JPH11294226A - Compression ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent soot from being discharged into the atmosphere by arranging a soot collecting device in an engine exhaust passage, and selectively switching first combustion having a large inert gas quantity in a combustion chamber and rarely generating soot with second combustion having a small inert gas quantity in the combustion chamber. SOLUTION: When the inert gas quantity in the combustion 5 of a compression ignition type internal combustion engine is increased, the generated quantity of soot is gradually increased and reaches a peak. When the inert gas quantity is further increased, the temperature of a fuel and the gas around it at the time of combustion in the combustion chamber 5 becomes lower than the generating temperature of soot, and soot is rarely generated. First combustion which has a larger inert gas quantity in the combustion chamber 5 than the inert gas quantity causing the peak of the generated quantity of soot and rarely generates soot and second combustion which is the normal operation state and has a small inert gas quantity in the combustion chamber 5 can be switched. The soot generated when the first combustion and second combustion are switched is collected by a soot collecting device 19, and the soot is prevented from being discharged into the atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

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

[0005]

As described above, the conventional E
Generation amount of the NO _x and smoke within a range not exceeding the EGR rate is the maximum allowable limit conventionally the maximum allowable limit was considered to be present were determined to be as small as possible with respect to GR ratio. However, this way there is a limit to the EGR rate to decrease of the NO _x and NO _x and the amount of smoke produced be determined so that the amount generated is as small as possible of smoke, the actual NO _x and still a significant amount to At present, smoke is generated.

However, if the EGR rate is made larger than the maximum allowable limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, the amount of generated smoke has a peak, and the peak exceeds this peak. EGR
When the rate is further increased, the smoke starts to decrease rapidly, and when the EGR rate is increased to 70% or more during idling operation, and when the EGR gas is cooled strongly, the smoke is reduced when the EGR rate is increased to about 55% or more. It was found that it was almost zero, that is, almost no soot was generated. In this case, N
Generation amount of O _x is also found that a very small amount.
After that, the reason why no soot was generated was examined based on this finding, and as a result, unprecedented soot and NO
_This has led to the construction of a new combustion system capable of simultaneously reducing _x . 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 studies, it has been found that when the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than a certain temperature, the growth of hydrocarbons is stopped at a halfway stage before reaching soot. However, when the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons grow into soot at a stretch. In this case, the temperature of the fuel and the surrounding gas is greatly affected by the heat absorbing action of the gas around the fuel when the fuel is burned, and the amount of heat absorbed by the gas around the fuel is adjusted according to the calorific value at the time of burning the fuel. As a result, the temperature of the fuel and the surrounding gas can be controlled.

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

By the way it is necessary to more than about 55 percent at a minimum the EGR rate is to simultaneously reduce the soot and NO _x under this new combustion system. However, it is possible to make the EGR rate approximately 55% or more when the intake air amount is small, that is, when the engine load is relatively low. If the intake air amount exceeds a certain limit, the intake air amount is reduced unless the EGR rate is reduced. Cannot be increased. Therefore, when the intake air amount exceeds a certain limit, the EGR rate is changed to the EG at which the generation amount of soot reaches a peak.
It is necessary to immediately switch to an EGR rate lower than the R rate.

However, no matter how fast the EGR rate is switched to an EGR rate lower than the EGR rate at which the amount of soot generation peaks, the EGR rate instantaneously becomes the EGR rate at which the amount of soot generation peaks. At this time, there is a problem that a large amount of soot is discharged into the engine exhaust passage.

[0011]

In order to solve the above problems, in the first invention, as the amount of inert gas in the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak.
In a compression ignition type internal combustion engine, when the amount of inert gas in the combustion chamber is further increased, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature and soot is hardly generated. A first soot collecting device for collecting soot in the engine exhaust passage, wherein the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of generated soot is a peak, and almost no soot is generated; And a 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 becomes a peak. Therefore, the soot generated at the time of switching between the first combustion and the second combustion is collected by the soot collecting device.

[0012] In the second invention, in the first invention,
A catalyst having an oxidation function is arranged in the engine exhaust passage. In a third aspect based on the first aspect, the soot collection device comprises a particulate filter. In a fourth aspect based on the third aspect, the air-fuel ratio in the combustion chamber is made rich when the first combustion is being performed when the temperature of the particulate filter exceeds a predetermined temperature. .

In the fifth invention, in the third invention,
A heating means for heating the particulate filter is provided, and when burning the particulates collected by the particulate filter, the particulate filter is heated by the heating means during the first combustion. ing. In the first invention in the sixth aspect, the absorption and the air-fuel ratio of the inflowing exhaust gas air-fuel ratio of the exhaust gas absorb and flowing the NO _x contained in the exhaust gas becomes the stoichiometric air-fuel ratio or rich when the lean was the _the NO _x absorbent to release the NO _x arranged in the soot trap downstream of the engine exhaust passage, the when releasing the NO _x from the NO _x absorbent when the first combustion is being performed combustion chamber Is temporarily set to the stoichiometric air-fuel ratio or rich.

In the seventh invention, in the sixth invention,
NO from _the NO _x absorbent when the second combustion is being performed
so that the air-fuel ratio of the exhaust gas flowing by injecting additional fuel during the latter half, or the exhaust stroke of the expansion stroke in _the NO _x absorbent the stoichiometric air-fuel ratio or rich to when releasing the _x. In an eighth aspect based on the first aspect, there is provided a recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises the recirculated exhaust gas.

In a ninth invention, in the eighth invention,
The exhaust gas recirculation rate in the first combustion state is at least about 55 percent. In a tenth aspect based on the first aspect, the operating range of the engine is divided into a first operating range on a low load side and a second operating range on a high load side, and the first combustion is performed in the first operating range. In the second operation region, the second combustion is performed.

[0016]

FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is 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, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes 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 an air cleaner 14 via an intake duct 13. A throttle valve 16 driven by an electric motor 15 is arranged in the intake duct 13. On the other hand, the exhaust port 10 is connected to the soot trap 19 through an exhaust manifold 17 and exhaust pipe 18, downstream of the soot collecting device 19 is disposed _the NO _x absorbent 20.

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

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

The electronic control unit 30 is composed of a digital computer and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, An output port 36 is provided. The output signal of the air-fuel ratio sensor 21 is input to the input port 35 via the corresponding AD converter 37, and the output signal of the fuel pressure sensor 28 is also input to the input port 35 via the corresponding AD converter 37. A load sensor 41 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is supplied to the input port 3 via the corresponding AD converter 37.
5 is input. The input port 35 is connected to a crank angle sensor 42 that generates an output pulse each time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 36 is connected to the fuel injection valve 6,
Electric motor 15, EGR control valve 23 and fuel pump 2
7 is connected.

FIG. 2 shows a change in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree and the EGR rate of the throttle valve 16 during the low load operation of the engine, and smoke represents HC, CO, an experimental example illustrating changes in emissions of NO _x. As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the smaller the E
When the GR rate increases and is equal to or lower than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is equal to or higher than 65%.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the smoke is reduced when the EGR rate becomes close to 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
The generation amount of O _x is considerably reduced. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3A shows a change in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is the largest when the air-fuel ratio A / F is around 18, and FIG. 3B shows the air-fuel ratio A / F. The graph shows a change in the combustion pressure in the combustion chamber 5 when F is around 13 and the amount of generated smoke is almost zero. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) 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
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
As shown in ₍₁₎ , the generation amount of NOx is considerably reduced. 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 becomes low when the soot is hardly generated I can say. The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low.
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. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot production process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of generated soot becomes substantially zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a precursor of soot or a hydrocarbon in a state before it. .

The above considerations based on the experimental results shown in FIGS. 2 and 3 can be summarized as follows. 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 became lower than a certain temperature.

The temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature, depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although the change can not be said that how many times since this certain temperature has a generation amount and the closely related of the nO _x, therefore this certain temperature is defined to a certain degree from the generation amount of the nO _x be able to. That is, the fuel and the gas temperature surrounding it at the time of combustion and the greater the EGR rate, decreases, the amount of the NO _x is reduced. Generation amount at this time NO _x is soot is hardly generated when it is around or less 10 ppm. Therefore, the above certain temperature is NO
It 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 used 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 oxidizes the hydrocarbons. The core is to oxidize with a catalyst having a function.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 is set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that the endothermic 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, the situation is slightly different when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air.
In this case, the fuel vapor diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion temperature is not increased so much because the combustion heat is absorbed by the surrounding inert gas. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be kept low by the endothermic effect of the inert gas.

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

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

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

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

FIG. 6 shows the mixing of EGR gas and air necessary to make the temperature of fuel during combustion and the surrounding gas temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. It shows the gas amount, the ratio of air in the mixed gas amount, and the ratio of EGR gas in the mixed gas. In FIG. 6, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load, and Z1 indicates the low load operation region.

Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is formed. The required minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate. 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. 6, 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. Further, the NO _x generation amount at this time is around 10 p.pm or less.
The amount of O _x generated is extremely small.

If the fuel injection amount increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which the soot is generated, the heat generated by the EGR gas is required. Must be increased. Therefore, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount increases.
That is, the EGR gas amount needs to increase as the required load increases.

On the other hand, in the load region Z2 of FIG. 6, the total intake gas amount X required to prevent the generation of soot exceeds the total intake gas amount Y that can be sucked. Therefore, in this case, in order to supply the total intake gas amount X required to prevent the generation of soot into the combustion chamber 5, both the EGR gas and the intake air, or EG
R gas needs to be supercharged or pressurized. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intake gas amount Y that can be sucked in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the amount of air is slightly reduced to increase the amount of EGR gas, and the fuel is burned under a rich air-fuel ratio.

As described above, FIG. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, in the low load operation region Z1 shown in FIG. 6, the air amount is made smaller than the air amount shown in FIG. less well, i.e. even if the air-fuel ratio to rich the generation amount of the NO _x while preventing generation of soot can be around or less 10 ppm, also the air in the low load region Z1 shown in FIG. 6 be more than the amount of air shown the amount in FIG. 6, that even if the average value of the air-fuel ratio to a lean 17 to 18 while preventing generation of soot generation amount of NO _x 10
It can be around ppm or less.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excess fuel does not grow into soot, and soot is generated. There is no. Further, at this time NO _x even only an extremely small amount of generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Furthermore, NO _x
Only very small amounts are generated.

As described above, in the engine low load operation region Z1, 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. not, the amount of the NO _x becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time. By the way, the temperature of the fuel and the surrounding gas at the time of combustion in the combustion chamber can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, only when the heat generation amount by combustion is small and the engine load is relatively low. Therefore, in the embodiment according to the present invention, when the engine load is relatively low, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the combustion below the temperature at which the growth of hydrocarbons stops halfway. In this way, when the engine load is relatively high, the second combustion, that is, the combustion that has been conventionally performed is performed. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been conventionally performed, is the combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot generation peaks. Say

The solid line in FIG. 7A shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when the first combustion is performed, and the broken line in FIG. 2 shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when the combustion of No. 2 is performed. The solid line in FIG. 7 (B) represents the fuel and gas temperature Tf around the fuel when the first combustion is performed.
7B shows the relationship between the fuel and the surrounding gas temperature Tf and the crank angle when the second combustion is performed.

When the first combustion, that is, the low-temperature combustion is being performed, the amount of the EGR gas is larger than when the second combustion, that is, the conventional ordinary combustion is being performed.
As shown in (A), before the compression top dead center, that is, during the compression process, the average gas temperature Tg during the first combustion shown by the solid line is better than the average gas temperature Tg during the second combustion shown by the broken line.
Is higher than. At this time, as shown in FIG. 7 (B), the temperature of the fuel and its surrounding gas Tf is substantially the same as the average gas temperature Tg.

Next, combustion is started near the compression top dead center. In this case, when the first combustion is being performed, the fuel and the gas temperature Tf around the fuel and Tf are changed as shown by the solid line in FIG. 7B. Not so high. The second
When the combustion is performed, the fuel and the surrounding gas temperature Tf become extremely high as shown by the broken line in FIG. 7B. When the second combustion is performed in this manner, the temperature Tf of the fuel and the surrounding gas becomes considerably higher than that in the case where the first combustion is performed, but the temperature of the other gas which occupies most of the temperature. Is lower in the case where the second combustion is performed than in the case where the first combustion is performed. Therefore, as shown in FIG. The average gas temperature Tg in the chamber 5 is higher when the first combustion is being performed than when the second combustion is being performed. As a result, as shown in FIG. 7A, the average gas temperature Tg in the combustion chamber 5 after the combustion is completed, that is, in the latter half of the expansion stroke, in other words, the temperature of the burned gas in the combustion chamber 5 becomes the second temperature. The case where the first combustion is performed is higher than the case where the second combustion is performed.

As described above, when the first combustion, that is, the low-temperature combustion is performed, the temperature of the fuel and the surrounding gas Tf during the combustion is considerably lower than when the second combustion is performed. The burned gas in the chamber 5 is higher than that in the case where the second combustion is performed. Therefore, the temperature of the exhaust gas discharged from the combustion chamber 5 is also lower than that in the case where the second combustion is performed. Get higher.

FIG. 8 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second combustion region II 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 40, 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.
2 shows a second boundary with II. 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.

FIG. 9 shows the output of the air-fuel ratio sensor 21. As shown in FIG. 9, the output current I of the air-fuel ratio sensor 21 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 21. Next, 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 16, the opening of the EGR control valve 23, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount with respect to the required load L. As shown in FIG. 10, in the first operating region I where the required load L is low, the opening degree of the throttle valve 16 is gradually increased from almost fully closed to about half open as the required load L increases, and the EGR is performed.
The opening of the control valve 23 is gradually increased from near full closure to full opening as the required load L increases. FIG.
In the example shown in FIG. 0, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

In other words, in the first operation region I, the EGR
The opening of the throttle valve 16 and the opening of the EGR control valve 23 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 23 based on the output signal of the air-fuel ratio sensor 21. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

During the idling operation, the throttle valve 16 is closed until the valve is almost fully closed. At this time, the EGR control valve 23 is also closed almost completely. Throttle valve 1
When the valve 6 is closed close to the fully closed state, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 16 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating range of the engine is the first operating range I
From the second operating region II, the opening of the throttle valve 16 is increased stepwise from the half-open state to the fully open direction. At this time, in the example shown in FIG.
The air-fuel ratio is reduced in steps from 40 percent to less than 40 percent, and the air-fuel ratio is increased in steps. In the second operation region II, the conventional combustion is performed. In this combustion method generates little soot and NO _x, but the heat efficiency is higher than the low temperature combustion, thus as the operating region of the engine is shown in Figure 10 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise.

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

FIG. 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 16 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 2A, the EGR is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N, 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 23 is as shown in FIG.
As shown in (1), it is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N.

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 1 required to set air-fuel ratio to this target air-fuel ratio
The target opening ST of No. 6 is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 14A, and the air-fuel ratio is set as the target air-fuel ratio. Opening SE of EGR control valve 23 required for
Are stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.

Incidentally, the soot collecting device 19 shown in FIG. 1 comprises a particulate filter for collecting soot and other particulates contained in the exhaust gas. Various types of particulate filters are known, but a typical example is a particulate filter made of a porous ceramic having a honeycomb structure. In the embodiment shown in FIG. 1, a catalyst having an oxidation function, for example, an oxidation catalyst type or a three-way catalyst is supported on a porous ceramic. Therefore, in the embodiment shown in FIG. 1, it can be seen that the soot collecting device 19 also functions as an oxidation catalyst.

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 soot precursor or a soot precursor. From the combustion chamber 5 in the form of However, as described above, the soot collecting device 19 also functions as an oxidation catalyst, so that the unburned hydrocarbons discharged from the combustion chamber 5 at this time are oxidized well by the soot collecting device 19.

On the other hand, the soot contained in the exhaust gas is also particulate, so that the soot contained in the exhaust gas is also collected by the particulate filter like other particulates. As shown in FIG. 10, in the embodiment according to the present invention, when the first combustion is switched to the second combustion, the throttle valve 16 is opened stepwise,
As a result, the EGR rate jumps over the region (FIG. 5) where the amount of generated soot is peaked. However, in practice, at this time, the EGR rate instantaneously becomes the EGR rate at which the amount of generated soot reaches a peak, so that a large amount of soot is temporarily generated in the combustion chamber 5. However, in the present invention, even if such a large amount of soot is generated, the soot is collected by the soot collecting device 19, and thus the soot is not released into the atmosphere.

The soot collected by the soot collecting device 19, that is, the soot collected by the particulate filter, starts burning in the presence of excess oxygen when the exhaust gas flowing into the particulate filter exceeds a certain temperature. . The temperature at which the soot starts burning varies depending on the catalyst supported on the particulate filter, and is about 400 ° C. in a low case and about 500 ° C. to 600 ° C. in a high case. Therefore, if the exhaust gas temperature becomes higher than these temperatures, soot and other particulates collected on the particulate filter will start burning naturally.

By the way, when low-temperature combustion is performed, the temperature of the exhaust gas increases, and the temperature of the exhaust gas further increases due to the heat of the oxidation reaction because the oxidation catalyst is supported on the particulate filter. Next, this will be described with reference to FIG. FIG. 15 schematically shows the relationship between various temperatures and the required load L. In FIG. 15, Ta indicates the temperature of the exhaust gas flowing into the soot trap 19, that is, the particulate filter when the first combustion, that is, the low-temperature combustion is performed in the first operation region I, and Tb indicates this temperature. The temperature of the particulate filter at that time is shown. Also,
Tc indicates the temperature of the particulate filter when the second combustion is performed in the first operation region I and the second operation region II.

As described above, when the low-temperature combustion is being performed, the exhaust gas temperature is higher than when the second combustion is being performed. Therefore, if the required load L is the same, the low-temperature combustion is performed. The temperature of the particulate filter when it is on is higher than the temperature Tc of the particulate filter when the second combustion is being performed. Even when low-temperature combustion is being performed, the higher the required load L, the greater the amount of heat generated during combustion. Therefore, the higher the required load L, the higher the exhaust gas temperature Ta flowing into the particulate filter. On the other hand, during low-temperature combustion, a large amount of unburned H
Since C and CO are discharged, the temperature Tb of the particulate filter is considerably higher than the temperature Ta of the exhaust gas flowing into the particulate filter due to the heat of oxidation reaction of the unburned HC and CO by the catalyst carried on the particulate filter. Get higher.

When the low-temperature combustion is being performed, the temperature of the particulate filter becomes considerably high,
Moreover, since low-temperature combustion is performed under a lean air-fuel ratio, excess oxygen is present in the exhaust gas. Therefore, the soot and other particulates collected by the particulate filter will be naturally combusted during low-temperature combustion.

On the other hand, the NO _x absorbent 20 disposed downstream of the soot collecting device 19 uses, for example, alumina as a carrier, and on the carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs. And at least one selected from 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. 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 20 upstream of the exhaust passage supplying air and fuel into the (hydrocarbon) to _the NO _x absorbent 20 _x absorbent 20 absorbs the NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, the air-fuel ratio of the inflowing exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich NO _x
Carry out the absorption and release action of NO _x to release.

[0066] _the NO _x absorbent 20 be disposed the _the NO _x absorbent 20 in the engine exhaust passage is performing absorption and release action of actually NO _x is also not clear portion detailed mechanism of action out this absorbing . However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

In the compression ignition type internal combustion engine shown in FIG. 1, combustion is normally performed in a state where the air-fuel ratio in the combustion chamber 5 is 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 as is shown in FIG. 16 (A) at this time O
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. 16 (A), it is diffused into the absorbent in the form of nitrate ion NO ₃ ⁻ while being combined. In this way, NO _x is absorbed in the NO _x absorbent 20. 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 20_xIs shown in FIG. 16 (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 _x20 absorbents
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 20_xIs released
Is done. However, the air-fuel ratio of the inflowing exhaust gas is
NO if ratio_xNO from absorbent 20_xGradually
NO because only _xAbsorbed by the absorbent 20
All NO_xIt takes a slightly longer time to release.

[0070] Incidentally there is a limit to the absorption of NO _x capacity of the NO _x absorbent 20, absorption of NO _x capacity of the NO _x absorbent 20 needs to release the NO _x from the NO _x absorbent 20 before saturation. For this purpose it is necessary to estimate the amount of NO _x is absorbed in the NO _x absorbent 20. Therefore, in this embodiment of the present invention of a map as shown in FIG. 17 (A) as a function of the NO _x absorption amount A of the required load L and engine speed N per unit time when it is performed first combustion is previously obtained in the form of a map as shown in FIG. 17 (B) the absorption of NO _x amount B per unit time as a function of the required load L and engine speed N when the second combustion is being performed It is previously obtained in the form, per these unit time of absorption of NO _x amount a, so that to estimate the amount of NO _x ΣNOX being absorbed in the NO _x absorbent 20 by integrating the B.

[0071] In the embodiment according to the present invention so that to release the NO _x from the NO _x absorbent 20 when exceeding the allowable maximum value MAX of the absorption of NO _x amount ΣNOX has predetermined. That is, when the absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX when the low temperature combustion is being performed is the air-fuel ratio is temporarily made rich in the combustion chamber 5, NO _x whereby from _the NO _x absorbent 20 Is released. As described above, even when the air-fuel ratio is made rich during low-temperature combustion, almost no soot is generated.

[0072] On the other hand, in the second embodiment absorption of NO _x amount ΣNOX allowable maximum value MAX when the second combustion is being performed
Is exceeded, additional fuel is injected during the second half of the expansion stroke or during the exhaust stroke. Fuel amount of the additional is determined as the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 20 becomes rich and therefore the additional fuel is injected NO
NO _x will be released from the _x absorbent 20.

[0073] Figure 18 shows the processing routine for _the NO _x releasing flag which is set when releasing the NO _x from the NO _x absorbent 20, this routine is executed by interruption every predetermined time. Referring to FIG. 18, 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 absorption of NO _x amount A per unit time from the map shown in FIG. 17 (A) is calculated proceeds to step 101 when a first operating region I You. Then A is added to the absorption of NO _x amount ΣNOX step 102. Next, at step 103 NO _x absorption amount ΣNOX whether exceeds the allowable maximum value MAX or not. ΣNO
If X> MAX, the routine proceeds to step 104, where processing for setting the NO _x release flag is performed for a predetermined time, and then, at step 105, ΣNOX is made zero.

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
Absorption of NO _x per unit from the map time shown in FIG. 17 (B) B is calculated willing to. Then B is added to the absorption of NO _x amount ΣNOX step 107. Next, at step 108, the NO _x absorption amount ΣNO _x is set to the allowable maximum value
It is determined whether or not X has been exceeded. ΣIf NOX> MAX, the routine proceeds to step 109, where N is set for a predetermined time.
A process for setting the O _x release flag is performed, and then in step 110, ΣNOX is made zero.

Next, the operation control will be described with reference to FIG. Referring to FIG. 19, first, Step 2
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. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, step 20 is executed.
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 203, where low-temperature combustion is performed.

That is, in step 203, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 204, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG.
The opening of the EGR control valve 23 is set as the target opening SE.
Next, at step 205 NO _x releasing flag whether it is set or not. When the NO _x release flag is not set, the routine proceeds to step 206, where
The fuel injection is performed so that the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.

On the other hand, when it is determined in step 205 that the NO _x release flag has been set, the routine proceeds to step 207, where injection control for enriching the average air-fuel ratio in the combustion chamber 5 is performed. At this time, NO _x absorbent 2
0 NO _x is released from the. On the other hand, when it is determined in step 201 that L> X (N), the routine proceeds to step 202, where the flag I is reset, and then the routine proceeds to step 210 where the second combustion is performed.

That is, in step 210, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 14A, and the opening of the throttle valve 16 is set to this target opening ST. Next, at step 211, the target opening degree SE of the EGR control valve 23 is calculated from the map shown in FIG.
The opening of the EGR control valve 23 is set as the target opening SE.
Next, at step 212, it is determined whether or not the NO _x release flag is set. When the NO _x release flag is not set, the process proceeds to step 213 and
The fuel injection is performed so that the air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.

On the other hand, when it is determined in step 212 that the NO _x release flag is set, the routine proceeds to step 214, in which additional fuel is supplied so that the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 20 becomes rich. It is injected. In this case NO _x is released from the NO _x absorbent 20. When the flag I is reset, in the next processing cycle, the process proceeds from step 200 to step 208, where the required load L
Is lower than the second boundary Y (N). When L ≧ Y (N), the process proceeds to step 210,
The second combustion is performed under the lean air-fuel ratio.

On the other hand, at step 208, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 209, where the flag I is set. Next, step 203
And the low-temperature combustion is performed. FIG. 20 shows a second embodiment. In this embodiment, a catalyst having an oxidizing function is not carried on the particulate filter of the soot trap 19, and instead, such as an oxidation catalyst or a three-way catalyst is provided in an exhaust passage upstream of the soot trap 19. A catalyst 50 having an oxidation function is provided.

FIG. 21 shows a third embodiment. In this embodiment, a temperature sensor 51 is provided to detect the temperature of the particulate filter of the soot trap 19. That is, as can be seen from FIG. 15, when the required load L increases during low-temperature combustion, the temperature of the particulate filter of the soot collecting device 19 increases, and as a result, the soot and the particulate matter collected by the particulate filter increase. Other particulates are spontaneously burned. In addition, the temperature of the particulate filter of the soot collecting device 19 becomes high even during the engine high load operation, so that the soot and other particulates collected by the particulate filter are spontaneously burned.

However, from such a state, low load operation,
For example, when the operation shifts to the idling operation, the heat of combustion of soot and the like carried away by the exhaust gas decreases because the flow rate of the exhaust gas becomes slow. As a result, there is a risk that the particulate filter will overheat, thus melting the particulate filter. In this case, when the oxygen concentration in the exhaust gas is reduced, the combustion of soot and the like is stopped, and thus the temperature of the particulate filter is reduced. Therefore, in the third embodiment, when the temperature of the particulate filter exceeds the allowable maximum temperature T1, the combustion chamber 5 is operated when the low-temperature combustion is performed until the temperature of the particulate filter decreases to a certain temperature T2 (<T1) or less. The air-fuel ratio inside is made rich.

FIG. 22 shows a control routine for a rich flag indicating that the air-fuel ratio should be made rich in order to avoid melting of the particulate filter. This routine is executed by interruption every predetermined time. Referring to FIG. 22, first, at step 300, it is determined whether or not the rich flag is set. If the rich flag has not been set, the routine proceeds to step 301, where it is determined whether or not the temperature T of the particulate filter detected by the temperature sensor 51 has become higher than the allowable maximum temperature T1. If T> T1, the routine proceeds to step 302, where the rich flag is set.

When the rich flag is set, step 3
Proceeds from 00 to step 303 NO _x absorption amount ΣNOX
Is set to zero. Next, the routine proceeds to step 304, where it is determined whether or not the temperature T of the particulate filter has become equal to or lower than a predetermined temperature T2 (<T1). When T <T2, the routine proceeds to step 305, where the rich flag is reset. FIG. 23 shows an operation control routine for executing the third embodiment. Incidentally, NO _x releasing flag in this routine is used which has been treated by a routine shown in FIG. 18.

Referring to FIG. 23, first, at step 400, 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 4
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 403, where low-temperature combustion is performed.

That is, in step 403, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 404, the target opening degree SE of the EGR control valve 23 is calculated from the map shown in FIG.
The opening of the EGR control valve 23 is set as the target opening SE.
Next, at step 405, it is determined whether or not the NO _x release flag is set. Whether the rich flag proceeds to step 406 when _the NO _x releasing flag has not been set has been set or not. If the rich flag has not been set, the routine proceeds to step 407, where fuel injection is performed so as to achieve the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.

[0087] On the other hand, the injection control of the average air-fuel ratio in the combustion chamber 5 proceeds to step 408 to rich is performed when _the NO _x releasing flag is judged as being set in step 405. At this time, NO _x absorbent 2
0 NO _x is released from the. When it is determined in step 406 that the rich flag is set, the flow proceeds to step 409, where injection control is performed to make the air-fuel ratio in the combustion chamber 5 rich so as to avoid melting of the particulate filter.

On the other hand, at step 401, L> X
When it is determined that (N) has been reached, the routine proceeds to step 402, where the flag I is reset.
And the second combustion is performed. That is, step 412
In FIG. 14A, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 14A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 413, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG. 14B, and the opening of the EGR control valve 23 is set as the target opening SE. Next, at step 414 NO _x releasing flag whether it is set or not. NO
Step 4 when the _x release flag is not set
Proceeding to 15, fuel injection is performed so as to attain the air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.

On the other hand, when it is determined in step 414 that the NO _x release flag is set, the routine proceeds to step 416, in which additional fuel is supplied so that the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 20 becomes rich. It is injected in the latter half of the expansion stroke or during the exhaust stroke. In this case NO _x is released from the NO _x absorbent 20. When the flag I is reset, the process proceeds from step 400 to step 410 in the next processing cycle, and it is determined whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the process proceeds to step 412, where the second
Is performed.

On the other hand, at step 410, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 411, where the flag I is set. Next, step 403
And the low-temperature combustion is performed. FIG. 24 shows a fourth embodiment. In this embodiment, an electric heater 52 is disposed at the upstream end of the particulate filter in the soot trap 19, and furthermore, a pressure difference for detecting a pressure difference between the upstream pressure and the downstream pressure of the particulate filter. A detection sensor 53 is provided. Further, the soot trap 19 in this embodiment Patty on filter not been catalysts supported having an oxidation function, instead _the NO _x absorbent 20 downstream of the exhaust passage of the oxidation catalyst or three-way catalyst A catalyst 54 having such an oxidizing function is provided.

In the fourth embodiment, when the amount of soot and other particulates collected by the particulate filter becomes equal to or greater than a predetermined amount, that is, when the upstream pressure and the downstream pressure of the particulate filter are reduced. When the pressure difference exceeds a certain pressure, electric power is supplied to the electric heater 52, so that the soot and the like collected by the particulate filter are burned.

By the way, when the unburned hydrocarbons, especially unburned hydrocarbons having a low boiling point, are collected as much as possible on the particulate filter when heated by the electric heater 52, the ignition becomes easier. In this regard, when low-temperature combustion is being performed, a large amount of unburned hydrocarbons is discharged, and these unburned hydrocarbons adhere to the particulate filter, so that it becomes easy to ignite when heated by the electric heater 52. Therefore, in the fourth embodiment, when the amount of soot and the like collected by the particulate filter becomes equal to or more than a predetermined amount, when the low-temperature combustion has continued for a certain period of time, that is, on the particulate filter, The heating operation by the electric heater 52 is started when a large amount of unburned hydrocarbons is attached.

FIG. 25 shows an operation control routine for executing the fourth embodiment. In this routine, NO
_{As the x} release flag, the one processed by the routine shown in FIG. 18 is used. Referring to FIG. 25, first, at step 500, 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, the routine proceeds to step 501, where the required load L is reduced to the first boundary X1 (N).
It is determined whether or not it has become larger. L ≦ X1
In the case of (N), the routine proceeds to step 503, where low-temperature combustion is performed.

That is, in step 503, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 504, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG.
The opening of the EGR control valve 23 is set as the target opening SE.
Next, at step 505 NO _x releasing flag whether it is set or not. When the NO _x release flag is not set, the routine proceeds to step 506, where FIG.
The fuel injection is performed so that the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.

Next, at step 507, the electric heater 52
Is turned on. Electric heater 5
If No. 2 is not turned on, the process proceeds to step 509, and based on the output signal of the pressure difference detection sensor 53, the pressure difference ΔP between the upstream pressure and the downstream pressure of the particulate filter is determined by the predetermined pressure difference. It is determined whether or not it has become larger than ΔP ₀ . When ΔP ≦ ΔP ₀ , the processing cycle is completed.

[0096] Step 50 when the _the NO _x releasing flag is judged as being set in step 505
Proceeding to 8, the injection control for enriching the average air-fuel ratio in the combustion chamber 5 is performed. In this case NO _x is released from the NO _x absorbent 20. In step 509, Δ
Step 510 when it is determined that becomes P> P ₀
It is determined whether or not the low-temperature combustion has been continuously performed for a predetermined time or more. When the low-temperature combustion has been continuously performed for a predetermined time or more, the process proceeds to step 511, and a process of turning on the electric heater 42 for a predetermined time is performed. At this time, combustion of soot and the like collected by the particulate filter is started.

On the other hand, at step 501, L> X
When it is determined that (N) has been reached, the routine proceeds to step 502, where the flag I is reset.
And the second combustion is performed. That is, step 514
In FIG. 14A, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 14A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 515, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG. 14B, and the opening of the EGR control valve 23 is set to the target opening SE. Next, at step 516, it is determined whether or not the NO _x release flag is set. NO
Step 5 when the _x release flag is not set
Proceeding to 17, fuel injection is performed so as to attain the air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.

On the other hand, when it is determined in step 516 that the NO _x release flag is set, the routine proceeds to step 518, in which additional fuel is supplied so that the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 20 becomes rich. It is injected in the latter half of the expansion stroke or during the exhaust stroke. In this case NO _x is released from the NO _x absorbent 20. When the flag I is reset, the process proceeds from step 500 to step 512 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). When L ≧ Y (N), the routine proceeds to step 514, where the second air-fuel ratio is determined under the lean air-fuel ratio.
Is performed.

On the other hand, at step 512, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 513, where the flag I is set. Then step 503
And the low-temperature combustion is performed.

[0100]

The soot can be prevented from being released into the atmosphere.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing fuel molecules.

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

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

FIG. 7 is a diagram showing changes in an average gas temperature Tg in a combustion chamber, and changes in fuel and a gas temperature Tf around the fuel.

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 in the second combustion.

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

FIG. 15 is a diagram showing a temperature Ta of exhaust gas flowing into a catalyst and catalyst bed temperatures Tb and Tc.

FIG. 16 is a view for explaining the NO _x absorption / release action.

FIG. 17 is a diagram showing a map of the NO _x absorption amount per unit time.

FIG. 18 is a flowchart for processing a NO _x release flag.

FIG. 19 is a flowchart for controlling operation of the engine.

FIG. 20 is an overall view showing another embodiment of the compression ignition type internal combustion engine.

FIG. 21 is an overall view showing still another embodiment of the compression ignition type internal combustion engine.

FIG. 22 is a flowchart for controlling a rich flag.

FIG. 23 is a flowchart showing another embodiment for controlling the operation of the engine.

FIG. 24 is an overall view showing still another embodiment of the compression ignition type internal combustion engine.

FIG. 25 is a flowchart showing still another embodiment for controlling the operation of the engine.

[Explanation of symbols]

6 ... fuel injection valve 16 ... throttle valve 19 ... soot trapping device 20 ... NO _x absorbent

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 21/08 ZAB F02D 21/08 ZAB 301 301H 43/00 ZAB 43/00 ZAB 301 301N 301H 301T 45/00 ZAB 45/00 ZAB 301 301F F02M 25/07 ZAB F02M 25/07 ZAB 550 550F 550A 550G (72) Inventor Nobumoto Ohashi 1st Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kazuhiro Ito Toyota City Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Yoshi ▲ zaki Koji 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd.

Claims (10)

[Claims] When the amount of inert gas in the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak. When the amount of inert gas in the combustion chamber further increases, the amount of soot generated during combustion in the combustion chamber increases. In a compression ignition type internal combustion engine in which the temperature of the fuel and the surrounding gas is lower than the soot generation temperature and soot is hardly generated, a soot collecting device for collecting soot is disposed in the engine exhaust passage. The first combustion in which the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot is peaked and little soot is generated, and the combustion is more than the amount of inert gas at which the amount of soot is peaked A compression ignition type internal combustion engine having a switching means for selectively switching between a second combustion in which the amount of inert gas in a room is small. 2. The compression ignition type internal combustion engine according to claim 1, wherein a catalyst having an oxidizing function is disposed in the engine exhaust passage. 3. The compression ignition type internal combustion engine according to claim 1, wherein said soot collecting device comprises a particulate filter. 4. The air-fuel ratio in the combustion chamber is made rich when the first combustion is being performed when the temperature of the particulate filter exceeds a predetermined temperature. Compression ignition type internal combustion engine. 5. A heating means for heating the particulate filter, wherein the heating means is used when the first combustion is performed when burning the particulates collected by the particulate filter. 4. The compression ignition type internal combustion engine according to claim 3, wherein the particulate filter is heated by the following. 6. An exhaust gas having a lean air-fuel ratio.
NO contained in exhaust gas_xAbsorbs and flows in
When the air-fuel ratio of exhaust gas becomes stoichiometric or rich.
NO collected_xReleases NO_xAbsorbent for soot collection device
The first combustion is performed in a downstream engine exhaust passage.
NO when being_xNO from absorbent _xShould be released
The air-fuel ratio in the combustion chamber
2. The compression ignition type according to claim 1, wherein
Internal combustion engine. 7. When the second combustion is being performed, N
O_xNO from absorbent _xShould be released during the expansion stroke
Injecting additional fuel during the second half or during the exhaust stroke and NO_xabsorption
The air-fuel ratio of exhaust gas flowing into the agent is stoichiometric or rich.
7. A compression ignition type internal combustion engine according to claim 6, wherein:
Seki. 8. The compression ignition type internal combustion engine according to claim 1, further comprising a recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises recirculated exhaust gas. organ. 9. The compression ignition type internal combustion engine according to claim 8, wherein the exhaust gas recirculation rate in the first combustion state is approximately 55% or more. 10. An engine operating region is divided into a first operating region on a low load side and a second operating region on a high load side, and a first combustion is performed in the first operating region, and a second operation is performed. Second in the area
2. The compression ignition type internal combustion engine according to claim 1, wherein the combustion is performed.