JP3092597B2 - 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 becomes almost zero. That is, it was found that soot was hardly 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]

The new combustion is performed under an air-fuel ratio having an EGR rate of approximately 55% or more and a relatively low air-fuel ratio. In the above-mentioned internal combustion engine, the new combustion is provided in an intake passage. Throttle valve and EG
A target EGR having an EGR rate of 55% or more by controlling the opening of an EGR control valve provided in the R passage.
And the air-fuel ratio is controlled to a relatively small target opening.

However, the EGR rate can be made approximately 55% or more when the intake air amount is relatively small. That is, if the intake air amount exceeds a certain amount, this new combustion cannot be performed. Therefore, if the intake air amount exceeds a certain amount, the conventional combustion must be performed. By the way, since this new combustion is performed under a smaller air-fuel ratio than the conventional combustion, when switching from the new combustion to the conventional combustion, the air-fuel ratio is increased stepwise. When switching from conventional combustion to new combustion, the air-fuel ratio must be increased stepwise. In this case, however, the air-fuel ratio after switching between the new combustion and the conventional combustion is EGR.
It is greatly affected by the amount of air contained in the gas.
That is, if the amount of air contained in the EGR gas is large, the air-fuel ratio after switching becomes large, and if the amount of air contained in the EGR gas is small, the air-fuel ratio after switching becomes small. Therefore, in order to change the air-fuel ratio stepwise toward the target air-fuel ratio when switching between new combustion and conventional combustion, it is necessary to consider the amount of air contained in the EGR gas. Become.

When the new combustion is being performed, the opening degree of the throttle valve and the EGR control valve is set in advance so that the EGR rate becomes a large target EGR rate and the air-fuel ratio becomes a small target air-fuel ratio. Controlled every time. As described above, when a new combustion is being performed, the EGR gas contains only a small amount of air because the air-fuel ratio is maintained at the small target air-fuel ratio.

On the other hand, when the conventional combustion is performed, the opening of the throttle valve and the EGR control valve is adjusted so that the EGR rate becomes a small target EGR rate and the air-fuel ratio becomes a large target air-fuel ratio. The opening is controlled to a predetermined target opening. As described above, when the conventional combustion is performed, a large amount of air is contained in the EGR gas because the air-fuel ratio is maintained at the large target air-fuel ratio.

By the way, when switching from the new combustion to the conventional combustion, the opening of the throttle valve and the EGR control valve is adjusted to a target opening suitable for the conventional combustion in order to increase the air-fuel ratio. Is done. However, at this time, only a small amount of air is contained in the EGR gas, and therefore, at this time, the average air-fuel ratio of the air-fuel mixture in the combustion chamber does not increase so much. Next, when the air-fuel mixture is burned and the burned gas is discharged into the exhaust passage, the amount of air in the EGR gas slightly increases. Therefore, when the EGR gas is recirculated, the average air-fuel ratio of the air-fuel mixture in the combustion chamber slightly increases. Thus, the average air-fuel ratio of the air-fuel mixture in the combustion chamber gradually approaches the target air-fuel ratio.

That is, even if the new combustion is switched to the conventional combustion, the air-fuel ratio does not change stepwise to the target air-fuel ratio, but gradually changes toward the target air-fuel ratio. As a result, not only is there a problem that good combustion cannot be obtained because the air-fuel ratio deviates from the target air-fuel ratio for a while after switching from the new combustion to the conventional combustion, but also smoke is generated. There is a risk of occurring.

A similar situation occurs when the conventional combustion is switched to a new combustion. That is, when switching from the conventional combustion to the new combustion, the throttle valve and the EGR are required to reduce the air-fuel ratio.
The opening of the control valve is set to a target opening suitable for new combustion.
However, at this time, a large amount of air is contained in the EGR gas, and therefore, at this time, the average air-fuel ratio of the air-fuel mixture in the combustion chamber does not decrease so much. Next, when this air-fuel mixture is burned and the burned gas is discharged into the exhaust passage, EG
The amount of air in the R gas is slightly reduced. Therefore, when the EGR gas is recirculated, the average air-fuel ratio of the air-fuel mixture in the combustion chamber slightly decreases. Thus, the average air-fuel ratio of the air-fuel mixture in the combustion chamber gradually approaches the target air-fuel ratio.

That is, even if the conventional combustion is switched to the new combustion, the air-fuel ratio does not change stepwise to the target air-fuel ratio, but gradually changes toward the target air-fuel ratio. As a result, not only the problem that the air-fuel ratio deviates from the target air-fuel ratio for a while after the conventional combustion is switched to the new combustion, but also the problem that good combustion cannot be obtained, There is a risk of occurring.

[0017]

In order to solve the above-mentioned problems, in the first invention, as the amount of recirculated exhaust gas supplied into the combustion chamber increases, 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. An internal combustion engine, comprising: a throttle valve for controlling an amount of intake air supplied to a combustion chamber; and a recirculation exhaust gas control valve for controlling an amount of recirculation exhaust gas recirculated into the combustion chamber. By changing the opening of at least one of the throttle valve and the recirculation exhaust gas control valve, the amount of recirculation exhaust gas supplied to the combustion chamber becomes smaller than the amount of recirculation exhaust gas at which the amount of soot generation reaches a peak. A lot of soot The first combustion, which does not occur, and the 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 reaches a peak, are selectively switched, and In the internal combustion engine in which the opening degree of the throttle valve and the recirculation exhaust gas control valve is set to a predetermined target opening degree when the combustion mode is switched to the second combustion mode, the first combustion mode is switched to the second combustion mode. When switched, the opening of at least one of the throttle valve and the recirculation exhaust gas control valve is temporarily changed in a direction in which the air-fuel ratio in the combustion chamber becomes larger than the target opening, and then the target opening is set. ing.

That is, when the first combustion is switched to the second combustion, the opening degree of at least one of the throttle valve and the recirculation exhaust gas control valve is increased so that the air-fuel ratio in the combustion chamber becomes larger than the target opening degree. , The air-fuel ratio immediately becomes the target air-fuel ratio even if the amount of air in the recirculated exhaust gas is small. According to a second aspect, in the first aspect, the opening degree of the throttle valve is temporarily made larger than the target opening degree when the first combustion is switched to the second combustion.

In the third invention, in the first invention,
When the first combustion is switched to the second combustion, the opening of the recirculation exhaust gas control valve is temporarily made smaller than the target opening. According to a fourth aspect of the present invention, in the first aspect, there is provided a method for temporarily stopping a throttle valve or a recirculation exhaust gas control valve for a predetermined period in a direction in which the air-fuel ratio in the combustion chamber becomes larger than the target opening. This period is shortened as the engine speed increases.

In the fifth invention, in order to solve the above-mentioned problem, when the amount of recirculated exhaust gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, so that An internal combustion engine in which when the amount of recirculated exhaust gas to be supplied is further increased, the temperature of fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the generation temperature of soot and soot is hardly generated, A throttle valve for controlling an amount of intake air supplied to the combustion chamber; and a recirculation exhaust gas control valve for controlling an amount of recirculated exhaust gas recirculated into the combustion chamber. By changing at least one of the opening degrees of the circulation exhaust gas control valve, the amount of recirculated exhaust gas supplied to the combustion chamber is larger than the amount of recirculated exhaust gas at which the generation amount of soot becomes a peak, and soot is hardly generated. No. And the 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 generation amount of soot is at a peak, is selectively switched, and the second combustion is switched to the first combustion. In the internal combustion engine in which the opening of the throttle valve and the recirculation exhaust gas control valve are set to the predetermined target opening when the combustion is switched to the second combustion, the second combustion is switched to the first combustion. The target opening is set after temporarily changing at least one of the throttle valve and the recirculation exhaust gas control valve in a direction in which the air-fuel ratio in the combustion chamber becomes smaller than the target opening.

That is, when the second combustion is switched to the first combustion, the opening degree of at least one of the throttle valve and the recirculation exhaust gas control valve is set so that the air-fuel ratio in the combustion chamber becomes smaller than the target opening degree. , The air-fuel ratio immediately becomes the target air-fuel ratio even if the amount of air in the recirculated exhaust gas is large. In the sixth invention, in the fifth invention, the second
When the combustion is switched from the first combustion to the first combustion, the opening of the throttle valve is temporarily made smaller than the target opening.

In the seventh invention, in the fifth invention,
When the second combustion is switched to the first combustion, the opening of the recirculation exhaust gas control valve is temporarily made larger than the target opening. In an eighth aspect based on the fifth aspect, in the fifth aspect, the opening degree of at least one of the throttle valve and the recirculation exhaust gas control valve is temporarily set for a predetermined period in a direction in which the air-fuel ratio in the combustion chamber becomes smaller than the target opening degree. This period is shortened as the engine speed increases.

According to a ninth aspect, in the first or fifth aspect, the exhaust gas recirculation rate during the first combustion is substantially 55% or more, and the second combustion is performed. The exhaust gas recirculation rate at that time is approximately 50% or less. In a tenth aspect based on the first or fifth aspect, a catalyst having an oxidation function is disposed in the engine exhaust passage.

[0024] In the tenth invention is a 11th invention, the catalyst is an oxidation catalyst, consisting of one at least of the three-way catalyst or _the NO _x absorbent. In a twelfth aspect based on the first or fifth 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 pipe 11. 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.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
1 and the exhaust turbocharger 15 via the exhaust pipe 22
The exhaust gas turbine 23 is connected to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function via an exhaust pipe 24. An air-fuel ratio sensor 27 is arranged in the exhaust manifold 21.

The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air suction pipe 17 downstream of the throttle valve 20 are connected to each other via an EGR passage 29. The EGR passage 29 is driven by a step motor 30. EGR
A control valve 31 is arranged. 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, engine cooling water is guided into the intercooler 32,
The EGR gas is cooled by the engine cooling water.

On the other hand, the fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 34, via a fuel supply pipe 33. 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 air-fuel ratio sensor 27 is input to the input port 45 via the corresponding AD converter 47, and the output signal of the fuel pressure sensor 36 is also input to the input port 45 via the corresponding AD converter 47. A load sensor 51 that generates an output voltage proportional to the depression amount 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 4 via the corresponding AD converter 47.
5 is input. 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,
It is connected to a throttle valve control step motor 19, an EGR control valve control step motor 30 and a fuel pump 35.

FIG. 2 shows the throttle valve 2 at the time of engine low load operation.
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 reduced by increasing the EGR rate, the smoke is reduced when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30. The generation starts to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more and the air-fuel ratio A / F is around 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and N
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 ₍₂₎ , the generation amount of NOx is considerably reduced. N
That the generation amount of O _x produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 becomes low when the soot is hardly generated I can say. The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low.
The combustion temperature inside is low.

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

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. 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 stops 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 is 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 the 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 locally becomes extremely high, the unburned hydrocarbons that have received the combustion heat 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 formed, an amount of the inert gas is required to absorb a sufficient amount of heat to do so. . 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 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 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 the fuel and the surrounding gas during combustion 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.

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. By the way, 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 the region where the required load is larger than Lo in FIG. Unless the EGR gas ratio is reduced, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio. 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, to 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 cause low-temperature combustion can be expanded.

In this case, when the EGR rate is set to 55% or more in the region where the required load is larger than Lo, the EGR control valve 31 is fully opened and the throttle valve 20
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. 10p.pm the generation amount of the NO _x while preventing the occurrence of longitudinal or can below, also be more than the amount of air shown the amount of air in FIG. 6, that is, the average of the air-fuel ratio Even when leaning from 17 to 18, the amount of generated NO _x can be reduced to around 10 ppm or less while preventing the generation of soot.

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, thus producing soot. There is no. Further, at this time NO _x even only an extremely small amount of generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Furthermore, NO _x
Only very small amounts are generated.

As described above, when low-temperature combustion is performed, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. 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 below the temperature at which the growth of hydrocarbons stops halfway, only during low load operation in the engine, which generates a relatively small amount of heat by combustion. 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 surrounding gas temperature to a temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. During the high load operation of the engine, the second combustion, that is, the combustion that is usually performed conventionally, 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 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 operating region from the first operating region I to the second operating region II is made based on the first boundary X (N), and the determination of the change from the second operating region II to the first operating region 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.

The two boundaries of the first boundary X (N) and the second boundary Y (N) having a lower load 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 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 to provide a hysteresis for a change in the operation region between the first operation region I and the second operation region 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, and instead, the unburned hydrocarbon is converted into 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, at least one selected from alkali metals such as lithium Li, cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. Is carried.

Not only the oxidation catalyst but also 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, an example of 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 opening of the throttle valve 20, the opening of the EGR control valve 31, the EGR rate,
An air-fuel ratio, an injection timing, and an injection amount are shown. 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. The opening degree of the EGR control valve 31 is gradually increased from near full close to full open as the required load L increases.
Further, in the example shown in FIG.
The R rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

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

At the time of idling, 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, and the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating range of the engine is the first operating range I.
From the second operation region II, the opening degree of the throttle valve 20 changes stepwise from about 2/3 opening degree to 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 so that the EGR rate jumps over the EGR rate range (FIG. 5) in which a large amount of smoke is generated, and the air-fuel ratio is reduced. It is enlarged in a shape.

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 Figure 9 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise. Second operating area
In II, conventional combustion is performed. This second
In the operating region II, the throttle valve 20 is held in a fully open state except for a part, and the opening degree of the EGR control valve 31 is equal to the required load L.
Are gradually reduced as they become higher. In addition, this operating area
In II, the EGR rate decreases as the required load L increases,
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. 10 shows the air-fuel ratio A / F in the first operating region I. In FIG. 10, A / F = 15.
The curves indicated by 5, A / F = 16, A / F = 17, and A / F = 18 have air-fuel ratios of 15.5, 16, 17, and 18, respectively.
And the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 10, the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the 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. 10, as the required load L decreases, the air-fuel ratio A / F increases. As the air-fuel ratio A / F increases, the fuel consumption rate increases. Accordingly, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the air-fuel ratio A / F increases as the required load L decreases.

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

FIG. 12 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 12, A / F = 24 and A / F = 3.
Curves indicated by 5, A / F = 45 and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. Throttle valve 2 required to set air-fuel ratio to this target air-fuel ratio
As shown in FIG. 13A, a target opening degree 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, and the air-fuel ratio is set as the target air-fuel ratio. Opening SE of EGR control valve 31 necessary for
Are stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.

As shown in FIG. 9, when the operating state of the engine shifts from the first operating region I to the second operating region II, the opening of the throttle valve 20 is increased stepwise. At this time, when the opening of the throttle valve 20 is switched from the target opening ST shown in FIG. 11A to the target opening ST shown in FIG. 13A, the air-fuel ratio in the combustion chamber 5 becomes as described at the beginning. The target air-fuel ratio A / F slowly changes from the target air-fuel ratio A / F shown in FIG. 10 to the target air-fuel ratio A / F shown in FIG. 12, and not only the problem that good combustion cannot be obtained during this time occurs, but also the danger that smoke is generated. is there.

Therefore, in the embodiment according to the present invention, when the operating state of the engine shifts from the first operating region I to the second operating region II as shown in FIG. Is temporarily larger than the target opening ST shown in FIG. 13 for a predetermined period Δt, and then the opening of the throttle valve 20 is set to the target opening ST shown in FIG.

That is, when the operating state of the engine is in the first operating region I
Immediately after shifting from the second operation region II to the second operation region II, the EGR gas in the EGR passage 29 contains only a small amount of air. Therefore, at this time, the air-fuel ratio in the combustion chamber 5 becomes smaller than the target air-fuel ratio A / F shown in FIG. However, at this time, if the opening of the throttle valve 20 is temporarily increased, the air-fuel ratio immediately becomes the target air-fuel ratio A / F shown in FIG. 12 because the amount of air supplied into the combustion chamber 5 increases. When the air-fuel ratio in the combustion chamber 5 reaches the target air-fuel ratio A / F, EG
The amount of air in the R gas increases, and thereafter the air-fuel ratio is maintained at the target air-fuel ratio A / F.

As described above, when the opening of the throttle valve 20 is temporarily increased, the air-fuel ratio immediately changes to the target air-fuel ratio A.
/ F. As a result, good combustion can be obtained,
Moreover, since the air-fuel ratio jumps over a region where a large amount of smoke is generated, it is possible to prevent the generation of smoke. In the embodiment according to the present invention, as shown in FIG. 14, the operating state of the engine is changed from the second operating region II to the first operating region I.
When the operation proceeds to FIG.
A predetermined period Δ from the target opening ST shown in FIG.
t is temporarily reduced, and then the opening of the throttle valve 20 is set to the target opening ST shown in FIG.

That is, when the operating state of the engine is in the second operating region II
Immediately after shifting to the first operation region I, the EGR gas in the EGR passage 29 contains a large amount of air. Therefore, at this time, the air-fuel ratio in the combustion chamber 5 becomes larger than the target air-fuel ratio A / F shown in FIG. However, at this time, if the opening of the throttle valve 20 is temporarily reduced, the air-fuel ratio immediately becomes the target air-fuel ratio A / F shown in FIG. 10 because the amount of air supplied into the combustion chamber 5 decreases. When the air-fuel ratio in the combustion chamber 5 reaches the target air-fuel ratio A / F, the amount of air in the EGR gas decreases, and thereafter the air-fuel ratio is maintained at the target air-fuel ratio A / F.

As described above, when the opening of the throttle valve 20 is temporarily reduced, the air-fuel ratio immediately changes to the target air-fuel ratio A.
/ F. As a result, good combustion can be obtained,
Moreover, since the air-fuel ratio jumps over a region where a large amount of smoke is generated, it is possible to prevent the generation of smoke. It is preferable that the opening degree of the throttle valve 20 be temporarily increased or decreased in this way, preferably in one cycle, and if it is difficult in one cycle, several cycles.
Is the target air-fuel ratio A / F. Accordingly, the period Δt during which the opening of the throttle valve 20 is temporarily increased or decreased.
Is shortened as the engine speed N increases as shown in FIG.

FIGS. 16 and 17 show other modifications of FIG. In the example shown in FIG. 16, the EGR control valve 31 is closed stepwise when shifting from the first operation region I to the second operation region II, and the EGR control valve 31 is changed from the second operation region II to the first operation region I. When shifting, the EGR control valve 31 is opened stepwise. On the other hand, in the example shown in FIG.
The switching operation between the operation region I and the second operation region II is EG
This is performed by the R control valve 31. In this case, when shifting from the first operation region I to the second operation region II, the throttle valve 2
0 is temporarily opened by a fixed amount, and when shifting from the second operation region II to the first operation region I, the throttle valve 20 is opened.
Is temporarily closed by a fixed amount.

FIG. 18 shows an operation control routine suitable for executing the control of the throttle valve 20 and the EGR control valve 31 shown in FIGS. 14, 16 and 17. FIG.
Referring to FIG. 8, first, at step 100, 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. Flag I
Is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 101, where it is determined whether the required load L has become larger than the first boundary X1 (N). . Step 1 when L ≦ X1 (N)
Proceeding to 03, 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. Next, at step 104, the period Δt is calculated from the relationship shown in FIG. Next, at step 105, it is determined whether or not the period Δt has elapsed after switching from the second combustion to the first combustion. If the period Δt has not elapsed, the routine proceeds to step 106, where the target opening ST of the throttle valve 20 is reduced by a constant value ΔST. That is,
While the period Δt elapses, the opening degree of the throttle valve 20 is changed as shown in FIG.
The target opening ST is made smaller than the target opening ST shown in FIG.

Next, at step 107, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 11B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 108, fuel injection is performed so as to attain the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed. On the other hand, in step 101, L> X
When it is determined that (N) has been reached, the routine proceeds to step 102, where the flag I is reset.
And the second combustion is performed.

That is, in step 111, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 112, the period Δt is calculated from the relationship shown in FIG. Next, at step 113, it is determined whether or not the period Δt has elapsed after switching from the first combustion to the second combustion. If the period Δt has not elapsed, the routine proceeds to step 114, where the target opening ST of the throttle valve 20 is increased by a constant value ΔST. That is,
While the period Δt elapses, the opening degree of the throttle valve 20 is changed as shown in FIG.
It is made larger than the target opening ST shown in FIG.

Next, at step 115, 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 to this target opening SE. Next, at step 116, fuel injection is performed so as to attain the lean air-fuel ratio shown in FIG. When the flag I is reset, in the next processing cycle, step 100 is executed.
To step 109, and the required load L is equal to the second boundary Y
It is determined whether it is lower than (N). L ≧ Y
In the case of (N), the routine proceeds to step 111, where the second combustion is performed under the lean air-fuel ratio.

On the other hand, at step 109, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 110, where the flag I is set. Then, the routine proceeds to step 103, where low-temperature combustion is performed. FIG. 19 shows another embodiment. In this embodiment, when shifting from the first operating region I to the second operating region II, the EGR rate is reduced stepwise by closing the EGR control valve 31, and the first operating region II is switched to the first operating region. When shifting to the region I, the EGR rate is increased by opening the EGR control valve 31.

In this embodiment, as shown in FIG. 19, when the operating state of the engine shifts from the first operating region I to the second operating region II, the opening of the EGR control valve 31 is set before the target opening SE. The predetermined period Δt is temporarily reduced, and then the opening of the EGR control valve 31 is set to the target opening SE. That is, immediately after the operating state of the engine shifts from the first operating region I to the second operating region II, E in the EGR passage 29
Only a small amount of air is contained in the GR gas. Therefore, at this time, the air-fuel ratio in the combustion chamber 5 becomes smaller than the target air-fuel ratio A / F shown in FIG. However, at this time EG
When the opening of the R control valve 31 is temporarily reduced, the combustion chamber 5
Since the amount of air supplied to the inside increases, the air-fuel ratio immediately becomes the target air-fuel ratio A / F shown in FIG. Combustion chamber 5
When the air-fuel ratio in the air reaches the target air-fuel ratio A / F, the amount of air in the EGR gas increases, and thereafter the air-fuel ratio is maintained at the target air-fuel ratio A / F.

As described above, when the opening of the EGR control valve 31 is temporarily reduced, the air-fuel ratio immediately changes to the target air-fuel ratio A.
/ F. As a result, good combustion can be obtained,
Moreover, since the air-fuel ratio jumps over a region where a large amount of smoke is generated, it is possible to prevent the generation of smoke. In this embodiment, as shown in FIG. 19, when the operating state of the engine shifts from the second operating region II to the first operating region I, the opening of the EGR control valve 31 is determined in advance from the target opening SE. Period Δt is temporarily increased, and then E
The opening of the GR control valve 31 is set to the target opening SE.

That is, when the operating state of the engine is in the second operating region II
Immediately after shifting to the first operation region I, the EGR gas in the EGR passage 29 contains a large amount of air. Therefore, at this time, the air-fuel ratio in the combustion chamber 5 becomes larger than the target air-fuel ratio A / F shown in FIG. However, at this time EG
When the opening of the R control valve 31 is temporarily increased, the combustion chamber 5
The air-fuel ratio immediately becomes the target air-fuel ratio A / F shown in FIG. 10 because the amount of air supplied to the inside decreases. Combustion chamber 5
When the air-fuel ratio in the air reaches the target air-fuel ratio A / F, the amount of air in the EGR gas decreases, and thereafter the air-fuel ratio is maintained at the target air-fuel ratio A / F.

As described above, when the opening of the EGR control valve 31 is temporarily increased, the air-fuel ratio is immediately changed to the target air-fuel ratio A.
/ F. As a result, good combustion can be obtained,
Moreover, since the air-fuel ratio jumps over a region where a large amount of smoke is generated, it is possible to prevent the generation of smoke. FIG. 20 and FIG. 21 each show another modification of FIG. In the example shown in FIG. 20, when shifting from the first operating region I to the second operating region II, the throttle valve 20 is opened in a step-like manner, and shifting from the second operating region II to the first operating region I. At this time, the throttle valve 20 is closed stepwise.

On the other hand, in the example shown in FIG. 21, the switching operation between the first operating region I and the second operating region II is performed by the throttle valve 2.
Performed by 0. In this case, when shifting from the first operation region I to the second operation region II, the EGR control valve 31 is temporarily closed by a fixed amount, and the EGR control valve 31 is changed from the second operation region II to the first operation region I. When shifting, the EGR control valve 31 is temporarily opened by a certain amount.

FIG. 22 shows an operation control routine suitable for executing the control of the throttle valve 20 and the EGR control valve 31 shown in FIGS. 19, 20 and 21. FIG.
Referring to FIG. 2, 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. Flag I
Is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 201, where it is determined whether the required load L has become larger than the first boundary X1 (N). . Step 2 when L ≦ X1 (N)
Proceeding to 03, low-temperature combustion is performed.

That is, in step 203, the throttle valve 2
The target opening ST of 0 is calculated, and the opening of the throttle valve 20 is set as the target opening ST. Next, at step 204, the target opening degree SE of the EGR control valve 31 is calculated. Next, at step 205, the period Δt is calculated from the relationship shown in FIG. Next, at step 206, it is determined whether or not the period Δt has elapsed after switching from the second combustion to the first combustion. If the period Δt has not elapsed, the routine proceeds to step 207, where the target opening SE of the EGR control valve 31 is set.
Is increased by a constant value ΔSE. That is, the opening of the EGR control valve 31 is made larger than the target opening SE while the period Δt elapses. Next, at step 208, fuel injection is performed so as to attain the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed.

On the other hand, in step 201, L> X
When it is determined that (N) has been reached, the routine proceeds to step 202, where the flag I is reset.
And the second combustion is performed. That is, step 211
Then, the target opening ST of the throttle valve 20 is calculated, and the opening of the throttle valve 20 is set as the target opening ST. Next, at step 212, the target opening degree SE of the EGR control valve 31 is set.
Is calculated. Next, at step 213, the period Δt is calculated from the relationship shown in FIG. Then step 214
In, it is determined whether or not a period Δt has elapsed after switching from the first combustion to the second combustion. If the period Δt has not elapsed, the routine proceeds to step 215, where the target opening degree SE of the EGR control valve 31 is reduced by a certain value ΔSE.
That is, the opening of the EGR control valve 31 is made smaller than the target opening ST while the period Δt elapses. Then step 21
In 6, fuel injection is performed so as to attain the lean air-fuel ratio shown in FIG.

When the flag I is reset, in the row processing cycle, the process proceeds from step 200 to step 209 to determine whether the required load L has become lower than the second boundary Y (N). If L ≧ Y (N), step 211
And the second combustion is performed under the lean air-fuel ratio.
On the other hand, when it is determined in step 209 that L <Y (N), the routine proceeds to step 210, where the flag I is set. Then, the routine proceeds to step 203, where low-temperature combustion is performed.

FIGS. 23 to 25 show still another modified example. In these modified examples, when shifting from the first operation region I to the second operation region II, the opening of the throttle valve 20 is temporarily increased by a certain amount from the target opening ST, and the opening of the EGR control valve 31 is opened. Is temporarily reduced by a fixed amount from the target opening SE, and when shifting from the second operating region II to the first operating region I, the opening of the throttle valve 20 is temporarily reduced by a certain amount from the target opening ST. And the opening of the EGR control valve 31 is temporarily increased by a certain amount from the target opening SE.

In the example shown in FIG. 23, the switching operation between the first operation region I and the second operation region II is performed by the throttle valve 2.
0, the switching operation between the first operating region I and the second operating region II is performed by the EGR control valve 3 in the example shown in FIG.
In the example shown in FIG. 25, the switching operation between the first operating region I and the second operating region II is performed by the throttle valve 2.
This is performed by both the 0 and the EGR control valve 31.

FIG. 26 shows an operation control routine suitable for executing the control of the throttle valve 20 and the EGR control valve 31 shown in FIGS. 23, 24 and 25. FIG.
Referring to FIG. 6, first, at step 300, 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. Flag I
Is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 301, where it is determined whether or not the required load L has become larger than the first boundary X1 (N). . Step 3 when L ≦ X1 (N)
Proceeding to 03, low-temperature combustion is performed.

That is, in step 303, the throttle valve 2
A target opening ST of 0 is calculated. Then step 304
Then, the target opening SE of the EGR control valve 31 is calculated. Next, at step 305, the period Δt
Is calculated. Next, at step 306, it is determined whether or not the period Δt has elapsed after switching from the second combustion to the first combustion. If the period Δt has not elapsed, the routine proceeds to step 307, where the target opening degree S of the throttle valve 20 is set.
T is reduced by a constant value ΔST. That is, the opening of the throttle valve 20 is made smaller than the target opening ST while the period Δt elapses. Next, at step 308, the target opening degree SE of the EGR control valve 31 is increased by a constant value ΔSE. That is, the opening of the EGR control valve 31 is made larger than the target opening ST while the period Δt elapses. Next, at step 309, fuel injection is performed so as to attain the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed.

On the other hand, in step 301, L> X
When it is determined that (N) has been reached, the routine proceeds to step 302, where the flag I is reset.
And the second combustion is performed. That is, step 312
Then, the target opening ST of the throttle valve 20 is calculated. Next, at step 313, the target opening S of the EGR control valve 31 is set.
E is calculated. Next, at step 314, the period Δt is calculated from the relationship shown in FIG. Then step 31
In 5, it is determined whether or not the period Δt has elapsed after switching from the first combustion to the second combustion. If the period Δt has not elapsed, the routine proceeds to step 316, where the target opening degree ST of the throttle valve 20 is increased by a constant value ΔST. That is, the opening of the throttle valve 20 is made larger than the target opening ST while the period Δt elapses. Next, at step 317, the target opening degree SE of the EGR control valve 31 is set to a constant value Δ.
It is reduced by SE. That is, during the period Δt elapses, E
The opening of the GR control valve 31 is made smaller than the target opening SE. Next, at step 318, fuel injection is performed so as to attain the lean air-fuel ratio shown in FIG.

When the flag I is reset, in the next processing cycle, the process proceeds from step 300 to step 310, and it is determined whether or not the required load L has become lower than the second boundary Y (N). If L ≧ Y (N), step 312
And the second combustion is performed under the lean air-fuel ratio.
On the other hand, when it is determined in step 310 that L <Y (N), the routine proceeds to step 311 where the flag I is set, and then proceeds to step 303 to perform low-temperature combustion.

[0096]

When switching between the first combustion and the second combustion, the air-fuel ratio can be immediately brought closer to the target air-fuel ratio.

[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 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 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 change in the opening degree of a throttle valve and an EGR control valve.

FIG. 15 is a diagram showing a period Δt.

FIG. 16 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

FIG. 17 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

FIG. 18 is a flowchart for controlling operation of the engine.

FIG. 19 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

FIG. 20 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

FIG. 21 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

FIG. 22 is a flowchart for controlling the operation of the engine.

FIG. 23 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

FIG. 24 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

FIG. 25 is a diagram showing a change in the opening degree of a throttle valve and an EGR control valve.

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

[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 F01N 3/24 F01N 3/24 ER F02D 9/02 F02D 9/02 S 21/08 301 21/08 301B 41/02 380 41 / 02 380E 41/14 320 41/14 320C 43/00 301 43/00 301K 301N 45/00 301 45/00 301F F02M 25/07 570 F02M 25/07 570D (72) Inventor Takekazu Ito Toyota City, Aichi Prefecture 1 Toyota Town Toyota Motor Corporation (72) Inventor Hiroki Murata 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Tsukasa Abe 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Stock In-company (56) References JP-A-10-89156 (JP, A) JP-A-5-340310 (JP, A) JP-A-9-287527 (JP, A) Flat 9-287528 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) F02D 41/04 - 41/14 F01N 3/24 F02D 9/02 F02D 21/08 F02D 43/00 301 F02D 45/00 301 F02M 25/07 570

Claims (12)

(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. As the temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, soot is hardly generated, and the amount of intake air supplied to the combustion chamber is controlled. And a recirculation exhaust gas control valve for controlling the amount of recirculated exhaust gas recirculated into the combustion chamber, and at least one of the throttle valve and the recirculation exhaust gas control valve is opened. By changing the degree, 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 reaches a peak and almost no soot is generated, and the amount of generated soot is reduced Peak recirculation The second combustion, in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the gas amount, is selectively switched, and when switched from the first combustion to the second combustion, the throttle valve and the recirculated exhaust gas are switched. In an internal combustion engine in which the opening of the gas control valve is set to a predetermined target opening, the first
When the combustion is switched to the second combustion, the opening of at least one of the throttle valve and the recirculation exhaust gas control valve is temporarily changed so that the air-fuel ratio in the combustion chamber becomes larger than the target opening. An internal combustion engine whose target opening is set later. 2. The internal combustion engine according to claim 1, wherein when the first combustion is switched to the second combustion, the opening of the throttle valve is temporarily made larger than the target opening. 3. The internal combustion engine according to claim 1, wherein the opening of the recirculation exhaust gas control valve is temporarily made smaller than the target opening when the first combustion is switched to the second combustion. organ. 4. An opening degree of at least one of a throttle valve and a recirculation exhaust gas control valve is temporarily changed for a predetermined period in a direction in which an air-fuel ratio in the combustion chamber becomes larger than a target opening degree. 2. The internal combustion engine according to claim 1, wherein the period is shortened as the engine speed increases. 5. 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. As the temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, soot is hardly generated, and the amount of intake air supplied to the combustion chamber is controlled. And a recirculation exhaust gas control valve for controlling the amount of recirculated exhaust gas recirculated into the combustion chamber, and at least one of the throttle valve and the recirculation exhaust gas control valve is opened. By changing the degree, 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 reaches a peak and almost no soot is generated, and the amount of generated soot is reduced Peak recirculation The second combustion, in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the gas amount, is selectively switched, and the throttle valve and the recirculated exhaust gas are switched when the second combustion is switched to the first combustion. In an internal combustion engine in which the opening of the gas control valve has a predetermined target opening, the second
When the combustion is switched from the first combustion to the first combustion, the opening of at least one of the throttle valve and the recirculation exhaust gas control valve is temporarily changed so that the air-fuel ratio in the combustion chamber becomes smaller than the target opening. An internal combustion engine whose target opening is set later. 6. The internal combustion engine according to claim 5, wherein the opening of the throttle valve is temporarily made smaller than the target opening when the second combustion is switched to the first combustion. 7. The internal combustion engine according to claim 5, wherein when the second combustion is switched to the first combustion, the opening of the recirculation exhaust gas control valve is temporarily made larger than the target opening. organ. 8. An opening degree of at least one of a throttle valve and a recirculation exhaust gas control valve is temporarily changed for a predetermined period in a direction in which an air-fuel ratio in a combustion chamber becomes smaller than a target opening degree. The internal combustion engine according to claim 5, wherein the period is shortened as the engine speed increases. 9. The exhaust gas recirculation rate during the first combustion is substantially equal to or greater than 55%, and the exhaust gas recirculation rate during the second combustion is substantially equal to or less than 50%. The internal combustion engine according to claim 1, wherein: 10. The internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is disposed in the engine exhaust passage. 11. The catalyst according to claim 1, wherein said catalyst is an oxidation catalyst, a three-way catalyst or NO.
An internal combustion engine according to claim 10, comprising at least one of the _x absorbents. 12. The 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 any one of claims 1 to 5, wherein combustion of the internal combustion engine is performed.