JPH11294152A - Compression ignition type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively inhibit emission of unburnt HC, CO to the atmosphere at the time of low temperature combustion by adjusting the heat absorbing quantity of gas in the periphery of fuel at the time of combustion in a fuel chamber, and restraining the gas temperature of fuel and its periphery at the time of combustion in the combustion chamber below such a temperature that growth of hydrocarbon is stopped in its course. SOLUTION: When an engine 1 is operated, the gas temperature of fuel and its periphery at the time of combustion in a fuel chamber 5 can be restrained below such a temperature that growth of hydrocarbon is stopped in its course only when the engine load is low. In the low load operation region, soot is not generated regardless of the air fuel ratio, so that the quantity of generated NOx is a very small. Accordingly, in the low load operation region, a first combustion (low temperature combustion) for restraining the gas temperature of fuel and its periphery at the time of combustion below such a temperature that growth of hydrocarbon is stopped in its course is performed, and when the engine load is comparatively high, a second combustion (normal combustion) is performed. When the engine is started and the catalyst of the catalytic converter 19 is not activated, an electric current is applied to an electric heater to activate the catalyst early.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression ignition type internal combustion engine.

[0002]

Conventionally than internal combustion engines, for example exhaust gas recirculation and engine exhaust passage and the engine intake passage in order to suppress the generation of the NO _X in the diesel engine (hereinafter, referred to as EGR) connected by passages, the Exhaust gas, that is, EGR gas, is recirculated through the EGR passage into the engine intake passage. In this case, the EGR gas has a relatively high specific heat, and therefore can absorb a large amount of heat.
The combustion temperature in the combustion chamber decreases as the GR gas amount increases, that is, as the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases. When the combustion temperature is lowered to decrease the generation amount of NO _X, thus the generation amount of the more NO _X to be increased EGR rate is lowered.

[0003] It has been found that can reduce the generation amount of the NO _X Thus increasing the EGR rate than before. However, when the EGR rate is increased, the soot generation amount, that is, smoke, starts to increase rapidly when the EGR rate exceeds a certain limit. In this regard, it has conventionally been considered that if the EGR rate is further increased, the smoke will increase indefinitely. Therefore, the smoke starts to increase rapidly.
The GR rate is considered to be the maximum allowable limit of the EGR rate.

Therefore, conventionally, the EGR rate has been set within a range not exceeding the maximum allowable limit (for example, Japanese Patent Laid-Open No.
-334750). The maximum allowable EGR rate varies considerably depending on the type of engine and fuel, but is approximately 30 to 50%. Therefore, in a conventional diesel engine, the EGR rate is suppressed to about 30% to 50% at the maximum.

[0005]

As described above, the conventional E
Since it was considered that there was a maximum allowable limit for the GR rate, the EGR rate was conventionally set so that the amount of generated NO _X and smoke was minimized within a range not exceeding the maximum allowable limit. However, even if the EGR rate is set such that the amount of generated NO _X and smoke is as small as possible, the reduction of the amount of generated NO _X and smoke is limited, and in fact, a considerable amount of NO _X and smoke is actually still present. At present, smoke is generated.

However, if the EGR rate is made larger than the maximum allowable limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, the amount of generated smoke has a peak, and the peak exceeds this peak. EGR
When the rate is further increased, the smoke starts to decrease rapidly, and when the EGR rate is increased to 70% or more during idling operation, and when the EGR gas is cooled strongly, the smoke is reduced when the EGR rate is increased to about 55% or more. It was found that it was almost zero, that is, almost no soot was generated. In this case, N
Generation amount of O _X is also found that a very small amount.
After that, based on this finding, the reason why no soot was generated was examined, and as a result, unprecedented soot and NO
A new combustion system capable of simultaneously reducing _X has been built. This new combustion system will be described in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle stage until the hydrocarbons grow into soot.

That is, as a result of repeated experimental studies, it has been found that when the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than a certain temperature, the growth of hydrocarbons is stopped at a halfway stage before reaching soot. However, when the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons grow into soot at a stretch. In this case, the temperature of the fuel and the surrounding gas is greatly affected by the heat absorbing action of the gas around the fuel when the fuel is burned, and the amount of heat absorbed by the gas around the fuel is adjusted according to the calorific value at the time of burning the fuel. As a result, the temperature of the fuel and the surrounding gas can be controlled.

Accordingly, if the combustion during combustion in the combustion chamber and the gas temperature around the combustion are suppressed below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the fuel during combustion in the combustion chamber and its surroundings will not be generated. Can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system.

As described above, this new combustion system is based on purifying hydrocarbons and the like whose growth has stopped halfway before reaching soot with an oxidation catalyst or the like. Therefore, when the oxidation catalyst or the like is not activated, this new combustion system is used. No new combustion can take place.

[0010]

Therefore, in the first invention, when 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. As the temperature further increases, the temperature of the fuel during combustion in the combustion chamber and the temperature of the gas around it become lower than the temperature at which soot is generated, so that in the compression ignition type internal combustion engine where almost no soot is generated, an oxidation function is provided in the engine exhaust passage. The first catalyst, in which the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of generated soot peaks, and soot is hardly generated
Switching means for selectively switching between the combustion of (i) 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 generation amount of soot becomes a peak, and heating means for heating the catalyst. Detecting means for detecting a representative temperature representing the temperature of the catalyst, wherein the representative temperature is a predetermined temperature at least when the first combustion is being performed or when the first combustion is to be performed. When the temperature becomes lower than that, the heating means heats the catalyst.

In the second invention, in the first invention,
The heating means comprises an electric heater. In a third aspect based on the first aspect, the catalyst comprises an oxidation catalyst or a three-way catalyst. In the first invention in the fourth invention, the absorption and the air-fuel ratio of the inflowing exhaust gas air-fuel ratio of the exhaust gas absorb and flowing the NO _X contained in the exhaust gas becomes the stoichiometric air-fuel ratio or rich when the lean the _the NO _X absorbent disposed in the catalyst downstream of the engine exhaust passage that releases the NO _X, N
When NO _X is to be released from the O _X absorbent, the air-fuel ratio in the combustion chamber is set to the stoichiometric air-fuel ratio or rich during the first combustion.

In a fifth aspect, in the fourth aspect,
Comprising a determining means for determining whether or not to release the NO _X from _the NO _X absorbent, the temperature at which the representative temperature is predetermined when it is determined that it should release the NO _X from _the NO _X absorbent If the temperature is lower than the predetermined value, the catalyst is heated by the heating means, and after the representative temperature becomes higher than the predetermined temperature, the air-fuel ratio in the combustion chamber is made the stoichiometric air-fuel ratio or rich.

In the sixth invention, in the first invention,
A recirculation device is provided for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, and the inert gas comprises the recirculated exhaust gas. In a seventh aspect based on the sixth aspect, the exhaust gas recirculation rate in the first combustion state is approximately 5%.
5% or more.

[0014]

FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to 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 has an oxidizing function via an exhaust manifold 17 and an exhaust pipe 18 and has a catalytic converter 19 containing a catalyst heated by an electric heater.
Linked to NO is located downstream of the catalytic converter 19.
_{An X} absorbent 20 is arranged. The catalytic converter 19
The of a downstream _the NO _X absorbent 20 upstream of the exhaust passage is arranged a temperature sensor 21 for detecting the exhaust gas temperature.

The exhaust manifold 17 and the surge tank 12 are connected to each other via an EGR passage 22, and an electrically controlled EGR control valve 23 is disposed in the EGR passage 22.
A cooling device 24 for cooling the EGR gas flowing in the EGR passage 22 is arranged around the EGR passage 22. In the embodiment shown in FIG.
4, and the EGR gas is cooled by the engine cooling water.

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

The electronic control unit 30 is comprised of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, An output port 36 is provided. The output signal of the temperature 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. An air-fuel ratio sensor 29 is mounted on the exhaust manifold 17, and an output signal of the air-fuel ratio sensor 29 is supplied to an input port 3 via a corresponding AD converter 37.
5 is input. A load sensor 41 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Is done. The input port 35 is connected to a crank angle sensor 42 that generates an output pulse each time the crankshaft rotates, for example, by 30 °. On the other hand, output port 3
Reference numeral 6 denotes a fuel injection valve 6, an electric motor 15, an electric heater in the catalytic converter 19, and an EG via a corresponding drive circuit 38.
It is connected to the R control valve 23 and the fuel pump 27.

FIG. 2 shows a change in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree of the throttle valve 16 and the EGR rate during low engine load operation, and 4 shows an experimental example showing a change in the amount of smoke, HC, CO, and NO _X emissions. As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the smaller the E
When the GR rate increases and is equal to or lower than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is equal to or higher than 65%.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR ratio, the smoke is reduced when the air-fuel ratio A / F becomes approximately 30 when the EGR ratio becomes approximately 40%. The generation starts to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more and the air-fuel ratio A / F is around 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and N
Generation amount of O _X is considerably lower. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3A 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 generated smoke is the largest, and FIG. 3B shows the air-fuel ratio A / F. The graph shows a change in the combustion pressure in the combustion chamber 5 when F is around 13 and the amount of generated smoke is almost zero. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) where the amount of smoke generation is almost zero, FIG.
It can be seen that the combustion pressure is lower than in the case shown in (A).

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

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

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

The temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature, depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although the change can not be said that how many times since has generated amount closely related to the certain temperature is nO _X, so that this certain temperature is defined to a certain degree from the generation amount of the nO _X be able to. That is, the fuel and the gas temperature surrounding it at the time of combustion and the greater the EGR rate, decreases, the amount of the NO _X is reduced. At this time, when the amount of generated NO _X becomes about 10 p.pm or less, soot is hardly generated. Therefore, the above certain temperature is NO
The temperature almost coincides with the temperature when the amount of generated _X is about 10 p.pm or less.

Once soot is produced, it cannot be purified by post-treatment using an oxidation catalyst or the like. On the other hand, the soot precursor or the hydrocarbon in the state before the soot can be easily purified by post-treatment using an oxidation catalyst or the like. Considering the post-treatment using an oxidation catalyst or the like, there is an extremely large difference in whether hydrocarbons are discharged from the combustion chamber 5 in the state of the precursor of soot or before it, or discharged from the combustion chamber 5 in the form of soot. There is. The new combustion system used in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and oxidizes the hydrocarbons. 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 during combustion in the combustion chamber 5 and the surrounding gas temperature are made lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel burns has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel.

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

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

In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is formed, an amount of the inert gas that can absorb a sufficient amount of heat to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, the endothermic effect becomes stronger as the specific heat of the inert gas increases, and therefore, the inert gas preferably has a higher specific heat. In this regard, it can be said that it is preferable to use EGR gas as the inert gas since CO ₂ and EGR gas have relatively large specific heats.

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

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

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

FIG. 6 shows the mixing of EGR gas and air necessary to make the temperature of fuel during combustion and the surrounding gas lower than the temperature at which soot is generated when EGR gas is used as the inert gas. It shows the gas amount, the ratio of air in the mixed gas amount, and the ratio of EGR gas in the mixed gas. In FIG. 6, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load, and Z1 indicates the low load operation region.

Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is formed. The required minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate. In the embodiment shown in FIG.
0% or more. That is, the total intake gas amount sucked into the combustion chamber 5 is indicated by a solid line X in FIG. 6, and the ratio of the air amount to the EGR gas amount in the total intake gas amount X is shown in FIG.
When the ratio is as shown in the following, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is generated, and thus no soot is generated. In this case, the amount of generated NO _X is about 10 p.pm or less, and
Generation of O _X becomes extremely small.

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

On the other hand, in the load zone Z2 in FIG. 6, the total intake gas amount X necessary to prevent the generation of soot exceeds the total intake gas amount Y that can be sucked. 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
R gas needs to be supercharged or pressurized. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intake gas amount Y that can be sucked in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the amount of air is slightly reduced to increase the amount of EGR gas, and the fuel is burned under a rich air-fuel ratio.

As described above, FIG. 6 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. 6, the air amount is set to be smaller than the air amount shown in FIG. less well, i.e. the generation amount of the NO _X even if the air-fuel ratio to the rich while preventing generation of soot can be around or less 10 ppm, also the air in the low load region Z1 shown in FIG. 6 Even if the amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is lean from 17 to 18, the amount of generated NO _X is reduced by 10 while preventing the generation of soot.
It can be around ppm 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 excess fuel does not grow to soot, thus producing soot. There is no. Further, at this time NO _X even only an extremely small amount of generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Furthermore, NO _X
Only very small amounts are generated.

As described above, 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. However, the amount of generated NO _X 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 surrounding gas at the time of combustion in the combustion chamber can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, only when the heat generation amount by combustion is small and the engine load is relatively low. Therefore, in the first embodiment according to the present invention, when the engine load is relatively low, the temperature of the fuel during combustion and the gas around it are suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, and the first combustion, that is, the low temperature The combustion is performed, and when the engine load is relatively high, the second combustion, that is, the combustion that is conventionally performed conventionally, is performed. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been conventionally performed, is the 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 generation peaks. Say

The solid line in FIG. 7A 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 broken line in FIG. 2 shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when the combustion of No. 2 is performed. The solid line in FIG. 7 (B) represents the fuel and gas temperature Tf around the fuel when the first combustion is performed.
7B shows the relationship between the fuel and the surrounding gas temperature Tf and the crank angle when the second combustion is performed.

When the first combustion, that is, the low-temperature combustion is being performed, the amount of the EGR gas is larger than when the second combustion, that is, the conventional ordinary combustion is being performed.
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 shown by the solid line is better than the average gas temperature Tg during the second combustion shown by the broken line.
Is higher than. At this time, as shown in FIG. 7 (B), the temperature of the fuel and its surrounding gas Tf is substantially 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, as shown by the solid line in FIG. Not so high. The second
When the combustion is performed, the fuel and the surrounding gas temperature Tf become extremely high as shown by the broken line in FIG. 7B. When the second combustion is performed in this manner, the temperature Tf of the fuel and the surrounding gas becomes considerably higher than that in the case where the first combustion is performed, but the temperature of the other gas which occupies most of the temperature. Is lower in the case where the second combustion is performed than in the case where the first combustion is performed. Therefore, as shown in FIG. The average gas temperature Tg in the chamber 5 is higher when the first combustion is being performed than when the second combustion is being performed. As a result, as shown in FIG. 7A, 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 temperature of the burned gas in the combustion chamber 5 becomes the second temperature. The case where the first combustion is performed is higher than the case where the second combustion is performed.

As described above, when the first combustion, that is, the low-temperature combustion is performed, the temperature of the fuel and the surrounding gas Tf during the combustion is considerably lower than when the second combustion is performed. The burned gas in the chamber 5 is higher than that in the case where the second combustion is performed. Therefore, the temperature of the exhaust gas discharged from the combustion chamber 5 is also lower than that in the case where the second combustion is performed. Get higher.

FIG. 8 shows a first operation 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. I have. In FIG. 8, the vertical axis L indicates the amount of depression of the accelerator pedal 40, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 8, X (N) is the first
Shows the first boundary between the operating region I and the second operating region II, and Y (N) represents the first operating region I and the second operating region.
2 shows a second boundary with II. The determination of the change of the operation range from the first operation range I to the second operation range II is made based on the first boundary X (N), and the change from the second operation range II to the first operation range II is performed.
The determination of the change of the operation region to the operation region I of the second boundary Y
(N).

That is, when the operating state of the engine is in the first operating region I
When the required load L exceeds a first boundary X (N), which is a function of the engine speed N, during low-temperature combustion, it is determined that the operation region has shifted to the second operation region II, Combustion is performed by a conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again.

In the embodiment according to the present invention, the second boundary Y (N) is set to the lower load side by ΔL (N) with respect to the first boundary X (N). As shown in FIG. 8 and FIG.
L (N) is a function of the engine speed N, and ΔL (N) decreases as the engine speed N increases. FIG. 10 shows the output of the air-fuel ratio sensor 29. As shown in FIG. 10, the output current I of the air-fuel ratio sensor 29 changes according to the air-fuel ratio A / F. Accordingly, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 29.

Next, operation control in the first operation region I and the second operation region II in the first embodiment will be schematically described with reference to FIG. FIG. 11 shows the opening degree of the throttle valve 16, the opening degree 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. 11, in the first operating region I where the required load L is low, the opening of the throttle valve 16 is gradually increased from almost fully closed to about half-open as the required load L becomes higher. Is gradually increased from near full close to full open as the required load L increases. In the example shown in FIG. 11, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

In other words, in the first operating region I, the EGR
The opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled such that the rate 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 of the EGR control valve 23 based on the output signal of the air-fuel ratio sensor 29. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

During the idling operation, the throttle valve 16 is closed until the valve is almost fully closed. At this time, the EGR control valve 23 is also closed almost completely. Throttle valve 1
When the valve 6 is closed close to the fully closed state, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 16 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating range of the engine is the first operating range I.
From the second operating region II, the opening of the throttle valve 16 is increased stepwise from the half-open state to the fully open direction. At this time, in the example shown in FIG.
The air-fuel ratio is reduced in steps from 40 percent to less than 40 percent, and the air-fuel ratio is increased in steps. That is, since the EGR rate jumps over the EGR rate range (FIG. 5) 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 operation region II, the conventional combustion is performed. Thermal efficiency is high, therefore the engine the second operating region operating region from the first operating region I in comparison to but soot and NO _X occurs slightly low temperature combustion in the combustion process
When the state changes to II, the injection amount is reduced stepwise as shown in FIG. In the second operating region II, the throttle valve 16 is held in a fully open state except for a part, and the opening of the EGR control valve 23 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 12 shows the target air-fuel ratio when the first combustion, that is, the low-temperature combustion is performed. In FIG. 12, A / F = 15.5, A / F = 16, A / F = 17,
Each curve represented by A / F = 18 represents a target air-fuel ratio of 15.
5, 16, 17, and 18 are shown. The target opening degree S of the throttle valve 16 necessary for setting the air-fuel ratio to the target air-fuel ratio
T 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. 13 (A), and the EGR necessary for setting the air-fuel ratio to the target air-fuel ratio is obtained. The target opening SE of the control valve 23 is as shown in FIG.
As shown in (1), it 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.

On the other hand, FIG. 14 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 14, A / F = 24, A / F
Curves indicated by F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. The target opening degree ST of the throttle valve 16 required for setting the air-fuel ratio to the target air-fuel ratio is previously stored 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. The target opening SE of the EGR control valve 23 required to set the air-fuel ratio to the target air-fuel ratio is calculated as a function of the required load L and the engine speed N as shown in FIG. ROM3 in advance in the form of a map
2 is stored.

FIG. 16 is a sectional view of the catalytic converter 19. As shown in FIG. 16, the catalytic converter 19 includes a cylindrical outer casing 50 and a center electrode 51. Around the center electrode 51, a flat metal plate 52 and a corrugated metal plate 53 are alternately formed. It is wound so that it may overlap.
A catalyst having an oxidation function, for example, an oxidation catalyst or a three-way catalyst is carried on the flat thin plate 52 and the corrugated thin plate 53.

When the oxidation catalyst or the three-way catalyst is to be heated, a voltage is applied between the center electrode 51 and the outer casing 50. When a voltage is applied between the center electrode 51 and the outer casing 50, a current flows through a contact portion between the flat thin plate 52 and the corrugated thin plate 53, and at this time, each contact portion between the flat thin plate 52 and the corrugated thin plate 53 Fever. As a result, the temperature of the flat plate 52 and the corrugated plate 53 increases, and the oxidation catalyst or the three-way catalyst is heated. Therefore, it can be seen that the flat thin plate 52 and the corrugated thin plate 53 constitute an electric heater.

When the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, almost no soot is generated, and instead, the unburned hydrocarbon is a precursor of the soot or the state before the soot. It is discharged from the combustion chamber 5 in the form. At this time, if the oxidation catalyst or the three-way catalyst in the catalytic converter 19 is activated, the unburned hydrocarbon discharged from the combustion chamber 5 can be oxidized well by these catalysts. However, at this time, if the catalyst is not activated, the unburned hydrocarbon is not oxidized by the catalyst, and thus a large amount of unburned hydrocarbon is released to the atmosphere. Therefore, in the first embodiment according to the present invention, when the catalyst is not activated, such as when starting the engine, electric power is supplied to the electric heater to activate the catalyst early, and after the catalyst is activated, the catalyst is not activated. When the catalyst is about to be activated, electric power is supplied to the electric heater to maintain the catalyst in the activated state.

The catalyst is activated when the temperature of the catalyst exceeds a certain temperature. The temperature at which the catalyst is activated varies depending on the type of the catalyst. A typical oxidation catalyst has an activation temperature of 35.
It is about 0 ° C. The temperature of the exhaust gas passing through the catalyst is slightly lower than the temperature of the catalyst by a certain temperature, and thus the temperature of the exhaust gas passing through the catalyst is representative of the temperature of the catalyst.
Therefore, in the embodiment according to the present invention, it is determined whether or not the catalyst has been activated based on the temperature of the exhaust gas passing through the catalyst.

FIG. 17 schematically shows the relationship between various temperatures and the required load L when power is not supplied to the electric heater. In FIG. 17, To indicates the temperature at which the catalyst is activated. In FIG. 17, Ta indicates the temperature of the exhaust gas flowing into the catalyst when the first combustion, that is, low-temperature combustion is performed in the first operation region I, and Tb indicates the catalyst bed temperature of the catalyst at this time. ing. Further, Tc indicates the catalyst bed temperature of the catalyst when the second combustion is performed in the first operation region I and the second operation region II.

Even when low-temperature combustion is performed, the higher the required load L, the greater the amount of heat generated during combustion. Therefore, the higher the required load L, the higher the exhaust gas temperature T flowing into the catalyst.
a becomes higher. On the other hand, during low-temperature combustion, a large amount of unburned HC and CO is discharged from the engine. Therefore, the catalyst bed temperature Tb of the catalyst due to the heat of oxidation of the unburned HC and CO in the catalyst is lower than the exhaust gas temperature Ta flowing into the catalyst. Considerably higher.
As shown in FIG. 17, when the required load L is low, the inflowing exhaust gas temperature Ta to the catalyst becomes lower than the activation temperature To of the catalyst, but when the inflowing exhaust gas temperature Ta is not much lower than the activation temperature To. Unburned HC, CO in catalyst
Therefore, the catalyst bed temperature Tb becomes higher than the activation temperature To at this time. That is, when low-temperature combustion is being performed, the normal catalyst bed temperature Tb is equal to the activation temperature To.
And thus the unburned HC and CO are oxidized well in the catalyst.

On the other hand, even when the second combustion is being performed, the higher the required load L, the greater the amount of heat generated during combustion. Therefore, the higher the required load L, the higher the catalyst bed temperature Tc. In this case, when the required load L is high, the catalyst bed temperature Tc becomes higher than the activation temperature To, but the required load L
Becomes lower, the catalyst bed temperature Tc becomes lower than the activation temperature To. In the first embodiment, when the catalyst is about to be deactivated, that is, when the temperature of the exhaust gas passing through the catalyst is reduced to the lower limit M
When it becomes lower than IN (FIG. 17), the catalytic converter 19
The electric power is supplied to the electric heater inside. As can be seen from FIG. 17, the catalyst bed temperature decreases mainly when the second combustion is performed, and therefore, when the second combustion is mainly performed, the electric heater in the catalytic converter 19 is reduced. Is turned on.

[0061] On the other hand, NO _X absorbent 20 disposed downstream of the catalytic converter 19 is, for example, alumina as a carrier, an alkali metal, such as the carrier on, for example, potassium K, sodium Na, lithium Li, cesium Cs, barium Ba And at least one selected from alkaline earths such as calcium Ca, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. Engine intake passage and _the NO _X absorbent 20 upstream of the exhaust supplied air and fuel into the passage (hydrocarbon) ratio is referred to as the air-fuel ratio of the exhaust gas flowing into _the NO _X absorbent 20 Toko of the NO _X absorbent 20 air-fuel ratio of the inflowing exhaust gas is absorbed NO _X when the lean air-fuel ratio of the inflowing exhaust gas is performed to absorbing and releasing action of the NO _X that releases NO _X absorbed to become stoichiometric or rich. Incidentally, NO _X air-fuel ratio of the absorbent 20 upstream of the exhaust passage fuel (hydrocarbons) or the inflowing exhaust gas when the air is not supplied matches the air-fuel ratio in the combustion chamber 5, therefore in this case NO When the air-fuel ratio in the combustion chamber 5 is lean, the _X absorbent 20
Absorbs O _X, the air-fuel ratio in the combustion chamber 5 is capable of releasing NO _X absorbed and becomes the stoichiometric air-fuel ratio or rich.

[0062] _the NO _X absorbent 20 when placing the _the NO _X absorbent 20 in the engine exhaust passage is performing absorption and release action of actually NO _X is also not clear portion detailed mechanism of action out this absorbing . However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, 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.
Combustion is performed with the air-fuel ratio in the normal combustion chamber 5 being lean.
Will be In this way, combustion is performed with a lean air-fuel ratio.
The oxygen concentration in the exhaust gas is high,
At this time, as shown in FIG._TwoBut
O_Two ^-Or O^2-On the surface of platinum Pt. one
On the other hand, NO in the inflowing exhaust gas becomes O on the surface of platinum Pt._Two ^-
Or O^2-Reacts with NO _Two(2NO + O_Two→ 2N
O_Two). NO generated next_TwoPart of is on platinum Pt
Barium oxide BaO is absorbed in the absorbent while being oxidized
As shown in FIG.
NO_Three ^-Diffuses into the absorbent in the form of Like this
NO_XIs NO_XIt is absorbed in the absorbent 20. Inflow exhaust gas
NO on the surface of platinum Pt as long as the oxygen concentration in the_TwoIs raw
NO_XNO unless absorption capacity is saturated
_TwoIs absorbed in the absorbent and nitrate ion NO_Three ^-Is generated
It is.

On the other hand, the air-fuel ratio of the inflowing exhaust gas is made rich.
The concentration of oxygen in the incoming exhaust gas decreases,
NO on the surface of gold Pt_TwoIs reduced. NO_Twoof
When the amount of production decreases, the reaction reverses (NO_Three ^-→ NO_Two)
And thus nitrate ion NO in the absorbent_Three ^-Is NO
_TwoReleased from the absorbent in the form of NO at this time_XAbsorbent
NO released from 20_XIs shown in FIG. 18 (B).
A large amount of unburned HC and CO contained in the inflow exhaust gas
It is reduced by reaction. In this way, platinum Pt
NO on surface_TwoWhen no longer exists, the next
NO_TwoIs released. Therefore, the air-fuel ratio of the incoming exhaust gas
Is enriched in a short time, NO _X20 absorbents
NO_XIs released, and the released NO_XIs returned
NO in the atmosphere to be removed_XWill not be released
No.

In this case, the air-fuel ratio of the inflowing exhaust gas is
NO even at stoichiometric air-fuel ratio_XNO from absorbent 20_XIs released
Is done. However, the air-fuel ratio of the inflowing exhaust gas is
NO if ratio_XNO from absorbent 20_XGradually
NO because only _XAbsorbed by the absorbent 20
All NO_XIt takes a slightly longer time to release.

[0066] Incidentally, there is a limit to the NO _X absorbing capacity of the NO _X absorbent 20, it is necessary to release the NO _X from _the NO _X absorbent 20 before the NO _X absorbing capacity of the NO _X absorbent 20 is saturated . For this purpose it is necessary to estimate the amount of NO _X is absorbed in the NO _X absorbent 20. Therefore, in the present invention beforehand in the form of a map as shown in FIG. 19 (A) the NO _X absorption amount A per unit time as a function of the required load L and engine speed N when being performed first combustion calculated advance, advance per unit time of the NO _X absorption B the required load L and the engine rotational speed form of a map as shown in FIG. 19 (B) as a function of N when the second combustion is being performed calculated advance, so that to estimate the amount of NO _X ΣNOX being absorbed in the NO _X absorbent 20 by accumulating NO _X absorption amount a per these unit time, the B.

[0067] On the other hand, when in the embodiment according to the present invention should be released NO _X from _the NO _X absorbent 20 is the air-fuel ratio is made rich. In this case, if the air-fuel ratio is made rich while the second combustion is being performed, a large amount of soot is generated.
It is not possible to make the air-fuel ratio rich when the combustion is performed. On the other hand, when the first combustion, that is, the low-temperature combustion is being performed, soot is hardly generated even if the air-fuel ratio is made rich. Thus, in the embodiment according to the present invention the maximum value MAX is NO _X absorption ΣNOX when first combustion is being performed predetermined air-fuel ratio When for example more than 30% of the maximum absorption is rich, the maximum value MA is NO _X absorption ΣNOX when second combustion is being performed
When it exceeds X, wait for the first combustion to start,
The air-fuel ratio is made rich when the first combustion is being performed.

Next, the operation control in the first embodiment will be described with reference to FIG. In FIG. 20, L
Represents the required load, TE represents the temperature of the exhaust gas flowing out of the catalytic converter 19, and ΣNOX represents NO _X
A / F indicates an air-fuel ratio. As shown in FIG. 20, the required load L is equal to the first boundary X (N).
And the operating state of the engine shifts from the first operating region I to the second operating region II. As a result, when the first combustion is switched to the second combustion, the air-fuel ratio A / F is stepped. growing. Further, .SIGMA.NOX to become many generation amount of the NO _X than the second combustion is started during the first combustion
Increases rapidly.

Next, when the required load L decreases during the second combustion, the exhaust gas temperature TE decreases. At this time, if the exhaust gas temperature TE becomes lower than the lower limit value MIN, the electric heater in the catalytic converter 19 is turned on for a predetermined time, and as a result, the catalyst bed temperature in the catalytic converter 19 is raised. Thus, the catalyst bed temperature is maintained above the activation temperature.

Next, when the second combustion is being performed, N
O _X absorption ΣNOX is to exceed the maximum value MAX. However, at this time, the air-fuel ratio is not made rich. Next, the required load L becomes lower than the second boundary Y (N), and the operating state of the engine shifts from the second operating region II to the first operating region I. As a result, the second combustion is changed to the first combustion. , The air-fuel ratio A / F is made rich for a predetermined time. Whereby NO _X is released from _the NO _X absorbent 20.

If a large amount of oxygen not contributing to combustion remains in the combustion chamber 5 when the air-fuel ratio in the combustion chamber 5 is made rich, the average air-fuel ratio in the combustion chamber 5 becomes rich at this time. However, a large amount of oxygen is contained in the exhaust gas. However NO _X becomes pleasure not released from _the NO _X absorbent 20 when contains a large amount of oxygen in the exhaust gas in this way. However, in the embodiment according to the present invention, when the air-fuel ratio is made rich, the catalyst in the catalytic converter 19 is activated, so that oxygen contained in the exhaust gas oxidizes unburned HC and CO in this catalyst. Consumed. N As a result, the oxygen amount contained in the exhaust gas flowing into the NO _X absorbent 20 is reduced
NO _X is satisfactorily released from the O _X absorbent 20.

FIG. 21 shows a routine for processing a NO _X release flag which is set when NO _X is to be released from the NO _X absorbent 20, and this routine is executed by interruption every predetermined time. Referring to FIG. 21, first, at step 100, it is determined whether or not a flag I indicating that the operation region of the engine is the first operation region I is set. When the flag I is set, that the operating region of the engine NO _X absorption amount A per unit time from the map shown in FIG. 19 (A) is calculated proceeds to step 101 when a first operating region I You. Then A is added to the NO _X absorption amount ΣNOX step 102. Next, at step 103 NO _X absorption amount ΣNOX whether exceeds the maximum value MAX or not. ΣNOX>
NO _X releasing flag is set the routine proceeds to step 104 becomes the MAX.

On the other hand, when it is determined in step 100 that the flag I has been reset, that is, when the operation region of the engine is the second operation region II, step 105
NO _X absorption amount per unit from the map time shown in FIG. 19 (B) B is calculated willing to. Then B is added to the NO _X absorption amount ΣNOX step 106. Next, at step 107 NO _X absorption amount ΣNOX whether exceeds the maximum value MAX or not. .SIGMA.NOX> becomes MAX when NO _X release flag proceeds to step 108 is set.

FIG. 22 shows a control routine for the electric heater. This routine is executed by interruption every predetermined time. Referring to FIG. 22, first, at step 20
At 0, it is determined whether or not the exhaust gas temperature TE detected by the temperature sensor 21 is lower than the minimum value MIN. T
When E ≦ MIN, the routine proceeds to step 201, where an energization process for energizing the electric heater for a predetermined time longer than the interruption time interval is performed. Next, at step 202, a process for inhibiting the first combustion, that is, a process for performing the second combustion even in the first operation region I is performed.

Accordingly, it can be seen that power is continuously supplied to the electric heater while TE ≦ MIN, and then when TE> MIN, power is continuously supplied to the electric heater for a predetermined time thereafter. Further, it can be seen that electric power is supplied to the electric heater when the engine is started, and the second combustion is performed until TE> MIN. Next, the operation control will be described with reference to FIG.

Referring to FIG. 23, first, in step 300, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. If the flag I is set, that is, if the operating state of the engine is in the first operating region I, step 3
In step 01, 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 303, where low-temperature combustion is performed.

That is, in step 303, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 304, the target opening degree SE of the EGR control valve 23 is calculated from the map shown in FIG.
The opening of the EGR control valve 23 is set as the target opening SE.
Next, at step 305, it is determined whether or not the NO _X release flag is set. When the NO _X release flag is not set, fuel injection is performed so as to achieve the lean air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.

On the other hand, in step 301, L> X
When it is determined that (N) has been reached, the routine proceeds to step 302, where the flag I is reset. Then step 31
Proceeding to 3, the second combustion is performed. That is, step 31
In FIG. 3, the throttle valve 16 is obtained from the map shown in FIG.
Is calculated, and the opening of the throttle valve 16 is set as the target opening ST. Next, at step 314, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG. 15B, and the opening of the EGR control valve 23 is set to this target opening SE. Next, in step 315, FIG.
The fuel injection is performed so as to achieve the lean air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.

When the flag I is reset, in the next processing cycle, the process proceeds from step 300 to step 311 to determine whether or not the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 313
And the second combustion is performed under the lean air-fuel ratio.
On the other hand, when it is determined in step 311 that L <Y (N), the routine proceeds to step 312, where the flag I is set. Next, the routine proceeds to step 303, where low-temperature combustion is performed.

[0080] On the other hand, if NO _X release flag is determined to be set in step 305 proceeds to step 307, fuel injection is performed such that the rich air-fuel ratio.
At this time, low-temperature combustion is performed under a rich air-fuel ratio. Next, at step 308, it is determined whether a predetermined time has elapsed since the air-fuel ratio was made rich. NO _X emission flag air-fuel ratio goes to step 309 after a lapse of the predetermined time since the rich is reset, then ΣNOX is made zero at step 310. Thus it can be seen that the air-fuel ratio is a predetermined time rich when NO _X release flag when set low temperature combustion is performed.

FIG. 24 shows a second embodiment of the operation control. The exemplary normal second operating region II in the example are performed also second combustion in well the first operating region I, the operating state of the engine is in when releasing the NO _X from _the NO _X absorbent 20 is first When the operation range is the first operation range, the second combustion is switched to the first combustion, and the air-fuel ratio is made rich. However, this time without unburnt hydrocarbons in the exhaust gas catalytic bed temperature is low in the catalytic converter 19 is cleaned, also the NO _X absorbent 20 in the exhaust gas containing a large amount of oxygen is supplied Become. Therefore, at this time, the catalyst in the catalytic converter 19 is heated by the electric heater to activate the catalyst, and after the catalyst is activated, the second combustion is switched to the first combustion to enrich the air-fuel ratio. .

That is, as shown in FIG.
Is low, the exhaust gas temperature TE is the NO _X absorption amount ΣNOX when it becomes lower than the lower limit value MIN exceeds the maximum value MAX. In this case, NO _X absorption amount ΣNOX is power to the electric heater exceeds the maximum value MAX is supplied. Thereafter, when the exhaust gas temperature TE rises to the upper limit value (MIN + α), the supply of electric power to the electric heater is stopped. When the exhaust gas temperature TE becomes lower than the lower limit value MIN, the electric heater is again supplied with electric power. Therefore, the exhaust gas temperature TE is maintained between the lower limit value MIN and the upper limit value (MIN + α).

As shown in FIG. 24, when the exhaust gas temperature TE is lower limit value MIN <TE and the operating state of the engine is in the first operating region I, the second combustion is temporarily switched to the first combustion. During this time, the air-fuel ratio is made rich. FIG. 25 shows a processing routine of the NO _X release flag in the second embodiment.

Referring to FIG. 25, first, in step 4
NO _X absorption B per unit time from the map shown in FIG. 19 (B) is calculated in 00. Then step 40
B is added to 1 in NO _X absorption .SIGMA.NOX. Maximum value MA Next, at step 402 NO _X absorption amount ΣNOX is
It is determined whether or not X has been exceeded. .SIGMA.NOX> becomes MAX when NO _X release flag proceeds to step 403 is set.

Next, referring to FIG. 26 and FIG.
The operation control in the embodiment will be described. Referring to FIGS. 26 and 27, first, at step 500, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set.
When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 501, where it is determined whether the required load L has become larger than the first boundary X (N). Is done. If L ≦ X1 (N), the process jumps to step 505. On the other hand, step 501
When it is determined that L> X (N), the routine proceeds to step 502, where the flag I is reset, and then the routine proceeds to step 505.

On the other hand, if it is determined in step 500 that the flag I has been reset, step 50
Proceeding to 3, it is determined whether or not the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the process proceeds to step 505. On the other hand, when it is determined in step 503 that L <Y (N), the routine proceeds to step 504, where the flag I is set, and then the routine proceeds to step 505.

[0087] whether step 505 NO _X release flag is set or not. The second combustion is performed proceeds to step 518 when the NO _X release flag is not set. That is, FIG.
The target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 5A, and the opening of the throttle valve 16 is set as the target opening ST. Next, at step 519, FIG.
From the map shown in (B), the target opening S of the EGR control valve 23 is obtained.
E is calculated, and the opening of the EGR control valve 23 is set as the target opening SE. Next, at step 520, fuel injection is performed to achieve the lean air-fuel ratio shown in FIG. That is, when the NO _X release flag is not set, the second combustion is always performed regardless of the required load L.

[0088] On the other hand, it determines whether or not the exhaust gas temperature TE detected by the temperature sensor 21 is higher than the lower limit value MIN proceeds to step 506 when the NO _X release flag is judged as being set in step 505 Is done. When TE ≦ MIN, the routine proceeds to step 507, where the electric heater of the catalytic converter 19 is turned on. Next, the routine proceeds to step 518, where the second combustion is performed.

On the other hand, in step 506, TE> MI
If determined to be N, the routine proceeds to step 508, where it is determined whether or not the exhaust gas temperature TE has become higher than the upper limit value (MIN + α). When TE> MIN + α, the routine proceeds to step 509, where the electric heater in the catalytic converter 19 is turned off. That is, the exhaust gas temperature TE and the NO _X release flag is set is controlled to MIN <TE <MIN + α.

At step 510, it is determined whether the flag I is set. When the flag I is not set, that is, when the operating state of the engine is in the second operating region II shown in FIG. 8, the routine proceeds to step 518, where the second combustion is performed. On the other hand, when the flag I is set, that is, when the operating state of the engine is in the first operating region I shown in FIG. 8, the routine proceeds to step 511, where the first combustion is performed for a fixed time under the rich air-fuel ratio. Is performed.

That is, in step 511, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 512, the target opening degree SE of the EGR control valve 23 is calculated from the map shown in FIG.
The opening of the EGR control valve 23 is set as the target opening SE.
Next, at step 513, fuel injection is performed to achieve a rich air-fuel ratio. Next, at step 514, it is determined whether a predetermined time has elapsed since the air-fuel ratio was made rich. NO _X emission flag air-fuel ratio goes to step 515 after a lapse of the predetermined time since the rich is reset, then ΣNOX is made zero at step 516. Next, at step 517, the electric heater in the catalytic converter 19 is turned off. Therefore, at this time, low-temperature combustion is performed for a certain time under the rich air-fuel ratio.

[0092]

According to the present invention, unburned hydrocarbons generated during low-temperature combustion can be satisfactorily purified.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing amounts of smoke and NO _X generated, and the like.

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing fuel molecules.

FIG. 5 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.

FIG. 6 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 7 is a diagram showing changes in an average gas temperature Tg in a combustion chamber, and changes in fuel and a gas temperature Tf around the fuel.

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

FIG. 9 is a diagram showing a relationship between ΔL (N) and an engine speed N.

FIG. 10 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 11 is a diagram showing an opening degree of a throttle valve and the like.

FIG. 12 is a view showing a target air-fuel ratio in the first combustion.

FIG. 13 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 14 is a view showing a target air-fuel ratio in the second combustion.

FIG. 15 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 16 is a sectional view of a catalytic converter.

FIG. 17 is a diagram showing a temperature Ta of exhaust gas flowing into a catalyst and catalyst bed temperatures Tb and Tc.

FIG. 18 is a diagram for explaining the effect of absorbing and releasing NO _X.

FIG. 19 is a view showing a map of the NO _X absorption amount per unit time.

FIG. 20 is a time chart showing a first example of operation control.

FIG. 21 is a flowchart for processing a NO _X release flag.

FIG. 22 is a flowchart for controlling an electric heater.

FIG. 23 is a flowchart of operation control in the first embodiment.

FIG. 24 is a time chart showing a second embodiment of the operation control.

FIG. 25 is a flowchart for processing a NO _X release flag.

FIG. 26 is a flowchart of operation control in the second embodiment.

FIG. 27 is a flowchart of operation control in the first embodiment.

[Explanation of symbols]

6 ... fuel injection valves 16 ... throttle valve 19 ... catalytic converter 20 ... NO _X absorbent

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/10 ZAB F01N 3/20 ZABK 3/20 ZAB 3/28 ZAB 3/28 ZAB 301E 301 F02D 21/08 ZAB F02D 21 / 08 ZAB 301B 301 41/04 355 41/04 355 F02M 25/07 ZAB F02M 25/07 ZAB 570D 570 570J B01D 53/36 103B 104A (72) Inventor Nobumoto Ohashi No. 1 Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Automobile Inside (72) Inventor Kazuhiro Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yoshi ▲ Saki ▼ Koji 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (7)

[Claims] When the amount of inert gas in the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak. When the amount of inert gas in the combustion chamber further increases, the amount of soot generated during combustion in the combustion chamber increases. In a compression ignition type internal combustion engine in which the temperature of the fuel and its surrounding gas is lower than the soot generation temperature and soot is hardly generated, a catalyst having an oxidation function is arranged in the engine exhaust passage, and the amount of soot generation is reduced. First combustion in which the amount of inert gas in the combustion chamber is larger than the peak amount of inert gas and little soot is generated, and the amount of inert gas in the combustion chamber is smaller than the amount of inert gas where the amount of generated soot is peaked Switching means for selectively switching between the second combustion with a small amount of heat, heating means for heating the catalyst, and detection means for detecting a representative temperature representing the temperature of the catalyst, and 1 combustion is taking place A compression ignition type internal combustion engine in which the catalyst is heated by the heating means when the representative temperature becomes lower than a predetermined temperature when the first combustion is to be performed. 2. The compression ignition type internal combustion engine according to claim 1, wherein said heating means comprises an electric heater. 3. The compression ignition type internal combustion engine according to claim 1, wherein said catalyst comprises an oxidation catalyst or a three-way catalyst. Air-fuel ratio of 4. inflowing exhaust gas when the lean releasing NO _X when the air-fuel ratio of the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich to absorb and flowing the NO _X contained in the exhaust gas the _the NO _X absorbent disposed on the catalyst downstream of the engine exhaust passage, or the stoichiometric air-fuel ratio in the combustion chamber when the when releasing the NO _X from _the NO _X absorbent is performed first combustion 2. The compression ignition type internal combustion engine according to claim 1, wherein the engine is rich. 5. comprising a determining means for determining whether or not to release the NO _X from _the NO _X absorbent, N from _the NO _X absorbent
O _X the representative temperature when it is determined that it should be released is the catalyst is heated by the heating means if Kere lower than a predetermined temperature, higher than the temperature at which the representative temperature is predetermined The compression ignition type internal combustion engine according to claim 4, wherein the air-fuel ratio in the combustion chamber is set to a stoichiometric air-fuel ratio or a rich air-fuel ratio. 6. The compression ignition type internal combustion engine according to claim 1, further comprising a recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises recirculated exhaust gas. organ. 7. The compression ignition type internal combustion engine according to claim 6, wherein the exhaust gas recirculation rate in the first combustion state is approximately 55% or more.