JP3528550B2 - 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 In an internal combustion engine, it is sometimes desired to temporarily increase the amount of unburned hydrocarbons emitted from the engine, that is, unburned HC. For example, when a catalyst having an oxidizing function is placed in the exhaust passage of an internal combustion engine in which combustion is performed under a lean air-fuel ratio, unburned fuel discharged from the engine when the temperature of the catalyst is likely to drop below the activation temperature. If the amount of HC can be temporarily increased, the temperature of the catalyst rises, and thus the temperature of the catalyst can be maintained above the activation temperature.

On the other hand, there is a diesel engine in which fuel is injected toward the combustion chamber at the time of valve overlap in which both the intake valve and the exhaust valve are opened in order to constantly discharge a certain amount or more of unburned HC from the engine. Known (Japanese Patent Laid-Open No. 6-
159041). In this diesel engine, a portion of the injected fuel is constantly discharged into the exhaust passage by the air blown from the intake passage through the combustion chamber into the exhaust passage during valve overlap.

[0004]

In this case, in order to discharge a sufficient amount of unburned HC from the engine, it is necessary to increase the amount of air blown through. Therefore, the valve overlap period must be lengthened. I have to. However, if the valve overlap period is lengthened, the output of the engine will decrease and the fuel consumption will increase significantly. Therefore, the valve overlap period cannot be constantly increased only to temporarily increase the amount of unburned HC discharged from the engine.

[0005]

Therefore, in the first invention, a fuel injection valve for injecting fuel into the combustion chamber is provided.
As the amount of inert gas in the combustion chamber increases, soot increases.
Generated gradually increases and reaches a peak,
When the amount of active gas is further increased, combustion in the combustion chamber
Temperature of fuel and gas around it is higher than the temperature of soot formation
In the internal combustion engine where the soot becomes low and almost no soot is generated
Valve overlap period control means for controlling the valve overlap period in which both the intake valve and the exhaust valve are open, and a determination means for determining whether or not the unburned hydrocarbon amount discharged from the engine should be increased. And the amount of soot generated
The amount of inert gas in the combustion chamber
The first combustion that produces almost no soot and the amount of soot produced
Of the inert gas in the combustion chamber
Switching means for selectively switching between the second combustion with a small amount of soot
And it is determined that the amount of unburned hydrocarbons exhausted from the engine should be increased during the second combustion, the valve overlap period is lengthened and at least a part of The fuel is injected during the valve overlap period.

In the second invention, in the first invention,
A catalyst having an oxidizing function is placed in the engine exhaust passage, and when the temperature of the catalyst is likely to drop below the activation temperature, the valve overlap period is lengthened and at least part of the fuel is injected during the valve overlap period. I am trying to do it. In the third invention, in the first invention, when the air-fuel ratio of the inflowing exhaust gas is lean, NOx is absorbed,
A NOx absorbent that releases NOx when the air-fuel ratio of the inflowing exhaust gas becomes rich is placed in the engine exhaust passage to
When NOx should be released from the absorbent, the valve overlap period is lengthened and at least a part of the fuel is injected during the valve overlap period.

[0007]

[0008]

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 to an air cleaner 14 via an intake duct 13. A throttle valve 16 driven by an electric motor 15 is arranged in the intake duct 13. On the other hand, the exhaust port 10 is connected via an exhaust manifold 17 and an exhaust pipe 18 to a catalytic converter 20 containing a catalyst 19 having an oxidizing function.
An air-fuel ratio sensor 21 is arranged inside 7.

The exhaust manifold 17 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 22, and an electric control type EGR control valve 23 is arranged in the EGR passage 22. In addition, the EGR passage 22
A cooling device 24 for cooling the EGR gas flowing in the EGR passage 22 is arranged around the cooling device 24. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 24, and the EGR gas is cooled by the engine cooling water.

On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 26, via a fuel supply pipe 25. Fuel is supplied into the common rail 26 from an electrically controlled variable fuel discharge fuel pump 27, and the fuel supplied into the common rail 26 is supplied to the fuel injection valve 6 via each fuel supply pipe 25. A fuel pressure sensor 28 for detecting the fuel pressure in the common rail 26 is attached to the common rail 26, and the fuel pump 27 so that the fuel pressure in the common rail 26 becomes a target fuel pressure based on the output signal of the fuel pressure sensor 28. Is controlled.

The electronic control unit 30 is composed of a digital computer, and has a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, and an input port 35, which are connected to each other by a bidirectional bus 31. An output port 36 is provided. The output signal of the air-fuel ratio sensor 21 is input to the input port 35 via the corresponding AD converter 37, and the output signal of the fuel pressure sensor 28 is also input to the input port 35 via the corresponding AD converter 37. A temperature sensor 29 for detecting the engine cooling water temperature is attached to the engine body 1, and the output signal of the temperature sensor 29 is input to the input port 35 via the corresponding AD converter 37. A temperature sensor 44 for detecting the temperature of a mixed gas of intake air and EGR gas is mounted in at least one intake branch pipe 11, and an output signal of this temperature sensor 44 is passed through a corresponding AD converter 37. Input to the input port 35.

A temperature sensor 45 for detecting the temperature of the exhaust gas flowing into the catalyst 19 is arranged in the exhaust passage upstream of the catalyst 19, and the exhaust gas flowing out of the catalyst 19 is provided in the exhaust passage downstream of the catalyst 19. A temperature sensor 46 is arranged to detect the temperature of the gas. These temperature sensors 45, 4
The output signal of No. 6 is input to the input port 35 via the corresponding AD converter 37.

The accelerator pedal 40 includes an accelerator pedal 4
A load sensor 41 that generates an output voltage proportional to the stepping amount L of 0 is connected, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse each time the crankshaft rotates, for example, 30 °. On the other hand, an actuator 47 for driving the intake valve 7 is attached to the intake valve 7, and an actuator 48 for driving the exhaust valve 9 is attached to the exhaust valve 9.
Is installed. The output port 36 is the corresponding drive circuit 3
8, the fuel injection valve 6, the electric motor 15, the EGR control valve 23, the fuel pump 27 and the actuators 47, 4
8 is connected.

FIG. 2A is an enlarged view of the actuator 47. Referring to FIG. 2A, 50 is a disk-shaped iron piece attached to the top of the intake valve 7, 51 and 52 are solenoids arranged on both sides of the iron piece 50, and 53 and 54 are arranged on both sides of the iron piece 50. The compression springs are shown respectively. When the solenoid 52 is energized, the iron piece 50 rises and the intake valve 7 closes. On the other hand, when the solenoid 51 is energized, the iron piece 50 descends and the intake valve 7 opens. Therefore, the intake valve 7 can be opened and closed at any time by controlling the energizing timing of each solenoid 51, 52. The actuator 48 also has a structure similar to that of the actuator 47 shown in FIG. 2A, and therefore the exhaust valve 9 can be opened and closed at any time.

FIG. 2B shows lift curves of the intake valve 7 and the exhaust valve 9. The solid line in FIG. 2B shows a case where the valve overlap period in which both the intake valve 7 and the exhaust valve 9 are opened is relatively short, and the broken line in FIG. 2B shows the valve overlap period. It shows the case where it is made longer. By driving the intake valve 7 and the exhaust valve 9 by actuators 47 and 48, respectively, as shown in FIG.
The valve overlap period can be easily controlled as shown by the solid and broken lines in (B).

By the way, in the compression ignition type internal combustion engine, exhaust gas, that is, EGR gas is conventionally recirculated into the engine intake passage through the EGR passage as shown in FIG. 1, for example. 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 R 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 NOx generation amount decreases, and therefore, the higher the EGR rate, the lower the NOx generation amount.

As described above, it has been known that the amount of NOx 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 not exceeding 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 NOx and smoke produced is as small as possible, there is a limit to the reduction in the amount of NOx and smoke produced, and in reality, there is still a considerable amount of N 2.
The present situation is that Ox and smoke are generated.

However, if the inventor makes the EGR rate larger than the maximum allowable limit in the process of studying the combustion of the diesel engine, the smoke increases rapidly as described above, but there is a peak in the amount of smoke generated, If the EGR rate is further increased beyond this peak, the smoke starts to decrease sharply. If the EGR rate is 70% or more during idling operation, and if the EGR gas is cooled strongly, the EGR rate becomes almost 55%. It was found that if it exceeds the percentage, smoke is almost zero, that is, soot is hardly generated. It has also been found that at this time, the amount of NOx generated is extremely small. Next, this will be described with reference to FIG.

FIG. 3 shows a change in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 3) is changed by changing the opening of the throttle valve 16 and the EGR rate during engine low load operation, and An example of an experiment showing changes in the amount of smoke, HC, CO, and NOx emissions is shown. As can be seen from FIG. 3, in this experimental example, as the air-fuel ratio A / F becomes smaller, E
When the GR rate becomes large and is equal to or less than the stoichiometric air-fuel ratio (≈14.6), the EGR rate becomes 65% or more.

As shown in FIG. 3, 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 Ox generated is considerably low. On the other hand, at this time, HC,
The amount of CO generated starts to increase.

FIG. 4 (A) shows a change in combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 18 and the amount of smoke generated is 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 13 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 NOx generated is considerably reduced. N
A decrease in the amount of generated Ox means that the combustion temperature in the combustion chamber 5 has decreased, and therefore, it can be said that the combustion temperature in the combustion chamber 5 is low when soot is hardly generated. . 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.

Secondly, when the amount of smoke produced, that is, the amount of soot produced, becomes almost zero, as shown in FIG. 3, HC and CO
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 soot precursor as 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, 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 NOx produced, so this certain temperature can be defined to some extent from the amount of NOx produced. it can. That is, as the EGR rate increases, the temperature of the fuel and the gas around it during combustion decreases, and the amount of NOx generated decreases. At this time, soot is hardly generated when the NOx generation amount becomes around 10 p.pm or less. Therefore, the above certain temperature is NO
It almost coincides with 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 an oxidation catalyst or the like. On the other hand, the soot precursor or the hydrocarbon in the state before it can be easily purified by a post-treatment using an oxidation catalyst or the like. Considering the post-treatment with an oxidation catalyst as described above, there is an extremely large difference in 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. The new combustion system used in the present invention allows hydrocarbons to be discharged from the combustion chamber 5 in the form of soot precursor or in the state before it without producing soot in the combustion chamber 5 and oxidizes this hydrocarbon. Its core is to oxidize with a catalyst.

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 heat of fuel is absorbed by the surrounding inert gas, so 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 generated, an amount of inert gas sufficient to absorb the amount of heat required to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas also increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action. Therefore, the inert gas is preferably a gas having a large specific heat. In this respect, since CO ₂ and EGR gas have a 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 amount reaches a peak when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Almost no soot is generated if the percentage is exceeded. On the other hand, as shown by the curve B in FIG. 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 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. 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. In addition, the horizontal axis represents the required load, and Z1 represents the low load operation region.

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% when expressed by the EGR rate, and is 70% or more in the embodiment shown in FIG. That is, if the total intake gas amount sucked into the combustion chamber 5 is shown by the solid line X in FIG. 7, and the ratio of the air amount to the EGR gas amount in this total intake gas amount X is set as shown in FIG. The temperature of the fuel and the gas around it is lower than the temperature at which soot is produced, and thus no soot is generated. Further, the amount of NOx generated at this time is around 10 p.pm or less, and therefore NOx
Is very 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.

On the other hand, in the load region Z2 of FIG. 7, the total intake gas amount X required to prevent the generation of soot exceeds the total intake gas amount Y that can be inhaled. Therefore, in this case, in order to supply the total intake gas amount X required to prevent the generation of soot into the combustion chamber 5, both the EGR gas and the intake air, or EG
It is necessary to supercharge or pressurize the R gas. When the EGR gas or the like is not supercharged or pressurized, the total intake air amount X matches the total intake air amount Y in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the air amount is slightly decreased to increase the EGR gas amount and the fuel is burned under the rich air-fuel ratio.

As described above, FIG. 7 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, in the low load operation region Z1 shown in FIG. 7, the air amount is set to be smaller than the air amount shown in FIG. At least, that is, even if the air-fuel ratio is made rich, the generation amount of NOx can be reduced to around 10 p.pm or less while preventing the generation of soot, and the air amount in the low load region Z1 shown in FIG. Even if the amount is larger than the air amount shown in FIG. 7, that is, even if the average value of the air-fuel ratio is lean from 17 to 18, the amount of NOx generated is reduced to 10 while preventing the generation of soot.
It can be around or below ppm.

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, only a very small amount of NOx 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, NOx
Also produces only a very small amount.

Thus, in the engine low load operation region Z1, 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. Therefore, the amount of NOx 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 amount of heat generated by combustion is small and the engine load is relatively low. Therefore, in the present invention, when the engine load is relatively low, 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, When the engine load is relatively high, the second combustion, that is, the combustion that is more commonly performed than before is performed. 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 usually performed conventionally, is the combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in which the soot generation peaks. Say.

The solid line in FIG. 8 (A) shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when the first combustion is performed, and the chain line in FIG. 2 shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when the second combustion is performed. The solid line in FIG. 8B indicates the fuel temperature when the first combustion is performed and the gas temperature Tf around the fuel.
And the crank angle. The broken line in FIG. 8B shows the relationship between the fuel temperature and the gas temperature Tf around the fuel when the second combustion is performed and the crank angle.

When the first combustion, that is, the low-temperature combustion is being performed, the EGR gas amount is larger than when the second combustion, that is, the conventional ordinary combustion is being performed, and therefore, FIG.
As shown in (A), before the compression top dead center, that is, during the compression stroke, the average gas temperature Tg during the first combustion indicated by the solid line is the average gas temperature Tg during the second combustion indicated by the broken line.
Is higher than. At this time, as shown in FIG. 8B, the gas temperature Tf of the fuel and its surroundings is almost the same as the average gas temperature Tg.

Next, combustion is started near the compression top dead center. In this case, when the first combustion is being performed, the combustion and the gas temperature Tf around it are as shown by the solid line in FIG. 8B. It doesn't get much higher. Second to this
8B, the gas temperature Tf of the fuel and its surroundings becomes extremely high as indicated by the broken line in FIG. 8B. In this way, when the second combustion is performed, the temperature Tf of the fuel and the gas around the fuel is considerably higher than that when the first combustion is performed, but the temperature of the other gases that occupy most of the temperature is large. Is lower when the second combustion is performed than when the first combustion is performed. Therefore, as shown in FIG. 8A, the combustion near the compression top dead center The average gas temperature Tg in the chamber 5 is higher in the case where the first combustion is performed than in the case where the second combustion is performed. As a result, as shown in FIG. 8A, the average gas temperature Tg in the combustion chamber 5 after the combustion is completed, that is, in the latter half of the expansion stroke, in other words, the burned gas temperature in the combustion chamber 5 is The value when the first combustion is performed is higher than that when the second combustion is performed.

As described above, when the first combustion, that is, the low temperature combustion is performed, the temperature Tf of the fuel and the surrounding gas at the time of combustion is considerably lower than that when the second combustion is performed, but the combustion is performed. The burnt gas in the chamber 5 is higher than that in the case where the second combustion is performed, and therefore the temperature of the exhaust gas discharged from the combustion chamber 5 is also higher than that in the case where the second combustion is performed. Become higher.

FIG. 9 shows a first operating region I in which the first combustion, that is, low temperature combustion is performed, and a second combustion region II in which the second combustion, that is, combustion by the conventional combustion method is performed. There is. In FIG. 9, the vertical axis L represents the depression amount of the accelerator pedal 40, that is, the required load, and the horizontal axis N represents the engine speed. Further, in FIG. 9, 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 state 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 the embodiment according to the present invention, the second boundary Y (N) is on the low load side by ΔL (N) with respect to the first boundary X (N). As shown in FIGS. 9 and 10, ΔL (N) is a function of the engine speed N, and ΔL (N) becomes smaller as the engine speed N becomes higher. 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 hydrocarbon is in the form of a soot precursor or a state before that. It is discharged from the combustion chamber 5. At this time, the unburned hydrocarbons discharged from the combustion chamber 5 are oxidized by the catalyst 19 having an oxidizing function.

As the catalyst 19, an oxidation catalyst, a three-way catalyst, or a NOx absorbent can be used. The NOx absorbent is NOx when the average air-fuel ratio in the combustion chamber 5 is lean.
And has a function of releasing NOx when the average air-fuel ratio in the combustion chamber 5 becomes rich. This NOx absorbent uses, for example, alumina as a carrier, and potassium K, sodium Na, lithium Li, and cesium Cs are supported on this carrier.
Alkali metals such as, barium Ba, calcium Ca
Alkaline earth such as, lanthanum La, yttrium Y
At least one selected from rare earths such as
A precious metal such as t is supported.

Not only oxidation catalysts, but also three-way catalysts and NO
The x-absorbent also has an oxidizing function, so that a three-way catalyst and a NOx absorbent can be used as the catalyst 19 as described above. The catalyst 19 is activated when the temperature of the catalyst 19 exceeds a certain temperature. The temperature at which the catalyst 19 is activated differs depending on the type of the catalyst 19, and the activation temperature of a typical oxidation catalyst is about 350 ° C. The temperature of the exhaust gas passing through the catalyst 19 becomes slightly lower than the temperature of the catalyst 19 by a certain constant temperature, and therefore the temperature of the exhaust gas passing through the catalyst 19 represents the temperature of the catalyst 19. Therefore, in one embodiment according to the present invention, the catalyst 19
I try to judge whether or not is activated.

FIG. 11 shows the output of the air-fuel ratio sensor 21. As shown in FIG. 11, the output current I of the air-fuel ratio sensor 21 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 21. 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. 12 shows the opening of the throttle valve 16, the opening of the EGR control valve 23, the EGR rate, the air-fuel ratio, the injection timing and the injection amount with respect to the required load L. As shown in FIG. 12, in the first operating region I where the required load L is low, the opening degree of the throttle valve 16 is gradually increased from near fully closed to about half opened as the required load L increases, and the EGR control valve 23 The opening degree of is gradually increased from near full close to full open as the required load L increases. Further, in the example shown in FIG. 12, the EGR rate is approximately 70 in the first operating region I.
%, And the air-fuel ratio is a lean air-fuel ratio of 15 to 18.

In other words, in the first operating region I, EGR
The ratio is almost 70%, and the air-fuel ratio is 15 to 18
The opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled so that the lean air-fuel ratio becomes. At this time, the air-fuel ratio is E based on the output signal of the air-fuel ratio sensor 21.
The target lean air-fuel ratio is controlled by correcting the opening degree of the GR control valve 23. 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.

When the engine is idling, the throttle valve 16 is opened to near full closure, and the EGR control valve 23 is also closed to near full closure at this time. Throttle valve 1
When the valve 6 is closed to close to the fully closed state, the pressure in the combustion chamber 5 at the beginning of compression becomes low, so that 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, in idling operation, the throttle valve 16 is closed to close to the fully closed state in order to suppress the vibration of the engine body 1.

When the operating state of the engine is in the first operating region I, soot and NOx are scarcely generated, and the soot precursor contained in the exhaust gas or the hydrocarbon in the state before the soot is generated by the catalyst 19. It is oxidized. On the other hand, when the operating region of the engine changes from the first operating region I to the second operating region II, the opening degree of the throttle valve 16 is increased stepwise from the half open state to the full open direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, since the EGR rate jumps over the EGR rate range (FIG. 6) in which a large amount of smoke is generated, a large amount of smoke is generated when the operating region of the engine changes from the first operating region I to the second operating region II. There is no.

In the second operating region II, the conventional combustion is performed. Although some soot and NOx are generated in this combustion method, the thermal efficiency is higher than that in low temperature combustion, and therefore the engine operating range is from the first operating range I to the second operating range.
When changing to II, the injection amount is reduced stepwise as shown in FIG. In the second operating region II, the throttle valve 16 is kept fully open except for a part, and the opening degree of the EGR control valve 23 is gradually reduced as the required load L increases. This operating region II, the EGR rate becomes lower as the higher the required load L, the air-fuel ratio is small as the required load L becomes higher Kunar. 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.

By the way, the first operating region I where low temperature combustion is possible
Range varies depending on the gas temperature in the combustion chamber 5 at the beginning of compression and the cylinder inner wall surface temperature. That is, when the required load increases and the amount of heat generated by combustion increases, the temperature of the fuel and the gas around it increases during combustion, thus making it impossible to perform low temperature combustion. On the other hand, when the gas temperature TG in the combustion chamber 5 at the beginning of compression becomes low, the gas temperature in the combustion chamber 5 immediately before the start of combustion becomes low, so the temperature of the fuel and the gas around it at the time of combustion becomes low. Therefore, if the gas temperature TG in the combustion chamber 5 at the beginning of compression becomes low, the temperature of the fuel and its surrounding gas at the time of combustion will not rise even if the amount of heat generated by combustion increases, that is, even if the required load increases.
Thus, low temperature combustion is performed. In other words, the lower the gas temperature TG in the combustion chamber 5 at the beginning of compression is, the wider the first operating region I where low temperature combustion can be performed becomes toward the high load side.

Further, the smaller the temperature difference (TW-TG) between the cylinder inner wall surface temperature TW and the gas temperature TG in the combustion chamber 5 at the beginning of compression, the larger the amount of heat escaping via the cylinder inner wall surface during the compression stroke. Therefore, the smaller the temperature difference (TW-TG), the smaller the temperature rise amount of the gas in the combustion chamber 5 during the compression stroke, and the lower the temperature of the fuel and the gas around it during combustion. Therefore, the temperature difference (TW
The smaller the value of (TG) is, the lower the first operation region I in which low temperature combustion can be performed.
Will be expanded to the high load side.

In the embodiment according to the present invention, when the gas temperature TG in the combustion chamber 5 at the beginning of compression becomes low, the first boundary is moved from Xo (N) to X (N) as shown in FIG. When the difference (TW-TG) becomes smaller, the first boundary is moved from Xo (N) to X (N) as shown in FIG. In addition, Xo (N) has shown the 1st boundary used as a reference | standard here. First boundary Xo serving as a reference
(N) is a function of the engine speed N, and X (N) is this X
It is calculated based on the following equation using o (N).

X (N) = Xo (N) + K (T) · K (N) K (T) = K (T) ₁ + K (T) ₂ where K (T) ₁ is shown in FIG. As shown, it is a function of the gas temperature TG in the combustion chamber 5 at the beginning of compression, and the value of K (T) ₁ increases as the gas temperature TG in the combustion chamber 5 at the beginning of compression decreases. Also, K (T) ₂ is a function of the temperature difference (TW-TG) as shown in FIG. 14B, and the value of K (T) ₂ is the temperature difference (TW-T).
It becomes larger as G) becomes smaller. Note that FIG.
14B, T ₁ is a reference temperature, T ₂ is a reference temperature difference, TG = T ₁ and (TW-TG) = T
When it is ₂ , the first boundary becomes Xo (N) in FIG.

On the other hand, K (N) is a function of the engine speed N as shown in FIG. 14 (C), and the value of K (N) becomes smaller as the engine speed N becomes higher. That is, when the gas temperature TG in the combustion chamber 5 at the beginning of compression becomes lower than the reference temperature T _1, the first boundary X (N) becomes Xo (N) as the gas temperature TG in the combustion chamber 5 at the beginning of compression becomes lower. In contrast, the temperature difference (TW-TG) moves to the high load side and the reference temperature difference T
_When it becomes lower than _2, the first boundary X (N) moves to the high load side with respect to Xo (N) as the temperature difference (TW-TG) becomes smaller. Further, the moving amount of X (N) with respect to Xo (N) becomes smaller as the engine speed N becomes higher.

FIG. 15A shows the air-fuel ratio A / F in the first operating region I when the first boundary is the first boundary Xo (N) which is the reference. In FIG. 15 (A), each curve indicated by A / F = 15, A / F = 16, A / F = 17 shows the case where the air-fuel ratio is 15, 16, and 17, respectively, and The air-fuel ratio of is determined by proportional distribution. As shown in FIG. 15 (A), the air-fuel ratio becomes lean in the first operating region I, and in the first operating region I, the air-fuel ratio A / F becomes leaner as the required load L becomes 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 reduced, the air-fuel ratio becomes large, so that the air-fuel ratio A / F becomes larger as the required load L becomes lower as shown in FIG. 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.

FIG. 15B shows the air-fuel ratio A / F in the first operating region I when the first boundary is X (N) shown in FIG. As can be seen by comparing FIGS. 15 (A) and 15 (B), when the first boundary X (N) moves to the high load side with respect to Xo (N), the first boundary X (N) follows each air-fuel ratio to indicate A / F = The curve of 15, A / F = 16, A / F = 17 also moves to the high load side. Therefore, the first boundary X (N) is X
The same required load L when moving to the high load side with respect to o (N)
Also, it can be seen that the air-fuel ratio A / F at the same engine speed N becomes large. That is, when the first operating region I is expanded to the high load side, not only the operating region where soot and NOx are hardly generated is expanded, but also the fuel consumption rate is improved.

In the embodiment according to the invention, the first boundary X
The target air-fuel ratio in the first operating region I when (N) changes variously, that is, the target air-fuel ratio in the first operating region I with respect to various values of K (T) is shown in FIGS.
As shown in FIG. 6 (D), it is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N. That is, in FIG. 16A, the value of K (T) is KT1.
16 shows the target air-fuel ratio AFKT1 at the time of
(B) is the target air-fuel ratio AF when the value of K (T) is KT2.
KT2 is shown, and the value of K (T) is K in FIG. 16 (C).
The target air-fuel ratio AFKT3 at T3 is shown in FIG.
6 (D) is the target air-fuel ratio A when the value of K (T) is KT4.
FKT4 is shown.

On the other hand, the air-fuel ratio is set to the target air-fuel ratio AFKT1, A
The target opening degree of the throttle valve 16 required for setting FKT2, AFKT3, AFKT4 is shown in FIG.
As shown in (D), required load L and engine speed N
Is stored in the ROM 32 in the form of a map in advance as a function of, and the air-fuel ratio is set to the target air-fuel ratio AFKT1, AF
EG required to make KT2, AFKT3, AFKT4
The target basic opening degree of the R control valve 23 is changed from FIG.
As shown in (D), required load L and engine speed N
Is previously stored in the ROM 32 in the form of a map as a function of.

That is, FIG. 17A shows the target opening ST15 of the throttle valve 16 when the air-fuel ratio is 15.
FIG. 18A shows the EGR control valve 23 when the air-fuel ratio is 15.
The target basic opening degree SE15 is shown. In addition, FIG.
FIG. 18B shows the target opening degree ST16 of the throttle valve 16 when the air-fuel ratio is 16, and FIG.
The target basic opening degree SE16 of the EGR control valve 23 at the time of 6 is shown.

FIG. 17C shows the target opening ST17 of the throttle valve 16 when the air-fuel ratio is 17.
FIG. 18C shows the EGR control valve 23 when the air-fuel ratio is 17.
The target basic opening degree SE17 is shown. In addition, FIG.
FIG. 18D shows the target opening degree ST18 of the throttle valve 16 when the air-fuel ratio is 18, and FIG.
The target basic opening degree SE18 of the EGR control valve 23 at the time of 8 is shown.

FIG. 19 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. Incidentally, in FIG. 19, 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 1 required to set the air-fuel ratio to this target air-fuel ratio
The target opening degree ST of 6 is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 20 (A), and the air-fuel ratio is set to this target air-fuel ratio. Target opening degree SE of the EGR control valve 23 necessary for
Is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N as shown in FIG.

Next, a specific embodiment of the present invention will be described with reference to the case where a NOx absorbent is used as the catalyst 19. As described above, a large amount of unburned HC and CO are discharged from the engine during the first combustion, that is, low temperature combustion, and these unburned HC and CO are oxidized by the NOx absorbent 19. When low temperature combustion is performed, the exhaust gas temperature is high as described above, and a large amount of unburned HC,
Since CO is discharged, a large amount of heat of oxidation reaction is generated. Therefore, when low temperature combustion is performed, the NOx absorbent 1
9 is usually maintained above the activation temperature.

On the other hand, when the second combustion is being performed, the exhaust gas temperature is low and unburned H
Since the amounts of C and CO emissions are also small, almost no heat of oxidation reaction is generated. Therefore, when the second combustion is being performed, there is a risk that the temperature of the NOx absorbent 19 will drop below the activation temperature. This is the same when an oxidation catalyst or a three-way catalyst is used as the catalyst 19.

Therefore, in the embodiment according to the present invention, when the temperature of the NOx absorbent 19 is about to drop below the activation temperature during the second combustion, the valve overlap period is set as shown in FIG. In addition to increasing the length, the first fuel injection Q ₁ is performed during the valve overlap period, and the second fuel injection Q ₂ is performed near the compression top dead center.

That is, in the internal combustion engine, when the exhaust valve 9 opens, the inside of the exhaust port 10 temporarily becomes positive pressure, and then this positive pressure wave propagates toward the downstream side, for example, in the form of a negative pressure wave at the manifold collecting portion. This negative pressure wave is reflected and propagates to the upstream side this time, and as a result, a negative pressure is generated in the exhaust port 10 immediately before the exhaust valve 9 is closed. As a result, a part of the air supplied from the intake port 10 into the combustion chamber 5 at the time of valve overlap blows into the exhaust port 10 due to this negative pressure, and the blow-through amount at this time increases as the valve overlap period becomes longer. .

Therefore, as shown in FIG. 21, if the valve overlap period is lengthened and the first combustion injection Q ₁ is performed during the valve overlap period, a large amount of unburned HC is discharged into the exhaust port 10 together with blown air. To be done. This unburned HC is oxidized in the NOx absorbent 19, and the temperature of the NOx absorbent 19 is raised by the heat of oxidation reaction at that time. Therefore, the temperature of the NOx absorbent 19 is prevented from falling below the activation temperature. At this time, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent 19 is made lean, for example, about 15 to 18, but at this time the air-fuel ratio may be made rich. That is,
Since excess oxygen in the exhaust gas is originally adsorbed on the NOx absorbent 19, even if the air-fuel ratio of the exhaust gas flowing into the NOx absorbent 19 is made rich, the oxidation reaction immediately occurs.

A part of the fuel in the _first fuel injection Q ₁ remains in the combustion chamber 5, and in this case, therefore, it has the same shape as when the rubber injection is performed. When it is not necessary to discharge a large amount of unburned HC from the engine, the valve overlap period is shortened to improve the engine output, and fuel injection is performed only once near the compression top dead center. On the other hand, the ratio of air and fuel (hydrocarbons) supplied into the engine intake passage and the exhaust passage upstream of the NOx absorbent 19 is set to N
The air-fuel ratio of the exhaust gas flowing into the Ox absorbent 19 is N
The Ox absorbent 19 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich.
It absorbs and releases.

If the NOx absorbent 19 is arranged in the exhaust passage of the engine, the NOx absorbent 19 actually acts to absorb and release NOx, but the detailed mechanism of this absorbing and releasing effect is not clear in some parts. However, it is considered that this absorbing and releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking the case where platinum Pt and barium Ba are supported on the carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

In the compression ignition type internal combustion engine shown in FIG. 1, combustion is performed with the air-fuel ratio being lean. When combustion is performed in a state where the air-fuel ratio is lean as described above, the oxygen concentration in the exhaust gas is high, and at this time, as shown in FIG. 22A, the oxygen O ₂ is O ₂ ⁻ or O _2. It adheres to the surface of platinum Pt in the form of ^2- . On the other hand, NO in the inflowing exhaust gas
Reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt, and NO ₂
(2NO + O ₂ → 2NO ₂ ). Next, a part of the generated NO ₂ is absorbed on the platinum Pt while being absorbed and absorbed in the absorbent to bond with barium oxide BaO.
As shown in (A), it diffuses into the absorbent in the form of nitrate ion NO ₃ ⁻ . In this way, NOx is absorbed in the NOx absorbent 19. As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of platinum Pt and NO
x Unless the absorption capacity is saturated, NO ₂ is absorbed in the absorbent and nitrate ion NO ₃ ⁻ is produced.

[0078] On the other hand, the air-fuel ratio is made rich, the oxygen concentration is decreased and the amount of NO ₂ is lowered by reaction backward in the inflowing exhaust gas ^- proceed to (NO ₃ → NO _2), thus to absorb The nitrate ion NO ₃ ^{− in the} agent is released from the absorbent in the form of NO ₂ . At this time, NOx released from the NOx absorbent 19 is reduced by reacting with a large amount of unburned HC and CO contained in the inflowing exhaust gas as shown in FIG. 22 (B). When NO ₂ is no longer present on the surface of platinum Pt in this way, NO ₂ is released one after another from the absorbent. Therefore, when the air-fuel ratio is made rich, NOx is released from the NOx absorbent 19 within a short time, and the released NOx is reduced, so that it is possible to prevent NOx from being discharged into the atmosphere. You can do it.

Therefore, in the embodiment according to the present invention, the air-fuel ratio is made rich when NOx is to be released from the NOx absorbent 19 during the first combustion. On the other hand, when NOx should be released from the NOx absorbent 19 during the second combustion, the valve overlap period is lengthened and the first combustion is performed so that the air-fuel ratio of the exhaust gas becomes rich. Injection Q ₁ is performed during the valve overlap period.

FIG. 23 shows the required load L and the NOx absorbent 19
The downstream exhaust gas temperature TE, the estimated NOx amount ΣNOx absorbed by the NOx absorbent 19, and the exhaust gas air-fuel ratio A /
F is shown. As shown in FIG. 23, when the estimated NOx amount ΣNOx exceeds the allowable maximum value MAX during the first combustion, the air-fuel ratio in the combustion chamber 5 becomes rich, which causes the exhaust gas air-fuel ratio A to rise. / F is made rich. At this time, NOx is released from the NOx absorbent 19.

Next, when the second combustion is being performed, N
If the exhaust gas temperature TE downstream of the Ox absorbent 19 decreases to a constant value, for example, 300 ° C., the valve overlap period is lengthened and, for example, the air-fuel ratio of the exhaust gas is 1
The first fuel injection Q ₁ is performed during the valve overlap period so as to be 7.0. At this time, the temperature of the NOx absorbent 19 is raised.

Next, when the estimated NOx amount ΣNOx exceeds the allowable maximum value MAX during the second combustion, the valve overlap period is lengthened and, for example, the air-fuel ratio of the exhaust gas becomes rich. The first fuel injection Q ₁ is performed during the valve overlap period. At this time, NOx is released from the NOx absorbent 19. FIG. 24 shows a routine for controlling the low temperature combustion region, that is, the first operation region I.

Referring to FIG. 24, first, at step 100, the gas temperature T in the combustion chamber 5 at the beginning of compression is increased.
G and the cylinder inner wall surface temperature TW are calculated. In this embodiment, the intake air detected by the temperature sensor 44 and the E
The mixed gas temperature of the GR gas is set to the gas temperature TG in the combustion chamber 5 at the beginning of compression, and the engine cooling water temperature detected by the temperature sensor 29 is set to the cylinder inner wall surface temperature TW. Next, at step 101, K is calculated from the relationship shown in FIG.
(T) ₁ is obtained, and K is calculated from the relationship shown in FIG.
(T) ₂ is calculated, and K (T) ₁ and K (T) ₂ are added to obtain K (T) (= K (T) ₁ + K
(T) ₂ ) is calculated.

Next, at step 102, K (N) is calculated from the relationship shown in FIG. 14 (C) based on the engine speed N. Next, at step 103, the value of the first boundary X (N) is calculated based on the following equation using the value of the first boundary Xo (N) stored in advance. X (N) = Xo (N) + K (T) · K (N) Next, at step 104, based on the engine speed N, as shown in FIG.
ΔL (N) is calculated from the relationship shown in 0. Next, at step 105, the value of the second boundary Y (N) (= X (N) −ΔL) is subtracted from X (N) by ΔL (N).
(N)) is calculated.

FIG. 25 shows a time interruption routine for processing the HC flag indicating that the amount of unburned HC discharged from the engine should be increased. Referring to FIG. 25, first, the NO detected by the temperature sensor 46 is detected.
x It is judged whether or not the exhaust gas temperature TE downstream of the absorbent 19 is higher than a predetermined constant temperature, for example, 300 ° C.
When TE ≦ 300 ° C., the routine proceeds to step 201, where HC
The flag is set, and then at step 202, it is judged if a fixed time has elapsed since the HC flag was set. When a certain time has elapsed since the HC flag was set, the routine proceeds to step 203, where the HC flag is reset. That is, when TE ≦ 300 ° C.
The flag will be set.

In step 200, TE> 300 ° C.
Instead of determining whether or not the temperature is equal to, the temperature difference (TE-TEI) between the exhaust gas temperature TE detected by the temperature sensor 46 and the exhaust gas temperature TEI upstream of the NOx absorbent 19 detected by the temperature sensor 45 is constant. It is also possible to determine whether the temperature is above 10 ° C., for example. That is, when the NOx absorbent 19 is activated, the exhaust gas temperature rises in the NOx absorbent 19, and if (TE-TEI)> 10 ° C, it is determined that the NOx absorbent 19 is activated. You can

FIG. 26 shows a time interruption routine for processing a rich flag indicating that the air-fuel ratio of the exhaust gas should be made rich in order to release NOx from the NOx absorbent 19. Referring to FIG. 26, first, at step 300, it is judged if the flag I is set or not. When the flag I is set, that is, when low temperature combustion is performed, the routine proceeds to step 301, where the NOx amount ΔNOx discharged from the engine per unit time is calculated. This NOx amount ΔNOx is stored in advance in the ROM 32 as a function of the required load L and the engine speed N. Then, it proceeds to step 303. On the other hand, flag I
Is reset, that is, when the second combustion is being performed, the routine proceeds to step 302, where the NOx amount ΔNOx discharged from the engine per unit time is calculated. This NOx
The amount ΔNOx is also stored in the ROM 32 in advance as a function of the required load L and the engine speed N. Then, it proceeds to step 303.

In step 303, the estimated NOx amount ΣNOx estimated to be absorbed by the NOx absorbent 19 is calculated by adding ΔNOx to ΣNOx. Next, at step 304, it is judged if the estimated NOx amount ΣNOx exceeds the allowable maximum value MAX. ΣNOx ＞ M
If it is AX, the routine proceeds to step 302, where the rich flag is set, and then at step 306, it is judged if a fixed time has elapsed since the rich flag was set. When a fixed time has elapsed since the rich flag was set, the routine proceeds to step 307, where the rich flag is reset, and at step 308 ΣNOx is made zero. That is, when ΣNOx> MAX, the rich flag is set for a certain period of time.

Next, a routine for controlling the operation of the engine will be described with reference to FIGS. 27 and 28. Referring to FIGS. 27 and 28, first, step 4 is performed.
At 00, it is determined whether or not the flag I indicating that the operating region of the engine is the first operating region I is set. When the flag I is set, that is, when the engine operating region is the first operating region I, step 40
In step 1, it is determined whether the required load L has become larger than the first boundary X (N). When L ≦ X (N), the routine proceeds to step 402, where the first combustion, that is, the low temperature combustion is performed.

That is, at step 402, the target air-fuel ratio AF is calculated by proportional distribution using two maps corresponding to K (T) among the maps shown in FIGS. 16 (A) to 16 (D). Next, at step 403, the throttle valve 1 is proportionally distributed using the two maps corresponding to the target air-fuel ratio AF among the maps shown in FIGS. 17 (A) to (D).
The target opening degree ST of 6 is calculated, and the opening degree of the throttle valve 16 is controlled to this target opening degree ST. Then step 40
In FIG. 4, the target basic opening degree SE of the EGR control valve 23 is calculated by proportional distribution using two maps corresponding to the target air-fuel ratio AF among the maps shown in FIGS. 18 (A) to (D). Next, at step 405, the injection start timing θS is calculated, and then the routine proceeds to step 406.

At step 406, it is judged if the rich flag is set. When the rich flag is not set, the routine proceeds to step 407, where the fuel injection amount Q is calculated. Next, at step 408, it is judged if the actual air-fuel ratio A / F detected by the air-fuel ratio sensor 21 is larger than the target air-fuel ratio AF. A / F> A
When it is F, the routine proceeds to step 409, where the EGR control valve 23
A constant value β is added to the correction value ΔSE for the opening degree of, and then the process proceeds to step 411. On the other hand, A / F ≦ AF
In case of, the routine proceeds to step 410, where the constant value β is subtracted from the correction value ΔSE, and then the routine proceeds to step 411. In step 411, the target opening degree SEO of the EGR control valve 23 is calculated by adding the correction value ΔSE to the target basic opening degree SE of the EGR control valve 23, and the opening degree of the EGR control valve 23 is controlled to this target opening degree SEO. To be done. That is, in this embodiment, the actual air-fuel ratio is controlled to the target air-fuel ratio AF by controlling the opening degree of the EGR control valve 23. Of course, in this case, the actual air-fuel ratio can be controlled to the target air-fuel ratio AF by controlling the opening of the throttle valve 16.

On the other hand, if it is determined in step 406 that the rich flag is set, step 4
12, the target air-fuel ratio AF is used to calculate the correction value ΔQ of the fuel injection amount required to make the air-fuel ratio A / F rich, for example, A / F = 13, based on the following equation. ΔQ = Q · (AF-13.0) / AF Next, at step 413, the correction value ΔQ is added to the fuel injection amount Q to obtain the final fuel injection amount Q (= Q + Δ
Q) is calculated. At this time, NOx from the NOx absorbent 19
x is emitted.

On the other hand, in step 401, L> X
When it is determined that the state has become (N), the routine proceeds to step 414, where the flag I is reset, then the routine proceeds to step 417, where the second combustion, that is, the normal combustion that has been performed conventionally is performed. That is, in step 417, the target opening degree ST of the throttle valve 16 is calculated from the map shown in FIG. 20 (A), and then in step 418, the target opening degree SE of the EGR control valve 23 is calculated from the map shown in FIG. 20 (B). To be done.
Next, at step 419, it is judged if the HC flag or the rich flag is set. When neither the HC flag nor the rich flag is set, the routine proceeds to step 420, where the fuel injection amount Q is calculated, and then at step 421, the injection start timing θS is calculated.

On the other hand, when it is determined in step 400 that the flag I is reset, that is, when the operating region of the engine is the second operating region II, step 415
Then, it is determined whether the required load L has become smaller than the second boundary Y (N). When L ≧ Y (N), the process proceeds to step 417. On the other hand, when L <Y (N), the routine proceeds to step 416, where the flag I is set. Next, in step 402, the first combustion, that is, the low temperature combustion is performed.

If it is judged at step 419 that the HC flag or rich flag is set, then the routine proceeds to step 422, where the actuators 47, 48 are
Is driven, and the valve overlap period is lengthened.
Next, at step 423, the first fuel injection amount Q
_{The first} and second fuel injection amounts Q ₂ are calculated. Incidentally, HC flag is stored in the ROM32 in as a function of Q ₁ and Q ₂ and when the rich flag has been set Q ₁ and Q ₂ and are each separately required load L and engine speed N in the case where it is set ing. When the HC flag is set, the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio of, for example, about 17.0, which causes the temperature of the NOx absorbent 19 to rise. On the other hand, when the rich flag is set, the air-fuel ratio of the exhaust gas becomes rich, whereby NOx is released from the NOx absorbent 19.

Next, at step 424, the first fuel injection start timing θS ₁ (FIG. 21) and the second fuel injection start timing θS ₂ (FIG. 21) are calculated.

[0097]

As described above, when it is not necessary to increase the amount of unburned HC discharged from the engine, a sufficient output of the engine is secured, and the valve overlap period is limited only when the amount of unburned HC discharged from the engine should be increased. Be lengthened.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an enlarged sectional view of an actuator.

FIG. 3 is a diagram showing a generation amount of smoke and NOx.

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 changes in the average gas temperature Tg in the combustion chamber and the gas temperature Tf of the fuel and its surroundings.

FIG. 9 is a diagram showing a first operating region I and a second operating region II.

FIG. 10 is a diagram showing a relationship between ΔL (N) and engine speed N.

FIG. 11 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 12 is a diagram showing an opening of a throttle valve and the like.

FIG. 13 is a diagram for explaining a method of controlling the first boundary X (N).

FIG. 14 is a diagram showing K (T) ₁ , K (T) ₂ and K (N).

FIG. 15 is a diagram showing an air-fuel ratio in a first operating region I.

FIG. 16 is a diagram showing a map of a target air-fuel ratio.

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

FIG. 18 is a diagram showing a target basic opening degree of an EGR control valve.

FIG. 19 is a diagram showing an air-fuel ratio and the like in the second combustion.

FIG. 20 is a diagram showing a target opening degree and the like of a throttle valve.

FIG. 21 is a diagram showing a valve overlap period, fuel injection timing, and the like.

FIG. 22 is a diagram for explaining the action of absorbing and releasing NOx.

FIG. 23 is a time chart for explaining air-fuel ratio control.

FIG. 24 is a flowchart for controlling the low temperature combustion region.

FIG. 25 is a flowchart for processing an HC flag.

FIG. 26 is a flowchart for processing a rich flag.

FIG. 27 is a flowchart for controlling the operation of the engine.

FIG. 28 is a flowchart for controlling the operation of the engine.

[Explanation of symbols]

6 ... Fuel injection valve 16 ... Throttle valve 19 ... Catalyst 23 ... EGR control valve

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI F01N 3/20 ZAB F01N 3/20 ZABE 3/24 ZAB 3/24 ZABR F02D 41/04 370 F02D 41/04 370 41/40 ZAB 41/40 ZABC 43/00 301 43/00 301G 301Z ZAB ZAB (56) Reference JP-A-9-273415 (JP, A) JP-A-6-159041 (JP, A) JP-A-7-4287 (JP , A) JP-A-9-119325 (JP, A) JP-A-7-238849 (JP, A) JP-A-5-86942 (JP, A) JP-A-8-121147 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 13/00 F02D 41/00

Claims (3)

(57) [Claims] 1. A fuel injection valve for injecting fuel into the combustion chamber is provided to increase the amount of inert gas in the combustion chamber.
As the amount of soot increases, the amount of soot gradually increases and reaches a peak.
If the amount of inert gas in the firing chamber is further increased,
The temperature of the fuel and the surrounding gas temperature during combustion in the combustion
Internal combustion where the temperature drops below the temperature and soot is hardly generated
In the engine, a valve overlap period control means for controlling the valve overlap period in which both the intake valve and the exhaust valve are opened, and a judgment for determining whether or not the amount of unburned hydrocarbons discharged from the engine should be increased Means and emission of soot
The amount of inert gas in the combustion chamber is more
The first combustion with a large amount of somatic gas and almost no soot,
The amount of soot generated peaks in the combustion chamber rather than the amount of inert gas
Second combustion with a small amount of inert gas is selectively switched
And a switching means for switching the second combustion.
Internal combustion when determining to increase the unburnt amount of hydrogen exhausted from the engine to come in, which inject the at least a portion of the fuel with a longer valve overlap period during the valve overlap period organ. 2. A catalyst having an oxidizing function is arranged in the engine exhaust passage, and when the temperature of the catalyst is likely to drop below the activation temperature, the valve overlap period is lengthened and at least a part of the fuel is valved. The internal combustion engine according to claim 1, wherein the injection is performed during the overlap period. 3. An NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases NOx when the air-fuel ratio of the inflowing exhaust gas becomes rich is arranged in the engine exhaust passage to absorb the NOx. The internal combustion engine according to claim 1, wherein when NOx is to be released from the agent, the valve overlap period is lengthened and at least a part of the fuel is injected during the valve overlap period.