JP2000130248A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure such proper combustion that the change of an operating state does not cause smoke or poor combustion. SOLUTION: A first combustion having more EGR gas amount in a combustion room 5 than EGR gas amount in which the generation amount of a soot becomes peek and in which the soot is scarcely generated and a second combustion having less EGR gas amount in the combustion room 5 than EGR gas amount in which the generation of the soot becomes peek are carried out selectively. The oxygen density in a re-circulation exhaust gas supplied in an engine suction passage is estimated and at least one side of the air fuel ratio or re- circulation exhaust gas ratio is controlled to a target value based on the oxygen density in the estimated re-circulation exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an 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 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 a conventional diesel engine, the EGR rate is at most 3
It is reduced from 0% to about 50%.

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 set so that the amount of _x and smoke generated was as small as possible. However, in this way EGR
Rate that there is a limit to the reduction of the NO _x and the amount of generated NO _x and the amount of smoke produced also defined to be as small as possible of smoke, in fact still a significant amount of N
At present, O _x and smoke are 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 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. An internal combustion engine employing this new combustion system has already been filed by the present applicant (Japanese Patent Application No. 9-305850).

[0009]

However, in order to perform good combustion under this new combustion, the air-fuel ratio and EG
There is an optimum value for the R ratio according to the engine operating state. Therefore, under this new combustion, when the engine operating state changes, the air-fuel ratio and the EGR rate are optimized according to the engine operating state. It is necessary to control the air-fuel ratio and the EGR rate to be high.

On the other hand, EGR supplied to the engine intake passage
The oxygen concentration in the gas has a large effect on the air-fuel ratio. That is, as the oxygen concentration in the EGR gas increases, the air-fuel ratio increases, and as the oxygen concentration in the EGR gas decreases, the air-fuel ratio decreases. As described above, when the operating state of the engine changes under new combustion, the optimum air-fuel ratio and EG
Even if the operating condition of the engine changes, the oxygen concentration in the EGR gas supplied into the engine intake passage does not change immediately, and the operating condition of the engine changes in the oxygen concentration in the EGR gas. It is the oxygen concentration in the previous engine operating state. Therefore, if the change in the oxygen concentration in the EGR gas is not taken into account when the operating state of the engine changes, the air-fuel ratio and the EGR rate deviate from the optimum air-fuel ratio and the EGR rate when the operating state of the engine changes. As a result, problems such as generation of smoke or poor combustion occur.

[0011]

In order to solve the above-mentioned problems, in the first invention, as the amount of recirculated exhaust gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and peaks. In the internal combustion engine, the recirculated exhaust gas is supplied into the engine intake passage and the amount of recirculated exhaust gas supplied to the combustion chamber is made larger than the amount of recirculated exhaust gas at which the generation amount of soot becomes a peak. Oxygen concentration estimating means for estimating the oxygen concentration in the recirculated exhaust gas supplied into the intake passage; and at least one of the air-fuel ratio or the recirculated exhaust gas rate based on the estimated oxygen concentration in the recirculated exhaust gas. And control means for controlling the target value to a target value.

[0012] In the second invention, in the first invention,
The oxygen concentration means detects the oxygen concentration in the exhaust gas in the engine exhaust passage, and estimates the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage based on the oxygen concentration. According to a third aspect, in the first aspect, a throttle valve is disposed in the engine intake passage,
The target opening of the throttle valve required to set the air-fuel ratio and the recirculated exhaust gas rate to target values according to the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage is stored in advance, The valve opening is controlled to this target opening.

In the fourth invention, in the third invention,
A target intake unit for detecting an air-fuel ratio and a recirculation exhaust gas rate according to an oxygen concentration in the recirculation exhaust gas supplied into the engine intake passage; The air amount is stored in advance, and the target opening of the throttle valve is corrected so that the detected intake air amount becomes the target intake air amount.

According to a fifth aspect, in the first aspect,
A recirculation exhaust gas control valve is disposed in the recirculation exhaust gas passage connecting the engine exhaust passage and the engine intake passage, and the air-fuel ratio is adjusted according to the oxygen concentration in the recirculation exhaust gas supplied into the engine intake passage. The target opening of the recirculation exhaust gas control valve necessary for setting the recirculation exhaust gas rate to the target value is stored in advance, and the recirculation exhaust gas control valve opening is controlled to this target opening.

In a sixth aspect, in the fifth aspect,
A detection means for detecting the amount of recirculated exhaust gas is provided, and necessary for setting the air-fuel ratio and the recirculated exhaust gas rate to target values according to the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage. The target recirculation exhaust gas amount is stored in advance, and the target opening of the recirculation exhaust gas control valve is corrected so that the detected recirculation exhaust gas amount becomes the target recirculation exhaust gas amount.

In a seventh aspect, in the fifth aspect,
It is provided with a detecting means for detecting the pressure in the engine intake passage, and is necessary for setting the air-fuel ratio and the recirculated exhaust gas rate to target values in accordance with the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage. The target pressure in the intake passage is stored in advance, and the target opening of the recirculation exhaust gas control valve is corrected so that the detected pressure in the intake passage becomes the target pressure.

In the eighth invention, in the fifth invention,
Detecting means for detecting the pressure in the combustion chamber at a predetermined crank angle during the compression stroke; and detecting the air-fuel ratio and the recirculated exhaust gas according to the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage. The target pressure in the combustion chamber at the above-described crank angle required to set the rate to the target value is stored in advance, and the recirculated exhaust gas is set so that the detected pressure in the combustion chamber at the above-described crank angle becomes the target pressure. The target opening of the control valve is corrected.

In the ninth invention, in the first invention,
A throttle valve is disposed in the engine intake passage, and a target opening of the throttle valve necessary for setting the air-fuel ratio to a target value is stored in advance, and the opening of the throttle valve is controlled to the target opening, and the estimated value is obtained. The target opening of the throttle valve is corrected based on the oxygen concentration in the recirculated exhaust gas so that the air-fuel ratio becomes the target air-fuel ratio.

According to a tenth aspect, in the ninth aspect, there is provided a calculating means for calculating the oxygen concentration in the burned gas when combustion is performed under the target air-fuel ratio, and the estimated recirculated exhaust gas is provided. When the oxygen concentration in the gas is higher than the oxygen concentration in the burned gas, the target opening of the throttle valve is corrected in a decreasing direction, and the estimated oxygen concentration in the recirculated exhaust gas is higher than the oxygen concentration in the burned gas. Is also low, the target opening of the throttle valve is corrected in the increasing direction.

According to an eleventh aspect, in the first aspect, a recirculation exhaust gas control valve is disposed in a recirculation exhaust gas passage connecting the engine exhaust passage and the engine intake passage, and the air-fuel ratio is set to a target value. The required opening degree of the recirculation exhaust gas control valve is stored in advance, and the opening degree of the recirculation exhaust gas control valve is controlled to this target opening degree. Based on this, the target opening of the recirculation exhaust gas control valve is corrected so that the air-fuel ratio becomes the target air-fuel ratio.

In a twelfth aspect based on the eleventh aspect, there is provided a calculating means for calculating an oxygen concentration in the burned gas when the combustion is performed under the target air-fuel ratio, and the estimated recirculated exhaust gas is provided. When the oxygen concentration in the gas is higher than the oxygen concentration in the burned gas, the target opening of the recirculation exhaust gas control valve is corrected in the increasing direction, and the estimated oxygen concentration in the recirculation exhaust gas is When the oxygen concentration is lower than the target oxygen concentration, the target opening of the recirculation exhaust gas control valve is corrected in a decreasing direction.

In a thirteenth aspect based on the first aspect, the exhaust gas recirculation rate is approximately 55% or more. According to a fourteenth aspect, in the first aspect, a catalyst having an oxidation function is disposed in the engine exhaust passage. Fifteen
Th In the invention in 14 th invention, the catalyst consists of one at least of the oxidation catalyst, three-way catalyst or _the NO _x absorbent.

In a sixteenth aspect based on the first aspect, in the first aspect, the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas at which the generation amount of soot reaches a peak, and soot is hardly generated. There is provided switching means for selectively switching between combustion and second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of recirculated gas at which the amount of generated soot becomes a peak.

In a seventeenth aspect based on the sixteenth aspect, the operating range of the engine is divided into a first operating range on the low load side and a second operating range on the high load side. Is performed, and the second combustion is performed in the second operation region.

[0025]

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 11, and the surge tank 12 is connected to an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Compressor 16
Is connected to an air cleaner 18 via an air suction pipe 17. On the other hand, the exhaust port 10 is the exhaust manifold 1
9 through the exhaust turbine 2 of the exhaust turbocharger
0, and the outlet of the exhaust turbine 20 is connected via an exhaust pipe 21 to a casing 23 containing a catalyst 22 having an oxidizing function.

A step motor 24 is provided in the intake duct 13.
Is disposed. The exhaust manifold 19 and the surge tank 12 are connected to the EGR passage 27.
And an EGR control valve 29 driven by a step motor 28 is disposed in the EGR passage 27. In addition, around the EGR passage 27, the EGR passage 27
A cooling device 30 for cooling the EGR gas flowing therein is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 30, 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 32, via a fuel supply pipe 31. Fuel is supplied to the common rail 32 from an electrically controlled fuel pump 33 of variable discharge amount, and the fuel supplied to the common rail 32 is supplied to the fuel injection valve 6 via each fuel supply pipe 31. A fuel pressure sensor 34 for detecting the fuel pressure in the common rail 32 is attached to the common rail 32. Based on an output signal of the fuel pressure sensor 34, a fuel pump 33 is provided so that the fuel pressure in the common rail 32 becomes a target fuel pressure. Is controlled.

The electronic control unit 40 is composed of a digital computer, and has 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 fuel pressure sensor 34 is input to the input port 45 via the corresponding AD converter 47. A temperature sensor 35 for detecting the temperature of the intake gas supplied into the combustion chamber 5 is disposed in the intake branch pipe 11.
5 is input to the input port 45 through the corresponding AD converter 47. Pressure sensors 36 and 37 are disposed in the surge tank 12 and the EGR passage 27 upstream of the EGR control valve 29, respectively.
The output signals 6 and 37 are input to the input port 45 via the corresponding AD converter 47.

On the other hand, a mass flow meter 38 for detecting a mass flow rate of intake air is disposed in the air suction pipe 17, and a pressure sensor 39 for detecting a pressure in the combustion chamber 5 is provided in the combustion chamber 5. Is arranged. The output signals of the mass flow meter 38 and the pressure sensor 39 are supplied to the corresponding AD converters 47, respectively.
Through the input port 45. An opening sensor 29a for detecting the opening of the EGR control valve 29 is attached to the EGR control valve 29.
Are input to the input port 45 via the corresponding AD converter 47.

The accelerator pedal 50 includes an accelerator pedal 5
A load sensor 51 that generates an output voltage proportional to the depression amount L of 0 is connected, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle motor control step motor 24, the EGR control valve control step motor 28, and the fuel pump 33 via the corresponding drive circuit 48.

FIG. 2 shows the throttle valve 2 when the engine is under low load operation.
5 and the opening degree of the air-fuel ratio A / F by changing the EGR rate change in the output torque when changing the (horizontal axis in FIG. 2), and smoke, HC, CO, a change in emission of the NO _x It shows the experimental example shown. As can be seen from FIG. 2, 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. 2, when the air-fuel ratio A / F is reduced by increasing the EGR ratio, the smoke is reduced when the EGR ratio 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. 3 (A) shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest, and FIG. 3 (B) shows the air-fuel ratio A / F. The graph shows the change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. As can be seen by comparing FIG. 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, HC and CO are reduced 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. .

Summarizing these considerations based on the experimental results shown in FIGS. 2 and 3, when the combustion temperature in the combustion chamber 5 is low, the amount of soot generation becomes almost zero, and at this time, the precursor of soot or 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.

The temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, ie, the above-mentioned certain temperature, depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although 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 the soot is produced, the soot is a post-treatment using a catalyst having an oxidizing function and cannot be purified. 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.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 are set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel 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 soot is generated, 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 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. 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 a mixture 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 50% 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.

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

On the other hand, in the load zone Z2 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, even if the air amount is smaller than the air amount shown in FIG. , i.e. even if the air-fuel ratio to the rich can the generation amount of the NO _x while preventing generation of soot in 10p.pm longitudinal or less,
In addition, even if the air amount is larger than the air amount shown in FIG. 6 in the low load region Z1 shown in FIG. the generation amount of NO _x 10 ppm can be around or less.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excess fuel does not grow to soot, and soot is generated. There is no. 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, regardless of 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 during 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 calorific value due to 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 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 is peaked. Say that.

FIG. 7 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second operation region II in which the second combustion, that is, combustion by the conventional combustion method, is performed. I have. In FIG. 7, the vertical axis TQ indicates the required torque, and the horizontal axis N indicates the engine speed. In FIG. 7, X (N) represents a first operation region I and a second operation region II.
, And Y (N) indicates a second boundary between the first operation region I and the second operation region II.
The determination of the change of the operating region from the first operating region I to the second operating region II is made based on the first boundary X (N),
Of the operating range from the operating range II to the first operating range I is determined based on the second boundary Y (N).

That is, when the operating state of the engine is in the first operating region I
The required torque TQ when low-temperature combustion is being performed
Exceeds the first boundary X (N) which is a function of the engine speed N, it is determined that the operating region has shifted to the second operating region II,
Combustion is performed by a conventional combustion method. Next, a second boundary Y (N) in which the required torque TQ is a function of the engine speed N
If it becomes lower than this, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again.

The two boundaries of the first boundary X (N) and the second boundary Y (N) on the lower torque side than the first boundary X (N) are provided as follows. For three reasons. The first reason is that the combustion temperature is relatively high on the high torque side of the second operating region II, and at this time, the required torque TQ
This is because even if the temperature becomes lower than (N), low-temperature combustion cannot be performed immediately. That is, the low-temperature combustion does not immediately start unless the required torque TQ becomes considerably low, that is, when the required torque TQ becomes lower than the second boundary Y (N). The second reason is that the first operating region I and the second operating region II
This is because hysteresis is provided for a change in the operating region during the period.

By the way, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and instead, the unburned hydrocarbon is replaced by the precursor of soot or the state before the soot. It is discharged from the combustion chamber 5 in the form. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is favorably oxidized by the catalyst 22 having an oxidizing function. Catalyst 2
As 2, an oxidation catalyst, a three-way catalyst, or a NO _x absorbent can be used. _The NO _x absorbent absorbs NO _x when the mean air-fuel ratio in the combustion chamber 5 of the lean, the combustion chamber 5
The average air-fuel ratio in the internal has a function of releasing NO _x becomes rich.

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

In addition to the oxidation catalyst, the three-way catalyst and the NO
_{The x} absorbent also has an oxidizing function, so that a three-way catalyst and a NO _x absorbent can be used as the catalyst 22 as described above. 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. 8 shows the opening degree of the throttle valve 25, the opening degree of the EGR control valve 29, the EGR rate, the air-fuel ratio, the injection timing and the injection amount with respect to the required torque TQ. As shown in FIG. 8, in the first operating region I where the required torque TQ is low, the opening of the throttle valve 25 is gradually increased from almost fully closed to about 2/3 as the required torque TQ increases. The degree of opening of the EGR control valve 29 is gradually increased from almost fully closed to fully open as the required torque TQ increases. Further, in the example shown in FIG.
In this example, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

In other words, in the first operating region I, the EGR
The opening of the throttle valve 25 and the opening of the EGR control valve 29 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes late as the required torque TQ increases, and the injection completion timing θE
Is also delayed as the injection start timing θS is delayed.

During the idling operation, the throttle valve 25 is closed until the valve is almost fully closed. At this time, the EGR control valve 29 is also closed almost completely. Throttle valve 2
When the valve 5 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 25 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating region of the engine is the first operating region I
From the second operation region II, the opening of the throttle valve 25 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 8, 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 jumps over the rate range (Fig. 5).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operation region II, the second combustion, that is, 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 FIG. 8 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise. In the second operation region II, the throttle valve 25 is maintained in a fully open state except for a part, and the opening of the EGR control valve 29 is gradually reduced as the required torque TQ increases. In addition, this operation area II
In this case, the EGR rate decreases as the required torque TQ increases, and the air-fuel ratio decreases as the required torque TQ increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required torque TQ increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 9A shows the relationship among the required torque TQ, the depression amount L of the accelerator pedal 50, and the engine speed N. In FIG. 9A, each curve represents an equal torque curve, the curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves are TQ = a, TQ
The required torque gradually increases in the order of Q = b, TQ = c, and TQ = d. The required torque TQ shown in FIG.
As shown in (B), the ROM is previously stored in the form of a map as a function of the depression amount L of the accelerator pedal 50 and the engine speed N.
42. In the embodiment according to the present invention, FIG.
A required torque TQ according to the depression amount L of the accelerator pedal 50 and the engine speed N is first calculated from the map shown in FIG. 3B, and the target opening degree of the throttle valve 25 is calculated based on the required torque TQ. You.

FIG. 10A shows the target air-fuel ratio A / F in the first operation region I when the temperature of the intake gas supplied into the combustion chamber 5 is at the reference temperature T ₀ . FIG.
In (A), A / F = 15.5, A / F = 16, A
Each curve indicated by / F = 17 and A / F = 18 indicates a case where the target air-fuel ratio is 15.5, 16, 17, and 18, respectively. The target air-fuel ratio between the curves is determined by proportional distribution. Can be As shown in FIG. 10A, the first operation region I
In the first operating region I, the target air-fuel ratio becomes leaner as the required torque TQ becomes lower.
/ F is made lean.

That is, the lower the required torque TQ, the smaller the amount of heat generated by combustion. Therefore, as the required torque TQ decreases, low-temperature combustion can be performed even if the EGR rate is reduced. As the EGR rate decreases, the air-fuel ratio increases,
Therefore, as shown in FIG. 10A, the target air-fuel ratio A / F increases as the required torque TQ decreases. As the air-fuel ratio increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, as the required torque TQ decreases, the target air-fuel ratio A /
F is increased.

On the other hand, if the temperature of the intake gas supplied to the combustion chamber 5 rises, the temperature of the fuel and the surrounding gas during combustion rises. Need to be reduced. Therefore, in the embodiment according to the present invention, as shown in FIG. 10 (B), the correction coefficient K1 which gradually decreases as the temperature T of the intake gas supplied into the combustion chamber 5 rises increases.
The final target air-fuel ratio (= K1 · (A / F)) is obtained by multiplying the target air-fuel ratio A / F shown in (A).

On the other hand, at 11 (A), the target E when the temperature of the intake gas supplied into the combustion chamber 5 is at the reference temperature T _0.
The target EGR rate EG is shown as a function of the required torque TQ and the engine speed N in FIG.
It is stored in the ROM 42 in advance in the form of a map as shown in FIG. As described above, when the temperature of the intake gas supplied into the combustion chamber 5 rises, the temperature of fuel and the surrounding gas during combustion rises. At this time, the amount of heat absorbed by the EGR gas is increased to suppress the rise in combustion temperature. Preferably. Therefore, in the embodiment according to the present invention, as shown in FIG. 11 (B), the correction coefficient K gradually increases as the intake gas temperature T supplied into the combustion chamber 5 increases.
2 is multiplied by a target EGR rate EG shown in FIG. 11A to obtain a final target EGR rate (= K2 · EG).

When the steady operation is being performed under a certain first operation state, the air-fuel ratio is set to the target air-fuel ratio K1 ·
(A / F), and the EGR rate EG is set to the target EGR rate K2 · E.
The opening degree and EG of the throttle valve 25 required to obtain G
The opening of the R control valve 29 is determined to a certain constant value. At this time, the intake air amount and the EGR gas amount are also set to certain constant values. Further, at this time, the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is also fixed to a certain value. That is, at this time, the amount of oxygen supplied into the combustion chamber 5 is determined by the amount of oxygen contained in the intake air supplied into the combustion chamber 5 and the amount of E supplied into the combustion chamber 5.
It is the sum of the amount of oxygen contained in the GR gas, and the sum of these oxygen amounts is a value at which the air-fuel ratio becomes the target air-fuel ratio K1 · (A / F).

On the other hand, the first operating state and the target air-fuel ratio K1 ·
(A / F) and a second different EGR rate K2 · EG
The throttle valve 2 necessary for setting the air-fuel ratio to the target air-fuel ratio K1 · (A / F) and setting the EGR rate to the target EGR rate K2 · EG even when the steady operation is performed in the operation state of FIG.
5, the opening degree of the EGR control valve 29, the intake air amount, the EG
The R gas amount and the oxygen concentration in the EGR gas have certain constant values. However, these values are different from those in the first operation state.

Therefore, the air-fuel ratio is changed to the target air-fuel ratio K1 · (A /
F), and the target opening of the throttle valve 25 and the EGR control valve 29 necessary for setting the EGR rate to the target EGR rate EG.
If the target opening of the throttle valve 25 and the opening of the EGR control valve 29 are controlled to these target openings in advance, the air-fuel ratio becomes the target air-fuel ratio K1 · (A / F), and E
The GR rate becomes the target EGR rate K2 · EG. However, actually, the oxygen concentration in the EGR gas supplied into the combustion chamber 5 does not change immediately when the operating state of the engine changes, and as a result, the air-fuel ratio and the EGR rate become the target air-fuel ratio K1 · (A / F ) And the target EGR rate K2 · EG.

That is, for example, the target air-fuel ratio K1 · (A / F)
From the first operating state where the target air-fuel ratio K1 ·
It is assumed that the operation mode is switched to the second operation state having a relatively small (A / F). In this case, in the first operating state, the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is high because the target air-fuel ratio K1 · (A / F) is relatively large. Next, even if the state is switched from the first operating state to the second operating state, the oxygen concentration in the EGR gas supplied into the combustion chamber 5 does not immediately decrease, but remains high for a while. As a result, the air-fuel ratio becomes larger than the target air-fuel ratio K1 · (A / F), and thus, smoke is generated. Such generation of smoke becomes remarkable especially when switching from the second combustion to the first combustion, in which the target air-fuel ratio is greatly reduced.

On the other hand, the target air-fuel ratio K1 · (A / F)
When the operating state changes from the small operating state to the large operating state with the target air-fuel ratio K1 · (A / F), the air-fuel ratio becomes smaller than the target air-fuel ratio K1 · (A / F), resulting in poor combustion. Such poor combustion becomes particularly noticeable when switching from the first combustion to the second combustion, in which the target air-fuel ratio increases greatly.

Therefore, in the embodiment according to the present invention, the air-fuel ratio is set to the target air-fuel ratio K1 · (A / F) according to the oxygen concentration in the EGR gas supplied into the combustion chamber 5, and the EGR rate is set to the target EG.
The target opening of the throttle valve 25 and the target opening of the EGR control valve 29 necessary for obtaining the R rate EG are obtained in advance,
The opening of the throttle valve 25 and the opening of the EGR control valve 29 are controlled to target opening in accordance with the oxygen concentration in the EGR gas supplied into the combustion chamber 5.

More specifically, in the embodiment according to the present invention, when the temperature of the intake gas into the combustion chamber 5 is at the reference temperature T ₀ , the air-fuel ratio is set to the target air-fuel ratio A / F shown in FIG. The target opening ST of the throttle valve 25 required to set the rate to the target EGR rate EG shown in FIG. 11A is determined based on the required torque and the engine for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5. The target opening degree ST of the throttle valve 25 is obtained as a function of the required torque TQ and the engine speed N by an experiment in advance as a function of the engine speed.
To (D) are stored in the ROM 42 in advance. 12 (A), (B), (C),
(D) shows the case where the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, 14%, and 21%, respectively.

Further, in the embodiment according to the present invention, when the temperature of the intake gas into the combustion chamber 5 is at the temperature T ₁ (FIG. 10B), the air-fuel ratio is set to the target air-fuel ratio K1 · (A / F), and EGR is performed. Throttle valve 2 required to set the rate to the target EGR rate K2 · EG
The target opening ST of the throttle valve 25 is determined in advance as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5. ST is stored in the ROM 42 in advance in the form of a map shown in FIGS. 13A to 13D as a function of the required torque TQ and the engine speed N. 13 (A), (B), (C) and (D) show the combustion chamber 5
The oxygen concentrations in the EGR gas supplied to the inside are 0% and 7%, respectively.
%, 14%, and 21%.

That is, in the embodiment according to the present invention, the oxygen concentration in the EGR gas supplied into the combustion chamber 5 and the combustion chamber 5
The target opening degree ST of the throttle valve 25 in accordance with the temperature of the intake gas supplied to the inside is shown in FIGS.
It is calculated by interpolation from the maps shown in (A) to (D). Further, in the embodiment according to the present invention, when the temperature of the gas sucked into the combustion chamber 5 is at the reference temperature T ₀ , the air-fuel ratio is set to the target air-fuel ratio A / F shown in FIG. EGR control valve 2 required to achieve target EGR rate EG shown in)
The target opening SE of 9 is previously determined by experiment as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5.
The target opening SE of the R control valve 29 is stored in advance in the ROM 42 as a function of the required torque TQ and the engine speed N in the form of maps shown in FIGS. 14 (A), (B), (C) and (D) show the combustion chamber 5
The oxygen concentrations in the EGR gas supplied to the inside are 0% and 7%, respectively.
%, 14%, and 21%.

On the other hand, in the embodiment according to the present invention, when the temperature of the intake gas into the combustion chamber 5 is at the temperature T ₁ (FIG. 11B), the air-fuel ratio is set to the target air-fuel ratio K1 · (A / F), and EGR is performed. EGR control valve 2 required to set the rate to the target EGR rate K2 · EG
The target opening SE of 9 is previously determined by experiment as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5.
The target opening SE of the R control valve 29 is stored in advance in the ROM 42 as a function of the required torque TQ and the engine speed N in the form of maps shown in FIGS. 15 (A), (B), (C) and (D) show the combustion chamber 5
The oxygen concentrations in the EGR gas supplied to the inside are 0% and 7%, respectively.
%, 14%, and 21%.

That is, in the embodiment according to the present invention, the oxygen concentration in the EGR gas supplied into the combustion chamber 5 and the combustion chamber 5
The target opening SE of the EGR control valve 29 according to the temperature of the intake gas supplied to the inside of the pump is shown in FIGS.
It is calculated by interpolation from the maps shown in (A) to (D). Note that the target opening ST of the throttle valve 25 and EG
Only one of the target opening degrees SE of the R control valve 29 may be a function of the oxygen concentration in the EGR gas supplied into the combustion chamber 5.

At the time of low-temperature combustion, the opening of the throttle valve 25 is set to the target opening calculated from the maps shown in FIGS. 12 and 13, and the opening of the EGR control valve 29 is set to FIGS.
If the target calculated from the map shown in FIG. 3 is used, the air-fuel ratio can be changed to the target air-fuel ratio K1 · (A /
F), and the EGR rate becomes the target EGR rate K2 · EG. Therefore, in the embodiment according to the present invention, the opening degree of the throttle valve 25 and the opening degree of the EGR control valve 29 are respectively set to the target opening degree ST.
And SE.

When deposits adhere to the throttle valve 25 or the EGR control valve 29, the air-fuel ratio and the EGR rate deviate from the target air-fuel ratios K1 · (A / F) and K2 · EG. Therefore, in the embodiment according to the present invention, the target value GA of the intake air amount Ga and the target value GE of the EGR gas amount Ge are determined in advance, and the throttle is set so that the intake air amount Ga and the EGR amount Ge become the target values GA and GE, respectively. The target opening ST of the valve 25 and the target opening SE of the EGR control valve 29 are corrected.

That is, in the embodiment according to the present invention, when the temperature of the gas sucked into the combustion chamber 5 is at the reference temperature T ₀ , the air-fuel ratio is changed as shown in FIG.
The target air-fuel ratio A / F shown in FIG.
A target value GA of the amount of intake air necessary for obtaining the target EGR rate EG shown in FIG. 7A is a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5. The target value GA of the intake air amount is previously stored in the ROM 42 as a function of the required torque TQ and the engine speed N in the form of maps shown in FIGS. I have. Note that FIG.
(A), (B), (C), and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, and 14%, respectively.
% And 21%.

Further, in the embodiment according to the present invention, when the temperature of the intake gas into the combustion chamber 5 is at the temperature T ₁ (FIG. 10B), the air-fuel ratio is set to the target air-fuel ratio K1 · (A / F), and EGR is performed. The target value GA of the intake air amount necessary for setting the rate to the target EGR rate K2 · EG is determined in advance as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5. The target value GA of the intake air amount is obtained by an experiment and stored in the ROM 42 in advance in the form of a map shown in FIGS. 17A to 17D as a function of the required torque TQ and the engine speed N. . In addition, FIG.
(B), (C) and (D) show EG supplied into the combustion chamber 5.
Oxygen concentration in R gas is 0%, 7%, 14%, 21% respectively
Is shown.

That is, in the embodiment according to the present invention, the oxygen concentration in the EGR gas supplied into the combustion chamber 5 and the combustion chamber 5
The target value GA of the intake air amount according to the temperature of the intake gas supplied to the inside is calculated by interpolation from the maps shown in FIGS. 16 (A) to (D) and FIGS. 17 (A) to (D). Next, the calculated target value GA of the intake air amount and the mass flow meter 38
Is compared with the mass flow rate (hereinafter simply referred to as intake air amount) Ga of the intake air, and the actual intake air amount Ga
Is corrected to the target opening GA, the target opening ST of the throttle valve 25 is corrected.

Further, in the embodiment according to the present invention, when the temperature of the gas inhaled into the combustion chamber 5 is at the reference temperature T ₀ , the air-fuel ratio is changed as shown in FIG.
The target air-fuel ratio A / F shown in FIG.
EGR necessary for achieving the target EGR rate EG shown in FIG.
The target value GE of the gas amount is previously determined experimentally as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5.
The target value GE of the GR gas amount is stored in advance in the ROM 42 in the form of a map shown in FIGS. 18A to 18D as a function of the required torque TQ and the engine speed N. 18 (A), (B), (C), and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, and 1%, respectively.
The cases of 4% and 21% are shown.

In the embodiment according to the present invention, when the temperature of the intake gas into the combustion chamber 5 is at the temperature T ₁ (FIG. 11B), the air-fuel ratio is set to the target air-fuel ratio K1 · (A / F), and EGR is performed. The target value GE of the amount of EGR gas necessary for setting the rate to the target EGR rate K2 · EG is determined in advance as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5. This target value GE of the EGR gas amount is obtained by an experiment, and is stored in advance in the ROM 42 in the form of a map shown in FIGS. 19A to 19D as a function of the required torque TQ and the engine speed N. . Note that FIG.
(A), (B), (C), and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, and 14%, respectively.
% And 21%.

That is, in the embodiment according to the present invention, the oxygen concentration in the EGR gas supplied to the combustion chamber 5 and the combustion chamber 5
18 (A) to 18 (D) and FIG. 19 (A) show the target value GE of the EGR gas amount according to the temperature of the intake gas supplied to the inside.
To (D) by interpolation from the map shown in FIG. On the other hand, the actual EGR gas amount Ge is determined by the differential pressure ΔP across the EGR control valve 29 detected by the pressure sensors 36 and 37 and EG.
It is calculated from the effective flow area S of the R control valve 29 (Ge =
S · Square root of ΔP). The actual opening SE of the EGR control valve 29 is detected by the opening sensor 29a, and the effective flow area S is calculated from the relationship shown in FIG. 19 based on the opening SE.

Next, the target value G of the calculated EGR gas amount
E is compared with the actual flow rate Ge, and the target opening SE of the EGR control valve 29 is set so that the actual flow rate Ge becomes the target value GE.
Is corrected. FIG. 21A shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 21, A / F = 2
4, curves A / F = 35, A / F = 45 and A / F = 60 indicate target air-fuel ratios 24, 35, 45 and 60, respectively. FIG. 21B shows the target EGR rate EG when the second combustion is being performed. The target EGR rate EG is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N as shown in FIG. In the embodiment according to the present invention, E supplied to the combustion chamber 5 even at the time of the second combustion.
The target opening ST of the throttle valve 25 and the target opening SE of the EGR control valve 29 are determined based on the oxygen concentration in the GR gas, and these target openings ST and SE are determined by the intake air amount Ga,
The correction is made based on the EGR gas amount Ge.

Specifically, in the embodiment according to the present invention, the air-fuel ratio is set to the target air-fuel ratio A / F shown in FIG.
The target opening degree ST of the throttle valve 25 necessary for setting the R rate to the target EGR rate EG shown in FIG. The target opening degree ST of the throttle valve 25 is obtained in advance as a function of the engine speed by an experiment, as a function of the required torque TQ and the engine speed N in FIG.
They are stored in the ROM 42 in advance in the form of maps shown in (A) to (D). 22 (A), (B),
(C) and (D) show the cases where the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, 14%, and 21%, respectively.

Further, in the embodiment according to the present invention, E required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 21A and the EGR rate to the target EGR rate EG shown in FIG.
The target opening degree SE of the GR control valve 29 is previously determined by experiment as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5. Is stored in the ROM 42 in advance in the form of maps shown in FIGS. 23A to 23D as a function of the required torque TQ and the engine speed N. 23 (A), (B), (C), (D)
Indicates a case where the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, 14%, and 21%, respectively.

Further, in the embodiment according to the present invention, intake air necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 21A and setting the EGR rate to the target EGR rate EG shown in FIG. EGR in which the target value GA of the air amount is supplied into the combustion chamber 5
The desired value GA of the intake air amount is determined in advance as a function of the required torque TQ and the engine speed N as a function of the required torque and the engine speed N as a function of the required torque and the engine speed for various oxygen concentrations in the gas. ) To (D) are stored in the ROM 42 in advance. 24 (A), (B), (C), and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, 1%, respectively.
The cases of 4% and 21% are shown.

Further, in the embodiment according to the present invention, E required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 21A and setting the EGR rate to the target EGR rate EG shown in FIG.
EG in which the target value GE of the GR gas amount is supplied into the combustion chamber 5
As a function of the required torque and the engine speed for various oxygen concentrations in the R gas, the target value EG of the EGR gas amount is determined in advance as a function of the required torque TQ and the engine speed N as shown in FIG. The information is stored in the ROM 42 in advance in the form of maps shown in FIGS. 25 (A), (B), (C) and (D) show the combustion chamber 5
The oxygen concentrations in the EGR gas supplied to the inside are 0% and 7%, respectively.
%, 14%, and 21%.

As described above, in the embodiment according to the present invention, the opening degree of the throttle valve 25 is controlled based on the oxygen concentration in the EGR gas supplied into the combustion chamber 5. Therefore, in order to control the opening degree of the throttle valve 25, it is necessary to detect, calculate, or estimate the oxygen concentration in the EGR gas. In the embodiment according to the present invention, the oxygen concentration in the EGR gas is estimated. Hereinafter, an example of a method for estimating the oxygen concentration in the EGR gas will be described.

The burned gas amount Wg (g / rev) discharged from the combustion chamber 5 per one revolution of the engine indicates the density of the fuel as ρ (g / m
m ³ ) is given by the following equation. Wg = intake air amount Ga (g / rev) + EGR gas amount Ge
(G / rev) + ρ · fuel injection amount Q (mm ³ / rev) On the other hand, if the EGR rate K2 · EG is used, the EGR gas amount Ge
Is expressed as follows.

Ge = Ga.K2.EG / (1-K2.E)
G) Accordingly, the burned gas amount Wg discharged from the combustion chamber 5 is expressed by the following equation. Wg = Ga + Ga.K2.EG / (1-K2.EG) +
ρ · Q On the other hand, assuming that the oxygen concentration in the EGR gas supplied to the surge tank 12 is OEGR, E supplied to the combustion chamber 5 is E
The oxygen amount Oe in the GR gas is represented by the following equation.

Oe = OEGR.Ge = OEGR.Ge.
K2 · EG / (1−K2 · EG) Also, the oxygen amount Oa in the intake air supplied into the combustion chamber 5
Is as follows. Oa = 0.21 · Ga On the other hand, the oxygen amount Ocon consumed by combustion in the combustion chamber 5 is expressed by the following equation.

Ocon = 0.21 · Theoretical air-fuel ratio · ρ · Q = 0.21 · 14.6 · ρ · Q = 3.1 · ρ · Q Therefore, oxygen in the burned gas discharged from the combustion chamber 5 Quantity Oe
x is represented as follows. Oex = Oe + Oa-Ocon = OEGR · Ga · K2
・ EG / (1-K2 ・ EG) +0.21 ・ Ga-3.1
· Ρ · Q Oxygen concentration in the exhaust gas in the exhaust port 10 OEX
Is the ratio of the oxygen amount Oex in the burned gas to the burned gas amount Wg, and this OEX is expressed by the following equation.

OEX = Oex / Wg (1) where Wg = Ga + Ga · K2 · EG / (1-K2 · EG) + ρ · Q (2) Oex = OEGR · Ga · K2 · EG / (1-K2 EG) + 0.2 / Ga-3.1 · ρ · Q (3) On the other hand, in the embodiment according to the present invention, the oxygen concentration O in the exhaust gas is
Using the EGR, the injection amount Q is determined such that the air-fuel ratio becomes the target air-fuel ratio K1 · (A / F). That is, the amount of oxygen supplied into the combustion chamber 5 becomes (Oe + Oa) as described above.

Therefore, the air-fuel ratio becomes equal to the target air-fuel ratio K1 · (A /
The injection quantity Q required to satisfy F) is as follows. (Oe + Oa) · (1 / 0.21) = K1 · (A / F) · ρ · Q Therefore, Q = (Oe + Oa) · (1 / 0.21) / [K1 · (A / F) · ρ] (4) Here, Oe + Oa = OEGR · Ga · K2 · EG / (1−K2 · EG) + 0.21 · Ga (5) Now, the operating state of the engine is determined by the above equations (4) and (5). And the correction coefficients K1 and K2, the target air-fuel ratio A / F and the target EGR rate EG, and the intake air amount Ga is detected by the mass flow meter 38. Therefore, if the oxygen concentration OEGR in the EGR gas is known, the injection amount Q is determined.

On the other hand, at this time, the oxygen concentration O in the EGR gas is
If the EGR is known, the target opening ST of the throttle valve 25 and the target opening SE of the EGR control valve 29 are determined. That is, E
If the oxygen concentration OEGR in the GR gas is known, the injection amount Q, the target opening ST of the throttle valve 25 and the EGR control valve 29
Is determined. By the way, combustion chamber 5
Part of the exhaust gas discharged from the exhaust manifold 19 into the exhaust manifold 19 flows into the EGR passage 27, and this exhaust gas, that is, EG
Each time the exhaust gas is discharged from the combustion chamber 5, the R gas is sequentially moved in the EGR passage 27 toward the surge tank 12. Therefore, after the exhaust gas flows into the EGR passage 27 and the engine rotates several times, the exhaust gas
The gas flows into the surge tank 12 as gas.
That is, the exhaust gas in the exhaust manifold 19 before the engine is rotated several times is supplied into the surge tank 12. In this case, assuming that the exhaust gas in the exhaust manifold 19 before the i-th rotation is supplied into the surge tank 12, the number i increases as the EGR gas amount Ge decreases.

In the embodiment according to the present invention, as shown in FIG. 26, the relationship between the number i and the EGR gas amount Ge is determined in advance by an experiment. From this relationship, the number i is determined based on the EGR gas amount Ge. Is required. In this case, the EGR gas amount Ge is, as described above, Ge = Ga · K2 · EG /
(1−K2 · EG). For example, now, EGR
Assuming that the gas amount is R in FIG.
Is 5. That is, the exhaust gas in the exhaust manifold 19 five rotations before is supplied into the surge tank 12. In other words, at this time, the oxygen concentration OEGR in the EGR gas supplied to the surge tank 12 becomes equal to the oxygen concentration of the exhaust gas in the exhaust manifold 19 five rotations before.

Here, when the oxygen concentration of the exhaust gas in the exhaust manifold 19 before the i-th rotation is represented by OEX (i), this OE
X (i) has already been calculated before i rotations using the above-described equations (1), (2), and (3). So this OEX
From (i), the oxygen concentration OEGR in the EGR gas supplied into the surge tank 12 can be calculated. FIG.
Shows a routine for estimating the oxygen concentration OEGR in the EGR gas supplied to the surge tank 12 and the oxygen concentration OEX in the exhaust gas in the exhaust manifold 19. This routine is executed when any of the cylinders has completed the exhaust stroke. Referring to FIG. 27, first, at step 100, the correction coefficient K2, the target EGR rate EG, and the intake air amount Ga in the current operating state of the engine are calculated from E to E.
The GR gas amount Ge is calculated, and the number i is calculated from the relationship shown in FIG. 26 based on the EGR gas amount Ge. Next, at step 101, the oxygen concentration OEX (i) in the exhaust gas in the exhaust manifold 19 before the i-th rotation is determined by the surge tank 1
The oxygen concentration OEGR in the EGR gas supplied to the inside 2 is set as OEGR.

Next, at step 102, the oxygen concentration O
The oxygen concentration OEX in the exhaust gas in the exhaust manifold 19 is calculated from the equations (1), (2), and (3) using the EGR. Next, in step 103, all stored OEX (i-1) are set as OEX (i), and the OEX calculated in step 102 is set as OEX (1).

Next, the operation control will be described with reference to FIG. Referring to FIG. 28, 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 torque TQ has become larger than the first boundary X1 (N). TQ ≦ X1 (N)
In the case of, the routine proceeds to step 203, where low-temperature combustion is performed.

That is, in step 203, the throttle valve 2
5 is performed. FIG. 29 shows a control routine of the throttle valve 25. Next, at step 204, the EGR control valve 29 is controlled. The control of the EGR control valve 29 is shown in FIG. Next, at step 205, the target air-fuel ratio K1 in the current engine operation state
(A / F), target EGR rate K2 · EG, intake air amount G
The injection amount Q is calculated from the above equations (4) and (5) based on a and the oxygen concentration OEGR in the EGR gas.

On the other hand, in step 201, TQ> 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 208
Then, the control of the throttle valve 25 is performed. The control routine for the throttle valve 25 is shown in FIG. Next, at step 209, the EGR control valve 29 is controlled. The control of the EGR control valve 29 is shown in FIG. Next, at step 210, the target air-fuel ratio K1 · (A / F) and the target EGR rate K2 ·
EG, intake air amount Ga, and oxygen concentration O in EGR gas
The injection amount Q is calculated from the above equations (4) and (5) based on the EGR.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 200 to step 206, where it is determined whether or not the required torque TQ has become lower than the second boundary Y (N). When TQ ≧ Y (N), the routine proceeds to step 208, where the second combustion is performed. On the other hand, when it is determined in step 206 that TQ <Y (N), the routine proceeds to step 207, where the flag I is set.
Next, the routine proceeds to step 203, where low-temperature combustion is performed.

Next, a control routine of the throttle valve 25 performed in step 203 of FIG. 28 will be described with reference to FIG. Referring to FIG. 29, first, in step 220, the target opening degree ST of the throttle valve 25 according to the oxygen concentration OEGR in the EGR gas is calculated from the maps shown in FIGS. Next, at step 221, the EGR is performed based on the maps shown in FIGS.
A target value GA of the intake air amount according to the oxygen concentration OEGR in the gas is calculated. Next, at step 222, the actual intake air amount Ga detected by the mass flow meter 38 is read.

Next, at step 223, it is determined whether or not the actual intake air amount Ga is larger than the target value GA of the intake air amount. If Ga> GA, the routine proceeds to step 224, where the correction value ΔST for the target opening of the throttle valve 25 is set.
The constant value α is subtracted from 1 and the routine proceeds to step 226. On the other hand, if Ga ≦ GA, step 225
Then, the constant value α is added to the correction value ΔST1, and then the process proceeds to step 226. In step 226, the correction value ΔST1 is added to the target opening ST of the throttle valve 25, so that the final target opening ST (=
ST + ΔST1) is calculated.

Next, a control routine of the EGR control valve 29 performed in step 204 of FIG. 28 will be described with reference to FIG. Referring to FIG. 30, first, at step 230, the target opening degree SE of the EGR control valve 29 according to the oxygen concentration OEGR in the EGR gas is calculated from the maps shown in FIGS. Next, at step 231, the EGR is performed based on the maps shown in FIGS. 18 and 19.
A target value GE of the EGR gas amount according to the oxygen concentration OEGR in the gas is calculated. Next, at step 232, the pressure P ₀ in the surge tank 12 detected by the pressure sensor 36 and the EG detected by the pressure sensor 37.
The pressure P ₁ in the R passage 27 is read.

[0110] Then the pressure difference ΔP between P ₁ and P ₀ at step 233 (= P ₁ -P ₀₎ is calculated. Next, at step 234, the EGR detected by the opening degree sensor 29a is detected.
Based on the opening degree SE of the control valve 29, the effective flow area S of the EGR control valve 29 is calculated from the relationship shown in FIG. Next, at step 235, the actual EGR gas amount Ge is calculated by multiplying the effective flow area S by the square root of the differential pressure ΔP.

Next, at step 236, it is determined whether or not the actual EGR gas amount Ge is larger than the target value GE of the EGR gas amount. If Ge> GE, step 237
To the correction value Δ for the target opening of the EGR control valve 29.
The constant value β is subtracted from SE1 and then step 239
Proceed to. On the other hand, when Ge ≦ GE, step 2
The routine proceeds to 38, where a fixed value β is added to the correction value ΔSE1, and then the routine proceeds to step 239. In step 239, EGR
By adding the correction value ΔSE1 to the target opening SE of the control valve 29, the final target opening SE of the EGR control valve 29 is obtained.
(= SE + ΔSE1) is calculated.

Next, a control routine of the throttle valve 25 performed in step 208 of FIG. 28 will be described with reference to FIG. Referring to FIG. 31, first, at step 250, the target opening degree ST of the throttle valve 25 according to the oxygen concentration OEGR in the EGR gas is calculated from the map shown in FIG. Next, at step 251, the oxygen concentration OEGR in the EGR gas is obtained from the map shown in FIG.
The target value GA of the amount of intake air according to is calculated. Next, at step 252, the actual intake air amount Ga detected by the mass flow meter 38 is read.

Next, at step 253, it is determined whether or not the actual intake air amount Ga is larger than the target value GA of the intake air amount. When Ga> GA, the routine proceeds to step 254, where the correction value ΔST for the target opening of the throttle valve 25 is set.
The constant value α is subtracted from 2 and then the routine proceeds to step 256. On the other hand, when Ga ≦ GA, step 255
Then, the fixed value α is added to the correction value ΔST2, and then the process proceeds to step 256. In step 256, the correction value ΔST1 is added to the target opening ST of the throttle valve 25, thereby obtaining the final target opening ST (=
ST + ΔST1) is calculated.

Next, a control routine of the EGR control valve 29 performed in step 209 of FIG. 28 will be described with reference to FIG. Referring to FIG. 32, first, in step 260, the target opening degree SE of the EGR control valve 29 according to the oxygen concentration OEGR in the EGR gas is calculated from the map shown in FIG. Next, at step 261, the oxygen concentration OEGR in the EGR gas is obtained from the map shown in FIG.
The target value GE of the EGR gas amount according to is calculated. Next, at step 262, the pressure P ₀ in the surge tank 12 detected by the pressure sensor 36 and the pressure sensor 3
The pressure P ₁ in the EGR passage 27, which is detected by 7 is read.

[0115] Then the pressure difference ΔP between P ₁ and P ₀ at step 263 (= P ₁ -P ₀₎ is calculated. Next, at step 264, the EGR detected by the opening sensor 29a
Based on the opening degree SE of the control valve 29, the effective flow area S of the EGR control valve 29 is calculated from the relationship shown in FIG. Next, at step 265, the actual EGR gas amount Ge is calculated by multiplying the effective flow area S by the square root of the differential pressure ΔP.

Next, at step 266, it is determined whether or not the actual EGR gas amount Ge is larger than the target value GE of the EGR gas amount. If Ge> GE, step 267
To the correction value Δ for the target opening of the EGR control valve 29.
The constant value β is subtracted from SE2, then step 269
Proceed to. On the other hand, when Ge ≦ GE, step 2
The routine proceeds to 68, where the fixed value β is added to the correction value ΔSE2, and then the routine proceeds to step 269. In step 269, EGR
By adding the correction value ΔSE1 to the target opening SE of the control valve 29, the final target opening SE of the EGR control valve 29 is obtained.
(= SE + ΔSE1) is calculated.

Next, another embodiment of the control of the EGR control valve 29 performed in steps 204 and 209 of FIG. 28 will be described. When the opening of the throttle valve 25 and the opening of the EGR control valve 29 are determined, the intake air amount, E
Not only the GR gas amount but also the pressure in the intake passage downstream of the throttle valve 25 is determined. Therefore, in this embodiment, the target pressure P in the intake passage according to the oxygen concentration OEGR in the EGR gas
M is obtained in advance, and the target opening SE of the EGR control valve 29 is set so that the pressure Pm in the intake passage becomes the target pressure PM.
Is corrected.

More specifically, in this embodiment, when the temperature of the gas taken into the combustion chamber 5 is at the reference temperature T ₀ , the air-fuel ratio is increased under the first combustion to the target air-fuel ratio shown in FIG. A / F, the target pressure PM in the surge tank 12 when the EGR rate is the target EGR rate EG shown in FIG. 11 (A), and various oxygen concentrations in the EGR gas supplied into the combustion chamber 5 The target pressure PM is determined in advance as a function of the required torque and the engine speed by experiments.
As a function of Q and the engine speed N, they are stored in the ROM 42 in advance in the form of maps shown in FIGS. 33 (A), (B), (C), (D)
Indicates a case where the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, 14%, and 21%, respectively.

In this embodiment, when the temperature of the gas sucked into the combustion chamber 5 is at the temperature T ₁ (FIG. 11B), the air-fuel ratio becomes the target air-fuel ratio K1 · A / under the first combustion. F and EG
The target pressure PM in the surge tank 12 when the R rate is set to the target EGR rate K2 · EG is supplied into the combustion chamber 5 E.
It has been previously determined experimentally as a function of the required torque and the engine speed for various oxygen concentrations in the GR gas,
The target pressure PM is equal to the required torque TQ and the engine speed N.
Are stored in the ROM 42 in advance in the form of maps shown in FIGS. Note that FIG.
(A), (B), (C), and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, and 14%, respectively.
% And 21%.

Further, in this embodiment, the air-fuel ratio under the second combustion is set to the target air-fuel ratio A / F shown in FIG.
The target pressure PM in the surge tank 12 when the EGR rate is set to the target EGR rate EG shown in FIG.
The target pressure PM is determined in advance as a function of the required torque and the engine speed N as a function of the required torque and the engine speed N as a function of the required torque and the engine speed for various oxygen concentrations in the EGR gas supplied into the engine. (A) to (D)
Are stored in the ROM 42 in advance in the form of a map shown in FIG. 35 (A), (B), (C) and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0, respectively.
%, 7%, 14%, and 21%.

Next, a control routine of the EGR control valve 29 performed in step 204 of FIG. 28 will be described with reference to FIG. Referring to FIG. 36, first, in step 300, the target opening degree SE of the EGR control valve 29 according to the oxygen concentration OEGR in the EGR gas is calculated from the maps shown in FIGS. Next, at step 301, the EGR is performed based on the maps shown in FIGS.
The target pressure PM in the surge tank 12 according to the oxygen concentration OEGR in the gas is calculated. Next, at step 302, the surge tank 1 detected by the pressure sensor 36 is detected.
The pressure Pm in 2 is read.

Next, at step 303, the surge tank 1
It is determined whether or not the actual pressure Pm in 2 is larger than the target pressure PM. Step 304 when Pm> PM
To the correction value Δ for the target opening of the EGR control valve 29.
The constant value β is subtracted from SE1.
Proceed to. On the other hand, when Pm ≦ PM, step 3
In step 05, a fixed value β is added to the correction value ΔSE1. In step 306, EGR
By adding the correction value ΔSE1 to the target opening SE of the control valve 29, the final target opening SE of the EGR control valve 29 is obtained.
(= SE + ΔSE1) is calculated.

Next, a control routine of the EGR control valve 29 performed in step 209 of FIG. 28 will be described with reference to FIG. Referring to FIG. 37, first, in step 310, the target opening degree SE of the EGR control valve 29 according to the oxygen concentration OEGR in the EGR gas is calculated from the map shown in FIG. Next, at step 311, the oxygen concentration OEGR in the EGR gas is obtained from the map shown in FIG.
The target pressure PM in the surge tank 12 according to the above is calculated. Next, at step 312, the pressure Pm in the surge tank 12 detected by the pressure sensor 36 is read.

Next, at step 313, the surge tank 1
It is determined whether or not the actual pressure Pm in 2 is larger than the target pressure PM. When Pm> PM, step 314
To the correction value Δ for the target opening of the EGR control valve 29.
The constant value β is subtracted from SE2, then step 316
Proceed to. On the other hand, when Pm ≦ PM, step 3
The routine proceeds to 15, where a fixed value β is added to the correction value ΔSE2, and then the routine proceeds to step 316. In step 316, EGR
By adding the correction value ΔSE2 to the target opening SE of the control valve 29, the final target opening SE of the EGR control valve 29 is obtained.
(= SE + ΔSE1) is calculated.

Next, still another embodiment of the control of the EGR control valve 29 performed in steps 204 and 209 of FIG. 28 will be described. As described above, when the opening of the throttle valve 25 and the opening of the EGR control valve 29 are determined, not only the intake air amount and the EGR gas amount but also the pressure in the intake passage downstream of the throttle valve 25 are determined. Further, at this time, the pressure Pc in the combustion chamber 5 at a predetermined crank angle during the compression stroke is also determined. Therefore, in this embodiment, the target pressure PC in the combustion chamber 5 according to the oxygen concentration OEGR in the EGR gas at a predetermined crank angle during the compression stroke.
Is determined in advance, and the target opening SE of the EGR control valve 29 is corrected so that the pressure Pc in the combustion chamber 5 at a predetermined crank angle in the compression stroke becomes the target pressure PC.

More specifically, in this embodiment, when the temperature of the gas inhaled into the combustion chamber 5 is at the reference temperature T ₀ , the air-fuel ratio under the first combustion is reduced to the target air-fuel ratio shown in FIG. K1 ・ (A
/ F), and the EGR rate is set to the target EG shown in FIG.
Target pressure P in combustion chamber 5 when R rate is K2 · EG
C is previously determined by experiment for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5 as a function of the required torque and the engine speed, and the target pressure PC is determined by the required torque TQ and the engine speed N. 38 as a function of
They are stored in the ROM 42 in advance in the form of maps shown in (A) to (D). 38 (A), (B),
(C) and (D) show the cases where the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, 14%, and 21%, respectively.

Further, in this embodiment, when the temperature of the gas sucked into the combustion chamber 5 is at the temperature T ₁ (FIG. 11B), the air-fuel ratio is changed to the target air-fuel ratio K1 · (A) under the first combustion. / F), and
EGR in which the target pressure PC in the combustion chamber 5 when the EGR rate is set to the target EGR rate K2 · EG is supplied into the combustion chamber 5
As a function of the required torque and the engine speed N for various oxygen concentrations in the gas, the target pressure PC is determined in advance by an experiment as a function of the required torque TQ and the engine speed N from FIG. ) Are stored in the ROM 42 in advance in the form of a map shown in FIG. Note that FIG.
(A), (B), (C), and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%, and 14%, respectively.
% And 21%.

Further, in this embodiment, under the second combustion, the air-fuel ratio is set to the target air-fuel ratio A / F shown in FIG.
When the EGR rate is set to the target EGR rate EG shown in FIG. 21 (B), the target pressure PC in the combustion chamber 5 and the required torque and engine for various oxygen concentrations in the EGR gas supplied into the combustion chamber 5 The target pressure PC is previously obtained by an experiment as a function of the rotational speed, and is stored in the ROM 42 in advance in the form of a map shown in FIGS. 40A to 40D as a function of the required torque TQ and the engine rotational speed N. ing. In addition,
40 (A), (B), (C) and (D) show that the oxygen concentration in the EGR gas supplied into the combustion chamber 5 is 0%, 7%,
14% and 21% are shown.

Next, a control routine of the EGR control valve 29 performed in step 204 of FIG. 28 will be described with reference to FIG. Referring to FIG. 41, first, at step 400, the target opening SE of the EGR control valve 29 according to the oxygen concentration OEGR in the EGR gas is calculated from the maps shown in FIGS. Next, at step 401, the EGR is performed based on the maps shown in FIGS.
A target pressure PC in the combustion chamber 5 according to the oxygen concentration OEGR in the gas is calculated. Next, at step 402, the pressure Pc in the combustion chamber 5 detected by the combustion pressure sensor 39 at a predetermined crank angle during the compression stroke is read.

Next, at step 403, it is determined whether or not the actual pressure Pc in the combustion chamber 5 is higher than the target pressure PC. When Pc> PC, the routine proceeds to step 404, where a fixed value β is subtracted from the correction value ΔSE1 for the target opening of the EGR control valve 29, and then the routine proceeds to step 406.
On the other hand, when Pc ≦ PC, the routine proceeds to step 405, where a fixed value β is added to the correction value ΔSE1, and then the routine proceeds to step 406. In step 406, the EGR control valve 2
9 by adding the correction value ΔSE1 to the target opening degree SE (= SE) of the EGR control valve 29.
+ ΔSE1) is calculated.

Next, a control routine of the EGR control valve 29 performed in step 209 of FIG. 28 will be described with reference to FIG. Referring to FIG. 42, first, at step 410, the target opening degree SE of the EGR control valve 29 according to the oxygen concentration OEGR in the EGR gas is calculated from the map shown in FIG. Next, at step 411, the oxygen concentration OEGR in the EGR gas is obtained from the map shown in FIG.
Is calculated according to the target pressure PC in the combustion chamber 5. Next, at step 412, the pressure Pc in the combustion chamber 5 detected by the combustion pressure sensor 39 at a predetermined crank angle during the compression stroke is read.

Next, at step 413, it is determined whether or not the actual pressure Pc in the combustion chamber 5 is higher than the target pressure PC. When Pc> PC, the routine proceeds to step 414, where a constant value β is subtracted from the correction value ΔSE2 for the target opening of the EGR control valve 29, and then the routine proceeds to step 416.
On the other hand, when Pc ≦ PC, the routine proceeds to step 415, where a fixed value β is added to the correction value ΔSE2, and then the routine proceeds to step 416. In step 416, the EGR control valve 2
9 by adding the correction value ΔSE2 to the target opening SE of the EGR control valve 29 (= SE).
+ ΔSE1) is calculated.

Next, a second embodiment according to the present invention will be described. FIG. 43 shows the first embodiment used in the second embodiment.
Shows the target air-fuel ratio A / F in the operation region I of FIG.
In FIG. 43, A / F = 15.5, A / F = 16, A
Each curve indicated by / F = 17 and A / F = 18 indicates a case where the target air-fuel ratio is 15.5, 16, 17, and 18, respectively. The target air-fuel ratio A / F is shown in FIG.
Is the same as the target air-fuel ratio A / F in the first embodiment shown in FIG.

In this embodiment, the air-fuel ratio is set as shown in FIG.
Throttle valve 25 required to achieve target air-fuel ratio shown in 3
As shown in FIG. 44A, the target opening ST is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N, and the air-fuel ratio is set to the target air-fuel ratio shown in FIG. The target opening SE of the EGR control valve 29 required for the above is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N as shown in FIG. As shown in FIG. 45A, the injection amount Q in the first operating region I is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N. Further, in this embodiment, the target opening ST of the throttle valve 25 and the EGR
The EGR rate EG is estimated based on the target opening SE of the control valve 29, and the estimated value EG of the EGR rate in the first operating region I is used as the target opening ST of the throttle valve 25 and the EGR.
The function of the target opening SE of the control valve 29 is stored in the ROM 42 in advance in the form of a map as shown in FIG.

FIG. 46 shows the target air-fuel ratio A / F in the second operating region II used in the second embodiment. In FIG. 46, A / F = 24, A / F =
Curves indicated by 35, A / F = 45, and A / F = 60 show when the target air-fuel ratios are 24, 35, 45, and 60, respectively. The target air-fuel ratio A / F is shown in FIG.
(A) Target air-fuel ratio A / F in the first embodiment shown in FIG.
Is the same as

In this embodiment, the air-fuel ratio is set as shown in FIG.
Throttle valve 25 necessary for achieving the target air-fuel ratio shown in FIG.
The target opening ST is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N as shown in FIG. 47B, the target opening SE of the EGR control valve 29 is stored in advance in the ROM 42 as a function of the required torque TQ and the engine speed N as shown in FIG. Also, as shown in FIG. 48A, the injection amount Q in the second operation region II is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N. Further, also in the second operating region II, the target opening degree ST of the throttle valve 25 is set.
EG based on the target opening SE of the EGR control valve 29 and
The R rate EG is estimated and this E in the second operating region II is calculated.
The estimated value EG of the GR rate is equal to the target opening ST of the throttle valve 25.
As a function of the target opening SE of the EGR control valve 29, a map as shown in FIG. 48B is stored in the ROM 42 in advance.

Also, in this embodiment, the above-described equations (1) and (1)
The oxygen concentration OEX in the exhaust gas in the exhaust port 10 is calculated using the following equation similar to (2) and (3). OEX = Oex / Wg (6) where Wg = Ga + Ga.EG / (1-EG) + ρ.Q (7) Oex = OEGR.Ga.EG / (1-EG) + 0.2 / Ga-3. 1 · ρ · Q (8) However, in this embodiment, the estimated value EG of the EGR rate shown in FIG. 45 (B) or FIG. 48 (B) is used as the target EGR rate EG, and FIG. (A) or the injection amount Q shown in FIG. 48 (A) is used.

Further, in this embodiment, the oxygen concentration OEGR in the EGR gas supplied to the surge tank 12 and the oxygen concentration OEX in the exhaust gas in the exhaust manifold 19 are calculated by the oxygen concentration estimation routine shown in FIG. You. This routine is also executed when any one of the cylinders completes the exhaust stroke, similarly to the routine shown in FIG.

That is, referring to FIG. 49, first, at step 500, the EG in the current operating state of the engine is set.
An EGR gas amount Ge (= Ga · EG / (1−EG)) is calculated from the estimated value EG of the R rate and the intake air amount Ga. Based on the EGR gas amount Ge, i is calculated from the relationship shown in FIG.
Is calculated. Next, at step 501, the oxygen concentration OEX in the exhaust gas in the exhaust manifold 19 before the i-th rotation.
(I) is the oxygen concentration OEGR in the EGR gas supplied into the surge tank 12.

Next, at step 102, the oxygen concentration O
The oxygen concentration OEX in the exhaust gas in the exhaust manifold 19 is calculated from the aforementioned equations (6), (7), and (8) using the EGR. Next, in step 503, all stored OEX (i-1) are set as OEX (i), and the OEX calculated in step 502 is set as OEX (1).

In the second embodiment, the air-fuel ratio is set to the target air-fuel ratio A / F based on the oxygen concentration OEGR in the EGR gas.
The opening of the throttle valve 25 and the opening of the EGR control valve 29 are controlled such that Therefore, a control method of the throttle valve 25 and the EGR control valve 29 in the second embodiment will be described next. Assuming that the air-fuel ratio is maintained at the target air-fuel ratio A / F, the oxygen concentration tO in the burned gas in the combustion chamber 5 can be calculated by the following equation.

TO = 0.21 · ρ · Q · Target air-fuel ratio (A / F) −0.21 · ρ · Q · Theoretical air-fuel ratio (A / F) _st = 0.21 · ρ · Q · [( (A / F)-(A / F) _st ] (9) At this time, the oxygen concentration OEGR in the EGR gas matches the calculated oxygen concentration tO in the burned gas. On the other hand, if the actual air-fuel ratio deviates from the target air-fuel ratio A / F, EGR
The oxygen concentration OEGR in the gas deviates from the oxygen concentration tO calculated based on the above equation (9),
If the oxygen concentration OEGR in the R gas does not match the oxygen concentration tO calculated based on the above equation (9), it means that the actual air-fuel ratio is not maintained at the target air-fuel ratio A / F.

That is, when the oxygen concentration OEGR in the EGR gas is higher than the oxygen concentration tO calculated based on the above equation (9), the actual air-fuel ratio is larger than the target air-fuel ratio A / F. At this time, as the difference between OEGR and Ot is larger, the deviation amount of the actual air-fuel ratio from the target air-fuel ratio A / F is larger. On the other hand, when the oxygen concentration OEGR in the EGR gas is lower than the oxygen concentration tO calculated based on the above equation (9), the actual air-fuel ratio becomes the target air-fuel ratio A /
F. At this time, the larger the difference between OEGR and Ot is, the larger the deviation of the actual air-fuel ratio from the target air-fuel ratio A / F is.

Therefore, in this embodiment, when the oxygen concentration difference ΔO (= OEGR−tO) between the oxygen concentration OEGR in the EGR gas and the oxygen concentration tO calculated based on the above equation (9) is positive, the air-fuel ratio The throttle valve 25 is closed and the EGR control valve 29 is opened in order to reduce the air pressure. Further, the closing amount of the throttle valve 25 and the opening amount of the EGR control valve 29 at this time are increased as the oxygen concentration difference ΔO increases. And EGR
An oxygen concentration difference ΔO (= OEGR−) between the oxygen concentration OEGR in the gas and the oxygen concentration tO calculated based on the above equation (9).
When tO) is negative, the throttle valve 25 is opened and the EGR control valve 29 is closed in order to increase the air-fuel ratio.
The valve closing amount of the control valve 29 is increased as the absolute value of the oxygen concentration difference ΔO increases.

More specifically, the correction value KST for the target opening ST of the throttle valve 25 is changed according to the oxygen concentration difference ΔO as shown in FIG. 50 (A), and the target opening SE of the EGR control valve 29 is changed. FIG. 50 shows the correction value KSE for
As shown in (B), it is changed according to the oxygen concentration difference ΔO. When the opening degree of the throttle valve 25 and the opening degree of the EGR control valve 29 are controlled based on the oxygen concentration difference ΔO, the oxygen concentration difference ΔO eventually becomes zero, and the actual air-fuel ratio becomes the target air-fuel ratio A / F. Matches.

Next, the operation control will be described with reference to FIG. Referring to FIG. 51, first, in step 6
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 60
The program proceeds to 1 to determine whether the required torque TQ has become larger than the first boundary X1 (N). TQ ≦ X1 (N)
In step 603, the routine proceeds to step 603, where low-temperature combustion is performed.

That is, in step 603, the target opening ST of the throttle valve 25 is calculated from the map shown in FIG. Next, at step 604, the target opening degree SE of the EGR control valve 29 is calculated from the map shown in FIG. Next, at step 605, the injection amount Q is calculated from the map shown in FIG. Next, at step 606, the oxygen concentration tO in the burned gas when the air-fuel ratio is equal to the target air-fuel ratio A / F is calculated by using the above-described equation (9). Next, at step 607, the oxygen concentration OEG in the EGR gas
The oxygen concentration difference ΔO (= OEGR-tO) is calculated by subtracting the oxygen concentration tO in the burned gas from R.

Next, at step 608, the oxygen concentration difference ΔO
Based on the relationship shown in FIG.
A correction value KST for the target opening ST of 5 is calculated.
Next, at step 609, the final target opening ST (= ST + KST) of the throttle valve 25 is calculated by adding the correction value KST to the target opening ST of the throttle valve 25. Next, at step 610, a correction value KSE for the target opening SE of the EGR control valve 29 is calculated from the relationship shown in FIG. 50 (B) based on the oxygen concentration difference ΔO. Next, at step 611, the target opening SE of the EGR control valve 29 is set.
Is added to the correction value KSE, the final target opening degree SE (= SE + KSE) of the EGR control valve 29 is calculated.

On the other hand, at step 601, TQ> X
When it is determined that (N) has been reached, the routine proceeds to step 602, where the flag I is reset.
And the second combustion is performed. That is, step 614
Then, the target opening degree ST of the throttle valve 25 is calculated from the map shown in FIG. Next, at step 615, the target opening degree SE of the EGR control valve 29 is calculated from the map shown in FIG. Next, in step 616, FIG.
The injection amount Q is calculated from the map shown in FIG. Next, at step 617, the oxygen concentration t in the burned gas when the air-fuel ratio is equal to the target air-fuel ratio A / F using the above-mentioned equation (9).
O is calculated. Next, at step 618, the oxygen concentration difference ΔO (= OEGR−t) is obtained by subtracting the oxygen concentration tO in the burned gas from the oxygen concentration OEGR in the EGR gas.
O) is calculated.

Next, at step 619, the oxygen concentration difference ΔO
Based on the relationship shown in FIG.
A correction value KST for the target opening ST of 5 is calculated.
Next, at step 620, the final target opening ST (= ST + KST) of the throttle valve 25 is calculated by adding the correction value KST to the target opening ST of the throttle valve 25. Next, at step 621, a correction value KSE for the target opening SE of the EGR control valve 29 is calculated from the relationship shown in FIG. 50B based on the oxygen concentration difference ΔO. Next, at step 622, the target opening SE of the EGR control valve 29 is set.
Is added to the correction value KSE, the final target opening degree SE (= SE + KSE) of the EGR control valve 29 is calculated.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 600 to step 612, where it is determined whether or not the required torque TQ has become lower than the second boundary Y (N). When TQ ≧ Y (N), the routine proceeds to step 614, where the second combustion is performed. On the other hand, when it is determined in step 612 that TQ <Y (N), the routine proceeds to step 613, where the flag I is set.
Next, the routine proceeds to step 603, where low-temperature combustion is performed.

[0152]

According to the present invention, good combustion can be ensured without generating smoke and without causing combustion failure even when the operating state of the engine changes.

[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 combustion molecules.

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

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

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

FIG. 8 is a view showing an opening degree of a throttle valve and the like.

FIG. 9 is a diagram showing a required torque.

FIG. 10 is a diagram showing a target air-fuel ratio in a first operation region I.

FIG. 11 is a diagram showing a target EGR rate in a first operation region I.

FIG. 12 is a view showing a map of a target opening of a throttle valve.

FIG. 13 is a view showing a map of a target opening of a throttle valve.

FIG. 14 is a view showing a map of a target opening of the EGR control valve.

FIG. 15 is a view showing a map of a target opening of the EGR control valve.

FIG. 16 is a diagram showing a map of a target value of the intake air amount.

FIG. 17 is a diagram showing a map of a target value of the intake air amount.

FIG. 18 is a view showing a map of a target value of the EGR gas amount.

FIG. 19 is a view showing a map of a target value of the EGR gas amount.

FIG. 20 is a diagram showing an effective flow area of the EGR control valve.

FIG. 21 shows a target air-fuel ratio and a target E in the second combustion.
It is a figure which shows a GR rate.

FIG. 22 is a view showing a map of a target opening of a throttle valve.

FIG. 23 is a view showing a map of a target opening of the EGR control valve.

FIG. 24 is a diagram showing a map of a target value of the intake air amount.

FIG. 25 is a view showing a map of a target value of the EGR gas amount.

FIG. 26 is a diagram showing a relationship between an EGR gas amount and the number of i.

FIG. 27 is a flowchart for estimating an oxygen concentration.

FIG. 28 is a flowchart for controlling operation of the engine.

FIG. 29 is a flowchart for controlling a throttle valve.

FIG. 30 is a flowchart for controlling an EGR control valve.

FIG. 31 is a flowchart for controlling a throttle valve.

FIG. 32 is a flowchart for controlling an EGR control valve.

FIG. 33 is a view showing a map of a target pressure in the intake passage.

FIG. 34 is a view showing a map of a target pressure in the intake passage.

FIG. 35 is a view showing a map of a target pressure in an intake passage.

FIG. 36 is a flowchart of another embodiment for controlling the EGR control valve.

FIG. 37 is a flowchart of another embodiment for controlling the EGR control valve.

FIG. 38 is a view showing a map of a target pressure in the combustion chamber.

FIG. 39 is a view showing a map of a target pressure in the combustion chamber.

FIG. 40 is a view showing a map of a target pressure in the combustion chamber.

FIG. 41 is a flowchart of yet another embodiment for controlling the EGR control valve.

FIG. 42 is a flowchart of yet another embodiment for controlling the EGR control valve.

FIG. 43 is a diagram showing a target air-fuel ratio in a first operation region I.

FIG. 44 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 45 is a diagram showing a map of an injection amount and the like.

FIG. 46 is a diagram showing a target air-fuel ratio in a second operation region II.

FIG. 47 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 48 is a view showing a map of an injection amount and the like.

FIG. 49 is a flowchart for estimating an oxygen concentration.

FIG. 50 is a diagram showing correction amounts for a throttle valve and an EGR control valve.

FIG. 51 is a flowchart for controlling operation of the engine.

[Explanation of symbols]

 6 Fuel injection valve 25 Throttle valve 29 EGR control valve

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 41/04 360 F02D 41/04 360Z 41/14 310 41/14 310E 310P 310C 320 320C 43/00 301 43/00 301N 301K 301E F02M 25/07 550 F02M 25/07 550F 570 570J 570D (72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Automobile Co., Ltd. (72) Inventor Yoshi ▲ Saki ▼ Koji Toyota 1 Toyota Town, Toyota City (72) Inventor Hiroki Murata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G062 AA01 BA02 BA06 CA07 CA08 DA01 DA02 EA10 FA04 FA05 FA06 GA00 GA01 GA02 GA04 GA06 GA17 3G084 AA01 BA05 BA09 BA20 CA03 CA04 DA05 DA10 EA11 EB09 EC03 EC04 FA07 FA10 FA11 FA21 FA29 FA33 FA38 3G091 HB05

Claims (17)

[Claims] When the amount of recirculated exhaust gas supplied to a combustion chamber is increased, the amount of soot generated gradually increases and the recirculated exhaust gas is supplied into an engine intake passage of an internal combustion engine that reaches a peak. At the same time, the amount of recirculated exhaust gas supplied into the combustion chamber is made larger than the amount of recirculated exhaust gas at which the generation amount of soot becomes a peak, and the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage is estimated. An internal combustion engine comprising: oxygen concentration estimation means; and control means for controlling at least one of an air-fuel ratio or a recirculation exhaust gas rate to a target value based on the estimated oxygen concentration in the recirculation exhaust gas. 2. The oxygen concentration means detects the oxygen concentration in the exhaust gas in the engine exhaust passage and estimates the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage based on the oxygen concentration. The internal combustion engine according to claim 1. 3. A throttle valve is disposed in an engine intake passage, and an air-fuel ratio and a recirculated exhaust gas ratio are set to target values in accordance with an oxygen concentration in recirculated exhaust gas supplied into the engine intake passage. The internal combustion engine according to claim 1, wherein a target opening of the throttle valve required for the engine is stored in advance, and the throttle valve opening is controlled to the target opening. 4. An air-fuel ratio and a recirculation exhaust gas rate are set to target values in accordance with an oxygen concentration in recirculation exhaust gas supplied into an engine intake passage. The internal combustion engine according to claim 3, wherein a target intake air amount required for the throttle valve is stored in advance, and the target opening of the throttle valve is corrected such that the detected intake air amount becomes the target intake air amount. 5. A recirculation exhaust gas control valve is disposed in a recirculation exhaust gas passage connecting the engine exhaust passage and the engine intake passage, and an oxygen concentration in the recirculation exhaust gas supplied into the engine intake passage. The target opening of the recirculation exhaust gas control valve required to set the air-fuel ratio and the recirculation exhaust gas rate to the target values in accordance with the predetermined value is stored in advance, and the recirculation exhaust gas control valve opening is set to the target opening. The internal combustion engine according to claim 1, which is controlled to: 6. A detecting means for detecting a recirculated exhaust gas amount, wherein an air-fuel ratio and a recirculated exhaust gas ratio are set to target values according to an oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage. The target amount of recirculation exhaust gas required to perform the operation is stored in advance, and the target opening of the recirculation exhaust gas control valve is corrected so that the detected amount of recirculation exhaust gas becomes the target amount of recirculation exhaust gas. The internal combustion engine according to claim 5. 7. An air-fuel ratio and a recirculation exhaust gas rate are set to target values according to an oxygen concentration in recirculation exhaust gas supplied into the engine intake passage. The target pressure in the intake passage required to perform the above operation is stored in advance, and the target opening of the recirculation exhaust gas control valve is corrected so that the detected pressure in the intake passage becomes the target pressure. 6. The internal combustion engine according to 5. 8. A detecting means for detecting pressure in a combustion chamber at a predetermined crank angle during a compression stroke,
The target pressure in the combustion chamber at the crank angle required to set the air-fuel ratio and the recirculated exhaust gas rate to target values in accordance with the oxygen concentration in the recirculated exhaust gas supplied into the engine intake passage is stored in advance. 6. The internal combustion engine according to claim 5, wherein the target opening of the recirculation exhaust gas control valve is corrected such that the pressure in the combustion chamber at the detected crank angle becomes the target pressure. 9. A throttle valve is disposed in an engine intake passage, and a target opening of the throttle valve required for setting an air-fuel ratio to a target value is stored in advance, and the opening of the throttle valve is set to the target opening. 2. The internal combustion engine according to claim 1, wherein the target opening of the throttle valve is corrected based on the estimated oxygen concentration in the recirculated exhaust gas so that the air-fuel ratio becomes the target air-fuel ratio. 10. A fuel supply system comprising: a calculating means for calculating an oxygen concentration in a burned gas when combustion is performed at a target air-fuel ratio, wherein the estimated oxygen concentration in the recirculated exhaust gas is calculated based on the burned gas. When the oxygen concentration in the gas is higher than the oxygen concentration, the target opening of the throttle valve is corrected in a decreasing direction. When the estimated oxygen concentration in the recirculated exhaust gas is lower than the oxygen concentration in the burned gas, the target opening of the throttle valve is adjusted. The internal combustion engine according to claim 9, wherein the opening is corrected in the increasing direction. 11. A recirculation exhaust gas control valve disposed in a recirculation exhaust gas passage connecting an engine exhaust passage and an engine intake passage, and required for setting an air-fuel ratio to a target value. The target opening is stored in advance and the opening of the recirculation exhaust gas control valve is controlled to the target opening, and the air-fuel ratio is set to the target air-fuel ratio based on the estimated oxygen concentration in the recirculation exhaust gas. 2. The internal combustion engine according to claim 1, wherein the target opening of the recirculation exhaust gas control valve is corrected so as to be as follows. 12. A combustion engine comprising: a calculating means for calculating an oxygen concentration in burned gas when combustion is performed at a target air-fuel ratio, wherein the estimated oxygen concentration in recirculated exhaust gas is calculated based on the burned gas. When the oxygen concentration in the gas is higher than the oxygen concentration in the gas, the target opening of the recirculation exhaust gas control valve is corrected in the increasing direction, and when the estimated oxygen concentration in the recirculation exhaust gas is lower than the oxygen concentration in the burned gas, The internal combustion engine according to claim 11, wherein the target opening of the recirculation exhaust gas control valve is corrected in a decreasing direction. 13. The internal combustion engine of claim 1, wherein the exhaust gas recirculation rate is greater than or equal to about 55 percent. 14. The internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is disposed in the engine exhaust passage. 15. The catalyst according to claim 1, wherein the catalyst is an oxidation catalyst, a three-way catalyst or NO.
15. The internal combustion engine of claim 14, comprising at least one of the _x absorbents. 16. The first combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is larger than the amount of recirculated exhaust gas at which the amount of generated soot is at a peak and little soot is generated, and the amount of generated soot is at a peak. 2. The internal combustion engine according to claim 1, further comprising a switching unit that selectively switches between a second combustion in which an amount of recirculated exhaust gas supplied to the combustion chamber is smaller than an amount of recirculated gas that becomes the second combustion. 17. 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
The internal combustion engine according to claim 16, wherein combustion of the internal combustion engine is performed.