JP3405217B2 - 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, it is necessary to increase the EGR rate to about 55% or more. The EGR rate can be set to about 55% or more when the intake air amount is relatively small. Is. That is, when the intake air amount exceeds a certain amount, this new combustion cannot be performed. Therefore, when the intake air amount exceeds a certain amount, the conventional combustion is performed.

By the way, the conventional combustion has a slightly higher thermal efficiency than the new combustion, and therefore the fuel injection amount required to obtain the same engine output torque is higher in the conventional combustion. Less than fresh combustion. Therefore, in order to prevent the output torque of the engine from fluctuating when switching between new combustion and conventional combustion, the fuel injection amount must be changed when switching between new combustion and conventional combustion. Must be increased or decreased.

[0011]

Therefore, in the first aspect of the invention, as the amount of inert gas in the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the amount of inert gas in the combustion chamber is reduced. With further increase, the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it become lower than the soot generation temperature, and in an internal combustion engine in which soot is hardly generated, the soot generation peaks Amount of inert gas in the combustion chamber is larger than the amount of soot, and soot is hardly generated, and second combustion is in which the amount of inert gas in the combustion chamber is less than the amount of soot generated at the peak. And switching means for selectively switching between the first combustion and the second combustion, the fuel injection amount is reduced, and when the second combustion is switched to the first combustion, the fuel injection amount is reduced. Increase the amount That.

In the second invention, in the first invention,
The fuel injection quantity for the first combustion is stored in advance in the first map as a function of the required load and the engine speed,
The fuel injection amount for combustion is stored in the second map in advance as a function of the required load and the engine speed, and the fuel injection amount on the first map at the same required load and the same engine speed is the second fuel injection amount. The fuel injection amount is larger than the fuel injection amount on the map, and when the first combustion is switched to the second combustion, the fuel amount to be injected is from the fuel injection amount on the first map to the fuel injection on the second map. When the second combustion is switched to the first combustion, the amount of fuel to be injected is switched from the fuel injection amount on the second map to the fuel injection amount on the first map.

In the third invention, in the first invention,
The first combustion fuel injection amount is stored in advance in the form of a first functional expression of the required load and the engine speed, and the second combustion fuel injection amount is stored in the second of the required load and the engine speed. Is stored in advance in the form of a functional equation of, the fuel injection amount obtained by the first functional equation at the same required load and the same engine speed is made larger than the fuel injection amount obtained by the second functional equation. When the first combustion is switched to the second combustion, the fuel amount to be injected is switched from the fuel injection amount obtained from the first functional expression to the fuel injection amount obtained from the second functional expression, and from the second combustion to the first When the combustion is switched to combustion, the amount of fuel to be injected is switched from the fuel injection amount obtained from the second functional expression to the fuel injection amount obtained from the first functional expression.

In the fourth invention, in the first invention,
In a low engine speed range where the engine speed is lower than a predetermined engine speed, the fuel injection amount increases as the engine speed decreases, and in this low engine speed range the fuel injection amount increases when the engine speed decreases. The rate is smaller during the first combustion than during the second combustion. In a fifth aspect, in the first aspect, when the first combustion is switched to the second combustion, the fuel injection amount for the first combustion is temporarily used for a predetermined period and is also determined in advance. When the period elapses, the fuel injection amount for the second combustion is reduced, and when the second combustion is switched to the first combustion, the fuel injection for the second combustion is temporarily performed for a predetermined period. The amount is used and is increased to the fuel injection amount for the first combustion when a predetermined period has elapsed.

In the sixth invention, in the fifth invention,
The fuel injection quantity for the first combustion is stored in advance in the first map as a function of the required load and the engine speed,
The fuel injection amount for combustion is stored in the second map in advance as a function of the required load and the engine speed, and the fuel injection amount on the first map at the same required load and the same engine speed is the second fuel injection amount. The fuel injection amount is larger than the fuel injection amount on the map, and when the fuel injection amount for the first combustion is reduced to the fuel injection amount for the second combustion, the fuel amount to be injected is the fuel on the first map. When the injection amount is switched to the fuel injection amount on the second map and the fuel injection amount for the second combustion is increased to the fuel injection amount for the first combustion, the fuel amount to be injected is the second map. The fuel injection amount above is switched to the fuel injection amount on the first map.

In the seventh invention, in the fifth invention,
The first combustion fuel injection amount is stored in advance in the form of a first functional expression of the required load and the engine speed, and the second combustion fuel injection amount is stored in the second of the required load and the engine speed. Is stored in advance in the form of a functional equation of, the fuel injection amount obtained by the first functional equation at the same required load and the same engine speed is made larger than the fuel injection amount obtained by the second functional equation. When the fuel injection amount for the first combustion is reduced from the fuel injection amount for the second combustion, the fuel amount to be injected is the fuel injection amount obtained from the second functional formula from the fuel injection amount obtained from the first functional formula. When the fuel injection amount for the second combustion is increased from the fuel injection amount for the second combustion to the fuel injection amount for the first combustion, the fuel amount to be injected is calculated from the fuel injection amount obtained from the second functional expression. Switching to the fuel injection amount that can be obtained more That.

In the eighth invention, in the first invention,
When the first combustion is switched to the second combustion
Is gradually reduced from the fuel injection amount for the second combustion to the fuel injection amount for the second combustion, and when the second combustion is switched to the first combustion, the fuel injection amount for the second combustion is changed to the first. The fuel injection amount for combustion is gradually increased.

In the ninth invention, in the eighth invention,
The fuel injection quantity for the first combustion is stored in advance in the first map as a function of the required load and the engine speed,
The fuel injection amount for combustion is stored in the second map in advance as a function of the required load and the engine speed, and the fuel injection amount on the first map at the same required load and the same engine speed is the second fuel injection amount. The fuel injection amount on the first map is made larger than the fuel injection amount on the map, and when the fuel injection amount for the first combustion is gradually reduced from the fuel injection amount for the second combustion. Fuel to be injected when gradually increasing from the fuel injection amount of the second map to the fuel injection amount on the second map and gradually increasing from the fuel injection amount for the second combustion to the fuel injection amount for the first combustion. The amount is gradually switched from the fuel injection amount on the second map to the fuel injection amount on the first map.

In the tenth invention, in the eighth invention, the fuel injection amount for the first combustion is stored in advance in the form of a first functional expression of the required load and the engine speed, and the fuel quantity for the second combustion is stored in advance. Fuel injection amount of the second of the required load and engine speed
Is stored in advance in the form of a functional equation of, the fuel injection amount obtained by the first functional equation at the same required load and the same engine speed is made larger than the fuel injection amount obtained by the second functional equation. When the fuel injection amount for the first combustion is gradually reduced from the fuel injection amount for the second combustion, the fuel amount to be injected is the fuel obtained from the second functional formula from the fuel injection amount obtained from the first functional formula. When the fuel injection amount is gradually switched to the fuel injection amount for the second combustion and gradually increased from the fuel injection amount for the first combustion, the fuel injection amount for which the fuel amount to be injected is obtained from the second functional expression From first
The fuel injection amount can be gradually switched to the fuel injection amount obtained from the function formula.

An eleventh aspect of the invention is the fuel cell system according to the first aspect, further comprising an exhaust gas recirculation device for recirculating the exhaust gas discharged from the combustion chamber into the engine intake passage, and the inert gas being the recirculated exhaust gas. . In the twelfth invention, in the eleventh invention, the exhaust gas recirculation rate in the first combustion state is approximately 55% or more.

According to the thirteenth invention, in the first invention, a catalyst having an oxidizing function is arranged in the engine exhaust passage. According to a fourteenth invention, in the thirteenth invention, the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst and a NO _x absorbent. In the fifteenth invention, in the first 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 combustion is performed in the first operating region. The second combustion is performed in the second operation area.

[0022]

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 load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 4 via the corresponding AD converter 47.
Input to 5. 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. 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 EGR control valve control step motor 30, and the fuel pump 35 are connected.

FIG. 2 shows the throttle valve 2 at the time of 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 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. 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, HC and CO are generated 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. .

When these considerations based on the experimental results shown in FIGS. 2 and 3 are summarized, the soot generation amount becomes almost zero when the combustion temperature in the combustion chamber 5 is low, 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, when 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, 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. 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 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. 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 produced 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 in terms of EGR rate, and 70% or more in the embodiment shown in FIG. That is, the total amount of intake gas sucked into the combustion chamber 5 is indicated by a solid line X in FIG.
If the ratio of the amount of air to the amount of EGR gas is set as shown in FIG. 6, 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. Disappear. Further, the NO _x generation amount at this time is 1
It is around 0 p.pm or less, and therefore the amount of NO _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 the supercharging is not performed, the upper limit of the total intake gas amount X drawn into the combustion chamber 5 is Y. Therefore, in FIG. 6, 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 the EGR gas is recirculated to the inlet side of the supercharger, that is, the air suction pipe 17 of the exhaust turbocharger 15 via 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.

In this case, the lower the EGR gas temperature, the wider the operating range in which low temperature combustion occurs. Therefore, as shown in FIG. 1, the exhaust gas having a relatively low temperature flowing out from the exhaust turbine 23 is recirculated as the EGR gas, and the EGR gas is further cooled by the intercooler 32. In the embodiment shown in FIG. 1, the EGR control valve 31 is fully opened and the throttle valve 20 is slightly closed when the EGR rate is 55% or more in the region where the required load is larger than Lo.

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 that shown in FIG. 6, that is, the air-fuel ratio is made rich. However, the amount of NO _x generated is 10 p.p. while preventing the generation of soot.
It can be around m or less, and even if the air amount is made larger than that shown in FIG. 6, 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 below the temperature at which the growth of hydrocarbons stops halfway only when the engine is operating at a 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. 7 shows a first operating region I in which the first combustion, that is, low temperature combustion is performed, and a second operating 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 L represents the depression amount of the accelerator pedal 50, that is, the required load, and the horizontal axis N represents the engine speed. Further, in FIG. 7, X (N) is the first
Shows the first boundary between the operating region I and the second operating region II, where Y (N) is the first operating region I and the second operating region.
The second boundary with II is shown. The determination of the change of the operating region from the first operating region I to the second operating region II is made based on the first boundary X (N), and the change from the second operating region II to the first operating region II is performed.
The determination of the change of the operating range to the operating range I of the second boundary Y
It is performed based on (N).

That is, the operating condition of the engine is the first operating region I.
If the required load L exceeds the first boundary X (N) which is a function of the engine speed N during low temperature combustion, it is determined that the operating region has moved to the second operating region II. Combustion is performed by a conventional combustion method. Next, when the required load L becomes lower than the second boundary Y (N) which is a function of the engine speed N, 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 load 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 load side of the second operating region II, and at this time, even if the required load L becomes lower than the first boundary X (N), low temperature combustion cannot be immediately performed. Because. That is, the low temperature combustion does not start immediately unless the required load L becomes considerably low, that is, when it becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for changes in the operating region between the first operating region I and the second operating region II.

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 a state of the soot precursor 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.

This NO _x absorbent uses, for example, alumina as a carrier, and potassium K, sodium N, etc. are supported on this 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. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.

Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. FIG. 9 shows the throttle valve 2 for the required load L.
The opening degree of 0, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing and the injection amount are shown. As shown in FIG. 9, in the first operating region I where the required load L 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. E
The opening degree of the GR control valve 31 is gradually increased from near full close to full open as the required load L increases. Also,
In the example shown in FIG. 9, the EGR rate is set to approximately 70% in the first operating region I, and the air-fuel ratio is made slightly lean.

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 load L becomes high, and the injection completion 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 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. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less so that the EGR rate jumps over the EGR rate range (FIG. 5) where a large amount of smoke is generated, and the air-fuel ratio is stepped. Be made larger.

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 load L increases. Further, in this operating region II, the EGR rate becomes lower as the required load L becomes higher, and the air-fuel ratio becomes smaller as the required load L becomes higher. However, the air-fuel ratio is a lean air-fuel ratio even if the required load L becomes high.
Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 10 shows the air-fuel ratio A / F in the first operating region I. In FIG. 10, A / F = 15.
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 air-fuel ratio A / F is leaner as the required load L is lower.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low temperature combustion can be performed even if the EGR rate is decreased.
When the EGR rate is decreased, the air-fuel ratio becomes large, so that as shown in FIG. 10, the air-fuel ratio A / F is made larger as the required load L becomes lower. The fuel consumption rate increases as the air-fuel ratio A / F increases. Therefore, in order to make the air-fuel ratio as lean as possible, the air-fuel ratio A / F is increased as the required load L decreases in the embodiment of the present invention.

It should be noted that 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. 1 (A), the EGR is stored in advance in the ROM 42 in the form of a map as a function of the required load L 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 (4), it is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N.

FIG. 12 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 12, A / F = 24, 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. Throttle valve 2 required to set the air-fuel ratio to this target air-fuel ratio
The target opening degree ST of 0 is pre-stored in the ROM 42 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 13 (A), and the air-fuel ratio is set to this target air-fuel ratio. Target opening degree SE of EGR control valve 31 required for
Is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N, as shown in FIG. 13 (B).

FIG. 14A shows the injection amount Q1, the engine speed N, and the accelerator pedal 50 when the first combustion is being performed.
Fig. 1 shows the relationship with the stepping amount, that is, the required load.
4 (B) is the injection amount Q2 when the second combustion is performed
Shows the relationship between the engine speed N and the depression amount of the accelerator pedal 50, that is, the required load. Note that FIG.
In (B), the solid line represents a line connecting points where the depression amount of the accelerator pedal 50 is equal, and the numerical value of each solid line represents the depression amount of the accelerator pedal 50 expressed as a percentage.

As described above, the second combustion has a slightly higher thermal efficiency than the first combustion, and therefore the fuel injection amount required to obtain the same engine output torque is the first combustion in the second combustion.
Less than burning. Therefore, FIG. 14A and FIG.
As you can see by comparing with (B), accelerator pedal 50
When the amount of depression of the engine is the same and the engine speed N is the same, the injection amount is the first in all operating regions except the low rotation region.
The injection amount Q1 when the second combustion is being performed is larger than the injection amount Q2 when the second combustion is being performed.

As shown in FIG. 14B, the second
In order to prevent the engine stall from occurring when the engine speed N decreases under the combustion of, the injection amount Q2 sharply decreases as the engine speed N decreases for the same accelerator pedal depression amount in the low speed region. Be increased. However, under the first combustion, if the injection amount is rapidly increased when the engine speed N decreases, the air-fuel ratio becomes excessively rich, that is, excessively rich. If the air-fuel ratio becomes excessively rich, misfiring occurs due to insufficient air, and engine stall is likely to occur. Therefore, in order to prevent the air-fuel ratio from becoming excessively rich when the engine speed N decreases when the first combustion is performed, the increase rate of the injection amount Q1 when the engine speed N decreases in the low rotation region. Is smaller than that during the second combustion shown in FIG. 14 (B).

The injection amount Q1 shown in FIG. 14A is stored in advance in the ROM 42 in the form of the map shown in FIG. 15A as a function of the depression amount L of the accelerator pedal 50 and the engine speed N. The injection amount Q2 shown in FIG. 14 (B) is also a ROM 42 in advance in the form of a map shown in FIG. 15 (B) as a function of the depression amount L of the accelerator pedal 50 and the engine speed N.
It is stored in. In this case, the injection amounts Q1 and Q2 are not stored in the form of a map, and the injection amount Q1 shown in FIG. 14A is expressed in the form of a first functional expression of the depression amount L of the accelerator pedal 50 and the engine speed N. It can be stored in advance in the ROM 42, and the injection amount Q2 shown in FIG. 14B is stored in advance in the ROM 42 in the form of a second functional expression of the depression amount L of the accelerator pedal 50 and the engine speed N. You can also keep it. In this case, the injection amount when the accelerator pedal 50 is the same and the engine speed N is the same, the injection amount Q1 obtained from the first functional expression is the first in all operating regions except the low rotation region. The injection amount Q2 is larger than the injection amount Q2 obtained from the functional expression 2.

16 and 17 show the first embodiment.
In this embodiment, when the first combustion is being performed, the injection amount Q1 is always calculated based on the map shown in FIG. 15A or from the first functional expression, and when the second combustion is being performed. The injection amount Q2 is constantly calculated based on the map shown in FIG. 15B or from the second functional expression. Therefore, FIG.
As shown in FIG. 6 (A), when the operating state of the engine shifts from the first operating region I to the second operating region II, the injection amount Q is immediately reduced, and as shown in FIG. The injection amount Q is immediately increased when the operating state of (1) shifts from the second operating region II to the first operating region I.

Next, the operation control will be described with reference to FIG. Referring to FIG. 17, first step 1
At 00, it is determined whether or not the operating state is such that low temperature combustion is possible. For example, when the temperature of the catalyst 25 is equal to or higher than the activation temperature, it is determined that the operating state is such that low temperature combustion is possible. When the engine is in the operating state capable of low temperature combustion, the routine proceeds to step 101, where it is judged if the flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 102, where it is determined whether the required load L has become larger than the first boundary X (N). To be done. When L ≦ X (N), the routine proceeds to step 104, where low temperature combustion is performed.

That is, at step 104, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening degree of the throttle valve 20 is made this target opening degree ST. Next, at step 105, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening degree of the EGR control valve 31 is set to this target opening degree SE.
Next, at step 106, the injection amount Q1 is calculated from the map shown in FIG. 15 (A) or the first functional expression. At this time, low temperature combustion is performed.

On the other hand, in step 102, L> X
When it is determined that (N) has been reached, the routine proceeds to step 103, where the flag I is reset, and then step 109
Then, the second combustion is performed. That is, step 109
Then, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. 13A, and the opening degree of the throttle valve 20 is set to this target opening degree ST. Next, at step 110, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. 13 (B), and the opening degree of the EGR control valve 31 is made this target opening degree SE. Next, at step 111, FIG.
The injection amount Q2 is calculated from the map shown in (B) or the second functional expression.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 101 to step 107, where it is judged if the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 109
Then, the second combustion is performed. On the other hand, when it is determined at step 107 that L <Y (N), the routine proceeds to step 108, where the flag I is set, and then to step 104, low temperature combustion is performed.

On the other hand, when it is determined in step 100 that the operating condition is not such that low temperature combustion is possible, the routine proceeds to step 109, where the second combustion is performed. A second embodiment is shown in FIGS. 18 and 19. In this embodiment, when the first combustion is performed, the injection amount Q1 is normally calculated based on the map shown in FIG. 15A or from the first functional expression, and the second combustion is performed. Sometimes, usually
The injection amount Q2 is calculated based on the map shown in (B) or from the second functional expression. However, in this embodiment, as shown in FIG. 18A, when the operating state of the engine shifts from the first operating region I to the second operating region II, the map shown in FIG. The injection amount Q1 is calculated based on or from the first functional expression, and the injection quantity Q2 is calculated based on the map shown in FIG. 15B or after the second functional expression after the elapse of the fixed time Δt. Also, FIG.
As shown in FIG. 8 (B), when the operating state of the engine changes from the second operating region II to the first operating region I, for a certain time Δt, based on the map shown in FIG.
The injection amount Q2 is calculated from the functional expression of, and the injection amount Q1 is calculated based on the map shown in FIG.

Therefore, in this embodiment, as shown in FIG. 18 (A), the operating state of the engine changes from the first operating region I to the second operating region I.
18B, the injection amount Q is reduced after a lapse of a certain time ΔT, and the operating state of the engine shifts from the second operating region II to the first operating region I as shown in FIG. 18B. Thus, the injection amount Q is increased after the elapse of the constant time ΔT.

That is, when the first combustion having a large EGR rate and a small air-fuel ratio and the second combustion having a small EGR rate and a large air-fuel ratio are selectively switched as in the present invention, EGR is performed. Due to the influence of air contained in the gas, the air-fuel ratio does not immediately switch to the target air-fuel ratio at the time of switching. For example, when the second combustion is being performed, the air-fuel ratio is large, so the exhaust gas contains a large amount of air. Therefore, the EGR gas also contains a large amount of air. Next, if the second combustion is switched to the first combustion, immediately after the switching, the EGR gas containing a large amount of air is supplied into the combustion chamber 5, so the air-fuel ratio does not immediately decrease. After that, the air-fuel ratio gradually decreases, and after a while after the switching, the air-fuel ratio decreases to the target air-fuel ratio.

On the other hand, when the first combustion is performed, the air-fuel ratio is small, and therefore the exhaust gas contains only a small amount of air at this time. Therefore, the EGR gas also contains only a small amount of air. Then from the first combustion to the second
If the combustion is switched to combustion, immediately after the switching, the EGR gas containing only a small amount of air is supplied into the combustion chamber 5, so the air-fuel ratio does not immediately increase. After that, the air-fuel ratio gradually increases, and after a while after the switching, the air-fuel ratio increases to the target air-fuel ratio.

As described above, in the embodiment according to the present invention, when the first combustion is switched to the second combustion, the air-fuel ratio does not immediately become the air-fuel ratio suitable for the second combustion, and the second combustion is changed to the first combustion. The air-fuel ratio does not immediately become the air-fuel ratio suitable for the first combustion when the combustion is switched to the combustion. Therefore, in the second embodiment, as described above, when the operating state of the engine shifts from the second operating region II to the first operating region I, the second combustion type shown in FIG. The injection amount Q2 is calculated based on the map or from the second functional expression, and the operating state of the engine changes from the first operating region I to the second operating region II.
When the flow shifts to, the injection amount Q1 is calculated based on the first combustion map shown in FIG. 15 (A) or from the first functional expression for a fixed time Δt.

Next, the operation control will be described with reference to FIG. Referring to FIG. 19, first, step 2
At 00, it is determined whether or not the operating state is such that low temperature combustion is possible. As described above, for example, when the temperature of the catalyst 25 is equal to or higher than the activation temperature, it is determined that the operating state is such that low temperature combustion is possible. When the engine is in an operating state where low temperature combustion is possible, the routine proceeds to step 201, where the operating state of the engine is the first operating region I.
It is determined whether or not the flag I indicating that is is set. 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 202, where it is judged if the required load L has become larger than the first boundary X (N). To be done. When L ≦ X (N), the routine proceeds to step 204.

At step 204, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG.
The opening of the throttle valve 20 is set to this target opening ST.
Next, at step 205, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening degree of the control valve 31 is set to this target opening degree SE. Next, at step 206, it is judged if a fixed time Δt has elapsed since the second combustion was switched to the first combustion. When the fixed time Δt has not elapsed, step 2
In step 13, the injection amount Q2 is calculated from the map shown in FIG. 15B or the second functional expression. On the other hand, when the fixed time Δt has elapsed, the routine proceeds to step 207, and FIG.
The injection amount Q1 is calculated from the map shown in or the first functional expression.

On the other hand, in step 202, L> X
When it is determined that (N) has been reached, the routine proceeds to step 203, where the flag I is reset, and then step 210
Proceed to. In step 210, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. 13 (A), and the opening degree of the throttle valve 20 is set to this target opening degree ST. Next, at step 211, E from the map shown in FIG.
The target opening degree SE of the GR control valve 31 is calculated, and the opening degree of the EGR control valve 31 is set to this target opening degree SE. Next, at step 212, it is judged if a certain time Δt has elapsed since the first combustion was switched to the second combustion. When the fixed time Δt has not elapsed, the routine proceeds to step 207, where the injection amount Q1 is calculated from the map shown in FIG. 15 (A) or the first functional expression. On the other hand, when the fixed time Δt has elapsed, the routine proceeds to step 213, where the injection amount Q2 is calculated from the map shown in FIG. 15B or the second functional expression.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 201 to step 208, where it is judged if the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 210
Proceed to. On the other hand, in step 208, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 209, the flag I is set, and then the routine proceeds to step 204.

On the other hand, when it is determined in step 200 that the engine is not in the operating state in which low temperature combustion is possible, the routine proceeds to step 210, where the second combustion is performed. 20 to 2
2 shows a third embodiment. As described above, when the first combustion is switched to the second combustion due to the influence of the air of the EGR gas, the air-fuel ratio gradually increases to the target air-fuel ratio, and the second combustion is switched to the first combustion. When this is done, the air-fuel ratio gradually decreases to the target air-fuel ratio. Therefore, in this embodiment, as shown in FIG. 20 (A), when the operating state of the engine changes from the first operating region I to the second operating region II, the injection amount gradually decreases in accordance with the change of the air-fuel ratio. As shown in FIG. 20 (B), when the operating state of the engine shifts from the second operating region II to the first operating region I, the injection amount is gradually increased according to the change of the air-fuel ratio. .

Specifically, when the engine operating state shifts from the first operating region I to the second operating region II, the injection amounts Q1 and Q2 depending on the required load L and the engine speed N.
Are calculated a plurality of times, for example, Co times from the maps shown in FIGS. 15A and 15B or the first and second functional expressions, respectively.
Then, the injection amount is the injection amount Q1 and the injection amount Q which are sequentially calculated.
It is gradually decreased by 1 / Co times the difference (Q1-Q2) from 2. Similarly, the operating condition of the engine is the second operating region II.
From the first to the first operating region I, the injection amounts Q1 and Q2 corresponding to the required load L and the engine speed N are the maps shown in FIGS. 15 (A) and 15 (B) or the first and second functional expressions, respectively. Is calculated a plurality of times, for example, Co times. Then, the injection amount is sequentially increased by 1 / Co times the difference (Q1-Q2) between the injection amount Q1 and the injection amount Q2 which are sequentially calculated.

Next, the operation control will be described with reference to FIGS. 21 and 22. 21 and 22, first, at step 300, it is judged if the operating state is such that low temperature combustion is possible. As described above, for example, when the temperature of the catalyst 25 is equal to or higher than the activation temperature, it is determined that the operating state is such that low temperature combustion is possible. When the engine is in the operating state capable of low temperature combustion, the routine proceeds to step 301, where it is judged if the flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 302, where the required load L
Is larger than the first boundary X (N). When L ≦ X (N), the process proceeds to step 305.

At step 305, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG.
The opening of the throttle valve 20 is set to this target opening ST.
Next, at step 306, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening degree of the control valve 31 is set to this target opening degree SE. Next, at step 307, it is judged if the completion flag indicating that the control of the injection amount at the time of switching between the first combustion and the second combustion is completed is set. Immediately after the operating state of the engine is changed from the second operating region II to the first operating region I, the completion flag is not set, and therefore, at this time, the routine proceeds to step 308.

At step 308, the count value C is incremented by 1. Next, at step 309, it is judged if the count value C has become a constant value Co. When the count value C is not the constant value Co, the routine proceeds to step 310, where the final injection amount Q _f is calculated based on the following equation. _Qf = Q2 + (Q1-Q2) * C / Co Then, in step 314, fuel injection is performed.

On the other hand, when it is judged at step 309 that C = Co, the routine proceeds to step 311, where the completion flag is reset. Next, at step 312, the count value C is cleared, then at step 313, the injection amount Q1 calculated from the map shown in FIG. 15 (A) or the first functional expression is made the final injection amount Q _f . When the completion flag is set, steps 307 to 31
Jump to 3.

Thus, when the operating state of the engine shifts from the second operating region II to the first operating region I, Q2 calculated from the map shown in FIG.
The difference between Q1 and Q2 calculated from the maps shown in (A) and FIG. 15 (B) or the first and second functional expressions (Q1-Q
The product of 2) and C / Co is added. Therefore, at this time, the final injection amount Q _f changes from Q2 to Q1 (Q1-Q
2) / C will be gradually increased.

On the other hand, in step 302, L> X
When it is determined that (N) has been reached, the routine proceeds to step 303, where the flag I is reset, and then step 304
And the completion flag is reset. Then, it proceeds to step 318. In step 318, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. 13 (A), and the opening degree of the throttle valve 20 is set to this target opening degree ST. Next, at step 319, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening degree of the GR control valve 31 is set to this target opening degree SE. Next, at step 320, it is judged if the completion flag is set. At this time, that is, immediately after the operating state of the engine shifts from the first operating region I to the second operating region II, the completion flag is not set, so at this time, the routine proceeds to step 321.

At step 321, the count value C is incremented by 1. Next, at step 322, it is judged if the count value C has become a constant value Co. When the count value C is not the constant value Co, the routine proceeds to step 323, where the final injection amount Q _f is calculated based on the following equation. Fuel is injected at _{Q f = Q1- (Q1-Q2} ) · C / Co then step 314.

Next, when it is judged at step 322 that C = Co, the routine proceeds to step 324, where the completion flag is reset. Next, at step 325, the count value C is cleared, then at step 326, the injection amount Q2 calculated from the map shown in FIG. 15 (B) or the second functional expression is made the final injection amount Q _f . When the completion flag is set, step 320 to step 32
Jump to 6.

As described above, when the operating state of the engine shifts from the first operating region I to the second operating region II, the map shown in FIG. 15A or Q1 calculated from the first functional expression
5A and the map shown in FIG. 15B or the difference between Q1 and Q2 calculated from the first and second functional expressions (Q1-
The product of Q2) and C / Co is subtracted. Therefore, at this time, the final injection amount Q _f changes from Q1 to Q2 (Q1-Q
2) / C will be gradually decreased.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 301 to step 315, where it is judged if the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 318
Proceed to. On the other hand, in step 315, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 316, where the flag I is set, and then the routine proceeds to step 317 where the completion flag is reset. Then step 3
Go to 05.

On the other hand, when it is determined in step 300 that the engine is not in the operating state in which low temperature combustion is possible, the routine proceeds to step 318, where the second combustion is performed.

[0097]

The engine output torque can be prevented from fluctuating at the time of switching between the first combustion and the second 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 output of an air-fuel ratio sensor.

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

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

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

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

FIG. 13 is a diagram showing a map of a target opening degree of a throttle valve or the like.

FIG. 14 is a diagram showing a relationship between an accelerator pedal depression amount, an engine speed and an injection amount.

FIG. 15 is a diagram showing a map of an injection amount.

FIG. 16 is a time chart showing changes in the injection amount in the first embodiment.

FIG. 17 is a flow chart for performing engine operation control in the first embodiment.

FIG. 18 is a time chart showing changes in the injection amount in the second embodiment.

FIG. 19 is a flow chart for performing engine operation control in the second embodiment.

FIG. 20 is a time chart showing changes in the injection amount in the third embodiment.

FIG. 21 is a flow chart for controlling the operation of the engine in the third embodiment.

FIG. 22 is a flow chart for performing engine operation control in the third embodiment.

[Explanation of symbols]

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

Front page continuation (51) Int.Cl. ⁷ Identification code FI F02M 25/07 550 F02M 25/07 550F (72) Inventor Takekazu Ito 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Corporation (72) Inventor Hiroki Murata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-9-287528 (JP, A) JP-A-9-287527 (JP, A) JP-A-8- 177654 (JP, A) JP 8-86251 (JP, A) JP 7-4287 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02B 1 / 00-23 / 06 F02D 41/00-45/00 F02M 25/07

Claims (15)

(57) [Claims] 1. When the amount of inert gas in the combustion chamber increases, the soot generation amount gradually increases and reaches a peak, and when the amount of inert gas in the combustion chamber further increases, combustion in the combustion chamber occurs. In an internal combustion engine in which the temperature of the fuel and the gas around it are lower than the soot generation temperature and soot is hardly generated, the amount of inert gas in the combustion chamber is higher than the amount of inert gas at which the soot generation peaks. A switching means is provided for selectively switching between the first combustion in which much soot is rarely generated and the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot is peaked. , An internal combustion engine in which the fuel injection amount is decreased when the first combustion is switched to the second combustion, and the fuel injection amount is increased when the second combustion is switched to the first combustion. 2. The fuel injection amount for the first combustion is stored in advance in the first map as a function of the required load and the engine speed, and the fuel injection amount for the second combustion is required and the engine speed. Pre-stored in the second map as a function of the number, the first at the same required load and the same engine speed.
Is larger than the fuel injection amount on the second map, and when the first combustion is switched to the second combustion, the fuel amount to be injected is the fuel on the first map. When the injection amount is switched to the fuel injection amount on the second map, and the fuel amount to be injected is switched from the second combustion to the first combustion, the fuel amount to be injected is changed from the fuel injection amount on the second map to the first map. 2. The fuel injection amount is changed to 1.
Internal combustion engine according to. 3. A first combustion fuel injection amount is stored in advance in the form of a first functional expression of a required load and an engine speed, and a second combustion fuel injection amount is required and an engine speed. It is stored in advance in the form of a second functional expression of the rotational speed, and the fuel injection amount obtained by the first functional expression at the same required load and the same engine rotational speed is larger than the fuel injection amount obtained by the second functional expression. When the first combustion is switched to the second combustion, the amount of fuel to be injected is switched from the fuel injection amount obtained from the first functional expression to the fuel injection amount obtained from the second functional expression. 2. The internal combustion engine according to claim 1, wherein when switching from the first combustion to the first combustion, the fuel amount to be injected is switched from the fuel injection amount obtained from the second functional expression to the fuel injection amount obtained from the first functional expression. 4. The fuel injection amount is increased as the engine speed decreases in a low engine speed range where the engine speed is lower than a predetermined engine speed, and when the engine speed decreases in the low engine speed range, The internal combustion engine according to claim 1, wherein the increase rate of the fuel injection amount is made smaller during the first combustion than during the second combustion. 5. When the first combustion is switched to the second combustion, the fuel injection amount for the first combustion is temporarily used for a predetermined period, and when the predetermined period elapses. Is reduced to the fuel injection amount for the second combustion, and when the second combustion is switched to the first combustion, the fuel injection amount for the second combustion is temporarily used for a predetermined period. The internal combustion engine according to claim 1, wherein the fuel injection amount for the first combustion is increased when the predetermined period has elapsed. 6. The fuel injection amount for the first combustion is prestored in the first map as a function of the required load and the engine speed, and the fuel injection amount for the second combustion is the required load and the engine speed. Pre-stored in the second map as a function of the number, the first at the same required load and the same engine speed.
Is larger than the fuel injection amount on the second map, and is injected when the fuel injection amount for the first combustion is reduced to the fuel injection amount for the second combustion. The fuel amount to be changed is switched from the fuel injection amount on the first map to the fuel injection amount on the second map, and the fuel injection amount for the second combustion is increased to the fuel injection amount for the first combustion. The internal combustion engine according to claim 5, wherein the fuel amount to be injected is sometimes switched from the fuel injection amount on the second map to the fuel injection amount on the first map. 7. The fuel injection amount for the first combustion is stored in advance in the form of a first functional expression of the required load and the engine speed, and the fuel injection amount for the second combustion is the required load and the engine. It is stored in advance in the form of a second functional expression of the rotational speed, and the fuel injection amount obtained by the first functional expression at the same required load and the same engine rotational speed is larger than the fuel injection amount obtained by the second functional expression. When the fuel injection amount for the first combustion is reduced from the fuel injection amount for the first combustion, the fuel amount to be injected is determined from the fuel injection amount obtained from the first functional expression to the second functional expression. When the fuel injection amount determined by the above is changed and the fuel injection amount for the second combustion is increased to the fuel injection amount for the first combustion, the fuel amount to be injected is calculated from the fuel injection amount determined by the second functional expression Fuel injection obtained from the first functional expression The internal combustion engine according to claim 5, which is switched to a quantity. 8. When the first combustion is switched to the second combustion, the fuel injection amount for the first combustion is gradually reduced from the fuel injection amount for the second combustion to the second combustion. The internal combustion engine according to claim 1, wherein the fuel injection amount for the second combustion is gradually increased from the fuel injection amount for the first combustion when switched to the first combustion. 9. The fuel injection amount for the first combustion is prestored in the first map as a function of the required load and the engine speed, and the fuel injection amount for the second combustion is the required load and the engine speed. Pre-stored in the second map as a function of the number, the first at the same required load and the same engine speed.
The fuel injection amount on the map is set to be larger than the fuel injection amount on the second map, and when the fuel injection amount for the first combustion is gradually reduced to the fuel injection amount for the second combustion, The fuel amount to be injected is gradually switched from the fuel injection amount on the first map to the fuel injection amount on the second map, and the fuel injection amount for the second combustion is changed to the fuel injection amount for the first combustion. 9. The internal combustion engine according to claim 8, wherein the fuel amount to be injected is gradually switched from the fuel injection amount on the second map to the fuel injection amount on the first map when the fuel injection amount is gradually increased. 10. The fuel injection amount for the first combustion is pre-stored in the form of a first functional expression of the required load and the engine speed, and the fuel injection amount for the second combustion is the required load and the engine. It is stored in advance in the form of a second functional expression of the rotational speed, and the fuel injection amount obtained by the first functional expression at the same required load and the same engine rotational speed is larger than the fuel injection amount obtained by the second functional expression. When the fuel injection amount for the first combustion is gradually reduced from the fuel injection amount for the second combustion, the fuel amount to be injected is determined from the fuel injection amount obtained from the first functional expression to the second fuel injection amount. The fuel injection amount is gradually changed to the fuel injection amount obtained from the functional expression, and the first fuel injection amount is changed from the second combustion fuel injection amount.
9. When the fuel injection amount for combustion is gradually increased, the fuel amount to be injected is gradually switched from the fuel injection amount obtained from the second functional expression to the fuel injection amount obtained from the first functional expression. Internal combustion engine described. 11. 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. 12. The internal combustion engine according to claim 11, wherein the exhaust gas recirculation rate in the first combustion state is approximately 55% or more. 13. The internal combustion engine according to claim 1, wherein a catalyst having an oxidizing function is arranged in the engine exhaust passage. 14. The catalyst is an oxidation catalyst, a three-way catalyst or NO.
14. The internal combustion engine of claim 13, comprising at least one _x absorbent. 15. 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 the 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 1, wherein the combustion is performed.