JPH11200839A - Compression ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of a large quantity of smoke at combustion state switching time by opening or closing an exhaust control valve when a combustion state is switched to second combustion from first combustion or vice versa, and changing an exhaust gas recirculating rate in a step shape. SOLUTION: An engine 1 to reflux a part of exhaust gas in an exhaust passage 11 to an intake passage 6 by an EGR passage 16 in which an EGR control valve 17 is interposed, is constituted so as to selectively switch first combustion of hardly generating soot since an EGR gas quantity is more than an EGR gas quantity being the peak in a soot generating quantity and second combustion smaller in an EGR gas quantity than an EGR gas quantity being the peak in a soot generating quantity since soot is hardly generated after a fuel/gas temperature at combustion time becomes lower than a soot generating temperature when the EGR gas quantity is increased over a peak value. An exhaust gas recirculating rate is changed in a step shape by controlling an exhaust control valve 24 at combustion state switching time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression ignition type internal combustion engine.

[0002]

Conventionally than internal combustion engines, for example exhaust gas recirculation and engine exhaust passage and the engine intake passage in order to suppress the generation of the NO _X in the diesel engine (hereinafter, referred to as EGR) connected by passages, the Exhaust gas, that is, EGR gas, is recirculated through the EGR passage into the engine intake passage. In this case, the EGR gas has a relatively high specific heat, and therefore can absorb a large amount of heat.
The combustion temperature in the combustion chamber decreases as the GR gas amount increases, that is, as the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases. When the combustion temperature is lowered to decrease the generation amount of NO _X, thus the generation amount of the more NO _X to be increased EGR rate is lowered.

[0003] It has been found that can reduce the generation amount of the NO _X Thus increasing the EGR rate than before. However, when the EGR rate is increased, the soot generation amount, that is, smoke, starts to increase rapidly when the EGR rate exceeds a certain limit. In this regard, it has conventionally been considered that if the EGR rate is further increased, the smoke will increase indefinitely. Therefore, the smoke starts to increase rapidly.
The GR rate is considered to be the maximum allowable limit of the EGR rate.

Therefore, conventionally, the EGR rate has been set within a range not exceeding the maximum allowable limit (for example, Japanese Patent Laid-Open No.
-334750). The maximum allowable EGR rate varies considerably depending on the type of engine and fuel, but is approximately 30 to 50%. Therefore, in a conventional diesel engine, the EGR rate is suppressed to about 30% to 50% at the maximum.

[0005]

As described above, the conventional E
Since it was considered that there was a maximum allowable limit for the GR rate, the EGR rate was conventionally set so that the amount of generated NO _X and smoke was minimized within a range not exceeding the maximum allowable limit. However, even if the EGR rate is set such that the amount of generated NO _X and smoke is as small as possible, the reduction of the amount of generated NO _X and smoke is limited, and in fact, a considerable amount of NO _X and smoke is actually still present. At present, smoke is generated.

However, the inventor of the present invention has found that if the EGR rate is made larger than the maximum allowable limit in the course of research on the combustion of a diesel engine, the smoke increases rapidly as described above, but the amount of generated smoke has a peak. If the EGR rate is further increased beyond this peak, the smoke starts to decrease rapidly. If the EGR rate is increased to 70% or more during idling operation, and if the EGR gas is cooled strongly, the EGR rate is reduced to approximately 55%. Above a percentage, smoke was found to be almost zero, ie, little soot was generated. At this time, it has been found that the amount of generated NO _X is extremely small. Studying the reason why soot is not generated on the basis of this finding Thereafter, than it came to build the result unprecedented allows simultaneous reduction of soot and NO _X new system of combustion. This new combustion system will be described in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle of the process until the hydrocarbons grow into soot.

That is, as a result of repeated experimental studies, it has been found that when the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than a certain temperature, the growth of hydrocarbons is stopped at a halfway stage before reaching soot. However, when the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons grow into soot at a stretch. In this case, the temperature of the fuel and the surrounding gas is greatly affected by the heat absorbing action of the gas around the fuel when the fuel is burned, and the amount of heat absorbed by the gas around the fuel is adjusted according to the calorific value at the time of burning the fuel. As a result, the temperature of the fuel and the surrounding gas can be controlled.

Accordingly, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the fuel during combustion in the combustion chamber and its surroundings will not be generated. Can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system.

By the way it is necessary to more than about 55 percent at a minimum the EGR rate is to simultaneously reduce the soot and NO _X under this new combustion system. However, it is possible to make the EGR rate approximately 55% or more when the intake air amount is small, that is, when the engine load is relatively low. If the intake air amount exceeds a certain limit, the intake air amount is reduced unless the EGR rate is reduced. Cannot be increased. However, in this case, if the EGR rate is gradually reduced from 55% as the intake air amount increases, a problem occurs in that a large amount of smoke is generated.

[0010]

According to a first aspect of the present invention, an engine exhaust passage and an engine intake passage are connected by a recirculation exhaust gas passage, and the recirculation exhaust gas supplied to the combustion chamber is provided. As the amount of gas increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of recirculated exhaust gas supplied into the combustion chamber further increases, fuel during combustion in the combustion chamber and its surroundings In an internal combustion engine in which the gas temperature is lower than the soot generation temperature and soot is hardly generated, when the valve is closed, the amount of recirculated exhaust gas increases, and when the valve is opened, the amount of recirculated exhaust gas is reduced. The first combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas in which the amount of generated soot is peaked and the amount of generated soot is less Peak recirculation Switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of exhaust gas, and the first combustion to the second combustion or the second combustion to the second combustion. The exhaust gas recirculation rate is changed stepwise by opening or closing the exhaust control valve when switching to the first combustion mode.

In the second invention, in the first invention,
NO air-fuel ratio of the inflowing exhaust gas to release NO _X when the air-fuel ratio of the exhaust gas flowing to absorb NO _X in the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich when the lean
_{When the X} absorbent is disposed in the engine exhaust passage and the NO _X is to be released from the NO _X absorbent, the air-fuel ratio of the predetermined cylinder is set to the stoichiometric air-fuel ratio or rich during the first combustion. I am trying to do it.

In a third invention, in the second invention,
When the exhaust control valve is fully closed, all the exhaust gas discharged from some of the cylinders is recirculated to the engine intake passage via the recirculated exhaust gas, and the exhaust gas discharged from the remaining cylinders is NO _X are allowed flowing into the absorbent, the stoichiometric air-fuel ratio of the exhaust control valve the air-fuel ratio of the remaining cylinders of the aforementioned fully closed when the when releasing the NO _X from _the NO _X absorbent is performed first combustion Or make it rich.

[0013]

FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is the engine body, # 1, # 2, # 3, and # 4 are 1
The cylinder No. 2, the cylinder No. 3, the cylinder No. 3, and the cylinder No. 4 are respectively shown, and an electrically controlled fuel injection valve 3 is attached to each cylinder.
Each cylinder is connected to a surge tank 5 via a corresponding intake branch pipe 4, and the surge tank 5 is connected to an air cleaner 7 via an intake duct 6. A throttle valve 9 driven by an electric motor 8 is arranged in the intake duct 6. On the other hand, each cylinder is connected to an exhaust manifold 11 via a corresponding exhaust branch pipe 10, and the exhaust manifold 11 is connected to an exhaust pipe 12.
Is connected to a catalytic converter 14 having a built-in catalyst 13 having an oxidation function. An air-fuel ratio sensor 15 is disposed at an outlet of the exhaust manifold 11.

The exhaust manifold 11 and the surge tank 5 are connected to each other via an EGR passage 16, and the EGR passage 1
An electric control type EGR control valve 17 is arranged in 6. Further, a cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is disposed around the EGR passage 16. In the embodiment shown in FIG.
8, and the EGR gas is cooled by the engine cooling water.

On the other hand, each fuel injection valve 3 is connected to a fuel reservoir, a so-called common rail 2, through a corresponding fuel supply pipe 19.
Connected to 0. Fuel is supplied into the common rail 20 from an electric control type variable discharge fuel pump 21.
The fuel supplied into the common rail 20 is supplied to each fuel supply pipe 1
9 to the fuel injection valve 3. Common rail 2
A fuel pressure sensor 22 for detecting the fuel pressure in the common rail 20 is attached to the fuel pump 21 so that the fuel pressure in the common rail 20 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 22. The discharge amount is controlled.

An electric motor 23 is provided in the exhaust manifold 11.
An exhaust control valve 24 driven by is provided. In the embodiment shown in FIG. 1, the manifold internal chamber area A where the exhaust branch pipes 10 of the # 1 cylinder # 1 and the # 2 cylinder # 2 open are located at positions where the manifold internal chamber of the exhaust manifold 11 is bisected. The exhaust control valve 2 is located at the boundary between the manifold internal chamber region B where the exhaust branch pipes 10 of the cylinders # 3 and # 4 open.
4 are arranged. As shown in FIG. 1, the manifold internal chamber area A communicates with the EGR passage 16, and the manifold internal chamber area B communicates with the exhaust pipe 12. Therefore, when the exhaust control valve 24 is open, the exhaust gas discharged from each cylinder flows into the EGR passage 16 on the one hand and into the exhaust pipe 12 on the other hand. On the other hand, when the exhaust control valve 24 is fully closed, all the exhaust gas discharged from the first cylinder # 1 and the second cylinder # 2 flows into the surge tank 5 via the EGR passage 16, and the third cylinder # The exhaust gas discharged from the third and fourth cylinders # 4 flows into the catalyst 13 via the exhaust pipe 12.

The electronic control unit 30 is comprised of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, An output port 36 is provided. The output signal of the air-fuel ratio sensor 15 is input to the input port 35 via the corresponding AD converter 37. The output signal of the fuel pressure sensor 22 is also input to the input port 35 via the corresponding AD converter 37. Accelerator pedal 4
To 0, a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the electric motors 8 and 23, the EGR control valve 17, and the fuel pump 21 via the corresponding drive circuit 38.

FIG. 2 shows a change in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree and the EGR rate of the throttle valve 9 during the engine low load operation, and 4 shows an experimental example showing a change in the amount of smoke, HC, CO, and NO _X emissions. As can be seen from FIG. 2, in this experimental example, as the air-fuel ratio A / F becomes smaller, EG becomes smaller.
When the R rate increases and is equal to or lower than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is equal to or higher than 65%.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR ratio, the smoke is reduced when the air-fuel ratio A / F becomes approximately 30 when the EGR ratio becomes approximately 40%. The generation starts to increase. Next, 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 is around 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 N
Generation amount of O _X is considerably lower. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3 (A) shows a change in the combustion pressure in the combustion chamber when the amount of generated smoke is the largest when the air / fuel ratio A / F is around 18, and FIG. 3 (B) shows the change in the air / fuel ratio A / F. 13 shows a change in the combustion pressure in the combustion chamber when the amount of generated smoke is substantially zero near 13. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), FIG.
In the case shown in FIG. 3B, a large amount of smoke is generated.
It can be seen that the combustion pressure is lower than the case shown in FIG.

The following can be said from the experimental results shown in FIGS. That is, first, the air-fuel ratio A / F is 1
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
Generation amount of the NO _X considerably decreases as shown in. N
That the generation amount of O _X produced falls means that the combustion temperature in the combustion chamber is decreased, when the soot is hardly generated is therefore said to be the combustion temperature in the combustion chamber is low. The same can be said from FIG. That is,
In the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low, and at this time, the combustion temperature in the combustion chamber is low.

Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, as shown in FIG.
Emissions increase. 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. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot growth 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 generated soot becomes substantially zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a precursor of soot or a hydrocarbon in a state before it. .

Summarizing these considerations based on the experimental results shown in FIGS. 2 and 3, when the combustion temperature in the combustion chamber is low, the amount of soot generation becomes almost zero. Hydrocarbons will be discharged from the combustion chamber. As a result of further detailed experimental research on this, if the temperature of the fuel and the surrounding gas in the combustion chamber is below a certain temperature, the growth process of soot stops halfway, that is, no soot is generated Instead, it was found that soot was generated when the temperature of the fuel and its surroundings in the combustion chamber exceeded 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, 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. Although the change can not be said that how many times since has generated amount closely related to the certain temperature is nO _X, so that this certain temperature is defined to a certain degree from the generation amount of the nO _X be able to. 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 p.pm 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 post-processing using an oxidation catalyst or the like. On the other hand, the soot precursor or the hydrocarbon in the state before the soot can be easily purified by post-treatment using an oxidation catalyst or the like. Considering the post-treatment using an oxidation catalyst or the like, there is an extremely large difference in whether hydrocarbons are discharged from the combustion chamber in the state of or before the soot precursor or in the form of soot from the combustion chamber. . The new combustion system used in the present invention discharges hydrocarbons from the combustion chamber in the form of a precursor of soot or a state before the soot without generating soot in the combustion chamber, and the hydrocarbon is oxidized by an oxidation catalyst or the like. The core is to oxidize.

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 is suppressed to a temperature lower than the temperature at which the soot is generated. There is a need. In this case, it has been found that the endothermic effect 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 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 fuel vapor diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion temperature is not increased 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 fuel amount 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, and therefore, 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. 5 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. 5, a curve A indicates that the EGR gas temperature is substantially 9
Curve B shows the case where the EGR gas is cooled by a small cooling device, and curve C shows the case where the temperature is maintained at 0 ° C.
Indicates a case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 5, when the EGR gas is cooled strongly, the soot generation peaks at a point where the EGR rate is slightly lower than 50%. Above a percentage, little soot is generated. On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the soot generation amount reaches a peak at a point where the EGR rate is slightly higher than 50%. In this case, the EGR rate is increased to about 65% or more. If so, almost no soot is generated.

As shown by the curve C in FIG.
When the R gas is not forcibly cooled, the EGR rate becomes 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. FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load decreases, the EGR rate at which the amount of soot peaks slightly decreases, and the EGR rate at which soot is hardly generated is reduced. 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. 6 shows the mixing of EGR gas and air necessary to make the temperature of fuel during combustion and the surrounding gas 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 the mixed gas amount, and the ratio of EGR gas in the mixed gas. In FIG. 6, the vertical axis indicates the total intake gas amount drawn into the combustion chamber, and the dashed line Y indicates the total intake gas amount that can be drawn into the combustion chamber when supercharging is not performed. The horizontal axis shows the required load,
Z1 indicates a low load operation region.

Referring to FIG. 6, 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. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is formed. The required minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate, and in the embodiment shown in FIG.
It is more than percent. That is, the total intake gas amount sucked into the combustion chamber is indicated by a solid line X in FIG. 6, and when 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 gas around it is lower than the temperature at which soot is produced, so that no soot is generated. Further, the amount of generated NO _{X at} this time is about 10 p.pm or less, so that 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 the soot is generated, the heat generated by the EGR gas is required. Must be increased. Therefore, as shown in FIG. 6, 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 zone Z2 in FIG. 6, the total intake gas amount X necessary to prevent the generation of soot exceeds the total intake gas amount Y that can be sucked. Accordingly, in this case, in order to supply the total intake gas amount X necessary for preventing the generation of soot into the combustion chamber, both the EGR gas and the intake air or the EGR gas is used.
The gas needs to be supercharged or pressurized. When the EGR gas or the like is not supercharged or pressurized, the total intake air amount X matches the total intake air amount Y that can be taken 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. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, in the low load operation region Z1 shown in FIG. 6, the air amount is set to be smaller than the air amount shown in FIG. less well, i.e. the generation amount of the NO _X even if the air-fuel ratio to the rich while preventing generation of soot can be around or less 10 ppm, also the air in the low load region Z1 shown in FIG. 6 Even if the amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is lean from 17 to 18, the amount of generated NO _X is reduced by 10 while preventing the generation of soot.
It can be around ppm 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, thus producing soot. There is no. Further, at this time NO _X even only an extremely small amount of 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 increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Furthermore, NO _X
Only very small amounts are generated.

As described above, in the engine low load operation region Z1, regardless of the air-fuel ratio, that is, regardless of whether the air-fuel ratio is rich,
Whether the stoichiometric air-fuel ratio, or the average air-fuel ratio is not generated soot and would lean, the amount of the NO _X becomes 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 lean at this time. However in order to simultaneously reduce the soot and NO _X under a new combustion system used in the present invention EGR
The rate should be at least approximately 55 percent or more. However, it is possible to make the EGR rate approximately 55% or more when the intake air amount is small, that is, when the engine load is relatively low, and when the intake air amount exceeds a certain limit, that is, when the required load exceeds the certain limit. If it becomes high, the intake air amount cannot be increased unless the EGR rate is reduced. However, in this case, in the experimental example shown in FIG. 2, as the intake air amount increases, that is, as the required load increases, the EGR rate gradually decreases from approximately 65%, that is, as the required load increases, the empty space gradually decreases. When the fuel ratio is increased, a large amount of smoke is generated. Therefore, as the required load increases when the required load exceeds a certain limit, the EGR rate is increased to approximately 65%.
It is not possible to gradually decrease the percentage and gradually increase the air-fuel ratio.

In this case, in order to prevent the generation of a large amount of smoke, when the required load exceeds a certain limit, a large amount of the smoke is generated from approximately 40% to approximately 6%.
It is necessary to jump over the 5 percent EGR rate range. That is, it is necessary to instantaneously change the EGR rate in a stepped manner. To change the EGR rate stepwise, the EGR
The opening of the control valve 17 is changed stepwise, the opening of the throttle valve 9 is changed stepwise, or EG
It is necessary to change the opening of the R control valve 17 and the opening of the throttle valve 9 stepwise.

However, even if one or both of the opening degree of the EGR control valve 17 and the opening degree of the throttle valve 9 are changed stepwise, the amount of the EGR gas flowing into the surge tank 5 from the EGR passage 16 is so sharp. , And the EGR rate in some cylinders falls within the EGR rate range in which a large amount of smoke is generated, which causes a problem that a large amount of smoke is generated.

Thus, EGR in some cylinders
In order to prevent the rate from becoming the EGR rate at which a large amount of smoke is generated, the EG flowing into the surge tank 5 is prevented.
It is necessary to change the R gas amount as soon as possible. For this reason, in the present invention, the EGR rate is changed from an EGR rate larger than an EGR rate at which a large amount of smoke is generated to a smaller EGR rate than an EGR rate at which a large amount of smoke is generated. EGR when large amount of smoke occurs
When it is necessary to change from an EGR rate smaller than the rate to an EGR rate larger than the EGR rate at which a large amount of smoke is generated, the exhaust control valve 24 is opened or closed.

As described above, when the EGR rate is approximately 55% or more, the temperature of the fuel and the surrounding gas is lower than the temperature at which the soot is generated. At this time, the first combustion, that is, the low-temperature combustion is performed. Is being done. On the other hand, when the EGR rate is reduced to approximately 50% or less, the temperature of the fuel and the surrounding gas becomes higher than the temperature at which the soot is formed, and at this time, the first temperature is no longer increased.
Combustion, that is, low-temperature combustion cannot be performed. When the low-temperature combustion cannot be performed in the embodiment according to the present invention, the second combustion, that is, the combustion conventionally performed conventionally, is performed. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been conventionally performed, is the combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot generation peaks. I say

FIG. 7 shows the first combustion in which the EGR rate is approximately 55% or more, that is, the first operation region I in which low-temperature combustion is performed, and the second combustion in which the EGR rate is approximately 50% or less. That is, a second combustion region II in which combustion is performed by a conventional combustion method is shown. In FIG. 7, the vertical axis L indicates the depression amount of the accelerator pedal 40, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 7, 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. The second boundary with the area II is shown. The determination of the change of the operating region from the first operating region I to the second operating region II is made based on the first boundary X (N), and the determination from the second operating region II to the first operating region I is performed. The determination of the change in the operating region 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
, The required load L is a function of the engine speed N when the first combustion, that is, the low-temperature combustion, is performed.
If (N) is exceeded, it is determined that the operation region has shifted to the second operation region II, and the operation is switched to the second combustion. 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 the second combustion is shifted to the first combustion. Is switched.

The two boundaries, that is, the first boundary X (N) and the second boundary Y (N) having a lower load than the first boundary X (N) are provided next. For three reasons. The first reason is that the combustion temperature is relatively high on the high load side of the second operation region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not immediately start unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for a change in the operation range between the first operation range I and the second operation range II.

By the way, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and the unburned hydrocarbon is replaced by the precursor of soot or the state before the soot. It is discharged from the combustion chamber in the form. At this time, the unburned hydrocarbon discharged from the combustion chamber is oxidized well by the catalyst 13 having an oxidizing function. As catalyst 13 may be an oxide catalyst, three-way catalyst, or _the NO _X absorbent. _The NO _X absorbent absorbs NO _X when the average air-fuel ratio is lean in the combustion chamber, has the function of releasing the NO _X when the average air-fuel ratio in the combustion chamber becomes the stoichiometric air-fuel ratio or rich.

This NO _X absorbent uses, for example, alumina as a carrier, and, for example, potassium K, sodium N
a, lithium Li, at least one selected from alkali metals such as cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and noble metals such as platinum Pt. Is carried.

Not only the oxidation catalyst but also the three-way catalyst and the NO
_{The X} absorbent also has an oxidizing function, and thus the three-way catalyst and the NO _X absorbent can be used as the catalyst 13 as described above. FIG. 8 shows the output of the air-fuel ratio sensor 15. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 15 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 15.

Next, a first embodiment of the operation control will be described with reference to FIG. FIG. 9 shows the opening degree of the throttle valve 9, the opening degree of the EGR control valve 17, the opening degree of the exhaust control valve 24, 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. 9, in the first operating region I where the required load L is low, the opening of the throttle valve 9 is gradually increased as the required load L increases, and the opening of the EGR control valve 17 is set to the required load L Is gradually increased from the fully closed state to the fully open state, and the exhaust control valve 24 is gradually increased.
Are held in a fully closed state. Therefore, at this time, all the exhaust gas discharged from the first cylinder # 1 and the second cylinder # 2 is E
It is supplied to the surge tank 5 via the GR passage 16. In the example shown in FIG. 9, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a lean air-fuel ratio of about 15 to 18. In other words, in the first operating region I, the opening of the throttle valve 9 and the opening of the EGR control valve 17 are controlled so that the EGR rate becomes approximately 70% and the air-fuel ratio becomes a lean air-fuel ratio of about 15 to 18. You. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening of the throttle valve 9, the opening of the EGR control valve 17, or the fuel injection amount based on the output signal of the air-fuel ratio sensor 15. 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.

When the operating state of the engine is in the first operating region I, almost no soot and NO _X are generated, and the precursor of soot contained in the exhaust gas or the hydrocarbon in a state before the soot is oxidized by the catalyst 13. I'm sick. On the other hand, when the operation region of the engine changes from the first operation region I to the second operation region II, the exhaust control valve 24 is fully opened from the fully closed state at a stretch,
The opening of the throttle valve 9 is stepwise increased to a fully opened state. When the throttle valve 9 is fully opened at a stretch, most of the exhaust gas discharged from the first cylinder # 1 and the second cylinder # 2 flows into the exhaust pipe 12, and the EGR passage 16
, The amount of EGR gas supplied into the surge tank 5 decreases instantaneously. Thus, the EGR rate instantaneously decreases.

At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio changes stepwise greatly toward the lean side. That is, since the EGR rate jumps over the EGR rate range in which a large amount of smoke is generated, a large amount of smoke is not generated when the operation region of the engine changes from the first operation region I to the second operation region II.

In the second operation region II, the second combustion, that is, the conventional combustion is performed. Although soot and NO _X in the combustion process occurs slightly heat efficiency is higher than the low temperature combustion, thus as the operating region of the engine is shown in Figure 9 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise. Second operating area
In II, the throttle valve 9 is kept fully open except for a part, and the opening of the EGR control valve 17 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 decreases.
The higher the value, the larger. 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.

On the other hand, the operation state of the engine is the first operation in which the low-temperature combustion is performed from the second operation region II in which the second combustion is performed.
9, the opening of the throttle valve 9 is reduced stepwise, and the exhaust control valve 24 is fully closed, as can be seen from FIG. When the exhaust control valve 24 is fully closed, all the exhaust gas discharged from the first cylinder # 1 and the second cylinder # 2 is supplied into the surge tank 5 through the EGR passage 16, and as a result, The supplied EGR gas amount instantaneously increases. At this time, in the example shown in FIG.
It is increased stepwise to a percentage.

Next, the operation control will be described with reference to FIG. Referring to FIG. 10, first, step 10 is executed.
At 0, it is determined whether or not a flag I indicating that the operating region of the engine is the first operating region I is set. When the flag I is set, that is, when the operation region of the engine is the first operation region I, step 101
It is determined whether the required load L has become larger than the first boundary X (N) shown in FIG.

When L ≦ X (N), the routine proceeds to step 102, where the exhaust control valve 24 is fully closed. Next, at step 103, the opening of the throttle valve 9 is controlled to an opening corresponding to the required load L shown in the first operating region I of FIG.
Next, at step 104, the opening of the EGR control valve 17 is controlled to an opening corresponding to the required load L shown in the first operation region I of FIG. Next, at step 105, the first of FIG.
The injection amount according to the required load L and the like shown in the operation region I of
The injection start timing θS and the injection completion timing θE are obtained,
Fuel injection is performed based on these. At this time, the air-fuel ratio is set to a lean air-fuel ratio of about 15 to 18.

On the other hand, in step 101, L> X
If it is determined that (N) has been reached, the routine proceeds to step 106, where the flag I is reset. Next, the routine proceeds to step 108, where the exhaust control valve 24 is fully opened. Then step 1
At 09, the opening of the throttle valve 9 is in the second operating region of FIG.
The opening is controlled to the opening corresponding to the required load L shown in II. Next, at step 110, the opening degree of the EGR control valve
Is controlled to an opening corresponding to the required load L shown in the second operation region II. Next, at step 111, the injection amount, the injection start timing θS, and the injection completion timing θE according to the required load L and the like shown in the second operation region II of FIG. 9 are obtained, and the fuel injection is performed based on these.

On the other hand, when it is determined in step 100 that the flag I has been reset, that is, when the operating region of the engine is in the second operating region II, step 107 is executed.
It is determined whether the required load L has become smaller than the second boundary Y (N) shown in FIG. When L ≧ Y (N), the process proceeds to step 108. On the other hand, L <Y
When (N) is reached, the routine proceeds to step 112, where the flag I is set, and then proceeds to step 102.

FIG. 11 shows a second embodiment. In this embodiment, when the required load L is the lowest in the first operating region I, that is, at the time of idling operation, the exhaust control valve 24 is fully opened.
Is gradually reduced, and when the required load L is the highest in the first operation region I, the exhaust control valve 24 is fully closed.

In this embodiment, during the idling operation, the throttle valve 9 is closed until it is almost fully closed, and at this time, the EGR control valve 17 is also closed until it is almost fully closed. When the throttle valve 9 is closed close to the fully closed state, the pressure in the combustion chamber at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston decreases, so that the vibration of the engine body 1 decreases. That is, in this embodiment, the vibration of the engine main body 1 is suppressed by closing the throttle valve 9 to nearly full close during idling operation.

Next, an operation control for executing the second embodiment will be described with reference to FIG. Referring to FIG. 12, first, at step 200, it is determined whether or not a flag I indicating that the operation region of the engine is the first operation region I is set. When the flag I is set, that is, when the operating region of the engine is the first operating region I, the routine proceeds to step 201, where the required load L is reduced as shown in FIG.
Is determined to be larger than the first boundary X (N) shown in FIG.

When L ≦ X (N), the routine proceeds to step 202, where the exhaust control valve 24 is controlled to the opening degree shown in FIG. Next, at step 203, the opening of the throttle valve 9 is controlled to an opening corresponding to the required load L shown in the first operating region I of FIG. Next, at step 204, EG
The opening of the R control valve 17 is controlled to an opening corresponding to the required load L shown in the first operation region I of FIG. Next, at step 205, the injection amount, the injection start timing θS, and the injection completion timing θE according to the required load L and the like shown in the first operation region I of FIG. 9 are obtained, and the fuel injection is performed based on these. At this time, the air-fuel ratio is set to a lean air-fuel ratio of about 15 to 18.

On the other hand, in step 201, L> X
If it is determined that (N) has been reached, the routine proceeds to step 206, where the flag I is reset. Next, the routine proceeds to step 208, where the exhaust control valve 24 is fully opened. Then step 2
In step 09, the opening of the throttle valve 9 is controlled to an opening corresponding to the required load L shown in the second operation area II of FIG.
Next, at step 210, the opening of the EGR control valve 17 is controlled to an opening corresponding to the required load L shown in the second operation region II of FIG. Next, at step 211, the injection amount, the injection start timing θS, and the injection completion timing θE according to the required load L and the like shown in the second operation region II of FIG. 9 are obtained, and the fuel injection is performed based on these.

On the other hand, when it is determined in step 200 that the flag I has been reset, that is, when the operation region of the engine is the second operation region II, step 207 is executed.
It is determined whether the required load L has become smaller than the second boundary Y (N) shown in FIG. When L ≧ Y (N), the process proceeds to step 208. On the other hand, L <Y
When (N) is reached, the routine proceeds to step 212, where the flag I is set, and then the routine proceeds to step 202.

FIG. 13 shows a third embodiment. In this embodiment, the exhaust control valve 24 is normally fully opened, and when the operating state of the engine shifts from the first operating region I to the second operating region II, and from the second operating region II to the first operating region. Region I
, The exhaust control valve 24 is temporarily closed. FIG. 14A shows a case where the required load L gradually decreases and at time t ₀ , the second combustion is switched to the first combustion. As shown in FIG.
When the throttle valve 9 is closed stepwise when the fuel is switched to the first fuel from the combustion of the fuel tank 5, the surge tank 5 is closed.
The pressure in the inside gradually decreases, and as a result, the amount of EGR gas supplied into the surge tank 5 gradually increases. That is, the amount of EGR gas supplied into the surge tank 5 does not increase instantaneously. Thus, in this embodiment, when the second combustion is switched to the first combustion, the exhaust control valve 24 is temporarily closed so that the amount of EGR gas supplied into the surge tank 5 is instantaneously increased. I have.

On the other hand, FIG. 14 (B) shows a case where the required load L gradually increases, and at time t ₀ , the first combustion is switched to the second combustion. In this case, time t ₀
, The opening of the throttle valve 9 is gradually increased so that the EGR rate does not greatly change, and the opening of the exhaust control valve 24 is gradually decreased. Then, at time t ₁ , the opening of the throttle valve 9 is stepped. And the exhaust control valve 24 is fully opened at a stretch. At this time, the EGR rate is reduced stepwise.

Next, the operation control for executing the third embodiment will be described with reference to FIG. Referring to FIG. 15, first, at step 300, it is determined whether or not a flag I indicating that the operation region of the engine is the first operation region I is set. When the flag I is set, that is, when the operating region of the engine is the first operating region I, the routine proceeds to step 301, where the required load L is reduced as shown in FIG.
Is determined to be larger than the first boundary X (N) shown in FIG.

When L ≦ X (N), the routine proceeds to step 302, where the opening of the exhaust control valve 24 is controlled as shown in FIG. Next, at step 303, the opening of the throttle valve 9 is controlled to an opening corresponding to the required load L shown in the first operation region I of FIG. Then step 304
In, the opening of the EGR control valve 17 is controlled to an opening corresponding to the required load L shown in the first operation region I of FIG. Next, at step 305, the injection amount, the injection start timing θS, and the injection completion timing θE corresponding to the required load L and the like shown in the first operation region I of FIG. 9 are obtained, and the fuel injection is performed based on these. At this time, the air-fuel ratio is set to a lean air-fuel ratio of about 15 to 18.

On the other hand, in step 301, L> X
When it is determined that (N) has been reached, the routine proceeds to step 306, where the flag I is reset. Next, the routine proceeds to step 308, where the opening of the exhaust control valve 24 is controlled as shown in FIG. Next, at step 309, the opening of the throttle valve 9 is controlled to an opening corresponding to the required load L shown in the second operation region II of FIG. Then step 31
At 0, the opening of the EGR control valve 17 is controlled to an opening corresponding to the required load L shown in the second operation region II of FIG.
Next, at step 311, the injection amount and the injection start timing θS according to the required load L and the like shown in the second operation region II of FIG.
And an injection completion timing θE, and fuel injection is performed based on these.

On the other hand, when it is determined in step 300 that the flag I has been reset, that is, when the operating region of the engine is in the second operating region II, step 307 is executed.
It is determined whether the required load L has become smaller than the second boundary Y (N) shown in FIG. When L ≧ Y (N), the process proceeds to step 308. On the other hand, L <Y
At (N), the routine proceeds to step 312, where the flag I is set, and then proceeds to step 302.

FIG. 16 shows a fourth embodiment. In this embodiment, an exhaust control valve is provided at the boundary between the manifold internal chamber region C where the exhaust branch pipe 10 of the first cylinder # 1 opens and the manifold internal chamber region D where the second cylinder # 2 to the fourth cylinder # 4 open. 24 is disposed, and the opening of the exhaust control valve 24 is controlled by any of the methods shown in the first to third embodiments. FIG.
In the fifth embodiment shown in FIG. 5, exhaust gas is exhausted at the boundary between the manifold internal chamber region E where the exhaust branch pipes 10 of the first cylinder # 1 to the third cylinder # 3 open and the manifold internal chamber region F where the fourth cylinder # 4 opens. A control valve 24 is provided. In the sixth embodiment shown in FIG. 18, the exhaust control valve 24 is provided in the exhaust pipe 12. In the fifth and sixth embodiments, as shown in FIG. 19, the exhaust control valve 24 is maintained in a half-open state in the first operation region I, and is maintained in a fully-open state in the second operation region II.

Next, in the embodiment shown in FIG.
It will be described using _the NO _X absorbent as 3.
The ratio of the engine intake passage and _the NO _X absorbent 13 upstream of the exhaust passage supplying air and fuel into the (hydrocarbon) NO _X
The air-fuel ratio of the exhaust gas flowing into the absorbent 13 is referred to as N
O _X absorbent 13 absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, the air-fuel ratio of the inflowing exhaust gas to release NO _X absorbed and becomes the stoichiometric air-fuel ratio or rich NO _X
Performs absorption and release action.

[0073] By arranging the _the NO _X absorbent 13 in the engine exhaust passage performs the absorbing and releasing action of the _the NO _X absorbent 13 actually NO _X is also part not clear detailed mechanism of action out this absorbing . However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

In the compression ignition type internal combustion engine shown in FIG.
NO when combustion of 1 is performed_XAlmost occurs
However, when the second combustion is performed, N
O_XOccurs. In the second combustion, the air-fuel ratio is lean
The oxygen concentration in the exhaust gas is high because
As shown in FIG._TwoIs O_Two ^-
Or O^2-On the surface of platinum Pt. Meanwhile, inflow
NO in the exhaust gas is O 2 on the surface of platinum Pt._Two ^-Or O^2-
Reacts with NO_Two(2NO + O_Two→ 2NO_Two).
NO generated next_TwoIs oxidized on platinum Pt
While being absorbed in the absorbent and binding with barium oxide BaO
Meanwhile, as shown in FIG._Three
^-Diffuses into the absorbent in the form of NO in this way_XBut
NO_XIt is absorbed in the absorbent 13. Acid in incoming exhaust gas
NO on the surface of platinum Pt as long as elemental concentration is high_TwoIs generated,
Absorbent NO_XNO unless absorption capacity is saturated_XIs absorbed
Nitrate ion NO absorbed in the agent_Three ^-Is generated.

On the other hand, when the air-fuel ratio of the inflowing exhaust gas becomes rich, the oxygen concentration in the inflowing exhaust gas decreases, and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ). comb nitrate ions NO in absorbent ₃ ^- are released from the absorbent in the form of NO _2. In this case _the NO _X absorbent 13
NO _X released from the large amount of unburned HC contained in the inflowing exhaust gas as shown in FIG. 20 (B), is caused to reduction by reaction with CO. In this way, when NO ₂ is no longer present on the surface of platinum Pt, NO ₂ is released from the absorbent one after another. Therefore, when the air-fuel ratio is made rich, NO _X is released from the NO _X absorbent 13 in a short time, and since the released NO _X is reduced, NO _X is discharged to the atmosphere. It can be blocked.

Since the NO _X absorbent 13 also has a function of a reduction catalyst, the NO _X released from the NO _X absorbent 13 is set to the stoichiometric air-fuel ratio when NO _X is to be released.
_X is reduced. However the slightly longer time to release all NO _X that is absorbed in the NO _X absorbent 13 to NO _X from _the NO _X absorbent 13 when the air-fuel ratio to the stoichiometric air-fuel ratio is not only released gradually It costs.

[0077] Incidentally is in the NO _X absorbing capacity of the NO _X absorbent 13 is limited, hence the need to NO _X absorbing capacity of the NO _X absorbent 13 to release the NO _X from _the NO _X absorbent 13 before the limit is there. _The NO _X absorbent 13 in order that
It is necessary to estimate the amount of NO _X absorbed in the air. In the embodiment according to the present invention previously experiment in the form of a map as shown in FIG. 21 as a function of per unit time of the NO _X absorption D the required load L and engine speed N when being performed second combustion From this map, the NO _X absorption amount D per unit time is obtained, and then, by integrating this NO _X absorption amount D, the NO _X amount ΣNO _X absorbed in the NO _X absorbent 13 is obtained. and so as to release the NO _X from _the NO _X absorbent 13 when this amount of NO _X ShigumaNO _X reaches the allowable maximum value MAX predetermined.

[0078] Incidentally, in order to release the _the NO _X absorbent 13 from the NO _X must be the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 13 to the stoichiometric air-fuel ratio or rich, the most convenient method in this case To make the air-fuel ratio in the combustion chamber stoichiometric or rich. However, when the air-fuel ratio in the combustion chamber is set to the stoichiometric air-fuel ratio or rich in a conventionally used compression ignition type internal combustion engine, a large amount of smoke is generated. The fuel ratio cannot be made stoichiometric or rich.

[0079] However in the compression ignition type internal combustion engine which is used in the present invention the first combustion, that is, soot and NO _X even if the air-fuel ratio in the combustion chamber the stoichiometric air-fuel ratio or rich when the low temperature combustion is being performed Almost never. Therefore when the amount of NO _X ShigumaNO _X exceeds the allowable maximum value MAX in the embodiment according to the present invention is the air-fuel ratio is the stoichiometric air-fuel ratio or rich when the first combustion is being performed, thereby _the NO _X absorbent 13 and so as to release the NO _X from.

Next, a specific example will be described with reference to FIG. FIG. 22 shows that the NO _X amount XNO at time t ₀ .
_{The case where X} exceeds the allowable maximum value MAX is shown. NO
_X amount ShigumaNO _X is set NO _X release flag showing that from _the NO _X absorbent 13 exceeds the allowable maximum value MAX should be released NO _X. However, at this time, since the second combustion is being performed, the air-fuel ratio of each cylinder is set to a lean air-fuel ratio.

Next, when the exhaust control valve 24 is fully closed from the fully opened state and the second combustion is shifted to the first combustion, FIG.
, The air-fuel ratio of the first cylinder # 1 and the second cylinder # 2 is a lean air-fuel ratio of about 15 to 18, whereas the air-fuel ratio of the third cylinder # 3 and the fourth cylinder # 4 is The rich air-fuel ratio is temporarily set. Third air-fuel ratio of the cylinder # 3 and fourth cylinder # 4 is the exhaust gas flowing into _the NO _X absorbent 13 As can be seen from Figure 1 when it is made rich becomes rich,
Thus was released NO _X is made to the reduction of _the NO _X absorbent 13 with NO _X is made to release. In addition,
At this time, the air-fuel ratio of the first cylinder # 1 and the second cylinder # 2 is set to the lean air-fuel ratio in order to improve the fuel consumption rate.

When it is determined that all the NO _X has been released from the NO _X absorbent 13, the NO _X release flag is reset, and the third cylinder # 3 and the fourth cylinder # 4 have lean air-fuel ratios of 15-18. It is said. Next, the time interruption routine will be described with reference to FIG. NO _X releasing flag first, at step 400 and referring to FIG. 23, whether it is set or not. When the NO _X release flag is not set, step 401
Then, it is determined whether or not the flag I indicating that the operation region of the engine is the first operation region I is set. Step 40 when the flag I is set
NO _X absorption D per unit time proceed to 2 is a small value D ₀ of predetermined then the routine proceeds to step 404. On the other hand, when the flag I is reset,
That is, when the second combustion is being performed, step 403 is performed.
The proceeds from the map shown in FIG. 21 per unit time in NO _X
The absorption amount D is calculated, and then the process proceeds to step 404.

In step 404, ΣNO_XAdd D to
NO by doing_XNO absorbed in absorbent 13
_XQuantity Σ NO_XIs calculated. Then in step 405
NO _XQuantity Σ NO_XHas exceeded the maximum allowable value MAX.
Determined, ΣNO_XStep when it becomes> MAX
Go to 406 and NO_XThe release flag is set. NO
_XWhen the release flag is set, the process proceeds from step 400.
Proceeding to step 407, the third cylinder # 3 and the fourth cylinder # 4
It is determined whether the air-fuel ratio has been enriched for a certain period of time.
The air-fuel ratio of the third cylinder # 3 and the fourth cylinder # 4 is reset for a certain time.
When the switch is turned on, the process proceeds to step 408 and NO_XRelease
The outgoing flag is reset, and then in step 409
NO_XIs set to zero.

Next, the operation control will be described with reference to FIG. Referring to FIG. 24, first, at step 45,
At 0, it is determined whether or not a flag I indicating that the operating region of the engine is the first operating region I is set. When the flag I is set, that is, when the operating region of the engine is the first operating region I, step 451 is executed.
It is determined whether the required load L has become larger than the first boundary X (N) shown in FIG.

When L ≦ X (N), the routine proceeds to step 452, where the exhaust control valve 24 is fully closed. Next, at step 453, the opening of the throttle valve 9 is controlled to an opening corresponding to the required load L shown in the first operation region I of FIG.
Next, at step 454, the opening of the EGR control valve 17 is controlled to an opening corresponding to the required load L shown in the first operation region I of FIG. Next, at step 455, it is determined whether or not the NO _X release flag is set.

If the NO _X release flag has not been set, the routine proceeds to step 456, where the first operating region I in FIG.
The injection amount, the injection start timing θS, and the injection completion timing θE according to the required load L and the like shown in the above are obtained, and the fuel injection is performed based on these. At this time, the air-fuel ratio is 15 to 1
The lean air-fuel ratio is about 8. On the other hand, when the NO _X release flag is set, the routine proceeds to step 457, where the air-fuel ratio of the first cylinder # 1 and the second cylinder # 2 becomes 15
, And the air-fuel ratio of the third cylinder # 3 and the fourth cylinder # 4 is a rich air-fuel ratio. In this case NO _X is released from _the NO _X absorbent 13.

On the other hand, at step 451, L> X
If it is determined that (N) has been reached, the routine proceeds to step 458, where the flag I is reset. Next, the routine proceeds to step 460, where the exhaust control valve 24 is fully opened. Then step 4
At 61, the opening of the throttle valve 9 is in the second operating region of FIG.
The opening is controlled to the opening corresponding to the required load L shown in II. Next, at step 462, the opening degree of the EGR control valve
Is controlled to an opening corresponding to the required load L shown in the second operation region II. Next, at step 463, an injection amount, an injection start timing θS, and an injection completion timing θE corresponding to the required load L and the like shown in the second operation region II of FIG. 9 are obtained, and fuel injection is performed based on these.

On the other hand, when it is determined in step 450 that the flag I has been reset, that is, when the operating region of the engine is in the second operating region II, step 459 is performed.
It is determined whether the required load L has become smaller than the second boundary Y (N) shown in FIG. When L ≧ Y (N), the process proceeds to step 460. On the other hand, L <Y
When (N) is reached, the routine proceeds to step 464, where the flag I is set, and then proceeds to step 452.

[0089]

When shifting from the first combustion to the second combustion,
In addition, it is possible to prevent a large amount of smoke from being generated when moving from the second combustion to the first combustion.

[Brief description of the drawings]

FIG. 1 is an overall view of a compression ignition type internal combustion engine.

FIG. 2 is a diagram showing amounts of smoke and NO _X generated, and the like.

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing fuel molecules.

FIG. 5 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.

FIG. 6 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 7 is a diagram showing a first operation region I and a second operation region II.

FIG. 8 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 9 is a diagram showing an opening degree of a throttle valve and the like.

FIG. 10 is a flowchart for controlling the operation of the engine.

FIG. 11 is a diagram showing an opening degree of a throttle valve and the like.

FIG. 12 is a flowchart for controlling operation of the engine.

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

FIG. 14 is a diagram showing an opening degree and the like of an exhaust control valve.

FIG. 15 is a flowchart for controlling operation of the engine.

FIG. 16 is an overall view of a compression ignition type internal combustion engine.

FIG. 17 is an overall view of a compression ignition type internal combustion engine.

FIG. 18 is an overall view of a compression ignition type internal combustion engine.

FIG. 19 is a view showing an opening degree of a throttle valve and the like.

FIG. 20 is a view for explaining the NO _X absorption / release action.

FIG. 21 is a diagram showing a map of an NO _X absorption amount D per unit time.

FIG. 22 is a time chart showing NO _X release control.

FIG. 23 is a diagram showing a time interruption routine.

FIG. 24 is a flowchart for controlling the operation of the engine.

[Explanation of symbols]

 9 ... Throttle valve 11 ... Exhaust manifold 17 ... EGR control valve 24 ... Exhaust control valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 7/08 ZAB F01N 7/08 ZABB 7/10 ZAB 7/10 ZAB F02D 9/04 F02D 9/04 EC 21/08 301 21/08 301D F02M 25/07 ZAB F02M 25/07 ZAB 550 550G (72) Inventor Shinichi Takeshima 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Takamitsu Asanuma Toyota Town, Toyota City, Aichi Prefecture No. 1 Toyota Motor Corporation

Claims (3)

[Claims] An engine exhaust passage and an engine intake passage are connected by a recirculation exhaust gas passage, and as the amount of recirculation exhaust gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and peaks. And when the amount of recirculated exhaust gas supplied to the combustion chamber is further increased, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, so that almost no soot is generated. In an internal combustion engine, an exhaust control valve in which the amount of recirculated exhaust gas increases when the valve is closed and the amount of recirculated exhaust gas decreases when the valve is opened is disposed in the engine exhaust passage, and the amount of generated soot is the recirculated exhaust gas. The first combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is larger than the amount and soot is hardly generated, and the recirculated exhaust gas supplied to the combustion chamber is larger than the amount of recirculated gas in which the amount of generated soot becomes a peak. 2nd with low gas volume Switching means for selectively switching between the first combustion and the second combustion, and when the first combustion is switched from the second combustion to the second combustion, the exhaust control valve is opened or closed. A compression ignition type internal combustion engine in which the exhaust gas recirculation rate is changed in a step-like manner. Wherein the air-fuel ratio of the inflowing exhaust gas is absorbed and the air-fuel ratio of the exhaust gas when the lean flowing absorbs NO _X in the exhaust gas becomes the stoichiometric air-fuel ratio or rich NO _X
The _the NO _X absorbent to release disposed engine exhaust passage, N
Compression ignition when the O _X absorbent should be released NO _X is claim 1 which is adapted to the stoichiometric air-fuel ratio or rich air-fuel ratio of the predetermined cylinder when being performed first combustion Type internal combustion engine. 3. When the exhaust control valve is fully closed, all exhaust gas discharged from some cylinders is recirculated to the engine intake passage via recirculated exhaust gas and discharged from the remaining cylinders. exhaust gas is made to flow into _the NO _X absorbent, the when releasing the NO _X from _the NO _X absorbent is first
3. The compression ignition type internal combustion engine according to claim 2, wherein the exhaust control valve is fully closed when the combustion is performed to make the air-fuel ratio of the remaining cylinders a stoichiometric air-fuel ratio or rich.