JP3341683B2 - Internal combustion engine - Google Patents

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 when the EGR rate is increased to about 55% or more. It was found that it was almost zero, that is, almost no soot was generated. In this case, N
Generation amount of O _x is also found that a very small amount.
After that, the reason why no soot was generated was examined based on this finding, and as a result, unprecedented soot and NO
_This has led to the construction of a new combustion system capable of simultaneously reducing _x . This new combustion system will be described in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle stage until the hydrocarbons grow into soot.

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

Accordingly, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the fuel during combustion in the combustion chamber and its surroundings will not be generated. Can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system. 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, this new combustion system requires that the EGR rate be approximately 55% or more. However, it is possible to make the EGR rate approximately 55% or more when the intake air amount is relatively small, that is, when the engine load is relatively low. If the intake air amount exceeds a certain limit, the intake air will not be reduced unless the EGR rate is reduced. The amount of air cannot be increased. Therefore, when the intake air amount exceeds a certain limit, it is necessary to switch to the conventional combustion.

In this case, the combustion method is different between the new combustion and the conventional combustion. Therefore, different operation control is performed between the case of performing the new combustion and the case of performing the conventional combustion. Required. In other words, under the conventional combustion, in other words, when the combustion is performed with excess air, the amount of air is increased because there is sufficient air around the fuel. However, the generated torque of the engine does not increase, and it is necessary to increase the fuel injection amount in order to increase the generated torque of the engine. That is, to increase the output torque of the engine in response to the request when the required load increases, it is necessary to immediately increase the fuel injection amount, and the intake air amount for setting the air-fuel ratio to the target air-fuel ratio is required. It is sufficient that the adjustment be performed after the effect of increasing the fuel injection amount has been performed.

On the other hand, the situation is slightly different under new combustion. That is, new combustion is performed in a state where the EGR rate is high, and combustion is performed in a state where the amount of air around the fuel is small. In this case, even if the fuel injection amount is increased, the generated torque of the engine does not increase because there is not enough air to burn the increased fuel. However, in this case, when the amount of air increases, the amount of air around the fuel increases, so that combustion becomes active, and thus the torque generated by the engine increases. That is, in order to increase the engine output torque in response to the request when the required load increases under new combustion, it is necessary to immediately increase the air amount,
It is sufficient to adjust the fuel injection amount so that the air-fuel ratio becomes the target air-fuel ratio after the air amount increasing operation is performed.

As described above, under the new combustion, the torque generated by the engine is sensitive to the change in the air amount and insensitive to the change in the fuel injection amount. The torque generated by the engine is sensitive to changes in the fuel injection amount and insensitive to changes in the air amount. An object of the present invention is to perform optimal operation control according to the type of combustion.

[0013]

In order to achieve the above object, according to the first invention, as the amount of recirculated exhaust gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and peaks. And when the amount of recirculated exhaust gas supplied to the combustion chamber is further increased, the temperature of fuel and surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, and soot is hardly generated. In the internal combustion engine, 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 soot generated becomes a peak and little soot is generated, and the amount of generated soot becomes a peak Switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of recirculated gas, control means for controlling the amount of intake gas supplied to the combustion chamber, Supplied into the combustion chamber Detecting means for detecting the amount of intake air, wherein when the first combustion is performed, the amount of intake gas is controlled based on the required load and the engine speed, and based on the amount of intake air detected by the detecting means. Thus, the fuel injection amount is controlled.

That is, when the intake gas amount is controlled, the detected value of the intake air amount changes, and the fuel injection amount is controlled based on the changed detected value of the intake air amount. In other words, the control of the intake gas amount is performed prior to the control of the fuel injection amount. In a second aspect based on the first aspect, the control means includes a throttle valve for controlling an amount of intake air supplied to the combustion chamber, and a throttle valve for controlling an amount of recirculated exhaust gas recirculated into the combustion chamber. The target opening of the throttle valve according to the required load and the engine speed, and the target opening of the recirculation exhaust gas control valve according to the required load and the engine speed are stored in advance. When the first combustion is being performed, the opening of the throttle valve and the opening of the recirculation exhaust gas control valve are respectively set to the corresponding target opening.

In a third aspect, in the first aspect,
When the first combustion is being performed, the fuel injection amount is controlled based on the intake air amount detected by the detection means so that the air-fuel ratio becomes the target air-fuel ratio. In a fourth aspect based on the first aspect, when the second combustion is being performed, the fuel injection amount is controlled based on the required load and the engine speed, and the suction is performed based on the intake air amount detected by the detection means. The amount of gas is controlled.

In the fifth invention, in the fourth invention,
A target fuel injection amount corresponding to the required load and the engine speed is stored in advance, and the fuel injection amount is set as the target fuel injection amount during the second combustion. In a sixth aspect based on the fourth aspect, the control means includes a throttle valve for controlling an amount of intake air supplied to the combustion chamber and a throttle valve for controlling an amount of recirculated exhaust gas recirculated into the combustion chamber. A circulating exhaust gas control valve. When the second combustion is being performed, the throttle valve or the recirculating exhaust gas control valve is controlled so that the air-fuel ratio becomes the target air-fuel ratio based on the intake air amount detected by the detecting means. At least one of them is controlled.

In the seventh invention, in the first invention,
The exhaust gas recirculation rate when the first combustion is performed is approximately 55% or more, and the exhaust gas recirculation rate when the second combustion is performed is approximately 50% or less. In an eighth aspect based on the first aspect, a catalyst having an oxidation function is disposed in the engine exhaust passage.

In the ninth invention, in the eighth invention,
The catalyst is an oxidation catalyst, a three-way catalyst or NO _xAt least the absorbent
Consists of one. In the tenth invention, the first invention
The operating range of the engine is different from that of the first operating range on the low load side.
It is divided into a second operation area on the loading side, and the first operation area
1 is performed, and the second combustion is performed in the second operation region.
Like that.

[0019]

FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a supercharger, for example, an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Be linked. An inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17, and a throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17. The air suction pipe 17 upstream of the throttle valve 20
A mass flow detector 21 for detecting a mass flow rate of the intake air is disposed therein.

[0020] the other hand, the exhaust port 10 is exhaust manifold 2
The exhaust turbine 2 of the exhaust turbocharger 15 via the
3 and an outlet of the exhaust turbine 23 is connected via an exhaust pipe 24 to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function. Exhaust manifold 22
Inside, an air-fuel ratio sensor 27 is arranged. Exhaust pipe 28 connected to the outlet of catalytic converter 26 and throttle valve 2
The exhaust gas recirculation (hereinafter referred to as E)
(Referred to as GR) through a passage 29, and
E driven by a step motor 30 is provided in the passage 29.
A GR control valve 31 is provided. In the EGR passage 29, an intercooler 32 for cooling the EGR gas flowing in the EGR passage 29 is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.

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

The electronic control unit 40 is composed of a digital computer, and is connected to 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 mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the output signals of the air-fuel ratio sensor 27 and the fuel pressure sensor 36 are also input to the input port via the corresponding AD converter 47, respectively. 45 is input. A load sensor 51 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . Also,
The input port 45 has a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °.
Is connected. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 3 via the corresponding drive circuit 48.
0 and the fuel pump 35.

FIG. 2 shows the throttle valve 2 when the engine is operating at a low load.
Change in the output torque when changing the air-fuel ratio A / F (abscissa in FIG. 2) by changing the opening and the EGR rate of 0, 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 decreased by increasing the EGR rate, the smoke is reduced when the air-fuel ratio A / F becomes about 30 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 18 and the amount of generated smoke is the largest. FIG. 3 (B) shows the air-fuel ratio A / F. The graph shows a change in the combustion pressure in the combustion chamber 5 when F is around 13 and the amount of generated smoke is almost zero. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) where the amount of smoke generation is almost zero, FIG.
It can be seen that the combustion pressure is lower than in the case shown in (A).

The following can be said from the experimental results shown in FIGS. That is, first, the air-fuel ratio A / F is 1
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
As shown in ₍₁₎ , the generation amount of NOx is considerably reduced. N
That the generation amount of O _x produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 becomes low when the soot is hardly generated I can say. The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low.
The combustion temperature inside is low.

Second, when the amount of generated smoke, that is, the amount of generated soot becomes substantially zero, as shown in FIG.
Emissions increase. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot production process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of generated soot becomes substantially zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a precursor of soot or a hydrocarbon in a state before it. .

These considerations based on the experimental results shown in FIGS. 2 and 3 are summarized as follows. When the combustion temperature in the combustion chamber 5 is low, the amount of generated soot becomes almost zero. Is discharged from the combustion chamber 5. As a result of further detailed experimental study on this, if the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.

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

Once soot has been produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

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

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

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

In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the 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, as the specific heat of the inert gas increases, the endothermic effect becomes stronger. 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 amount of soot generation peaks at a position where the EGR rate is slightly lower than 50%. Above a percentage, little soot is generated. On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the soot generation amount reaches a peak at a point where the EGR rate is slightly higher than 50%. In this case, the EGR rate is increased to about 65% or more. If so, almost no soot is generated.

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

FIG. 6 shows the mixing of EGR gas and air necessary to make the fuel during combustion and the gas temperature around it 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.

Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is formed. The required minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate. In the embodiment shown in FIG.
0% or more. That is, the total intake gas amount sucked into the combustion chamber 5 is indicated by a solid line X in FIG. 6, and the ratio of the air amount to the EGR gas amount in the total intake gas amount X is shown in FIG.
When the ratio is as shown in the following, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is generated, and thus no soot is generated. Further, the NO _x generation amount at this time is around 10 p.pm or less.
The amount of O _x generated is extremely small.

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

When the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. Therefore, in FIG. 6, in the region where the required load is larger than Lo, the required load is reduced. As the ratio increases, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced. In other words, when the supercharging is not performed and the required air-fuel ratio is maintained at the stoichiometric air-fuel ratio in an area where the required load is larger than Lo, the EGR rate decreases as the required load increases, and In the region where the required load is larger than Lo, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.

However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 to the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15, the required load is larger than Lo. In EGR rate 5
It can be maintained at 5% or more, for example 70%, so that the temperature of the fuel and its surrounding gas can be kept below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which soot is generated, to the extent that the pressure can be increased by the compressor 16. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, E
The throttle valve 20 is opened when the GR control valve 31 is fully opened.
Is slightly closed.

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. 6, that is, the air-fuel ratio is made rich. 10p.p. the generation amount of the NO _x even while preventing generation of soot by
m or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. while the generation amount of the NO _x can be around or less 10 ppm.

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

As described above, when low-temperature combustion is performed, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. Sarezu, 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 lower than the temperature at which the growth of hydrocarbons stops halfway, only during the low load operation in the engine where the calorific value due to combustion is relatively small. Can be Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In addition, the second combustion, that is, the combustion that is usually performed conventionally, is performed during the high load operation of the engine. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been performed normally in the past, is a combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot 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 L indicates the amount of depression of the accelerator pedal 50, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 7, X (N) is the first
Shows the first boundary between the operating region I and the second operating region II, and Y (N) represents the first operating region I and the second operating region.
2 shows a second boundary with II. The determination of the change of the operation range from the first operation range I to the second operation range II is made based on the first boundary X (N), and the change from the second operation range II to the first operation range II is performed.
The determination of the change of the operation region to the operation region I of the second boundary Y
(N).

That is, when the operating state of the engine is in the first operating region I
When the required load L exceeds a first boundary X (N), which is a function of the engine speed N, during low-temperature combustion, it is determined that the operation region has shifted to the second operation region II, Combustion is performed by a conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again. Thus, the first boundary X
The two boundaries of (N) and the second boundary Y (N) on the load side lower than the first boundary X (N) are provided for the following two reasons. The first reason is that the combustion temperature is relatively high on the high load side of the second operation region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not immediately start unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is that the first operating region I and the second operating region
This is because hysteresis is provided for a change in the operating range between II.

By the way, when the operating region of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, but the unburned hydrocarbon is instead replaced by the precursor of soot or the state before it. It is discharged from the combustion chamber 5 in the form. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is oxidized well by the catalyst 25 having an oxidizing function. Catalyst 2
As 5, 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 25 as described above. FIG. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.

Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. FIG. 9 shows the throttle valve 2 with respect to the required load L.
0 indicates the opening degree, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount. As shown in FIG. 9, in the first operating region I where the required load L is low, the opening of the throttle valve 20 is gradually increased from almost fully closed to about 2/3 opening as the required load L increases. E
The degree of opening of the GR control valve 31 is gradually increased from almost fully closed to fully open as the required load L increases. Also,
In the example shown in FIG. 9, in the first operation region I, the EGR rate is set to approximately 70%, and the air-fuel ratio is set to a slightly lean air-fuel ratio.

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

During the idling operation, the throttle valve 20 is closed until the valve is almost fully closed. At this time, the EGR control valve 31 is also closed almost completely. Throttle valve 2
If the valve is closed close to 0, 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 20 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 operating region II to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 9, 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 operating region II, the conventional combustion is performed. In the second operating region II, the throttle valve 20 is held in a fully open state except for a part, and the opening of the EGR control valve 31 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 10A shows the target air-fuel ratio A / F in the first operation region I. In FIG. 10A, A / F = 15.5, A / F = 16, A / F = 17,
Each curve represented by A / F = 18 has a target air-fuel ratio of 1
5.5, 16, 17, and 18, and the air-fuel ratio between the curves is determined by proportional distribution. FIG.
As shown in (A), the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the target air-fuel ratio A / F becomes leaner as the required load L decreases.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low-temperature combustion can be performed even if the EGR rate is reduced as the required load L decreases.
When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 10A, as the required load L decreases, the target air-fuel ratio A / F increases. Target air-fuel ratio A /
As F 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, the target air-fuel ratio A / F is increased as the required load L decreases.

The target air-fuel ratio A / F shown in FIG. 10A is preliminarily stored in a ROM 4 as a function of the required load L and the engine speed N as shown in FIG.
2 is stored. Also, the throttle valve 2 required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
The target opening ST of 0 is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.
EGR required to achieve target air-fuel ratio A / F shown in (A)
As shown in FIG. 11B, the target opening SE of the control valve 31 is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.

FIG. 12A shows the target air-fuel ratio A when the second combustion, that is, ordinary combustion by the conventional combustion method is performed.
/ F. Note that A / F in FIG.
= 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios of 24, 35, 45, and 6, respectively.
0 is shown. The target air-fuel ratio A shown in FIG.
/ F is a function of the required load L and the engine speed N as shown in FIG.
Is stored within. Also, the throttle valve 20 required to set the air-fuel ratio to the target air-fuel ratio A / F 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 load L and the engine speed N as shown in FIG.
As shown in FIG. 13 (B), the target opening degree SE of the EGR control valve 31 required to obtain the target air-fuel ratio A / F shown in FIG. It is stored in the ROM 42.

When the second combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. Next, FIG.
The operation control will be described with reference to FIG.

Referring to FIG. 15, first, at step 100, it is determined whether a flag I indicating that the operating state of the engine is in the first operating region I is set or not. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, step 1
In step 01, it is determined whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 103, where low-temperature combustion is performed.

That is, in step 103, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to this target opening ST. Next, at step 104, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Next, at step 105, the mass flow rate of the intake air (hereinafter simply referred to as the intake air amount) Ga detected by the mass flow rate detector 21 is taken in. Next, at step 106, FIG.
The target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 107, based on the intake air amount Ga and the target air-fuel ratio A / F, a fuel injection amount Q necessary for setting the air-fuel ratio to the target air-fuel ratio A / F is calculated.

When the required load L or the engine speed N changes during the low-temperature combustion, the opening of the throttle valve 20 and the opening of the EGR control valve 31 immediately change to the required load L and the engine speed N. Target opening ST according to
Matched to SE. Therefore, for example, when the required load L is increased, the amount of air in the combustion chamber 5 is immediately increased, and the generated torque of the engine is immediately increased.

On the other hand, the opening degree of the throttle valve 20 or the EGR
When the opening degree of the control valve 31 changes and the intake air amount changes, the change in the intake air amount Ga is detected by the mass flow rate detector 21, and the fuel injection amount Q is controlled based on the detected intake air amount Ga. Is done. That is, the fuel injection amount Q is changed after the intake air amount Ga actually changes.

When it is determined in step 101 that L> X (N), the routine proceeds to step 102, where the flag I is reset. Then, the routine proceeds to step 110, where the second combustion is performed. That is, in step 110, FIG.
The target fuel injection amount Q is calculated from the map shown in FIG. Next, at step 111, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 112, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 13B, and the opening of the EGR control valve 31 is set as the target opening SE.

Next, at step 113, the intake air amount Ga detected by the mass flow detector 21 is taken. Next, at step 114, the fuel injection amount Q and the intake air amount Ga
From this, the actual air-fuel ratio (A / F) _R is calculated. Next, at step 115, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 116, it is determined whether or not the actual air-fuel ratio (A / F) _R is larger than the target air-fuel ratio A / F. (A / F) When _R > A / F, the routine proceeds to step 117, where the throttle opening correction value ΔS
T is reduced by a constant value α, then step 11
Go to 9. On the other hand, when (A / F) _R ≤A / F, the routine proceeds to step 118, where the correction value ΔST is increased by a constant value α, and then the routine proceeds to step 119. In step 119, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20, and the opening of the throttle valve 20 is set as the final target opening ST. That is, the opening of the throttle valve 20 is controlled so that the actual air-fuel ratio (A / F) _R becomes the target air-fuel ratio A / F.

When the required load L or the engine speed N changes during the second combustion, the fuel injection amount immediately matches the target fuel injection amount Q corresponding to the required load L and the engine speed N. I'm sullen. For example, the required load L
Is increased, the fuel injection amount is immediately increased, and thus the generated torque of the engine is immediately increased.

On the other hand, when the fuel injection amount Q is increased and the air-fuel ratio deviates from the target air-fuel ratio A / F, the opening of the throttle valve 20 is controlled so that the air-fuel ratio becomes the target air-fuel ratio A / F. That is, the air-fuel ratio is changed after the fuel injection amount Q changes. When the flag I is reset, in the next processing cycle, steps 100 to 10 are executed.
Proceeding to 8, it is determined whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the routine proceeds to step 110, where the second combustion is performed under a lean air-fuel ratio.

On the other hand, at step 108, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 109, where the flag I is set, and then proceeds to step 103 to perform low-temperature combustion. In the embodiments described above, the fuel injection amount Q is controlled by open loop when low-temperature combustion is being performed, and the air-fuel ratio changes the opening of the throttle valve 20 when second combustion is being performed. Is controlled by However, the fuel injection amount Q can be feedback-controlled based on the output signal of the air-fuel ratio sensor 27 when the low-temperature combustion is being performed, and the air-fuel ratio can be controlled by the EGR control when the second combustion is being performed. The control can also be performed by changing the opening of the valve 31.

FIG. 16 shows that the fuel injection amount Q is feedback-controlled based on the output signal of the air-fuel ratio sensor 27 during low-temperature combustion, and the air-fuel ratio is controlled during second combustion by controlling the opening of the EGR control valve 31. An embodiment is shown. Referring to FIG. 16, first, in step 200, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, step 2
In step 01, it is determined whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 203, where low-temperature combustion is performed.

That is, in step 203, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 204, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Next, at step 205, the target fuel injection amount Q is calculated. The target fuel injection amount Q is stored in the ROM 42 in advance as a function of the required load L and the engine speed N as shown in FIG.

Next, at step 206, the air-fuel ratio sensor 2
7, the actual air-fuel ratio (A / F) _R is calculated. Next, at step 207, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 208, the actual air-fuel ratio (A / F) _R is changed to the target air-fuel ratio A / F.
It is determined whether it is larger than F or not. (A / F) _R > A
If / F, the routine proceeds to step 209, where the correction value ΔQ of the fuel injection amount is increased by a constant value β, and then the routine proceeds to step 211. On the other hand, when (A / F) _R ≤A / F, the routine proceeds to step 210, where the correction value ΔQ is
And then go to step 211. In step 211, the final target fuel injection amount Q is calculated by adding the correction value ΔQ to the target fuel injection amount Q,
The fuel injection amount is set as the final target fuel injection amount Q.
That is, the fuel injection amount is controlled so that the actual air-fuel ratio (A / F) _R becomes the target air-fuel ratio A / F.

Also in this embodiment, when the required load L or the engine speed N changes during low-temperature combustion, the opening of the throttle valve 20 and the opening of the EGR control valve 31 immediately change to the required load L and the engine speed. The target opening degrees ST and SE according to N are made to coincide with each other. Therefore, for example, when the required load L is increased, the amount of air in the combustion chamber 5 is increased immediately, and the generated torque of the engine is immediately increased. In this embodiment, the fuel injection amount Q is changed after the air amount in the combustion chamber 5 changes.

On the other hand, in step 201, L> X
When it is determined that (N) has been reached, the routine proceeds to step 202, where the flag I is reset.
And the second combustion is performed. That is, step 214
In FIG. 14, the target fuel injection amount Q is calculated from the map shown in FIG. 14, and the fuel injection amount is used as the target fuel injection amount Q.
Next, at step 215, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 216, the map shown in FIG.
The target opening SE of the R control valve 31 is calculated.

Next, at step 217, the intake air amount Ga detected by the mass flow detector 21 is taken. Next, at step 218, the fuel injection amount Q and the intake air amount Ga
From this, the actual air-fuel ratio (A / F) _R is calculated. Next, at step 219, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 220, it is determined whether or not the actual air-fuel ratio (A / F) _R is larger than the target air-fuel ratio A / F. (A / F) When _R > A / F, the routine proceeds to step 221, where the EGR control valve opening correction value Δ
SE is increased by a constant value α, then step 2
Proceed to 23. On the other hand, when (A / F) _R ≦ A / F, the routine proceeds to step 222, where the correction value ΔSE is decreased by a constant value α, and then the routine proceeds to step 223. In step 223, the final target opening SE is calculated by adding the correction value ΔSE to the target opening SE of the EGR control valve 31, and the opening of the EGR control valve 31 is set as the final target opening SE. You. That is, the opening of the EGR control valve 31 is controlled such that the actual air-fuel ratio (A / F) _R becomes the target air-fuel ratio A / F.

Also in this embodiment, when the required load L or the engine speed N changes during the second combustion, the fuel injection amount immediately changes to the target fuel injection amount Q corresponding to the required load L and the engine speed N. Are matched. Therefore, for example, when the required load L is increased, the fuel injection amount is immediately increased, and thus the generated torque of the engine is immediately increased. Also in this embodiment, the air-fuel ratio is changed after the fuel injection amount Q changes.

When the flag I is reset, the process proceeds from step 200 to step 212 in the next processing cycle, and it is determined whether or not the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 214
And the second combustion is performed under the lean air-fuel ratio.
On the other hand, when it is determined in step 212 that L <Y (N), the routine proceeds to step 213, where the flag I is set, and then proceeds to step 203 to perform low-temperature combustion.

FIG. 18 shows another embodiment for detecting the amount of intake air. In this embodiment, a pressure difference detector 60 for detecting the pressure difference ΔP between the upstream side and the downstream side of the throttle valve 20 is provided, and the product of the square root of the pressure difference ΔP and the effective flow area S of the throttle valve 20 is provided. Is used to determine the intake air amount Ga. In this case, as shown in FIG. 19, the effective flow passage area S of the throttle valve 20 has a throttle valve opening TA
The relationship shown in FIG. 19 is obtained in advance by an experiment.

[0080]

The responsiveness of the engine output torque can be improved.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing fuel molecules.

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

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

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

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

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

FIG. 10 is a diagram showing an air-fuel ratio and the like in a first operation region I.

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

FIG. 12 is a diagram showing an air-fuel ratio and the like in a second combustion.

FIG. 13 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 14 is a diagram showing a map of a fuel injection amount.

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

FIG. 16 is a flowchart showing another embodiment for controlling the operation of the engine.

FIG. 17 is a diagram showing a map of a fuel injection amount.

FIG. 18 is a view showing another embodiment of the compression ignition type internal combustion engine.

FIG. 19 is a diagram showing an effective flow path area of a throttle valve.

[Explanation of symbols]

 6 Fuel injection valve 15 Exhaust turbocharger 20 Throttle valve 29 EGR passage 31 EGR control valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/02 330 F02D 41/02 330E F02M 25/07 550 F02M 25/07 550R 570 570J (72) Inventor Yoshi ▲ zaki Koji 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Hiroki Murata 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-7-4287 (JP, A JP-A-8-177654 (JP, A) JP-A-8-86251 (JP, A) JP-A-9-287527 (JP, A) JP-A-9-287528 (JP, A) JP-A-7-287 279718 (JP, A) JP-A-10-141125 (JP, A) JP-A-9-4519 (JP, A) JP-A-9-14026 (JP, A) JP-A-11-36923 (JP, A) (58) Survey (Int.Cl. ^7, DB name) F02D 41/00 - 45/00 395

Claims (10)

(57) [Claims] As the amount of recirculated exhaust gas supplied to the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and the amount of recirculated exhaust gas supplied to the combustion chamber further increases. In an internal combustion engine where the temperature of the fuel during combustion in the combustion chamber and the surrounding gas temperature is lower than the soot generation temperature and soot is hardly generated, the amount of soot generation peaks, In the first case, the amount of recirculated exhaust gas supplied into the combustion chamber is large and soot is hardly generated.
And the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of recirculated gas at which the amount of soot generation reaches a peak.
Switching means for selectively switching between combustion and combustion, control means for controlling the amount of intake gas supplied to the combustion chamber, and detection means for detecting the amount of intake air supplied to the combustion chamber,
An internal combustion engine that controls an intake gas amount based on a required load and an engine speed while performing first combustion, and controls a fuel injection amount based on an intake air amount detected by a detection unit. 2. A throttle valve for controlling the amount of intake air supplied to the combustion chamber by the control means, and a recirculation exhaust gas control valve for controlling the amount of recirculated exhaust gas recirculated into the combustion chamber. The target opening of the throttle valve according to the required load and the engine speed, and the target opening of the recirculation exhaust gas control valve according to the required load and the engine speed are stored in advance. 2. The internal combustion engine according to claim 1, wherein the opening of the throttle valve and the opening of the recirculation exhaust gas control valve are respectively set to the corresponding target opening when the control is performed. 3. The fuel injection amount is controlled such that the air-fuel ratio becomes a target air-fuel ratio based on the intake air amount detected by the detection means when the first combustion is being performed.
An internal combustion engine according to claim 1. 4. When the second combustion is being performed, the fuel injection amount is controlled based on the required load and the engine speed, and the intake gas amount is controlled based on the intake air amount detected by the detection means. The internal combustion engine according to claim 1, wherein: 5. A target fuel injection amount corresponding to a required load and an engine speed is stored in advance, and when the second combustion is being performed, the fuel injection amount is set to the target fuel injection amount. An internal combustion engine according to claim 1. 6. A throttle valve for controlling the amount of intake air supplied to the combustion chamber, and a recirculation exhaust gas control valve for controlling the amount of recirculated exhaust gas recirculated into the combustion chamber. When the second combustion is being performed, at least one of the throttle valve and the recirculation exhaust gas control valve is controlled such that the air-fuel ratio becomes the target air-fuel ratio based on the intake air amount detected by the detection means. 5. The internal combustion engine according to claim 4, wherein is controlled. 7. An exhaust gas recirculation rate when the first combustion is performed is approximately 55% or more, and an exhaust gas recirculation rate when the second combustion is performed is approximately 50% or less. The internal combustion engine according to claim 1, wherein 8. The internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is arranged in the engine exhaust passage. 9. The catalyst according to claim 1, wherein the catalyst is an oxidation catalyst, a three-way catalyst or NO _x.
9. The internal combustion engine of claim 8, comprising at least one absorbent. 10. An engine operating region is divided into a first operating region on a low load side and a second operating region on a high load side, and a first combustion is performed in the first operating region, and a second operation is performed. Second in the area
The internal combustion engine according to claim 1, wherein combustion of the internal combustion engine is performed.