JP2002115524A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently purify NOX in exhaust gas in an exhaust emission control device of an internal combustion engine having a particulate filter carrying an NOX storage reduction catalyst. SOLUTION: This exhaust emission control device is provided with the particulate filter 70 arranged in an engine exhaust system by carrying the NOX storage reduction catalyst for absorbing NOX when a vicinal atmosphere is the lean air-fuel ratio and blowing off and reduction-purifying the NOX when the atmosphere is the theoretical air-fuel ratio or the rich air-fuel ratio and an NOX purifying catalyst device having the oxidizing function and arranged in the engine exhaust system on the upstream side of the particulate filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002]

Internal combustion engines, includes a NO _X in particular the exhaust gas of a diesel engine, in order to purify the NO _X, proposed to place the _the NO _X storage reduction catalyst device in the engine exhaust system Have been. The NO _X storage reduction catalyst absorbs NO _X in the form of nitrate when the oxygen concentration in the nearby atmosphere is high, and absorbs NO when the oxygen concentration in the nearby atmosphere becomes low.
_It releases and purifies _X by releasing _X. Thereby, N
O _X occluding and reducing catalyst is satisfactorily absorbed NO _X from the exhaust gas of the diesel engine combustion under excess air takes place, regularly lowering the oxygen concentration of the atmosphere in the vicinity as the stoichiometric air-fuel ratio or a rich air-fuel ratio By doing so, NO _X can be released and reduced and purified by a reducing substance such as HC, and NO _X can be satisfactorily purified without being released into the atmosphere.

[0003] By the way, the exhaust gas of a diesel engine also contains particulates mainly composed of soot. This particulate needs to be treated before it is released to the atmosphere, and it has been proposed to arrange a particulate filter for collecting the particulate in the engine exhaust system. Such a particulate filter has the aforementioned N
When supporting the O _X occluding and reducing catalyst, the particulates not only occludes NO _X can be effectively oxidized and removed. Thus, placing the one obtained by carrying _the NO _X storage reduction catalyst to the particulate filter in the exhaust system of a diesel engine is very effective.

[0004]

However, the structure of the particulate filter is generally of a wall flow type in which the exhaust gas passes through the pores of the trapping wall, and the exhaust gas flows along the partition supporting the catalyst. compared to the general catalytic converter flows, mainly catalyst supporting area is less of the collecting wall surface which the exhaust gas contacts, in such a particulate filter, to sufficiently purify NO _X in the exhaust gas Can not.

Accordingly, an object of the present invention is to make it possible to sufficiently purify NO _{X in} exhaust gas in an exhaust gas purifying apparatus for an internal combustion engine equipped with a particulate filter carrying a NO _X storage reduction catalyst.

[0006]

According to the first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine according to the present invention, which absorbs NO _X when a nearby atmosphere has a lean air-fuel ratio and has a stoichiometric air-fuel ratio or a rich air-fuel ratio. a particulate filter disposed in the exhaust system carries _the NO _X storage reduction catalyst to reduce and purify by releasing NO _X, are arranged in the engine exhaust system upstream of the particulate filter has an oxidation function T
Characterized by comprising the O _X purification catalyst device.

[0007] The exhaust purification system of an internal combustion engine according to claim 2 of the present invention, in the exhaust purification system of an internal combustion engine according to claim 1, the exhaust gas downstream of the NO _X purification catalyst apparatus wherein The present invention is characterized in that a bypass means is provided for enabling the particulate filter to be bypassed.

According to a third aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine according to the second aspect, wherein the NO _X purifying catalytic device is the NO _X storage reduction catalyst. was supported, during sO _X poisoning restoration of the NO _X purification catalyst device, the exhaust gas by function of the bypass means is characterized in that so as to bypass the particulate filter.

According to a fourth aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine according to the second aspect, wherein the NO _X purifying catalytic device is the NO _X storage reduction catalyst. the supported, immediately after sO _X poisoning restoration completion of the NO _X purification catalyst apparatus, the exhaust gas does not function the bypass means is characterized in that to pass through the particulate filter.

[0010]

FIG. 1 is a schematic longitudinal sectional view of a four-stroke diesel engine provided with an exhaust emission control device according to the present invention, and FIG. 2 is an enlarged longitudinal sectional view of a combustion chamber in the diesel engine of FIG. FIG. 3 is a bottom view of the cylinder head in the diesel engine of FIG. Referring to FIGS. 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
Denotes a pair of exhaust valves, and 10 denotes an exhaust port. The intake port 8 is connected to the surge tank 1 via the corresponding intake branch 11.
2 and the surge tank 12 is connected to an air cleaner 14 via an intake duct 13. A throttle valve 16 driven by an electric motor 15 is provided in the intake duct 13.
Is arranged. On the other hand, the exhaust port 10 is connected to an exhaust pipe 18 via an exhaust manifold 17.

As shown in FIG. 1, the exhaust manifold 17
An air-fuel ratio sensor 21 is disposed inside. The exhaust manifold 17 and the surge tank 12 are connected to each other via an EGR passage 22, and an electrically controlled 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 provided 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 via a fuel supply pipe 25 to a fuel reservoir, a so-called common rail 26. Fuel is supplied into the common rail 26 from an electric control type variable discharge fuel pump 27, and the fuel supplied into the common rail 26 is supplied to the fuel injection valve 6 through 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. The fuel pump 27 is controlled so that the fuel pressure in the common rail 26 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 28. Is controlled.

An electronic control unit 30 receives an output signal of the air-fuel ratio sensor 21 and an output signal of the fuel pressure sensor 28. A load sensor 41 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 40 is connected to the accelerator pedal 40, and an output signal of the load sensor 41 is also input to the electronic control unit 30. For example, an output signal of the crank angle sensor 42 that generates an output pulse every time the motor rotates by 30 ° is also input. In this way, the electronic control unit 30 controls the fuel injection valve 6, the electric motor 15, the EGR control valve 2 based on various signals.
3. Operate the fuel pump 27 and the switching valve 71a disposed on the exhaust pipe 18. 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 comprises a hole nozzle having six nozzle openings, and the nozzle opening of the fuel injection valve 6 is slightly downwardly directed to the horizontal plane. The fuel F is injected at equal angular intervals. As shown in FIG. 3, two of the six fuel sprays F scatter along the lower surface of the valve body of each exhaust valve 9. FIGS. 2 and 3 show a case where 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, a case is shown in which 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 traveling in the valve body direction of the exhaust valve 9 is directed between the back of the head of the exhaust valve 9 and the exhaust port 10. That is, in other words, two of the six nozzle ports of the fuel injection valve 6 emit fuel spray F when additional fuel Qa is injected while the exhaust valve 9 is open. It is formed so as to be directed between the back surface of the head of the valve 9 and the exhaust port 10. In this case, in the embodiment shown in FIG. 4, at this time, the fuel spray F collides with the back of the umbrella of the exhaust valve 9, and the fuel mist F colliding with the back of the umbrella of the exhaust valve 9 is reflected on the back of the umbrella of the exhaust valve 9. Then, it goes into the exhaust port 10.

Normally, no additional fuel Qa is injected,
Only the main injection Qm is performed. FIG. 6 shows a change in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 6) is changed by changing the opening degree and the EGR rate of the throttle valve 16 during the engine low load operation, and the smoke, HC, and the like. , CO,
5 shows an experimental example showing a change in the amount of emission of NO _X. FIG.
As can be seen from the graph, in this experimental example, as the air-fuel ratio A / F decreases, the EGR rate increases, and the stoichiometric air-fuel ratio (# 14.
6) In the following cases, 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 smoke is generated when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30. The volume starts 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 is sharply reduced. When the EGR rate is increased to 65% or more, and the air-fuel ratio A / F becomes about 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and NO
The amount of _X generation is significantly lower. On the other hand, at this time, the generation amounts of HC and CO begin to increase.

FIG. 7 (A) shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest, and FIG. 7 (B) shows the air-fuel ratio A / F. The graph shows a change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. As can be seen by comparing FIG. 7A and FIG. 7B, in the case of FIG. 7B in which the amount of smoke generation is almost zero, FIG.
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. That is, first, the air-fuel ratio A / F is 15.
0 generation amount of the NO _X as shown in FIG. 6 when the smoke generation amount approximately zero or less drops significantly. That the generation amount of the NO _X produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 when the soot is hardly generated is lower I can say. The same can be said from FIG. That is, in the state shown in FIG. 7B where almost no soot is generated, the combustion pressure is low, and thus the combustion temperature in the combustion chamber 5 is low at this time.

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

Summarizing these considerations based on the experimental results shown in FIGS. 6 and 7, when the combustion temperature in the combustion chamber 5 is low, the amount of soot generation becomes almost zero. Is discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is Not generated at all, combustion chamber 5
It was found that soot was formed when the temperature of the fuel and its surroundings fell below a certain temperature.

The temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, ie, the above-mentioned certain temperature, depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although not say that how many times so changed, this certain temperature has a generation amount and the deep relationship between nO _X, thus to some extent defined from the generation of this certain temperature is nO _X can do. That is, the fuel and the gas temperature surrounding it at the time of combustion and the greater the EGR rate, decreases, the amount of the NO _X is reduced. At this time, when the amount of generated NO _X becomes about 10 ppm or less, soot is hardly generated. Therefore, the above certain temperature is NO
The temperature almost coincides with the temperature when the amount of generated _X is about 10 p.pm or less.

Once soot has been produced, it cannot be purified by simply post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Thus, NO _X
It is extremely effective in purifying exhaust gas to reduce the generation amount of methane and to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or before the soot.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 are 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 effect of the gas around the fuel when the fuel is burned has an extremely large effect in suppressing the temperature of the fuel and the gas around the fuel.

That is, if there is only air 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 becomes extremely high locally. That is, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.

On the other hand, when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air, the situation is slightly different.
In this case, the evaporated fuel diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion temperature does not rise so much because the combustion heat is absorbed by the surrounding inert gas. 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 kept low by the endothermic effect of the inert gas.

In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is formed, an amount of the inert gas that can absorb a sufficient amount of heat to do so is required. . Therefore, if the amount of fuel increases, the required amount of inert gas increases accordingly. In this case, the endothermic effect becomes stronger as the specific heat of the inert gas increases, so that the inert gas preferably has a higher specific heat. In this regard, it can be said that it is preferable to use EGR gas as the inert gas since CO ₂ and EGR gas have relatively large specific heats.

FIG. 9 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 9, the curve A shows that the EGR gas is cooled
Curve B shows the case where the EGR gas is cooled by a small cooling device, and 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 amount of soot generation peaks at a position where the EGR rate is slightly lower than 50%. Above a percentage, soot is hardly generated. On the other hand, as shown by the curve B in FIG. 9, when the EGR gas is slightly cooled, the amount of soot generation peaks at a point where the EGR rate is slightly higher than 50%, and in this case, the EGR rate is increased to about 65% or more. So that almost no soot is generated.

As shown by a curve C in FIG.
When the R gas is not forcibly cooled, the EGR rate becomes 5
The soot generation amount peaks near 5%. In this case, if the EGR rate is set to approximately 70% or more, soot is hardly generated. FIG. 9 shows the amount of smoke generated when the engine load is relatively high. When the engine load is small, the EGR rate at which the amount of soot peaks slightly decreases, and the EGR rate at which soot is hardly generated is shown. Also lowers slightly. As described above, the lower limit of the EGR rate at which almost no soot is generated varies depending on the degree of cooling of the EGR gas and the engine load.

FIG. 10 shows the mixing of EGR gas and air necessary to reduce the temperature of fuel during combustion and the surrounding gas to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. It shows the gas amount, the ratio of air in this mixed gas amount, and the ratio of EGR gas in this mixed gas. The vertical axis in FIG.
The dashed line Y indicates 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 proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 10, the ratio between the amount of air and the amount of injected fuel is the stoichiometric air-fuel ratio. On the other hand, in FIG. 10, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas is necessary to make the temperature of the fuel and the surrounding gas 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 the 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 indicated by a solid line X in FIG. 10, and the ratio between the air amount and the EGR gas amount in the total intake gas amount X is as shown in FIG. The temperature of the fuel and its surrounding gas will be lower than the temperature at which soot is produced,
Thus, no soot is generated. Also, NO
_The amount of generated _X is around 10 p.pm or less, and therefore the amount of generated NO _X is extremely small.

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

On the other hand, in the load region Z2 in 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 sucked. 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 the intake air, or EG
R gas needs to be supercharged or pressurized. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intake gas amount Y that can be sucked in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the amount of air is slightly reduced to increase the amount of EGR gas, and the fuel is burned under a rich air-fuel ratio.

As described above, FIG.
FIG. 10 shows the case of burning under
FIG. 10 shows the air amount in the low load operation region Z1.
Even if it is less than the amount of air
NO while preventing soot generation _XGeneration of around 10p.p.m
Or less and is shown in FIG.
In the low load region Z1, the amount of air shown in FIG.
Larger than the amount, that is, the average value of the air-fuel ratio is 17 to 1
NO 8 while preventing soot generation even with a lean of 8 _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 excess fuel does not grow to soot, and soot is generated. There is no. In addition, NO _X is also only an extremely small amount of generated at this time. 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 increases, but in the present invention, the soot is suppressed to a low temperature, so the soot is reduced. Not generated at all. Furthermore, NO _X
Only a very small amount is generated.

As described above, 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. However, the amount of generated NO _X 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 surrounding gas during combustion in the combustion chamber to a temperature at which the growth of hydrocarbons stops halfway, 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 first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the combustion to a temperature at which the growth of hydrocarbons stops halfway. Then, when the engine load is relatively high, the second combustion, that is, the combustion that is usually performed conventionally, is performed. Here, the first combustion, that is, low-temperature combustion, as is clear from the description so far, the amount of inert gas in the combustion chamber is larger than the worst inert gas amount at which the generation amount of soot is maximum, and soot is almost generated. The second combustion, that is, the combustion that is usually performed in the past, is the combustion in which the amount of inert gas in the combustion chamber is smaller than the worst inert gas amount that produces the largest amount of soot. Say

FIG. 11 shows a first operation 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 represents the accelerator pedal 40.
, That is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 11, X (N) indicates a 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. The second boundary with the area II is shown. First operating region I
Is determined based on the first boundary X (N), and the determination of the change in the operating region from the second operating region II to the first operating region I is made based on the first boundary X (N). The determination is performed based on the second boundary Y (N).

That is, when the operating state of the engine is in the first operating region I
When the required load L exceeds a first boundary X (N), which is a function of the engine speed N, during low-temperature combustion, it is determined that the operation region has shifted to the second operation region II. Combustion is performed by the combustion method of (1). Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation 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, with reference to FIG.
The operation control in the operation region II will be schematically described.

FIG. 13 shows the opening degree of the throttle valve 16, the opening degree 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 of the throttle valve 16 is gradually increased from almost fully closed to about half-open as the required load L increases, and the EGR control valve 23 Is gradually increased from near fully closed to fully open as the required load L increases. FIG.
In the example shown in (1), in the first operating region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

In other words, in the first operating region I, the EGR
The opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled so that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In addition,
The air-fuel ratio at this time is controlled to the target lean air-fuel ratio by correcting the opening of the EGR control valve 23 based on the output signal of the air-fuel ratio sensor 21. 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 is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

During the idling operation, the throttle valve 16 is closed to almost fully closed, and at this time, the EGR control valve 23 is also closed to almost fully closed. When the throttle valve 16 is closed close to the fully closed position, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 16 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating range of the engine is the first operating range I.
From the second operation region II, the opening of the throttle valve 16 is increased stepwise from the half-open state to the fully open direction. At this time, in the example shown in FIG.
The air-fuel ratio is reduced stepwise from a percentage to less than 40%, and the air-fuel ratio is increased stepwise. 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 operation region of the engine changes from the first operation region I to the second operation region II. There is no.

In the second operation area 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
The injection amount is reduced stepwise as shown in FIG.

In the second operating region II, the throttle valve 16 is maintained in a fully open state except for a part, and the opening of the EGR control valve 23 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. 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, the curves indicated by A / F = 16, A / F = 17, and A / F = 18 have air-fuel ratios of 15.5, 16, 17, and 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 becomes leaner as the required load L decreases.

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 reduced. When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 14, as the required load L decreases, the air-fuel ratio A / F increases. As the air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, in this embodiment, the air-fuel ratio A / F is increased as the required load L decreases.

The target opening degree ST of the throttle valve 16 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
5 (A), the required load L and the engine speed N
FIG. 15B shows the target opening degree SE of the EGR control valve 23 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. As described above, a map is stored in advance in the ROM 32 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. In FIG. 16, A / F = 24 and A / F = 3.
Curves indicated by 5, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. Throttle valve 1 required to set the air-fuel ratio to this target air-fuel ratio
The target opening ST of No. 6 is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 17A, and the air-fuel ratio is set as the target air-fuel ratio. 17B, the target opening SE of the EGR control valve 23 is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.

Thus, in the diesel engine of the present 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. The switching is performed, and in each combustion, the opening control of the throttle valve 16 and the EGR valve is performed 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 FIG.

FIG. 18 is a plan view showing the exhaust gas purifying apparatus of this embodiment, and FIG. 19 is a side view thereof. The present exhaust gas purification apparatus includes a switching section 71 connected to the downstream side of the exhaust manifold 17 via an exhaust pipe 18, a particulate filter 70, and a first section connecting one side of the particulate filter 70 and the switching section 71. A connecting portion 72a, a second connecting portion 72b connecting the other side of the particulate filter 70 and the switching portion 71, and an exhaust passage 73 downstream of the switching portion 71
Is provided. The switching unit 71 includes a valve body 71a that can shut off the exhaust gas flow in the switching unit 71. The valve body 71a is driven by a negative pressure actuator, a step motor, or the like. In the first shut-off position of the valve body 71a, the upstream side in the switching unit 71 is connected to the first connection unit 72a.
The exhaust gas flows from one side of the particulate filter 70 to the other side as shown by an arrow in FIG. 18 and the downstream side in the switching section 71 is communicated with the second connecting section 72b.

FIG. 20 shows the second blocking position of the valve body 71a. In this shutoff position, the upstream side in the switching section 71 is communicated with the second connection section 72b, and the downstream side in the switching section 71 is communicated with the first connection section 72a, and the exhaust gas is discharged as shown by an arrow in FIG. , Flows from the other side of the particulate filter 70 to one side. By switching the valve body 71a from one of the first shut-off position and the second shut-off position to the other, the direction of the exhaust gas flowing into the particulate filter 70 can be reversed. It is possible to reverse the upstream side and the exhaust downstream side. FIG. 21 shows the open position of the valve body 71a between the first shut-off position and the second shut-off position. In this open position, the exhaust gas is
As shown by an arrow in FIG. 21, the gas flows by bypassing the particulate filter 70.

FIG. 22 shows the structure of the particulate filter 70. 22A is a front view of the particulate filter 70, and FIG. 22B is a side sectional view. As shown in these figures, the particulate filter 70 has an elliptical front shape, and is, for example, a wall flow type having a honeycomb structure formed of a porous material such as cordierite. It has a number of axial spaces subdivided by directional partitions 54. In the two adjacent axial spaces, one is closed downstream of the exhaust and the other is closed upstream of the exhaust by a plug 53. In this manner, one of the two adjacent axial spaces becomes the exhaust gas inflow passage 50, and the other becomes the outflow passage 51, and the exhaust gas flows in FIG.
As shown by the arrow in (B), it always passes through the partition wall 54.
Although the particulates in the exhaust gas are very small compared to the size of the pores of the partition wall 54, they collide with and are trapped on the exhaust upstream surface of the partition wall 54 and the pore surface in the partition wall 54. Gathered. Thus, each partition wall 54 functions as a collecting wall for collecting particulates. In the present particulate filter 70, on both surfaces of each partition wall 54,
And preferably a noble metal catalyst is supported, such as _the NO _X absorbent and platinum Pt is on the pore surfaces of the partition walls to be explained below using alumina.

[0056] _the NO _X absorbent which is supported on the partition wall 20a, the
In this embodiment, potassium K, sodium Na, lithium Li, cesium Cs, alkali metals such as rubidium Rb, barium Ba, calcium Ca, alkaline earths such as strontium Sr, lanthanum La, rare earths such as yttrium Y, And at least one selected from transition metals. This _the NO _X absorbent is (the ratio of air and fuel, wherein, how much fuel is not relevant whether the burned using oxygen in the air) air-fuel ratio in the vicinity of the atmosphere is lean sometimes absorbs NO _X, the air-fuel ratio to perform the absorbing and releasing action of the NO _X that releases NO _X absorbed and becomes the stoichiometric air-fuel ratio or rich.

Although the NO _X absorbent actually performs the absorption and release of NO _X , there are some parts whose detailed mechanism of the absorption and release is not clear. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, regarding this mechanism, platinum Pt and barium Ba are deposited on the particulate filter partition.
Will be described as an example in the case of carrying other precious metals,
The same mechanism is obtained by using an alkali metal, an alkaline earth, or a rare earth.

Air-fuel ratio regardless of low-temperature combustion and normal combustion
If the combustion is performed while the engine is lean, the exhaust gas
The oxygen concentration in the gas is high, and at this time, as shown in FIG.
These oxygen O_TwoIs O_Two ^-Or O^2-Platinum in the form of
Attaches to the surface of Pt. On the other hand, NO in the inflow exhaust gas is
O on the surface of platinum Pt_Two ^-Or O^2-Reacts with NO_TwoTona
(2NO + O_Two→ 2NO_Two). NO generated next_Two
Is partially absorbed into the absorbent while being oxidized on platinum Pt
As shown in FIG. 23 (A) while being combined with barium oxide BaO
Nitrate ion as NO_Three ^-Diffuses into the absorbent in the form of
You. NO in this way_XIs NO_XAbsorbed in the absorbent
You. As long as the oxygen concentration in the nearby atmosphere is high,
NO_TwoIs generated, and the NO_XAbsorption capacity does not saturate
As long as NO _TwoIs absorbed in the absorbent and nitrate ion NO_Three ^-
Is generated.

On the other hand, when the air-fuel ratio in the nearby atmosphere is made rich, the oxygen concentration decreases, and as a result, the N
O ₂ generation decreases. When the production amount of NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent is released from the absorbent in the form of NO ₂ . In this case NO _X released from _the NO _X absorbent is 2
As shown in FIG. 3 (B), HC contained in the nearby atmosphere
And react with CO and the like to be reduced. In this way, when NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another. NO _X Thus the air-fuel ratio of the atmosphere in the vicinity NO _X is released from _the NO _X absorbent in a short time when it is rich, yet which is this released
There is no possibility that NO _X is discharged into the atmosphere to be reduced.

[0060] In this case, NO _X is released from _the NO _X absorbent and the air-fuel ratio of the atmosphere in the vicinity to the stoichiometric air-fuel ratio.
However, in this case it takes a slightly longer time to emit all NO _X absorbed in the particulate filter to not only gradually _the NO _X absorbent from NO _X emission.

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, before the amount of NO _X absorbed in the particulate filter 70 reaches the NO _X storable amount, it is necessary for reproduction to be reduced and purified to release the NO _X, For this purpose,
It is necessary to estimate this NO _X amount. Therefore, in the present embodiment, NO _X per unit time during low-temperature combustion is performed.
The absorption amount A is determined in advance as a function of the required load L and the engine speed N in the form of a map as shown in FIG.
FIG units a function of time per of the NO _X absorption B the required load L and the engine speed N when the ordinary combustion is being performed 2
4 (B) is obtained in advance in the form of a map, and by integrating these NO _x absorption amounts A and B per unit time, the N absorbed in the particulate filter is calculated.
So that to estimate the O _X amount. Here, per unit of time when the low temperature combustion is being performed NO _X absorption A
, Of course, in order to be able to be NO _X is released when low temperature combustion is performed at a rich air-fuel ratio, a negative value. For the present embodiment for reproducing the particulate filter when exceeding the allowable value that this NO _X absorption is predetermined, either to implement the low-temperature combustion at the stoichiometric air-fuel ratio or a rich air-fuel ratio, or the exhaust stroke The atmosphere in the vicinity of the particulate filter 70 is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio by injecting fuel into the cylinder at a time, for at least the time until the regeneration is completed (the shorter the air-fuel ratio in the nearby atmosphere, the shorter the time). This state is maintained.

[0062] Thus, when supporting the _the NO _X absorbent in the particulate filter, it is possible to satisfactorily oxidize and remove the particulates were collected on the collecting wall. This mechanism will be described with reference to FIG. As previously mentioned,
NO _X is absorbed in the NO _X absorbent 61 in the form of nitrate ion NO ₃ ⁻ via platinum Pt60. When particulates 62 in the _the NO _X absorbent is attached, the oxygen concentration decreases in the contact surface between the particulates 62 and _the NO _X absorbent 61. NO _x with high oxygen concentration when oxygen concentration decreases
A difference in concentration occurs between the inside of the absorbent 61 and the oxygen in the NO _x absorbent 61, which tends to move toward the contact surface between the particulate 62 and the NO _x absorbent 61. As a result, NO _X absorbent 61 nitrate ions NO ₃ ^- it is oxygen O
And is decomposed into NO, oxygen O heads toward the contact surface between the particulates 62 and _the NO _X absorbent 61, NO is emitted to the outside from _the NO _X absorbent 61. The NO released to the outside is oxidized on platinum Pt on the downstream side, and is again absorbed in the NO _x absorbent 61.

On the other hand, the oxygen O heading toward the contact surface between the particulate 62 and the NO _x absorbent 61 is a nitrate,
Oxygen decomposed from a compound. Oxygen O decomposed from the compound has high energy and extremely high activity. Thus oxygen toward the contact surface between the particulates 62 and _the NO _X absorbent 61 has a active oxygen O. When the active oxygen O comes in contact with the particulate 62, the particulate 62 is oxidized in a short time of several minutes to several tens minutes without emitting a bright flame. Moreover, the active oxygen O to oxidize the particulate matter 62, NO to _the NO _X absorbent 61 is also released when being absorbed. That, NO _X is nitrate ions NO ₃ within _the NO _X absorbent 61 while repeating the coupling and separation of the oxygen atom ^- believed to diffuse in the form of, active oxygen also occurs during this period. The particulate 62 is also oxidized by the active oxygen. In addition, the particulate filter 70
The particulates adhered to above are not only oxidized by the active oxygen O, but also these particulates 62 are oxidized by the oxygen in the exhaust gas.

As described above, by supporting the NO _x absorbent and the noble metal catalyst (hereinafter referred to as “NO _x storage reduction catalyst”) on the particulate filter, the collected particulates can be removed together with the purification of NO _x in the exhaust gas. This is effective for preventing the particulate filter from being clogged by oxidization and removal.

However, as described above, the structure of the particulate filter is a wall flow type in which the exhaust gas passes through the pores of the trapping wall, and the general structure in which the exhaust gas flows along the partition wall supporting the catalyst. In order to allow the same amount and the same amount of exhaust gas to pass in comparison with the catalyst device, the dimension between the collecting walls must be larger than the dimension between the partition walls. As a result, in the particulate filter, the exhaust gas carried on the trapping wall surface
Opportunity to contact with the O _X occluding and reducing catalyst is smaller than in the catalyst system. The exhaust gas, when passing through the pores of the collection wall is in contact with the NO _X occluding and reducing catalyst carried on the pores, mainly was carried on the surface of the collection wall NO
Contact only with _X storage reduction catalyst. However, the catalyst supporting area on the surface of the collecting wall is not so large due to the large number of pores. Thus, be supported on _the NO _X storage reduction catalyst to the particulate filter, it is impossible to sufficiently purify the NO _X in the exhaust gas.

[0066] In order to solve this problem, in the present embodiment, as shown in FIGS. 18 and 19, the exhaust pipe 18 of the switching unit 71 upstream, NO _X purification catalyst 74 is arranged. The NO _X purification catalyst device 74 supplements the NO _X purification by the particulate filter 70, and does not require a large capacity. Thus, the NO _X purification catalyst device 74 and the particulate filter 70 having the NO _X storage reduction catalyst can sufficiently purify NO _X in the exhaust gas.

As the NO _X purification catalyst device 74, the above-mentioned NO _X storage reduction catalyst or a catalyst having a honeycomb structure is used.
What is necessary is just to carry a catalyst capable of purifying NO _X such as a NO _X selective reduction catalyst.

Incidentally, the soluble organic component S is contained in the exhaust gas.
OF is contained, and this SOF is sticky and causes the particulates to adhere to each other on the particulate filter and grow into a large mass. This makes it difficult for the particulate filter to oxidize and remove the particulate, thereby promoting clogging of the particulate filter. Thus, by arranging the NO _X purification catalyst device 74 carrying a catalyst having an oxidation function as of the NO _X occluding and reducing catalyst on the upstream side of the particulate filter 70, in the exhaust gas upstream of the particulate filter SOF
And burning of the particulate filter due to SOF can be prevented.

Incidentally, the fuel of the internal combustion engine contains sulfur, and SO _X is generated during combustion. SO _X is
It is absorbed in the form of sulfate by the same mechanism as NO _X into the particulate filter 70. This sulfate can release active oxygen by the same mechanism as nitrate.However, since sulfate is a stable substance, it is difficult to be released from the particulate filter even when the surrounding atmosphere is set to a rich air-fuel ratio. , Remaining in the particulate filter, and the amount of occlusion gradually increases. The amount of nitrate or sulfate that can be stored in the particulate filter is finite. If the amount of sulfate stored in the particulate filter increases (hereinafter referred to as SO _X poisoning),
Storable amount of nitrate is reduced, finally, it becomes impossible to absorb the NO _X at all.

[0070] Thus, in the present embodiment, NO _X purifying catalyst device 74 is supported to _the NO _X storage reduction catalyst, actively absorbed by NO _X purification catalyst device 74 located sulfur in the exhaust gas on the upstream side , Particulate filter 70
Thereby preventing the SO _X poisoning. Recovery of SO _X poisoning of the NO _X purification catalyst device 74 with this is done by the following procedure.

[0071] First, a determination is made as to whether the recovery time of the SO _X poisoning is performed. The determination, by integrating the fuel consumed so far, it can be determined that the recovery time of the SO _X poisoning when the cumulative fuel amount reaches the set amount. Also, (release purification process of the NO _X) particulate filter similar reproduction process is required in NO _X purification catalyst device, in this regeneration process, the air-fuel ratio of the exhaust upstream side of the NO _X purification catalyst unit is made rich However, during regeneration, since the reducing substance such as HC is used for the reduction and purification of the released NO _X , the air-fuel ratio on the downstream side of the NO _X purification catalyst device becomes close to the stoichiometric air-fuel ratio. However, when the reproduction is completed, the air-fuel ratio on the downstream side of the NO _X purification catalyst device is substantially equal to the rich air-fuel ratio on the upstream side. By detecting the playback time using this recovery time of SO _X poisoning can be determined. This is because, when the recovery is SO _X poisoning as necessary in progress, has become less in practice the NO _X absorption amount at regeneration timing, because the reproduction time is shortened.

[0072] When a regeneration timing of the SO _X poisoning, the combustion air-fuel ratio as lean as well as to the exhaust gas contains relatively large amount of oxygen, cylinder fuel injection in the exhaust stroke or such as by injecting fuel into the engine exhaust system upstream of the NO _X purification catalyst device, to supply a reducing substance such as sufficient oxygen and unburned fuel to the NO _X purification catalyst device, N
O _X sufficiently burn the reducing substance by oxidation capability possessed by the purifying catalyst device.

[0073] Thus, the NO _X purification catalyst device 600 °
When the temperature is raised to about C, stable sulfate can be released as SO _X by lowering the oxygen concentration by setting the nearby atmosphere to a stoichiometric air-fuel ratio or a rich air-fuel ratio.
When raising the temperature of the NO _X purification catalyst device than 700 ° C, for the oxidation catalyst of platinum Pt or the like is carried to degraded causing sintering, the exhaust gas temperature immediately downstream of the NO _X purification catalyst device such It is preferable to monitor this so that this does not occur. S The NO _X in the purification of SO _X poisoning restoration process of the catalytic converter, the valve body 71a in the switching section 71 is an open position, released from the NO _X purification catalyst device
O _X is not absorbed by the NO _X absorbent of the particulate filter 70 because it bypasses the particulate filter 70. When the temperature of the NO _X purification catalyst device is set to a high temperature and the surrounding atmosphere is set to a rich air-fuel ratio for a certain time, the SO
It can be determined that the _X poisoning recovery processing has been completed, and the combustion air-fuel ratio is returned to an air-fuel ratio suitable for normal operation.

By the way, the platinum Pt and the NO _x absorbent 61 carried on the particulate filter are activated as the temperature of the particulate filter becomes higher, so the active oxygen O from which the NO _x absorbent 61 is released per unit time is increased.
Increases as the temperature of the particulate filter increases. Naturally, the higher the temperature of the particulates themselves, the more easily they are oxidized and removed. Therefore, the amount of oxidizable particles that can oxidize and remove particulates per unit time on the particulate filter without emitting luminous flame per unit time increases as the temperature of the particulate filter increases. Thereby, immediately after completion simultaneously or completion of SO _X poisoning restoration process of the NO _X purification catalyst device, it is as one blocking position switching valve 71a of the switching unit 71, a high temperature (approximately 600 ° C) NO It is preferable that the exhaust gas heated through the _X purification catalyst device be guided to the particulate filter, thereby raising the temperature of the particulate filter and facilitating the removal of the particulate by oxidation.

The solid line in FIG. 26 indicates the amount G of oxidizable particles that can be oxidized and removed without emitting a luminous flame per unit time. In FIG. 26, the horizontal axis indicates the temperature TF of the particulate filter. FIG. 26 shows the amount of fine particles G that can be oxidized and removed per second when the unit time is 1 second, that is, the unit time is as follows.
Any time such as 1 minute, 10 minutes, etc. can be adopted. For example, when 10 minutes is used as the unit time, the amount G of oxidizable and removable particles per unit time represents the amount G of oxidizable and removable particles per 10 minutes. As shown in FIG. 26, the amount G of the oxidizable particles that can be oxidized and removed without emitting a bright flame per hour increases as the temperature of the particulate filter 70 increases.

When 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 removable by oxidation, for example, per second When the amount M of discharged fine particles is smaller than the amount G of oxidizable and removable particles per second, or when the amount M of discharged fine particles per 10 minutes is smaller than the amount of oxidizable and removable fine particles G per 10 minutes, that is, the region of FIG. I
In the method, all the particulates discharged from the combustion chamber are sequentially oxidized and removed within a short period of time on the particulate filter 70 without emitting a bright flame.

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 in FIG. 26, the amount of active oxygen is insufficient to sequentially oxidize all the particulates. FIGS. 27A to 27C show how particulates are oxidized in such a case.

[0078] That is, all of the particulates when the particulates 62 as shown in FIG. 27 (A) if the amount of active oxygen is insufficient to oxidize is deposited on _the NO _X absorbent 61 particulate 62 Is oxidized, and the particulate portion that has not been sufficiently oxidized remains on the exhaust upstream side surface of the particulate filter.
Next, when the state of the shortage of the amount of active oxygen continues, the particulate portion that has not been oxidized from one to the next remains on the exhaust upstream surface, and as a result, as shown in FIG. The exhaust upstream surface of the partition is covered with the residual particulate portion 63.

The residual particulate portion 63 as described above
Gradually changes into a carbon material which is hardly oxidized, and when the upstream surface of the exhaust gas is covered with the residual particulate portion 63, the oxidizing action of NO and SO ₂ by platinum Pt and N
Action of release of active oxygen by O _X absorbent 61 is suppressed. As a result, the residual particulate portion 63 can be gradually oxidized over time.
As shown in (C), the residual particulate portion 63
On top of this, another particulate 64 is deposited one after another. That is, when the particulates deposited in layers, these particulates, in order to have at a distance from the platinum Pt or _the NO _X absorbent, it is oxidized by for example reactive oxygen even easily particulates are oxidized Absent. Therefore, further particulates accumulate on this particulate 64 one after another. In other words, if the state in which the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation continues, the particulates will be deposited in layers on the particulate filter.

As described above, in the region I of FIG. 26, the particulates are oxidized in a short time without emitting a bright flame on the particulate filter. In the region II of FIG. 26, the particulates are laminated on the particulate filter. Deposit in a shape. Therefore, if the relationship between the discharged fine particle amount M and the oxidizable and removable fine particle amount G is set to the region I, it is possible to prevent the accumulation of particulates on the particulate filter. As a result, the pressure loss of the exhaust gas flow in the particulate filter 70 is maintained at a substantially constant minimum pressure loss value without changing at all. In this way, a reduction in engine power can be kept to a minimum. However, this is not always achieved, and if nothing is done, particulates may accumulate on the particulate filter.

In this embodiment, the electronic control unit 3
0 according to the flowchart shown in FIG.
The switching control of a is performed to prevent accumulation of a large amount of particulates on the particulate filter. This flowchart is repeated every predetermined time. First, in step 101, the running distance integrated value A is calculated, and in step 102, it is determined whether or not the running distance integrated value A has reached the set running distance As. When this determination is denied, the process is terminated as it is, but when affirmed, the process proceeds to step 103 to reset the running distance integrated value A to 0, and then, in step 104, the valve body 71a is moved to the first shutoff position and the second shutoff position. It switches from one to the other, and reverses the upstream side and the downstream side of the exhaust of the particulate filter.

FIG. 29 is an enlarged sectional view of the partition wall 54 of the particulate filter. While the vehicle travels the set traveling distance As, the driving in the region II of FIG. 26 may be performed. As shown by a grid in FIG. exhaust gas flow facing surface of the exhaust upstream surface and in the pores of collide collecting particulates as one collecting surface, although oxidation removing particulates by the active oxygen released by _the NO _X absorbent, This oxidative removal may be insufficient and particulates may remain. At this time, the exhaust resistance of the particulate filter does not adversely affect the running of the vehicle, but if the particulates accumulate further, a problem such as a drastic decrease in engine output occurs. In this flowchart, at this time, the exhaust gas upstream and the exhaust downstream of the particulate filter are reversed. As a result, no more particulates accumulate on the particulates remaining on one of the collecting surfaces of the partition wall 54, and the remaining particulates are gradually oxidized and removed by the active oxygen released from the one collecting surface. Is done. Further, the residual particulates are caused by the exhaust gas flow in the opposite direction as shown in FIG.
As shown in (B), it is easily broken and fragmented, and flows mainly inside the pores to the downstream side.

[0083] Thus, many particulates subdivided is dispersed in the pores of the partition walls are oxidized and removed in direct contact with _the NO _X absorbent which is supported in the pores in the surface of the partition wall More opportunities. In this way, N
O _X absorbent by supporting the, it tends to greatly oxidizing remove residual particulates. Furthermore, in addition to this oxidation removal, the other trapping surface of the partition wall 54 that has become upstream due to the backflow of the exhaust gas, that is, the exhaust upstream surface of the partition wall 54 where the exhaust gas currently mainly collides and the inside of the pores is oxidized and removed by the released active oxygen from _the NO _X absorbent in the (a opposite relationship with one of the trapping surfaces), the new particulates in exhaust gas adhere exhaust gas flow facing surface of the . Some of the active oxygen released from _the NO _X absorbent during these oxidation removal moves to the downstream side together with the exhaust gas to oxidize and remove the particulates still remaining by backflow of exhaust gas.

That is, not only the active oxygen released from this collecting surface but also the particulates on the other collecting surface of the partition due to the backflow of the exhaust gas are included in the residual particulates on one collecting surface of the partition. The remaining active oxygen used for the oxidation removal comes with the exhaust gas. Thereby, even when the particulates are deposited to some extent on one of the collecting surfaces of the partition wall at the time of switching the valve body, if the exhaust gas is made to flow backward, the particulates are deposited on the residual particulates. In addition to the arrival of active oxygen, no more particulates accumulate, so the accumulated particulates are gradually oxidized and removed, and if there is some time before the next backflow,
During this time, it can be sufficiently oxidized and removed. In this way, by alternately using the two collecting surfaces of the partition walls for collecting the particulates, the particulates on each collecting surface can be compared with the case where the particulates are always collected on a single collecting surface. Since the amount of trapped particulates can be reduced, which is advantageous for removing the particulates by oxidation, the particulates do not accumulate on the particulate filters, and the particulate filters can be prevented from being clogged.

In the present flow chart, the switching of the valve element is performed at every set traveling distance, and the valve element is switched before the residual particulates on the particulate filter are changed into carbon which is hardly oxidized. Also, oxidizing and removing particulates before a large amount of particulates are deposited prevents problems such as a large amount of deposited particulates being ignited and burnt at once and a large amount of heat of combustion causing the particulate filter to be melted and damaged. Also. Further, even if a large amount of particulates accumulates on one collecting surface of the particulate filter partition wall at the time of switching of the valve element for some reason, if the valve element is switched, the accumulated particulates will be in the opposite direction. Some of the finely divided particulates that could not be oxidized and removed in the pores of the partition walls are discharged from the particulate filter because they are relatively easily broken and fragmented by the exhaust gas flow. The exhaust resistance of the filter is not further increased and does not adversely affect the traveling of the vehicle, and new particulates can be collected by the other collecting surface of the particulate filter partition.

In this way, by switching the valve body for each set traveling distance, it is possible to reliably prevent a large amount of particulates from accumulating on the particulate filter.
The switching time of the valve body for this purpose is not limited to each set traveling distance, and may be, for example, set time or irregular.

Further, by utilizing the fact that the differential pressure between the exhaust gas upstream side and the exhaust downstream side of the particulate filter 70 increases in accordance with the amount of particulates remaining and deposited on the particulate filter, this differential pressure is set to a predetermined value. When the pressure becomes equal to or more than the pressure, it may be determined that a certain amount of particulates has accumulated on the particulate filter, and the valve element may be switched. Specifically, the exhaust pressure on one side of the particulate filter 70, that is, the first connection portion 7
2a (see FIG. 18), the exhaust pressure in the first connection portion 72a
And the exhaust pressure on the other side of the particulate filter, that is,
The exhaust pressure in the second connection part 72b (see FIG. 18) is detected by a pressure sensor arranged in the second connection part 72b,
It is determined whether or not the absolute value of the difference between the exhaust pressures is equal to or greater than the set pressure difference. Here, the reason why the absolute value of the differential pressure is used is that the rise in the differential pressure can be grasped regardless of which of the first connection portion 72a and the second connection portion 72b is on the exhaust upstream side. Strictly, this differential pressure also changes depending on the exhaust gas pressure exhausted from the cylinders. Therefore, it is preferable that the determination of the accumulation of particulates is performed by specifying the operating state of the engine.

In addition to the differential pressure, for example, a change in the electric resistance value on a predetermined partition wall of the particulate filter is monitored, and when the electric resistance value becomes lower than the set value due to the accumulation of the particulates, Assuming that a certain amount of particulates has accumulated on the particulate filter, the valve element may be switched. Further, the valve may be switched at a predetermined partition wall of the particulate filter by utilizing the fact that the light transmittance is reduced or the light reflectance is reduced due to the accumulation of the particulates. As described above, by directly determining the accumulation of particulates and switching the valve element, it is possible to more reliably prevent a large decrease in engine output.

Further, in order to prevent the accumulation of a large amount of particulates, even if the valve body is not switched as described above, the N
In SO _X poisoning restoration process of O _X purification catalyst device, in order to open position the valve element, upon completion of the SO _X poisoning restoration process, the shut-off position at the start so as to shut-off position in the opposite Is also good.

The present exhaust gas purifying apparatus makes it possible to reverse the upstream side and the downstream side of the exhaust gas of the particulate filter with a very simple structure as described above. Also,
In the particulate filter, a large opening area is required to facilitate the inflow of exhaust gas.
In the present exhaust gas purification apparatus, as shown in FIGS. 18 and 19, a particulate filter having a large opening area can be used without deteriorating vehicle mountability.

[0091] Further, when the atmosphere in the vicinity of the particulate filter a rich air-fuel ratio, the active oxygen O is released all at once i.e. from lowering the oxygen concentration in the vicinity of the atmosphere _the NO _X absorbent 61 to the outside. Due to the active oxygen O released at once, the deposited particulates are easily oxidized and easily oxidized and removed.

On the other hand, if the nearby atmosphere 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 oxygen when poisoning occurs oxidative effect on NO _X decreases the absorption efficiency of the NO _X to be reduced, the active oxygen release from _the NO _X absorbent 61 and thus decreases. NO However addresses the oxygen poisoning to the air-fuel ratio of oxygen on the platinum Pt surface is consumed when it is rich, and hence oxidation when the air-fuel ratio is switched again from rich to lean against NO _X becomes stronger _{The X} absorption efficiency increases, and thus the amount of active oxygen released from the NO _X absorbent 61 increases.

Therefore, when the air-fuel ratio is temporarily switched 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 reduced when the air-fuel ratio is lean. The active oxygen release amount is increased, and thus the oxidizing action of the particulate on the particulate filter 70 can be promoted.

Further, the elimination of this oxygen poisoning is, so to speak,
Since the combustion of the reducing substance occurs, the temperature of the particulate filter is increased with heat generation. As a result, the amount of fine particles that can be oxidized and removed in the particulate filter is improved, and the oxidization and removal of residual and deposited particulates is facilitated. If the air-fuel ratio of the exhaust gas is made rich immediately after switching between the exhaust gas upstream side and the exhaust downstream side of the particulate filter by the valve body 71a, the other trapping surface in the particulate filter partition where no particulate remains remains. Since the active oxygen is more easily released than the one collecting surface, the residual particulates on the one collecting surface can be more reliably oxidized and removed by a larger amount of the released active oxygen. Of course, valve 7
Irrespective of the switching of 1a, the surrounding atmosphere may sometimes be set to a rich air-fuel ratio, thereby making it difficult for particulates to remain and accumulate in the particulate filter.

As a method of setting the nearby atmosphere to a rich air-fuel ratio, for example, the above-described low-temperature combustion may be performed. Of course, when switching from normal combustion to low temperature combustion, or
Prior to this, the upstream side and the downstream side of the exhaust of the particulate filter may be switched. Also,
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 is injected into the cylinder by the engine fuel injection valve in the exhaust stroke or the expansion stroke (post injection).
Alternatively, the fuel may be injected into the cylinder during the intake stroke (bi rubber injection). Of course, the post injection or the rubber injection does not necessarily require an interval between the post injection and the rubber injection. It is also possible to supply fuel to the engine exhaust system. Further, in the NO _X purification catalyst device and the particulate filter, the NO
_For regeneration to release NO _X from the _X absorbent, the surrounding atmosphere must be at least temporarily set to a rich air-fuel ratio,
It is preferable to perform this enrichment control after the reversal of the upstream and downstream sides of the particulate filter.

Incidentally, calcium Ca in the exhaust gas produces calcium sulfate CaSO ₄ when SO ₃ is present. This calcium sulfate CaSO ₄ is hard to be oxidized and removed, and remains as ash on the particulate filter. Therefore, in order to prevent clogging of the particulate filter due to residual calcium sulfate, it is preferable to use an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, such as potassium K, as the NO _x absorbent 61. ,Thereby,
SO ₃ diffused into the NO _X absorbent 61 combines with potassium K to form potassium sulfate K ₂ SO ₄ , and calcium Ca passes through the partition wall of the particulate filter without binding to SO ₃ . Therefore, the particulate filter is not clogged by the ash. Thus, NO _X absorbent ionization tendency higher alkali metal or alkaline earth metal than calcium Ca as 61 as described above, i.e. potassium K, lithium Li, cesium Cs, rubidium Rb, barium Ba, the use of strontium Sr Is preferred.

[0097]

[Effect of the Invention] Thus, according to the exhaust purification system of an internal combustion engine according to the present invention, emission near atmosphere absorbs NO _X when the lean air-fuel ratio, the NO _X when the stoichiometric air-fuel ratio or a rich air-fuel ratio _the NO _X storage reduction catalyst is supported with a particulate filter arranged in the engine exhaust system, NO _X purification catalyst arranged in the exhaust system upstream of the particulate filter has an oxidation function of reducing and purifying by to and a device, the NO _X purification is insufficient only particulate filter, in order to compensate that NO _X purification catalyst device, it is possible to sufficiently purify the NO _X in the exhaust gas. By oxidation function of the NO _X purification catalyst device also can be burned off SOF in the exhaust gas at the upstream side of the particulate filter, particulates are prevented from growing into large chunks by SOF on the particulate filter Thus, clogging of the particulate filter can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a diesel engine provided with an exhaust gas purification device according to the present invention.

FIG. 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. 1;

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

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

FIG. 6 is a diagram showing amounts of smoke and NO _X generated, and the like.

FIG. 7 is a diagram showing a combustion pressure.

FIG. 8 is a diagram showing fuel molecules.

FIG. 9 is a diagram showing a relationship between a generation amount of smoke 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 operation region I and a second operation region II.

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

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

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

FIG. 15 is a diagram showing a map of a target opening degree of a throttle valve and the like.

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

FIG. 17 is a view showing a target opening degree of a throttle valve and the like.

FIG. 18 is a plan view showing the vicinity of a switching unit and a particulate filter in an engine exhaust system.

FIG. 19 is a side view of FIG. 18;

FIG. 20 is a view showing another blocking position of the valve body in the switching unit different from that in FIG. 18;

FIG. 21 is a diagram illustrating an open position of a valve body in a switching unit.

FIG. 22 is a diagram showing a structure of a particulate filter.

FIG. 23 is a diagram for explaining the effect of absorbing and releasing NO _X.

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

FIG. 25 is a diagram for explaining the oxidizing action of particulates.

FIG. 26 is a diagram showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of a particulate filter.

FIG. 27 is a view for explaining the accumulation action of particulates.

FIG. 28 is a flowchart for preventing accumulation of a large amount of particulates on a particulate filter.

FIG. 29 is an enlarged sectional view of a partition wall of the particulate filter.

[Explanation of symbols]

6 ... fuel injection valves 16 ... throttle valve 71 ... switching portion 70 ... particulate filter 74 ... NO _X purification catalyst device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/08 F01N 3/08 H 4D058 3/20 E 3/20 3/24 C 3/24 3/28 301E 3/28 301 F02D 41/04 305A F02D 41/04 305 B01D 46/44 // B01D 46/44 53/36 103B 103C 101B (72) Inventor Shinya Hirota 1st Toyota Town, Toyota City, Toyota City, Aichi Prefecture Toyota Automobile Stock Inside the company (72) Inventor Kazuhiro Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Koichiro Nakatani 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Koichi Kimura 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G090 AA03 BA01 CB24 EA02 3G091 AA02 AA11 AA18 AB02 AB06 AB09 AB13 BA11 BA14 BA27 BA33 CA12 CA13 CA26 DA04 DC01 EA38 FC01 GA09 GB02W GB03W GB04W GB06W GB10X HA10 HA19 HA29 HA36 HB03 HB05 3G301 HA02 HA13 JA21 JA24 JA25 LB11 MA01 ND01 NE02 NE13 PA11Z PA17B01A01 PDB CB04 4D048 AA06 AA13 AA14 AA18 AB01 AB02 AB05 AB07 BA02X BA14X BA15X BA18X BA30X BB02 BC01 BC04 BD01 CC26 CC32 CC41 CC47 DA01 DA02 DA20 EA04 4D058 JA32 MA44 QA01 QA19 QA23 SA08 TA06 UA25

Claims (4)

[Claims] 1. When the surrounding atmosphere has a lean air-fuel ratio, NO
_XAt the stoichiometric air-fuel ratio or rich air-fuel ratio._XTo
NO to be released and reduced and purified_XA storage and reduction catalyst
Particulate filter placed in the exhaust system
Upstream of the particulate filter
NO located in the engine exhaust system _XPurification catalyst device and
An exhaust gas purifying apparatus for an internal combustion engine, comprising: 2. The exhaust system for an internal combustion engine according to claim 1, further comprising a bypass unit that allows exhaust gas to bypass the particulate filter downstream of the NO _X purification catalyst device. Purification device. 3. The NO _X purification catalyst device carries the NO _X storage reduction catalyst, and during recovery of SO _X poisoning of the NO _X purification catalyst device, causes the bypass unit to function so that the exhaust gas is discharged. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the particulate filter is bypassed. 4. The NO _X purification catalyst device carries the NO _X storage reduction catalyst. Immediately after the completion of the SO _X poisoning recovery of the NO _X purification catalyst device, the exhaust gas is discharged without operating the bypass means. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas passes through the particulate filter.