JP2003106141A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine having a three-way catalyst upstream of a occlusion-type NOx catalyst which can favorably execute NOx purge without deteriorating fuel cost with securing heat deterioration resistance while maintaining oxygen occlusion function of the three-way catalyst. SOLUTION: This exhaust emission control device is provided with a NOx occlusion type NOx catalyst converter (34) and a three-way catalyst converter (32) provided in an exhaust passage upstream than the NOx catalyst converter and having oxygen occlusion function, and the three-way catalyst converter comprises a fist catalyst part (32a) located on the upstream side of the exhaust passage and having higher oxygen occlusion function and a second catalyst part (32b) located on the downstream side of the exhaust passage and having the oxygen occlusion function lower than the first catalyst part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly, to an exhaust gas purification apparatus having a three-way catalyst upstream of an occlusion type NOx catalyst while ensuring heat deterioration resistance while NOx purging. Related to technology for preventing deterioration of fuel efficiency.

[0002]

2. Related Background Art In an exhaust gas purification apparatus equipped with a storage type NOx catalyst, a three-way catalyst for oxidizing and removing HC and CO is generally provided on the upstream side thereof. However, basically, the three-way catalyst can satisfactorily oxidize and remove HC and CO when the exhaust air-fuel ratio is a lean air-fuel ratio, while it cannot sufficiently purify HC and CO at a stoichiometric air-fuel ratio or a rich air-fuel ratio. have.

Therefore, recently, ceria (C
A substance (oxygen storage material) having an oxygen storage function (O ₂ storage function) such as e) is added, whereby the NOx stored in the storage type NOx catalyst at a lean air-fuel ratio is reduced / released. Even if the exhaust air-fuel ratio is set to the rich air-fuel ratio (or stoichiometric air-fuel ratio) in order to (NOx purge), surplus HC that does not contribute to NOx reduction,
CO can be excellently oxidized and removed by oxygen (O ₂ ) stored at a lean air-fuel ratio.

[0004]

By the way, when a substance having an oxygen storage function such as ceria is added to the three-way catalyst, the purification efficiency is improved, but the amount of oxygen stored in the three-way catalyst is increased. If there is a large amount, when performing NOx purging, even if the exhaust air-fuel ratio is set to a rich air-fuel ratio, most of HC and CO will be oxidized by the stored oxygen before reaching the occlusion type NOx catalyst, and NOx cannot be reduced and removed well. There's a problem.

In this case, it is possible to increase the rich degree of the exhaust air-fuel ratio, but this is not preferable because it leads to deterioration of fuel consumption. Further, it is possible to reduce the added amount of ceria or the like to weaken the oxygen storage function, but in order to maintain the purification efficiency of the exhaust gas purification device, a certain amount of oxygen storage function is required, and the oxygen storage function of ceria or the like is required. If the amount of addition is reduced, there is a problem that the thermal deterioration resistance such as sintering resistance and high temperature oxidation poisoning resistance is deteriorated.

The present invention has been made in order to solve the above problems, and its object is the occlusion type N.
In an exhaust emission control device having a three-way catalyst upstream of an Ox catalyst, an exhaust gas of an internal combustion engine that can perform NOx purging satisfactorily without deteriorating fuel consumption while ensuring heat resistance deterioration while maintaining the oxygen storage function of the three-way catalyst. To provide a purification device.

[0007]

In order to achieve the above-mentioned object, the invention of claim 1 is provided in an exhaust passage of an internal combustion engine mounted on a vehicle, and when the exhaust air-fuel ratio is at least a lean air-fuel ratio. The NOx stored in the exhaust gas is stored when the exhaust air-fuel ratio is at least the stoichiometric air-fuel ratio or a rich air-fuel ratio that is richer than the stoichiometric air-fuel ratio.
A NOx catalytic converter having the property of releasing components,
A three-way catalytic converter provided in the exhaust passage upstream of the NOx catalytic converter and having an oxygen storage function, wherein the three-way catalytic converter is located upstream of the exhaust passage and is set to have a high oxygen storage function. And a second catalyst part located downstream of the exhaust passage and having an oxygen storage function lower than that of the first catalyst part.

Therefore, in the three-way catalytic converter, when the internal combustion engine is in a high load operation state, the exhaust gas temperature is high, and therefore the temperature of the upstream first catalyst portion exposed to the high temperature exhaust gas is the downstream side. Although it is higher than that of the second catalyst section and the NOx catalytic converter, the oxygen storage function of the first catalyst section is set to be higher, so that thermal deterioration of the three-way catalytic converter, and thus of the exhaust gas purification device, is favorably prevented.

Further, when the combustion air-fuel ratio is the lean air-fuel ratio, the exhaust gas temperature is low and the first exhaust gas is exposed to the low temperature exhaust gas.
Since the catalyst section is in a low activity state, even if the combustion air-fuel ratio is set to the rich air-fuel ratio (or stoichiometric air-fuel ratio) in order to perform the NOx purge after that, HC, CO, etc. are oxidized in the first catalyst section. Moreover, since the oxygen storage function is set low in the second catalyst portion, HC, CO, etc. are not oxidized again. Therefore, HC, CO, etc. will surely reach the NOx catalytic converter after passing through the three-way catalytic converter, and NOx can be reduced and removed satisfactorily without increasing the rich degree, so that the fuel consumption does not deteriorate and N
Good Ox purging.

Further, the invention of claim 2 is characterized in that the NOx catalytic converter and the three-way catalytic converter are arranged under the floor of the vehicle. in this way,
N under the floor of the vehicle that is far from the internal combustion engine and is easily cooled by air
By disposing the Ox catalytic converter and the three-way catalytic converter, it is possible to prevent thermal deterioration of the exhaust purification device and to implement NOx purging more favorably.

Further, the invention of claim 3 is characterized in that the first catalyst portion and the second catalyst portion of the three-way catalytic converter are continuously and integrally formed. As described above, in the one-way three-way catalytic converter, the first catalyst portion on the front side is a portion having a high oxygen storage function, and the second catalyst portion on the rear side is a portion having a low oxygen storage function in succession thereto. As a result, the heat of the first catalyst portion is satisfactorily transferred to the second catalyst portion, and the overheating of the first catalyst portion is prevented.

Further, the invention of claim 4 is characterized in that the first catalyst portion and the second catalyst portion of the three-way catalytic converter are separate bodies. Thus, the three-way catalytic converter is divided, the front three-way catalytic converter has a high oxygen storage function, and the rear three-way catalytic converter has a low oxygen storage function. It becomes easy to give the oxygen storage function to the catalyst part and the second catalyst part respectively, and the productivity and maintainability of the three-way catalytic converter are improved.

Further, according to the invention of claim 5, the oxygen storage function of the three-way catalytic converter is defined by the amount of ceria added to the first catalyst portion and the second catalyst portion. . That is, the oxygen storage function of the three-way catalytic converter is easily adjusted by the amount of ceria (Ce) that is the oxygen storage material.

Further, the invention of claim 6 is characterized in that, in the invention of claim 5, the amount of ceria is set to zero in the second catalyst portion. That is, the second catalyst portion, which is not directly exposed to high-temperature exhaust gas, does not require so high heat deterioration resistance, and therefore does not have an oxygen storage function so as not to oxidize HC and CO during NOx purging. Therefore, by reducing the amount of ceria in the second catalyst portion to zero, the NOx purge is performed even better.

In this case, in order to maintain the oxygen storage function, it is preferable to increase the amount of ceria in the first catalyst portion by the amount of zero in the amount of ceria in the second catalyst portion. The heat deterioration resistance is also improved. According to a seventh aspect of the present invention, in addition to the first to sixth aspects, the combustion air-fuel ratio of the internal combustion engine is changed to a lean air-fuel ratio and a stoichiometric air-fuel ratio or a rich air-fuel ratio in order to release the NOx stored in the NOx catalytic converter. NOx release control means for switching control to the fuel ratio is provided, and the NOx release control means, when switching to the stoichiometric air-fuel ratio or the rich air-fuel ratio, switches to the air-fuel ratio set according to the temperature of the first catalyst section. It is characterized by that.

Therefore, for example, when performing NOx purging,
When the temperature of the first catalyst portion is low and the first catalyst portion is in a low activity state, HC and CO are not oxidized by the oxygen storage function, so the degree of the rich air-fuel ratio is closer to the lean air-fuel ratio. When the temperature of the first catalyst portion is high and in a more active state, HC and CO are easily oxidized by the oxygen storage function, so the rich degree of the rich air-fuel ratio is set to be large. As a result, the NOx purge is optimally carried out without deteriorating the fuel consumption, and the exhaust gas purification efficiency is kept good.

According to the invention of claim 8, in addition to the inventions of claims 1 to 6, the combustion air-fuel ratio of the internal combustion engine is changed to a lean air-fuel ratio and a stoichiometric air-fuel ratio in order to release the NOx stored in the NOx catalytic converter. Or a NOx release control means for controlling switching between the rich air-fuel ratio and the rich air-fuel ratio, wherein the NOx release control means, when switching to the stoichiometric air-fuel ratio or the rich air-fuel ratio, a period set according to the temperature of the first catalyst section. It is characterized by maintaining the stoichiometric air-fuel ratio or the rich air-fuel ratio over the entire range.

Therefore, for example, when performing NOx purging,
When the temperature of the first catalyst unit is low and the activity of the first catalyst unit is low, NOx is satisfactorily reduced without being oxidized by the oxygen storage function of HC and CO, so that the theoretical air-fuel ratio or rich When the period of the air-fuel ratio is relatively short, the temperature of the first catalyst portion is high, and when it is in a more active state, HC and CO are easily oxidized by the oxygen storage function, and therefore the stoichiometric air-fuel ratio or rich air-fuel ratio is set. The period of time is extended. As a result, the NOx purge is properly carried out without deteriorating the fuel consumption, and the exhaust gas purification efficiency is kept good.

According to a ninth aspect of the present invention, in addition to the first to sixth aspects, the combustion air-fuel ratio of the internal combustion engine is changed to the lean air-fuel ratio and the stoichiometric air-fuel ratio in order to release the NOx stored in the NOx catalytic converter. Alternatively, there is provided NOx release control means for switching control between the rich air-fuel ratio and the rich air-fuel ratio, and the NOx release control means prohibits operation at a lean air-fuel ratio when the second catalyst section is at a predetermined temperature or higher. .

That is, the second catalyst portion is apt to be thermally deteriorated due to its low oxygen storage function. On the other hand, when the combustion air-fuel ratio of the internal combustion engine is set to the rich air-fuel ratio, the exhaust gas temperature rises as the combustion temperature rises. By making the combustion air-fuel ratio of the internal combustion engine not to be the lean air-fuel ratio when the temperature of the two-catalyst portion becomes equal to or higher than a predetermined temperature corresponding to the heat-resistant deterioration temperature of the second catalyst portion,
Thermal deterioration of the second catalyst portion and thus of the exhaust purification device is prevented.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust emission control device for an internal combustion engine according to the present invention, which is mounted on a vehicle, and the configuration of the exhaust emission control device according to the present invention will be described below with reference to the same figure.

As the engine body (hereinafter, simply referred to as an engine) 1, for example, fuel injection in the intake stroke (intake stroke injection) and fuel injection in the compression stroke (compression stroke injection) are performed by switching the fuel injection mode. A possible cylinder injection type spark ignition gasoline engine is adopted. This in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (Stoichio) or at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio operation). Is configured to be feasible.

As shown in the figure, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, whereby the fuel is directly injected into the combustion chamber. It is possible. An ignition coil 8 that outputs a high voltage is connected to the spark plug 4. A fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, which supplies the fuel in the fuel tank to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 toward the combustion chamber at a desired fuel pressure.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. Further, the cylinder head 2 is formed with an exhaust port in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected so as to communicate with each exhaust port.

Since the in-cylinder injection type engine 1 is already known, its detailed description is omitted here. The intake manifold 10 is provided with an electromagnetic throttle valve 14 that adjusts the intake air amount and a throttle position sensor (TPS) 16 that detects the opening degree θth of the throttle valve 14.

On the other hand, an exhaust pipe (exhaust passage) 20 is connected to the exhaust manifold 12, and an exhaust purification catalyst unit 30 is disposed under the floor of the vehicle in the exhaust pipe 20. The exhaust purification catalyst unit 30 includes an upstream three-way catalyst (upstream TWC) 32 and an occlusion type NOx catalyst 3.
4. A downstream three-way catalyst (downstream TWC) 36 is arranged in this order from the upstream side.

The storage type NOx catalyst 34 stores the NOx component in the exhaust gas when the exhaust air-fuel ratio is lean, and when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or a rich air-fuel ratio on the rich side of the stoichiometric air-fuel ratio. The catalyst has a characteristic of releasing the NOx component stored in the. The configuration, function, and the like of the storage type NOx catalyst 34 are publicly known, and the description thereof is omitted here.

The upstream three-way catalyst 32 and the downstream three-way catalyst 36
Is a carrier containing copper (Cu), cobalt (C) as an active noble metal.
o), silver (Ag), platinum (Pt), rhodium (Rh),
It is configured to have any of palladium (Pd). Further, ceria (Ce), zirconia (Zr), etc. having an oxygen storage function (O ₂ storage function) are further added to the upstream three-way catalyst 32.

When ceria (Ce) adsorbs oxygen (O ₂ ) in an oxidizing atmosphere where the exhaust air-fuel ratio is a lean air-fuel ratio, the exhaust air-fuel ratio becomes a rich air-fuel ratio and retains the O ₂ until a reducing atmosphere is obtained. have. Therefore, the upstream side three-way catalyst 32 is separated from the storage type NOx catalyst 34 by N
Even if the exhaust air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio (hereinafter referred to as NOx purge) to release the Ox component, the stored O ₂ causes excess HC (hydrocarbon) or CO.
(Carbon monoxide) can be removed by oxidation. In other words, the upstream three-way catalyst 32 having the O ₂ storage function can, of course, purify HC and CO in an oxidizing atmosphere, and the stored O ₂ will not only release NOx but also excess NOx even in a reducing atmosphere. It is possible to satisfactorily purify HC and CO that become

Ceria (Ce) is also related to the heat deterioration resistance of the catalyst, and has the property that the heat deterioration resistance of the catalyst increases as the amount of ceria (Ce) added to the catalyst increases. . The upstream side three-way catalyst 32 has a high OSC-TWC portion (first catalyst portion) 32a with a large amount of ceria (Ce) added and a low OSC with a small amount of ceria (Ce) added.
-TWC part (2nd catalyst part) 32b is comprised from two parts. That is, the upstream three-way catalyst 32 has a high OSC.
-The TWC section 32a has a high oxygen storage function (OSC), and the low OSC-TWC section 32b has an oxygen storage function (OS).
C) is set to be low. However, the total amount of ceria (Ce) added to the upstream three-way catalyst 32 is N
It is set to a predetermined amount necessary and sufficient for purifying excess oxygen in Ox purging. Furthermore, high OSC here
-The capacity of the TWC section 32a and the capacity of the low OSC-TWC section 32b are the same (for example, 0.5 l),
The capacities may be different from each other and are not limited to this.

Exhaust gas purification catalyst unit 30 in the exhaust passage 20
An O ₂ sensor 22 is provided on the upstream side. Further, the high OSC-TWC section 32a and the low OSC-TWC section 32b of the upstream three-way catalyst 32 have high OSC-
High temperature sensor 24 for detecting the temperature of the TWC section 32a and high temperature sensor 2 for detecting the temperature of the low OSC-TWC section 32b.
6 is provided.

ECU (electronic control unit) 40
Is equipped with an input / output device, a storage device (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. With this ECU 40, a comprehensive exhaust gas purification device including the engine 1 Control is performed. ECU
On the input side of 40, the above-mentioned TPS 16, O ₂ sensor 2
2 and various sensors such as the high temperature sensors 24 and 26 are connected, and the detection information from these sensors is input.

On the other hand, various output devices such as the above-mentioned fuel injection valve 6 and ignition coil 8 are connected to the output side of the ECU 40, and these various output devices are calculated based on the detection information from various sensors. The fuel injection amount, fuel injection timing, ignition timing, etc. are output respectively.
A proper amount of fuel is injected from the fuel injection valve 6 at proper timing, and spark ignition is performed by the spark plug 4 at proper timing. Further, the combustion air-fuel ratio is switched between the lean air-fuel ratio and the stoichiometric air-fuel ratio or the rich air-fuel ratio according to the NOx storage amount of the storage-type NOx catalyst 34, whereby the NOx purge is appropriately performed (NOx release). Control means).

The operation of the exhaust gas purifying apparatus according to the present invention having the above-mentioned structure will be described below. As described above, since the high OSC-TWC portion 32a of the upstream three-way catalyst 32 contains a large amount of ceria (Ce), the heat deterioration resistance is high, that is, the heat resistant temperature is high. Therefore, for example, when the engine 1 is operating under high load, the exhaust temperature is high, and the high OSC-TWC portion of the upstream three-way catalyst 32 located on the most upstream side of the exhaust purification catalyst unit 30. 32
Although a is most heated to a high temperature, even in such a case, the high OSC-TWC portion 32a is set to have high heat deterioration resistance, so that the heat deterioration of the upstream three-way catalyst 32 is prevented. It

That is, referring to FIG. 2, the temperature distribution of each part of the upstream three-way catalyst 32 during high load operation is shown. From the figure, the most upstream part of the upstream three-way catalyst 32,
That is, it can be seen that the high OSC-TWC portion 32a has the highest temperature, and the downstream side does not have that high temperature. However, even in such a case, the high OSC-TWC portion 32 on the upstream side is obtained.
Since a is set to have a higher heat resistant temperature than the low OSC-TWC portion 32b on the downstream side, the temperature of the upstream three-way catalyst 32 is high OSC-TWC heat resistant temperature, low OSC-T.
The WC heat resistance temperature (both indicated by broken lines) is not exceeded, and thermal deterioration of the upstream three-way catalyst 32 is prevented.

Further, here, the high OSC-TWC section 32a is used.
Since the low OSC-TWC portion 32b and the low OSC-TWC portion 32b are integrally formed, the heat of the high OSC-TWC portion 32a is low.
The high OSC-TWC portion 32a is prevented from being overheated by being reliably transmitted to the C portion 32b, which also prevents thermal deterioration of the upstream three-way catalyst 32. Further, since the upstream side three-way catalyst 32 is located under the floor of the vehicle away from the engine 1 together with the occlusion type NOx catalyst 34, there is also a cooling effect by air cooling or the like, which also causes the heat of the upstream side three-way catalyst 32. Deterioration is prevented.

On the other hand, the low OSC-of the upstream three-way catalyst 32
The TWC part 32b has a high OSC content of ceria (Ce).
Since it is less than the TWC portion 32a, the heat deterioration resistance is inferior, but the oxygen storage function is low, and even when the exhaust air-fuel ratio is set to the rich air-fuel ratio, HC and CO have the low OSC-T.
Almost no oxidation occurs in the WC portion 32b. Therefore, generally, in lean operation, the exhaust temperature is low, and the high OSC-TWC portion 32a of the upstream three-way catalyst 32 located on the most upstream side of the exhaust purification catalyst unit 30 is cooled to be in a low temperature inactive state, In this state, even if the exhaust air-fuel ratio is made rich and the NOx purge is started, the high OSC
-In the TWC section 32a, HC and CO are hardly oxidized despite the large amount of ceria (Ce) added, and as described above, the low OSC with a small amount of ceria (Ce)-
Since HC and CO are hardly oxidized even in the TWC section 32b, HC and CO are satisfactorily supplied to the storage type NOx catalyst 34. As a result, at the time of NOx purging, the NOx stored in the storage-type NOx catalyst 34 can be reliably reduced without increasing the rich degree of the rich air-fuel ratio so much.
Will be released.

That is, referring to FIG. 3, the temperature distribution of each part of the upstream three-way catalyst 32 during lean operation is shown. From the figure, the upstream three-way catalyst 3 during lean operation is shown.
It can be seen that the most upstream portion of 2, ie, the high OSC-TWC portion 32a has the lowest temperature and has not reached the catalyst activation temperature (dashed line), but in such a state where the high OSC-TWC portion 32a has low activity, NOx Even if the purge is started, H
C and CO pass through the low OSC-TWC portion 32b without being oxidized in the high OSC-TWC portion 32a and are supplied to the storage type NOx catalyst 34, and the NOx stored in the storage type NOx catalyst 34 is deteriorated in fuel efficiency. Will be reliably reduced and released.

Further, since the upstream side three-way catalyst 32 is located under the floor of the vehicle away from the engine 1, the high OSC-TWC section 32a is likely to be at a low temperature due to the cooling effect of air cooling or the like, which deteriorates fuel efficiency. More prevented, N
Ox is reduced and released more reliably. When the lean operation is continued, as described above, the high OSC-TWC section 32a is
However, as shown in FIG. 3, the low OSC-TWC portion 32b on the downstream side is maintained at the catalyst activation temperature with almost no cooling. Therefore, even during lean operation, at least the low OSC-TWC unit 32
As for b, the three-way catalytic function is ensured, and HC and CO are satisfactorily oxidized and removed by the low OSC-TWC section 32b. Further, since HC and CO are also oxidized and removed by the downstream three-way catalyst 36, HC and C
O is surely purified by the exhaust purification catalyst unit 30.

Further, referring to FIG. 4, a NOx purge A / F (NOx purge combustion air-fuel ratio) and NOx purge time setting control routine in the case of performing NOx purge is shown in a flowchart. , NOx purge A
/ F and NOx purge time are set based on the flowchart. In the flowchart, first, in step S10, the temperature of the high OSC-TWC unit 32a,
That is, the high OSC-TWC detected by the high temperature sensor 24.
The NOx purge A / F is set based on the temperature. Specifically, as shown in FIG. 5, high OSC-TWC temperature and NOx
A map showing the relationship with the purge A / F is provided in advance, and the NOx purge A / F is set based on the map. That is, when the high OSC-TWC temperature is low, the air-fuel ratio is set to the rich air-fuel ratio having a small rich degree close to the stoichiometric air-fuel ratio, and when the high OSC-TWC temperature is high, the air-fuel ratio is set to the rich air-fuel ratio having a large rich degree.

Then, in step S12, the high OS
Further, the NOx purge time is set based on the temperature of the C-TWC section 32a, that is, the high OSC-TWC temperature. More specifically, as shown in FIG. 6, a high OSC-value is obtained for each air-fuel ratio A / F.
A map showing the relationship between the TWC temperature and the NOx purge time is provided in advance, and the NOx purge time is set based on this map. That is, NO in step S10.
When the x purge A / F is set, the NOx purge A / F is set.
Based on the above, an appropriate NOx purge time is set.

That is, the high OSC at the time of NOx purge
-When the TWC part 32a is at a considerably low temperature, since almost all of HC and CO in the exhaust gas can be supplied to the occlusion type NOx catalyst 34, the rich degree is made small and the NOx purge time is made short so that HC, When the amount of CO is suppressed to a low level, while the high OSC-TWC part 32a is in a relatively high temperature and close to the active state, a part of HC and CO in the exhaust gas is oxidized by the high OSC-TWC part 32a. Therefore, the rich degree is made large and the NOx purge time is made long to secure the amounts of HC and CO supplied to the occlusion type NOx catalyst 34.

As a result, the NOx purge can be satisfactorily carried out while the fuel consumption amount during the NOx purge is suppressed to a necessary minimum, and the deterioration of fuel consumption can be appropriately prevented, and the exhaust gas purification efficiency can be improved. Further, referring to FIG. 7, a control routine of lean operation prohibition control is shown in a flowchart, and the flowchart will be described below.

In step S20, it is determined whether or not the temperature of the low OSC-TWC portion 32b, that is, the low OSC-TWC temperature, is higher than a predetermined temperature (which depends on the catalyst, here, for example, 600 ° C.). Specifically, the predetermined temperature is, for example, a temperature slightly lower than the heat resistant temperature of the low OSC-TWC portion 32b, and here it is determined whether or not the low OSC-TWC temperature is higher than the temperature. The determination result is true (Ye
If it is determined in s) that the low OSC-TWC temperature is higher than the predetermined temperature, the process proceeds to step S22.

In step S22, operation of the engine 1 at a lean air-fuel ratio, that is, lean operation is prohibited. Note that lean operation includes fuel cut, and implementation of fuel cut is also prohibited. This further prevents thermal degradation of the upstream three-way catalyst 32. On the other hand, if the determination result of step S20 is false (No) and the low OSC-TWC temperature does not reach the predetermined temperature, it can be considered that the thermal deterioration of the upstream three-way catalyst 32 is small. Step S
24, the lean operation is permitted, and the occlusion type NOx catalyst 3
Let 4 work as usual.

By the way, in the above embodiment, in the upstream side three-way catalyst 32, the upstream side portion is provided with the high OSC-TWC portion 3.
2a and the downstream side portion is the low OSC-TWC portion 32b. However, as shown in FIG.
The part 32a and the low OSC-TWC part 32b may be completely separated and configured separately. In this way, the high OSC-TWC unit 32a and the low OSC-TWC unit 3
The work of adding ceria (Ce) to 2b is facilitated, and the productivity and maintenance of the exhaust purification catalyst unit 30 are improved.

Further, in the above embodiment, the storage type NOx catalyst 34 and the downstream side three-way catalyst (downstream side TWC) 36 are provided independently, but as shown in FIG. The original function integrated storage type NOx catalyst 37 may be used. In addition, in the above embodiment, the low OSC
The case where the -TWC portion 32b contains ceria (Ce) has been described. However, the amount of ceria may be zero without adding ceria (Ce) to the low OSC-TWC portion 32b. By doing so, it is possible to surely supply HC and CO to the occlusion-type NOx catalyst 34 during the NOx purging without oxidizing them in the low OSC-TWC section 32b, and it is possible to perform the NOx purging even better. it can. In this case, the amount of ceria (Ce) in the high OSC-TWC portion 32a is increased by the amount of ceria (Ce) removed from the low OSC-TWC portion 32b, and the high OSC is increased.
-The heat deterioration resistance of the TWC section 32a is further improved.

In the above embodiment, the cylinder injection type engine is used as the engine 1, but the intake pipe injection type engine may be used as the engine 1. In addition, in the above-described embodiment, ceria (C
Although e) is used, it may be zirconia (Zr).

[0049]

As described in detail above, according to the exhaust gas purifying apparatus for an internal combustion engine according to claim 1 of the present invention, the three-way catalytic converter has an exhaust gas temperature when the internal combustion engine is in a high load operation state. Because of the high temperature, the temperature of the upstream first catalyst portion exposed to the high temperature exhaust gas becomes higher than that of the downstream second catalyst portion and NOx catalytic converter, but the oxygen storage function of the first catalyst portion is high. Since it is set, it is possible to favorably prevent thermal deterioration of the three-way catalytic converter and eventually the exhaust purification device.

When the combustion air-fuel ratio is the lean air-fuel ratio, the exhaust temperature is low and the first exhaust gas is exposed to the low-temperature exhaust gas.
Since the catalyst section is in a low activity state, even if the combustion air-fuel ratio is set to the rich air-fuel ratio (or stoichiometric air-fuel ratio) in order to perform the NOx purge after that, HC, CO, etc. are oxidized in the first catalyst section. In addition, since the oxygen storage function of the second catalyst section is set low, there is no HC or C
O, etc. are not oxidized, and therefore HC, CO
Etc. will surely reach the NOx catalytic converter after passing through the three-way catalytic converter, so that NOx can be reduced and removed satisfactorily without increasing the rich degree, and NOx purge can be satisfactorily carried out without deterioration of fuel consumption. You can

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of the second aspect, the NOx catalytic converter and the three-way catalytic converter are arranged at a position below the floor of the vehicle that is far from the internal combustion engine and is easily air-cooled. It is possible to prevent heat deterioration of the exhaust purification device and to implement NOx purging more favorably. Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 3, in the integrated three-way catalytic converter, the front side first catalyst portion is a portion having a high oxygen storage function, and the rear side second catalyst portion is continuous with this portion. Since the portion has a low oxygen storage function, the heat of the first catalyst portion can be satisfactorily transferred to the second catalyst portion, and the overheating of the first catalyst portion can be prevented.

Further, according to the exhaust gas purifying apparatus of the internal combustion engine of claim 4, the three-way catalytic converter is divided, the front three-way catalytic converter has a high oxygen storage function, and the rear three-way catalytic converter is Since the oxygen storage function is set to be low, it becomes easy to provide the first catalyst section and the second catalyst section with oxygen storage functions, and the productivity and maintenance of the three-way catalytic converter are improved. You can

According to the exhaust gas purifying apparatus for an internal combustion engine of claim 5, the oxygen storage function of the three-way catalytic converter can be easily adjusted by the amount of ceria (Ce) which is the oxygen storage material. Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 6, the second catalyst portion, which is not directly exposed to the high temperature exhaust gas, does not require so high heat deterioration resistance. It is better not to have an oxygen storage function so as not to oxidize CO.
By reducing the amount of ceria in the catalyst portion to zero, the NOx purge can be performed even better.

In this case, in order to maintain the oxygen storage function, it is preferable to increase the amount of ceria in the first catalyst portion by the amount of zero of the amount of ceria in the second catalyst portion. The heat deterioration resistance can also be improved. Further, according to the exhaust purification system of an internal combustion engine of claim 7, for example, when performing NOx purging, when the temperature of the first catalyst portion is low and the first catalyst portion is in a low activity state, HC, CO
Is not oxidized by the oxygen storage function, the rich air-fuel ratio is set to lean air-fuel ratio, and when the temperature of the first catalyst portion is high and in the active state,
Since HC and CO are easily oxidized by the oxygen storage function, the rich degree of the rich air-fuel ratio is set to a large value, so that NOx purging can be optimally performed without deteriorating fuel consumption, and exhaust purification efficiency can be maintained excellent.

According to the exhaust gas purifying apparatus for an internal combustion engine of claim 8, for example, when performing NOx purging, when the temperature of the first catalyst portion is low and the first catalyst portion is in a low activity state, HC, Since COx is reduced satisfactorily without being oxidized by the oxygen storage function, the period of the stoichiometric air-fuel ratio or rich air-fuel ratio is made relatively short, and the temperature of the first catalyst section is high and in an active state. When
Since HC and CO are easily oxidized by the oxygen storage function, the stoichiometric air-fuel ratio or the rich air-fuel ratio is extended, so that NOx purge can be properly performed without deteriorating the fuel consumption and the exhaust gas purification efficiency is maintained well. be able to.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 9, the second catalyst portion is liable to be thermally deteriorated due to the low oxygen storage function, and on the other hand, when the combustion air-fuel ratio of the internal combustion engine is set to the rich air-fuel ratio, the combustion is performed. Although the exhaust gas temperature rises as the temperature rises, the combustion air-fuel ratio of the internal combustion engine becomes the lean air-fuel ratio when the temperature of the second catalyst portion becomes equal to or higher than a predetermined temperature corresponding to the heat-resistant deterioration temperature of the second catalyst portion. I decided not to do so, so NOx
Is no longer stored in the NOx catalytic converter,
Therefore, the NOx purge is not required, the rise in exhaust temperature can be suppressed, and the thermal deterioration of the second catalyst portion and thus the exhaust purification device can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention, which is mounted on a vehicle.

FIG. 2 is a diagram showing a temperature distribution of each part of the upstream three-way catalyst during high load operation.

FIG. 3 is a diagram showing a temperature distribution of each part of an upstream three-way catalyst during lean operation.

FIG. 4 is a flowchart showing a NOx purge A / F and NOx purge time setting control routine when performing NOx purge.

FIG. 5 is a map showing the relationship between high OSC-TWC temperature and NOx purge A / F.

FIG. 6 is a map showing the relationship between high OSC-TWC temperature and NOx purge time.

FIG. 7 is a flowchart showing a control routine of lean operation prohibition control.

FIG. 8 is a diagram showing a case where a high OSC-TWC part and a low OSC-TWC part are completely separated and separated in the upstream three-way catalyst.

FIG. 9 is a diagram showing a case where an occlusion type NOx catalyst and a downstream side three-way catalyst are integrated.

[Explanation of symbols]

1 Engine Body 4 Spark Plug 6 Fuel Injection Valve 20 Exhaust Pipe 22 O ₂ Sensor 24 High Temperature Sensor 26 High Temperature Sensor 30 Exhaust Gas Purification Catalyst Unit 32 Upstream Three Way Catalyst 32a High OSC-TWC Part (First Catalyst Part) 32b Low OSC- TWC section (second catalyst section) 34 Storage type NOx catalyst 36 Downstream three-way catalyst 40 ECU (electronic control unit)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 F01N 3/28 J 301 301C F02D 41/04 301 F02D 41/04 301A 305 305A 43/00 301 43/00 301E 301T F-term (reference) 3G084 AA04 BA09 BA13 BA15 BA17 DA10 EB12 EC03 FA10 FA27 FA29 3G091 AA12 AA17 AA24 AB03 AB06 BA10 BA14 CB02 CB03 CB05 DA06 DA08 DC03 EA07 EA18 EA34 GB00W GB04W GB05X GB06X GB07X HA08 HA12 HA19 HA20 3G301 HA01 HA04 HA15 JA21 JA25 LB04 MA01 MA11 MA18 ND02 NE13 NE14 NE15 NE23 PA11Z PD02A PD12Z

Claims (9)

[Claims] 1. An NOx component in exhaust gas is stored in an exhaust passage of an internal combustion engine mounted on a vehicle when the exhaust air-fuel ratio is at least a lean air-fuel ratio, and the exhaust air-fuel ratio is at least the theoretical air-fuel ratio or the theoretical air-fuel ratio. A NOx catalytic converter having a characteristic of releasing the stored NOx component at a rich air-fuel ratio on the rich side of the fuel ratio, and an oxygen storage function provided in an exhaust passage upstream of the NOx catalytic converter. A three-way catalytic converter, wherein the three-way catalytic converter is located upstream of the exhaust passage and has a high oxygen storage function; and the first catalytic converter is located downstream of the exhaust passage. An exhaust gas purification device for an internal combustion engine, comprising: a second catalyst part having a lower oxygen storage function than the second part. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the NOx catalytic converter and the three-way catalytic converter are arranged under the floor of the vehicle. 3. The exhaust gas of an internal combustion engine according to claim 1, wherein the first catalyst portion and the second catalyst portion of the three-way catalytic converter are continuously and integrally formed. Purification device. 4. The first catalyst part and the second catalyst part of the three-way catalytic converter are separate bodies.
An exhaust emission control device for an internal combustion engine according to claim 1 or 2. 5. The oxygen storage function of the three-way catalytic converter is defined by the amount of ceria added to the first catalyst part and the second catalyst part.
5. An exhaust emission control device for an internal combustion engine according to any one of 4 to 4. 6. The exhaust gas purification device for an internal combustion engine according to claim 5, wherein the amount of ceria in the second catalyst portion is set to zero. 7. A NOx release control means for controlling the combustion air-fuel ratio of the internal combustion engine to switch between a lean air-fuel ratio and a stoichiometric air-fuel ratio or a rich air-fuel ratio in order to release the NOx stored in the NOx catalytic converter. 7. The NOx release control means, when switching to a stoichiometric air-fuel ratio or a rich air-fuel ratio, switches to an air-fuel ratio set according to the temperature of the first catalyst portion, any one of claims 1 to 6. Or an exhaust gas purification device for an internal combustion engine. 8. A NOx release control means for controlling the combustion air-fuel ratio of the internal combustion engine to switch between a lean air-fuel ratio and a stoichiometric air-fuel ratio or a rich air-fuel ratio in order to release the NOx stored in the NOx catalytic converter. The NOx release control means, when switching to the stoichiometric air-fuel ratio or the rich air-fuel ratio, maintains the state of the stoichiometric air-fuel ratio or the rich air-fuel ratio for a period set according to the temperature of the first catalyst portion. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 6, which is characterized in that. 9. A NOx release control means for controlling the combustion air-fuel ratio of the internal combustion engine to switch between a lean air-fuel ratio and a stoichiometric air-fuel ratio or a rich air-fuel ratio in order to release the NOx stored in the NOx catalytic converter. The exhaust purification of an internal combustion engine according to any one of claims 1 to 6, characterized in that the NOx release control means prohibits operation at a lean air-fuel ratio when the second catalyst portion is at a predetermined temperature or higher. apparatus.