JP3405167B2 - Compression ignition type internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, for example, a diesel engine, an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation (hereinafter referred to as EGR) passage in order to suppress the generation of NO _X. Exhaust gas, that is, EGR gas, is recirculated into the engine intake passage via the EGR 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 decreases, the NO _X generation amount decreases, and therefore, the higher the EGR rate, the lower the NO _X generation amount.

As described above, it has been known that the amount of NO _x generated can be reduced by increasing the EGR rate. However, when the EGR rate is increased, when the EGR rate exceeds a certain limit, the amount of soot generated, that is, the smoke starts to increase rapidly. In this regard, it has been conventionally thought that if the EGR rate is further increased, the smoke will increase infinitely, and therefore the smoke will start to increase rapidly.
The GR rate is considered to be the maximum allowable limit for the EGR rate.

Therefore, conventionally, the EGR rate is set within a range that does not exceed the maximum allowable limit (for example, Japanese Patent Laid-Open No. Hei 4).
-334750 gazette). The maximum allowable limit of this EGR rate is approximately 30 to 50 percent, though it varies considerably depending on the engine type and fuel. Therefore, in the conventional diesel engine, the EGR rate is suppressed to about 30% to 50% at the maximum.

[0005]

As described above, in the prior art, E
Generation amount of the NO _X and smoke within a range not exceeding the EGR rate is the maximum allowable limit than conventional since it has been considered that the maximum allowable limit exists has been determined to be as small as possible with respect to GR ratio. However, even if the EGR rate is set in such a manner that the NO _X and smoke generation amounts are made as small as possible, there is a limit to the reduction of the NO _X and smoke generation amounts, and in reality, a considerable amount of NO _X and smoke is still generated. The current situation is that smoke is generated.

However, the inventor of the present invention, when the EGR rate is made larger than the maximum allowable limit in the process of studying the combustion of the diesel engine, the smoke increases rapidly as described above, but there is a peak in the amount of smoke produced, If the EGR rate is further increased beyond this peak, the smoke starts to decrease sharply this time. If the EGR rate is 70% or more during idling, and if the EGR gas is strongly cooled, the EGR rate becomes almost 55%. It was found that if it exceeds the percentage, smoke is almost zero, that is, soot is hardly generated. It has also been found that at this time, the amount of NO _x generated 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 stage until the growth of hydrocarbons into soot.

[0007] That is, as a result of repeated experimental research, it was found that when the temperature of the fuel and the gas around it during combustion in the combustion chamber were below a certain temperature, the growth of hydrocarbons stopped in the middle of the process before reaching soot. However, if the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons will suddenly grow to soot. In this case, the temperature of the fuel and its surrounding gas is greatly affected by the endothermic action of the gas around the fuel when the fuel burns, and the endothermic amount of the gas around the fuel is adjusted according to the amount of heat generated during fuel combustion. Thus, the temperature of the fuel and the gas around it can be controlled.

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

By the way, in order to simultaneously reduce soot and NO _x under this new combustion system, it is necessary to make the EGR rate at least about 55% or more. However, the EGR rate can be increased to 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 decreased. Cannot be increased. However, in this case, if the EGR rate is gradually decreased from 55% as the intake air amount increases, a large amount of smoke will occur.

[0010]

In order to solve the above problems, in the first aspect of the invention, the recirculation exhaust gas is supplied to the combustion chamber by connecting the engine exhaust passage and the engine intake passage by the recirculation exhaust gas passage. When the gas amount is increased, the soot generation amount gradually increases and reaches the peak, and when the amount of recirculated exhaust gas supplied to the combustion chamber is further increased, the fuel and the surrounding fuel during combustion in the combustion chamber In an internal combustion engine where the gas temperature becomes lower than the soot generation temperature and soot is hardly generated, the recirculation exhaust gas amount increases when closed and the recirculation exhaust gas amount decreases when opened. The first combustion, which is located in the passage, has a larger amount of recirculated exhaust gas supplied to the combustion chamber than the amount of solute generated peak recirculated exhaust gas, and soot is hardly generated. Peak recirculation The second combustion, in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of exhaust gas, and the second combustion is selectively switched from the first combustion to the second combustion or from the second combustion to the second combustion. The exhaust gas recirculation rate is changed stepwise by opening or closing the exhaust control valve when the combustion is switched to No. 1.

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
_{The X} absorbent is arranged in the engine exhaust passage, and when the NO _X is to be released from the NO _X absorbent, the predetermined air-fuel ratio of the cylinder is made to be the theoretical air-fuel ratio or rich when the first combustion is performed. I am trying to do it.

In the third invention, in the second invention,
All exhaust exhaust gas discharged from the remaining cylinders with gas is recirculated to the engine intake passage through the recirculated exhaust gas NO _X discharged from the part of the cylinders when the exhaust control valve is completely closed When the first combustion is performed when the NO _X is to be released into the absorbent and the NO _X is to be released from the NO _X absorbent, the exhaust control valve is fully closed to set the air-fuel ratio of the remaining cylinders to the theoretical air-fuel ratio. Or try to make it rich.

[0013]

FIG. 1 shows the case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, # 1, # 2, # 3 and # 4 are 1
No. 2 cylinder, No. 3 cylinder, No. 3 cylinder, No. 4 cylinder are shown respectively, 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 the exhaust pipe 12.
Is connected to a catalytic converter 14 containing a catalyst 13 having an oxidizing function. An air-fuel ratio sensor 15 is arranged at the 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 electrically controlled EGR control valve 17 is arranged in the control unit 6. A cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is arranged around the EGR passage 16. In the embodiment shown in FIG. 1, the engine cooling water is the cooling device 1.
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 corresponding fuel supply pipe 19 to form a fuel reservoir, a so-called common rail 2.
It is connected to 0. Fuel is supplied into the common rail 20 from an electrically controlled variable discharge fuel pump 21.
The fuel supplied into the common rail 20 is supplied to each fuel supply pipe 1
It is supplied to the fuel injection valve 3 via 9. Common rail 2
A fuel pressure sensor 22 for detecting the fuel pressure in the common rail 20 is attached to 0, and the fuel pump 21 is controlled 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 installed in the exhaust manifold 11.
An exhaust control valve 24 driven by is arranged. In the embodiment shown in FIG. 1, the manifold internal chamber region A and the manifold internal chamber region A where the exhaust branch pipes 10 of the first cylinder # 1 and the second cylinder # 2 are open are located at a position that divides the manifold internal chamber of the exhaust manifold 11 into two. The exhaust control valve 2 is provided at the boundary with the manifold internal chamber region B where the exhaust branch pipes 10 of the cylinders # 3 and # 4 are open.
4 are arranged. As shown in FIG. 1, the manifold internal chamber region A communicates with the EGR passage 16, and the manifold internal chamber region 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 through the EGR passage 16 and enters into the third cylinder # 1. The exhaust gas discharged from the # 3 and # 4 cylinder # 4 flows into the catalyst 13 via the exhaust pipe 12.

The electronic control unit 30 is composed of a digital computer, and has a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an input port 35 which are connected to each other by a bidirectional bus 31. 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. Further, 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
A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to 0, 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 each time the crankshaft rotates, for example, 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 output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening of the throttle valve 9 and the EGR rate during engine low load operation, and An example of an experiment showing changes in the amount of smoke, HC, CO, and NO _x emissions is shown. As can be seen from FIG. 2, in this experimental example, as the air-fuel ratio A / F becomes smaller, EG
When the R ratio becomes large and is equal to or less than the stoichiometric air-fuel ratio (≈14.6), the EGR ratio becomes 65% or more.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the EGR rate becomes around 40%, and when the air-fuel ratio A / F reaches about 30, smoke is generated. The amount of generation begins to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is made smaller, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke sharply decreases this time, the EGR rate is increased to 65% or more, and the smoke becomes almost zero when the air-fuel ratio A / F is around 15.0. . That is, soot is hardly generated. At this time, the output torque of the engine slightly decreases, and N
Generation amount of O _X is considerably lower. On the other hand, at this time, HC,
The amount of CO generated starts to increase.

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

From the experimental results shown in FIGS. 2 and 3, the following can be said. That is, first of all, the air-fuel ratio A / F is 1
When the amount of smoke generated is 5.0 or less and the amount of smoke is almost zero,
As shown in (3), the amount of NO _x generated is considerably reduced. N
A decrease in the amount of O _X generated means that the combustion temperature in the combustion chamber has decreased, and therefore, it can be said that the combustion temperature in the combustion chamber is low when soot is scarcely generated. The same can be said from FIG. That is,
The combustion pressure is low in the state shown in FIG. 3 (B) where almost no soot is generated, and therefore the combustion temperature in the combustion chamber is low at this time.

Second, when the amount of smoke produced, that is, the amount of soot produced, becomes almost zero, as shown in FIG.
Emissions will increase. This means that hydrocarbons are discharged without growing to soot. That is, linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed to form soot precursors when the temperature is raised in a state of oxygen deficiency, and then mainly soot is formed. Soot consisting of a solid with carbon atoms gathered is produced. In this case, the actual soot 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. After that, it will grow to soot. Therefore, as described above, when the amount of soot generated becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. 2. At this time, HC is a soot precursor or a hydrocarbon in the 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 generated becomes almost zero, and at this time, the soot precursor or the state before the soot is generated. Hydrocarbons will be discharged from the combustion chamber. As a result of further detailed experimental research on this, when the temperature of the fuel in the combustion chamber and the gas around it is below a certain temperature, the soot growth process stops halfway, that is, soot is generated at all. 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.

By the way, the temperature of the fuel and its surroundings when the hydrocarbon production process 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. It cannot be said how many times it changes, but this certain temperature is closely related to the amount of NO _x produced, and therefore this certain temperature is defined to some extent from the amount of NO _x produced. be able to. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas surrounding it decrease, and the amount of NO _x generated decreases. At this time, soot is hardly generated when the amount of NO _x generated is about 10 p.pm or less. Therefore, the above certain temperature is NO
It is almost the same as the temperature when the amount of _X generation is around 10 p.pm or less.

Once soot is produced, this soot cannot be purified by a post-treatment using an oxidation catalyst or the like. On the other hand, the soot precursor or the hydrocarbon in the state before it can be easily purified by a post-treatment using an oxidation catalyst or the like. Considering the post-treatment with an oxidation catalyst, etc., there is an extremely large difference in whether hydrocarbons are discharged from the combustion chamber in the form of soot precursor or in the state before it, or discharged from the combustion chamber in the form of soot. . The new combustion system used in the present invention allows hydrocarbons to be discharged from the combustion chamber in the form of soot precursor or the state before it without producing soot in the combustion chamber, and this hydrocarbon is oxidized by an oxidation catalyst or the like. Its core is to oxidize.

In order to stop the growth of hydrocarbons before the soot is produced, the temperature of the fuel during combustion in the combustion chamber and the gas around it are suppressed to a temperature lower than the temperature at which the soot is produced. There is a need. In this case, it has been found that, in order to suppress the temperature of the fuel and the gas around it, the endothermic action of the gas around the fuel when the fuel burns has an extremely large effect.

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

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

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

FIG. 5 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the cooling degree of the EGR gas is changed. That is, in FIG. 5, the curve A strongly cools the EGR gas to bring the EGR gas temperature to about 9
The curve B shows the case where the EGR gas is cooled by a small cooling device, and the curve C shows the case where the temperature is maintained at 0 ° C.
Indicates the case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 5, when the EGR gas is strongly cooled, the soot generation amount peaks when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Almost no soot is generated if the percentage is exceeded. 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 when the EGR rate is slightly higher than 50%. In this case, the EGR rate is approximately 65% or more. If so, soot is hardly generated.

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

FIG. 6 shows a mixture of EGR gas and air required to bring the temperature of the fuel and its surrounding gas during combustion to a temperature lower than the temperature at which soot is produced when EGR gas is used as the inert gas. The amount of gas, the ratio of air in this mixed gas amount, and the ratio of EGR gas in this mixed gas are shown. Note that in FIG. 6, the vertical axis represents the total intake gas amount sucked into the combustion chamber, and the chain line Y represents the total intake gas amount that can be sucked 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, shows the amount of air required 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 theoretical air-fuel ratio. On the other hand, in FIG. 6, the ratio of EGR gas, that is, the amount of EGR gas in the mixed gas is set so that when the injected fuel is burned, the temperature of the fuel and its surrounding gas is lower than the temperature at which soot is formed. The minimum required EGR gas amount is shown. This EGR gas amount is approximately 55% or more when expressed by the EGR rate, and is 70% in the embodiment shown in FIG.
It is more than a percentage. That is, the total intake gas amount sucked into the combustion chamber is indicated by the solid line X in FIG. 6, and the ratio of the air amount to the EGR gas amount in the total intake gas amount X is set to the ratio shown in FIG. The temperature of the gas around it becomes lower than the temperature at which soot is generated, so that soot is not generated at all. Further, the amount of NO _x generated at this time is around 10 p.pm or less, and therefore NO _x
Is very 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 gas around it at a temperature lower than the temperature at which soot is generated, heat generated by the EGR gas is used. The amount of absorption must be increased. Therefore, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount is increased.
That is, the EGR gas amount needs to increase as the required load increases.

On the other hand, in the load region Z2 of FIG. 6, the total intake gas amount X required to prevent the generation of soot exceeds the total intake gas amount Y that can be inhaled. Therefore, in this case, in order to supply the total intake gas amount X required to prevent the generation of soot into the combustion chamber, both EGR gas and intake air, or EGR
It is necessary to supercharge or pressurize the gas. 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 in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the air amount is slightly decreased to increase the EGR gas amount and the fuel is burned under the rich air-fuel ratio.

As described above, FIG. 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 smaller than the air amount shown in FIG. At least, that is, even if the air-fuel ratio is made rich, the generation amount of NO _X can be reduced to around 10 p.pm or less while preventing the generation of soot, and the air flow can be reduced in the low load region Z1 shown in FIG. Even if the amount is made 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 NO _x generated is 10 while preventing the generation of soot.
It can be around or below ppm.

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

As described above, in the engine low load operation region Z1, regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich,
Soot is not generated regardless of the stoichiometric air-fuel ratio or the average air-fuel ratio is lean, and the amount of NO _x generated is extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time. By the way, in order to simultaneously reduce soot and NO _x under the new combustion system used in the present invention, EGR
The rate should be at least about 55 percent or higher. However, the EGR rate can be increased to approximately 55% or more when the intake air amount is small, that is, when the engine load is relatively low. When the intake air amount exceeds a certain limit, that is, the required load is less than the certain limit. If it becomes higher, the intake air amount cannot be increased unless the EGR rate is lowered. However, in this case, in the experimental example shown in FIG. 2, as the intake air amount increases, that is, as the required load becomes higher, the EGR rate is gradually decreased from approximately 65%, that is, as the required load becomes higher. If the fuel ratio is increased, a large amount of smoke will be generated. Therefore, when the required load exceeds a certain limit, the EGR rate becomes approximately 65 as the required load increases.
It is not possible to gradually decrease from the percentage and gradually increase the air-fuel ratio.

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

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 EGR gas flowing from the EGR passage 16 into the surge tank 5 is very rapid. However, since the EGR rate in some cylinders falls within the EGR rate range in which a large amount of smoke is generated, a problem occurs in which a large amount of smoke is generated.

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

As described above, when the EGR rate is about 55% or more, the temperature of the fuel and the gas around it is lower than the temperature at which soot is generated, and at this time, the first combustion, that is, the low temperature combustion occurs. Has been done. On the other hand, when the EGR rate is reduced to approximately 50% or less, the temperature of the fuel and the gas around it becomes higher than the temperature at which soot is generated, at which time the first temperature is no longer the first.
However, 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 which is more commonly performed than the conventional one is performed. It should be noted that here, the first combustion, that is, low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generated peaks, and soot is almost generated. The second combustion, that is, the combustion that is usually performed conventionally, is the combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in which the soot generation peaks. Say.

FIG. 7 shows the first combustion region I in which the EGR rate is approximately 55% or more, that is, the low temperature combustion, and the second combustion in which the EGR rate is approximately 50% or less. That is, it shows the second combustion region II in which the combustion is performed by the conventional combustion method. In FIG. 7, the vertical axis L represents the depression amount of the accelerator pedal 40, that is, the required load, and the horizontal axis N represents the engine speed. Further, in FIG. 7, 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. A second boundary with region II is shown. The change determination of the operating region from the first operating region I to the second operating region II is performed based on the first boundary X (N), and the change from the second operating region II to the first operating region I is performed. The change judgment of the operating region is made based on the second boundary Y (N).

That is, the operating condition of the engine is the first operating region I.
Therefore, when the first combustion, that is, the low temperature combustion is performed, the required load L is the first boundary X which is a function of the engine speed N.
When (N) is exceeded, it is determined that the operating region has moved to the second operating region II, and the second combustion is switched to. Next, when the required load L becomes lower than the second boundary Y (N) which is a function of the engine speed N, it is determined that the operating region has moved to the first operating region I, and the second combustion is switched to the first combustion. Can be switched.

In this way, the two boundaries of the first boundary X (N) and the second boundary Y (N) on the low load side of the first boundary X (N) are provided next. For one reason. The first reason is that the combustion temperature is relatively high on the high load side of the second operating region II, and at this time, even if the required load L becomes lower than the first boundary X (N), low temperature combustion cannot be immediately performed. Because. That is, the low temperature combustion does not start immediately unless the required load L becomes considerably low, that is, when it becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for changes in the operating region between the first operating region I and the second operating region II.

By the way, when the engine is operating in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and instead, unburned hydrocarbons are in a soot precursor or in a state before that. Exhausted from the combustion chamber in shape. At this time, the unburned hydrocarbons discharged from the combustion chamber are favorably oxidized 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.

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

Not only oxidation catalysts, but also three-way catalysts and NO
_{The X} absorbent also has an oxidizing function, so that 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 of the throttle valve 9, the opening of the EGR control valve 17, the opening 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 operation region I where the required load L is low, the opening degree of the throttle valve 9 is gradually increased as the required load L becomes higher, and the opening degree of the EGR control valve 17 is changed to the required load L. The exhaust control valve 24 is gradually increased from near full close to full open.
Is kept fully closed. Therefore, at this time, the total 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. Further, in the example shown in FIG. 9, the EGR rate is approximately 70% in the first operating region I, 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 EGR rate becomes approximately 70%, and the opening degree of the throttle valve 9 and the opening degree of the EGR control valve 17 are controlled so that the air-fuel ratio becomes a lean air-fuel ratio of about 15 to 18. It 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. Further, in the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes late as the required load L becomes high, and the injection completion timing θE also becomes late as the injection start timing θS becomes late.

When the operating condition of the engine is in the first operating region I, soot and NO _x are scarcely generated, and the soot precursor contained in the exhaust gas or the hydrocarbon in the preceding state is oxidized by the catalyst 13. Be punished. On the other hand, when the operating range of the engine changes from the first operating range I to the second operating range II, the exhaust control valve 24 is fully opened at once from the fully closed state,
The opening degree of the throttle valve 9 is increased stepwise to the fully open state. When the throttle valve 9 is fully opened at once, most of the exhaust gas discharged from the first cylinder # 1 and the second cylinder # 2 flows out into the exhaust pipe 12, and the EGR passage 16
Then, the amount of EGR gas supplied into the surge tank 5 immediately decreases. As a result, the EGR rate is instantly reduced.

At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from about 70% to 40% or less, and the air-fuel ratio changes stepwise to 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 does not occur when the engine operating region changes from the first operating region I to the second operating region II.

In the second operating region II, the second combustion, that is, the combustion which is conventionally performed is performed. Although soot and NO _X are slightly generated in this combustion method, the thermal efficiency is higher than that in low temperature combustion, and therefore, when the operating region of the engine changes from the first operating region I to the second operating region II, as shown in FIG. In addition, 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 degree of the EGR control valve 17 is gradually reduced as the required load L increases. In this operating region II, the EGR rate becomes lower as the required load L becomes higher, and the air-fuel ratio becomes equal to the required load L.
The higher the, the larger. However, the air-fuel ratio is a lean air-fuel ratio even if the required load L becomes high. Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

On the other hand, the first operating condition of the engine is low-temperature combustion from the second operating region II in which the second combustion is performed.
When shifting to the operating region I, the opening degree of the throttle valve 9 is decreased stepwise as shown in FIG. 9, and the exhaust control valve 24 is fully closed. 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 via the EGR passage 16, and as a result, the surge tank 5 is supplied with the exhaust gas. The amount of EGR gas supplied instantly increases. At this time, in the example shown in FIG. 9, the EGR rate is from 40% or less to almost 70%.
It is increased stepwise up to a percentage.

Next, the operation control will be described with reference to FIG. Referring to FIG. 10, first, step 10
At 0, it is determined whether or not the flag I indicating that the engine operating region 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 101
Then, 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 degree of the throttle valve 9 is controlled to the opening degree according to the required load L shown in the first operating region I of FIG.
Next, at step 104, the opening degree of the EGR control valve 17 is controlled to the opening degree according to the required load L shown in the first operating region I of FIG. Next, at step 105, the first step shown in FIG.
Of the injection amount according to the required load L and the like shown in the operating region I of
The injection start timing θS and the injection completion timing θE are calculated,
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
When it is determined that the state has become (N), the routine proceeds to step 106, where the flag I is reset. Next, at step 108, the exhaust control valve 24 is fully opened. Then step 1
In 09, the opening degree of the throttle valve 9 is in the second operation range of FIG.
The opening is controlled according to the required load L indicated by II. Next, at step 110, the opening degree of the EGR control valve 17 is changed to that shown in FIG.
The opening degree is controlled in accordance with 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 operating 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 100 that the flag I is reset, that is, when the engine operating region is the second operating region II, step 107
Then, 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 routine proceeds to step 108. On the other hand, L <Y
When it becomes (N), the routine proceeds to step 112, where the flag I is set, and then the routine proceeds to step 102.

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

In this embodiment, during idling operation, the throttle valve 9 is closed to near full closure, and at this time, the EGR control valve 17 is also closed to near full closure. When the throttle valve 9 is closed to near full closure, the pressure in the combustion chamber at the beginning of compression becomes low, and the compression pressure becomes small. When the compression pressure becomes small, the compression work by the piston becomes small, so that the vibration of the engine body 1 becomes small. That is, in this embodiment, the vibration of the engine body 1 is suppressed by closing the throttle valve 9 close to full closing during idling operation.

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

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 degree of the throttle valve 9 is controlled to the opening degree according to the required load L shown in the first operating region I of FIG. Next, at step 204, EG
The opening degree of the R control valve 17 is controlled to the opening degree according 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 operating region I of FIG. 9 are obtained, and 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
When it is determined that the condition is (N), 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
At 09, the opening degree of the throttle valve 9 is controlled to the opening degree according to the required load L shown in the second operating region II of FIG.
Next, at step 210, the opening degree of the EGR control valve 17 is controlled to the opening degree according 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 fuel injection is performed based on these.

On the other hand, when it is determined in step 200 that the flag I is reset, that is, when the engine operating region is the second operating region II, step 207
Then, 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 routine proceeds to step 208. On the other hand, L <Y
When it becomes (N), 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 II. Region I
The exhaust control valve 24 is temporarily closed when moving to. FIG. 14 (A) shows a case where the required load L gradually decreases and the second combustion is switched to the first combustion at time t ₀ . The second as shown in FIG.
When the throttle valve 9 is closed stepwise when the combustion of fuel is switched to the first fuel, the surge tank 5
The internal pressure 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. Therefore, 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 instantly increased. There is.

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

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

When L ≦ X (N), the routine proceeds to step 302, where the opening degree of the exhaust control valve 24 is controlled as shown in FIG. 14 (A). Next, at step 303, the opening degree of the throttle valve 9 is controlled to the opening degree according to the required load L shown in the first operating region I of FIG. Then step 304
Then, the opening degree of the EGR control valve 17 is controlled to the opening degree according to the required load L shown in the first operating region I of FIG. Next, at step 305, 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 operating region I of FIG. 9 are obtained, and 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
If 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 degree of the exhaust control valve 24 is controlled as shown in FIG. 14 (B). Next, at step 309, the opening degree of the throttle valve 9 is controlled to the opening degree according to the required load L shown in the second operation region II of FIG. Then step 31
At 0, the opening degree of the EGR control valve 17 is controlled to the opening degree according 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 the injection completion timing θE is obtained, and the 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 the second operating region II, step 307
Then, 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
When (N) is reached, the routine proceeds to step 312, where the flag I is set, and then the routine proceeds to step 302.

FIG. 16 shows a fourth embodiment. In this embodiment, the exhaust control valve is located at the boundary between the manifold internal chamber region C where the exhaust branch pipe 10 of the first cylinder # 1 is open and the manifold internal chamber region D where the second cylinder # 2 to the fourth cylinder # 4 are open. 24 is arranged, and the opening degree of the exhaust control valve 24 is controlled by any of the methods shown in the first to third embodiments. FIG. 17
In the fifth embodiment shown in FIG. 5, exhaust is performed 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 are open and the manifold internal chamber region F where the fourth cylinder # 4 is open. The control valve 24 is arranged, and in the sixth embodiment shown in FIG. 18, the exhaust control valve 24 is arranged in the exhaust pipe 12. In these fifth and sixth embodiments, as shown in FIG. 19, the exhaust control valve 24 is maintained in the half-open state in the first operating region I and is held in the fully open state in the second operating region II.

Next, in the example shown in FIG. 1, the catalyst 1
A case where a NO _x absorbent is used as No. 3 will be described.
The ratio of air and fuel (hydrocarbons) supplied to the engine intake passage and the exhaust passage upstream of the NO _x absorbent 13 is calculated as NO _x.
The air-fuel ratio of the exhaust gas flowing into the absorbent 13 is 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
Absorb and release.

[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 absorbing / releasing action is performed by the mechanism as shown in FIG. Next, this mechanism will be described by taking the case where platinum Pt and barium Ba are supported on the carrier as an example, 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 1 combustion is performed_XAlmost occurs
No, but when the second combustion is performed, N
O_XOccurs. The second combustion is when the air-fuel ratio is lean
The oxygen concentration in the exhaust gas is high because
As shown in FIG. 20 (A), these oxygen O₂Is O₂ ^-
Or O^2-It adheres to the surface of platinum Pt in the form of. Meanwhile, the inflow
NO in the exhaust gas is O on the surface of platinum Pt.₂ ^-Or O^2-
Reacts with NO₂Becomes (2NO + O₂→ 2 NO₂).
NO generated next₂Part of is oxidized on platinum Pt
At the same time, it is absorbed in the absorbent and binds to barium oxide BaO.
Meanwhile, as shown in FIG.₃
^-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 the elemental concentration is high₂Is generated,
Absorbent NO_XNO unless the absorption capacity is saturated_XIs absorbed
Nitrate ion NO absorbed by the agent₃ ^-Is generated.

[0075] On the other hand, the air-fuel ratio of the inflowing exhaust gas becomes rich, the oxygen concentration is decreased and the amount of NO ₂ is lowered by reaction backward in the inflowing exhaust gas ^- proceed to (NO ₃ → NO _2),斯In turn, the nitrate ions NO ₃ ⁻ in the absorbent are released from the absorbent in the form of NO ₂ . At this time, the NO _X absorbent 13
As shown in FIG. 20 (B), the NO _x released from is reacted with a large amount of unburned HC and CO contained in the inflowing exhaust gas to be reduced. When NO ₂ is no longer present on the surface of platinum Pt in this way, NO ₂ is released one after another from the absorbent. Therefore, when the air-fuel ratio is made rich, NO _X is released from the NO _X absorbent 13 within a short time, and the released NO _X is reduced, so that NO _X is discharged into the atmosphere. You will be able to prevent it.

Since the NO _X absorbent 13 also has the function of a reduction catalyst, the NO _X released from the NO _X absorbent 13 is changed to the stoichiometric air-fuel ratio when NO _X should 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. For that, NO _X absorbent 13
It is necessary to estimate the amount of NO _x absorbed in the. In the embodiment according to the present invention, the NO _X absorption amount D per unit time when the second combustion is being performed is preliminarily tested in the form of a map as shown in FIG. 21 as a function of the required load L and the engine speed N. the advance determined, determine the NO _X absorption amount D per unit time from the map, then determine the amount of NO _X ShigumaNO _X that is absorbed in the NO _X absorbent 13 by cumulatively adding this NO _X absorption D, 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, in the conventional compression ignition type internal combustion engine, a large amount of smoke is generated when the air-fuel ratio in the combustion chamber is set to the stoichiometric air-fuel ratio or rich, and therefore, in the conventionally used compression ignition type internal combustion engine, the air in the combustion chamber is increased. The fuel ratio cannot be made stoichiometric or rich.

However, in the compression ignition type internal combustion engine used in the present invention, when the first combustion, that is, the low temperature combustion is performed, even if the air-fuel ratio in the combustion chamber is stoichiometric air-fuel ratio or rich, soot and NO _x are generated. It rarely happens. Therefore, in the embodiment according to the present invention, when the NO _X amount ΣNO _X exceeds the maximum allowable value MAX, the air-fuel ratio is set to the stoichiometric air-fuel ratio or rich when the first combustion is performed, whereby the NO _X absorbent 13 is formed. NO _x is released from the.

Next, a specific example will be described with reference to FIG. FIG. 22 shows the NO _X amount ΣNO at time t ₀ .
_{The case where X} exceeds the maximum allowable 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, since the second combustion is being performed at this time, the air-fuel ratio of each cylinder is set to the lean air-fuel ratio.

Next, when the exhaust control valve 24 is fully closed from the fully open state to shift from the second combustion to the first combustion, as shown in FIG.
As shown in, 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, while the air-fuel ratio of the third cylinder # 3 and the fourth cylinder # 4 is The rich air-fuel ratio is temporarily set. When the air-fuel ratios of the third cylinder # 3 and the fourth cylinder # 4 are made rich, the exhaust gas flowing into the NO _X absorbent 13 becomes rich, as can be seen from FIG.
Thus, NO _X is released from the NO _X absorbent 13 and the released NO _X is reduced. In addition,
At this time, in order to improve the fuel consumption rate, the air-fuel ratio of the first cylinder # 1 and the second cylinder # 2 is set to the lean air-fuel ratio.

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 lean air-fuel ratios of the third cylinder # 3 and the fourth cylinder # 4 are the lean air-fuel ratios of 15 to 18. It is said that Next, the time interruption routine will be described with reference to FIG. Referring to FIG. 23, first, at step 400, it is judged if the NO _x release flag is set. When the NO _X release flag is not set, step 401
Then, it is determined whether or not the flag I indicating that the operating region of the engine is the first operating region I is set. Step 40 when flag I is set
The routine proceeds to step 2, where the NO _X absorption amount D per unit time is set to a predetermined small value D _0, and 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
21. From the map shown in FIG. 21, proceed to NO _X per unit time.
The absorption amount D is calculated, and then the process proceeds to step 404.

At step 404, ΣNO_XAdd D to
NO by doing_XNO absorbed in the absorbent 13
_XQuantity ΣNO_XIs calculated. Then in step 405
NO _XQuantity ΣNO_XHas exceeded the maximum allowable value MAX.
Determined, ΣNO_X> When MAX, step
Go to 406 and NO_XThe release flag is set. NO
_XWhen the release flag is set
Proceed to step 407 and proceed to No. 3 cylinder # 3 and No. 4 cylinder # 4
It is determined whether the air-fuel ratio has been made rich for a certain period of time.
The air-fuel ratios of # 3 cylinder # 3 and # 4 cylinder # 4 will be
When the switch is turned on, the process proceeds to step 408 and NO._XRelease
The exit flag is reset, then step 409
ΣNO_XIs zero.

Next, the operation control will be described with reference to FIG. Referring to FIG. 24, first, step 45
At 0, it is determined whether or not the flag I indicating that the engine operating region 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
Then, 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 degree of the throttle valve 9 is controlled to the opening degree according to the required load L shown in the first operating region I of FIG.
Next, at step 454, the opening degree of the EGR control valve 17 is controlled to the opening degree according to the required load L shown in the first operating region I of FIG. Next, at step 455, it is judged if the NO _x releasing flag is set or not.

When the NO _X releasing flag is not 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 are calculated in accordance with the required load L and the like shown in, and fuel injection is performed based on these. At this time, the air-fuel ratio is 15 to 1
A lean air-fuel ratio of about 8 is used. 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 is 15
The lean air-fuel ratio is about 18 to about 18 and the air-fuel ratios of the third cylinder # 3 and the fourth cylinder # 4 are rich air-fuel ratios. In this case NO _X is released from _the NO _X absorbent 13.

On the other hand, in 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 degree of the throttle valve 9 is set to the second operation range in FIG.
The opening is controlled according to the required load L indicated by II. Next, at step 462, the opening degree of the EGR control valve 17 is changed to that shown in FIG.
The opening degree is controlled in accordance with the required load L shown in the second operation region II. Next, at step 463, 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 operating 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 the second operating region II, step 459
Then, 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 routine 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 the routine proceeds to step 452.

[0089]

When moving from the first combustion to the second combustion,
And 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 drawings]

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

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

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing a fuel molecule.

FIG. 5 is a diagram showing a relationship between a smoke generation amount 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 operating region I and a second operating 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 of a throttle valve and the like.

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

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

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

FIG. 15 is a flowchart for controlling the 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 diagram showing the opening of a throttle valve and the like.

FIG. 20 is a diagram for explaining the action of absorbing and releasing NO _X.

FIG. 21 is a diagram showing a map of the 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

Front page continuation (51) Int.Cl. ⁷ Identification code FI F01N 3/24 F01N 3/24 S 7/08 7/08 B 7/10 7/10 F02D 21/08 301 F02D 21/08 301D 41/02 380 41/02 380E 41/04 355 41/04 355 F02M 25/07 550 F02M 25/07 550G (72) Inventor Shinichi Takeshima 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Asanuma Takamitsu 1 Toyota-cho, Toyota-shi, Aichi Within Toyota Motor Corporation (56) Reference JP-A-7-4287 (JP, A) JP-A-8-177654 (JP, A) JP-A-8-86251 (JP , A) JP-A-9-287527 (JP, A) JP-A-9-287528 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02B 1/00-23/10 F02D 9/04-45/00 F01N 3/02-7/10 F02M 25/07

Claims (3)

(57) [Claims] 1. When the engine exhaust passage and the engine intake passage are connected by a recirculation exhaust gas passage and the amount of recirculation exhaust gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and peaks. And the amount of recirculated exhaust gas supplied to the combustion chamber is further increased, the temperature of the fuel and the gas around it during combustion in the combustion chamber becomes lower than the soot generation temperature, and soot is hardly generated. In an internal combustion engine, when the valve is closed, the amount of recirculated exhaust gas increases, and when it is opened, the amount of recirculated exhaust gas decreases, an exhaust control valve is placed in the engine exhaust passage, and the amount of soot generated reaches a peak. Amount of recirculated exhaust gas supplied to the combustion chamber is larger than the amount of soot, and soot is rarely generated, and recirculated exhaust gas supplied to the combustion chamber is greater than the amount of recirculated gas at which soot generation peaks The second with a small amount of gas The exhaust control valve is opened or closed when the first combustion is switched to the second combustion or the second combustion is switched to the first combustion. A compression ignition type internal combustion engine in which the exhaust gas recirculation rate is changed stepwise by. 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
A NO _x absorbent that emits N is placed in the engine exhaust passage, and N
The compression ignition according to claim 1, wherein, when NO _X is to be released from the O _X absorbent, the predetermined air-fuel ratio of the cylinder is set to the stoichiometric air-fuel ratio or rich when the first combustion is performed. Internal combustion engine. 3. When the exhaust control valve is fully closed, all the exhaust gas discharged from a part of the cylinders is recirculated to the engine intake passage via the 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 while the combustion is being performed so that the air-fuel ratio of the remaining cylinders becomes the stoichiometric air-fuel ratio or rich.