JP2000080954A - Compression ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge NOX from NOX absorbent by suppressing the discharging of unburned HC or soot as much as possible. SOLUTION: First combustion generating an EGR gas quantity larger in a combustion chamber 5 than an EGR gas quantity having the peak quantity of generated soot, and generating little soot, and second combustion 2 generating an EGR gas quantity smaller in the combustion chamber 5 than an EGR gas quantity having the peak quantity of generated soot, are selectively performed. NOX absorbent 25 is disposed in an engine exhaust passage. To discharge NOX or SOX from the NOX absorbent 25, the air-fuel ratio of one cylinder is set to a rich side, and those of remaining cylinders are set to lean sides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compression ignition type internal combustion engine.

[0002]

Air-fuel ratio of the Related Art inflowing exhaust gas is absorbed NO _X when the lean, NO _X absorbent to the engine exhaust passage to the exhaust gas flowing emits NO _X absorbed to become rich or stoichiometric air-fuel ratio arranged, the NO _X generated when lean air-fuel mixture is burned is absorbed by _the NO _X absorbent, the air-fuel ratio in the combustion chamber of all the cylinders before NO _X absorbing capacity of the NO _X absorbent is saturated unburned HC contained in the NO _X exhaust gas discharged, compression ignition internal combustion engine so as to reduce the CO are known causes temporarily releasing NO _X from _the NO _X absorbent in the rich (the International Publication WO93 / 07363). So that the air-fuel ratio in the combustion chamber of all the cylinders rich by increasing the fuel injection amount with this compression ignition type internal combustion engine closes the throttle valve is when releasing the NO _X from _the NO _X absorbent .

[0003] Also, SO _X is contained in the exhaust gas, and this SO _X is also absorbed by the NO _X absorbent. This SO
It is necessary to make the air-fuel ratio to the richer when to release _X from _the NO _X absorbent.

[0004]

However, if the air-fuel ratio in the combustion chambers of all cylinders is made rich by closing the throttle valve and increasing the fuel injection amount in the compression ignition type internal combustion engine, a large amount of unburned HC and a large amount There is a problem that smoke is generated.

[0005]

In the first to solve the above problems, there is provided a means for solving] invention, when the air-fuel ratio of the inflowing exhaust gas is lean absorbs NO _X, the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air in a compression ignition type internal combustion engine arranged _the NO _X absorbent in the engine exhaust passage that releases NO _X absorbed and becomes fuel ratio or rich, _the NO _X absorbent to when releasing the NO _X or SO _X from _the NO _X absorbent The air-fuel ratio of some of the cylinders is made rich so that the air-fuel ratio of the exhaust gas flowing into the cylinder becomes rich, and the air-fuel ratio of the remaining cylinders is made lean. That is, when NO _X or SO _X is to be released from the NO _X absorbent, only the air-fuel ratio of some cylinders is made rich, so that unburned HC and smoke generated compared to the case where the air-fuel ratio of all cylinders are made rich are made rich. Is reduced.

In the second invention, in the first invention,
As the compression ignition type internal combustion engine increases the amount of inert gas in the combustion chamber, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas in the combustion chamber further increases, combustion in the combustion chamber increases. Internal combustion engine where the temperature of the fuel and the surrounding gas is lower than the soot generation temperature and soot is hardly generated, and the inert gas in the combustion chamber is less than the amount of inert gas at which the amount of soot is peaked Switching to selectively switch between the first combustion in which the amount of gas is large and little soot is generated, and the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in which the amount of generated soot is peaked comprising means, air-fuel ratio is part so that the rich cylinder exhaust gas is when releasing the NO _X from _the NO _X absorbent flowing into _the NO _X absorbent when the second combustion is being performed Of the remaining cylinders So that to lean the fuel ratio.

In the third invention, in the second invention,
In some of the cylinders described above, the air-fuel ratio is made rich under the second combustion. In the fourth invention, in the second invention,
In some of the cylinders described above, the air-fuel ratio is made rich under the first combustion after switching from the second combustion to the first combustion.
In the second invention in the fifth aspect of the invention, or temporarily stoichiometric air-fuel ratio in the combustion chamber of all the cylinders in when releasing the NO _X from _the NO _X absorbent when the first combustion is being performed I try to be rich.

[0008] In the sixth invention, in the second invention,
An exhaust gas recirculation device is provided for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, and the inert gas is composed of the recirculated exhaust gas. In a seventh aspect based on the sixth aspect, the exhaust gas recirculation rate in the first combustion state is approximately 55% or more.

In the eighth invention, in the second invention,
The operating region of the engine is divided into a first operating region on the low load side and a second operating region on the high load side, and a first combustion is performed in the first operating region, and a second combustion is performed in the second operating region. Combustion is performed. In the ninth invention, in the first invention,
As the compression ignition type internal combustion engine increases the amount of inert gas in the combustion chamber, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas in the combustion chamber further increases, the combustion in the combustion chamber increases. The internal temperature of the internal combustion engine is such that the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is generated and soot is hardly generated, and the amount of generated soot is more inert in the combustion chamber than in the amount of inert gas Switching for selectively switching between the first combustion in which the amount of gas is large and little soot is generated, and the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in which the amount of generated soot is peaked comprising means, air-fuel ratio is part so that the rich cylinder of the exhaust gas flowing into the NO _X absorbent when the when releasing the sO _X from _the NO _X absorbent is performed first combustion Rich air-fuel ratio of the remaining cylinders So that to lean the fuel ratio.

According to a tenth aspect, in the ninth aspect, when SO _X is to be released from the NO _X absorbent, NO _X
Air-fuel ratio of the remaining cylinders with air-fuel ratio of the exhaust gas when the temperature of the absorbent is lower than a predetermined temperature is flowing into _the NO _X absorbent is a rich air-fuel ratio of as part of the cylinders becomes a lean was lean, rich air-fuel ratio of some cylinders so that the air-fuel ratio becomes rich of the exhaust gas flowing into the NO _X absorbent when the temperature is higher than a predetermined temperature of the NO _X absorbent And the air-fuel ratio of the remaining cylinders is made lean.

[0011]

1 and 2 show a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIGS. 1 and 2, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, and 8 is intake air. Port 9 indicates an exhaust valve, and 10 indicates an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a supercharger, for example, a compressor 1 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14.
6 is connected to the outlet. The inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17,
A throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
1 and the exhaust turbocharger 15 via the exhaust pipe 22
Is connected to the inlet of the exhaust turbine 23, the outlet of the exhaust turbine 23 is connected to _the NO _X absorbent 25 and the oxidation catalyst 26 through the exhaust pipe 24. An air-fuel ratio sensor 27 is arranged in the exhaust manifold 21. The exhaust pipe 28 downstream of the oxidation catalyst 26 and the air suction pipe 17 downstream of the throttle valve 20
Are connected to each other through an exhaust gas recirculation (hereinafter, referred to as EGR) passage 29, and an EGR control valve 31 driven by a step motor 30 is disposed in the EGR passage 29. An intercooler 32 for cooling EGR gas flowing through the EGR passage 29 is provided in the EGR passage 29.
Is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.

On the other hand, the fuel injection valve 6 is connected via a fuel supply pipe 33 to a fuel reservoir, a so-called common rail 34. Fuel is supplied into the common rail 34 from an electric control type variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34, and the fuel pump 35 is controlled so that the fuel pressure in the common rail 34 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 36. Is controlled.

The electronic control unit 40 is composed of a digital computer, and a ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the air-fuel ratio sensor 27 is input to the input port 45 via the corresponding AD converter 47, and the output signal of the fuel pressure sensor 36 is also input to the input port 45 via the corresponding AD converter 47. Further, the NO _X absorbent 25 is attached a temperature sensor 37 for detecting the temperature of the NO _X absorbent 25, the input to the AD converter 47 through the input port 45 an output signal corresponding to the temperature sensor 37 Is done. A load sensor 51 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50 is provided to the accelerator pedal 50.
Is connected, and the output voltage of the load sensor 51 is
The data is input to the input port 45 via the converter 47. The input port 45 has a crankshaft of, for example, 30.
A crank angle sensor 52 that generates an output pulse each time it rotates by an angle is connected. On the other hand, in the embodiment shown in FIG. 1, as shown in FIG. 2, the internal combustion engine has four cylinders including the first cylinder # 1, the second cylinder # 2, the third cylinder # 3, and the fourth cylinder # 4. The injection order is 1-3-4-2. As shown in FIG. 1, the output port 46 is connected to a fuel injection valve 6, a throttle valve control step motor 19, an EGR control valve control step motor 30, and a fuel pump 35 of each cylinder via a corresponding drive circuit 48. You.

By the way connected by an EGR passage and an engine exhaust passage and the engine intake passage in order to suppress the generation of the NO _X in the internal combustion engine, for example a compression ignition engine conventionally,
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 can absorb a large amount of heat. Therefore, as the EGR gas amount increases, the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases. the more increase the combustion temperature in the combustion chamber is decreased. generation amount of the combustion temperature decreases NO _X is reduced and thus the generation amount of the more NO _X to be increased EGR rate is lowered.

[0016] 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 is set within a range not exceeding the maximum allowable limit. The maximum allowable EGR rate varies considerably depending on the type of engine and fuel, but is approximately 30 to 50%.
Therefore, in the conventional compression ignition type internal combustion engine, the EGR rate is suppressed to 30 to 50% at the maximum.

As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate.
If the R rate is within the range not exceeding this maximum allowable limit, NO
_It was determined that the amount of _X and smoke generated was as small as possible. However, this way there is a limit to the EGR rate to decrease of the NO _X and the amount of generated NO _X and the amount of smoke produced be determined as possible becomes less of smoke, the fact still significant amounts NO _X
At present, smoke is generated.

However, in the course of research on combustion of a compression ignition type internal combustion engine, if the EGR rate is made larger than the maximum permissible limit, the smoke increases sharply as described above, but the amount of generated smoke has a peak. E beyond the peak
When the GR rate is further increased, the smoke starts to decrease sharply, and the EGR rate is reduced to 70 during eye drink driving.
It has been found that when the EGR gas is cooled to more than 50%, and when the EGR gas is strongly cooled, when the EGR rate is set to about 55% or more, smoke becomes almost zero, that is, almost no soot is generated. At this time, it has been found that the amount of generated NO _X is extremely small. The reason why the soot on the basis Thereafter this finding does not occur considered advanced, resulting unprecedented allows simultaneous reduction of soot and NO _X new combustion system is had come to be constructed. 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 hydrocarbons grow into soot.

That is, as a result of repeated experimental research, 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 during combustion in the combustion chamber and its surrounding gas temperature 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 lower than 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.

FIGS. 1 and 2 show a compression ignition type internal combustion engine employing the new combustion system. FIG. 3 shows the compression ignition type internal combustion engine shown in FIG. 1 and FIG.
The opening degree of the throttle valve 20 and the EG
An experimental example showing a change in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 3) is changed by changing the R ratio, and a change in smoke, HC, CO, and NO _X emissions are shown. ing. As can be seen from FIG. 3, in this experimental example, the smaller the air-fuel ratio A / F, the higher the EGR rate. When the air-fuel ratio A / F is smaller than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is 65% or more.

As shown in FIG. 3, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the smoke is reduced when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30. 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. 4A shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest. FIG. 4B shows the air-fuel ratio A / F. The graph shows a change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is almost zero when F is around 18. As can be seen by comparing FIG. 4A and FIG. 4B, in the case of FIG. 4B where the amount of smoke generation is almost zero, FIG.
It can be seen that the combustion pressure is lower than in the case shown in (A).

The following can be said from the experimental results shown in FIGS. That is, first, the air-fuel ratio A / F is 1
When the amount of generated smoke is almost zero at 5.0 or less, FIG.
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 5 is reduced, thus the combustion temperature in the combustion chamber 5 when the soot is hardly generated is lower I can say. The same can be said from FIG. That is, in the state shown in FIG. 4B where almost no soot is generated, the combustion pressure is low.
The combustion temperature inside 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. 5 are thermally decomposed when the temperature is increased in a state of lack of oxygen, so that a precursor of soot is formed. Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot generation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of soot generation becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. 3, but HC at this time is a soot precursor or a hydrocarbon in a state before the soot. .

Summarizing these considerations based on the experimental results shown in FIG. 3 and FIG. 4, when the combustion temperature in the combustion chamber 5 is low, the amount of soot generation becomes almost zero. Is discharged from the combustion chamber 5. As a result of further detailed experimental study on this, if the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.

By the way, the temperature of the fuel and its surrounding 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 it cannot be said how many times it changes, this certain temperature has a deep relationship with the amount of generated NO _X , and therefore, this certain temperature is defined to some extent from the amount of generated 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-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

In order to stop the growth of hydrocarbons before soot is generated, the temperature of fuel and the surrounding gas during combustion in the combustion chamber 5 is set to a temperature lower than the temperature at which soot is generated. It needs to be suppressed. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel 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 its 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. 6 shows the relationship between the EGR rate and the smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 6, the 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. 6, when the EGR gas is strongly cooled, the amount of soot generation peaks at a position where the EGR rate is slightly lower than 50 percent, and in this case, the EGR rate becomes approximately 55%. Above a percentage, soot is hardly generated. On the other hand, as shown by the curve B in FIG. 6, when the EGR gas is slightly cooled, the amount of soot generation peaks at a point where the EGR rate is slightly higher than 50%, and in this case, the EGR rate is increased to about 65% or more. 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. 6 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 almost no soot is generated 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. 7 shows the mixture of EGR gas and air necessary to make the temperature of the fuel during combustion and the surrounding gas temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. A gas amount, a ratio of air in the mixed gas amount, and a ratio of the EGR gas in the mixed gas are shown. In FIG. 7, the vertical axis indicates the total intake gas amount drawn into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be drawn into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load.

Referring to FIG. 7, 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. 7, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 7, 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 made 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.
0% or more. That is, the total intake gas amount sucked into the combustion chamber 5 is indicated by a solid line X in FIG. 7, and the ratio of the air amount to the EGR gas amount in the total intake gas amount X is shown in FIG.
When the ratio is as shown in the following, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is generated, and thus no soot is generated. In this case, the amount of generated NO _X is about 10 p.pm or less, and
Generation of O _X becomes 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. 7, 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.

By the way, when supercharging is not performed,
The upper limit of the total intake gas amount X sucked into the firing chamber 5 is Y.
Therefore, in FIG.₀Territory larger than
In the region, the EGR gas ratio increases as the required load increases.
The air-fuel ratio can be maintained at the stoichiometric air-fuel ratio unless reduced.
Can not. In other words, it is necessary when there is no supercharging.
Load demand is L₀Air-fuel ratio in the larger area than theoretical
When trying to maintain the fuel ratio, the required load increases.
As a result, the EGR rate decreases, and thus the required load becomes L ₀Than
In areas where the fuel and the surrounding gas temperature are
It will not be possible to maintain a temperature lower than the temperature produced.

[0041] However recirculating the required load is larger than L ₀ of the EGR gas into the air intake pipe 17 on the inlet side i.e. the exhaust turbocharger 15 via the EGR passage 29 supercharger as shown in FIG. 1 EGR rate of 5 in the region
It can be maintained at 5% or more, for example 70%, so that the temperature of the fuel and its surrounding gas can be kept below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which soot is generated, to the extent that the pressure can be increased by the compressor 16. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded.

[0042] Incidentally, the required load is EGR control valve 31 is fully opened is when the EGR rate more than 55 percent in the region larger than L _0, the throttle valve 20 is closed slightly. As described above, FIG. 7 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. 10p generation amount of the NO _X, while the occurrence blocking.
pm or less, and even if the air amount is larger than the air amount shown in FIG. 7, that is, even if the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. Meanwhile, the amount of generated NO _X can be reduced to around 10 p.pm 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, when low-temperature combustion is performed, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. However, the amount of generated NO _X is extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.

By the way, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber can be suppressed below the temperature at which the growth of hydrocarbons stops on the way. Limited. Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In addition, the second combustion, that is, the combustion that is usually performed conventionally, is performed during the high load operation of the engine.
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 performed normally in the past, is a 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. Say that.

FIG. 8 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second operation region 1I in which the second combustion, that is, combustion by the conventional combustion method, is performed. I have. In FIG. 8, the vertical axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 8, X (N) is the first
Shows the first boundary between the operating region I and the second operating region II, and Y (N) represents the first operating region I and the second operating region.
The second boundary with 1I is shown. The determination of the change of the operation range from the first operation range I to the second operation range II is made based on the first boundary X (N), and the change from the second operation range II to the first operation range II is performed.
The determination of the change of the operation region to the operation region I of the second boundary Y
(N).

That is, when the operating state of the engine is in the first operating region I
When the required load L exceeds a first boundary X (N), which is a function of the engine speed N, during low-temperature combustion, it is determined that the operation region has shifted to the second operation region II, Combustion is performed by a conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again. Thus, the first boundary X
The two boundaries of (N) and the second boundary Y (N) on the load side lower than the first boundary X (N) are provided for the following two 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 the first operating region I and the second operating region
This is because hysteresis is provided for a change in the operating range between II.

FIG. 9 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 9, the output current I of the air-fuel ratio sensor 27 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 27. Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.

FIG. 10 shows the opening of the throttle valve 20, the opening of the EGR control valve 31, 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. 10, in the first operating region I where the required load L is low, the opening of the throttle valve 20 is gradually increased from almost fully closed to about ／ as the required load L increases.
The opening degree of the EGR control valve 31 is gradually increased from near full close to full open as the required load L increases. Further, in the example shown in FIG.
The R rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

In other words, in the first operating region I, the EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening of the EGR control valve 31 based on the output signal of the air-fuel ratio sensor 27. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start time θS is delayed as the required load L is increased, and the injection completion timing θE is also delayed as the injection start timing θS is delayed.

During the idling operation, the throttle valve 20 is closed until the valve is almost fully closed. At this time, the EGR control valve 31 is also closed almost completely. Throttle valve 2
When the valve is closed to near zero, the pressure in the combustion chamber 5 at the start of compression increases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating range of the engine is the first operating range I
From the second operating region II to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 10, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, the EGR rate at which the EGR rate generates a large amount of smoke
The engine operating range is the first because it exceeds the rate range (Fig. 6)
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operating region II, the conventional combustion is performed. In the second operation region II, the throttle valve 20 is maintained in a fully open state except for a part, and the opening of the EGR control valve 31 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 11 shows the air-fuel ratio A / F in the first operating region I. In FIG. 11, A / F = 15.
The curves indicated by 5, A / F = 16, A / F = 17, and A / F = 18 have air-fuel ratios of 15.5, 16, 17, and 18, respectively.
And the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 11, the air-fuel ratio is lean in the first operating region I, and the air-fuel ratio A / F is leaner in the first operating region I as the required load L decreases.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low-temperature combustion can be performed even if the EGR rate is reduced as the required load L decreases.
When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 11, as the required load L decreases, the air-fuel ratio A / F increases. As the air-fuel ratio A / F increases, the fuel consumption rate increases. Accordingly, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the air-fuel ratio A / F increases as the required load L decreases.

The target opening degree ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 2 (A), the EGR is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N, and is necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. The target opening SE of the control valve 31 is as shown in FIG.
As shown in (1), a map is previously stored in the ROM 42 as a function of the required load L and the engine speed N.

FIG. 13 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 13, A / F = 24 and A / F = 3.
Curves indicated by 5, A / F = 45 and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. Throttle valve 2 required to set air-fuel ratio to this target air-fuel ratio
The target opening ST of 0 is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 14A, and the air-fuel ratio is set as the target air-fuel ratio. Opening SE of EGR control valve 31 necessary for
Are stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.

Meanwhile, NO _X absorbent 25 disposed on the exhaust turbocharger 15 the engine exhaust passage downstream of the, for example alumina as a carrier, for example, potassium K on the carrier, sodium Na, lithium Li, such as cesium Cs At least one selected from alkali metals, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are supported. Engine intake passage, NO of Toko called air-fuel ratio of exhaust gas flowing the ratio of the combustion chamber 5 and _the NO _X absorbent 25 upstream of the exhaust passage supplying air and fuel into the (hydrocarbon) to _the NO _X absorbent 25 _X absorbent 25 absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, perform absorption and release action of the NO _X that releases NO _X the air-fuel ratio is absorbed and becomes the stoichiometric air-fuel ratio or rich of the inflowing exhaust gas .

If this NO _X absorbent 25 is disposed in the engine exhaust passage, the NO _X absorbent 25 actually performs the NO _X absorbing / releasing action, but there is a portion where the detailed mechanism of this absorbing / releasing action is not clear. . 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. 1, combustion is performed with the air-fuel ratio in the normal combustion chamber 5 being lean. Thus the oxygen concentration in the exhaust gas when the air-fuel ratio is performed is combusted in a lean state is high, these oxygen O ₂ is O as is shown in FIG. 15 (A) to the time
₂ ^- or O ^2- shape is deposited on the surface of the platinum Pt. on the other hand,
NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2N).
O ₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt, and the barium oxide BaO
As shown in FIG. 15 (A), it diffuses into the absorbent in the form of nitrate ions NO ₃ ⁻ while being combined. In this way, NO _X is absorbed in the NO _X absorbent 25. As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and NO ₂ is generated unless the NO _X absorption capacity of the absorbent is saturated.
₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- are produced.

On the other hand, the air-fuel ratio of the inflowing exhaust gas is made rich.
The concentration of oxygen in the incoming exhaust gas decreases,
NO on the surface of gold Pt_TwoIs reduced. NO_Twoof
When the amount of production decreases, the reaction reverses (NO_Three ^-→ NO_Two)
And thus nitrate ion NO in the absorbent_Three ^-Is NO
_TwoReleased from the absorbent in the form of NO at this time_XAbsorbent
NO released from 25_XIs shown in FIG. 15 (B).
A large amount of unburned HC and CO contained in the inflow exhaust gas
It is reduced by reaction. In this way, platinum Pt
NO on surface_TwoWhen no longer exists, the next
NO_TwoIs released. Therefore, the air-fuel ratio of the incoming exhaust gas
Is enriched in a short time, NO _XAbsorbent 25?
NO_XIs released, and the released NO_XIs returned
NO in the atmosphere to be removed_XWill not be released
No.

In this case, the air-fuel ratio of the inflowing exhaust gas is
NO even at stoichiometric air-fuel ratio_XNO from absorbent 25_XIs released
Is done. However, the air-fuel ratio of the inflowing exhaust gas is
NO if ratio_XNO from absorbent 25_XGradually
NO because only _XAbsorbed by the absorbent 25
All NO_XIt takes a slightly longer time to release.

As described above, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, almost no soot is generated, and instead, the unburned hydrocarbon is converted into a precursor of soot or a soot. From the combustion chamber 5 in the form of At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is N
By the oxidation catalyst 26 located downstream of the O _X absorbent 25 is caused to favorably oxidized. Note that as described above, NO _X
Absorbent 25 includes a noble metal such as platinum Pt, thus _the NO _X absorbent 25 also has an oxidation function. Accordingly, the unburned hydrocarbons exhausted from the combustion chamber 5 is induced to satisfactorily oxidized by _the NO _X absorbent 25 when the low temperature combustion is being performed.

[0064] Incidentally is in the NO _X absorbing capacity of the NO _X absorbent 25 is limited, NO _X absorbing capacity of the NO _X absorbent 25 needs to release NO _X from _the NO _X absorbent 25 before saturation. For this purpose it is necessary to estimate the amount of NO _X is absorbed in the NO _X absorbent 25. Therefore, in this embodiment of the present invention of a map as shown in FIG. 16 (A) as a function of per unit time of the NO _X absorption A of the required load L and engine speed N when the first combustion is being performed is previously obtained in the form of a map as shown as a function of per unit time of the NO _X absorption B the required load L and engine speed N in FIG. 16 (B) when the second combustion is being performed is previously obtained in the form, per these unit time NO _X absorption a, so that to estimate the amount of NO _X ΣNOX being absorbed in the NO _X absorbent 25 by integrating the B.

In the embodiment according to the present invention, when the NO _x absorption amount ΣNO _x exceeds a predetermined allowable maximum value,
NO _X is released from the O _X absorbent 25. Next, this will be described with reference to FIG. Referring to FIG. 17, in the embodiment according to the present invention, there are two allowable maximum values, namely, an allowable maximum value MAX1 and an allowable maximum value MA.
X2 is set. The maximum allowable value MAX1 is NO _X
The maximum absorption amount MAX2 is about 30% of the maximum NO _X absorption amount that can be absorbed by the absorbent 25, and the allowable maximum value MAX2 is about 80% of the maximum absorption amount that the NO _X absorbent 25 can absorb. NO _X during the first combustion
NO air-fuel ratio from _X absorbent 25 so as to release the NO _X is rich, NO _X absorption amount ΣNOX permissible maximum when the second combustion is being performed when the absorption amount ΣNOX has exceeded the allowable maximum value MAX1 When the value exceeds MAX1, the second
Air-fuel ratio in order to release the NO _X from _the NO _X absorbent 25 when it is switched from the combustion to the first combustion is made rich,
NO _X absorption when the second combustion is being performed ΣNOX
_The NO _X absorbent 2 when but exceeding the maximum allowable value MAX2
Air-fuel ratio of only some of the cylinders so as to release the NO _X 5 is made rich.

That is, in FIG. 17, the period X is the required load L
Is lower than the first boundary X (N), indicating that the first combustion is being performed. At this time, the air-fuel ratio is a lean air-fuel ratio slightly leaner than the stoichiometric air-fuel ratio. When the first combustion is being performed, the amount of generated NO _X is extremely small. Therefore, at this time, the amount of absorbed NO _X ＮＯNOX rises very slowly as shown in FIG. NO _X absorption ΣN when first combustion is being performed
When OX exceeds the allowable maximum value MAX1, the air-fuel ratio A of all cylinders
/ F is temporarily made rich, whereby _the NO _X absorbent 25 from the NO _X is released. In this case NO _X absorption ΣNOX is made zero.

As described above, when the first combustion is being performed, no soot is generated regardless of whether the air-fuel ratio is lean, the stoichiometric air-fuel ratio, or rich, so that the first combustion is performed. and does not soot generated at this time is also the air-fuel ratio a / F in order to release the nO _X from _the nO _X absorbent 25 is made rich when being. Then the required load L at time t ₁ is switched from the first combustion exceeds the first boundary X (N) to the second combustion. As shown in FIG.
When the combustion is performed, the air-fuel ratio A / F becomes considerably lean. When the second combustion is being performed, the amount of generated NO _X is larger than when the first combustion is being performed. Therefore, when the second combustion is being performed, the NO _X amount ΣNOX is relatively rapid. To rise.

When the air-fuel ratio A / F of all the cylinders is made rich during the second combustion, a large amount of soot is generated. Therefore, when the second combustion is performed, the air-fuel ratio A of all the cylinders is increased. / F
Is not preferable. Therefore, even NO _X absorption amount ΣNOX has exceeded the allowable maximum value MAX1 when the second combustion is being performed as shown in FIG. 17 N
O _X from the absorbent 25 so as to release the NO _X fuel ratio A / F is not made rich. The required load L as at time t ₂ in FIG. 17 when the _the NO _X absorbent when it is switched from the second combustion is lower in the first combustion than the second boundary Y (N) 25 air-fuel ratio a / F of all the cylinders in order to release the NO _X is rich temporarily from.

[0069] Next is switched to the second combustion from the first combustion at time t ₃ in FIG. 17, the second combustion during interim pleasure continues. In this case NO _X absorption amount ΣNOX exceeds the allowable maximum value MAX1, then assuming that exceeds the allowable maximum value MAX2 at time t ₄ flows from _the NO _X absorbent 25 at this time in _the NO _X absorbent 25 to be released NO _X The air-fuel ratio A / F of some of the cylinders is made rich so that the air-fuel ratio of the exhaust gas becomes rich, and the air-fuel ratio of the remaining cylinders is made lean.

For example, when the second combustion is performed with the injection amount shown by the solid line in FIG.
_The NO _X absorbent in order to release the NO _X from _X absorbent 25 25
1 to make the air-fuel ratio of the exhaust gas flowing into
Injection amount to turn the cylinder # 1 cylinder # 1 so that the air-fuel ratio becomes, for example, of about 8 rich in 1 is made to increase as the greatly indicated by the dashed line Q _1. On the other hand, at this time, the injection amounts to the cylinders # 2, # 3, and # 4 are also indicated by broken lines Q ₂ , Q ₃ , It is made to increase as shown by Q _4.

That is, in the example shown in FIG. 18 (A), when the air-fuel ratio of the first cylinder # 1 is made to be very rich, the output torque of the first cylinder # 1 decreases. In order to compensate for this decrease in output torque, the remaining cylinders # 2, # 3, #
4 is increased. The thus remaining cylinders # 2, # 3, the rich average of the air-fuel ratio of each cylinder by allowed to increase the injection quantity of the # 4, i.e. the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 25 It becomes easy to do.

If the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 25 cannot be made rich or even if the air-fuel ratio of one cylinder is greatly rich even if the air-fuel ratio cannot be made sufficiently rich, FIG. As shown in FIG. 18 (B), the injection timing for two cylinders, for example, the first cylinder # 1 and the first cylinder # 1 is 3
As indicated by broken lines Q ₁ , Q ₄ , the injection amounts to the first cylinder # 1 and the fourth cylinder # 4 are so set that the air-fuel ratio in the fourth cylinder # 4, which is shifted by 60 crank angles, becomes significantly rich. It can be greatly increased. Also in this case, the remaining cylinders # 2 and #
The injection amounts Q ₂ and Q ₃ to the remaining cylinders # 2 and # ₃ are also increased so that the air-fuel ratio of No. 3 becomes as small as possible.

When the second combustion is being performed, the air-fuel ratio varies considerably depending on the operating state of the engine, and
FIG. 18 when NO _X is to be released from the O _X absorbent 25
(A) or each of the injection quantities Q ₁ , Q ₂ , Q shown in FIG.
_3, Q ₄ are different depending on the operating state of the engine. In the embodiment according to the present invention, each of these injection quantities Q ₁ , Q ₂ ,
Q ₃ and Q ₄ are stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.

[0074] large amount of NO _X from the absorbent 25 when the air-fuel ratio in the first cylinder # 1 so as to release the NO _X is made rich by a large margin the first cylinder # 1 as shown in FIG. 18 (A) unburned HC and soot are discharged, the air-fuel ratio by a large margin in the first cylinder # 1 and the fourth cylinder # 4 so as to release the NO _X from _the NO _X absorbent 25, as shown in FIG. 18 (B) When enriched, a large amount of unburned HC and soot are discharged from the first cylinder # 1 and the fourth cylinder # 4. However, in any case, the discharge amount of unburned HC and soot is smaller than that in the case where all the cylinders are made rich, so that the discharge amount of unburned HC and soot can be reduced. When all the cylinders are made rich, the output torque of the engine fluctuates.
8 (A) and FIG. 18 (B), there is an advantage that the output torque of the engine hardly fluctuates.

As described above, when only some of the cylinders are made rich, the amount of unburned HC and soot is reduced as compared with when all the cylinders are made rich. However, unburned HC and soot are still discharged. . Therefore, it is preferable to minimize the chances of enriching only some of the cylinders. Thus when the NO _X absorption amount ΣNOX when the second combustion is performed has exceeded the allowable maximum value MAX1 is temporarily rich air-fuel ratio A / F when it is switched to the first combustion from the second combustion to, NO _X absorption amount ΣNOX allowable maximum value MAX
Only in a special case exceeding 2, only some of the cylinders are made rich.

FIG. 19 shows a routine for processing a NO _X release flag which is set when NO _X is to be released from the NO _X absorbent 25. This routine is executed by interruption every predetermined time. Referring to FIG. 19, first, at step 100, 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 the operating region of the engine NO _X absorption amount A per unit time from the map shown in FIG. 16 (A) is calculated proceeds to step 101 when a first operating region I You. Then A is added to the NO _X absorption amount ΣNOX step 102. Next, at step 103 NO _X absorption amount ΣNOX whether exceeds the allowable maximum value MAX1 is determined. ΣN
Becomes the OX> MAX1 proceeds to step 104, NO _X emission flag I is set indicating that it should release the NO _X when the first combustion is being performed.

On the other hand, when it is determined in step 100 that the flag I has been reset, that is, when the operation region of the engine is the second operation region II, step 106
NO _X absorption amount per unit from the map time shown in FIG. 16 (B) B is calculated willing to. Next, at step 107 NO _X absorption amount ΣNOX is added to B. Next, at step 108 NO _X absorption amount ΣNOX permissible maximum value MA
It is determined whether or not X1 has been exceeded. ΣNOX> MAX1
Advances to become the step 109 to, NO _X releasing flag I indicating that it should release the NO _X is set when it is switched from the second combustion to the first combustion.

[0078] On the other hand, in step 110, whether NO _X absorption amount ΣNOX has exceeded the allowable maximum value MAX2 is determined. Becomes a .SIGMA.NOX> MAX2 proceeds to step 111, is set NO _X release flag II indicating that it should release the NO _X by the part of the cylinders rich.
Next, the operation control will be described with reference to FIG.

Referring to FIG. 20, first, at step 200, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, step 2
In step 01, it is determined whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 203, where low-temperature combustion is performed.

That is, in step 203, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 204, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Next, at step 205, it is determined whether or not the NO _X release flag I is set. Fuel injection is performed such that the air-fuel ratio shown in FIG. 11 proceeds to step 206 when the NO _X release flag I has not been set. At this time, low-temperature combustion is performed under a lean air-fuel ratio. On the other hand, NO _X releasing flag I in step 205
If it is determined that is set, step 20
Then, the rich process I shown in FIG. 21 is performed.

On the other hand, in step 201, L> X
When it is determined that (N) has been reached, the routine proceeds to step 202, where the flag I is reset.
And the second combustion is performed. That is, step 210
In FIG. 14A, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 14A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 211, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 14B, and the opening of the EGR control valve 31 is set to the target opening SE. Next, at step 212, it is determined whether or not the NO _X release flag II is set. N
O _X release flag II fuel injection so that the air-fuel ratio shown in FIG. 13 proceeds to step 213 when it is not set is performed. At this time, the second combustion is performed under the lean air-fuel ratio. On the other hand, in step 212, N
O _X when releasing flag II is judged to have been set rich processing II shown in FIG. 22 proceeds to step 214 is performed.

When the flag I is reset, the process proceeds from step 200 to step 208 in the next processing cycle, and it is determined whether or not the required load L has become lower than the second boundary Y (N). If L ≧ Y (N), step 210
And the second combustion is performed under the lean air-fuel ratio.
On the other hand, when it is determined in step 208 that L <Y (N), the routine proceeds to step 209, where the flag I is set. Then, the routine proceeds to step 203, where low-temperature combustion is performed.

Next, the rich processing I will be described with reference to FIG. Rich time t _r necessary to release all NO _X .SIGMA.NOX which is estimated to be absorbed in _the NO _X absorbent 25 is calculated first, at step 300 and referring to FIG. 21. Then the elapsed time t after the start rich processing I step 301 whether exceeds the rich time t _r is determined. Step 3 at the time of t ≦ t _r
In step 02, the fuel injection amount is increased, and the air-fuel ratio is made rich. On the other hand, when it is determined in step 301 that t> t _r , the process proceeds to step 303 and NO _X
The release flag I is reset, and then in step 304, ΣNOX is made zero.

Next, the rich process II will be described with reference to FIG. Rich time t _r necessary to release all NO _X .SIGMA.NOX which is estimated to be absorbed in _the NO _X absorbent 25 is calculated first, at step 400 and referring to FIG. 22. Then the elapsed time t after the rich processing II starts at step 401 whether exceeds the rich time t _r is determined. Step 4 at the time of t ≦ t _r
Going to step 02, FIG. 18 (A) or FIG.
8 (B), the injection amounts Q ₁ , Q ₂ ,
Q ₃ and Q ₄ are calculated. On the other hand, if it is determined in step 401 that t> t _r , then step 40
Proceed to 3 NO _X release flag I and II are reset, then ΣNOX is made zero at step 404.

FIG. 23 shows another embodiment. In this embodiment, for example, an intake control valve 61 that is driven and controlled by an actuator 60 is disposed at the inlet of the intake branch pipe 11 of the first cylinder # 1. Further, the intercooler 32 and the EGR control valve 3
An EGR branch passage 62 is branched from the EGR passage 29 between the two, and the EGR branch passage 62 is connected to the intake branch pipe 11 downstream of the intake control valve 61. An auxiliary EGR control valve 64 driven and controlled by an actuator 63 is disposed in the EGR branch pipe 62.

In this embodiment, normally, the intake control valve 61 is fully opened, and the auxiliary EGR control valve 64 is fully closed. At this time, the first combustion is performed in the first operation region I and the second combustion is performed in the second operation region II, similarly to the embodiment shown in FIGS. On the other hand, in this embodiment, when the second combustion is being performed, N
O _X absorption of the cylinders when the ΣNOX exceeds the allowable maximum value MAX2, 1 cylinder in the embodiment illustrated in FIG. 23 # 1
There is switched to the first combustion from the second combustion, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 25 is that flies air-fuel ratio of the cylinder # 1 so as to be rich is made rich by a large margin. That is, when referred to specifically, NO _X absorption amount ΣNOX permissible maximum value MAX2 auxiliary EGR control valve 64 is made to open a large amount of EGR gas that flies with caused to closing the intake control valve 61 when the cross The fuel is supplied to the cylinder # 1, and at this time, low-temperature combustion is performed in the first cylinder # 1 under a rich air-fuel ratio. At this time, the injection amounts Q ₂ , Q ₃ , Q ₄ to the remaining cylinders # 2, # 3, # ₄ are increased.

Also in this embodiment, the first cylinder # 1
To perform the first combustion, and to the remaining cylinders # 2, # 3, and # 4.
And perform the second combustion to reduce NO_XFrom absorbent 25
NO _X# 1, # 2, # 3, # when releasing
Injection amount Q to 4₁, Q_Two, Q _Three, Q_Four, Intake control valve 61
And the opening of the auxiliary EGR control valve 64 are equal to the required load L
And RO in the form of a map as a function of the engine speed N
It is stored in M42. In addition, it smells the first cylinder # 1
NO even at low temperature combustion under rich air-fuel ratio_Xabsorption
Cannot make air-fuel ratio of exhaust gas flowing into agent 25 rich
Or if you can't make it rich enough,
Rich in cylinders, for example, cylinder # 1 and cylinder # 4
Low-temperature combustion can be performed under the air-fuel ratio. However,
In this case, the EGR branch passage 62 is connected to the intake branch of the fourth cylinder # 4.
It also needs to be connected to the tube 11.

In this embodiment, the routines shown in FIGS. 19 to 21 are used as they are. However, for the rich process II, a routine shown in FIG. 24 is used instead of the routine shown in FIG. Therefore, only the routine shown in FIG. 24 will be described below. Rich time t _r necessary to release all NO _X .SIGMA.NOX estimated and reference is absorbed in the NO _X absorbent 25, first, at step 500 is calculated to FIG. Then the elapsed time t after the rich processing II starts at step 501 whether exceeds the rich time t _r is determined. When t ≦ tr, the _routine proceeds to step 502, where the cylinders # 1, # 2, # 3
# Injection amount to _{4 Q 1, Q 2, Q} 3, Q 4 is calculated.
Next, in step 503, the opening of the intake control valve 61 is controlled to close to an opening determined from the operating state of the engine. Next, in step 504, the opening of the auxiliary EGR control valve 64 is opened to the opening determined from the operating state of the engine. Controlled. On the other hand, the NO _X release flag I and II are reset routine proceeds to step 505 when a determination is made that the t> t _r in step 501, then in step 506 sigma
NOX is set to zero.

The exhaust gas contains SO _X , and the NO _X absorbent 25 contains not only NO _X but also SO _X
Is also absorbed. It is considered that the absorption mechanism of SO _X into the NO _X absorbent 25 is the same as the absorption mechanism of NO _X. That is, the case where platinum Pt and barium Ba are carried on the carrier in the same manner as when the NO _X absorption mechanism is described will be described. As described above, when the air-fuel ratio of the inflowing exhaust gas is lean, oxygen O ₂ Is O ₂
^- or O is deposited on the surface of the platinum Pt in ^2-form, SO ₂ in the inflowing exhaust gas on the surface of the platinum Pt O ₂ ^- or O ^2-
And SO ₃ . Next, a part of the generated SO ₃ is further oxidized on the platinum Pt, is absorbed in the absorbent and combines with the barium oxide BaO to form the sulfate ion SO 3.
₄ Diffusion into the absorbent in the form of ^2- , stable sulfate BaSO
Generate ₄ .

However, the sulfate BaSO ₄ is stable and difficult to decompose. Even if the air-fuel ratio of the inflowing exhaust gas is simply made rich, the sulfate BaSO ₄ remains without being decomposed. Thus will be sulfates BaSO ₄ increases over time in _the NO _X absorbent 25 has elapsed, that the amount of NO _{X the} NO _X absorbent 25 can absorb as thus to time has elapsed is reduced Become.

[0091] However the temperature of the sulfate BaSO ₄ is _the NO _X absorbent 25 is fixed temperature or higher, for example decomposes becomes 600 ° C. or higher, when the air-fuel ratio of the exhaust gas flowing into this time _the NO _X absorbent 25 rich is released from _the NO _X absorbent 25 in the form of SO _X. Therefore, in the embodiment described below, when SO _X is to be released from the NO _X absorbent 25,
Air-fuel ratio of the exhaust gas flowing into the O _X absorbent 25 is such that the air-fuel ratio of the remaining cylinders to lean with the air-fuel ratio of some cylinders so as to be rich rich. That is, when the air-fuel ratio of some of the cylinders is made rich and the air-fuel ratio of the remaining cylinders is made lean, a large amount of unburned HC and CO is discharged from the cylinder whose air-fuel ratio is made rich, and the air-fuel ratio is made lean. A large amount of residual oxygen is discharged from the closed cylinder.

When a large amount of unburned HC, CO and a large amount of residual oxygen are simultaneously discharged, a large amount of unburned HC, C
O is being oxidized in _the NO _X absorbent 25, the temperature of the NO _X absorbent 25 by oxidation reaction heat in this case is quickly elevated temperature. As a result, from _the NO _X absorbent 25 SO _X
Will be released. Incidentally, it takes a much longer time than the case in the release of SO _X from _the NO _X absorbent 25 to release NO _X from _the NO _X absorbent 25, during which the air-fuel ratio of some cylinders is made rich to continue. Therefore, in the embodiment described below, the control of releasing SO _X from the NO _X absorbent 25 is performed during the first combustion, that is, during the low-temperature combustion.

[0093] Next referring to FIG. 25 NO _X absorbent 25
The processing routine of the SO _X release flag set when SO _X is to be released from is described. Referring to FIG. 25, first, at step 600, the current injection amount Q is added to ΔQ. Therefore, ΣQ represents the integrated value of the injection amount. Next, at step 601, it is determined whether or not the integrated value ΣQ of the injection amount has exceeded a fixed value QMAX. Σ
If Q> QMAX, the routine proceeds to step 602, where SO _X
The release flag is set. That is, since a certain amount of sulfur is contained in the fuel, when ΣQ> QMAX, it can be determined that a certain amount or more of SO _X has been absorbed by the NO _X absorbent 25. At this time, the SO _X release flag is set.

Next, the operation control will be described with reference to FIG. Referring to FIG. 26, first, in step 7
At 00, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. If the flag I is set, that is, if the operating state of the engine is in the first operating region I, step 70
The program proceeds to 1 to determine whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 703, where low-temperature combustion is performed.

That is, in step 703, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 704, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Next, at step 705, it is determined whether or not the SO _X release flag is set. When the SO _X release flag has not been set, the routine proceeds to step 706, where NO _X
It is determined whether or not the release flag I is set.
Fuel injection is performed such that the air-fuel ratio shown in FIG. 11 proceeds to step 707 when the NO _X release flag I has not been set. At this time, low-temperature combustion is performed under a lean air-fuel ratio. On the other hand, in step 706, N
O _X release flag I rich processing I already described is when it is determined to have been set as shown in FIG. 21 proceeds to step 208 is performed.

On the other hand, at step 701, L> X
When it is determined that (N) has been reached, the routine proceeds to step 702, where the flag I is reset.
And the second combustion is performed. That is, step 712
In FIG. 14A, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 14A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 713, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 14B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 714, it is determined whether or not the NO _X release flag II is set. N
O _X release flag II fuel injection so that the air-fuel ratio shown in FIG. 13 proceeds to step 715 when it is not set is performed. At this time, the second combustion is performed under the lean air-fuel ratio. On the other hand, in step 714, N
O _X release rich processing II already described is shown in FIG. 22 proceeds to step 716 when the flag II has been determined to have been set is performed. When the flag I is reset, in the next processing cycle, the process proceeds from step 700 to step 710, where it is determined whether or not the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the routine proceeds to step 712, where the second combustion is performed under a lean air-fuel ratio. On the other hand, in step 710, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 711, where the flag I is set, and then proceeds to step 703 to perform low-temperature combustion.

On the other hand, if it is determined in step 705 that the SO _X release flag is set during low-temperature combustion, the process proceeds to step 709, where rich processing III is performed. FIG. 27 shows a first embodiment of the rich process III. Next, a first embodiment of the rich process III will be described with reference to FIG. Referring to FIG. 27, first, at step 800, the rich time t _s required to release all the SO _X estimated to be absorbed by the NO _X absorbent 25 is calculated. Next, at step 801, it is determined whether or not the elapsed time t after the start of the rich processing III has exceeded the rich time t _s . t ≦ t _s
Have the air-fuel ratio of the air-fuel ratio is partially so that the rich cylinder of the exhaust gas flowing into the NO _X absorbent 25 proceeds to step 802 to rich to the air-fuel ratio of the remaining cylinders to lean when The injection amounts Q ₁ , Q ₂ , Q ₃ , Q ₄ of the respective cylinders # 1, # 2, # 3, # ₄ are calculated.

In this embodiment, the air-fuel ratio of the first cylinder # 1 and the fourth cylinder # 4 is set to 12, and the air-fuel ratio of the second cylinder # 2 and the third cylinder # 3 is set to 17. At this time, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 25 becomes a rich air-fuel ratio of about 14. Therefore, in this embodiment, a large amount of unburned HC and CO is discharged from the first cylinder # 1 and the fourth cylinder # 4,
From 2 cylinder # 2 and the third cylinder # 3 temperature of the NO _X absorbent 25 is rapidly increased by the oxidation reaction heat since a large amount of residual oxygen is discharged, S from _the NO _X absorbent 25 and thus
O _X is to be released.

[0099] On the other hand, when a determination is made that the t> t _s in step 801 proceeds to step 803 S
O _X release flag is reset, then step 804
NO _X emission flag I is reset in. Next, at step 805, ΣQ and ΣNOX are made zero. Next, a second embodiment of the rich control III will be described.

In this embodiment, the NO _x absorbent 25
Temperature T _o to a temperature T _c is predetermined in _the NO _X absorbent 25 detected by the temperature sensor 37 when releasing the _X, when for example lower than 600 ° C. of the exhaust gas flowing into the NO _X absorbent 25 air-fuel ratio is part so that the lean cylinder # 1, the remaining cylinders # 2 with the air-fuel ratio is made rich in # 4, the air-fuel ratio of # 3 is lean, NO _X
NO order to release the SO _X from _the NO _X absorbent 25 when the temperature T _c of the absorbent 25 exceeds the temperature T _C of predetermined
The air-fuel ratio of some of the cylinders # 1 and # 4 is made rich so that the air-fuel ratio of the exhaust gas flowing into the _X absorbent 25 becomes rich, and the air-fuel ratio of the remaining cylinders # 2 and # 3 becomes lean. Is done.

[0102] as well as thus T _c> T cylinder # 1 air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 25 is part so that the lean time _o, the air-fuel ratio of # 4 to the rich When the air-fuel ratio of the remaining cylinders # 2 and # 3 is made lean, the oxygen concentration in the exhaust gas increases. As a result, NO _X absorbent 2
5 can be raised more rapidly, and T _c > T _{o in} a short time.

Next, a second embodiment of the rich process III will be described with reference to FIG. Is higher or not than the temperature T _o the temperature T _c is predetermined in _the NO _X absorbent 25, first, at step 900 that the reference is determined to FIG. T _c ≦ T _o NO _X absorbent 25 of the cylinders # 1, as the air-fuel ratio of the inflowing exhaust gas becomes lean proceeds to step 901 when, the air-fuel ratio of # 4 to rich, remaining cylinders The injection amounts Q ₁ , Q of the cylinders # 1, # 2, # 3, # 4 necessary to make the air-fuel ratio of # 2, # 3 lean.
₂ , Q ₃ and Q ₄ are calculated.

Next, when T _c ≦ T _c , step 902 is executed.
Then, the rich time t _s required to release all the SO _X estimated to have been absorbed by the NO _X absorbent 25 is calculated. Next, at step 903, it is determined whether or not the elapsed time t after the start of the rich processing III has exceeded the rich time t _s . and t ≦ t NO _X absorbent 25 of the cylinders # 1, as the air-fuel ratio of the inflowing exhaust gas becomes rich in the routine proceeds to step 904 when the _s, the air-fuel ratio of # 4 to rich, the remaining cylinders # The injection amounts Q ₁ , Q of the cylinders # 1, # 2, # 3, and # 4 necessary to make the air-fuel ratios of the cylinders # 2 and # 3 lean.
₂ , Q ₃ and Q ₄ are calculated.

[0104] On the other hand, when a determination is made that the t> t _s in step 903 proceeds to step 905 S
O _X release flag is reset, then step 906
NO _X emission flag I is reset in. Next, at step 907, ΣQ and ΣNOX are made zero. Next, a third embodiment of the rich control III will be described with reference to FIG.

In this embodiment, as shown in FIG.
A first exhaust manifold 21a common to cylinders # 2 and # 3 is attached, and a first catalytic converter 38a containing an oxidation catalyst or a three-way catalyst is connected to the first exhaust manifold 21a. You. The first cylinder # 1
And a fourth exhaust manifold 21b common to the fourth cylinder # 4 and the second exhaust manifold 21b.
Is connected to a second catalytic converter 38b containing an oxidation catalyst or a three-way catalyst. These catalytic converters 38a,
38b is connected to the NO _x absorbent 25 through the common exhaust pipe 22 as shown in FIG.

[0106] In other words, all the cylinders in the upstream of _the NO _X absorbent 25 #
1, # 2, # 3, the air-fuel ratio of some cylinders in order to release the SO _X from _the NO _X absorbent 25 when placing common oxidation catalyst or three-way catalyst with respect to # 4 are made rich and the rest of the When the air-fuel ratio of the cylinder is made lean, a large amount of unburned HC and CO discharged from the cylinder having the rich air-fuel ratio and a large amount of oxygen discharged from the cylinder having the lean air-fuel ratio are oxidized by the oxidation catalyst. or reacted in a three-way catalyst, NO _X absorbent 2
In the case of 5, the oxidation reaction of unburned HC and CO is hardly performed. As a result, it is impossible to raise the temperature of the NO _X absorbent 25.

However, in the embodiment shown in FIG. 29, for example, the first cylinder # 1 and the fourth cylinder # 4 are made rich,
When the No. 2 cylinder and the No. 3 cylinder # 3 are made lean, a large amount of unburned H discharged from the No. 1 cylinder # 1 and the No. 4 cylinder # 4
C, CO flows into the _the NO _X absorbent 25 is passed through the inside second catalytic converter 38b, a large amount of residual oxygen that is discharged from the second cylinder # 2 and the third cylinder # 3 is the first catalytic converter It flows into the NO _x absorbent 25 through the inside of the NO 38 a. As a result, unburned H within _the NO _X absorbent 25
C, the temperature of the NO _X absorbent 25 since the oxidation reaction of CO is carried out it will be caused to rise rapidly.

Incidentally, SO _X also adheres to the oxidation catalyst or the three-way catalyst. SO _X from _the NO _X absorbent 25 to In the embodiment according to the present invention for removing SO _X attached to the these catalysts
To be released, the first cylinder # 1 and the fourth cylinder # 4
And the air-fuel ratio of the second cylinder # 2 and the third cylinder # 3 are made rich alternately. Next, a third embodiment of the rich process III will be described with reference to FIG.

Referring to FIG. 30, first, in step 1
000, the rich time t required to release the total SO _X presumed to be absorbed by the NO _X absorbent 25
_s is calculated. Next, at step 1001, it is determined whether or not the elapsed time t after the start of the rich processing III has exceeded the rich time t _s . step at the time of t ≦ t _s 100
Proceeding to 2, it is determined whether or not the flag X indicating that the air-fuel ratio of the first cylinder # 1 and the fourth cylinder # 4 should be made rich is set. _The NO _X absorbent proceeds to step 1003 when the flag X is set 25
The air-fuel ratios of some of the cylinders # 1 and # 4 are made rich so that the air-fuel ratio of the exhaust gas flowing into the cylinders becomes rich, and the remaining cylinders # 1 and # 4 are made rich.
Each cylinder required to make the air-fuel ratio of # 2 and # 3 lean
Injection amounts Q ₁ , Q ₂ , Q ₃ , Q _{4 of} # 1, # 2, # 3, # ₄
Is calculated. _The NO _X absorbent 2 proceeds to step 1004 when the flag X is not set for this
The air-fuel ratio of some of the cylinders # 2 and # 3 is made rich so that the air-fuel ratio of the exhaust gas flowing into the cylinder 5 becomes rich, and the air-fuel ratio of the remaining cylinders # 1 and # 4 is made lean. Each cylinder #
Injection amounts Q ₁ , Q ₂ , Q ₃ , Q _{4 of} # 1, # 2, # 3, # ₄
Is calculated.

On the other hand, in step 1001, t> _ts.
When it is determined that the state has reached, the routine proceeds to step 1005, where the SO _X release flag is reset.
NO _X emission flag I is reset at 006.
Next, at step 1007, ΣQ and ΣNOX are made zero. Next, at step 1008, the flag X is inverted from set to reset or from reset to set.

[0111] Incidentally, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 25 in the third embodiment from the first embodiment of the rich control III described so far the output of the air-fuel ratio sensor 27 when the rich or lean Based on each injection quantity Q ₁ ,
Q ₂ , Q ₃ and Q ₄ can be controlled. That is, the final injection amount Q _{1 is} obtained by multiplying each of the injection amounts Q ₁ , Q ₂ , Q ₃ , and Q ₄ by the feedback correction coefficient FAF.
・ FAF, Q ₂・ FAF, Q ₃・ FAF, Q ₄・ FAF
Is calculated. Feedback correction coefficient FAF
As shown in FIGS. 31 (A) and 31 (B), when the air-fuel ratio becomes rich, the air-fuel ratio is decreased in a skip manner and then gradually decreased with a constant integration constant K. A constant integration constant K after being increased
Thus, it is controlled so as to gradually increase.

In this case, as shown in FIG. 31A, the FAF skip amount SR when the air-fuel ratio changes from rich to lean is determined by the FAF skip amount SL when the air-fuel ratio changes from lean to rich. Fig. 31
Rich time becomes long lean time as indicated (A), the air-fuel ratio of the exhaust gas flowing into the result _the NO _X absorbent 25 becomes rich. That is, it is possible to make the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 25 by the SR> SL rich.

On the other hand, as shown in FIG. 31B, the FAF skip amount SR when the air-fuel ratio changes from rich to lean is set to the FA value when the air-fuel ratio changes from lean to rich.
If less than the skip amount SL of F lean time becomes long rich time as shown in FIG. 31 (B), the air-fuel ratio of the exhaust gas flowing into the result _the NO _X absorbent 25 becomes lean. That is, by setting SR <SL, N
The air-fuel ratio of the exhaust gas flowing into the O _X absorbent 25 will be able to lean.

[0114]

[Effect of the Invention] capable of releasing NO _X or SO _X from _the NO _X absorbent while suppressing as much as possible the discharge of unburned HC and soot.

[Brief description of the drawings]

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

FIG. 2 is a plan view of a compression ignition type internal combustion engine.

FIG. 3 is a diagram showing amounts of smoke and NO _X generated, and the like.

FIG. 4 is a diagram showing a combustion pressure.

FIG. 5 is a diagram showing fuel molecules.

FIG. 6 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.

FIG. 7 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 8 is a diagram showing a first operation region I and a second operation region II.

FIG. 9 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 10 is a diagram showing an opening degree of a throttle valve and the like.

FIG. 11 is a diagram showing an air-fuel ratio in a first operation region I.

FIG. 12 is a diagram showing a map of a target opening degree of a throttle valve and the like.

FIG. 13 is a diagram showing an air-fuel ratio of a second fuel.

FIG. 14 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 15 is a diagram for explaining the NO _X releasing action.

FIG. 16 is a diagram showing a map of the NO _X absorption amount per unit time.

FIG. 17 is a diagram for explaining NO _X release control.

FIG. 18 is a diagram for explaining an injection amount.

FIG. 19 is a flowchart for processing a NO _X release flag.

FIG. 20 is a flowchart for controlling operation of the engine.

FIG. 21 is a flowchart for executing a rich process I.

FIG. 22 is a flowchart for executing a rich process II.

FIG. 23 is a plan view showing another embodiment of the compression ignition type internal combustion engine.

FIG. 24 is a flowchart for executing a rich process II.

FIG. 25 is a flowchart for processing a SO _X release flag.

FIG. 26 is a flowchart for controlling operation of the engine.

FIG. 27 is a flowchart for executing a first embodiment of a rich process III.

FIG. 28 is a flowchart for executing a second embodiment of the rich process III.

FIG. 29 is a plan view showing another embodiment of the compression ignition type internal combustion engine.

FIG. 30 is a flowchart for executing a third embodiment of the rich process III.

FIG. 31 is a time chart showing changes in the feedback correction coefficient.

[Explanation of symbols]

 6: fuel injection valve 15: exhaust turbocharger 20: throttle valve 29: EGR passage

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 41/04 355 F02D 41/04 355 41/40 41/40 N 43/00 301 43/00 301E 301N 301T F02M 25 / 07 570 F02M 25/07 570J 570D (72) Inventor Masato Goto 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Hiroki Murata 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (10)

[Claims] 1. A fuel ratio of the inflowing exhaust gas is absorbed NO _X when is lean, the engine and _the NO _X absorbent when the air-fuel ratio of the exhaust gas flowing emits NO _X absorbed and becomes the stoichiometric air-fuel ratio or rich in disposed in the exhaust passage compression ignition type internal combustion engine, the air-fuel ratio is partially so that the rich cylinder of the exhaust gas flowing into the NO _X absorbent to when releasing the NO _X or sO _X from _the NO _X absorbent A compression ignition type internal combustion engine wherein the air-fuel ratio of the remaining cylinders is made rich and the air-fuel ratio of the remaining cylinders is made lean. 2. As the amount of inert gas in the combustion chamber of the compression ignition type internal combustion engine increases, the amount of soot generated gradually increases and reaches a peak, and the amount of inert gas in the combustion chamber further increases. And an internal combustion engine in which the temperature of fuel and surrounding gas during combustion in the combustion chamber becomes lower than the generation temperature of soot and almost no soot is generated, and the amount of generated soot is less than the amount of inert gas at which peak occurs. The first combustion in which the amount of inert gas in the combustion chamber is large and little soot is generated, and the second 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 generated soot peaks. comprising a switching means for selectively switching, so that the air-fuel ratio of the exhaust gas is when releasing the NO _X from _the NO _X absorbent when the second combustion is being performed flowing into _the NO _X absorbent becomes rich In addition to making the air-fuel ratio of some cylinders rich 2. The compression ignition type internal combustion engine according to claim 1, wherein the air-fuel ratio of the remaining cylinders is made lean. 3. The compression ignition type internal combustion engine according to claim 2, wherein the air-fuel ratio is made rich under the second combustion in some of the cylinders. 4. The compression ignition type internal combustion engine according to claim 2, wherein in some of the cylinders, the air-fuel ratio is made rich under the first combustion after switching from the second combustion to the first combustion. . 5. When the first combustion is being performed, N
O_XNO from absorbent _XWhen all the cylinders
Temporarily set the stoichiometric air-fuel ratio or rich air-fuel ratio in the firing chamber
The compression ignition type internal combustion engine according to claim 2, wherein
Seki. 6. An exhaust gas recirculation device for recirculating exhaust gas discharged from a combustion chamber into an engine intake passage,
3. A compression ignition type internal combustion engine according to claim 2, wherein said inert gas comprises recirculated exhaust gas. 7. The compression ignition type internal combustion engine according to claim 6, wherein an exhaust gas recirculation rate in the first combustion state is approximately 55% or more. 8. An operation region of the engine is divided into a first operation region on a low load side and a second operation region on a high load side, and a first combustion is performed in the first operation region. The compression ignition type internal combustion engine according to claim 2, wherein the second combustion is performed in the region. 9. When the compression ignition type internal combustion engine increases the amount of inert gas in the combustion chamber, the amount of generated soot gradually increases and reaches a peak, and the amount of inert gas in the combustion chamber further increases. And an internal combustion engine in which the temperature of fuel and surrounding gas during combustion in the combustion chamber becomes lower than the generation temperature of soot and almost no soot is generated, and the amount of generated soot is less than the amount of inert gas at which peak occurs. The first combustion in which the amount of inert gas in the combustion chamber is large and little soot is generated, and the second 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 generated soot peaks. comprising a switching means for selectively switching the first to when releasing the sO _X from _the NO _X absorbent
To the air-fuel ratio of the remaining cylinders to lean with the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is a rich air-fuel ratio of some cylinders so as to be rich when combustion is being performed The compression ignition type internal combustion engine according to claim 1, wherein Air-fuel ratio of the exhaust gas flowing into the NO _X absorbent becomes lean when lower than the temperature at which the temperature reaches a predetermined of the NO _X absorbent when releasing the SO _X from 10. _the NO _X absorbent the air-fuel ratio of the remaining cylinders to lean, flows into _the NO _X absorbent when the temperature of the NO _X absorbent is higher than a predetermined temperature with so that the air-fuel ratio of some cylinders rich 10. The compression ignition type internal combustion engine according to claim 9, wherein the air-fuel ratios of some of the cylinders are made rich and the air-fuel ratios of the remaining cylinders are made lean so that the air-fuel ratio of the exhaust gas becomes rich.