JP3525912B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust emission control device for an internal combustion engine.

[0002]

Internal combustion engines, in particular contain toxic NO _X in the exhaust gas from diesel engines, in order to purify the NO _X, placing _the NO _X storage reduction catalyst device in the engine exhaust system Is proposed. The NO _X storage reduction catalyst device absorbs NO _X in the form of nitrate when the oxygen concentration in the vicinity atmosphere is high, and releases the absorbed NO _X when the oxygen concentration in the vicinity atmosphere becomes low. As a result, NO _X
The storage reduction catalyst device satisfactorily absorbs NO _x from the exhaust gas of a diesel engine that is burned under excess air. However, since the NO _X storable amount absorbed in the NO _X storage reduction catalyst device in the form of nitrate is finite, before the NO _X storable amount is reached, the near air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio. To release NO _X from the NO _X storage reduction catalyst device and reduce and purify NO _X released by the reducing component in the atmosphere, that is,
It is necessary to regenerate the NO _X storage reduction catalyst device.

[0003]

In order to regenerate the NO _X storage reduction catalyst device, in the cylinder or in the engine exhaust system, the vicinity atmosphere is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio, that is, the regenerated air-fuel ratio. Fuel for that is supplied. However, even if the exhaust gas is made to have a regeneration air-fuel ratio in this way, a large amount of the supplied fuel simply passes through the NO _X storage reduction catalyst device together with the exhaust gas, so that a relatively large amount of fuel is required for regeneration, Fuel consumption rate deteriorates.

Therefore, an object of the present invention is to provide an exhaust emission control system for an internal combustion engine, which makes it possible to surely regenerate the NO _X storage reduction catalytic converter without deteriorating the fuel consumption rate.

[0005]

According to a first aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine, which is arranged in an engine exhaust system and absorbs NO _X when a nearby atmosphere has a lean air-fuel ratio.
A NO _x storage reduction catalyst device that is regenerated at a regeneration air fuel ratio that is a stoichiometric air fuel ratio or a rich air fuel ratio; and a bypass means that enables at least part of the exhaust gas to bypass the NO _x storage reduction catalyst device. A fuel supply device for supplying fuel to the vicinity of the NO _x storage reduction catalyst device, the internal combustion engine having an inert gas supply means for supplying an inert gas into the cylinder, To perform low temperature combustion in which a larger amount of the inert gas than the worst inert gas amount that maximizes the soot generation is supplied into the cylinder for combustion, and normal combustion in which a lean air-fuel ratio is used for combustion. Can
In the case of regenerating the NO _X storage reduction catalyst device, a first regeneration unit that makes the atmosphere near the NO _X storage reduction catalyst a regeneration air-fuel ratio by the exhaust gas when the low temperature combustion is performed at the regeneration air-fuel ratio; At the time of combustion, at least part of the exhaust gas is bypassed by the bypass means, and fuel is supplied by the fuel supply device to select the second regenerating means for regenerating the air-fuel ratio in the atmosphere near the NO _X storage reduction catalyst. It is characterized by being.

According to a second aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first aspect, wherein the NO _x storage reduction catalyst device has a temperature lower than a set temperature. when it is predicted to be lower than at or above the set temperature, the first reproducing means is selected to regenerate the _the NO _X storage reduction catalyst device, the temperature of the _the NO _X storage reduction catalyst device is in the set temperature or more At the time or when it is predicted that the temperature is above the set temperature, the NO _x
The second regenerating means is selected to regenerate the storage reduction catalyst device.

According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the second aspect, wherein the NO _x storage reduction catalyst device has a temperature equal to or higher than the preset temperature. Even when the temperature is equal to or higher than the preset temperature, it is predicted that the amount of harmful substances emitted from the cylinder during the normal combustion is equal to or higher than the preset amount or equal to or higher than the preset amount. In this case, the first reproducing means is selected.

According to a fourth aspect of the present invention, there is provided an exhaust gas purification device for an internal combustion engine according to the second aspect, wherein the NO _x storage reduction catalyst device is a particulate matter in the exhaust gas. Even when the temperature of the NO _X storage reduction catalyst device is above the preset temperature or when it is predicted to be above the preset temperature. The first regeneration means is selected when the amount of particulates discharged from the cylinder at the time is equal to or more than a set amount or is predicted to be equal to or more than the set amount.

According to a fifth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the fourth aspect, wherein the particulate matter collected on the collecting wall is oxidized. It is characterized by being.

According to a sixth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the fifth aspect, wherein the trapping wall carries an active oxygen releasing agent. The active oxygen released from the active oxygen releasing agent oxidizes the particulates.

According to a seventh aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the sixth aspect, wherein the active oxygen release agent has excess oxygen in the surroundings. It is characterized in that it takes in oxygen, retains oxygen, and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases.

An exhaust purification system for an internal combustion engine according to claim 8 of the present invention is the exhaust purification system for an internal combustion engine according to any one of claims 5 to 7, wherein the exhaust gas of the NO _x storage reduction catalyst device is exhausted. Inverting means for reversing the upstream side and the exhaust downstream side is provided integrally with or separately from the bypass means, the collecting wall has a first collecting surface and a second collecting surface, and the reversing means is provided. The exhaust gas upstream side and the exhaust gas downstream side of the NO _x storage reduction catalyst device are reversed by the means, so that the first collection surface and the second collection surface of the collection wall for collecting particulates. It is characterized in that the surface and the surface are used alternately.

[0013]

1 is a schematic vertical sectional view of a four-stroke diesel engine equipped with an exhaust emission control device according to the present invention, and FIG. 2 is an enlarged vertical sectional view of a combustion chamber in the diesel engine of FIG. Yes, FIG. 3 is a bottom view of the cylinder head in the diesel engine of FIG. 1 to 3, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston,
5a is a cavity formed on the top surface of the piston 4,
Is a combustion chamber formed in the cavity 5a, 6 is an electrically controlled fuel injection valve, 7 is a pair of intake valves, 8 is an intake port, 9
Indicates a pair of exhaust valves, and 10 indicates an exhaust port, respectively. The intake port 8 is connected to the surge tank 1 via the corresponding intake branch pipe 11.
2, the surge tank 12 is connected to the air cleaner 14 via the intake duct 13. A throttle valve 16 driven by an electric motor 15 is provided in the intake duct 13.
Are placed. On the other hand, the exhaust port 10 is connected to an exhaust pipe 18 via an exhaust manifold 17.

Exhaust manifold 17 as shown in FIG.
An air-fuel ratio sensor 21 is arranged inside. The exhaust manifold 17 and the surge tank 12 are connected to each other via an EGR passage 22, and an electric control type EGR is provided in the EGR passage 22.
A control valve 23 is arranged. A cooling device 24 for cooling the EGR gas flowing in the EGR passage 22 is arranged around the EGR passage 22. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 24, and the engine cooling water cools the EGR gas.

On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 26, via a fuel supply pipe 25. Fuel is supplied into the common rail 26 from an electrically controlled variable fuel discharge fuel pump 27, and the fuel supplied into the common rail 26 is supplied to the fuel injection valve 6 via each fuel supply pipe 25. A fuel pressure sensor 28 for detecting the fuel pressure in the common rail 26 is attached to the common rail 26, and the fuel pump 27 so that the fuel pressure in the common rail 26 becomes a target fuel pressure based on the output signal of the fuel pressure sensor 28. Is controlled.

An electronic control unit 30 receives the output signal of the air-fuel ratio sensor 21 and the output signal of the fuel pressure sensor 28. Further, a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, an output signal of the load sensor 41 is also input to the electronic control unit 30, and a crankshaft is further provided. For example, the output signal of the crank angle sensor 42, which generates an output pulse each time it rotates by 30 °, is also input. In this way, the electronic control unit 30 is based on various signals, the fuel injection valve 6, the electric motor 15, the EGR control valve 2
3, the fuel pump 27, and the switching valve 71a arranged in the exhaust pipe 18 are operated. The switching valve 71a will be described later.

As shown in FIGS. 2 and 3, in the embodiment according to the present invention, the fuel injection valve 6 is composed of a hole nozzle having six nozzle openings, and the nozzle opening of the fuel injection valve 6 faces slightly downward with respect to the horizontal plane. Fuel F is injected at equal angular intervals. As shown in FIG. 3, of the six fuel sprays F, two fuel sprays F are scattered along the lower side surface of the valve body of each exhaust valve 9. 2 and 3 show the time when fuel injection is performed at the end of the compression stroke. At this time, the fuel spray F advances toward the inner peripheral surface of the cavity 5a and is then ignited and burned.

FIG. 4 shows a case where additional fuel is injected from the fuel injection valve 6 when the lift amount of the exhaust valve 9 is maximum during the exhaust stroke. That is, as shown in FIG. 5, the main injection Qm is performed near the compression top dead center, and then the additional fuel Qa is injected in the middle of the exhaust stroke. In this case, the fuel spray F advancing toward the valve body of the exhaust valve 9 goes between the rear surface of the umbrella portion of the exhaust valve 9 and the exhaust port 10. In other words, in other words, of the six nozzle openings of the fuel injection valve 6, two nozzle openings eject the fuel spray F when the additional fuel Qa is injected while the exhaust valve 9 is open. It is formed so as to face between the rear surface of the umbrella portion of the valve 9 and the exhaust port 10. In the embodiment shown in FIG. 4, the fuel spray F collides with the rear surface of the exhaust valve 9 at this time, and the fuel spray F that collides with the rear surface of the exhaust valve 9 is reflected on the rear surface of the exhaust valve 9. Then, it goes into the exhaust port 10.

Normally, the additional fuel Qa is not injected,
Only the main injection Qm is performed. FIG. 6 shows changes in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 6) is changed by changing the opening degree of the throttle valve 16 and the EGR rate during engine low load operation, and smoke, HC , CO,
It represents the experimental examples showing the emissions changes in NO _X. Figure 6
As can be seen from this, in this experimental example, the EGR rate increases as the air-fuel ratio A / F decreases, and the theoretical air-fuel ratio (≈14.
When it is 6) or less, the EGR rate is 65% or more.

As shown in FIG. 6, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the EGR rate becomes around 40% and the smoke is generated when the air-fuel ratio A / F becomes about 30. The quantity begins to increase. Then
When the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke sharply decreases this time, the EGR rate is increased to 65% or more, and the smoke becomes almost zero when the air-fuel ratio A / F is around 15.0. . That is, soot is hardly generated. At this time, the output torque of the engine slightly decreases, and NO
The amount of _X generated is considerably low. On the other hand, at this time, the amounts of HC and CO generated start to increase.

FIG. 7 (A) shows the change in combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of smoke generated is the largest, and FIG. 7 (B) shows the air-fuel ratio A / F. It shows a change in the combustion pressure in the combustion chamber 5 when F is around 18 and the amount of smoke generated is almost zero. As can be seen by comparing FIG. 7 (A) and FIG. 7 (B), in the case of FIG. 7 (B) where the amount of smoke generated is almost zero, the amount of smoke generated is large.
It can be seen that the combustion pressure is lower than in the case shown in (A).

The following can be said from the experimental results shown in FIGS. 6 and 7. That is, first, the air-fuel ratio A / F is 15.
When the amount of smoke produced is less than 0 and the amount of smoke produced is almost zero, the amount of NO _x produced decreases considerably as shown in FIG. The decrease in the amount of NO _x generated means that the combustion temperature in the combustion chamber 5 is decreased, and therefore, when the soot is hardly generated, the combustion temperature in the combustion chamber 5 is decreased. I can say. The same can be said from FIG. 7. That is, the combustion pressure is low in the state shown in FIG. 7 (B) where soot is hardly generated, and therefore the combustion temperature in the combustion chamber 5 is low at this time.

Secondly, when the amount of smoke produced, that is, the amount of soot produced, becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. This means that hydrocarbons are discharged without growing to soot. That is, linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 8 are thermally decomposed to form soot precursors when the temperature is raised in a state of oxygen deficiency, and then mainly soot is formed. Soot consisting of a solid with carbon atoms gathered is produced. In this case, the actual soot formation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. After that, it will grow to soot. Therefore, as described above, when the amount of soot generated becomes almost zero, the amounts of HC and CO emissions increase as shown in FIG. 6, but at this time HC is a soot precursor or a hydrocarbon in the state before it. .

When these considerations based on the experimental results shown in FIGS. 6 and 7 are summarized, the soot generation amount becomes almost zero when the combustion temperature in the combustion chamber 5 is low, and at this time, the soot precursor or the soot precursor The hydrocarbons in this state are discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the gas around it in the combustion chamber 5 is below a certain temperature, the soot growth process stops halfway, that is, the soot is generated. No combustion, combustion chamber 5
It has been found that soot is produced when the temperature of the fuel inside and inside it falls below a certain temperature.

By the way, the temperature of the fuel and its surroundings when the hydrocarbon production process stops in the state of the soot precursor, that is, the above-mentioned certain temperature depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. It cannot be said how many times it changes, but this certain temperature has a deep relationship with the amount of NO _x produced, and therefore this certain temperature is defined to some extent from the amount of NO _x produced. can do. That is, as the EGR rate increases, the temperature of the fuel and the gas around it during combustion decreases, and the amount of NO _x generated decreases. At this time, when the amount of NO _x generated is around 10 p.pm or less, soot is hardly generated. Therefore, the above certain temperature is NO
It is almost the same as the temperature when the amount of _X generation is around 10 p.pm or less.

Once soot is produced, it cannot simply be purified by post-treatment with a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before it can be easily purified by a post-treatment using a catalyst having an oxidizing function. In this way, NO _X
It is extremely effective to purify the exhaust gas by reducing the amount of the exhaust gas generated and discharging hydrocarbons from the combustion chamber 5 in the state of the soot precursor or in the state before it.

In order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the gas around it in the combustion chamber 5 during combustion is set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that the endothermic action of the gas around the fuel when the fuel burns has an extremely large effect on suppressing the temperature of the fuel and the gas around it.

That is, when only air exists around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel locally becomes extremely high. That is, at this time, the air separated from the fuel hardly absorbs the combustion heat of the fuel. In this case, since the combustion temperature locally becomes extremely high, the unburned hydrocarbons that have received this heat of combustion generate soot.

On the other hand, the situation is slightly different when the fuel is present in a mixed gas of a large amount of inert gas and a small amount of air.
In this case, the evaporated fuel diffuses into the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion heat is absorbed by the surrounding inert gas, so that the combustion temperature does not rise so much. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be suppressed low by the endothermic action of the inert gas.

In this case, in order to suppress the temperature of the fuel and the gas around it to a temperature lower than the temperature at which soot is produced, an amount of inert gas sufficient to absorb the amount of heat required to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas also increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action. Therefore, the inert gas is preferably a gas having a large specific heat. In this respect, since CO ₂ and EGR gas have a relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.

FIG. 9 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the cooling degree of the EGR gas is changed. That is, the curve A in FIG. 9 strongly cools the EGR gas to bring the EGR gas temperature to about 9
The curve B shows the case where the EGR gas is cooled by a small cooling device, and the curve C shows the case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 9, when the EGR gas is strongly cooled, the soot generation amount peaks when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Almost no soot will be generated if the percentage is exceeded. On the other hand, as shown by the curve B in FIG. 9, when the EGR gas is slightly cooled, the soot generation amount reaches a peak when the EGR rate is slightly higher than 50%, and in this case, the EGR rate is approximately 65% or more. If so, soot is hardly generated.

Further, as shown by the curve C in FIG. 9, EG
When the R gas is not forcibly cooled, the EGR rate is 5
The soot generation amount peaks near 5%, and in this case, if the EGR rate is set to approximately 70% or more, soot is hardly generated. Note that FIG. 9 shows the amount of smoke generated when the engine load is relatively high, and the EGR rate at which the amount of soot generated peaks when the engine load decreases and the EGR rate at which soot hardly occurs is slightly decreased. The lower limit of is also slightly lowered. Thus, the lower limit of the EGR rate at which soot is hardly generated changes depending on the cooling degree of EGR gas and the engine load.

FIG. 10 shows a mixture of EGR gas and air required to bring the temperature of the fuel and its surrounding gas at the time of combustion to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. The amount of gas, the ratio of air in this mixed gas amount, and the ratio of EGR gas in this mixed gas are shown. In FIG. 10, the vertical axis represents the combustion chamber 5
The total amount of intake gas sucked into the combustion chamber 5 is shown, and the chain line Y shows the total amount of intake gas that can be drawn into the combustion chamber 5 when supercharging is not performed. The horizontal axis shows the required load,
Z1 indicates a low load operation region.

Referring to FIG. 10, the ratio of air, that is, the amount of air in the mixed gas, shows the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 10, the ratio between the air amount and the injected fuel amount is the theoretical air-fuel ratio. On the other hand, in FIG. 10, the proportion of EGR gas, that is, the amount of EGR gas in the mixed gas, is necessary to bring the temperature of the fuel and its surrounding gas to a temperature lower than the temperature at which soot is formed when the injected fuel is burned. The minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of EGR rate, and is 70% or more in the embodiment shown in FIG. That is, the total intake gas amount sucked into the combustion chamber 5 is shown by the solid line X in FIG. 10, and the ratio of the air amount to the EGR gas amount of this total intake gas amount X is set as shown in FIG. The temperature of the fuel and the gas around it is lower than the temperature at which soot is produced,
Thus, no soot is generated. Also, NO at this time
_The amount of _X generation is about 10 p.pm or less, and therefore the amount of NO _X generation is extremely small.

Since the amount of heat generated when the fuel burns increases as the fuel injection amount increases, in order to maintain the temperature of the fuel and the gas around it at a temperature lower than the temperature at which soot is produced, heat generated by the EGR gas is used. The amount of absorption must be increased. Therefore, as shown in FIG. 10, the EGR gas amount must be increased as the injected fuel amount is increased. That is, the EGR gas amount needs to increase as the required load increases.

On the other hand, in the load region Z2 of FIG. 10, the total intake gas amount X required to prevent the generation of soot exceeds the total intake gas amount Y that can be inhaled. Therefore, in this case, in order to supply the total intake gas amount X required to prevent the generation of soot into the combustion chamber 5, both the EGR gas and intake air, or EG
It is necessary to supercharge or pressurize the R gas. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intakeable gas amount Y in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the air amount is slightly decreased to increase the EGR gas amount and the fuel is burned under the rich air-fuel ratio.

As described above, FIG. 10 shows that the fuel is stoichiometric.
Fig. 10 shows the case of combustion under
FIG. 10 shows the air flow rate in the low load operating range Z1.
Less than the amount of air
NO while preventing the generation of soot _XThe generation amount of around 10p.p.m
Or less, and also shown in FIG.
The air amount in the low load region Z1 is the air shown in FIG.
More than the amount, that is, the average value of the air-fuel ratio is 17 to 1
Even if it is lean, NO while preventing the generation of soot _XOccurrence of
The amount can be around 10 p.p.m or less.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excessive fuel does not grow to soot, and soot is generated. There is no. Further, at this time, a very small amount of NO _X is also generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature rises, but in the present invention the combustion temperature is suppressed to a low temperature, soot Not generated at all. Furthermore, NO _X
Also produces only a very small amount.

Thus, in the engine low load operation region Z1, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. Therefore, the amount of NO _x generated is extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio at this time lean.

By the way, in order to suppress the temperature of the fuel and the gas around it during combustion in the combustion chamber to a temperature below the temperature at which the growth of hydrocarbons stops halfway, when the engine load is relatively low and the calorific value due to combustion is small. Is preferred. Therefore, in the embodiment according to the present invention, when the engine load is relatively low, the temperature of the fuel and the gas around it during combustion are suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, and first combustion, that is, low temperature combustion is performed. When the engine load is relatively high, the second combustion, that is, the combustion that is more commonly performed than the conventional one is performed. It should be noted that here, the first combustion, that is, the low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the worst amount of inert gas in which the amount of soot is maximized, and soot is almost generated. Second combustion, that is, combustion that is more commonly performed than before, is combustion that has less inert gas in the combustion chamber than the worst inert gas that produces maximum soot. Say

FIG. 11 shows a first operating region I in which first combustion, that is, low temperature combustion is performed, and a second combustion region II in which second combustion, that is, combustion by a conventional combustion method is performed. In FIG. 11, the vertical axis L indicates the accelerator pedal 40.
Represents the amount of depression, that is, the required load, and the horizontal axis N represents the engine speed. Further, in FIG. 11, X (N) indicates the first boundary between the first operating region I and the second operating region II, and Y (N) indicates the first operating region I and the second operating region II. A second boundary with region II is shown. First operating area I
Determination of the operating range from the second operating range II to the second operating range II is performed based on the first boundary X (N), and the change of the operating range from the second operating range II to the first operating range I is determined. It is performed based on the second boundary Y (N).

That is, the operating condition of the engine is the first operating region I.
If the required load L exceeds the first boundary X (N) which is a function of the engine speed N during low temperature combustion, it is determined that the operating region has moved to the second operating region II. Combustion is performed by the combustion method of. Next, when the required load L becomes lower than the second boundary Y (N) which is a function of the engine speed N, it is determined that the operating region has moved to the first operating region I, and low temperature combustion is performed again.

FIG. 12 shows the output of the air-fuel ratio sensor 21. As shown in FIG. 12, the output current I of the air-fuel ratio sensor 21 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 21. Next, referring to FIG. 13, the first operating region I and the second
The operation control in the operation area II will be schematically described.

FIG. 13 shows the opening of the throttle valve 16, the opening of the EGR control valve 23, the EGR rate, the air-fuel ratio, the injection timing and the injection amount with respect to the required load L. As shown in FIG. 13, in the first operating region I where the required load L is low, the opening degree of the throttle valve 16 is gradually increased from near full close to about half open as the required load L increases, and the EGR control valve 23 The opening degree of is gradually increased from near full close to full open as the required load L increases. In addition, FIG.
In the example shown in (1), the EGR rate is set to approximately 70% in the first operating region I, and the air-fuel ratio is set to a slightly lean lean air-fuel ratio.

In other words, in the first operating region I, EGR
The opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled so that the ratio becomes approximately 70%, and the air-fuel ratio becomes a lean air-fuel ratio which is slightly lean. In addition,
The air-fuel ratio at this time is controlled to the target lean air-fuel ratio by correcting the opening degree of the EGR control valve 23 based on the output signal of the air-fuel ratio sensor 21. Further, in the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes late as the required load L becomes high, and the injection completion timing θE also becomes late as the injection start timing θS becomes late.

During the idling operation, the throttle valve 16 is closed to the fully closed state, and at this time, the EGR control valve 23 is also closed to the fully closed state. When the throttle valve 16 is closed to near full closure, the pressure in the combustion chamber 5 at the beginning of compression becomes low and the compression pressure becomes small. When the compression pressure becomes small, the compression work by the piston 4 becomes small, so that the vibration of the engine body 1 becomes small. That is, in idling operation, the throttle valve 16 is closed to close to the fully closed state in order to suppress the vibration of the engine body 1.

On the other hand, the engine operating region is the first operating region I.
When changing from the second operating region II to the second operating region II, the opening degree of the throttle valve 16 is increased stepwise from the half open state to the full open direction. At this time, in the example shown in FIG. 13, the EGR rate is approximately 70.
The air-fuel ratio is increased stepwise from a percentage to 40% or less. That is, since the EGR rate jumps over the EGR rate range (FIG. 9) in which a large amount of smoke is generated, a large amount of smoke is generated when the engine operating region changes from the first operating region I to the second operating region II. There is no.

In the second operating region II, the conventional combustion is performed. Soot and NO _X is slightly higher for although thermal efficiency as compared with low temperature combustion occurs, thus operating region of the engine is the first second from operating region I of the operation area II in the combustion process
When changed to, the injection amount is reduced stepwise as shown in FIG.

In the second operating region II, the throttle valve 16 is kept fully open except for a part, and the opening degree of the EGR control valve 23 is gradually reduced as the required load L increases. In this operating region II, the EGR rate becomes lower as the required load L becomes higher, and the air-fuel ratio becomes smaller as the required load L becomes higher. However, the air-fuel ratio is a lean air-fuel ratio even if the required load L becomes high. Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 14 shows the air-fuel ratio A / F in the first operating region I. In FIG. 14, A / F = 15.
5, each curve shown by A / F = 16, A / F = 17, A / F = 18 has an air-fuel ratio of 15.5, 16, 17, 18 respectively.
And the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 14, the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the air-fuel ratio A / F is leaner as the required load L is lower.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low temperature combustion can be performed even if the EGR rate is decreased. When the EGR rate is reduced, the air-fuel ratio becomes large, so that the air-fuel ratio A / F becomes larger as the required load L becomes lower as shown in FIG. The fuel consumption rate increases as the air-fuel ratio A / F increases. Therefore, in order to make the air-fuel ratio as lean as possible, the air-fuel ratio A / F is increased as the required load L decreases in this embodiment.

The target opening degree ST of the throttle valve 16 required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 5 (A), the required load L and the engine speed N
The target opening degree SE of the EGR control valve 23, which is stored in advance in the ROM 32 in the form of a map as a function of, and is required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG. 14, is shown in FIG. 15 (B). As described above, it is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N.

FIG. 16 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. Note that in FIG. 16, A / F = 24, A / F = 3
The curves indicated by 5, A / F = 45 and A / F = 60 respectively show the target air-fuel ratios 24, 35, 45 and 60. Throttle valve 1 required to set the air-fuel ratio to this target air-fuel ratio
The target opening ST of 6 is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 17 (A), and the air-fuel ratio is set to this target air-fuel ratio. The target opening degree SE of the EGR control valve 23 required for the above is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 17 (B).

Thus, in the diesel engine of this embodiment, the first combustion, that is, the low temperature combustion and the second combustion, that is, the normal combustion are performed based on the depression amount L of the accelerator pedal 40 and the engine speed N. In each combustion, the opening control of the throttle valve 16 and the EGR valve is performed in each combustion based on the depression amount L of the accelerator pedal 40 and the engine speed N according to the map shown in FIG. 15 or 17.

FIG. 18 is a plan view showing the exhaust gas purification device of this embodiment, and FIG. 19 is a side view thereof. The exhaust purification system includes a switching unit 71 connected to the downstream side of the exhaust manifold 17 via an exhaust pipe 18, and a NO _X storage reduction catalyst device 7.
0, one side of the NO _X storage reduction catalyst device 70 and the switching unit 7
1, a second connecting portion 72b connecting the other side of the NO _X storage reduction catalyst device 70 and the switching portion 71, and an exhaust passage 73 on the downstream side of the switching portion 71. is doing. The fuel supply device 7 for supplying fuel to the vicinity of the NO _X storage reduction catalyst device 70 is connected to the first connecting portion 72a.
4 are provided. The switching unit 71 includes a valve body 71a that allows the exhaust flow to be blocked in the switching unit 71. The valve body 71a is driven by a negative pressure actuator, a step motor, or the like. At one shutoff position of the valve body 71a, the upstream side in the switching portion 71 is the first connecting portion 7
The exhaust gas flows from one side to the other side of the NO _X storage reduction catalyst device 70 as shown by the arrow in FIG. .

FIG. 20 shows the other shut-off position of the valve body 71a. In this cutoff position, the switching unit 71
Downstream of the switching unit 71 with the upstream side of the inner is communicated with the second connecting portion 72b is communicated with the first connecting portion 72a, the exhaust gas, as shown by the arrows in FIG. 20, NO _X occluding and reducing catalyst device 70 Flows from the other side of the to one side. Thus, by switching the valve body 71a, the direction of the exhaust gas flowing into the NO _X storage reduction catalyst device 70 can be reversed, that is, the exhaust upstream side and the exhaust downstream side of the NO _X storage reduction catalyst device 70 can be switched. It is possible to reverse.

Further, FIG. 21 shows an intermediate position between the two shut-off positions of the valve body 71a. At this intermediate position, the inside of the switching unit 71 is not shut off, and the exhaust gas does not pass through the NO _X storage reduction catalyst device 70 having high passage resistance, that is, as shown by the arrow in FIG.
The NO _X storage reduction catalyst device 70 bypasses the NO _X storage reduction catalyst device 70 and flows directly to the exhaust passage 73. Of course, if the valve body 71a is set to a position between the intermediate position and the shut-off position, some of the exhaust gas is
The remaining exhaust gas passes through the O _X storage reduction catalyst device 70 and bypasses the NO _X storage reduction catalyst device 70. In this way, by controlling the opening degree of the valve body 71a, a part or all of the exhaust gas can bypass the NO _X storage reduction catalyst device 70. However, it is usually used in one of the blocking positions.

FIG. 22 shows the structure of the NO _X storage reduction catalyst device 70. 22, (A) is a front view of the NO _X storage reduction catalyst device 70, and (B) is a side sectional view. As shown in these figures, the present NO _X storage reduction catalyst device 70 has a wall-flow type having an oval front shape and a honeycomb structure formed of a porous material such as cordierite. It has a number of axial spaces subdivided by a number of axially extending partitions 54. In two adjacent axial spaces, the stopper 5
According to 3, one is closed on the exhaust downstream side and the other is closed on the exhaust upstream side. In this way, one of the two adjacent axial spaces serves as the exhaust gas inflow passage 50 and the other serves as the outflow passage 51, and the exhaust gas always passes through the partition wall 54, as indicated by the arrow in FIG. A NO _x absorbent and a noble metal catalyst such as platinum Pt described below are supported using alumina or the like on both side surfaces of each partition wall 54, and preferably on the pore surface of each partition wall.

The NO _x absorbent supported on the partition wall 54 is potassium K, sodium Na, lithium L in this embodiment.
i, alkali metal such as cesium Cs, barium B
a, at least one selected from alkaline earth metals such as calcium Ca, lanthanum La, and rare earths such as yttrium Y. This NO _x absorbent is lean when the air-fuel ratio in the atmosphere (the ratio of air to fuel, regardless of how much fuel is burning using oxygen in the air) is lean. absorbs NO _X, the air-fuel ratio to release NO _X absorbed and becomes the stoichiometric air-fuel ratio or rich N
It acts to absorb and release O _X.

This NO _x absorbent actually performs the action of absorbing and releasing NO _x , but the detailed mechanism of this action of absorbing and releasing some parts is not clear. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, about this mechanism NO _X
Pt and barium Ba on the partition wall of the storage reduction catalyst device
The explanation will be made taking as an example the case of supporting other precious metals,
The same mechanism can be obtained by using alkali metals, alkaline earths, and rare earths.

Regardless of low temperature combustion or normal combustion, when the combustion is performed in a lean air-fuel ratio state, the oxygen concentration in the exhaust gas is high, and at this time, as shown in FIG. 23 (A). These oxygen O ₂ adheres to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . On the other hand, NO 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 ). NO ₂ produced next
Part of Pd is absorbed in the absorbent while being oxidized on platinum Pt, and is combined with barium oxide BaO to diffuse into the absorbent in the form of nitrate ion NO ₃ ⁻ as shown in FIG. 23 (A). In this way, NO _X is absorbed in the NO _X absorbent. NO on the surface of platinum Pt as long as the oxygen concentration in the atmosphere is high
_{As long as 2} is produced and the NO _x absorption capacity of the absorbent is not saturated, NO ₂ will be absorbed in the absorbent to produce nitrate ion NO ₃ ⁻ .

On the other hand, when the air-fuel ratio of the atmosphere is made rich, the oxygen concentration is lowered, and as a result, NO _{2 on} the surface of platinum Pt is reduced.
The production amount of is reduced. Reacting with the amount of NO ₂ is lowered backward ^- proceed to (NO ₃ → NO _2), nitrate ion NO in absorbent ₃ and thus ^- are released from the absorbent in the form of NO _2. In this case NO _X released from _the NO _X absorbent is 23
As shown in (B), HC and C contained in the atmosphere
It is reduced by reacting with O and the like. When NO ₂ is no longer present on the surface of platinum Pt in this way, NO ₂ is released one after another from the absorbent. Therefore, if the air-fuel ratio of the atmosphere is made rich, the NO _x absorbent will reach N
O _X is released, and the released NO _X is reduced, so that NO _X is not released into the atmosphere.

[0064] In this case, NO _X is released from _the NO _X absorbent and the air-fuel ratio of the atmosphere to the stoichiometric air-fuel ratio. However, it takes a slightly longer time to emit all NO _X that is absorbed in the NO _X occluding and reducing catalyst device for NO _X from _the NO _X absorbent is not only released gradually in this case.

By the way is in the NO _X absorbing capacity of the NO _X absorbent is limited, NO _X absorbing capacity of the NO _X absorbent is required to release NO _X from _the NO _X absorbent before saturation. That is, the N absorbed by the NO _X storage reduction catalyst device 70.
Before the O _X amount reaches the NO _X storable amount, it is necessary for reproduction to be reduced and purified to release the NO _X, For that purpose, it is necessary to estimate the amount of NO _X. Therefore, in the present embodiment, the NO _X absorption amount A per unit time when low temperature combustion is being performed is shown in FIG. 24 as a function of the required load L and the engine speed N.
The NO _x absorption amount B per unit time when normal combustion is performed is obtained in advance in the form of a map as shown in (A).
24 as a function of the required load L and the engine speed N
It is obtained in advance in the form of a map (B), the estimating the amount of NO _X is absorbed in the NO _X occluding and reducing catalyst device by integrating per these unit time NO _X absorption amount A, B I am trying. Here, the NO _X absorption amount A per unit time when the low temperature combustion is performed is, of course, a negative value because NO _X is released when the low temperature combustion is performed at the rich air-fuel ratio. Become.

In this embodiment, the NO _X storage reduction catalyst device is regenerated when the NO _X absorption amount exceeds a predetermined allowable value. FIG. 25 is a first flowchart for this purpose. This flowchart is repeated every predetermined time. First, in step 101, NO _X
It is determined whether it is time to regenerate the storage reduction catalyst device 70. If it is not the reproduction time, the process ends as it is, but NO
_{When the X} absorption amount exceeds the predetermined allowable value, this determination is affirmative and the routine proceeds to step 102.

At step 102, it is judged if the low temperature combustion is currently performed. When this judgment is affirmed, it is judged in step 103 whether or not the temperature T of the NO _X storage reduction catalyst device is equal to or higher than the set temperature T1. In order to grasp this temperature T, a temperature sensor may be provided in the NO _X storage reduction catalyst device to directly detect it, or it may be estimated based on the exhaust gas temperature estimated by the engine operating state or measured. . When the determination in step 103 is negative, low temperature combustion is performed at the stoichiometric air-fuel ratio or the rich air-fuel ratio, that is, the regenerated air-fuel ratio. If the low temperature combustion that is currently performed is the low temperature combustion with a lean air-fuel ratio, the amount of injected fuel is increased to make the combustion air-fuel ratio the stoichiometric air-fuel ratio or the rich air-fuel ratio. Thus, the oxygen concentration in the atmosphere in the vicinity of the NO _X storage reduction catalyst is reduced and NO _X is released.

As described above, during low temperature combustion, a relatively large amount is generated.
A quantity of HC and CO is included, in particular this hydrocarbon HC
High activity due to soot precursor or previous state
NO _XNO released from the storage reduction catalyst device_XEven at low temperatures
It can be satisfactorily reduced and purified. Thus, simply the institution
Even if fuel is supplied to the exhaust system, this HC has high activity.
Most of them are NO along with exhaust gas._XStorage reduction catalyst device
However, if low temperature combustion is used, a small amount of fuel will pass.
And NO_XThe storage reduction catalyst device can be regenerated. Na
As mentioned above, when low temperature combustion is performed, air-fuel
Soot is hardly generated even if the ratio is rich.

Further, when the determination in step 103 is affirmative, that is, the temperature T of the NO _x storage reduction catalyst device.
Is relatively high, when the low temperature combustion is switched to the normal combustion with the lean air-fuel ratio in step 104,
It is determined whether or not the emission amount E of the harmful component, for example, HC, CO, or NO _{X from} the cylinder becomes equal to or larger than the set amount E1. In order to grasp the emission amount E1, it is sufficient to map the emission amount in advance based on the engine load, the engine speed and the like. Of course, it may be detected directly or indirectly from the exhaust gas. Even when the determination in step 104 is affirmative, low temperature combustion at the regenerated air-fuel ratio is performed in step 108. However, when the determination in step 104 is denied, that is, when the harmful components in the exhaust gas are small even if the normal combustion is switched to, the low temperature combustion is switched to the normal combustion with a lean air-fuel ratio in step 105.

Next, at step 106, the switching valve 71a is set to a position slightly rotated from the intermediate position to the one shutoff position side shown in FIG.
The O _X storage reduction catalyst device 70 is bypassed.
At this time, since there are few harmful components in the exhaust gas, there is no problem. Next, fuel is supplied to the vicinity of the NO _X storage reduction catalyst device 70 by the fuel supply device 74. If the NO _X storage reduction catalyst device has a relatively high temperature, this fuel is well oxidized by the supported oxidation catalyst such as platinum Pt and consumes oxygen, so that the oxygen concentration in the atmosphere near the NO _X storage reduction catalyst is reduced. NO _x is released by lowering. Also, the released NO _x is reduced and purified well.

Since most of the exhaust gas supplied here bypasses the NO _X storage reduction catalyst device,
The amount discharged to the downstream side of the NO _X storage reduction catalyst device together with the exhaust gas is small, and it is mainly used to bring only the atmosphere in the vicinity of the NO _X storage reduction catalyst device into the regenerated air-fuel ratio state. As a result, the NO _x storage reduction catalyst device can be regenerated with a smaller amount of fuel even when compared with the low temperature combustion at the regeneration air-fuel ratio described above.

When the determination in step 102 is negative, that is, when the normal combustion is being performed at the regeneration timing of the NO _X storage reduction catalyst device, the routine proceeds to step 109, and the harmful components are discharged as in step 104. It is determined whether the amount E is the set amount E1. When this is denied, as described above, in step 106, a large amount of exhaust gas bypasses the NO _x storage reduction catalyst device, and then in step 107, fuel is sent from the fuel supply device 74 to the vicinity of the NO _x storage reduction catalyst device. Supplied. On the other hand, when the determination in step 109 is affirmative, that is, when there are many harmful components in the exhaust gas, it is not preferable to bypass the exhaust gas, and the fuel is supplied in step 107 without doing so. However, in the reproduction of such ordinary combustion time of the NO _X occluding and reducing catalyst device, when the low temperature T of the NO _X occluding and reducing catalyst device, in order to fuel supplied from the fuel supply device 74 does not work well for reproduction The same judgment as in step 103 may be provided before step 109 to abandon regeneration until the temperature of the NO _X storage reduction catalyst device rises.

In step 106 of this flow chart, the valve body 71a is set to a position slightly rotated from the intermediate position to the one shutoff position side shown in FIG. 18, and a part of the exhaust gas is NO _X storage reduction catalyst device 70. To flow into.
This is in order to avoid a lack of oxygen when the fuel supplied to _the NO _X storage reduction catalyst device near burned by supported oxidation catalyst in the NO _X occluding and reducing catalyst device, the first connecting portion 72a If this fuel can be sufficiently combusted with oxygen in the exhaust gas, all of the exhaust gas may be bypassed with the valve body 71a at the intermediate position. As a result, the fuel supplied from the fuel supply device does not flow out from the NO _X storage reduction catalyst device together with the exhaust gas, and the fuel consumption rate can be further reduced.

By the way, the diesel engine of this embodiment switches between low temperature combustion and normal combustion as described above, and soot, that is, particulates are hardly generated during low temperature combustion, but during normal combustion. A relatively large amount of particulates is produced. Since this particulate is also a harmful substance, its release to the atmosphere must be suppressed.

The NO _X storage reduction catalyst device 70 is of the wall flow type as described above. As a result, the particulate matter in the exhaust gas is very small compared to the size of the pores of the partition wall 54, but the exhaust gas is not
When they pass through, they collide with and are collected on the surface of the partition wall 54 on the exhaust upstream side and on the surface of the pores in the partition wall 54. In this way, the present NO _X storage reduction catalyst device 70 can also function each partition wall 54 as a collection wall for collecting particulates. Of course, if it is not intended to collect the particulates, the NO _X storage reduction catalyst device does not have to be a wall flow type, that is, the plug 53 may be omitted in FIG.

The particulates thus collected are
If nothing is done, the NO _x storage reduction catalyst device 70 is gradually deposited to increase the exhaust resistance, and finally the vehicle running is adversely affected. Therefore, in each partition wall of the present NO _x storage reduction catalyst device, alumina or the like is used on both side surfaces and preferably also on the surface of the pores in order to oxidize and remove the collected particulates, which will be described below. An active oxygen releasing agent and a noble metal catalyst are supported.

The active oxygen releasing agent is one which promotes the oxidation of particulates by releasing active oxygen, and preferably, when excess oxygen is present in the surroundings, it takes in oxygen and retains it, and When the oxygen concentration decreases, the retained oxygen is released in the form of active oxygen.

As the noble metal catalyst, platinum Pt is usually used, and as the active oxygen releasing agent, potassium K, sodium Na, lithium Li, cesium Cs, alkali metals such as rubidium Rb, barium Ba, calcium Ca, strontium. An alkaline earth metal such as Sr,
At least one selected from lanthanum La, rare earths such as yttrium Y, and transition metals is used.

In this case, as the active oxygen releasing agent, alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, cesium Cs, rubidium Rb, barium Ba,
It is preferable to use strontium Sr.

Next, with respect to how platinum and Pt and potassium K are collected, how the collected particulates are oxidized and removed by the partition walls of the NO _X storage reduction catalyst device carrying such an active oxygen releasing agent will be described. Will be described as an example. Similar noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals can be used to perform the same particulate removing action.

Diesel engines normally burn under excess air, so the exhaust gas contains a large amount of excess air. That is, when the ratio of the air supplied to the intake passage and the combustion chamber to the fuel is called the air-fuel ratio of the exhaust gas, this air-fuel ratio is lean. In addition, NO in the combustion chamber
Therefore, NO is contained in the exhaust gas. Also, the fuel contains sulfur S, and this sulfur S
Reacts with oxygen in the combustion chamber to become SO ₂ . Therefore, the exhaust gas contains SO ₂ . Therefore, excess oxygen, N
The exhaust gas containing O and SO ₂ flows into the exhaust gas upstream side of the NO _X storage reduction catalyst device 70.

FIGS. 26A and 26B schematically show enlarged views of the exhaust gas contact surface of the NO _X storage reduction catalyst device 70. In FIGS. 26A and 26B, 60 indicates particles of platinum Pt, and 61 indicates potassium K.
2 shows an active oxygen releasing agent containing

As described above, since the exhaust gas contains a large amount of excess oxygen, when the exhaust gas comes into contact with the exhaust gas contact surface of the partition wall of the NO _X storage reduction catalyst device, the result shown in FIG.
As shown in 6 (A), the oxygen O ₂ is O ₂ ⁻ or O _2.
It adheres to the surface of platinum Pt in the form of ^2- . On the other hand, NO in the exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt, and N
It becomes O ₂ (2NO + O ₂ → 2NO ₂ ). Next, a part of the NO ₂ thus generated is absorbed on the active oxygen release agent 61 while being oxidized on the platinum Pt and is bonded to the potassium K.
As shown in FIG. 6 (A), nitrate ions NO ₃ ⁻ are diffused in the active oxygen release agent 61 to form potassium nitrate KNO ₃ .

On the other hand, as described above, the exhaust gas contains SO.
_{2 is} also included, and this SO ₂ is also absorbed in the active oxygen release agent 61 by the same mechanism as NO. That is, the oxygen O ₂ as described above O ₂ ^- are attached to or O ^2- form on the surface of the platinum Pt in, SO ₂ in the exhaust gas on the surface of the platinum Pt O ₂ ^- or O ^2- and Reacts to SO ₃ . Then, a part of the generated SO ₃ is absorbed on the active oxygen releasing agent 61 while being further oxidized on the platinum Pt, and is bound to the potassium K to form the sulfate ion SO ₄ ²⁻ in the active oxygen releasing agent 61. Diffuses to produce potassium sulfate K ₂ SO ₄ . In this way, potassium nitrate KNO is stored in the active oxygen release catalyst 61.
₃ and potassium sulfate K ₂ SO ₄ are produced.

The particulates in the exhaust gas are shown in FIG.
As shown by 62 in (B), it adheres to the surface of the active oxygen release agent 61 carried by the NO _X storage reduction catalyst device. At this time, the oxygen concentration decreases at the contact surface between the particulate 62 and the active oxygen release agent 61. When the oxygen concentration decreases, a difference in concentration occurs between the active oxygen release agent 61 and the active oxygen release agent 61 having a high oxygen concentration, so that the oxygen in the active oxygen release agent 61 is transferred to the contact surface between the particulate 62 and the active oxygen release agent 61. Try to move towards. As a result, potassium nitrate KNO ₃ formed in the active oxygen release agent 61 is decomposed into potassium K, oxygen O and NO, and the oxygen O moves toward the contact surface between the particulate 62 and the active oxygen release agent 61, and NO Are released from the active oxygen release agent 61 to the outside.
The NO released to the outside is oxidized on the platinum Pt on the downstream side and is again absorbed in the active oxygen release agent 61.

On the other hand, at this time, potassium sulfate K ₂ SO ₄ formed in the active oxygen release agent 61 is also decomposed into potassium K, oxygen O and SO _2, and the oxygen O is particulate 6
SO ₂ is released from the active oxygen release agent 61 to the outside toward the contact surface between the 2 and the active oxygen release agent 61. The SO ₂ released to the outside is oxidized on the platinum Pt on the downstream side,
It is again absorbed in the active oxygen release agent 61. However, since potassium sulfate K ₂ SO ₄ is stabilized, it is more difficult to release active oxygen than potassium nitrate KNO ₃ .

On the other hand, oxygen O toward the contact surface between the particulate 62 and the active oxygen release agent 61 is potassium nitrate KN.
Oxygen decomposed from compounds such as O ₃ and potassium sulfate K ₂ SO ₄ . Oxygen O decomposed from the compound has high energy and has extremely high activity. Therefore, oxygen toward the contact surface between the particulate 62 and the active oxygen release agent 61 is active oxygen O. When these active oxygen O comes into contact with the particulate 62, the particulate 62 is oxidized in a short time of several minutes to tens of minutes without emitting a bright flame. The active oxygen O that oxidizes the particulates 62 is also released when NO and SO ₂ are absorbed by the active oxygen release agent 61. That is, NO _X
Is believed to diffuse in the form of nitrate ions NO ₃ ^{− in} the active oxygen release agent 61 while repeating the bonding and separation of oxygen atoms, and active oxygen is also generated during this period. The particulate 62 is also oxidized by this active oxygen. Further, the particulates 62 thus deposited on the NO _X storage reduction catalyst device 70 are oxidized by the active oxygen O, but these particulates 62 are also oxidized by the oxygen in the exhaust gas.

By the way, platinum Pt and the active oxygen release agent 61
Is activated as the temperature of the NO _x storage reduction catalyst device rises, so the amount of active oxygen O released from the active oxygen release agent 61 per unit time increases as the temperature of the NO _x storage reduction catalyst device rises. Further, as a matter of course, the higher the temperature of the particulate itself, the easier it is to be oxidized and removed. Thus _the NO _X storage reduction particulate removable by oxidation amount oxidizable remove particulates without emitting a luminous flame per unit time on the catalytic converter increases as the temperature of the NO _X occluding and reducing catalyst device increases.

The solid line in FIG. 27 represents the amount G of oxidatively removable fine particles that can be oxidatively removed without emitting a luminous flame per unit time, and the horizontal axis in FIG. 27 represents the temperature TF of the NO _X storage reduction catalyst device. ing. Note that FIG. 27 shows the amount G of fine particles that can be removed by oxidation when the unit time is 1 second, that is, per unit second.
Any time such as minutes and 10 minutes can be adopted. For example, when 10 minutes is used as the unit time, the amount G of fine particles that can be removed by oxidation per unit time represents the amount G of fine particles that can be removed by oxidation per 10 minutes.
As shown in FIG. 27, the amount G of oxidatively removable fine particles that can be oxidized and removed on the O _X storage reduction catalyst device 70 without emitting a bright flame per unit time increases as the temperature of the NO _X storage reduction catalyst device 70 increases. To do.

The amount of particulates discharged from the combustion chamber per unit time is referred to as the amount M of discharged fine particles. When the amount M of discharged fine particles is smaller than the amount G of fine particles that can be removed by oxidation, for example, per second. When the amount M of discharged fine particles is smaller than the amount G of fine particles that can be oxidized and removed per second, or when the amount M of discharged fine particles per 10 minutes is smaller than the amount G of fine particles that can be oxidized and removed per 10 minutes, that is, the region of FIG. In I, all the particulates discharged from the combustion chamber are sequentially oxidized and removed in a short time without emitting a bright flame on the NO _X storage reduction catalyst device 70.

On the other hand, when the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation, that is, in the region II of FIG. 27, the amount of active oxygen is insufficient to sequentially oxidize all the particulates. FIGS. 28 (A) to 28 (C) show how particulates are oxidized in such a case.

That is, when the amount of active oxygen is insufficient to oxidize all the particulates, the particulate 62 is converted into the active oxygen releasing agent 61 as shown in FIG. 28 (A).
When it adheres to the upper part, only a part of the particulate 62 is oxidized, and the part of the particulate that is not sufficiently oxidized remains on the exhaust gas upstream side surface of the NO _X storage reduction catalyst device.
Next, if the state in which the amount of active oxygen is insufficient continues, the particulates that have not been oxidized one after another remain on the upstream surface of the exhaust gas, resulting in NO _x storage reduction as shown in FIG. 28 (B). The exhaust gas upstream surface of the catalyst device is covered with the residual particulate portion 63.

Such residual particulate portion 63
Gradually changes into carbon that is difficult to oxidize, and when the exhaust upstream surface is covered by the residual particulate portion 63, the platinum Pt oxidizes NO and SO ₂ and the active oxygen release agent 61 releases active oxygen. Suppressed. As a result, the residual particulate portion 63 can be gradually oxidized over time, but FIG.
As shown in (C), the residual particulate portion 63 is
Another particulate 64 is deposited on the top of the top one after another. That is, when the particulates are deposited in a laminated form, since the particulates are separated from the platinum Pt and the active oxygen releasing agent, even if they are easily oxidized, they will not be oxidized by the active oxygen. Absent. Therefore, further particulates are deposited one after another on the particulates 64. That is, if the state in which the amount M of discharged particulates is larger than the amount G of particulates that can be removed by oxidation continues, particulates will be accumulated in a layered manner on the NO _X storage reduction catalyst device.

As described above, in the region I of FIG. 27, the particulates are oxidized on the NO _X storage reduction catalyst device in a short time without emitting a bright flame, and in the region II of FIG. 27, the particulates are NO _X storage. It is deposited in layers on the reduction catalyst device. Therefore, by setting the relationship between the amount M of discharged fine particles and the amount G of particles that can be removed by oxidation in the region I, it is possible to prevent the accumulation of particulates on the NO _X storage reduction catalyst device. As a result, the NO _X storage reduction catalyst device 7
The pressure loss of the exhaust gas flow at 0 remains almost unchanged and is maintained at a substantially constant minimum pressure loss value. In this way, the reduction in engine output can be kept to a minimum. However, this is not always achieved,
If nothing is done, particulates may accumulate on the NO _X storage reduction catalyst device.

In this embodiment, the electronic control unit 3 described above is used.
29, the switching control of the valve element 71a is performed according to the second flowchart shown in FIG. 29 to prevent the accumulation of a large amount of particulates on the NO _X storage reduction catalyst device. This flowchart is repeated every predetermined time. First, in step 201, it is judged whether or not it is the set time for switching the valve body 71a. This setting time is
It is set every predetermined time or every predetermined traveling distance. When this determination is denied, the processing is ended as it is, but when the determination is affirmed, the routine proceeds to step 202, where it is determined whether or not the current particulate emission amount from the engine combustion chamber, that is, the exhaust particulate amount M is equal to or greater than the set amount M1. To be judged. In order to grasp the discharged particulate amount, a map may be prepared in advance based on the engine operating state determined by the engine load, the engine speed, etc., or a particulate sensor for optically detecting the particulate amount in the exhaust gas may be used. You may use. The mapping also considers whether low temperature combustion or normal combustion is performed in the case of the diesel engine of this embodiment.

When the determination in step 202 is denied, for example, when the engine is decelerating, when the engine is idling, when the engine has a low load,
Alternatively, during low temperature combustion or the like, the amount of particulates contained in the exhaust gas is not so large, and the switching of the valve body 71a is executed in step 203. That is, NO
The exhaust upstream side and the exhaust downstream side of the _X storage reduction catalyst device are reversed. On the other hand, when the determination in step 202 is affirmative, the amount of particulates contained in the exhaust gas is relatively large, so switching of the valve body 71a is stopped in step 204, and only when the determination in step 202 is denied. 71a is switched.

FIG. 30 is an enlarged sectional view of the partition wall 54 of the NO _X storage reduction catalyst device. While the vehicle travels for a predetermined time or a predetermined travel distance, driving in a region II of FIG. 27 may be performed, and as shown by a grid in FIG.
The exhaust upstream surface of the partition wall 54 on which the exhaust gas mainly collides and the exhaust gas flow facing surface in the pores collide and collect particulates as one collection surface and are oxidized and removed by the active oxygen release agent. This oxidation removal may be insufficient and particulates may remain. At this point, the exhaust resistance of the NO _X storage reduction catalyst device does not adversely affect the running of the vehicle, but further accumulation of particulates causes a problem such as a significant decrease in engine output. In the second flow chart, at this point, when the amount of particulates contained in the exhaust gas is not so large,
The exhaust upstream side and the exhaust downstream side of the NO _X storage reduction catalyst device are reversed. As a result, no further particulates are deposited on the particulates remaining on the one collecting surface of the partition wall 54, and the residual particulates are gradually oxidized and removed by the active oxygen released from the one collecting surface. To be done. In addition, the residual particulates are easily broken and subdivided by the exhaust gas flow in the opposite direction, as shown in FIG. 30 (B), and flow mainly in the pores to the downstream side.

As a result, many of the finely-divided particulates are dispersed in the pores of the partition walls and are directly contacted with the active oxygen releasing agent carried on the inner surfaces of the pores of the partition walls to be oxidized and removed. More opportunities. By thus supporting the active oxygen-releasing agent also in the pores of the partition wall, the residual particulates can be markedly easily oxidized and removed. Further, in addition to this oxidation removal, the other collection surface of the partition wall 54 that is upstream due to the backflow of exhaust gas, that is, the exhaust upstream surface and the inside of the pores of the partition wall 54 where the exhaust gas mainly collides at present. On the surface facing the exhaust gas flow (the relationship opposite to the one collecting surface), new particulates in the exhaust gas adhere and are oxidized and removed by the active oxygen released from the active oxygen release agent. . A part of the active oxygen released from the active oxygen release agent during the oxidative removal moves to the downstream side together with the exhaust gas, and oxidizes and removes the particulates still remaining due to the reverse flow of the exhaust gas.

That is, in the residual particulate matter on one of the collecting surfaces of the partition wall, not only the active oxygen released from this collecting surface but also the particulate matter on the other collecting surface of the partition wall due to the backflow of the exhaust gas. The remaining active oxygen used for oxidative removal comes with the exhaust gas. As a result, at the time of switching of the valve body, even if some particulates are accumulated in a layered manner on one collecting surface of the partition wall, if exhaust gas is made to flow backward, the particulates will be accumulated on the residual particulates. Also, in addition to the arrival of active oxygen, further particulates will not be deposited, so the deposited particulates will be gradually oxidized and removed, and if there is some time before the next backflow,
During this period, it can be sufficiently oxidized and removed. Thus, when the first collecting surface and the second collecting surface are alternately used for collecting the particulates, each collecting surface is compared with the case where the single collecting surface is used to collect the particulates. Since the amount of particulates trapped on the collecting surface can be reduced, which is advantageous for oxidizing and removing the particulates, no particulates are deposited in the NO _X storage reduction catalyst device, and the NO _X storage reduction catalyst It is possible to prevent clogging of the device.

In the second flow chart, the switching of the valve element is performed every predetermined time or every predetermined traveling distance, and the residual particulates on the NO _X storage reduction catalyst device are transformed into a carbon material which is difficult to be oxidized. The valve body was previously switched. Also, it is possible to oxidize and remove the particulates before a large amount of particulates are deposited,
A large amount of accumulated particulates are ignited and burned at one time to generate a large amount of combustion heat, and this large amount of combustion heat also prevents problems such as melting damage of the NO _X storage reduction catalyst device. Further, even if a large amount of particulates is accumulated on one collecting surface of the partition wall of the NO _X storage reduction catalyst device at the time of switching the valve element due to some factor, if the valve element is switched, the accumulated particulate matter is Some of the fragmented particulates that could not be oxidized and removed in the pores of the partition wall are discharged from the NO _X storage reduction catalyst device because they are relatively easily broken and fragmented by the exhaust gas flow in the opposite direction. However, the exhaust resistance of the NO _X storage reduction catalyst device does not further increase and does not adversely affect the running of the vehicle, and the other collection surface of the partition wall of the NO _X storage reduction catalyst device collects new particulates. Is possible.

As described above, in the present exhaust gas purifying apparatus, while the valve body 71a is switched from one shut-off position to the other shut-off position, the exhaust gas is NO _x storage reduction catalyst device 70.
According to this flowchart, the exhaust gas does not contain particulates or even if it contains particulates, the amount of particulates is not so large. Even if the exhaust gas bypasses the NO _X storage reduction catalyst device for a short period of switching, almost no particulate matter is released into the atmosphere.

[0102] Further, by utilizing the fact that the pressure difference between the exhaust upstream side and the exhaust downstream side of the NO _X occluding and reducing catalyst device 70 in accordance with the particulate amount of the residual and deposited on _the NO _X storage reduction catalyst device is raised, When the pressure difference becomes equal to or higher than the set pressure difference, it may be set as a set timing for switching the valve body, assuming that a certain amount of particulates are accumulated on the NO _X storage reduction catalyst device. Specifically, the exhaust pressure on one side of the NO _X storage reduction catalyst device 70, that is, the exhaust pressure in the first connecting portion 72a (see FIG. 18) is set to the first connecting portion 72.
It is detected by the pressure sensor arranged in a and N
Exhaust pressure on the other side of the O _X storage reduction catalyst device, that is,
Exhaust pressure in the second connection portion 72b (see FIG. 18) is detected by a pressure sensor arranged in the second connection portion 72b,
It is determined whether or not the absolute value of the differential pressure between these exhaust pressures is equal to or greater than the set pressure difference. Here, the absolute value of the differential pressure is used because it is possible to grasp the increase in the differential pressure regardless of which of the first connecting portion 72a and the second connecting portion 72b is on the exhaust upstream side. Strictly speaking, the pressure difference between the two sides of the NO _X storage reduction catalyst device also changes depending on the exhaust gas pressure discharged from the cylinder for each engine operating state. Is preferably specified.

Besides this differential pressure, for example, NO _x
A change in the electric resistance value on a predetermined partition in the storage reduction catalyst device is monitored, and when the electric resistance value becomes equal to or less than a set value due to the accumulation of particulates, a certain amount of particulate matter is present on the NO _x storage reduction catalyst device. It is also possible to set the timing for switching the valve bodies, assuming that they have accumulated. Further, in a predetermined partition wall of the NO _X storage reduction catalyst device, a setting for switching the valve body is utilized by utilizing the fact that the light transmittance or the light reflectance is reduced due to the accumulation of particulates. You may set the time. As described above, by directly determining the accumulation of particulates and setting the set timing for switching the valve body, it is possible to more reliably prevent a significant decrease in the engine output.

In this way, the NO _X storage reduction catalyst device 70
When using also for particulate collection,
In order to prevent the accumulation of a large amount of particulates, it is very effective to reverse the exhaust gas upstream side and the exhaust gas downstream side. Thereby, without following the second flow chart
For example, the valve body 71a may be occasionally switched without determining the timing. Further, in the first flowchart, the valve body 71a may be switched to the other shut-off position instead of returning to the one shut-off position after bypassing the exhaust gas. In this case, since the fuel supply device 74 is provided only in the first connecting portion 72a, when the exhaust gas is bypassed except for a part in the next regeneration of the NO _X storage reduction catalyst device, The valve body 71a is located between one of the shutoff positions and the intermediate position.
Of course, when the fuel supply device 74 is provided not only on the first connecting portion 72a but also on the second connecting portion 72b, the valve body 71a is configured such that a part of the exhaust gas is discharged to the connecting portion on the fuel supply side. The opening is controlled so as to flow in.

Thus, NO_XStorage reduction catalyst device deposited
Exhaust gas upstream and exhaust with the intention of oxidizing and removing particulates.
NO when the air downstream side is switched and used
_XStorage is mainly NO_XOne in the partition wall of the storage reduction catalyst device
It is performed alternately on the one side and the other side. As in this example,
NO_XFuel only on one side of the partition of the storage reduction catalyst device
Even if you can not supply the other, if you spend some time, the other side of the partition
NO stored on the side _XIt is possible to purify the released
It However, to shorten the playback time, NO_XStorage reduction
When regenerating the catalyst device, the above two fuel supply devices
Alternately used to_XMainly occludes
It is preferable to supply the fuel to the other side. of course,
Bypass almost all the exhaust gas during this regeneration
The fuel from two fuel supply devices at the same time.
NO by supplying_XBoth of the partition walls of the storage reduction catalyst device
NO from the side at the same time_XCan be purified and released
It is possible to further reduce the time.

As described above, the exhaust purification system of the present invention makes it possible to reverse the exhaust upstream side and the exhaust downstream side of the NO _X storage reduction catalyst device. Also, N
In the O _X storage reduction catalyst device, a large opening area is required for facilitating the inflow of exhaust gas, but this exhaust gas purification device deteriorates vehicle mountability as shown in FIGS. 18 and 19. N having a large opening area without
An O _X storage reduction catalyst device can be used. Further, when the NO _X storage reduction catalyst device is used for collecting particulates, step 1 of the first flowchart
In 04 and 109, it is preferable to include particulates as a harmful substance. That is, it is preferable that the exhaust gas does not bypass the NO _X storage reduction catalyst device when the particulate emission amount is large.

31. Instead of the second flow chart shown in FIG.
7 is a third flowchart for preventing a large amount of particulates from depositing on the NO _X storage reduction catalyst device. This flowchart is repeated every predetermined time.
First, in step 301, the current fuel injection amount TA
It is determined whether U is smaller than the set fuel injection amount TAU1. When this determination is denied, the fuel injection amount TAU
, The exhaust gas temperature is high, and the valve body ends with one shutoff position.

On the other hand, when the determination in step 301 is affirmative, the exhaust gas temperature is low, and when all the exhaust gas is passed through the particulates, the temperature of the NO _X storage reduction catalyst device is lowered and the active oxygen releasing agent The amount of fine particles that can be removed by oxidation is reduced. As a result, particulates are easily deposited on the NO _X storage reduction catalyst device. In this flowchart, in step 302, the lower the exhaust gas temperature or the smaller the fuel injection amount, the more the exhaust gas bypasses the NO _x storage reduction catalyst device without passing through the NO _x storage reduction catalyst device. It is calculated. Next, at step 303, the opening degree of the valve body is controlled between the shutoff position and the intermediate position based on this bypass exhaust gas amount.

Thus, for example, the exhaust gas has a very low temperature.
At the time of the fuel cut which becomes a degree, all exhaust gas
Bypass the exhaust gas and the exhaust gas is not so cold
By partially bypassing the exhaust gas,
O_XKeep the storage reduction catalyst device at a relatively high temperature to activate the active acid.
Maintain a high amount of fine particles that can be oxidized and removed in the elementary release agent, and _X
Accumulation of a large amount of particulates on the storage reduction catalyst device
Is prevented. Of course, in this flowchart
When the judgment in step 301 is affirmative,
Is NO_XSurely prevent temperature drop of the storage reduction catalyst device
In order to bypass all the exhaust gas,
Is also good. In this way, some or all of the exhaust gas is
NO when the fuel supply device 74_XOcclusion
If fuel is supplied to the vicinity of the reduction catalyst device (a part of exhaust gas
When bypassing the engine, supply fuel from the exhaust upstream side
Yes, this fuel is NO_XToo many storage reduction catalyst devices
NO without passing_XSupported by the storage reduction catalyst device
It is burned well by the oxidation catalyst. By that
NO due to this combustion heat_XTemperature rise of storage reduction catalyst device
It is possible to remove the active oxygen releasing agent by oxidation.
Improves the amount of fine particles, NO_XLarge amount to storage reduction catalyst device
To prevent the accumulation of particulates.
You can Also, after bypassing the exhaust gas, the valve body
By switching 71a to the other blocking position,
And NO_XParticulate deposits on the storage reduction catalyst device
Even as mentioned above, good deposition particulates
Can be removed by oxidation.

Further, in this flowchart, instead of the determination of the fuel injection amount in step 301, for example,
It is detected that the driver depresses the brake pedal or releases the accelerator pedal while the vehicle is running,
At this time, all the exhaust gas may be bypassed because the fuel cut is performed. In addition, for example, it is detected that the driver depresses the brake pedal or releases the accelerator pedal while the vehicle is stopped. You may make it bypass the exhaust gas of a part. When the exhaust gas temperature is low as described above, since the fuel is not injected or the fuel injection amount is small, the exhaust gas contains almost no particulates and even if the exhaust gas is bypassed. No particulates are released into the atmosphere. Also, the amount of harmful substances such as HC, CO, or NO _X emitted is small, and a large amount of these substances is not released into the atmosphere.

In this way, it is effective to bypass at least part of the exhaust gas without passing through the NO _X storage reduction catalyst device, if necessary. In this exhaust emission control device, including this first flow chart, NO _X
The switching unit 71 for reversing the exhaust gas upstream side and the exhaust gas downstream side of the storage reduction catalyst device was used. The exhaust gas may be bypassed.

When the atmosphere in the vicinity of the NO _X storage reduction catalyst device has a rich air-fuel ratio, that is, when the oxygen concentration in the atmosphere is reduced, the active oxygen releasing agent 61 releases active oxygen O to the outside at once. . Due to the active oxygen O released all at once, the deposited particulates are easily oxidized and easily removed by oxidation.

On the other hand, when the atmosphere in the vicinity is maintained at a lean air-fuel ratio, the surface of platinum Pt is covered with oxygen, and so-called oxygen poisoning of platinum Pt occurs. Such oxidising effect on poisoning occurs when NO _X is decreased absorption efficiency of the NO _X to be reduced, the active oxygen release amount from the active oxygen release agent 61 is lowered by thus. However, when the air-fuel ratio is made rich, oxygen on the surface of platinum Pt is consumed and oxygen poisoning is eliminated. Therefore, when the air-fuel ratio is switched from rich to lean again, the oxidizing action on NO _x is strengthened, and NO The absorption efficiency of _X is increased, and thus the amount of active oxygen released from the active oxygen release agent 61 is increased.

Therefore, if the air-fuel ratio is occasionally changed temporarily from lean to rich while the air-fuel ratio is maintained lean, the oxygen poisoning of platinum Pt is eliminated each time and the air-fuel ratio is lean. The amount of active oxygen released is increased, and thus the oxidizing action of particulates on the NO _X storage reduction catalyst device 70 can be promoted.

Furthermore, the elimination of this oxygen poisoning is, so to speak,
Since the reducing substance is combusted, the NO _x storage reduction catalyst device is heated with heat generation. As a result, the amount of fine particles that can be removed by oxidation in the NO _X storage reduction catalyst device is improved, and further, the removal of residual and accumulated particulates by oxidation becomes easy. If the air-fuel ratio of the exhaust gas is made rich immediately after switching the exhaust upstream side and the exhaust downstream side of the NO _X storage reduction catalyst device by the valve body 71a, in the NO _X storage reduction catalyst device partition wall where no particulate remains. On the other collecting surface, it is easier to release active oxygen than on the other collecting surface, so that by a larger amount of released active oxygen,
Residual particulates on one of the collection surfaces can be more reliably oxidized and removed. Of course, regardless of the switching of the valve body 71a, the atmosphere in the vicinity may occasionally have a rich air-fuel ratio, which makes it difficult for particulates to remain and accumulate in the NO _X storage reduction catalyst device.

As a method for making the atmosphere near the rich air-fuel ratio, for example, the above-mentioned low temperature combustion may be carried out. Of course, when switching from normal combustion to low temperature combustion, or
Before that, the exhaust upstream side and the exhaust downstream side of the NO _X storage reduction catalyst device may be switched. Further, the combustion air-fuel ratio may simply be made rich in order to make the nearby atmosphere a rich air-fuel ratio. In addition to the normal main fuel injection in the compression stroke, fuel may be injected (post-injection) into the cylinder in the exhaust stroke or expansion stroke by the engine fuel injection valve, or fuel may be injected into the cylinder in the intake stroke. May be jetted (rubber jet). Of course, it is not always necessary to provide an interval between the main fuel injection and the post injection or the rubber injection. It is also possible to supply fuel to the engine exhaust system, and in this embodiment, the fuel supply device 74 may supply fuel to the vicinity of the NO _X storage reduction catalyst device. Further, as described above, since the low temperature combustion is performed on the engine low load side, the low temperature combustion is performed immediately after the fuel cut during deceleration of the engine, and immediately after the valve body 71a is set to the intermediate position in the third flowchart. There are many occasions when low-temperature combustion is carried out, and it is possible to satisfactorily oxidize and remove the deposited particulates by switching the valve element.

By the way, calcium SO in the exhaust gas produces calcium sulfate CaSO ₄ when SO ₃ is present. This calcium sulfate CaSO ₄ is difficult to be removed by oxidation and remains as ash on the NO _X storage reduction catalyst device. Therefore, N due to residual calcium sulfate
In order to prevent clogging of the O _X storage reduction catalyst device,
As the active oxygen release agent 61, it is preferable to use an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, for example, potassium K, so that SO ₃ diffusing into the active oxygen release agent 61 binds to potassium K. To form potassium sulfate K ₂ SO ₄ , calcium Ca
Pass through the partition walls of the NO _X storage reduction catalyst device without binding to SO ₃ . Therefore, the NO _x storage reduction catalyst device will not be clogged with ash. Thus, as described above, calcium C is used as the active oxygen release agent 61.
Alkali metal or alkaline earth metal having a higher ionization tendency than a, that is, potassium K, lithium Li, cesium C
s, rubidium Rb, barium Ba, strontium S
It will be preferred to use r.

Further, even if a NO _x storage reduction catalyst device as an active oxygen releasing agent is loaded with only a noble metal such as platinum Pt, active oxygen is released from NO ₂ or SO ₃ retained on the surface of platinum Pt. be able to. However, in this case, the solid line showing the amount G of fine particles that can be removed by oxidation moves to the right of the solid line shown in FIG. It is also possible to use ceria as the active oxygen releasing agent. Ceria
If the oxygen concentration in the exhaust gas is high, it absorbs oxygen (Ce ₂ O ₃
→ 2CeO _2), the oxygen concentration in the exhaust gas release active oxygen when reduced (for 2CeO ₂ → Ce ₂ O ₃₎ is intended, for the oxidation removal of particulate matter, NO _X
The atmosphere in the vicinity of the storage reduction catalyst device needs to have a rich air-fuel ratio regularly or irregularly. Iron or tin may be used instead of ceria.

It is also possible to use, as the active oxygen releasing agent, a NO _X storage reduction catalyst used for purifying NO _X in the exhaust gas. In this case, in order to release NO _X or SO _X , it is necessary to temporarily set the vicinity atmosphere to the regeneration air-fuel ratio, that is, the rich air-fuel ratio as described above, and this enrichment control is performed by the NO _X storage reduction catalyst. It is preferable to carry out after reversing the upstream side and the downstream side of the apparatus.

FIG. 32 is a fourth flow chart for regeneration of the NO _X storage reduction catalyst apparatus which is carried out in place of the first flow chart of FIG. In this flowchart, the internal combustion engine normally carries out normal combustion. The difference between this flowchart and the first flowchart will be described below. In this flowchart, step 40
When it is determined in step 1 that it is time to regenerate the NO _X storage reduction catalyst device 70, in step 402, N
It is determined whether or not the temperature T of the O _X storage reduction catalyst device is equal to or higher than the set temperature T1. When this decision is denied,
Proceeding to step 403, it is determined whether or not the current operating state is a region where low temperature combustion is possible. In the internal combustion engine in the first flow chart, low temperature combustion and normal combustion are switched according to the map shown in FIG. However, the normal combustion region in this map does not indicate the low temperature combustion impossible region, and the low temperature combustion is possible even in the region on the higher load side than the low temperature combustion region.

When the determination in step 403 is affirmative, in step 407, low temperature combustion is performed at the stoichiometric air-fuel ratio or the rich air-fuel ratio, that is, the regenerated air-fuel ratio. Thus, the oxygen concentration in the atmosphere in the vicinity of the NO _X storage reduction catalyst is reduced to release NO _X , and at the same time, CO contained in a relatively large amount in the exhaust gas during low temperature combustion and highly active H 2.
Due to C, the released NO _x can be satisfactorily reduced and purified even if the temperature of the NO _x storage reduction catalyst device is low.

On the other hand, when the determination in step 402 is affirmative, that is, the temperature T of the NO _X storage reduction catalyst device.
When is relatively high, the routine proceeds to step 404, where a harmful component in normal combustion at the current lean air-fuel ratio, for example, H
It is determined whether or not the emission amount E of C, CO, or NO _{X from} the cylinder is equal to or greater than the set amount E1. When this judgment is affirmative, that is, when the harmful components in the exhaust gas are relatively large, the routine proceeds to step 403, where it is judged whether or not it is in the low temperature combustible region, and if possible, regeneration by low temperature combustion is performed. Carry out.

When the determination in step 404 is negative, that is, when the harmful components in the exhaust gas are small, the routine proceeds to step 405, where the switching valve 71a slightly moves from the intermediate position to one of the shut-off positions shown in FIG. The exhaust gas is turned to the side so that the exhaust gas except a part bypasses the NO _X storage reduction catalyst device 70. At this time, since there are few harmful components in the exhaust gas, there is no problem. Next, fuel is supplied to the vicinity of the NO _X storage reduction catalyst device 70 by the fuel supply device 74. This fuel is NO _x
Since the storage reduction catalyst device has a relatively high temperature, it is oxidized well by the supported oxidation catalyst such as platinum Pt and consumes oxygen, and the oxygen concentration in the atmosphere near the NO _x storage reduction catalyst is reduced to reduce NO. _{Emit X.} Further, the released NO _X is reduced and purified well.

Since the fuel supplied here is mainly used to bring the atmosphere in the vicinity of the NO _X storage reduction catalyst device into the regenerated air-fuel ratio state as described in the first flow chart, the fuel supplied by the low temperature combustion is used. Compared to regeneration, the NO _x storage reduction catalyst device can be regenerated with a smaller amount of fuel.

In this flowchart, even when the NO _X storage reduction catalyst device is at a low temperature or when the harmful components in the exhaust gas during normal combustion are relatively large, in the region where low temperature combustion is impossible, step 405 And 406, the regeneration by the fuel supply is performed. In this case, particularly when the harmful components in the exhaust gas are relatively large, the fuel may be supplied to the vicinity of the NO _X storage reduction catalyst device without bypassing the exhaust gas. In any case, in these cases, it is difficult to reduce the fuel consumption rate at the time of regeneration as compared with the conventional case, but such regeneration is not always performed, and in the long term, Low fuel consumption regeneration. Therefore, according to this flowchart, the fuel consumption rate at the time of regeneration can be reduced compared to the conventional case.

In the present embodiment, the NO _x storage reduction catalyst device itself carries the active oxygen releasing agent, and the particulate matter is oxidized and removed by the active oxygen released by the active oxygen releasing agent. However, the present invention is not limited thereto. For example, active oxygen and particulate oxides such as nitrogen dioxide that function equivalently to active oxygen are
_{Even if} it is released from the _X storage reduction catalyst device or the substance supported on it, it may flow into the NO _X storage reduction catalyst device from the outside. Even when the particulate oxidant flows in from the outside, the first collecting surface and the second collecting surface of the collecting wall are alternately used to collect the particulate matter, so that the exhaust downstream side On the other collecting surface, the new particulates will not be accumulated, and the accumulated particulates will be gradually oxidized and removed by the particulate oxidizing component flowing from the other collecting surface to form the accumulated particulates. Can be sufficiently oxidized and removed in a certain time. In the meantime, since the other collecting surface collects the particulates and oxidizes by the particulate oxidization component, the same effect as described above is obtained. Also in this case,
Increasing the temperature of the NO _X storage reduction catalyst device raises the temperature of the particulates themselves and facilitates oxidation removal.

[0127]

As described above, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, NO _X is absorbed when the atmosphere located in the engine exhaust system and the nearby atmosphere has a lean air-fuel ratio, and the stoichiometric air-fuel ratio or rich air-fuel ratio is obtained. NO regenerated at the regeneration air-fuel ratio
And _X occluding and reducing catalyst device, and a bypass means for at least part of the exhaust gas _the NO _X storage reduction catalyst device makes it possible to bypass the fuel supply device for supplying fuel to _the NO _X storage reduction catalyst device near The internal combustion engine has an inert gas supply means for supplying an inert gas into the cylinder, and supplies a larger amount of inert gas than the worst inert gas amount that maximizes the soot generation amount to the cylinder. It is possible to perform low-temperature combustion in which it is supplied to the inside to perform combustion and normal combustion in which combustion is performed at a lean air-fuel ratio, and when regenerating the NO _X storage reduction catalyst device, low-temperature combustion is performed at a regeneration air-fuel ratio. fuel supplied with bypassing at least a portion of the exhaust gas and the first reproducing means to reproduce air-fuel ratio _the NO _X storage reduction catalyst near ambient by the exhaust gas when performed, by the bypass means during ordinary combustion NO _X and fueled by location
It is possible to select the second regenerating means for setting the regeneration air-fuel ratio in the atmosphere in the vicinity of the storage reduction catalyst.

As a result, in the first regenerating means, the NO _X storage reduction catalyst device is regenerated mainly by the highly active HC contained in the exhaust gas at the time of low temperature combustion. Playback can be realized. Further, in the second regeneration means, part of the exhaust gas is NO _x.
Since the fuel is supplied while bypassing the storage reduction catalyst device, it is difficult for the supplied fuel to pass through the NO _x storage reduction catalyst device, and the regeneration can be surely realized with a little additional fuel. Thus, whichever regeneration means is selected, the fuel supplied to the cylinder or the engine exhaust system is more likely to pass through the NO _X storage reduction catalyst device together with the exhaust gas than the ordinary regeneration means. Although the consumption rate can be reduced, if the second regeneration means is selected, the fuel consumption rate during regeneration can be further reduced.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a diesel engine including an exhaust emission control device according to the present invention.

2 is an enlarged vertical sectional view of the combustion chamber of FIG.

FIG. 3 is a bottom view of the cylinder head of FIG.

FIG. 4 is a side sectional view of a combustion chamber.

FIG. 5 is a diagram showing lift of intake and exhaust valves and fuel injection.

FIG. 6 is a diagram showing a generation amount of smoke and NO _x , and the like.

FIG. 7A is a diagram showing a change in combustion pressure when the air-fuel ratio is around 21 and the amount of smoke generated is the largest, and FIG. 7B is a graph showing that the amount of smoke generated is almost zero when the air-fuel ratio is around 18. It is a figure which shows the combustion pressure change at the time.

FIG. 8 is a diagram showing a fuel molecule.

FIG. 9 is a diagram showing a relationship between an amount of smoke generated and an EGR rate.

FIG. 10 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 11 is a diagram showing a first operating region I and a second operating region II.

FIG. 12 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 13 is a diagram showing the opening of a throttle valve and the like.

FIG. 14 is a diagram showing an air-fuel ratio in a first operating region I.

15A is a diagram showing a map of a target opening of a throttle valve, and FIG. 15B is a diagram showing a map of a target opening of an EGR control valve.

FIG. 16 is a diagram showing an air-fuel ratio in second combustion.

17A is a diagram showing a map of a target opening of a throttle valve, and FIG. 17B is a diagram showing a map of a target opening of an EGR control valve.

FIG. 18 is a plan view of the vicinity of a switching unit and an NO _X storage reduction catalyst device in the engine exhaust system.

FIG. 19 is a side view of FIG.

FIG. 20 is a view showing another shut-off position of the valve body in the switching portion, which is different from FIG. 18.

FIG. 21 is a diagram showing an intermediate position of the valve element in the switching section.

22A is a front view showing the structure of a NO _X storage reduction catalyst device, and FIG. 22B is a side sectional view showing the structure of a NO _X storage reduction catalyst device.

FIG. 23 is a diagram for explaining the action of NO _X absorption and release.

FIG. 24 is a diagram showing a map of NO _X absorption amount per unit time.

FIG. 25 is a first flowchart for regenerating the NO _X storage reduction catalyst device.

FIG. 26 is a diagram for explaining an oxidizing action of particulates.

FIG. 27 is a diagram showing a relationship between the amount of fine particles that can be removed by oxidation and the temperature of the NO _X storage reduction catalyst device.

FIG. 28 is a diagram for explaining a deposition action of particulates.

FIG. 29 is a second flowchart for preventing the accumulation of particulates on the NO _X storage reduction catalyst device.

FIG. 30 is an enlarged cross-sectional view of a partition wall of the NO _X storage reduction catalyst device.

FIG. 31 is a third flowchart for preventing the accumulation of particulates on the NO _X storage reduction catalyst device.

FIG. 32 is a fourth flowchart for the regeneration of the NO _X storage reduction catalyst device.

[Explanation of symbols]

6 ... Fuel injection valve 16 ... Throttle valve 70 ... NO _X storage reduction catalyst device 71 ... Switching part 71a ... Valve body

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/02 F01N 3/08 A 3/08 G 3/20 B 3/20 F 3/24 R 3/24 S F02D 41 / 04 355 F02D 41/04 355 41/14 310K 41/14 310 43/00 301E 43/00 301 301N 301T 45/00 312R 45/00 312 312 312B 01D 46/42 B // B01D 46/42 53/36 101B ( 72) Inventor Takamitsu Asanuma 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Koichiro Nakatani 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation, (72) Inventor, Koichi Kimura 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (56) Reference JP 63-198717 (JP, A) JP 11-132029 (JP, A) JP 2000-45755 ( P, A) JP 2000-145501 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) F01D 3/02 321 F01D 3/24 F02D 41/04 355 F02D 41/14 310 F02D 43/00 301 F02D 45/00 312

Claims (8)

(57) [Claims] 1. A NO _X storage reduction catalyst device which is arranged in an engine exhaust system and absorbs NO _X when a nearby atmosphere has a lean air-fuel ratio, and which is regenerated at a regenerated air-fuel ratio which is a stoichiometric air-fuel ratio or a rich air-fuel ratio. , the _the NO _X storage reduction catalyst device comprises a bypass means for at least part of the exhaust gas makes it possible to bypass the fuel supply device for supplying the _the NO _X storage reduction catalyst device fuel to the vicinity, The internal combustion engine has an inert gas supply means for supplying an inert gas into the cylinder, and introduces the inert gas into the cylinder in an amount larger than the worst inert gas amount that maximizes the soot generation amount. It is possible to carry out low temperature combustion in which the combustion is performed by supplying and normal combustion in which the combustion is performed at a lean air-fuel ratio, and when the NO _x storage reduction catalyst device is regenerated, the low temperature combustion is performed at a regenerated air fuel ratio Elimination when carried out A first reproducing means to reproduce air the _the NO _X storage reduction catalyst near ambient by the gas,
At least a part of the exhaust gas is bypassed by the bypass means at the time of the normal combustion, and the second regenerating means for supplying the fuel by the fuel supply device to make the atmosphere in the vicinity of the NO _X storage reduction catalyst the regeneration air-fuel ratio An exhaust gas purification device for an internal combustion engine, which is characterized in that it is possible. 2. When the temperature of the NO _X storage reduction catalyst device is lower than a set temperature or when it is predicted that the temperature is lower than the set temperature, the first regeneration means is used to regenerate the NO _X storage reduction catalyst device. When the temperature of the NO _X storage reduction catalyst device is selected and is predicted to be equal to or higher than the set temperature, the second regeneration means is used to regenerate the NO _X storage reduction catalyst device. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein 3. A harmful substance from the inside of the cylinder during the normal combustion even when the temperature of the NO _X storage reduction catalyst device is equal to or higher than the preset temperature or is predicted to be equal to or higher than the preset temperature. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the first regenerating unit is selected when the emission amount is equal to or greater than a set amount or is predicted to be equal to or greater than the set amount. 4. The NO _X storage reduction catalyst device has a collection wall for collecting particulates in exhaust gas,
Even when the temperature of the NO _X storage reduction catalyst device is equal to or higher than the preset temperature or is predicted to be equal to or higher than the preset temperature, the particulate emission amount from the cylinder during the normal combustion is equal to the preset amount. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the first regenerating unit is selected when the amount is equal to or more than the predetermined amount or when the amount is predicted to be equal to or more than the set amount. 5. The exhaust gas purification device for an internal combustion engine according to claim 4, wherein the particulate matter collected on the collection wall is oxidized. 6. The internal combustion engine according to claim 5, wherein the trapping wall carries an active oxygen releasing agent, and the active oxygen released from the active oxygen releasing agent oxidizes particulates. Exhaust purification device. 7. The active oxygen releasing agent takes in oxygen to retain oxygen when excess oxygen is present in the surroundings, and releases the retained oxygen in the form of active oxygen when the ambient oxygen concentration decreases. The exhaust emission control device for an internal combustion engine according to claim 6. 8. A reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the NO _X storage reduction catalyst device is provided integrally with or separately from the bypass means, and the collecting wall has the first collecting means. A NOx storage reduction catalyst device having an exhaust surface and a second collection surface, and the exhaust upstream side and the exhaust downstream side of the NO _x storage reduction catalyst device are reversed by the reversing means to collect particulates. The exhaust gas purification device for an internal combustion engine according to any one of claims 5 to 7, wherein the first collecting surface and the second collecting surface of the wall are alternately used.