JP3473496B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitrogen oxide (NO) from exhaust gas discharged from an internal combustion engine capable of lean combustion.
x) is related to an exhaust gas purification device.

[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 a lean air-fuel ratio (that is,
It absorbs NOx in an oxygen excess atmosphere) and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases. The NOx storage-reduction type NOx catalyst, which is a kind of this NOx absorbent, It is a catalyst that absorbs NOx when the air-fuel ratio of the exhaust gas is lean (that is, in an oxygen-excess atmosphere), releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases, and reduces it to N ₂ .

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

By the way, generally, the fuel of an internal combustion engine contains a sulfur content, and when the fuel is burned in the internal combustion engine, the sulfur content in the fuel is burned and sulfur oxides (SOx) such as SO ₂ and SO ₃ are burned. ) Occurs. The storage reduction type NOx catalyst is N
Since SOx in the exhaust gas is absorbed by the same mechanism that absorbs 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 this NOx catalyst.

However, the S absorbed by the NOx catalyst is
Ox forms a stable sulfate with the passage of time,
Under the same conditions as when NOx is released and reduced from the NOx catalyst, it is difficult to decompose and release, and tends to accumulate in the catalyst. When the amount of SOx accumulated in the NOx catalyst increases,
Since the NOx absorption capacity of the catalyst decreases, NOx in the exhaust gas cannot be sufficiently removed, and the NOx purification efficiency decreases. This is the so-called SOx poisoning.

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

The SOx absorbing material absorbs SOx when the air-fuel ratio of the inflow gas is lean and releases the absorbed SOx as SO ₂ when the air-fuel ratio of the inflow gas is the stoichiometric air-fuel ratio or rich. However, since the SOx absorption capacity of this SOx absorbent is also limited, it is necessary to perform a process of releasing SOx from the SOx absorbent, that is, a regeneration process before the SOx absorbent is saturated with SOx.

Regarding the SOx absorbent reprocessing technology,
For example, it is disclosed in the patent publication of Japanese Patent No. 2605580. According to this publication, in order to release the SOx absorbed by the SOx absorber, the air-fuel ratio of the inflowing exhaust gas needs to be the stoichiometric air-fuel ratio or the rich air-fuel ratio.
It is said that the higher the temperature of the SOx absorbent, the easier the SOx is released.

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 arranged downstream. In addition, a bypass passage that branches from the exhaust pipe connecting the SOx absorbent and the NOx catalyst to bypass the NOx catalyst is provided, and an exhaust switching valve that selectively switches the exhaust gas to either the NOx catalyst or the bypass passage is provided. When the regeneration process for releasing SOx from the SOx absorbent is performed, the exhaust switching valve causes the exhaust gas to flow to the bypass passage so that it does not flow to the NOx catalyst.
When the regeneration process is not executed, the exhaust gas is made to flow to the NOx catalyst by the exhaust switching valve so that it does not flow to the bypass passage. With this configuration, during the regeneration process, the SOx released from the SOx absorbent does not flow into the NOx catalyst.
Can prevent poisoning.

[0010]

According to the regeneration processing technique 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 that it does not flow.

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

As described above, when the exhaust gas leaking from the exhaust switching valve flows to the NOx catalyst during the regeneration process of the SOx absorbent, this exhaust gas is the regeneration exhaust of the SOx absorbent and SO ₂
Since the concentration is high, the inflowing gas flow rate is very small, but N
The Ox catalyst is poisoned by SOx.

The present invention has been made in view of the above problems of the prior art, and the problem to be solved by the present invention is to solve the problem of SOx absorption of NOx absorbent caused by regeneration of SOx absorbent. To prevent poison.

[0014]

The present invention adopts the following means in order to solve the above problems. The exhaust gas purification 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, absorbs SOx when the air-fuel ratio of the inflowing exhaust gas is lean, and oxygen of the inflowing exhaust gas. An SOx absorbent that releases absorbed SOx when the concentration is low, and (b) is arranged in the exhaust passage downstream of the SOx absorbent and absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx absorbent that releases NOx absorbed when the oxygen concentration of the inflowing exhaust gas is low; (c) an exhaust path switching means arranged between the SOx absorbent and the NOx absorbent; Exhaust path switching means and the N
The exhaust path switching means includes a first exhaust path that can form a closed loop including an Ox absorbent, and (e) a second exhaust path provided downstream of the exhaust path switching means.
The first exhaust passage is closed loop and the SO
x A first path for flowing the exhaust gas flowing out of the absorbent material to the second exhaust passage by bypassing the first exhaust passage,
It is possible to switch to a second path in which the exhaust gas flowing out of the SOx absorbent is made to be a non-closed loop in the first exhaust passage after passing through the first exhaust passage and then to the second exhaust passage. Is characterized by.

In this exhaust gas purification apparatus for an internal combustion engine,
During the regeneration process in which the SOx absorbed by the SOx absorbent is released from the SOx absorbent, the exhaust path switching means is held in the first path. During the regeneration process of the SOx absorbent, the SOx concentration of the exhaust gas (regenerated exhaust) flowing out from the SOx absorbent increases, but if the exhaust path switching means is held in the first path, this recycled exhaust bypasses the NOx absorbent. And is discharged through the second exhaust passage. Further, at this time, since the first exhaust passage forms a closed loop together with the exhaust path switching means and the NOx absorbent, the regenerated exhaust gas is exhausted from the exhaust path switching means to the first exhaust path switching means due to incomplete sealing property of the exhaust path switching means. Even if it flows into the exhaust passage, the pressure in the closed loop immediately rises and enters a balanced state, so that the flow of regenerated exhaust gas stops instantaneously. Then, the pressure in the closed loop becomes equal throughout, 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 regeneration of the SOx absorbent, and the NOx absorbent is not poisoned by SOx.

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 combustion include a direct injection type lean burn gasoline engine and a diesel engine. In the case of a lean burn gasoline engine, air-fuel ratio control of exhaust gas can be realized by air-fuel ratio control of air-fuel mixture supplied to the combustion chamber. The air-fuel ratio control of the exhaust gas in the case of a diesel engine is performed by so-called sub-injection in which fuel is injected in the intake stroke, the expansion stroke, or the exhaust stroke, or in the exhaust passage upstream of the SOx absorbent or NOx absorbent. It can be realized by supplying a reducing agent. Here, the air-fuel ratio of the exhaust gas means the ratio of air and fuel (hydrocarbons) supplied into the exhaust passage upstream of the engine intake passage and the SOx absorbent or the NOx absorbent.

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the NOx absorbent may be a NOx storage reduction catalyst. The NOx storage reduction catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean,
N absorbed when the oxygen concentration in the inflowing exhaust gas decreases
It is a catalyst that releases Ox and reduces it to N ₂ . This occlusion reduction type NOx catalyst uses, for example, alumina as a carrier, and 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 earths such as yttrium Y, and a noble metal such as platinum Pt are supported.

In the exhaust gas purification 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 that adsorbs SOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases it in a stoichiometric or rich manner or a selective reduction type NOx catalyst can 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 composed of 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 provided in the middle of the first exhaust passage. Is arranged to hold the valve body of the switching valve at the first valve body position so that the first port and the second port communicate with each other and the third port and the fourth port communicate with each other, and the second valve body By holding it in the position, the first port and the third port may communicate with each other and the second port and the fourth port may communicate with each other.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the flow path length from the exhaust path switching means to the outlet of the NOx absorbent is determined from the exhaust path switching means to the N
It is preferably shorter than the flow path length to the inlet of the Ox absorbent. In such a case, during regeneration of the SOx absorbent, the regeneration exhaust flows into the first exhaust passage due to the incomplete sealing property of the exhaust path switching means, so that the NOx absorbent is slightly poisoned by SOx. Also, the poisoning place can be specified on the outlet side of the NOx absorbent. SOx poisoning on the outlet side of the NOx absorbent is easier to recover from SOx poisoning (release of SOx) than when the inlet side is poisoned by SOx.

Further, when the flow path length from the exhaust path switching means to the outlet of the NOx absorbent is shortened as described above, the SOx absorbed in 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 SOx absorbent regeneration processing, the exhaust path switching means is switched to the second path, and a part of the cylinders of the internal combustion engine is also used. For the above, the cylinder-by-cylinder air-fuel ratio control may be executed in which the combustion is performed at the rich air-fuel ratio and the other cylinders are burned at the lean air-fuel ratio. In this way, when the cylinder-by-cylinder air-fuel ratio control is executed, the outlet side of the NOx absorbent can be raised to a higher temperature due to the oxidizing of the reducing agent in the NOx absorbent, and the outlet side of the NOx absorbent is poisoned by SOx. In addition, recovery from SOx poisoning becomes easier.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments 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 of FIGS.

[First Embodiment] First, a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 is a diagram showing a schematic configuration when the present invention is applied to a gasoline engine for a vehicle capable of lean combustion. In this figure, reference numeral 1 is the engine body,
Reference numeral 2 is a piston, reference numeral 3 is a combustion chamber, reference numeral 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
Is connected to a casing 18 having a built-in SOx absorber 17, and an outlet portion of the casing 18 is connected via an exhaust pipe 19 to a first port of an exhaust gas switching valve (exhaust path switching means) 28 having four ports. Has been done. Exhaust gas switching valve 2
The second port of No. 8 is connected to an exhaust pipe (second exhaust passage) 24 for discharging exhaust gas to the atmosphere, and the third port of the exhaust switching valve 28 is connected to the third port.
The port is connected through an exhaust pipe (first exhaust passage) 25 to an inlet portion 21a of a casing 21 containing a NOx storage reduction catalyst (NOx absorbent) 20, and a fourth port of the exhaust switching valve 28 is an exhaust pipe. It is connected to the outlet portion 21 b of the casing 21 via the (first exhaust passage) 26. Hereinafter, the NOx storage reduction catalyst 20 is abbreviated as the NOx catalyst 20. SOx
The absorber 17 and the NOx catalyst 20 will be described in detail later.
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 the actuator 27 according to a command from an electronic control unit (hereinafter abbreviated as ECU) 30 for engine control. More specifically, the valve element of the exhaust switching valve 28 is a first valve that connects the exhaust pipe 25 and the exhaust pipe 26 to form a closed loop and connects the exhaust pipe 19 and the exhaust pipe 24 as shown in FIG. The body position and the 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. Two
It is activated by 7.

By switching the valve position of the exhaust switching valve 28, the exhaust gas exhaust path is determined. First, when the valve body of the exhaust gas switching valve 28 is set to 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 the exhaust pipe 25 and the exhaust pipe 26 are both 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 the incomplete sealing property 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 gas switching valve 28, the pressure in the exhaust pipe 19 is instantly equilibrated in the closed loop and the inflow of exhaust gas is stopped. In addition, since the pressure inside the closed loop is equal and there is no pressure difference between the inlet portion 21a and the outlet portion 21b of the casing 21, no exhaust gas flow occurs in the NOx catalyst 20.

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

The ECU 30 comprises a digital computer, and ROMs connected to each other by a bidirectional bus 31.
A (read only memory) 32, a RAM (random access memory) 33, a CPU (central processor unit) 34, an input port 35, and an output port 36 are provided. The air flow meter 13 generates an output voltage proportional to the intake air amount, and this output voltage is input to the input port 35 via the AD converter 37.

On the other hand, the exhaust pipe 1 downstream of the SOx absorber 17
A temperature sensor 23, which generates an output voltage proportional to the temperature of the exhaust gas that has passed through the SOx absorbent 17, is attached inside 9, and the output voltage of this temperature sensor 23 is an AD converter 38.
Is input to the input port 35 via. Further, the input port 35 is connected to a rotation speed sensor 41 that generates an output pulse representing the engine rotation speed. The output port 36 is connected to the spark 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 the following equation, for example. TAU = TP · K Here, TP indicates the basic fuel injection time, and K indicates the correction coefficient. The basic fuel injection time TP indicates the fuel injection time required to make the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained by an experiment in advance, 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.
It is stored in 2. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder, and if K = 1.0, the air-fuel mixture supplied to the engine cylinder has a stoichiometric air-fuel ratio. On the other hand, when K <1.0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, the lean air-fuel ratio, and K
When> 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, the 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 to perform lean air-fuel ratio control, and the engine high load operation region, warm-up operation at engine start, 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 theoretical air-fuel ratio control is performed, and in the engine full load operation region, the value of the correction coefficient K is larger than 1.0. It is set so that the rich air-fuel ratio control is performed.

In an internal combustion engine, a low-medium-load operation is usually most frequently performed, and therefore, the correction coefficient K is made smaller than 1.0 in most of the operating period to burn the lean air-fuel mixture. become.

FIG. 4 schematically shows the concentrations of typical components in the exhaust gas discharged from the combustion chamber 3. As can be seen from this figure, the concentrations of unburned HC and CO in the exhaust gas discharged from the combustion chamber 3 increase 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 exhaust gas discharged increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes leaner.

NOx contained in the casing 21
The catalyst 20 uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, an alkaline earth such as barium Ba, calcium Ca, lanthanum La, and yttrium Y are supported on the carrier. 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 abbreviated as 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.
It absorbs and releases.

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
0 absorbs NOx when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 3 is lean, and releases the absorbed NOx when the oxygen concentration of the air-fuel mixture supplied to the combustion chamber 3 decreases.

The detailed mechanism of the action of NOx absorption and release by the NOx catalyst 20 is not clear at all. However, it is considered that this absorbing and releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking as an example the case where platinum Pt and barium Ba are supported on a carrier, but other noble metals,
The same mechanism can be achieved by using alkali metals, alkaline earths and rare earths.

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 as shown in FIG. 5 (A), oxygen O ₂ becomes O ₂ ⁻ or O ^{2 −.} It adheres to the surface of platinum Pt in the form of. On the other hand, NO contained in the inflowing exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ).

Next, a part of the generated NO ₂ is absorbed on the NOx catalyst 20 while being oxidized on the platinum Pt and is bonded to the barium oxide BaO, as shown in FIG. 5 (A). It diffuses in the NOx catalyst 20 in the form of NO ₃ ⁻ . 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 ion NO ₃ ⁻ is generated.

On the other hand, when the oxygen concentration of the inflowing exhaust gas decreases and the amount of NO ₂ produced decreases, the reaction proceeds in the opposite direction (N
O ₃ ^- → NO ₂₎ proceeds to nitrate ions N of 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 lean degree of the inflowing exhaust gas is low, the oxygen concentration of the inflowing exhaust gas is low. Therefore, when the leaning degree of the inflow exhaust gas is low, NOx is reduced.
NOx is released from the catalyst 20.

On the other hand, at this time, when the air-fuel mixture supplied into 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 oxygen O ₂ ⁻ or O ²⁻ on platinum Pt.
It reacts with and is oxidized.

When the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the NOx catalyst 20 releases NO ₂ or NO because the oxygen concentration of the inflowing exhaust gas extremely decreases, and this NO ₂ or NO is As shown in FIG. 5B, it reacts with unburned HC and CO and is 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 the consumption of
NOx discharged from the NOx catalyst and NOx discharged from the engine are reduced to N ₂ by C and CO.

In this way, NO ₂ is formed 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 further reduced to N ₂ . Therefore, when the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio, the NOx catalyst 2 is exhausted within a short time.
NOx will be released from 0.

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 becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, NOx becomes the NOx catalyst 2.
It is released from 0 in a short time and reduced to N ₂ . Therefore, it is possible to prevent the emission of NOx into the atmosphere.

In this embodiment, as described above, the air-fuel mixture supplied to the combustion chamber 3 has a rich air-fuel ratio during full load operation, and during high load operation and during warm-up operation during engine startup. During acceleration, acceleration, and constant speed operation of 120 km / h or more, the air-fuel mixture has a stoichiometric air-fuel ratio, and during low-medium load operation, the air-fuel mixture has a lean air-fuel ratio, so NOx in the exhaust gas during low-medium-load operation It is absorbed by the NOx catalyst 20, and NOx is released and reduced from the NOx catalyst 20 during full load operation and high load operation. However, if the frequency of full load operation or high load operation is low and the frequency of low and medium load operation is high and the operation time is long, NO
The release and reduction of x cannot be done in time, and the N of the NOx catalyst 20
The absorption capacity of Ox is saturated and NOx cannot be absorbed.

Therefore, in the present embodiment, when the lean air-fuel mixture is being burned, that is, when the low-medium load operation is being performed, the stoichiometric or rich condition is spiked (short-time) 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. In this way, the exhaust air-fuel ratio (air-fuel ratio of the air-fuel mixture in this embodiment) is used for intake and release of NOx.
In the following description, the lean / rich spike control is referred to as "lean" and "spike theoretical 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 sulfur in the fuel burns, sulfur oxides (SOx) such as SO ₂ and SO ₃ are generated, and the NOx catalyst 20 is contained in the exhaust gas. These SOx are also absorbed. The SOx absorption mechanism of the NOx catalyst 20 is considered to be the same as the NOx absorption mechanism. That is, when the platinum Pt and barium Ba are carried on the carrier as an example similar to the case of explaining the NOx absorption mechanism, as described above, when the exhaust air-fuel ratio is lean, the oxygen O ₂ is O ₂ ^- or O ^2-
Is adhered to the surface of platinum Pt of the NOx catalyst 20, and SOx (for example, SO ₂ ) in the inflowing exhaust gas is platinum Pt.
Is oxidized to SO ₃ on the surface of.

Thereafter, the produced SO ₃ is absorbed in the NOx catalyst 20 while being further oxidized on the surface of platinum Pt and is bonded to barium oxide BaO, and is absorbed in the NOx catalyst 20 in the form of sulfate ion SO ₄ ^2−. It diffuses to form the sulfate salt BaSO ₄ . This sulfate BaSO ₄ is stable and difficult to decompose, and is not decomposed even if the air-fuel ratio of the inflowing exhaust gas is changed 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 production amount of BaSO _{4 in} the NOx catalyst 20 increases with the lapse 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
It is poisoned.

Therefore, in this exhaust emission control device, when the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio, the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio so that SOx does not flow into the NOx catalyst 20. Or when the rich air-fuel ratio is reached and the oxygen concentration drops, the absorbed SOx is released S
The Ox absorbent 17 is arranged 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 7 is a lean air-fuel ratio, it also absorbs NOx together with SOx, but when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio and the oxygen concentration decreases, the absorbed SOx Not only is NOx released.

As described above, the NOx catalyst 20 uses SOx.
Is absorbed, stable sulfate BaSO ₄ is produced,
As a result, even if the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 is stoichiometric or rich, the SOx will be NOx catalyst 2
It will not be released from 0. Therefore, SOx absorber 1
In order for SOx to be released from the SOx absorber 17 when the air-fuel ratio of the exhaust gas flowing into 7 is made to be the stoichiometric air-fuel ratio or rich, the absorbed SOx is sulfate ion SO ₄
^To exist in the SOx absorbent 17 in the form of ^2-
Alternatively, even if the 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 absorbent 17, a transition metal such as copper Cu, iron Fe, manganese Mn, nickel Ni, sodium Na, titanium Ti and lithium L are formed on a carrier made of alumina.
The SOx absorbent 17 supporting at least one selected from i can be used.

In this SOx absorbent 17, the SOx absorbent 1
When the air-fuel ratio of the exhaust gas flowing into 7 is lean, SO ₂ in the exhaust gas is absorbed in the SOx absorbent 17 in the form of sulfate ions SO ₄ ²⁻ while being oxidized on the surface of the SOx absorbent 17,
Then, it is diffused in the SOx absorbent 17. In this case, S
On the carrier of the Ox absorbent 17, platinum Pt, palladium Pd,
If one of rhodium Rh is carried, SO
₂ is easily adsorbed on platinum Pt, palladium Pd, and rhodium Rh in the form of SO ₃ ²⁻ , and thus SO ₂ is easily absorbed in the SOx absorbent 17 in the form of sulfate ion SO ₄ ²⁻ .
Therefore, in order to promote the absorption of SO ₂ , it is preferable to carry any of platinum Pt, palladium Pd, and rhodium Rh on the carrier of the SOx absorbent 17.

When this 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
SOx does not flow into 0, 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, SOx absorber 1
When the air-fuel ratio of the exhaust gas flowing into 7 becomes the stoichiometric air-fuel ratio or becomes rich and the oxygen concentration decreases, the SOx absorbed in the SOx absorbent 17 is easily released from the SOx absorbent 17.

By the way, according to the research by the present applicant, SOx
The following has been found regarding the absorbing and releasing action of the absorbent material 17.
When the amount of SOx absorbed by the SOx absorbent 17 is small, the SOx adsorption force of the SOx absorbent 17 is strong, so
Even 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. With respect to this, the present applicant considers that the rich spike duration time in the lean rich spike control performed to release NOx from the NOx catalyst 20 when the SOx amount absorbed by the SOx absorbent 17 is small. It has been confirmed that SOx is not released from the SOx absorber 17. However, SOx absorber 17
Even when the amount of SOx absorbed in S is small, S
When a stoichiometric or rich air-fuel ratio exhaust gas is passed through the Ox absorbent 17 for a long period of time,
Is released.

However, when the amount of SOx absorbed by the SOx absorbent 17 increases, the SOx adsorption force of the SOx absorbent 17 becomes weaker, so that the exhaust gas having a stoichiometric or rich air-fuel ratio is supplied to the SOx absorbent 17 for a short time. Even if it flows, SOx leaks from the SOx absorbent 17 and NOx in the downstream is leaked.
There is a risk of poisoning the catalyst 20.

Therefore, in this embodiment, the SOx absorber 17 absorbs the SOx absorbed from the history of the operating state of the engine.
The amount of the SOx absorbent 17 is estimated, and when the estimated amount of SOx absorbed reaches a predetermined amount, it is determined that the SOx absorbent 17 is to be regenerated, and a regeneration process for releasing SOx from the SOx absorbent 17 is executed. SOx
When executing the regeneration process of the absorber 17, 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 detected at that time 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, the stoichiometric or rich conditions and the processing time that can release SOx most efficiently with less deterioration in fuel consumption are selected, and the exhaust gas under the selected air-fuel ratio condition is selected as the SOx absorbent 17 for the selected processing time. Run by running.

Further, it is known that in order to release SOx from the SOx absorbent 17, it is necessary to raise the temperature of the SOx absorbent 17 to a high temperature above a predetermined temperature (for example, 550 ° C.). During the regeneration process of the SOx absorbent 17, the temperature of the exhaust gas temperature is controlled by an appropriate means to control the temperature of the SOx absorbent 17 to the predetermined temperature (hereinafter, referred to as SOx release temperature) or higher.

When the SOx absorbent 17 is regenerated, a large amount of SOx released from the SOx absorbent 17 is included in the exhaust gas flowing out from the SOx absorbent 17 (hereinafter referred to as regeneration exhaust gas).
Therefore, if this regenerated exhaust flows into the NOx catalyst 20, the SOx in the regenerated exhaust is absorbed by the NOx catalyst 20, and the NOx catalyst 20 is poisoned by SOx, and SO
x The meaning of providing the absorbing material 17 is lost. Therefore, in this exhaust emission control device, in order to prevent the SOx released from the SOx absorbent 17 from being absorbed by the NOx catalyst 20 during the regeneration processing of the SOx absorbent 17, the exhaust switching is performed during the regeneration processing of the SOx absorbent 17. The valve element of the valve 28 is held at the first valve element position as shown in FIG. 1 so that the exhaust gas is allowed to flow through the first path and the NOx catalyst 20 is prevented from flowing with the regenerated exhaust gas.

If the valve body of the exhaust gas switching valve 28 is held at the first valve body position while the SOx absorbent 17 is being regenerated as described above, 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 some regeneration exhaust gas leaks into the exhaust pipes 25 and 26 due to the incomplete sealing property of the exhaust switch valve 28, the exhaust pipes 25 and 26 form a closed loop together with the casing 21 and the exhaust switch valve 28. Therefore, the pressure in the exhaust pipe 19 is instantly balanced in the closed loop to stop the inflow of the regenerated exhaust gas. Moreover, since the pressure inside the closed loop is equal and there is no pressure difference between the inlet portion 21a and the outlet portion 21b of the casing 21, the flow of regenerated exhaust gas does not occur in the NOx catalyst 20. Therefore, it is possible to prevent SOx poisoning of the NOx catalyst 20 during the regeneration process of the SOx absorbent 17.

On the other hand, during the non-regeneration process of the SOx absorbent 17, the valve body of the exhaust gas switching valve 28 is held at the second valve body position as shown in FIG. Run down the path. That is, when the valve body of the exhaust switching valve 28 is set to the second valve body position to connect the exhaust pipe 19 and the exhaust pipe 25 and the exhaust pipe 26 and the exhaust pipe 24, the exhaust gas flows from the exhaust pipe 19 to the exhaust pipe 25. The exhaust gas flowing through the NOx catalyst 20 and passing through the NOx catalyst 20 further flows out to the exhaust pipe 24 through the exhaust pipe 26. When the exhaust gas is caused to flow in the second path in this way, the exhaust gas becomes SOx.
The absorbent 17 and the NOx catalyst 20 are sequentially passed and discharged. When the lean-rich spike-controlled exhaust gas passes through the SOx absorbent 17, the SOx in the exhaust gas is absorbed by the SOx absorbent 17, and then the SOx is absorbed.
When the exhaust gas from which x has been removed flows through the NOx catalyst 20, N
Ox 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. 6 and 7. 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 arranged 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 portion 21b of the casing 21 is set to be smaller than the inlet portion 21a. It is placed 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
The advantage of arranging it closer to the exhaust gas 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 body of the exhaust gas switching valve 28 at the first valve body position shown by the solid line in FIG. 6 during the regeneration process of the SOx absorbent 17. Even if the exhaust gas does not flow in, the regenerated exhaust gas flows from the exhaust gas switching valve 28 to the exhaust pipe 2 due to the incomplete sealing property of the exhaust gas switching valve 28.
There is a possibility that it may leak into 5, 26. However, even if the regenerated exhaust gas leaks into the exhaust pipes 25 and 26, the pressure inside the exhaust pipe 19 is instantaneously balanced in the closed loop formed by the casing 21, the exhaust pipes 25 and 26, and the exhaust gas switching valve 28. Since the inflow of the regeneration exhaust is stopped and there is no pressure difference between the inlet portion 21a and the outlet portion 21b of the casing 21, N
No regeneration exhaust should 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 is stopped. Further, even if the regenerated exhaust does not directly reach the NOx catalyst 20, the regenerated exhaust that has once entered the exhaust pipes 25, 26 is not exhausted while the SOx absorbent 17 is being regenerated.
The exhaust pipe 2 as long as the valve body is held in the first valve body position.
The exhaust pipes 25, 2 are not discharged from the exhaust pipes 5, 26.
It is conceivable that the exhaust gas stays in the inside of the NOx catalyst 6, and the accumulated regeneration exhaust gas gradually diffuses and reaches the end portion of the NOx catalyst 20. In this case, the end portion of the NOx catalyst 20 on the side closer to the exhaust pipe having the shorter pipe length should be more likely to be SOx poisoned. Therefore, the length of the exhaust pipe 25 is equal to that of the exhaust pipe 2.
If the length of the exhaust pipe 26 is shorter than 6, the end of the NOx catalyst 20 closer to the inlet 21a of the casing 21 is likely to be poisoned by SOx, and if the length of the exhaust pipe 26 is shorter than the length of the exhaust pipe 25, the NOx is reduced. The catalyst 20 is the outlet 21b of the casing 21.
It can be said that the end nearer to is susceptible to SOx poisoning.

Here, when the end of the NOx catalyst 20 on the side closer to the inlet 21a of the casing 21 is poisoned by SOx, the valve body of the exhaust gas switching valve 28 is changed to the second valve after the SOx absorbent 17 is regenerated. When switching to the valve body position and flowing the exhaust gas under lean / rich spike control to the second path,
SOx poisoned at the inlet side of the NOx catalyst 20 is decomposed when exhaust gas of a rich spike flows, and the decomposed SOx is N
The NOx catalyst 20 moves to the downstream side of the Ox catalyst 20 and is again adsorbed by the NOx catalyst 20, and SOx diffuses widely throughout the NOx catalyst 20 and cannot be released from 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 with SOx, the valve body of the exhaust switching valve 28 after the SOx absorbent 17 is regenerated. Is switched to the second valve position (shown by the broken line in FIG. 6) and the exhaust gas subjected to lean / rich spike control is passed through the second path, the NOx catalyst 20
SOx poisoned on the outlet side of the NOx catalyst 20 is decomposed when rich spike exhaust gas flows, and becomes SO ₂ which is released from the NOx catalyst 20.

Therefore, as in the second embodiment, the length of the exhaust pipe 26 is made shorter than the length of the exhaust pipe 25 so that the outlet side of the NOx catalyst 20 is exhausted more than the inlet side.
A value closer to 8 is advantageous in that the poisoned SOx can be easily released even if the NOx catalyst 20 is poisoned by SOx during the regeneration process of the SOx absorbent 17.

Further, when the length of the exhaust pipe 26 is shorter than the length of the exhaust pipe 25 in this way, the valve body of the exhaust switching valve 28 after the regeneration treatment of the SOx absorbent 17 is indicated by the second broken line in FIG. When the exhaust gas is made to flow to the second path by switching to the valve body position of, the SOx release temperature is equal to or higher than the SOx release temperature during a predetermined time immediately after the exhaust switch valve 28 switches the exhaust path. It is preferable to control the exhaust gas of high temperature stoichiometric or rich air-fuel ratio to flow, and switch the air-fuel ratio control of the exhaust gas to the lean rich spike control after the elapse of the predetermined time.

In this way, the SOx in the regenerated exhaust that has flowed into the exhaust pipe 25 during the regeneration process of the SOx absorbent 17 and stayed in the exhaust pipe 25 during the regeneration process is caused by the exhaust switching valve 28. Since the NOx catalyst 20 passes through the NOx catalyst 20 together with the exhaust gas having the stoichiometric or rich air-fuel ratio which flows in immediately after the switching of the exhaust path, it is possible to prevent the NOx catalyst 20 from being poisoned by the SOx in the regenerated exhaust gas. Moreover,
Exhaust gas of stoichiometric or rich air-fuel ratio at high temperature is NO
Surely decomposes SOx poisoning the outlet side of the x catalyst 20.
discharge.

Further, as described above, when exhaust gas having a stoichiometric or rich air-fuel ratio is flowed 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 air is separated by cylinder. It is more effective to control the air-fuel ratio of the exhaust gas by controlling the fuel ratio. This will be described with reference to FIG.

FIG. 7 shows an example of a 4-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 have SOx absorbent 17 18 with built-in
Connected to A, the exhaust manifold 16B and 3 of the 2nd cylinder
The exhaust manifold 16C of the No. cylinder is connected to the casing 18B containing the SOx absorber 17,
A and the casing 18B are connected to the first port of the exhaust switching valve 28 via the exhaust pipe 19. The structure downstream of the exhaust gas switching valve 28 has the same configuration as that shown in FIG.

In this internal combustion engine, the exhaust switching valve 28
7, the SOx absorber 17 of the casing 18A and the SOx absorber 17 of the casing 18B are simultaneously regenerated by holding the valve disc at the first valve disc position shown by the solid line in FIG. 7 is switched to the second valve position shown by the broken line in FIG. 7, and at the same time, the No. 1 cylinder and No. 4 cylinder are operated at the lean air-fuel ratio, and the No. 2 cylinder and No. 3 cylinder are operated at the rich air-fuel ratio. Cylinder-specific air-fuel ratio control is executed to make the air-fuel ratio of the entire exhaust gas stoichiometric or slightly rich (slight rich).

In this way, both casings 18A,
Since the SOx absorber 17 of 18B is in a state immediately after the regeneration process and hardly adsorbing SOx, the exhaust gas of the rich air-fuel ratio discharged from the cylinder 1B of the second cylinder and the cylinder 1C of the third cylinder is the casing 18B. SOx absorber 1
Reducing agent (HC, CO, etc.) in the exhaust gas when passing 7
Exhaust pipe 19
Spill to. On the other hand, when the lean air-fuel ratio exhaust gas discharged from the cylinder 1A of the first cylinder and the cylinder 1D of the fourth cylinder passes through the SOx absorbent 17 of the casing 18A, SOx in the exhaust gas is adsorbed by the SOx absorbent 17. , SOx-removed lean air-fuel ratio exhaust gas flows into the exhaust pipe 19. Exhaust gas having a lean air-fuel ratio and exhaust gas having a rich air-fuel ratio are discharged from the exhaust pipe 19 to the exhaust switching valve 28 and the exhaust pipe 2.
When flowing into the casing 21 through 5, the NOx catalyst 2
At 0, a large amount of oxygen contained in the exhaust gas with a lean air-fuel ratio and a large amount of reducing agents (HC, CO, etc.) contained in the exhaust gas with a rich air-fuel ratio react 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 way, NO
Since the SOx poisoning outlet side of the x catalyst 20 can be heated to a high temperature, the SOx poisoning the NOx catalyst 20 outlet side can be more reliably decomposed and released. The above-described cylinder-by-cylinder air-fuel ratio control is not limited to the four-cylinder engine, and can also be applied to a six-cylinder engine or the like.

[Other Embodiments] In each of the above-described embodiments, an example in which the present invention is applied to a gasoline engine has been described, but it goes without saying that the present invention can be applied to a diesel engine. In the case of a diesel engine, combustion in the combustion chamber takes place in a lean range far beyond the stoichiometric air-fuel ratio, so under normal engine operating conditions, the SOx absorbent 17
Also, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 is extremely lean, and SOx and NOx are absorbed, but SOx and NOx are hardly released.

Further, in the case of a gasoline engine, as described above, the air-fuel mixture supplied to the combustion chamber 3 is made to have a stoichiometric air-fuel ratio or a rich air-fuel ratio, whereby exhaust gas flowing into the SOx absorbent 17 and the NOx catalyst 20 is The air-fuel ratio can be set to the stoichiometric air-fuel ratio or the rich air-fuel ratio to release the SOx and NOx absorbed by the SOx absorbent 17 and the NOx catalyst 20, but in the case of a diesel engine,
When the air-fuel mixture supplied to the combustion chamber has a stoichiometric air-fuel ratio or a rich air-fuel ratio, there is a problem that soot is generated during combustion and it cannot be adopted.

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

Even if the diesel engine is equipped 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 the stoichiometric air-fuel ratio or the rich air-fuel ratio.

[0079]

According to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, (a) an SOx absorbent disposed in an exhaust passage of an internal combustion engine capable of lean burn, and (b) a downstream of the SOx absorbent. A NOx absorbent disposed in the exhaust passage of
(C) An exhaust path switching means arranged between the SOx absorbent and the NOx absorbent, and (d) a first closed loop that includes the exhaust path switching means and the NOx absorbent,
Of the exhaust passage and (e) a second exhaust passage provided downstream of the exhaust passage switching means, the exhaust passage switching means making the first exhaust passage into a closed loop and absorbing the SOx. A first exhaust gas flowing out of a material is flowed into the second exhaust passage by bypassing the first exhaust passage.
The path and the first exhaust passage are made into a non-closed loop, and the S
It is possible to switch to a second path in which the exhaust gas flowing out from the Ox absorbent passes through the first exhaust passage and then flows into the second exhaust passage. The excellent effect that the absorber can be almost completely prevented from being poisoned by SOx is exhibited.

Further, the NO from the exhaust path switching means.
If the flow path length to the outlet of the x absorbent is set shorter than the flow path length from the exhaust path switching means to the inlet of the NOx absorbent, in the unlikely event that the NOx absorbent is regenerated during the SOx absorbent regeneration, Even when SOx is poisoned, SOx from the NOx absorbent
Is easily released, and recovery from SOx poisoning can be facilitated.

The exhaust path switching means is held in the first path during the SOx absorbent regeneration processing, and after the SOx absorbent is recycled, the exhaust path switching means is switched to the second path. When the 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, the NOx absorbent outlet side is heated to high heat. Therefore, when the NOx absorbent is poisoned by SOx during the regeneration process of the SOx absorbent, recovery from SOx poisoning can be promoted.

[Brief description of drawings]

1 is a first embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
FIG. 3 is a schematic configuration diagram of the embodiment of FIG. 6 and is a view showing a state in which the exhaust path switching means has changed to a first path.

FIG. 2 is a main part configuration diagram showing a state in which an exhaust path switching unit has switched to a second path in the exhaust emission control device of the first embodiment.

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

FIG. 4 shows unburned HC in exhaust gas discharged from the engine,
It is a diagram which shows the concentration of CO and oxygen roughly.

FIG. 5 is a view for explaining the NOx absorption / release action of the NOx storage reduction catalyst.

FIG. 6 is a second part of the exhaust purification system for an internal combustion engine according to the present invention.
It is a principal part block diagram in embodiment of this.

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

[Explanation of symbols]

1 Engine body (internal combustion engine) 3 Combustion chamber 4 Spark plug 11 Fuel injection valve 16, 19 Exhaust pipe (exhaust passage) 17 SOx absorber 20 NOx catalyst (NOx absorbent) 24 Exhaust pipe (second exhaust passage) 25,26 Exhaust pipe (first exhaust passage) 28 Exhaust gas switching valve (exhaust path switching means) 30 ECU

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI 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 (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/28 B01D 53/94 F02D 41/02 F02D 41/04

Claims (3)

(57) [Claims] (A) SOx is absorbed when the air-fuel ratio of the inflowing exhaust gas is lean, and SOx is absorbed when the air-fuel ratio of the inflowing exhaust gas is lean, and it is absorbed when the oxygen concentration of the inflowing exhaust gas is low. SOx absorbent that releases SOx, (b)
NOx is arranged when the air-fuel ratio of the inflowing exhaust gas is lean, which is arranged in the exhaust passage downstream of the SOx absorbent.
A NOx absorbent that absorbs NOx and releases the NOx absorbed when the oxygen concentration of the inflowing exhaust gas is low;
An exhaust path switching means disposed between the absorbent and the NOx absorbent, and (d) a first exhaust passage that can form a closed loop including the exhaust path switching means and the NOx absorbent,
(E) A second exhaust passage provided downstream of the exhaust passage switching means, and the exhaust passage switching means makes the first exhaust passage into a closed loop and exhaust gas flowing out from the SOx absorbent. A first path that allows gas to bypass the first exhaust passage and flow to the second exhaust passage, and an exhaust gas that has flowed out of the SOx absorbent with the first exhaust passage being in a non-closed loop. An exhaust emission control device for an internal combustion engine, which is switchable to a second path that passes through the exhaust passage and then flows into the second exhaust passage. 2. The flow path length from the exhaust path switching means to the outlet of the NOx absorbent is shorter than the flow path length from the exhaust path switching means to the NOx absorbent inlet. 1. An exhaust gas purification device for an internal combustion engine according to 1. 3. The exhaust path switching means is held in the first path during the regeneration processing of the SOx absorbent that releases the SOx absorbed in 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 the cylinder-by-cylinder air-fuel ratio control is performed in which some of the cylinders of the internal combustion engine burn at a rich air-fuel ratio and other cylinders burn at a lean air-fuel ratio. The exhaust gas purification device for an internal combustion engine according to claim 2.