JP3424565B2 - Internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, for example, a diesel engine, an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation (hereinafter referred to as EGR) passage in order to suppress the generation of NO _x. Exhaust gas, that is, EGR gas, is recirculated into the engine intake passage via the EGR 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 decreases, the amount of NO _x generated decreases. Therefore, the higher the EGR rate, the lower the amount of NO _x generated.

As described above, it has been known that the amount of NO _x generated can be reduced by increasing the EGR rate. However, when the EGR rate is increased, when the EGR rate exceeds a certain limit, the amount of soot generated, that is, the smoke starts to increase rapidly. In this regard, it has been conventionally thought that if the EGR rate is further increased, the smoke will increase infinitely, and therefore the smoke will start to increase rapidly.
The GR rate is considered to be the maximum allowable limit for the EGR rate.

Therefore, conventionally, the EGR rate is set within a range that does not exceed the maximum allowable limit. The maximum allowable limit of this EGR rate is approximately 30 to 50 percent, though it varies considerably depending on the engine type and fuel.
Therefore, in the conventional diesel engine, the maximum EGR rate is 3
It is suppressed from 0% to 50%.

As described above, in the past, it was considered that the maximum allowable limit exists for the EGR rate.
The R rate is NO within the range that does not exceed this maximum allowable limit.
_It was stipulated that the amount of _x and smoke generated should be as small as possible. However, in this way EGR
Even if the rate is set so that the amount of NO _x and smoke produced is as small as possible, there is a limit to the reduction in the amount of NO _x and smoke produced, and in reality, a considerable amount of N 2 is still left.
The O _x, and smoke is generated at present.

However, if the EGR rate is made larger than the maximum permissible limit in the process of studying the combustion of a diesel engine, the smoke increases sharply as described above, but there is a peak in the amount of smoke produced, and the peak is exceeded. EGR
When the rate is further increased, the smoke starts to decrease sharply this time. When the EGR rate is 70% or more during idling operation, and when the EGR gas is strongly cooled, the EGR rate is almost 55% or more. It was found that it was almost zero, that is, soot was hardly generated. At this time, N
It has also been found that the amount of O _x generated is extremely small.
After that, the reason why soot was not generated was examined based on this finding, and as a result, soot and NO
_This led to the construction of a new combustion system capable of simultaneously reducing _x . This new combustion system will be explained in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle of the process until the hydrocarbons grow into soot.

[0007] That is, as a result of repeated experimental research, it was found that when the temperature of the fuel and the gas around it during combustion in the combustion chamber were below a certain temperature, the growth of hydrocarbons stopped in the middle of the process before reaching soot. However, if the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons will suddenly grow to soot. In this case, the temperature of the fuel and its surrounding gas is greatly affected by the endothermic action of the gas around the fuel when the fuel burns, and the endothermic amount of the gas around the fuel is adjusted according to the amount of heat generated during fuel combustion. Thus, the temperature of the fuel and the gas around it can be controlled.

Therefore, if the temperature of the fuel and the gas around it during combustion in the combustion chamber is suppressed below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated and the fuel and the surroundings during combustion in the combustion chamber will be eliminated. It is possible to control the gas temperature in the range below the temperature at which the growth of hydrocarbons stops halfway by adjusting the heat absorption amount of the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of the new combustion system. The applicant has already applied for an internal combustion engine that employs this new combustion system (Japanese Patent Application No. 9-305850).

[0009]

By the way, in this new combustion system, as described above, it is basically based on purifying hydrocarbons and the like, which have stopped growing before reaching soot, by an oxidation catalyst or the like. This new combustion cannot be performed when the etc. are not activated. However, when the engine is idling, the exhaust gas temperature becomes low, so if the engine is left in the idling operation state for a long period of time, the temperature of the catalyst gradually decreases, and finally the temperature of the catalyst becomes an activation that can oxidize hydrocarbons etc. The temperature becomes lower than that, and as a result, a problem that a large amount of hydrocarbon and the like is released to the atmosphere occurs.

[0010]

In order to solve the above problems, in the first invention, as the amount of the inert gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and reaches the peak. and reaches, further increasing the amount of inert gas supplied to the combustion chamber
The fuel used during combustion in the combustion chamber and its
The ambient gas temperature becomes lower than the soot formation temperature,
In command generated not become an internal combustion engine, combustion in the combustion chamber by the inert gas amount supplied to the combustion chamber than the inert gas where the amount of production of soot peaks multi Kusuru
Soot is generated when burning fuel and the gas temperature around it
The temperature is controlled to a temperature lower than the temperature, a catalyst having an oxidizing function is arranged in the engine exhaust passage, temperature detection means for detecting the temperature of the catalyst, and the lower limit temperature of the catalyst when the engine is idling And a temperature raising means for raising the temperature of the catalyst when the temperature becomes below.

In the second invention, in the first invention,
The temperature raising means raises the temperature of the catalyst by raising the exhaust gas temperature when the temperature of the catalyst becomes lower than or equal to the lower limit temperature during engine idling operation.
In the third invention, in the second invention, the temperature increasing means increases the temperature of the catalyst by delaying the fuel injection timing when the temperature of the catalyst becomes equal to or lower than the lower limit temperature during the engine idling operation.

In the fourth invention, in the second invention,
The temperature raising means performs pilot injection when the temperature of the catalyst becomes lower than or equal to the lower limit temperature during engine idling operation, and raises the temperature of the catalyst by setting the injection timing of the main injection to after compression top dead center. . In the fifth invention, in the second invention, the temperature raising means raises the temperature of the catalyst by lowering the fuel injection pressure when the temperature of the catalyst becomes equal to or lower than the lower limit temperature during engine idling operation.

In the sixth invention, in the second invention,
The inert gas consists of recirculated exhaust gas that is recirculated from the engine exhaust passage into the engine intake passage.The temperature raising means controls the amount of recirculated exhaust gas when the temperature of the catalyst falls below the lower limit temperature during engine idling operation. The temperature of the catalyst is increased by decreasing the temperature. In the seventh invention, in the second invention, the temperature raising means is
When the temperature of the catalyst becomes lower than the lower limit temperature during the idling operation of the engine, the idling speed of the engine is increased to raise the temperature of the catalyst.

In the eighth invention, in the first invention,
The temperature increasing means increases the temperature of the catalyst by increasing the amount of unburned HC and CO discharged into the engine exhaust passage when the temperature of the catalyst becomes lower than or equal to the lower limit temperature during engine idling operation. There is. In the ninth invention, in the eighth invention, the temperature raising means raises the temperature of the catalyst by making the air-fuel ratio rich when the temperature of the catalyst becomes equal to or lower than the lower limit temperature during engine idling operation.

In the tenth aspect of the invention, in the eighth aspect of the invention, the temperature increasing means injects the fuel into two portions during the intake stroke and the end of the compression stroke when the temperature of the catalyst becomes lower than the lower limit temperature during the engine idling operation. By doing so, the temperature of the catalyst is raised. In the eleventh aspect of the invention, in the eighth aspect of the invention, the temperature increasing means instantly increases the air-fuel ratio when the temperature of the catalyst becomes lower than or equal to the lower limit temperature during engine idling operation, and thereafter increases the air-fuel ratio for a predetermined period. By making it lean, the temperature of the catalyst is raised.

In the twelfth invention, in the eighth invention, the temperature raising means injects additional fuel into the latter half of the expansion stroke or the exhaust stroke when the temperature of the catalyst becomes lower than the lower limit temperature during the engine idling operation. By doing so, the temperature of the catalyst is raised. In the thirteenth invention, in the first invention, the temperature raising means raises the exhaust gas temperature when the temperature of the catalyst becomes lower than or equal to the lower limit temperature during the engine idling operation, and unburned HC discharged into the engine exhaust passage. , The temperature of the catalyst is raised by increasing the amount of CO.

According to a fourteenth invention, in the first invention, the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst and an NO _x absorbent. According to a fifteenth invention, in the first invention, an exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage is provided, and the inert gas is recirculation exhaust gas.

According to the sixteenth invention, in the fifteenth invention, the exhaust gas recirculation rate is about 55% or more. In the seventeenth invention, in the first invention, the amount of the inert gas supplied to the combustion chamber is larger than the amount of the inert gas at which the amount of generated soot reaches its peak, and soot is hardly generated.
And the second combustion in which the amount of the inert gas supplied to the combustion chamber is smaller than the amount of the inert gas at which the amount of generated soot peaks.

According to the eighteenth invention, in the seventeenth invention, the operating region of the engine is divided into a first operating region on the low load side and a second operating region on the high load side, and the first operating region is divided into the first operating region and the first operating region. Is performed, and the second combustion is performed in the second operation region.

[0020]

FIG. 1 shows the 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, and 9 is an intake port. Indicates an exhaust valve, and 10 indicates an exhaust port, respectively. 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 via an intake duct 13 and an intercooler 14 to a supercharger, for example, an outlet portion of a compressor 16 of an exhaust turbocharger 15. Be connected. The 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 pipe 22 through the exhaust turbocharger 15
Of the exhaust turbine 23, and the outlet of the exhaust turbine 23 is connected via an exhaust pipe 24 to a catalytic converter 26 containing a catalyst 25 having an oxidizing function. A temperature sensor 27 for detecting the temperature of the catalyst 25 is attached to the catalytic converter 26.

The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air intake pipe 17 downstream of the throttle valve 20 are connected to each other via an EGR passage 29, and the EGR passage 29 is driven by a step motor 30. EGR
A control valve 31 is arranged. An intercooler 32 for cooling the EGR gas flowing in the EGR passage 29 is arranged in the EGR passage 29. In the embodiment shown in FIG. 1, engine cooling water is introduced into the intercooler 32,
The EGR gas is cooled by the engine cooling water.

On the other hand, fuel injectors 6 are connected through a fuel supply pipe 33 the fuel reservoir, a so-called common rail 34. The common rail is to Le 34 is supplied with fuel from a variable discharge fuel pump 35 of the electrically controlled, common rail
The fuel supplied into the fuel cell 34 is supplied to the fuel injection valve 6 via each fuel supply pipe 33. The common rail 34 is mounted a fuel pressure sensor 36 for detecting the fuel pressure in Como <br/> Nre Le 34, the target fuel fuel pressure common rail 34 based on the output signal of the fuel pressure sensor 36 The discharge amount of the fuel pump 35 is controlled so that the pressure becomes a pressure.

The crankshaft 37 is connected to an automatic transmission 38 as shown in FIG. The electronic control unit 40 is composed of a digital computer, and has a ROM (read only memory) 42 and a RAM (random access memory) 4 connected to each other by a bidirectional bus 41.
3, CPU (microprocessor) 44, input port 4
5 and output port 46. The output signal of the temperature 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 pressure sensor 39 for detecting the absolute pressure in the surge tank 12 is arranged in the surge tank 12, and a mass flow meter for detecting the mass flow rate of intake air is provided in the air suction pipe 17 upstream of the throttle valve 20. 49 are arranged. The output signals of the pressure sensor 39 and the mass flowmeter 49 are input to the input port 45 via the corresponding AD converter 47.

On the other hand, a load sensor 51 for generating 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 via an associated AD converter 47. 45 is input. A crank angle sensor 52 that generates an output pulse each time the crankshaft rotates, for example, 30 ° is connected to the input port 45. Further, an output pulse representing the vehicle speed of the vehicle speed sensor 53 is input to the input port 45, and an output signal of the neutral sensor 54 for detecting whether the automatic transmission 38 is in the neutral position is input to the input port 45. It 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 the corresponding drive circuit 48.

FIG. 2 shows the throttle valve 2 during engine low load operation.
The change in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree of 0 and the EGR rate, and the change in the amount of smoke, HC, CO, and NO _x emissions. It represents the experimental example shown. As can be seen from FIG. 2, in this experimental example, the EGR rate becomes larger as the air-fuel ratio A / F becomes smaller, and when the air-fuel ratio is equal to or less than the theoretical air-fuel ratio (≈14.6), the EGR rate becomes 65% or more.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the EGR rate becomes around 40%, and when the air-fuel ratio A / F reaches about 30, smoke is generated. The amount of generation begins to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is made smaller, 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 sharply decreases this time, the EGR rate is increased to 65% or more, and the smoke becomes almost zero when the air-fuel ratio A / F is around 15.0. . That is, soot is hardly generated. At this time, the output torque of the engine slightly decreases, and N
The amount of O _x generated is considerably low. On the other hand, at this time, HC,
The amount of CO generated starts to increase.

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

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

Secondly, when the amount of smoke produced, that is, the amount of soot produced, becomes almost zero, as shown in FIG.
Emissions will increase. This means that hydrocarbons are discharged without growing to soot. That is, linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed to form soot precursors when the temperature is raised in a state of oxygen deficiency, and then mainly soot is formed. Soot consisting of a solid with carbon atoms gathered 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. After that, it will grow to soot. Therefore, as described above, when the amount of soot generated becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. 2. At this time, HC is a soot precursor or a hydrocarbon in the 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 soot generation amount becomes almost zero, and at this time, the soot precursor or the soot precursor The hydrocarbons in this state are discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the gas around it in the combustion chamber 5 is below a certain temperature, the soot growth process stops halfway, that is, the soot is generated. It was found that soot was not generated at all and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 reached a certain temperature or higher.

By the way, the temperature of the fuel and its surroundings when the hydrocarbon production process 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. It cannot be said how many times it changes, but this certain temperature has a deep relationship with the amount of NO _x produced, and therefore this certain temperature is defined to some extent from the amount of NO _x produced. be able to. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas around it decreases, and the amount of NO _x generated decreases. At this time, soot is hardly generated when the amount of NO _x generated is about 10 p.pm or less. Therefore, the above certain temperature is NO
It is almost the same as the temperature when the amount of _x generation is around 10 p.pm or less.

Once soot is produced, this soot cannot be purified by a post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before it can be easily purified by a post-treatment using a catalyst having an oxidizing function. Considering the post-treatment with a catalyst having an oxidizing function as described above, it is extremely difficult to determine whether the hydrocarbon is discharged from the combustion chamber 5 in the state of the soot precursor or in the state before it, or is discharged from the combustion chamber 5 in the form of soot. There is a big difference. The new combustion system employed in the present invention allows hydrocarbons to be discharged from the combustion chamber 5 in the form of soot precursors or pre-presence conditions without producing soot in the combustion chamber 5 The core is to oxidize with a catalyst having an oxidizing function.

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

That is, if only air exists 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 locally becomes extremely high. That is, at this time, the air separated from the fuel hardly absorbs the combustion heat of the fuel. In this case, since the combustion temperature locally becomes extremely high, the unburned hydrocarbons that have received this heat of combustion generate soot.

On the other hand, the situation is slightly different when the fuel is present in a mixed gas of a large amount of inert gas and a small amount of air.
In this case, the evaporated fuel diffuses into the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion heat is absorbed by the surrounding inert gas, so that the combustion temperature does not rise so much. 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 suppressed low by the endothermic action of the inert gas.

In this case, in order to suppress the temperature of the fuel and the gas around it to a temperature lower than the temperature at which soot is produced, an amount of inert gas sufficient to absorb the amount of heat required to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas also increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action. Therefore, the inert gas is preferably a gas having a large specific heat. In this respect, since CO ₂ and EGR gas have relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.

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

As shown by the curve A in FIG. 5, when the EGR gas is strongly cooled, the soot generation amount reaches a peak when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Almost no soot is generated if the percentage is exceeded. 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 when the EGR rate is slightly higher than 50%. In this case, the EGR rate is approximately 65% or more. If so, soot is hardly generated.

Further, as shown by the curve C in FIG. 5, EG
When the R gas is not forcibly cooled, the EGR rate is 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. Note that FIG. 5 shows the amount of smoke generated when the engine load is relatively high, and the EGR rate at which the amount of soot generated peaks when the engine load decreases and the EGR rate at which soot almost does not occur decreases. The lower limit of is also slightly lowered. Thus, the lower limit of the EGR rate at which soot is hardly generated changes depending on the cooling degree of EGR gas and the engine load.

FIG. 6 shows a mixture of EGR gas and air required to bring the temperature of the fuel and its surrounding gas at the time of combustion to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. The amount of gas, the ratio of air in this mixed gas amount, and the ratio of EGR gas in this mixed gas are shown. Note that, in FIG. 6, the vertical axis represents the total intake gas amount sucked into the combustion chamber 5, and the chain line Y represents the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis shows the required load.

Referring to FIG. 6, the ratio of air, that is, the amount of air in the mixed gas indicates the amount of air required 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 theoretical air-fuel ratio. On the other hand, in FIG. 6, the ratio of EGR gas, that is, the amount of EGR gas in the mixed gas is set so that when the injected fuel is burned, the temperature of the fuel and its surrounding gas is lower than the temperature at which soot is formed. The minimum required EGR gas amount is shown. This EGR gas amount is approximately 55% or more when expressed by the EGR rate, and is 7 in the embodiment shown in FIG.
It is 0% or more. That is, the total intake gas amount sucked into the combustion chamber 5 is shown by a solid line X in FIG. 6, and the ratio of the air amount and the EGR gas amount in the total intake gas amount X is shown in FIG.
When the ratio is as shown in (1), the temperature of the fuel and the gas around it becomes lower than the temperature at which soot is generated, and thus soot is not generated at all. Further, the amount of NO _x generated at this time is around 10 p.pm or less, so N
The amount of O _x generated is extremely small.

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

By the way, when supercharging is not performed,
The upper limit of the total intake gas amount X drawn into the baking chamber 5 is Y.
Therefore, the required load is L in FIG.₀Greater than
In the region, the EGR gas ratio is increased as the required load increases.
It is possible to maintain the air-fuel ratio at the theoretical air-fuel ratio unless it is decreased.
Can not. In other words, it is necessary when supercharging is not done.
Load demand is L₀The theoretical air-fuel ratio in a region larger than
If you try to maintain the fuel ratio, the required load will increase.
As a result, the EGR rate decreases, so the required load is L ₀Than
In a large area, the temperature of the fuel and the gas around it is sooted
It cannot be maintained below the temperature at which it is produced.

However, as shown in FIG. 1, when EGR gas is recirculated to the inlet side of the supercharger, that is, in the air suction pipe 17 of the exhaust turbocharger 15 via the EGR passage 29, the required load is larger than L _0. EGR rate is 5 in the region
It can be maintained above 5 percent, for example 70 percent, thus maintaining the fuel and surrounding gas temperatures 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 intake gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the gas around it can be maintained below the temperature at which soot is produced, up to the limit that can be boosted by the compressor 16. Therefore, the operating range of the engine capable of producing the 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 L ₀ , the EGR control valve 31 is fully opened and the throttle valve 20
Is closed a little. 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 made smaller than the air amount shown in FIG. It is possible to reduce the amount of NO _x generated to around 10 p.pm or less while preventing the generation of air, and to make the air amount larger than that shown in FIG. Even if it is lean from 17 to 18, the generation amount of NO _x can be reduced to about 10 p.pm 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 excessive fuel does not grow to soot, and soot is generated. There is no. Further, at this time, a very small amount of NO _x is 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 becomes high, but in the present invention the combustion temperature is suppressed to a low temperature, soot Not generated at all. Furthermore, NO _x
Also produces only a very small amount.

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. However, the amount of NO _x generated is 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 gas around it during combustion in the combustion chamber can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway only when the engine is operating at low load, where the calorific value of combustion is relatively small. Therefore, in the embodiment according to the present invention, when the engine is operated at low load, the temperature of the fuel and the gas around it during combustion is suppressed below the temperature at which the growth of hydrocarbons stops halfway, and the first combustion, that is, low temperature combustion is performed. In addition, the second combustion, that is, the combustion normally performed from the conventional one, is performed during the engine high load operation. It should be noted that here, the first combustion, that is, low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generated peaks, and soot is almost generated. The second combustion, that is, the combustion that is normally performed in the past, is the combustion that does not have the amount of soot generated and the amount of the inert gas in the combustion chamber is smaller than the amount of the inert gas that does not reach the peak. Say that.

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

That is, the operating condition of the engine is the first operating region I.
Required torque TQ when low temperature combustion is performed
Is above the first boundary X (N) which is a function of the engine speed N, it is judged that the operating region has moved to the second operating region II,
Combustion is performed by a conventional combustion method. Next, the required torque TQ is a second boundary Y (N) which is a function of the engine speed N.
When it becomes lower than that, it is determined that the operating region has moved to the first operating region I, and low temperature combustion is performed again.

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

By the way, when the engine is operating in the first operating region I and low-temperature combustion is performed, soot is hardly generated, and instead, unburned hydrocarbons are in the state of the soot precursor or the state before it. It is discharged from the combustion chamber 5 in shape. At this time, if the catalyst 25 is activated, the unburned hydrocarbons discharged from the combustion chamber 5 can be favorably oxidized by the catalyst 25 having an oxidizing function.

As the catalyst 25, an oxidation catalyst, a three-way catalyst, or a NO _x absorbent can be used. The NO _x absorbent is NO _x when the average air-fuel ratio in the combustion chamber 5 is lean.
And has a function of releasing NO _x when the average air-fuel ratio in the combustion chamber 5 becomes rich. This NO _x absorbent uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, and cesium Cs are provided on the carrier.
Alkali metals such as, barium Ba, calcium Ca
Alkaline earth such as, lanthanum La, yttrium Y
At least one selected from rare earths such as
And a precious metal such as

Not only oxidation catalysts, but also three-way catalysts and NO
_{The x-} absorbent also has an oxidizing function, so that the three-way catalyst and the 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 opening of the throttle valve 20, the opening of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing and the injection amount with respect to the required torque TQ. As shown in FIG. 8, in the first operating region I where the required torque TQ is low, the opening degree of the throttle valve 20 is gradually increased from near full closing to about 2/3 opening degree 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 torque TQ increases. Further, in the example shown in FIG. 8, the EGR rate is set to approximately 70% in the first operating region I, and the air-fuel ratio is a slightly lean lean air-fuel ratio.

In other words, in the first operating region I, EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled so that the ratio 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 the required torque.
The injection end timing θE
Also becomes late as the injection start timing θS becomes late.

During the idling operation, the throttle valve 20 is closed to the fully closed state, and at this time, the EGR control valve 31 is also closed to the fully closed state. Throttle valve 2
When 0 is closed to near full closure, the pressure in the combustion chamber 5 at the beginning of compression becomes low and the compression pressure becomes small. When the compression pressure becomes small, the compression work by the piston 4 becomes small, so that the vibration of the engine body 1 becomes small. That is, during idling operation, the throttle valve 20 is closed close to the fully closed state in order to suppress the vibration of the engine body 1.

On the other hand, the operating region of the engine is the first operating region I.
When changing from the second operating range II to the second operating range II, the opening degree of the throttle valve 20 is increased stepwise from about 2/3 opening degree 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 that produces a large amount of smoke with an EGR rate
The operating range of the engine is the first because the rate range (Fig. 5) is skipped.
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 combustion which is conventionally performed is performed. Although some soot and NO _x are generated in this combustion method, the thermal efficiency is higher than that in low temperature combustion, so that when the operating region of the engine changes from the first operating region I to the second operating region II, as shown in FIG. In addition, the injection amount is reduced stepwise. In the second operating region II, the throttle valve 20 is kept fully open except for a part, and the opening degree of the EGR control valve 31 is gradually reduced as the required torque TQ increases. Also, this operating area II
Then, the EGR rate becomes lower as the required torque TQ becomes higher, and the air-fuel ratio becomes smaller as the required torque TQ becomes higher. However, the air-fuel ratio is set to the lean air-fuel ratio even if the required torque TQ becomes high. Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 9A shows the relationship between the required torque TQ, the depression amount L of the accelerator pedal 50, and the engine speed N. In FIG. 9A, each curve represents an equal torque curve, the curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves indicate TQ = a, T.
The required torque gradually increases in the order of Q = b, TQ = c, and TQ = d. The required torque TQ shown in FIG.
As shown in (B), the ROM is previously stored in the form of a map as a function of the depression amount L of the accelerator pedal 50 and the engine speed N.
It is stored in 42. In the present invention, the required torque TQ corresponding to the depression amount L of the accelerator pedal 50 and the engine speed N is first calculated from the map shown in FIG. 9B, and the fuel injection amount and the like are calculated based on this required torque TQ. To be done.

FIG. 10 shows the air-fuel ratio A / F in the first operating region I. In FIG. 10, A / F = 15.
5, each curve indicated by A / F = 16, A / F = 17, A / F = 18 has an air-fuel ratio of 15.5, 16, 17, 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 lower the required torque TQ is, the air-fuel ratio A /
F is lean.

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

[0063] Figure 11 (A) shows the injection amount Q in the first operating region I, FIG. 11 (B) shows the injection start timing θS in the first operating region I. Figure 11
As shown in (A), the injection amount Q in the first operating region I is stored in advance in the ROM 42 in the form of a map in the form of a map as a function of the required torque TQ and the engine speed N.
As shown in FIG. 1 (B), the injection start timing θS in the first operation region I is also stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N.

Further, the target opening degree ST of the throttle valve 20 required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 2 (A), the EGR is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N, and is required to set the air-fuel ratio to the target air-fuel ratio shown in FIG. The target opening degree SE of the control valve 31 is shown in FIG.
As shown in (B), it is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N.

Further, in the embodiment according to the present invention, the fuel injection pressure in the first operating region I, that is, the target fuel pressure P in the common rail 34, is the required torque TQ and the engine speed N as shown in FIG. 12 (C). It is stored in advance in the ROM 42 in the form of a map as a function. FIG. 13 shows the second combustion,
That is, it shows the target air-fuel ratio when normal combustion is performed by the conventional combustion method. In FIG. 13, the A / F
= 24, A / F = 35, A / F = 45, and A / F = 60, the respective curves indicated by the target air-fuel ratios of 24, 35, 45, 6 respectively.
0 is shown.

FIG. 14A shows the injection amount Q in the second operating region II, and FIG. 14B shows the second operating region.
The injection start timing θS in II is shown. 14
As shown in (A), the injection amount Q in the second operation region II is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N, and FIG.
As shown in FIG. 4 (B), the injection start timing θS in the second operation region II is also stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N.

Further, the target opening degree ST of the throttle valve 20 required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 5 (A), it is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N, and the EGR required to make the air-fuel ratio the target air-fuel ratio shown in FIG. The target opening degree SE of the control valve 31 is shown in FIG.
As shown in (B), it is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N.

Further, in the embodiment according to the present invention, the fuel injection pressure in the second operating region II, that is, the target fuel pressure P in the common rail 34, is the required torque TQ and the engine speed N as shown in FIG. It is stored in advance in the ROM 42 in the form of a map as a function. By the way, the catalyst 25 does not exhibit a good oxidation function unless it becomes higher than the activation temperature corresponding to the kind of the catalyst, for example, 350 ° C. Therefore, in order to satisfactorily oxidize unburned hydrocarbons contained in the exhaust gas. It is necessary to keep the temperature of the catalyst 25 at an activation temperature or higher, for example, 350 ° C. or higher.

However, when the engine is idling, the amount of fuel injection is small and therefore the amount of heat generated is small, so the exhaust gas temperature becomes low. Therefore, if the engine is left in the idling operation state for a long period of time, the temperature of the catalyst 25 will drop below the activation temperature. Therefore, in the present invention, when the temperature of the catalyst 25 falls below the lower limit temperature which is slightly higher than the activation temperature during engine idling operation, the temperature of the catalyst 25 is raised so that the temperature of the catalyst 25 does not fall below the activation temperature. There is.

Before specifically describing this, the idling operation control performed in the embodiment of the present invention will be described first. In the embodiment according to the present invention, the idling operation is performed under the low temperature combustion, and at this time, as described above, the throttle valve 20 and the EGR control valve 3 are operated.
1 is closed to near full closure. During idling operation, the idling speed N of the engine is controlled so as to reach the target idling speed tN. The idling speed is controlled by controlling the opening of the throttle valve 20, that is, the intake air amount. Done by.

On the other hand, the mass flow rate Ga of the actual intake air sucked into the combustion chamber 5 (hereinafter, simply referred to as the intake air amount Ga) is detected by the mass flow meter 49. In the embodiment of the present invention, idling is performed. During operation, the fuel injection amount Q required to bring the air-fuel ratio to the target air-fuel ratio A / F is calculated from the actual intake air amount Ga and the target air-fuel ratio A / F during idling. Therefore, during idling operation, if the intake air amount is increased to increase the engine speed, the fuel injection amount Q is increased, and if the intake air amount is decreased to decrease the engine speed, the fuel injection amount Q is decreased. To be

Further, in the embodiment according to the present invention, the EGR rate during idling operation is controlled so as to become the target EGR rate during idling operation based on the pressure PM in the intake passage downstream of the throttle valve 20. That is, when the intake air amount Ga and the EGR gas amount are determined, the pressure PM in the intake passage downstream of the throttle valve 20 is determined. During the idling operation, the intake air amount Ga is almost constant, so if the EGR gas amount was the target amount at this time, that is, EG
If the R rate is equal to the target EGR rate, the pressure PM in the intake passage downstream of the throttle valve 20 becomes a certain constant pressure. Therefore, conversely, the EGR is performed so that the pressure PM in the intake passage downstream of the throttle valve 20 becomes a certain constant pressure.
If the amount is controlled, the EGR rate becomes the target EGR rate.

Therefore, in the embodiment of the present invention, a certain constant pressure in the intake passage is stored in advance as the target pressure PM0 so that the pressure PM in the intake passage downstream of the throttle valve 20 becomes the target pressure PM0. By controlling the opening degree of the EGR control valve 31, the EGR rate is adjusted to the target EG.
The R rate is set. Next, a first embodiment for preventing the temperature of the catalyst 25 from falling below the activation temperature during idling operation will be described with reference to FIG.

During the idling operation, fuel injection is usually performed before the compression top dead center, and this fuel injection is indicated by Q'in FIG. Temperature T _c is slightly higher limit temperature than the activation temperature T of the catalyst 25 in the first embodiment
When it becomes lower than _min , the injection timing is delayed by ΔθS at Q in FIG. 16, that is, the fuel injection is performed after the compression top dead center.

As shown by Q in FIG. 16, when the injection timing is delayed, the output of the engine is reduced, and thus the engine speed N
Is reduced. When the engine speed N decreases, the intake air amount is increased so as to increase the engine speed N to the target idling speed N _0, and the fuel injection amount Q is accordingly increased. When the fuel injection amount Q is increased, the exhaust gas temperature rises and thus the temperature _{Tc of the} catalyst 25 rises. Thus, it is possible to prevent the temperature T _{c of the} catalyst 25 from dropping below the activation temperature.

Next, the operation control of the engine will be described with reference to FIGS. 17 and 18. Referring to FIGS. 17 and 18, first, at step 100, it is judged if the flag I indicating that the engine operating condition is the first operating region I is set or not. When the flag I is set, that is, when the operating region of the engine is the first operating region I, the routine proceeds to step 101, where the required load L
Is larger than the first boundary X (N). When L ≦ X (N), the routine proceeds to step 103, where low temperature combustion is performed.

That is, at step 103, the required torque TQ is calculated from the map shown in FIG. 9 (B). Next, at step 104, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 105, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. 12 (B). Then step 10
6, the injection start timing θS from the map shown in FIG.
Is calculated. Next, at step 107, FIG.
The target fuel pressure in the common rail 34, that is, the injection pressure P is calculated from the map shown in FIG.

Next, at step 108, it is judged if the depression amount of the accelerator pedal 50 is zero. When the depression amount of the accelerator pedal 50 is zero, step 1
At 09, it is judged from the output pulse of the vehicle speed sensor 53 whether or not the vehicle speed is zero. When the vehicle speed is zero, the routine proceeds to step 110, where it is judged from the output signal of the neutral switch 54 whether or not the automatic transmission 38 is in the neutral position. When the automatic transmission 38 is in the neutral position, the routine proceeds to step 111, where it is determined whether or not a fixed time has elapsed since the automatic transmission 38 was in the neutral position. To be done.

[0079] when it is determined that the Aidorindo operating state temperature control of the catalyst 25 is made the routine proceeds to step 1 12. This temperature control routine is shown in FIG. On the other hand, when "NO" is determined in any of steps 108 to 111, that is, when the engine is not in the idling operation state, the routine proceeds to step 113, where the injection amount Q is calculated from the map shown in FIG. 11 (A).

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 then step 116.
Then, the second combustion is performed. That is, step 116
Then, the required torque TQ is calculated from the map shown in FIG. 9 (B). Next, at step 117, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 118, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. 15 (B).
Next, at step 119, the injection amount Q is calculated from the map shown in FIG. Next, at step 120, the injection start timing θS is calculated from the map shown in FIG. 14 (B). Next, at step 121, the target fuel pressure in the common rail 34, that is, the injection pressure P is calculated from the map shown in FIG.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 100 to step 114, where it is judged if the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 116
Then, the second combustion is performed. On the other hand, step 114
When it is determined that L <Y (N), the routine proceeds to step 115, where the flag I is set, then the routine proceeds to step 103, where low temperature combustion is performed.

Next, the first embodiment of the temperature control performed in step 112 of FIG. 18 will be described with reference to FIG. Referring to FIG. 19, first, step 20
At 0, the engine speed N is the target idling speed tN
Is higher than the above. When N> tN, the routine proceeds to step 201, where the constant value α is subtracted from the correction value ΔST for the opening of the throttle valve 20, and then the routine proceeds to step 203. On the other hand, when N ≦ tN, step 20
Proceeding to step 2, the constant value α is added to the correction value ΔST. Next, at step 203, the target opening ST of the throttle valve 20
The final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to.

Next, at step 204, the target air-fuel ratio A /
F is calculated, and then in step 205, the mass flowmeter 4
The intake air amount Ga detected by 9 is taken in. Next, at step 206, the fuel injection amount Q required to bring the air-fuel ratio to the target air-fuel ratio A / F is calculated based on the target air-fuel ratio A / F and the intake air amount Ga. That is, when N> tN, the opening degree ST of the throttle valve 20 is decreased, so that the intake air amount Ga is decreased. When the intake air amount Ga decreases, the fuel injection amount Q is decreased, and thus the engine speed N decreases. On the other hand, when N ≦ tN, the opening ST of the throttle valve 20 is increased and the intake air amount Ga is increased. When the intake air amount Ga increases, the fuel injection amount Q increases, and thus the engine speed N increases. In this way, the engine speed N is controlled to the target idling speed tN.

Next, at step 207, the temperature sensor 27
Temperature T of the catalyst 25 detected by _cIs the lower limit temperature T_min
Is lower than that. T_c≧ T_minAt
Jumps to step 209. On the other hand, T_c<
T_minIf so, proceed to step 208 and shown in FIG.
The injection start timing θS is a predetermined value ΔθS
Be slowed down. As a result, the exhaust gas temperature
The temperature of the catalyst 25 is raised._cRise
It is tightened.

Next, at step 209, the pressure sensor 39
It is determined whether the pressure PM in the surge tank 12 detected by is higher than the target pressure PM0. PM> PM
When it is 0, the routine proceeds to step 210, where the EGR control valve 31
The constant value β is subtracted from the correction value ΔSE for the opening degree of
Then, it proceeds to step 212. On the other hand, when PM ≦ PM0, the routine proceeds to step 211, where the correction value ΔSE is a constant value β.
Is added, and then the process proceeds to step 212. Step two
12, the correction value ΔS is added to the target opening degree SE of the EGR control valve 31.
By adding E, the final opening SE of the EGR control valve 31 is calculated.

Thus, the opening S of the EGR control valve 31 is adjusted so that the pressure PM of the surge tank 12 becomes the target pressure PM0.
E is controlled so that the EGR rate becomes the target EGR rate. Next, a second embodiment of the temperature control performed in step 112 of FIG. 18 will be described. In this embodiment the pilot injection Q _p to the compression top dead center prior to the main injection Q _m when the temperature T _c becomes lower than the lower limit temperature T _min of the catalyst 25 as shown in Figure 20 is performed. The injection amount of this pilot injection Q _p is small and constant.
On the other hand, the main injection Q _m is performed after the compression top dead center, and when the injection amount Q increases, the injection amount of the main injection Q _m is increased.

Also in this case, since the injection timing of the main injection Q _m is late, the output of the engine is reduced and thus the engine speed N is reduced. When the engine speed N decreases, the intake air amount is increased so as to increase the engine speed N to the target idling speed N _0, and the fuel injection amount Q is accordingly increased. When the fuel injection amount Q is increased, the exhaust gas temperature rises and thus the temperature _{Tc of the} catalyst 25 rises. Thus the catalyst 25
It will be possible to prevent the temperature T _{c of C} from falling below the activation temperature.

Next, the temperature control routine for executing the second embodiment will be described with reference to FIG. Figure 21
First, at step 300, it is judged if the engine speed N is higher than the target idling speed tN. When N> tN, the routine proceeds to step 301, where a constant value α is subtracted from the correction value ΔST for the opening of the throttle valve 20, and then the routine proceeds to step 303. On the other hand, when N ≦ tN, the routine proceeds to step 302, where a constant value α is added to the correction value ΔST. Then step 303
Then, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 304, the target air-fuel ratio A /
F is calculated, and then in step 305, the mass flowmeter 4
The intake air amount Ga detected by 9 is taken in. Next
At step 306, the target air-fuel ratio A / F and intake air
To set the air-fuel ratio to the target air-fuel ratio A / F based on the amount Ga
The required fuel injection amount Q is calculated. Then step 30
7, the temperature of the catalyst 25 detected by the temperature sensor 27
T _cIs the lower limit temperature T_minIs lower than that.
T_c≧ T_minIf so, jump to step 310
It On the other hand, T_c<T_minThen step 308
To the pilot injection amount Q from the fuel injection amount Q_pSubtract
The main injection quantity Q_mIs calculated. Next,
In step 309, the injection start timing θS of pilot injection_pOh
And the injection start timing θS of the main injection_mIs calculated.

Next, at step 310, the pressure sensor 39
It is determined whether the pressure PM in the surge tank 12 detected by is higher than the target pressure PM0. PM> PM
When it is 0, the routine proceeds to step 311, and the EGR control valve 31
The constant value β is subtracted from the correction value ΔSE for the opening degree of
Then, it proceeds to step 313. On the other hand, when PM ≦ PM0, the routine proceeds to step 312, where the correction value ΔSE is a constant value β.
Is added, and then the process proceeds to step 313. Step 3
At 13, the correction value ΔS is added to the target opening degree SE of the EGR control valve 31.
By adding E, the final opening SE of the EGR control valve 31 is calculated.

Next, a third embodiment of the temperature control performed in step 112 of FIG. 18 will be described. In this embodiment, when the temperature T _{c of the} catalyst 25 becomes lower than the lower limit temperature T _min , the target fuel pressure P in the common rail 34 is reduced by a predetermined value ΔP. When the target fuel pressure in the common valve 34 is reduced, the fuel injection period becomes longer. When the fuel injection period becomes long, the output of the engine decreases, and thus the engine speed N decreases. When the engine speed N decreases, the intake air amount is increased so as to increase the engine speed N to the target idling speed N _0, and the fuel injection amount Q is accordingly increased. When the fuel injection amount Q is increased, the exhaust gas temperature rises, and thus the catalyst 25
Temperature T _c of the temperature rises. Thus, it is possible to prevent the temperature T _{c of the} catalyst 25 from dropping below the activation temperature.

Next, a temperature control routine for executing the third embodiment will be described with reference to FIG. FIG. 22
First, at step 400, it is judged if the engine speed N is higher than the target idling speed tN. When N> tN, the routine proceeds to step 401, where the constant value α is subtracted from the correction value ΔST for the opening of the throttle valve 20, and then the routine proceeds to step 403. On the other hand, when N ≦ tN, the routine proceeds to step 402, where a constant value α is added to the correction value ΔST. Then step 403
Then, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 404, the target air-fuel ratio A /
F is calculated, and then in step 405, the mass flowmeter 4
The intake air amount Ga detected by 9 is taken in. Next
At step 406, the target air-fuel ratio A / F and intake air
To set the air-fuel ratio to the target air-fuel ratio A / F based on the amount Ga
The required fuel injection amount Q is calculated. Then step 40
7, the temperature of the catalyst 25 detected by the temperature sensor 27
T _cIs the lower limit temperature T_minIs lower than that.
T_c≧ T_minIf, jump to step 409
It On the other hand, T_c<T_minThen step 408
To the target fuel pressure P in the common rail 34 in advance.
The final common by subtracting the value ΔP
The target fuel pressure P in the rail 34 is calculated. Thus
The fuel pressure in the Monrail 34 will be reduced.
It

Next, at step 409, the pressure sensor 39
It is determined whether the pressure PM in the surge tank 12 detected by is higher than the target pressure PM0. PM> PM
When it is 0, the routine proceeds to step 410, where the EGR control valve 31
The constant value β is subtracted from the correction value ΔSE for the opening degree of
Then, the process proceeds to step 412. On the other hand, when PM ≦ PM0, the routine proceeds to step 411, where the correction value ΔSE is a constant value β.
Is added, and then the process proceeds to step 412. Step 4
12, the correction value ΔS is added to the target opening degree SE of the EGR control valve 31.
By adding E, the final opening SE of the EGR control valve 31 is calculated.

Next, a fourth embodiment of the temperature control performed in step 112 of FIG. 18 will be described. The supply amount of the EGR gas is caused to decrease when the temperature T _c of the catalyst 25 is lower than the lower limit temperature T _min in this embodiment. When the EGR gas supply decreases, the surge tank 12
The pressure inside will decrease and thus the pumping loss will increase. When pumping loss increases, the output of the engine decreases,
Thus, the engine speed N decreases. When the engine speed N decreases, the intake air amount is increased so as to increase the engine speed N to the target idling speed N _0, and the fuel injection amount Q is accordingly increased. When the fuel injection amount Q is increased, the exhaust gas temperature rises, and thus the temperature T _{c of the} catalyst 25 is increased.
Rises. Thus, it is possible to prevent the temperature T _{c of the} catalyst 25 from dropping below the activation temperature.

In this embodiment, the target pressure PM0 in the surge tank 12 is reduced by a constant value ΔPM to reduce the supply amount of EGR gas. That is, when the target pressure PM0 in the surge tank 12 is lowered, the pressure PM in the surge tank 12 becomes equal to the target pressure PM.
The EGR control valve 31 is closed until it becomes 0, and thus the supply amount of EGR gas is reduced.

Next, a temperature control routine for executing the fourth embodiment will be described with reference to FIG. FIG. 23
First, in step 500, it is judged if the engine speed N is higher than the target idling speed tN. When N> tN, the routine proceeds to step 501, where a constant value α is subtracted from the correction value ΔST for the opening of the throttle valve 20, and then the routine proceeds to step 503. On the other hand, when N ≦ tN, the routine proceeds to step 502, where a fixed value α is added to the correction value ΔST. Then step 503
Then, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 504, the target air-fuel ratio A /
F is calculated, and then in step 505, the mass flowmeter 4
The intake air amount Ga detected by 9 is taken in. Next
At step 506, the target air-fuel ratio A / F and the intake air are
To set the air-fuel ratio to the target air-fuel ratio A / F based on the amount Ga
The required fuel injection amount Q is calculated. Then step 50
7, the temperature of the catalyst 25 detected by the temperature sensor 27
T _cIs the lower limit temperature T_minIs lower than that.
T_c≧ T_minIf yes, jump to step 509
It On the other hand, T_c<T_minThen step 508
To the target pressure PM0 in the surge tank 12
The final target pressure PM by subtracting the value ΔPM
0 is calculated. As a result, as described above, the EGR gas
The supply amount of is reduced.

Next, at step 509, the pressure sensor 39
It is determined whether the pressure PM in the surge tank 12 detected by is higher than the target pressure PM0. PM> PM
When it is 0, the routine proceeds to step 510, where the EGR control valve 31
The constant value β is subtracted from the correction value ΔSE for the opening degree of
Then, it proceeds to step 512. On the other hand, when PM ≦ PM0, the routine proceeds to step 511, where the correction value ΔSE is set to a constant value β.
Is added, and then the process proceeds to step 512. Step 5
12, the correction value ΔS is added to the target opening degree SE of the EGR control valve 31.
By adding E, the final opening SE of the EGR control valve 31 is calculated.

Next, a fifth embodiment of the temperature control performed in step 112 of FIG. 18 will be described. Target idling speed tN is raised when the temperature T _c of the catalyst 25 becomes lower than the lower limit temperature T _min in this embodiment. If the target idling speed tN is increased, the intake air amount is increased, and the fuel injection amount Q is increased accordingly. When the fuel injection amount Q is increased, the exhaust gas temperature rises and thus the temperature _{Tc of the} catalyst 25 rises. Thus, it is possible to prevent the temperature T _{c of the} catalyst 25 from dropping below the activation temperature.

In this embodiment, even if the intake air amount is increased, the target pressure PM0 in the surge tank 12 is also increased when the target idling speed tN is increased so as to maintain the EGR ratio at the target EGR ratio. To be
Next, a temperature control routine for executing the fifth embodiment will be described with reference to FIG.

Referring to FIG. 24, first, step 6
Catalyst detected by temperature sensor 27 at 00
It is determined whether or not the temperature T _{c of} is lower than the lower limit temperature T _min . When T _c ≧ T _min, the process jumps to step 603. On the other hand, when T _c <T _min , step 6
Go to 01 and set a constant value ΔN for the target idling speed tN.
Is added. That is, the target idling speed tN is increased. Next, at step 602, the target pressure PM0 in the surge tank 12 is raised by a predetermined value δ in order to maintain the EGR rate at the target EGR rate.
Then, the process proceeds to step 603.

At step 603, it is judged if the engine speed N is higher than the target idling speed tN.
When N> tN, the routine proceeds to step 604, where the constant value α is subtracted from the correction value ΔST for the opening degree of the throttle valve 20, and then the routine proceeds to step 606. On the other hand, when N ≦ tN, the routine proceeds to step 605, where a fixed value α is added to the correction value ΔST. Next, at step 606, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 607, the target air-fuel ratio A /
F is calculated, and then in step 608, the mass flowmeter 4
The intake air amount Ga detected by 9 is taken in. Next, at step 609, the fuel injection amount Q required to bring the air-fuel ratio to the target air-fuel ratio A / F is calculated based on the target air-fuel ratio A / F and the intake air amount Ga. Then step 61
At 0, the surge tank 1 detected by the pressure sensor 39
It is determined whether or not the pressure PM in 2 is higher than the target pressure PM0. When PM> PM0, the routine proceeds to step 611, where the constant value β is subtracted from the correction value ΔSE for the opening degree of the EGR control valve 31, and then the routine proceeds to step 613. On the other hand, when PM ≦ PM0, the routine proceeds to step 612, where a fixed value β is added to the correction value ΔSE, and then step 61
Go to 3. In step 613, the final opening SE of the EGR control valve 31 is calculated by adding the correction value ΔSE to the target opening SE of the EGR control valve 31.

Next, a sixth embodiment of the temperature control performed in step 112 of FIG. 18 will be described. In the first operating region I, low temperature combustion is normally performed under a lean air-fuel ratio. Therefore, the exhaust gas contains excess oxygen, and this excess oxygen is adsorbed in the catalyst 15. Therefore, when a large amount of unburned HC and CO are discharged from the combustion chamber 5, these unburned HC and CO are oxidized by the large amount of oxygen adsorbed on the catalyst 15, and the temperature of the catalyst 25 is increased by the heat of oxidation reaction at this time. Is raised.

Therefore, in the sixth embodiment, the air-fuel ratio is made rich when the temperature T _{c of the} catalyst 25 becomes lower than the lower limit temperature T _min . When the air-fuel ratio is made rich, a large amount of unburned HC and CO are discharged from the engine, and thus the temperature _Tc of the catalyst 25 rises due to the heat of oxidation reaction. As a result, it is possible to prevent the temperature T _{c of the} catalyst 25 from falling below the activation temperature.

Next, a temperature control routine for executing the sixth embodiment will be described with reference to FIG. Figure 25
First, at step 700, it is judged if the engine speed N is higher than the target idling speed tN. When N> tN, the routine proceeds to step 701, where a constant value α is subtracted from the correction value ΔST for the opening of the throttle valve 20, and then the routine proceeds to step 703. On the other hand, when N ≦ tN, the routine proceeds to step 702, where a fixed value α is added to the correction value ΔST. Then step 703
Then, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 704, the temperature sensor 27
Temperature T of the catalyst 25 detected by _cIs the lower limit temperature T_min
Is lower than that. T_c≧ T_minAt
Proceeds to step 706 to calculate the target air-fuel ratio A / F
It The target air-fuel ratio calculated at this time is lean.
It Then, it proceeds to step 707. On the other hand, T_c<
T_minIf so, the routine proceeds to step 705, where the target air-fuel ratio A /
F is a predetermined rich air-fuel ratio (A / F)_RTo be
It Next, at step 707, the mass flowmeter 49 detects
The taken out intake air amount Ga is taken in. Then step
708 is based on the target air-fuel ratio A / F and the intake air amount Ga.
Fuel required to set the air-fuel ratio to the target air-fuel ratio A / F
The injection amount Q is calculated.

Next, at step 709, the pressure sensor 39
It is determined whether the pressure PM in the surge tank 12 detected by is higher than the target pressure PM0. PM> PM
When it is 0, the routine proceeds to step 710, where the EGR control valve 31
The constant value β is subtracted from the correction value ΔSE for the opening degree of
Then, it proceeds to step 712. On the other hand, when PM ≦ PM0, the routine proceeds to step 711, where the correction value ΔSE is a constant value β.
Is added, and then the process proceeds to step 712. Step 7
12, the correction value ΔS is added to the target opening degree SE of the EGR control valve 31.
By adding E, the final opening SE of the EGR control valve 31 is calculated.

Next, a seventh embodiment of the temperature control performed in step 112 of FIG. 18 will be described. In this embodiment, when the temperature T _{c of the} catalyst 25 becomes lower than the lower limit temperature T _min , the first fuel injection Q _i is performed at the beginning of the intake stroke and the first fuel injection Q _i is made at the end of the compression stroke as shown in FIG. the second fuel injection, that is the main injection Q _m is performed. In other words, in this embodiment, so-called VIGOM injection is performed. In the embodiment shown in FIG. 16, the injection amount of the first fuel injection Q _i is small and constant, and when the fuel injection amount Q increases, the injection amount of the main injection Q _m increases.

As shown in FIG. 26, when the first fuel injection Q _i is performed during the intake stroke, this fuel forms a premixed gas that spreads throughout the combustion chamber 5. When the premixed air is thus formed, the ignition delay when the main injection Q _m is performed becomes short, but a part of the premixed air is discharged from the engine without being burned. That is, when such a rubber injection is performed, a large amount of unburned HC and CO are discharged from the engine. As a result, the temperature T _c of the catalyst 25 is raised by the heat of oxidation reaction, and thus it is possible to prevent the temperature T _{c of the} catalyst 25 from dropping below the activation temperature.

Next, the temperature control routine for executing the seventh embodiment will be described with reference to FIG. FIG. 27
First, at step 800, it is judged if the engine speed N is higher than the target idling speed tN. When N> tN, the routine proceeds to step 801, where the constant value α is subtracted from the correction value ΔST for the opening of the throttle valve 20, and then the routine proceeds to step 803. On the other hand, when N ≦ tN, the routine proceeds to step 802, where a fixed value α is added to the correction value ΔST. Then Step 803
Then, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 804, the target air-fuel ratio A /
F is calculated, and then in step 805, the mass flowmeter 4
The intake air amount Ga detected by 9 is taken in. Next
At step 806, the target air-fuel ratio A / F and the intake air are
To set the air-fuel ratio to the target air-fuel ratio A / F based on the amount Ga
The required fuel injection amount Q is calculated. Then step 80
7, the temperature of the catalyst 25 detected by the temperature sensor 27
T _cIs the lower limit temperature T_minIs lower than that.
T_c≧ T_minIf yes, jump to step 810
It On the other hand, T_c<T_minThen step 808
To the first fuel which is predetermined from the fuel injection amount Q.
Injection amount Q_iBy subtracting the main injection amount Q_mIs arithmetic
Will be issued. Next, at step 809, the first injection Q
_iInjection start timing θS_iAnd main injection Q_mWhen the injection of
Period θS_mIs calculated.

Next, at step 810, the pressure sensor 39
It is determined whether the pressure PM in the surge tank 12 detected by is higher than the target pressure PM0. PM> PM
When it is 0, the routine proceeds to step 811, and the EGR control valve 31
The constant value β is subtracted from the correction value ΔSE for the opening degree of
Then, the process proceeds to step 813. On the other hand, when PM ≦ PM0, the routine proceeds to step 812, where the correction value ΔSE is set to a constant value β.
Is added, and then the process proceeds to step 813. Step 8
At 13, the correction value ΔS is added to the target opening degree SE of the EGR control valve 31.
By adding E, the final opening SE of the EGR control valve 31 is calculated.

Next, an eighth embodiment of the temperature control performed in step 112 of FIG. 18 will be described. In this embodiment, when the temperature T _{c of the} catalyst 25 becomes lower than the lower limit temperature T _{min, the} air-fuel ratio is made extremely rich only during one fuel injection, for example. That is, in this embodiment, a large amount of unburned HC and CO are sent to the catalyst 25 at once, and the temperature of the catalyst 25 is rapidly raised by the heat of the oxidation reaction at this time.

Next, a temperature control routine for executing the eighth embodiment will be described with reference to FIG. FIG. 28
First, in step 900, it is judged if the engine speed N is higher than the target idling speed tN. When N> tN, the routine proceeds to step 901, where the constant value α is subtracted from the correction value ΔST for the opening of the throttle valve 20, and then the routine proceeds to step 903. On the other hand, when N ≦ tN, the routine proceeds to step 902, where a fixed value α is added to the correction value ΔST. Then step 903
Then, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 904, it is judged if a fixed time has elapsed since the air-fuel ratio was made extremely rich only during one fuel injection. When the fixed time has elapsed, the routine proceeds to step 905, where it is judged if the temperature T _{c of the} catalyst 25 detected by the temperature sensor 27 is lower than the lower limit temperature T _min . When T _c ≧ T _min , step 9
In step 07, the target air-fuel ratio A / F is calculated. The target air-fuel ratio calculated at this time is lean. Then, it proceeds to step 908. In contrast are T _c <T _mi becomes the _n greatly rich air-fuel ratio the target air-fuel ratio A / F is predetermined proceeds to step 906 (A / F) _R. At this time, the air-fuel ratio is greatly enriched only during one injection. After that, the routine jumps from step 904 to step 907 until the fixed time elapses, and the air-fuel ratio is made lean.

Next, at step 908, the mass flowmeter 49
The intake air amount Ga detected by is taken in. Next, at step 909, the fuel injection amount Q required to bring the air-fuel ratio to the target air-fuel ratio A / F is calculated based on the target air-fuel ratio A / F and the intake air amount Ga. Then step 910
Then, the surge tank 12 detected by the pressure sensor 39
It is determined whether the internal pressure PM is higher than the target pressure PM0. When PM> PM0, the routine proceeds to step 911, where the constant value β is subtracted from the correction value ΔSE for the opening degree of the EGR control valve 31, and then the routine proceeds to step 913. On the other hand, when PM ≦ PM0, the routine proceeds to step 912, where a fixed value β is added to the correction value ΔSE, and then step 91
Go to 3. In step 913, the final opening SE of the EGR control valve 31 is calculated by adding the correction value ΔSE to the target opening SE of the EGR control valve 31.

Next, a ninth embodiment of the temperature control performed in step 112 of FIG. 18 will be described. In this embodiment, when the temperature T _{c of the} catalyst 25 becomes lower than the lower limit temperature T _{min, the} additional fuel Q _add is injected during the latter half of the expansion stroke or during the exhaust stroke, for example, only during one fuel injection. This additional fuel Q _add is discharged from the engine without burning. Therefore, also in this embodiment, a large amount of unburned HC and CO are sent all at once to the catalyst 25, and the temperature of the catalyst 25 is rapidly raised by the heat of the oxidation reaction at this time.

Next, a temperature control routine for executing the ninth embodiment will be described with reference to FIG. FIG. 29
First, at step 1000, it is judged if the engine speed N is higher than the target idling speed tN. When N> tN, step 1001
To the correction value ΔST for the opening of the throttle valve 20.
A constant value α is subtracted from, and the process proceeds to step 1003. On the other hand, when N ≦ tN, the routine proceeds to step 1002, where the fixed value α is added to the correction value ΔST. Next, at step 1003, the final opening ST of the throttle valve 20 is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20.

Next, at step 1004, the target air-fuel ratio A
/ F is calculated, and then in step 1005, the intake air amount Ga detected by the mass flowmeter 49 is taken in.
Next, at step 1006, the fuel injection amount Q required to bring the air-fuel ratio to the target air-fuel ratio A / F is calculated based on the target air-fuel ratio A / F and the intake air amount Ga. Next, at step 1007, the additional fuel Q _{add is} added only at the time of one fuel injection.
It is determined whether or not a fixed time has elapsed since the injection of. When a certain period of time has passed, the routine proceeds to step 1008, where the temperature T of the catalyst 25 detected by the temperature sensor 27 is detected.
_It is determined whether or not _c is lower than the lower limit temperature T _min . T
_{When c} ≧ T _min, the process jumps to step 1010. On the other hand, if T _c <T _min , step 100
In step 9, the additional fuel amount Q _add is calculated. At this time, the additional fuel Q _add is injected only at the time of one injection. After that, the routine jumps from step 1007 to step 1010 until a certain time elapses, during which the additional fuel Q _add is not injected.

Next, at step 1010, the pressure sensor 3
It is determined whether the pressure PM in the surge tank 12 detected by 9 is higher than the target pressure PM0. PM> P
When M0, the routine proceeds to step 1011 where the constant value β is subtracted from the correction value ΔSE for the opening degree of the EGR control valve 31, and then the routine proceeds to step 1013. On the other hand, PM ≦ PM
When it is 0, the routine proceeds to step 1012, where the fixed value β is added to the correction value ΔSE, and then the routine proceeds to step 1013.
In step 1013, the target opening degree SE of the EGR control valve 31
By adding the correction value ΔSE to
The opening degree SE of the control valve 31 is calculated.

[0123]

EFFECTS OF THE INVENTION It is possible to prevent the catalyst from dropping below the activation temperature when the idling operation is performed under low temperature combustion.

[Brief description of 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 a fuel molecule.

FIG. 5 is a diagram showing a relationship between a smoke generation amount 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 operating region I and a second operating region II.

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

FIG. 9 is a diagram showing a required torque.

FIG. 10 is a diagram showing an air-fuel ratio in a first operating region I.

FIG. 11 is a diagram showing a map of an injection amount and the like.

FIG. 12 is a diagram showing a map of a target opening degree of a throttle valve and the like.

FIG. 13 is a diagram showing an air-fuel ratio in the second combustion.

FIG. 14 is a diagram showing a map of an injection amount and the like.

FIG. 15 is a diagram showing a map of a target opening degree etc. of a throttle valve.

FIG. 16 is a diagram showing an injection timing in the first embodiment.

FIG. 17 is a flowchart for controlling the operation of the engine.

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

FIG. 19 is a flowchart for executing temperature control in the first embodiment.

FIG. 20 is a diagram showing an injection timing in the second embodiment.

FIG. 21 is a flow chart for executing temperature control in the second embodiment.

FIG. 22 is a flow chart for executing temperature control in the third embodiment.

FIG. 23 is a flow chart for executing temperature control in the fourth embodiment.

FIG. 24 is a flow chart for executing temperature control in the fifth embodiment.

FIG. 25 is a flow chart for executing temperature control in the sixth embodiment.

FIG. 26 is a diagram showing an injection timing in the seventh embodiment.

FIG. 27 is a flow chart for executing temperature control in the seventh embodiment.

FIG. 28 is a flow chart for executing temperature control in the eighth embodiment.

FIG. 29 is a flow chart for executing temperature control in the ninth embodiment.

[Explanation of symbols]

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

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI F02D 41/02 325 F02D 41/02 325E 41/40 41/40 C 43/00 301 43/00 301E 301J 301N F02M 25/07 570 F02M 25/07 570G 570J (72) Inventor Masato Goto 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Hiroki Murata 1-cho, Toyota-shi, Aichi Toyota-motor Co., Ltd. (56 ) References JP-A-7-4287 (JP, A) JP-A-8-177654 (JP, A) JP-A-8-86251 (JP, A) JP-A-9-287527 (JP, A) JP-A-9-287527 (JP, A) 9-287528 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/00-41/40

Claims (18)

(57) [Claims] 1. When the amount of inert gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak.
However, by further increasing the amount of inert gas supplied to the combustion chamber,
When going, the fuel at the time of combustion in the combustion chamber and the surrounding
When the gas temperature becomes lower than the soot formation temperature, soot is almost emitted.
In an internal combustion engine that does not live , the amount of the inert gas supplied to the combustion chamber is made larger than the amount of the inert gas at which the amount of soot generated reaches a peak .
The temperature of the fuel and the gas around it is the temperature at which soot is produced.
A temperature detecting means for suppressing the temperature to a lower temperature and arranging a catalyst having an oxidizing function in the engine exhaust passage, and detecting the temperature of the catalyst, and the lower limit of the temperature of the catalyst set in advance during engine idling operation. An internal combustion engine comprising a temperature raising means for raising the temperature of the catalyst when the temperature becomes lower than the temperature. 2. The internal combustion engine according to claim 1, wherein the temperature raising means raises the temperature of the catalyst by raising the exhaust gas temperature when the temperature of the catalyst becomes equal to or lower than the lower limit temperature during engine idling operation. . 3. The internal combustion engine according to claim 2, wherein the temperature increasing means increases the temperature of the catalyst by delaying the fuel injection timing when the temperature of the catalyst becomes equal to or lower than the lower limit temperature during engine idling operation. 4. The temperature increasing means performs pilot injection when the temperature of the catalyst becomes lower than or equal to a lower limit temperature during engine idling operation, and sets the injection timing of the main injection to after compression top dead center to thereby improve the temperature of the catalyst. The internal combustion engine according to claim 2, wherein the engine is increased. 5. The internal combustion engine according to claim 2, wherein the temperature raising means raises the temperature of the catalyst by lowering the fuel injection pressure when the temperature of the catalyst becomes lower than or equal to the lower limit temperature during engine idling operation. 6. The inert gas is recirculated exhaust gas that is recirculated from the engine exhaust passage into the engine intake passage, and the temperature increasing means keeps the temperature of the catalyst below a lower limit temperature during engine idling operation. The internal combustion engine according to claim 2, wherein the temperature of the catalyst is raised by reducing the amount of recirculated exhaust gas. 7. The internal combustion engine according to claim 2, wherein the temperature raising means raises the temperature of the catalyst by raising the idling speed of the engine when the temperature of the catalyst becomes equal to or lower than the lower limit temperature during engine idling operation. organ. 8. The temperature increasing means increases the amount of unburned HC and CO discharged into the engine exhaust passage when the temperature of the catalyst becomes lower than or equal to a lower limit temperature during engine idling operation. The internal combustion engine according to claim 1, wherein the temperature is raised. 9. The internal combustion engine according to claim 8, wherein the temperature raising means raises the temperature of the catalyst by making the air-fuel ratio rich when the temperature of the catalyst becomes equal to or lower than the lower limit temperature during engine idling operation. 10. The temperature raising means increases the temperature of the catalyst by injecting fuel twice during the intake stroke and at the end of the compression stroke when the temperature of the catalyst becomes lower than the lower limit temperature during engine idling operation. The internal combustion engine according to claim 8, which is raised. 11. The temperature increasing means instantly makes the air-fuel ratio rich when the temperature of the catalyst becomes lower than or equal to a lower limit temperature during engine idling operation, and thereafter makes the air-fuel ratio lean for a predetermined period. The internal combustion engine according to claim 8, wherein the temperature of the catalyst is raised by the method. 12. The temperature raising means raises the temperature of the catalyst by injecting additional fuel during the latter half of the expansion stroke or during the exhaust stroke when the temperature of the catalyst becomes lower than the lower limit temperature during engine idling operation. The internal combustion engine according to claim 8, further comprising: 13. The temperature raising means raises the exhaust gas temperature when the temperature of the catalyst becomes lower than or equal to the lower limit temperature during engine idling operation, and the amount of unburned HC and CO discharged into the engine exhaust passage. The internal combustion engine of claim 1, wherein the temperature of the catalyst is raised by increasing the temperature. 14. The catalyst is an oxidation catalyst, a three-way catalyst or NO.
The internal combustion engine of claim 1, wherein the internal combustion engine comprises at least one _x absorbent. 15. An exhaust gas recirculation device for recirculating exhaust gas discharged from a combustion chamber into an engine intake passage, wherein the inert gas is recirculated exhaust gas.
Internal combustion engine according to. 16. The internal combustion engine of claim 15, wherein the exhaust gas recirculation rate is approximately 55 percent or more. 17. The first combustion in which the amount of inert gas supplied to the combustion chamber is larger than the amount of soot generated and the soot is hardly generated, and the soot generation becomes peak. The internal combustion engine according to claim 1, further comprising switching means for selectively switching between the second combustion in which the amount of the inert gas supplied to the combustion chamber is smaller than the amount of the inert gas. 18. The engine operating region is divided into a first operating region on the low load side and a second operating region on the high load side, and first combustion is performed in the first operating region to perform the second operating region. Second in the area
The internal combustion engine according to claim 17, wherein the combustion is performed.