JP3409715B2 - 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]

In the vehicle, a brake booster is used to increase the braking force.
The brake booster has a first chamber and a second chamber separated by a power piston, and the first chamber is connected to a negative pressure source. Further, when the braking action is not performed, the second chamber is connected to the first chamber, and therefore, at this time, negative pressure is introduced from the negative pressure source into the first chamber and the second chamber. On the other hand, when the brake pedal is depressed, the first chamber and the second chamber
At the same time as the communication with the chamber is cut off, the second chamber is opened to the atmosphere. Therefore, at this time, a large pressure difference occurs between the first chamber and the second chamber, and the power piston is driven by this pressure difference,
As a result, a large braking force is generated.

As described above, when using the brake booster, a negative pressure source is required. In this case, in an internal combustion engine in which a large negative pressure is generated in the intake passage, the negative pressure generated in the intake passage can be used as a negative pressure source, but in the compression ignition type internal combustion engine, a large negative pressure is usually generated in the intake passage. Since it does not occur, therefore, the compression ignition type internal combustion engine is forced to use a negative pressure pump which is normally driven by the engine.

However, even if the new combustion method is applied to the compression ignition type internal combustion engine, a large negative pressure is generated in the intake passage. Therefore, when the new combustion method is used, it is generated in the intake passage. The negative pressure to be applied can be used as a negative pressure source.

[0012]

In [SUMMARY OF Thus the first invention, the amount of As you increase the amount of inert gas supplied to the combustion chamber soot reached the peak gradually increased, the combustion chamber
If the amount of inert gas supplied to the combustion chamber is further increased,
The temperature of the fuel and the gas around it during combustion inside the soot
In the internal combustion engine, the amount of the inert gas supplied to the combustion chamber is made larger than the amount of the inert gas at which the soot generation peaks .
The fuel and
The temperature of the gas around is lower than the temperature at which soot is produced
The throttle valve is arranged in the engine intake passage so that the negative pressure generated in the intake passage downstream of the throttle valve is introduced into the brake booster.

In the second invention, in the first invention,
When the negative pressure introduced into the brake booster becomes smaller than a preset negative pressure, the opening of the throttle valve is made smaller. In the third invention, in the second invention, the above-mentioned setting is made. The negative pressure is increased as the vehicle speed increases.

In the fourth invention, in the first invention,
Inert gas consists of recirculation exhaust gas supplied into the intake passage downstream of the throttle valve, and is equipped with a recirculation exhaust gas control valve for controlling the supply amount of recirculation exhaust gas, which is introduced into the brake booster. When the generated negative pressure becomes smaller than a preset negative pressure, the opening degree of the recirculation exhaust gas control valve is reduced.

In the fifth invention, in the fourth invention,
When the opening degree of the recirculation exhaust gas control valve is reduced, the fuel injection timing is delayed. According to a sixth aspect of the invention, in the first aspect of the invention, the inert gas comprises recirculation exhaust gas supplied into the intake passage downstream of the throttle valve, and recirculation exhaust gas control for controlling the supply amount of recirculation exhaust gas. With the valve, when the negative pressure introduced into the brake booster becomes smaller than the preset negative pressure, the opening degree of the throttle valve is first reduced, and still it is introduced into the brake booster. When the negative pressure is lower than a preset negative pressure, the opening degree of the recirculation exhaust gas control valve is reduced.

In the seventh invention, in the sixth invention,
When the opening degree of the recirculation exhaust gas control valve is reduced, the fuel injection timing is delayed. In an eighth aspect based on the sixth aspect, the opening degree of the throttle valve is reduced until the air-fuel ratio reaches a predetermined air-fuel ratio. In a ninth aspect based on the first aspect, the inert gas comprises recirculated exhaust gas supplied into the intake passage downstream of the throttle valve, and the exhaust gas recirculation rate is approximately 55% or more.

According to a tenth aspect of the present invention, in the first aspect, a catalyst having an oxidizing function is arranged in the engine exhaust passage. According to the eleventh invention, in the tenth invention, the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst and an NO _x absorbent. In the twelfth invention, in the first invention, in the first combustion in which the amount of the inert gas supplied to the combustion chamber is larger than the amount of the inert gas at which the soot generation peaks and the soot is hardly generated, There is provided a 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 in which the generation amount is the peak.

According to a thirteenth invention, in the twelfth 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. Is performed, and the second combustion is performed in the second operation region.

[0019]

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. An air-fuel ratio sensor 27 is arranged in the exhaust manifold 21.

The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air 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, the fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 34, via a fuel supply pipe 33. Fuel is supplied into the common rail 34 from an electrically controlled variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 via each fuel supply pipe 33. A fuel pressure sensor 36 for detecting a fuel pressure in the common rail 34 is attached to the common rail 34, and a fuel pump 35 is arranged so that the fuel pressure in the common rail 34 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 36. Is controlled.

The electronic control unit 40 is composed of a digital computer and has a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45 and an input port 45 which are connected to each other by a bidirectional bus 41. The output port 46 is provided. The output signal of the air-fuel ratio sensor 27 is input to the input port 45 via the corresponding AD converter 47, and the output signal of the fuel pressure sensor 36 is also input to the input port 45 via the corresponding AD converter 47. A mass flowmeter 37 for detecting the mass of intake air is arranged in the air suction pipe 17 upstream of the throttle valve 20, and an output signal of this mass flowmeter 37 is input via a corresponding AD converter 47 to an input port 45. Entered in. The accelerator pedal 5 has an accelerator pedal 5
A load sensor 51 that generates an output voltage proportional to the stepping amount L of 0 is connected, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. 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, the output pulse of the vehicle speed sensor 53 indicating the vehicle speed is input to the input port 45. On the other hand, the output port 46 is connected via the corresponding drive circuit 48 to the fuel injection valve 6, the throttle valve control step motor 19,
The step motor 30 for controlling the EGR control valve and the fuel pump 35 are connected.

The air suction pipe 17 downstream of the throttle valve 20 is connected to the brake booster 60 via a negative pressure conduit 61. As shown in FIG. 2, the brake booster 60 includes a power piston 63, a first chamber 64 and a second chamber 65 formed on both sides of the power piston 63, and a plunger 6.
It has an operating rod 67 with 6 and an operating valve 68. A push rod 69 is fixed to the power piston 63, and a master cylinder 70 that generates a brake hydraulic pressure is driven by the push rod 69. Further, the operating rod 67 is connected to the brake pedal 71.

The negative pressure conduit 61 is connected to the first chamber 64, and inside the negative pressure conduit 61, a check valve 62 is arranged which can flow only from the first chamber 64 toward the air suction pipe 17. When a negative pressure larger than the negative pressure in the first chamber 64 is generated in the air suction pipe 17, the check valve 62 is opened, and thus the first chamber 64 is opened.
The negative pressure therein is maintained at the maximum negative pressure generated in the air suction pipe 17.

As shown in FIG. 2, the brake pedal 71
Is released, the first chamber 64 and the second chamber 65 communicate with each other through a pair of communication passages 72, 73,
Therefore, the same negative pressure is generated in the first chamber 64 and the second chamber 65. Next, when the brake pedal 71 is depressed, the operating valve 68 moves leftward together with the operating rod 67. As a result, the communication passage 72 is blocked by the operation valve 68, and the plunger 66 is separated from the operation valve 68, so that the second chamber 65 is opened to the atmosphere through the atmosphere communication passage 74, and thus the second chamber 65 is opened.
The inside is atmospheric pressure. Therefore, a pressure difference is generated between the first chamber 64 and the second chamber 65, and this power difference causes the power piston 63 to move to the left.

On the other hand, when the brake pedal 71 is released, the plunger 66 closes the atmosphere communication passage 74 and opens the communication passages 72 and 73, so that the first chamber 64 and the second chamber 65 are re-established. They communicate with each other via 73.
A pressure sensor 75 for detecting the absolute pressure in the first chamber 64 is attached to the brake booster 60, and the output signal of this pressure sensor 75 is input to the input port 45 via the corresponding AD converter 47.

FIG. 3 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. 3) 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. 3, in this experimental example, the EGR rate increases as the air-fuel ratio A / F decreases, and when the air-fuel ratio is equal to or less than the theoretical air-fuel ratio (≈14.6), the EGR rate is 65% or more.

As shown in FIG. 3, when the air-fuel ratio A / F is decreased 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. 4 (A) shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of smoke generated is the largest, and FIG. 4 (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. 4 (A) and FIG. 4 (B), in the case shown in FIG. 4 (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. 3 and 4, 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 generated is almost zero, FIG.
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. 4 (B) in which almost no soot is generated.
The combustion temperature inside is low.

Second, 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, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 5 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 formation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon shown in FIG. After that, it will grow to soot. Therefore, as described above, when the soot generation amount becomes almost zero, the HC and CO emission amounts increase as shown in FIG. 3, but 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. 3 and 4, when the combustion temperature in the combustion chamber 5 is low, the amount of soot generated 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 generated, 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 generated. 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 there is only air around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel 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, and 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. 6 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, the curve A in FIG. 6 strongly cools the EGR gas to keep the EGR gas temperature at 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. 6, when the EGR gas is strongly cooled, the soot generation peaks 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. 6, when the EGR gas is slightly cooled, the soot generation amount reaches a peak when the EGR rate is slightly higher than 50%, and 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. 6, 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. 6 shows the amount of smoke generated when the engine load is relatively high. The EGR rate at which the amount of soot generated reaches a peak when the engine load decreases, the EGR rate slightly decreases, and the EGR rate at which soot almost does not occur. 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. 7 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. In addition, in FIG. 7, 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. 7, the ratio of air, that is, the amount of air in the mixed gas, shows the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 7, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 7, the ratio of the EGR gas, that is, the amount of EGR gas in the mixed gas is such 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. 7, 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. 7, 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 the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. Therefore, in FIG. 7, the required load is larger than Lo in the required load region. The air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced as it becomes larger. In other words, when supercharging is not performed and the air-fuel ratio is maintained at the stoichiometric air-fuel ratio in a region where the required load is larger than Lo, the EGR rate decreases as the required load increases, thus In the region where the required load is larger than Lo, the temperature of the fuel and the gas around it cannot be maintained below the temperature at which soot is generated.

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 through the EGR passage 29, the required load is larger than Lo. EGR rate at 5
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.

When the EGR rate is set to 55% or more in the region where the required load is larger than Lo, the EGR control valve 31 is fully opened and the throttle valve 20 is slightly closed. As described above, FIG. 7 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is made smaller than that shown in FIG. The generation amount of NO _x is reduced to 10 _p .
It can be around pm or less, and even if the air amount is made larger than that shown in FIG. 7, that is, even if the average value of the air-fuel ratio is lean from 17 to 18, the soot generation is prevented. Meanwhile, the amount of NO _x generated can be set to around 10 p.pm or less.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the 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.

Thus, 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. To be 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. 8 shows the first operating region I where the first combustion, that is, the low temperature combustion is performed, and the second operating region II where the second combustion, that is, the combustion by the conventional combustion method is performed. There is. In FIG. 8, the vertical axis TQ shows the required torque, and the horizontal axis N shows the engine speed. Further, in FIG. 8, 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 state 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.

As described above, the two boundaries of the first boundary X (N) and the second boundary Y (N) on the side of lower torque than 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 being performed, soot is hardly generated, and instead, unburned hydrocarbons are in the state of the precursor of soot or the state before it. It is discharged from the combustion chamber 5 in shape. At this time, the unburned hydrocarbons discharged from the combustion chamber 5 are satisfactorily oxidized by the catalyst 25 having an oxidizing function. Catalyst 2
As 5, an oxidation catalyst, a three-way catalyst, or a NO _x absorbent can be used. _The NO _x absorbent absorbs NO _x when the mean air-fuel ratio in the combustion chamber 5 of the lean, the combustion chamber 5
It has a function of releasing NO _x when the average air-fuel ratio in the inside becomes rich.

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

Not only 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. FIG. 9 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 9, the output current I of the air-fuel ratio sensor 27 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.

Next, referring to FIG. 10, the first operating region I
The operation control in the second operation area II will be briefly described. FIG. 10 shows the opening of the throttle valve 20, the opening of the EGR control valve 31, and the EGR with respect to the required torque TQ.
The ratio, the air-fuel ratio, the injection timing and the injection amount are shown. Figure 1
As shown by 0, 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 torque TQ increases, and the EGR The opening degree of the 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. 10, the EGR rate is set to approximately 70% in the first operating region I, and the air-fuel ratio is set to 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. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening degree of the EGR control valve 31 based on the output signal of the air-fuel ratio sensor 27. Further, in the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes late as the required torque TQ becomes high, and the injection completion timing θE also becomes the injection start timing θS.
Becomes slower as it gets slower.

During the idling operation, the throttle valve 20 is closed to the fully closed state, and the EGR control valve 31 is also closed to the fully closed state at this time. 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. 10, 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 it exceeds the rate range (Fig. 6).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operating region II, the 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 this 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 equal to the required torque TQ.
Becomes higher and smaller. Also, this operating area
In II, 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. 11A shows the relationship between the required torque TQ, the depression amount L of the accelerator pedal 50, and the engine speed N. Note that each curve in FIG. 11A represents an equal torque curve, the curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves indicate TQ =
The required torque gradually increases in the order of a, TQ = b, TQ = c, TQ = d. Required torque T shown in FIG. 11 (A)
Q is the accelerator pedal 50 as shown in FIG. 11 (B).
It is stored in advance in the ROM 42 in the form of a map as a function of the depression amount L and the engine speed N. In the present invention, FIG.
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 (B), and the fuel injection amount and the like are calculated based on this required torque TQ.

FIG. 12 shows the target air-fuel ratio A / F in the first operating region I. In FIG. 12, A / F = 1
The target air-fuel ratios of the curves shown by 5.5, A / F = 16, A / F = 17, and A / F = 18 are 15.5, 16, and 1, respectively.
7 and 18, the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 12, the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the air-fuel ratio A / F is leaner as the required torque TQ is lower.

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. 12, the target air-fuel ratio A / F is increased as the required torque TQ decreases. The fuel consumption rate increases as the air-fuel ratio increases, and therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment of the present invention, the target air-fuel ratio A / F is increased as the required torque TQ decreases.

FIG. 13 (A) shows the injection amount Q in the first operation region I, and FIG. 13 (B) shows the injection start timing θS in the first operation region I. FIG.
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. 3 (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 air-fuel ratio is shown in FIG.
Target opening degree ST of the throttle valve 20 required for setting / F
Is a ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N as shown in FIG.
The target opening degree S of the EGR control valve 31 that is stored in the EGR control valve 31 and is required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
As shown in FIG. 14 (B), E is a ROM 4 in advance in the form of a map as a function of the required torque TQ and the engine speed N.
It is stored in 2.

FIG. 15 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. Note that in FIG. 15, A / F = 24, A / F = 3
5, each curve shown by A / F = 45 and A / F = 60 shows the target air-fuel ratios 24, 35, 45, 60, respectively. 16 (A) shows the injection amount Q in the second operation region II, and FIG. 16 (B) shows the injection start timing θS in the second operation region II. As shown in FIG. 16 (A), the injection amount Q in the second operating region II is the required torque T
R in advance in the form of a map as a function of Q and engine speed N
It is stored in the OM 42, and as shown in FIG. 16B, 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. Has been done.

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. 7 (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.

By the way, in the brake booster 60 shown in FIG. 2, the larger the pressure difference between the absolute pressure in the first chamber 64 and the absolute pressure in the second chamber 65, the higher the braking force during braking. In other words, the smaller the absolute pressure in the first chamber 64, that is, the larger the negative pressure in the first chamber 64, the higher the braking force during braking. By the way, in order to satisfactorily brake the vehicle, a higher vehicle speed requires a larger braking force. Therefore, it is preferable that the minimum required negative pressure in the first chamber 64 be increased as the vehicle speed becomes faster. Therefore, in the embodiment according to the present invention, as shown in FIG. 18, a target limit value tP of the absolute pressure in the first chamber 64, which decreases as the vehicle speed SP increases, is set in advance, and the absolute pressure in the first chamber 64 is The target limit value tP is prevented from becoming higher than the target limit value tP.

By the way, in the embodiment according to the present invention, as described above, when the idling operation is performed under the low temperature combustion, the throttle valve 20 and the EGR control valve 31 are closed until they are almost fully closed. A large negative pressure is generated in the air suction pipe 17 downstream of the valve 20. Also, the required torque T is not required even during idling operation.
When Q is small, the opening degrees of the throttle valve 20 and the EGR control valve 31 become small as can be seen from FIG. 10, and therefore the air intake pipe 1 downstream of the throttle valve 20 also at this time.
A large negative pressure is generated in 7.

Further, in the embodiment according to the present invention, the fuel injection is stopped during the deceleration operation, and at this time, the throttle valve 20
Is completely closed. When the throttle valve 20 is fully closed, the negative pressure in the air suction pipe 17 downstream of the throttle valve 20 and the negative pressure in the combustion chamber 5 become extremely large, and as a result, the lubricating oil between the piston 4 and the inner surface of the cylinder bore burns. Room 5
It causes the problem of being sucked inside. Therefore, in the present invention, when the throttle valve 20 is fully closed so that the negative pressure in the combustion chamber 5 becomes somewhat small, the EGR control valve 3
1 is opened and maintained at a predetermined opening. However, at this time, a large negative pressure is generated in the air suction pipe 17 downstream of the throttle valve 20.

As described above, in the embodiment according to the present invention, when the required torque TQ becomes smaller, a large negative pressure is generated in the air suction pipe 17 downstream of the throttle valve 20, and the air suction pipe 17 downstream of the throttle valve 20 is generated even during deceleration operation. Since a large negative pressure is generated therein, the absolute pressure in the first chamber 64 of the brake booster 60 is usually much smaller than the target limit value tP shown in FIG. However, for some reason, the absolute pressure in the first chamber 64 may exceed the target limit value tP shown in FIG.

Therefore, in the present invention, the absolute pressure in the first chamber 64 of the brake booster 60 is the target limit value t shown in FIG.
When it becomes higher than P, the throttle valve 20 or the EGR control valve 31 is gradually closed during low temperature combustion. That is, when the throttle valve 20 is closed, the absolute pressure in the air intake pipe 17 downstream of the throttle valve 20 decreases, and even if the EGR control valve 31 is closed, the absolute pressure in the air intake pipe 17 downstream of the throttle valve 20 is reduced. Since the absolute pressure decreases, the absolute pressure in the first chamber 64 can be decreased by closing the throttle valve 20 or the EGR control valve 31.

In the concrete example according to the present invention, when the absolute pressure in the first chamber 64 of the brake booster 60 becomes higher than the target limit value tP, the throttle valve 20 is first gradually closed. When the throttle valve 20 is closed, the air-fuel ratio gradually decreases, and when the air-fuel ratio reaches a predetermined air-fuel ratio, for example, the stoichiometric air-fuel ratio, the EGR control valve 31 is gradually closed this time.

That is, the EGR rate has a great influence on the low temperature combustion. In this case, when the opening degree of the throttle valve 20 is changed, E is larger than that when the opening degree of the EGR control valve 31 is changed.
The change in GR rate is small. Moreover, at this time, the amount of decrease in the absolute pressure in the air suction pipe 17 downstream of the throttle valve 20 becomes large. Therefore, in the embodiment according to the present invention, the throttle valve 2
The valve 0 is closed before the EGR control valve 31. Note that the EGR control valve 31 is closed and the EG
When the R rate decreases, the optimum injection timing becomes late. Therefore, in the embodiment according to the present invention, the injection start timing is delayed as the EGR control valve 31 is closed.

Next, the processing routine of the injection stop flag indicating that the fuel injection should be stopped will be described with reference to FIG. Referring to FIG. 19, first, step 10
At 0, it is judged if the injection stop flag is set. When the injection stop flag is not set, the routine proceeds to step 101, where it is judged if the depression amount L of the accelerator pedal 50 is zero. When L = 0, the routine proceeds to step 102, where it is judged if the engine speed N is higher than a constant value, for example, 1300 rpm. N>
If it is 1300 rpm, proceed to step 103. That is, when L = 0 and N> 1300 rpm, it is determined that deceleration operation is in progress, and at this time, the routine proceeds to step 103, where the injection stop flag is set.

When the injection stop flag is set, the routine proceeds from step 100 to step 104, where the accelerator pedal 50
It is determined whether or not the depression amount L of is not zero. When L = 0, the routine proceeds to step 105, where it is judged if the engine speed N has become lower than a constant value, for example, 900 rpm. When N <900 rpm, the routine proceeds to step 106, where the injection stop flag is reset. On the other hand, when it is determined in step 104 that L = 0 is not satisfied, the process also proceeds to step 106, and the injection stop flag is reset.

Next, the operation control will be described with reference to FIGS. 20 and 21. Referring to FIGS. 20 and 21, first, at step 200, 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 state of the engine is in the first operating region I, the routine proceeds to step 201, where it is determined whether the required torque TQ has become larger than the first boundary X (N). To be done. When TQ ≦ X (N), the routine proceeds to step 203, where it is judged if the injection stop flag is set or not. When the injection stop flag is not set, the routine proceeds to step 204, where low temperature combustion is performed.

That is, at step 204, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. 14 (A). Next, at step 205, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. 14 (B). Next, at step 206, the injection amount Q is calculated from the map shown in FIG. 13 (A), and the injection start timing θS is calculated from the map shown in FIG. 13 (B). Then step 2
At 07, the target limit value tP in the first chamber 64 of the brake booster 60 is calculated from the relationship shown in FIG. 18 based on the vehicle speed detected by the vehicle speed sensor 53. Next, at step 208, the first chamber 64 detected by the pressure sensor 75
It is determined whether the absolute pressure P therein is higher than the target limit value tP. When P ≦ tP, the routine proceeds to step 209, where the correction values ΔST, ΔSE, ΔθS are made zero.

On the other hand, when it is judged at step 208 that P> tP, the routine proceeds to step 210, where the actual air-fuel ratio A / F is calculated from the mass flow rate of the intake air detected by the mass flow meter 37 and the injection quantity Q. To be done. Next, at step 211, the actual air-fuel ratio A / F is the theoretical air-fuel ratio 14.
It is determined whether it is greater than 6. Actual air-fuel ratio A /
When F> 14.6, the routine proceeds to step 212, where the correction value ΔST for the target opening of the throttle valve 20 is changed to a constant value α.
Is subtracted. Next, at step 213, the correction value ΔST is added to the target opening degree ST of the throttle valve 20 to obtain the final target opening degree ST (= ST of the throttle valve 20.
+ ΔST) is calculated. Therefore, the actual air-fuel ratio A / F>
It can be seen that at 14.6, the throttle valve 20 is gradually closed.

On the other hand, when the actual air-fuel ratio A / F ≦ 14.6, the routine proceeds to step 214, where the constant value β is subtracted from the correction value ΔSE for the target opening of the EGR control valve 31. Next, at step 215, the target opening S of the EGR control valve 31
By adding the correction value ΔSE to E, the final EG
The target opening degree SE (= SE + ΔSE) of the R control valve 31 is calculated. Next, at step 216, the target injection start timing θ
The constant value γ is subtracted from the correction value ΔθS for S. Next, at step 217, the final target injection start timing θS (= θS + ΔθS) is calculated by adding the correction value ΔθS to the target injection start timing θS. Therefore, it is understood that when the actual air-fuel ratio A / F ≦ 14.6, the EGR control valve 31 is gradually closed and the injection start timing θS is gradually delayed.

On the other hand, in step 201, TQ> X
When it is determined that (N) has been reached, the routine proceeds to step 202, where the flag I is reset, and then step 220
Then, the second combustion is performed. That is, step 220
Then, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 221, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. 17 (B). Then, in step 222, FIG.
The injection amount Q is calculated from the map shown in FIG.
The injection start timing θS is calculated from the map shown in (B).

When the flag I is reset, in the next processing cycle, the routine proceeds from step 200 to step 218, where it is judged if the required torque TQ has become lower than the second boundary Y (N). When TQ ≧ Y (N), the routine proceeds to step 220, where the second combustion is performed. On the other hand, if it is determined at step 218 that TQ <Y (N), then the routine proceeds to step 219, at which the flag I is set,
Then, it proceeds to step 203.

When it is determined in step 203 that the injection stop flag is set, step 223
Then, the injection amount Q is made zero. Then step 224
Then, the target opening degree ST of the throttle valve 20 is set to zero. That is, the throttle valve 20 is fully closed. Next, at step 225, the target opening degree SE of the EGR control valve 31 is made the predetermined opening degree SE0.

[0086]

As described above, a good braking action by the brake booster can be secured.

[Brief description of drawings]

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

FIG. 2 is an enlarged side sectional view of a brake booster.

FIG. 3 is a diagram showing amounts of smoke and NO _x generated, and the like.

FIG. 4 is a diagram showing a combustion pressure.

FIG. 5 is a diagram showing a fuel molecule.

FIG. 6 is a diagram showing a relationship between an amount of smoke generated and an EGR rate.

FIG. 7 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 8 is a diagram showing a first operating region I and a second operating region II.

FIG. 9 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 10 is a diagram showing the opening of a throttle valve and the like.

FIG. 11 is a diagram showing a required torque.

FIG. 12 is a diagram showing a target air-fuel ratio in a first operating region I.

FIG. 13 is a diagram showing a map of an injection amount and the like.

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

FIG. 15 is a diagram showing a target air-fuel ratio in the second combustion.

FIG. 16 is a diagram showing a map of an injection amount and the like.

FIG. 17 is a diagram showing a map of a target opening degree of a throttle valve and the like.

FIG. 18 is a diagram showing a target limit value in the first chamber of the brake booster.

FIG. 19 is a flowchart for processing an injection stop flag.

FIG. 20 is a flowchart for controlling the operation of the engine.

FIG. 21 is a flowchart for controlling the operation of the engine.

[Explanation of symbols]

6 ... Fuel injection valve 20 ... Throttle valve 31 ... EGR control valve 60 ... Brake booster

Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01N 3/08 F01N 3/24 S 3/24 F02D 9/02 315B F02D 9/02 315 315K 21/08 301B 21/08 301 41/02 360 41/02 360 41/04 360Z 41/04 360 385G 385 43/00 301K 43/00 301 301N F02M 25/07 570D F02M 25/07 570 B60T 13/52 Z (56) Reference JP-A-7-4287 ( JP, A) JP-A-8-177654 (JP, A) JP-A-8-86251 (JP, A) JP-A-9-287527 (JP, A) JP-A-9-287528 (JP, A) (58 ) Fields surveyed (Int.Cl. ⁷ , DB name) F02M 25/07 F02D 41/00-45/00 F02B 1/00-23/10 B60K 41/20 B60T 17/00 B60T 13/52

Claims (13)

(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.
An internal combustion engine that suppresses the temperature to a much lower temperature, arranges a throttle valve in the engine intake passage, and guides the negative pressure generated in the intake passage downstream of the throttle valve into the brake booster. 2. The internal combustion engine according to claim 1, wherein the opening degree of the throttle valve is reduced when the negative pressure introduced into the brake booster becomes lower than a preset negative pressure. 3. The internal combustion engine according to claim 2, wherein the set negative pressure is increased as the vehicle speed increases. 4. The recirculation exhaust gas control valve for controlling the supply amount of the recirculation exhaust gas, wherein the inert gas is recirculation exhaust gas supplied into the intake passage downstream of the throttle valve. The internal combustion engine according to claim 1, wherein the opening degree of the recirculation exhaust gas control valve is reduced when the negative pressure introduced into the brake booster becomes lower than a preset negative pressure. 5. The internal combustion engine according to claim 4, wherein the fuel injection timing is delayed when the opening degree of the recirculation exhaust gas control valve is reduced. 6. The recirculation exhaust gas control valve for controlling the supply amount of the recirculation exhaust gas, wherein the inert gas is recirculation exhaust gas supplied into the intake passage downstream of the throttle valve. , When the negative pressure introduced into the brake booster becomes smaller than the preset negative pressure, the opening degree of the throttle valve is reduced first, and the negative pressure introduced into the brake booster is still reduced. The internal combustion engine according to claim 1, wherein the opening degree of the recirculation exhaust gas control valve is reduced when the pressure is lower than a preset negative pressure. 7. The internal combustion engine according to claim 6, wherein the fuel injection timing is delayed when the opening degree of the recirculation exhaust gas control valve is reduced. 8. The internal combustion engine according to claim 6, wherein the opening degree of the throttle valve is reduced until the air-fuel ratio reaches a predetermined air-fuel ratio. 9. The internal combustion engine according to claim 1, wherein the inert gas comprises recirculated exhaust gas supplied into the intake passage downstream of the throttle valve, and the exhaust gas recirculation rate is approximately 55% or more. 10. The internal combustion engine according to claim 1, wherein a catalyst having an oxidizing function is arranged in the engine exhaust passage. 11. The catalyst is an oxidation catalyst, a three-way catalyst or NO.
An internal combustion engine according to claim 10, wherein the _x absorbent comprises at least one. 12. 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. 13. 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
13. The internal combustion engine according to claim 12, wherein the combustion is performed.