JP3331981B2 - 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 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]

However, in this new combustion system, as described above, it is necessary to suppress the temperature of fuel during combustion in the combustion chamber and the surrounding gas temperature to a certain temperature or less. And the air-fuel ratio must be maintained within a predetermined range. However, in practice, the values of the operating parameters of the engine, such as the amount of EGR gas and the amount of intake air, deviate from predetermined values due to changes in weather, aging of the control device, and the like, and as a result, soot is generated, or causing a problem that the generation amount of the NO _x increases.

[0010]

In order to solve the above problems, in the first invention, as the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and peaks. In an internal combustion engine that reaches, the amount of inert gas supplied into the combustion chamber is made larger than the amount of inert gas at which the amount of generated soot becomes a peak, so that the fuel and the surrounding gas temperature during combustion in the combustion chamber can be reduced. Detecting means for controlling the temperature to be lower than the generated temperature and detecting the amount or concentration of the exhaust gas component that changes according to the temperature of the fuel during combustion and the surrounding gas; and the fuel during combustion and the surrounding gas. Control means for controlling the value of the operating parameter of the engine that changes the temperature, and by controlling the value of the operating parameter based on the amount or concentration of the exhaust gas component, the fuel during combustion and its fuel So as to control the gas temperature of circumference.

In the second invention, in the first invention,
Exhaust gas component is NO _x in the exhaust gas, a timing operating parameters fuel injection control means so as to delay the fuel injection timing when it exceeds the upper limit amount or concentration of a predetermined of the NO _x I have. In the second invention in the third invention, the control means so that advancing the fuel injection timing when less than the lower limit the amount or concentration of a predetermined of NO _x.

In a fourth aspect, in the first aspect,
An exhaust gas component is NO _x in the exhaust gas, an exhaust gas recirculation amount operating parameters is made to recycle the engine intake passage from an engine exhaust passage, control means the amount or concentration of NO _x is predetermined When the upper limit is exceeded, the amount of recirculated exhaust gas is increased. In the fifth aspect in the fourth invention, the control means when lower than the lower limit amount or concentration of a predetermined of the NO _x is to reduce the exhaust gas recirculation amount.

In the sixth invention, in the first invention,
A NO _x in the exhaust gas component exhaust gases, operating parameters are the intake air amount, the control means is to reduce the amount of intake air when exceeding the upper limit amount or concentration of a predetermined of the NO _x ing. In the sixth invention in the seventh invention, the control means when lower than the lower limit amount or concentration of a predetermined of the NO _x is to increase the amount of intake air.

In the eighth invention, in the first invention,
The exhaust gas component is soot in the exhaust gas, the operation parameter is fuel injection timing, and the control means delays the fuel injection timing when the amount or concentration of soot exceeds a predetermined upper limit. In a ninth aspect based on the eighth aspect, the control means advances the fuel injection timing when the amount or concentration of soot is lower than a predetermined lower limit.

In the tenth invention, the first invention
The exhaust gas component is NO in the exhaust gas. _xAnd the driving
Parameters are recirculated from the engine exhaust passage into the engine intake passage.
The amount of recirculated exhaust gas to be measured, the control means is the amount of soot
Or, if the concentration exceeds a predetermined upper limit,
The ring exhaust gas amount is increased. Eleventh
In the tenth aspect of the present invention, the control means controls the amount of soot or
Is recirculated when the concentration is below a predetermined lower limit.
The amount of ring exhaust gas is reduced.

In the twelfth invention, the first invention
The exhaust gas component is NO in the exhaust gas. _xAnd the driving
The parameter is the amount of intake air and the control means is the amount or concentration of soot.
When the degree exceeds a predetermined upper limit, the amount of intake air
Is to be reduced. In the thirteenth invention, 12
In the second invention, the control means sets the soot amount or concentration in advance.
Increase the intake air volume when it is lower than the specified lower limit
I try to make it.

According to a fourteenth aspect, in the first aspect, a catalyst having an oxidation function is disposed in the engine exhaust passage. In 14 th invention is a 15 th invention, the catalyst consists of one at least of the oxidation catalyst, three-way catalyst or _the NO _x absorbent. In a sixteenth aspect based on the first aspect, there is provided a recirculation device for recirculating the exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises the recirculated exhaust gas.

According to a seventeenth aspect, in the sixteenth aspect, the exhaust gas recirculation rate is approximately 55% or more. In an eighteenth aspect based on the first aspect, the first combustion in which the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of generated soot becomes a peak and soot is hardly generated,
There is provided switching means for selectively switching between the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in which the generation amount of soot becomes a peak.

According to a nineteenth aspect, in the eighteenth aspect, when the amount or concentration of the exhaust gas component does not become lower than a predetermined upper limit even if the value of the operating parameter reaches the permissible limit, the first combustion is started. 2 is switched to combustion. In a twentieth aspect based on the eighteenth 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, and the first combustion is performed in the first operating range. In the second operation region, the second combustion is performed.

[0020]

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.

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 exhaust gas sensor 27 for detecting the amount or concentration of an exhaust gas component that changes according to the temperature of the fuel during combustion in the combustion chamber 5 and the surrounding gas is provided in the exhaust manifold 21.
Is arranged. The exhaust gas sensor 27 in the embodiment according to the present invention in the exhaust gas, NO _x sensors for detecting the concentration of NO _x, or the concentration of soot in the exhaust gas, that is, from the smoke sensor for detecting a concentration of smoke Become.

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, and are driven in the EGR passage 29 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 exhaust gas 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 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. . The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 30, and the fuel pump 35 via a corresponding drive circuit 48.

FIG. 2 shows the throttle valve 2 when the engine is under 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 21 and the amount of generated smoke is the largest, and FIG. 3 (B) shows the air-fuel ratio A / F. The graph shows the change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) where the amount of smoke generation is almost zero, FIG.
It can be seen that the combustion pressure is lower than in the case shown in (A).

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

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

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

By the way, the temperature of the fuel and its surrounding when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although 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 a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

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

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

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

In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is formed, an amount of the inert gas that can absorb a sufficient amount of heat to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, 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 EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, a curve A indicates that the EGR gas temperature is substantially 9
Curve B shows the case where the EGR gas is cooled by a small cooling device, and curve C shows the case where the temperature is maintained at 0 ° C.
Indicates a case where the EGR gas is not forcibly cooled.

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

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

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

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, 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 generate 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, 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 fuel and the surrounding gas temperature at the time of combustion in the combustion chamber can be suppressed below the temperature at which the growth of hydrocarbons stops halfway, only during the low load operation in the engine, which generates a relatively small amount of heat by combustion. 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.

The two boundaries of the first boundary X (N) and the second boundary Y (N) on the 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 that hysteresis is provided for a change in the operation range between the first operation range I and the second operation range 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 the unburned hydrocarbon is 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.

The 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. Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.

FIG. 8 shows the 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. 8, 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 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. 8, 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 operation 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 range of the engine is the first operating range I.
From the second operating region II to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 8, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, the EGR rate at which the EGR rate generates a large amount of smoke
The engine operating range is the first because it jumps over the rate range (Fig. 5).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operation region II, the second combustion, that is, the conventional combustion is performed. In this combustion method generates little soot and NO _x, but the heat efficiency is higher than the low temperature combustion, thus as the operating region of the engine is shown in FIG. 8 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise. In the second 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. 9 shows the air-fuel ratio A in the first operating region I.
/ F. In FIG. 9, A / F = 15.5,
Curves indicated by A / F = 16, A / F = 17, and A / F = 18 indicate when the air-fuel ratio is 15.5, 16, 17, and 18, respectively, and the air-fuel ratio between the curves is shown. Is determined by proportional distribution. As shown in FIG.
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. 9, 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.

FIG. 10A shows the injection amount Q in the first operation region I, and FIG. 10B shows the injection start timing θS in the first operation region I. FIG.
As shown in FIG. 10A, the injection amount Q in the first operating region I is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.
As shown in (B), the injection start timing θS in the first operation region I is also 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.

The target opening degree ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in (A), the required load L and the engine speed N
The target opening degree SE of the EGR control valve 31 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 9 is shown in FIG. 11 (B). As described above, a map is stored in advance 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. FIG. 13A shows the injection amount Q in the second operation region II, and FIG. 13B shows the injection start timing θS in the second operation region II. As shown in FIG. 13A, the injection amount Q in the second operating region II is determined in advance in the form of a map in the form of a map as a function of the required load L and the engine speed N.
The injection start timing θS in the second operation region II is also 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. Have been.

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. 4A, 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.

Next, the exhaust gas sensor 2 will be described with reference to FIG.
Operation control will be described in the first time of combustion in the case of using the NO _x sensor as 7. When the first combustion is being performed, the injection start timing θS is set to a value on the map shown in FIG. 10B, and the opening ST of the throttle valve 20 is set to the value shown in FIG.
When the opening degree SE of the EGR control valve 31 is set to a value on the map shown in FIG. 11A and the opening degree SE of the EGR control valve 31 is set to a value on the map shown in FIG. 11B, the NOx concentration in the exhaust gas is usually 10 _p . However, when the gas temperature of the fuel and its surroundings at the time of combustion due to changes in the weather in the combustion chamber 5 becomes higher no longer performed good low temperature combustion, NO _x concentration in the resulting exhaust gas is increased.

Therefore, in order to perform good low-temperature combustion even if there is a change in weather or the like, as shown in FIG.
O _x concentration NO upper limit NO _max, for example, when exceeded 30p.pm will reduce the advance amount of the injection start timing .theta.S in the first embodiment, i.e. delaying the injection start timing .theta.S, in the second embodiment The opening SE of the EGR control valve 31 is increased, and in the third embodiment, the opening ST of the throttle valve 20 is reduced.

[0067] That is, good low temperature combustion to the combustion temperature delaying the injection start timing θS as in the first embodiment is lowered is carried out, in the exhaust gas and thus concentration of NO _x N
O decreases. Also, as in the second embodiment, the EGR
When the opening degree SE of the control valve 31 is increased, the EGR rate is increased, so that the combustion temperature is reduced, and favorable low-temperature combustion is performed. Thus was concentration of NO _x NO in the exhaust gas is lowered.
Further, when the opening ST of the throttle valve 20 is decreased as in the third embodiment, the intake air amount is reduced, so that the combustion temperature is reduced and good low-temperature combustion is performed. Thus was concentration of NO _x NO in the exhaust gas is lowered.

Meanwhile, NO _x concentration NO lower limit NO _min in the exhaust gas as shown in FIG. 15, for example, when lower than 3p.pm the time start of injection θ in the first embodiment
In the second embodiment, the opening SE of the EGR control valve 31 is decreased, and in the third embodiment, the opening ST of the throttle valve 20 is increased.
Is to be increased.

[0069] Thus, based on the concentration of NO _x NO in the exhaust gas fuel injection timing .theta.S, degree of opening SE of the EGR control valve 31
Alternatively, good low-temperature combustion can be performed by controlling any one of the opening degrees ST of the throttle valve 20. Next, an operation control routine for executing the first embodiment will be described with reference to FIGS.

Referring to FIG. 16, first, in 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. 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 104, where it is determined whether or not a prohibition flag indicating that low-temperature combustion should be prohibited is set. If the prohibition flag has not been set, the routine proceeds to step 105, where low-temperature combustion is performed.

That is, at step 105, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and then at step 106, the target opening ST of the EGR control valve 31 is obtained from the map shown in FIG. SE is calculated. Next, at step 107, the injection amount Q is calculated from the map shown in FIG. Next, at step 108, the injection start timing θS is calculated from the map shown in FIG. Next, at step 109, combustion control is performed. This combustion control is shown in FIG.

Referring to FIG. 17, first, in step 2
Concentration of NO _x NO whether exceeds the upper limit value NO _max is determined at 00. When NO> NO _max, the routine proceeds to step 203, where the constant value a1 is subtracted from the correction value ΔθS for the injection start timing. Next, at step 204, the final injection start timing θS is calculated by adding the correction value ΔθS to the injection start timing θS. That is, NO
When> NO _max , the injection start timing θS is gradually delayed.

On the other hand, in step 200, NO ≦ NO
When it is determined that _max whether concentration of NO _x NO proceeds to step 201 is smaller than the lower limit NO _min is determined. Step NO 20 when NO ≦ NO _min
Proceeding to 2, the fixed value a2 (<a1) is added to the correction value ΔθS. Next, the routine proceeds to step 204. Therefore, at this time, the injection start timing θS is gradually advanced.

In step 201, NO> NO_minso
When it is determined that there is, that is, NO_{ma x}≧ NO> NO_min
In the case of, the process jumps to step 204. At this time
Does not update the correction value ΔθS. Step 20
In 5, the injection start timing θS is predetermined according to the engine operating state.
Maximum allowable retard timing θS_dSlower than
Is determined, θS <θS_dThen step 20
Proceeding to 6, the prohibition flag is set. That is, NO> N
O _maxAnd the injection start timing θS is delayed, and θS = θ
S_dNO> NO _maxBanned when
Is set. Low temperature fuel when prohibition flag is set
The mode is switched from baking to the second combustion.

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 prohibition flag is reset. Next, the routine proceeds to step 112, where the second combustion is performed. That is, in step 112, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG.
Then, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. Next, at step 114, the injection amount Q is calculated from the map shown in FIG.
Next, at step 115, the injection start timing θS is calculated from the map shown in FIG.

When the flag I is reset, in the next processing cycle, the process proceeds from step 100 to step 110 to determine whether the required load L has become lower than the second boundary Y (N). Step L 112 when L ≧ Y (N)
And the second combustion is performed. On the other hand, step 110
When it is determined that L <Y (N), the routine proceeds to step 111, where the flag I is set, and then the routine proceeds to step 104. At this time, since the prohibition flag has been reset, the routine proceeds to step 105, where low-temperature combustion is performed. If the prohibition flag is set during low-temperature combustion, the process proceeds from step 104 to step 112, where the second combustion is performed.

FIG. 18 shows a second embodiment of the combustion control performed in step 109 of FIG. Concentration of NO _x NO first, at step 300 and referring to FIG. 18, whether or exceeds the upper limit value NO _max is determined.
When NO> NO _max , the routine proceeds to step 303, where EG
The correction value ΔSE for the opening of the R control valve 31 is a constant value b1
Is added. Next, at step 304, the final opening degree SE of the EGR control valve 31 is calculated by adding the correction value ΔSE to the target opening degree SE of the EGR control valve 31. That is, when NO> NO _max , the EGR control valve 31
Is gradually increased.

On the other hand, in step 300, NO ≦ NO
When it is determined that _max whether concentration of NO _x NO proceeds to step 301 is smaller than the lower limit NO _min is determined. If NO ≦ NO _min , step 30
Proceeding to 2, the constant value b2 (<b1) is subtracted from the correction value ΔSE. Next, the routine proceeds to step 304. Therefore, at this time, the opening degree SE of the EGR control valve 31 is gradually reduced.

[0079] When it is determined that in step 301 NO> NO _min, i.e. NO _{ma x} ≧ NO> NO _min
In the case of, the process jumps to step 304. At this time, the updating operation of the correction value ΔSE is not performed. Step 30
5, the opening degree SE of the EGR control valve 31 is set to the allowable maximum opening degree SE.
Whether it is larger than _max , for example, EGR control valve 3
It is determined whether or not 1 has been fully opened. If SE ≧ SE _max , the routine proceeds to step 306, where a prohibition flag is set.
That is, NO> NO _max , the opening degree SE of the EGR control valve 31 is increased, and even if SE = SE _max , NO
If> NO _max , the prohibition flag is set.
When the prohibition flag is set, low-temperature combustion is switched to second combustion.

FIG. 19 shows a third embodiment of the combustion control performed in step 109 of FIG. Concentration of NO _x NO first, at step 400 and referring to FIG. 19, whether or not exceeds the upper limit value NO _max is determined.
If NO> NO _max, the routine proceeds to step 403, where the correction value ΔST for the opening degree of the throttle valve 20 is set to a fixed value c.
1 is subtracted. Next, at step 404, the final opening degree ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening degree ST of the throttle valve 20. That is, when NO> NO _max , the throttle valve 20
Is gradually reduced.

On the other hand, in step 400, NO ≦ NO
When it is determined that _max whether concentration of NO _x NO proceeds to step 401 is smaller than the lower limit NO _min is determined. If NO ≦ NO _min , step 40
The routine proceeds to step 2, where a fixed value c2 (<c1) is added to the correction value ΔST. Next, the routine proceeds to step 404. Therefore, at this time, the opening degree ST of the throttle valve 20 is gradually increased.

[0082] When it is determined that in step 401 NO> NO _min, i.e. NO _{ma x} ≧ NO> NO _min
In the case of, the process jumps to step 404. At this time, the updating operation of the correction value ΔST is not performed. Step 40
Degree of opening ST of 5, the throttle valve 20 is whether it is smaller than the allowable minimum opening ST _min which is determined in advance according to the engine operating condition is determined, prohibited the routine proceeds to step 406 becomes a ST <ST _min The flag is set. That is, NO> NO _max, and the opening degree S of the throttle valve 20 is set.
T is decreased, and even if ST = ST _min , NO>
If NO _max , the prohibition flag is set. When the prohibition flag is set, low-temperature combustion is switched to second combustion.

Next, the exhaust gas sensor 2 will be described with reference to FIG.
The operation control at the time of the first combustion when the smoke sensor is used as 7 will be described. When the first combustion is being performed, the injection start timing θS is set to a value on the map shown in FIG. 10B, and the opening ST of the throttle valve 20 is set to the value shown in FIG.
When the opening degree SE of the EGR control valve 31 is set to a value on the map shown in FIG. 11A and a value on the map shown in FIG. 11B, the smoke concentration in the exhaust gas is generally almost zero. However, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 increases due to a change in weather or the like, favorable low-temperature combustion is not performed, and as a result, the smoke concentration in the exhaust gas increases.

Therefore, in order to perform good low-temperature combustion even when there is a change in weather or the like, when the smoke concentration SM in the exhaust gas exceeds the upper limit value _SMmax as shown in FIG.
In the fifth embodiment, the advance amount of the injection start timing θS is reduced, that is, the injection start timing θS is delayed, and in the fifth embodiment, EGR is performed.
The opening SE of the control valve 31 is increased, and the opening ST of the throttle valve 20 is reduced in the sixth embodiment.

That is, if the injection start timing θS is delayed as in the fourth embodiment, the combustion temperature is reduced, and good low-temperature combustion is performed, and the smoke concentration SM in the exhaust gas is reduced. Further, as in the fifth embodiment, EG
When the opening degree SE of the R control valve 31 is increased, the EGR rate is increased, so that the combustion temperature is reduced and good low-temperature combustion is performed. Thus, the smoke concentration SM in the exhaust gas decreases. Also, as in the sixth embodiment, the throttle valve 20
When the opening degree ST is reduced, the intake air amount is reduced, so that the combustion temperature is reduced, and favorable low-temperature combustion is performed. Thus, the smoke concentration SM in the exhaust gas decreases.

[0086] On the other hand, to increase the advance amount of the injection start timing θS in the fourth embodiment when it is smoke concentration SM lower limit SM _{mi n,} for example, zero in the exhaust gas as shown in FIG. 20, That is, the injection start timing θS is advanced, and in the fifth embodiment, the opening degree SE of the EGR control valve 31 is reduced.
In the embodiment, the opening ST of the throttle valve 20 is increased.

As described above, the smoke concentration SM in the exhaust gas
Injection timing θS, the opening degree S of the EGR control valve 31 based on
By controlling either E or the opening ST of the throttle valve 20, good low-temperature combustion can be performed. FIG. 21 shows a fourth embodiment of the combustion control performed in step 109 of FIG.

Referring to FIG. 21, first, in step 5
00 whether smoke concentration SM exceeds the upper limit value SM _max is determined in. When SM> SM _max, the routine proceeds to step 503, where the correction value ΔθS for the injection start timing
Is subtracted from the constant value a1. Next, at step 504, the final injection start timing θS is calculated by adding the correction value ΔθS to the injection start timing θS. That is, S
When M> SM _max , the injection start timing θS is gradually delayed.

On the other hand, in step 500, SM ≦ SM
_If it is determined to be _max , the routine proceeds to step 501, where it is determined whether or not the smoke density SM is smaller than the lower limit value SM _min . Step 5 when SM ≦ SM _min
In step 02, a fixed value a2 (<a1) is added to the correction value ΔθS. Next, the routine proceeds to step 504. Therefore, at this time, the injection start timing θS is gradually advanced.

In step 501, SM> SM_minso
When it is determined that there is, ie, SM_{ma x}≧ SM> SM_min
In the case of, the process jumps to step 504. At this time
Does not update the correction value ΔθS. Step 50
In 5, the injection start timing θS is predetermined according to the engine operating state.
Maximum allowable retard timing θS_dSlower than
Is determined, θS <θS_dAnd then step 50
Proceeding to 6, the prohibition flag is set. That is, NO> N
O _maxAnd the injection start timing θS is delayed, and θS = θ
S_dNO> NO _maxBanned when
Is set. Low temperature fuel when prohibition flag is set
The mode is switched from baking to the second combustion.

FIG. 22 shows a fifth embodiment of the combustion control performed in step 109 of FIG. Smoke concentration SM, first, at step 600 and referring to FIG. 22, whether or exceeds the upper limit value SM _max is determined. When SM> SM _max, the routine proceeds to step 603, where a fixed value b1 is added to the correction value ΔSE for the opening of the EGR control valve 31. Next, at step 604, the final opening degree SE of the EGR control valve 31 is calculated by adding the correction value ΔSE to the target opening degree SE of the EGR control valve 31. That is, when SM> SM _max , the EGR control valve 3
The opening degree SE of 1 is gradually increased.

On the other hand, in step 600, SM ≦ SM
_If it is determined to be _max , the routine proceeds to step 601, where it is determined whether or not the smoke density SM is smaller than the lower limit value SM _min . Step 6 when SM ≦ SM _min
Proceeding to 02, a constant value b2 (<b1) is subtracted from the correction value ΔSE. Next, the routine proceeds to step 604. Therefore, at this time, the opening degree SE of the EGR control valve 31 is gradually reduced.

[0093] When it is judged that SM> SM _min in step 601, i.e. SM _{ma x} ≧ SM> SM _min
In the case of, the process jumps to step 604. At this time, the updating operation of the correction value ΔSE is not performed. Step 60
5, the opening degree SE of the EGR control valve 31 is set to the allowable maximum opening degree SE.
Whether it is larger than _max , for example, EGR control valve 3
It is determined whether or not 1 has been fully opened. If SE ≧ SM _max , the routine proceeds to step 606, where a prohibition flag is set.
That is, SM> SM _max , the opening degree SE of the EGR control valve 31 is increased, and even if SE = SE _max , SM
When> SM _max , the prohibition flag is set.
When the prohibition flag is set, low-temperature combustion is switched to second combustion.

FIG. 23 shows a sixth embodiment of the combustion control performed in step 109 of FIG. Smoke concentration SM, first, at step 700 and referring to FIG. 23, whether or exceeds the upper limit value SM _max is determined. When SM> SM _max, the routine proceeds to step 703, where the fixed value c1 is subtracted from the correction value ΔST for the opening of the throttle valve 20. Next, at step 704, the final opening degree ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening degree ST of the throttle valve 20. That is, when SM> SM _max , the opening ST of the throttle valve 20 is gradually reduced.

On the other hand, at step 700, SM ≦ SM
_If it is determined to be _max , the routine proceeds to step 701, where it is determined whether or not the smoke density SM is smaller than the lower limit value SM _min . Step 7 when SM ≦ SM _min
In step 02, a fixed value c2 (<c1) is added to the correction value ΔST. Next, the routine proceeds to step 704. Therefore, at this time, the opening degree ST of the throttle valve 20 is gradually increased.

[0096] When it is determined that in step 701 SM> SM _min, i.e. SM _{ma x} ≧ SM> SM _min
In the case of, the process jumps to step 704. At this time, the updating operation of the correction value ΔST is not performed. Step 70
Degree of opening ST of 5, the throttle valve 20 is whether it is smaller than the allowable minimum opening ST _min which is determined in advance according to the engine operating condition is determined, prohibited the routine proceeds to step 706 becomes a ST <ST _min The flag is set. That is, SM> SM _max and the opening degree S of the throttle valve 20
T is decreased, and even when ST = ST _min , SM>
When SM _max , the prohibition flag is set. When the prohibition flag is set, low-temperature combustion is switched to second combustion.

[0097]

As described above, good low-temperature combustion can be performed even if the temperature of the fuel and its surrounding gas during combustion change for some reason.

[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 view showing an opening degree of a throttle valve and the like.

FIG. 9 is a diagram showing an air-fuel ratio in a first operation region I.

FIG. 10 is a diagram showing a map of an injection amount and the like.

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

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

15 is a time chart showing changes in the concentration of NO _x NO in the exhaust gas, the injection start timing .theta.S, degree of opening SE of the EGR control valve, the throttle valve opening ST.

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

FIG. 17 is a flowchart showing a first embodiment for executing combustion control.

FIG. 18 is a flowchart showing a second embodiment for executing the combustion control.

FIG. 19 is a flowchart showing a third embodiment for executing the combustion control.

FIG. 20 is a time chart showing changes in smoke concentration SM in exhaust gas, injection start timing θS, EGR control valve opening SE, and throttle valve opening ST.

FIG. 21 is a flowchart showing a fourth embodiment for executing the combustion control.

FIG. 22 is a flowchart showing a fifth embodiment for executing the combustion control.

FIG. 23 is a flowchart showing a sixth embodiment for executing the combustion control.

[Explanation of symbols]

 6. Fuel injection valve 20 Throttle valve 31 EGR control valve

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/08 F02D 21/08 301D 41/02 351 F02D 21/08 301 43/00 301J 301K 41/02 351 301N 43/00 301 F02M 25 / 07 570D 570J B01D 53/34 129Z F02M 25/07 570 135Z 53/36 B (72) Inventor Hiroki Murata 1st Toyota Town, Toyota City, Aichi Prefecture Examiner in Toyota Motor Corporation Tetsu Murakami (56) References JP JP-A-7-4287 (JP, A) JP-A-8-86251 (JP, A) JP-A 8-17761 (JP, A) JP-A 9-287527 (JP, A) JP-A 9-287528 (JP) JP-A-8-254152 (JP, A) JP-A-8-296469 (JP, A) JP-A-8-303309 (JP, A) JP-A-9-96606 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-45/00 F02M 25/07

Claims (20)

(57) [Claims] 1. An internal combustion engine in which the amount of generated soot gradually increases as the amount of inert gas supplied into the combustion chamber increases and reaches a peak, the amount of generated inert gas becomes smaller than the amount of inert gas when the amount of generated soot reaches a peak. Also, by increasing the amount of inert gas supplied into the combustion chamber, the temperature of the fuel during combustion in the combustion chamber and the surrounding gas temperature are suppressed to a temperature lower than the temperature at which soot is generated, and the fuel and the fuel during combustion are suppressed. Detecting means for detecting the amount or concentration of the exhaust gas component that changes in accordance with the temperature of the surrounding gas, and control means for controlling the value of the operating parameter of the engine that changes the temperature of the fuel during combustion and the surrounding gas. An internal combustion engine comprising: controlling the value of an operation parameter based on the amount or concentration of an exhaust gas component to control the temperature of fuel during combustion and the gas surrounding the fuel. 2. The method according to claim 1, wherein the exhaust gas component is NO _x in the exhaust gas.
, And the a said operating parameter is the fuel injection timing, according to claim 1 wherein said control means for delaying the fuel injection timing when it exceeds the upper limit amount or concentration of a predetermined of said NO _x
An internal combustion engine according to claim 1. Wherein said control means an internal combustion engine according to claim 2 when lower than the lower limit amount or concentration of a predetermined of said NO _x is advancing the fuel injection timing. 4. A NO _x of the exhaust gas components in the exhaust gas
, And the a recirculated exhaust gas amount which the operating parameter is made to recycle the engine intake passage from an engine exhaust passage, when the control means exceeding the upper limit amount or concentration of the NO _x were previously determined The internal combustion engine according to claim 1, wherein the amount of recirculated exhaust gas is increased. Wherein said control means an internal combustion engine according to claim 4 when lower than the lower limit amount or concentration of the NO _x is a predetermined decreasing the exhaust gas recirculation amount. 6. The exhaust gas component comprising NO _x in the exhaust gas.
, And the said operating parameter is the intake air quantity, an internal combustion engine according to claim 1 to reduce the intake air amount when said control means exceeding the upper limit amount or concentration of the NO _x is predetermined. 7. The internal combustion engine according to claim 6, wherein said control means increases the intake air amount when the amount or concentration of said NO _x is lower than a predetermined lower limit. 8. The exhaust gas component is soot in the exhaust gas, the operating parameter is fuel injection timing, and the control means controls the fuel when the amount or concentration of the soot exceeds a predetermined upper limit. 2. The internal combustion engine according to claim 1, wherein the injection timing is delayed. 9. The internal combustion engine according to claim 8, wherein the control means advances the fuel injection timing when the amount or concentration of the soot is lower than a predetermined lower limit. 10. The method according to claim 1, wherein the exhaust gas component is NO in the exhaust gas.
_x , the operating parameter is the amount of recirculated exhaust gas that is recirculated from the engine exhaust passage into the engine intake passage, and the control means performs control when the amount or concentration of the soot exceeds a predetermined upper limit. The internal combustion engine according to claim 1, wherein the amount of recirculated exhaust gas is increased. 11. The internal combustion engine according to claim 10, wherein said control means reduces the amount of recirculated exhaust gas when the amount or concentration of said soot is lower than a predetermined lower limit. 12. The method according to claim 1, wherein the exhaust gas component is NO in the exhaust gas.
The internal combustion engine according to claim 1, wherein _x is the operating parameter is an intake air amount, and the control means reduces the intake air amount when the amount or concentration of the soot exceeds a predetermined upper limit. 13. The internal combustion engine according to claim 12, wherein the control means increases the intake air amount when the amount or concentration of the soot is lower than a predetermined lower limit. 14. The internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is disposed in the engine exhaust passage. 15. The catalyst according to claim 1, wherein the catalyst is an oxidation catalyst, a three-way catalyst or NO.
15. The internal combustion engine of claim 14, comprising at least one of the _x absorbents. 16. The internal combustion engine according to claim 1, further comprising a recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises recirculated exhaust gas. 17. The internal combustion engine according to claim 16, wherein the exhaust gas recirculation rate is about 55% or more. 18. The first combustion in which the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the generation amount of soot is at a peak and little soot is generated, and the inert gas at which the generation amount of soot is at a peak. 2. A switching means for selectively switching between the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in the combustion chamber.
An internal combustion engine according to claim 1. 19. The method according to claim 1, wherein the first combustion is switched to the second combustion when the amount or concentration of the exhaust gas component does not become lower than a predetermined upper limit even when the value of the operation parameter reaches an allowable limit. Item 19. The internal combustion engine according to Item 18. 20. 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. Second in the area
19. The internal combustion engine according to claim 18, wherein combustion of the internal combustion engine is performed.