capable of forming a closed loop including the exhaust path switching means and the NOx absorbent.
(E) a second exhaust path provided downstream of the exhaust path switching means, wherein the exhaust path switching means sets the first exhaust path in a closed loop and absorbs the SOx. A first exhaust gas that flows out of the material and flows into the second exhaust passage while bypassing the first exhaust passage;
Path and the first exhaust passage in a non-closed loop
Since the exhaust gas flowing out of the Ox absorbent can be switched to a second path through which the exhaust gas passes through the first exhaust passage and then flows into the second exhaust passage, NOx can be generated during the regeneration processing of the SOx absorbent. An excellent effect is obtained that the SOx poisoning of the absorber can be almost completely prevented.

Further, when the exhaust path switching means sets the NO
If the length of the flow path to the outlet of the x absorbent is shorter than the length of the flow path from the exhaust path switching means to the inlet of the NOx absorbent, the NOx absorbent may be lost during the regeneration process of the SOx absorbent. Even when SOx is poisoned, the SOx
Can be easily released, and recovery from SOx poisoning can be facilitated.

Further, the exhaust path switching means is held in the first path during the regeneration processing of the SOx absorbent, and after the regeneration processing of the SOx absorbent, the exhaust path switching means is switched to the second path. When performing cylinder-by-cylinder air-fuel ratio control in which some cylinders of an internal combustion engine burn at a rich air-fuel ratio and other cylinders burn at a lean air-fuel ratio, the exit side of the NOx absorbent is heated to a high temperature. Therefore, recovery from SOx poisoning when the NOx absorbent is SOx poisoned during the regeneration processing of the SOx absorbent can be promoted.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
FIG. 3 is a schematic configuration diagram of an embodiment of the present invention, showing a state where a first path is set by an exhaust path switching unit.

FIG. 2 is a main part configuration diagram showing a state in which the exhaust gas purification apparatus according to the first embodiment is set to a second path by exhaust path switching means.

FIG. 3 is a diagram showing an example of a map of a basic fuel injection time.

FIG. 4 shows unburned HC in exhaust gas discharged from the engine,
FIG. 3 is a diagram schematically showing the concentrations of CO and oxygen.

FIG. 5 is a diagram for explaining the NOx absorbing / releasing action of a storage reduction type NOx catalyst.

FIG. 6 shows a second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
It is a principal part block diagram in embodiment.

FIG. 7 is a schematic configuration diagram showing a modified example of the exhaust gas purification device of the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 engine body (internal combustion engine) 3 combustion chamber 4 spark plug 11 fuel injection valve 16, 19 exhaust pipe (exhaust passage) 17 SOx absorbent 20 NOx catalyst (NOx absorbent) 24 exhaust pipe (second exhaust passage) 25, 26 exhaust pipe (first exhaust passage) 28 exhaust switching valve (exhaust path switching means) 30 ECU

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/20 F01N 3/24 ZABE 3/28 301C 3/24 ZAB F02D 41/02 301H 3/28 301 41/04 305A F02D 41/02 301 305C 41/04 305 B01D 53/36 D 101A F term (reference) 3G091 AA02 AA11 AA12 AA13 AA17 AA18 AA23 AA24 AA28 AB03 AB05 AB06 AB08 AB09 BA04 BA11 BA14 BA15 BA19 BA33 CA02 CA13 CB02 DA02 DA03 DA04 DB10 EA01 EA05 EA07 EA17 FA04 FA12 FA13 FA14 FA17 FA18 FB03 FB10 FB11 FB12 FC02 FC08 GB01X GB01Y GB02W GB02Y GB03W GB04W GB05W GB05Y GB06W GB06Y GB07Y GB10X GB10Y GB16HA02 HA18 H01 HA03 HA02 HA18 HA03 HA02 HA18 HA03 MA01 MA12 PA01Z PD11Z PE01Z 4D048 AA06 AB02 BA03X BA14X BA15X BA18X BA30X BA41X CC25 CC26 DA02 DA06 EA04

Claims (3)

[Claims] (1) The exhaust gas is disposed in an exhaust passage of an internal combustion engine capable of lean combustion and absorbs SOx when the air-fuel ratio of the inflowing exhaust gas is lean and absorbs it when the oxygen concentration of the inflowing exhaust gas is low. An SOx absorber that releases SOx, (b)
NOx is disposed in the exhaust passage downstream of the SOx absorbent and when the inflowing exhaust gas has a lean air-fuel ratio.
A NOx absorbent for absorbing NOx and releasing the NOx absorbed when the oxygen concentration of the inflowing exhaust gas is low;
Exhaust path switching means disposed between the absorbent and the NOx absorbent; (d) a first exhaust passage capable of forming a closed loop including the exhaust path switching means and the NOx absorbent;
(E) a second exhaust path provided downstream of the exhaust path switching means, wherein the exhaust path switching means makes the first exhaust path a closed loop and exhaust gas flowing out of the SOx absorbent. A first path for allowing gas to flow through the second exhaust path by bypassing the first exhaust path, and a first path for closing the first exhaust path to allow the exhaust gas flowing out of the SOx absorbent to flow into the first exhaust path. An exhaust gas purifying apparatus for an internal combustion engine, which is switchable to a second path that passes through the exhaust path and then flows to the second exhaust path. 2. A flow path length from said exhaust path switching means to an outlet of said NOx absorbent is shorter than a flow path length from said exhaust path switching means to said NOx absorbent inlet. 2. The exhaust gas purification device for an internal combustion engine according to claim 1. 3. The exhaust path switching means is held in the first path during the regeneration processing of the SOx absorbent for releasing the SOx absorbed by the SOx absorbent, and the exhaust path switching is performed after the regeneration processing of the SOx absorbent. The means is switched to the second path, and cylinder-by-cylinder air-fuel ratio control is performed in which some cylinders of the internal combustion engine burn at a rich air-fuel ratio and other cylinders burn at a lean air-fuel ratio. An exhaust purification device for an internal combustion engine according to claim 2.