JP2000130154A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exactly estimate NOx amount absorbed in NOx absorbent by determining subtraction amount of an NOx absorbed amount counter based on NOx discharge amount at the time of a prescribed operation of an internal combustion engine and making the NOx absorbed amount counter perform subtraction corresponding to NOx amount discharged from NOx absorbent actually. SOLUTION: At the time of an operation by a lean air fuel ratio at the time of operating an internal combustion engine 1, prescribed added amount is added to an NOx absorbed amount counter showing NOx absorbed amount of NOx absorbent 25 provided on an exhaust system every fixed time by an ECU 40. At the time of an operation by a rich air fuel ratio, prescribed subtraction amount is subtracted from the NOx absorbed amount counter every fixed time and NOx absorbed amount of an NOx absorbent 25 is estimated. When the internal combustion engine 1 is operated by the rich air fuel ratio, NOx amount discharged from the NOx absorbent 25 is estimated. At the time of the operation by the rich air fuel ratio, subtraction amount of the NOx absorbed amount counter is determined based on the estimated NOx discharge amount and NOx amount absorbed by the NOx absorbent 25 is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an 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 generated 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 conventionally increasing the EGR rate. 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 is set within a range not exceeding the maximum allowable limit. 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 at most 3
It is reduced from 0% to about 50%.

As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate.
If the R rate is within the range not exceeding this maximum allowable limit, NO
_It was set so that the amount of _x and smoke generated was as small as possible. However, in this way EGR
Rate that there is a limit to the reduction of the NO _x and the amount of generated NO _x and the amount of smoke produced also defined to be as small as possible of smoke, in fact still a significant amount of N
At present, O _x and smoke are 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 becomes almost zero. That is, it was found that soot was hardly generated. In this case, N
Generation amount of O _x is also found that a very small amount.
After that, the reason why no soot was generated was examined based on this finding, and as a result, unprecedented soot and NO
_This has led to the construction of a new combustion system capable of simultaneously reducing _x . 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 temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature 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. An internal combustion engine employing this new combustion system has already been filed by the present applicant (Japanese Patent Application No. 9-305850).

[0009]

However, this new combustion system requires that the EGR rate be approximately 55% or more. However, it is possible to make the EGR rate approximately 55% or more when the intake air amount is relatively small, that is, when the engine load is relatively low. If the intake air amount exceeds a certain limit, the intake air will be reduced unless the EGR rate is reduced. The amount of air cannot be increased. Therefore, when the intake air amount exceeds a certain limit, it is necessary to switch to the conventional combustion.

[0010] When switched to the combustion being done conventionally, NO _x it is not a little discharged from the engine. Further, under the conventional combustion, combustion is performed under excess air. Thus the air-fuel ratio of the exhaust gas flowing in the internal combustion engine at the time of 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 arranged in an engine exhaust passage, NO _x is prevented from being released into the atmosphere.

In the above internal combustion engine, when NO _x is to be released and reduced, the air-fuel ratio is made rich under fresh combustion,
The air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is made rich, and reduced to release NO _x. Since the new combustion is performed at the stoichiometric air-fuel ratio or slightly lean, the amount of fuel to be increased in order to make the air-fuel ratio rich is very small.

By the way provided absorption of NO _x amount counter which represents the absorption of NO _x of _the NO _x absorbent for _the NO _x absorbent is to estimate the absorption of NO _x amount absorbed, when the engine is operated at a lean air-fuel ratio adds a predetermined addition amount determined in accordance with the engine operating state to the absorption of NO _x amount counter at predetermined time intervals, when the engine is operated in a rich or stoichiometric air-fuel ratio, the NO in accordance with the operating time There is known an internal combustion engine configured to decrease the value of an _x absorption counter.

[0013] That is, the load from the engine during engine operation, the amount of the NO _x in accordance with the engine operating conditions such as rotational speed is generated,
When the engine is operating at a lean air-fuel ratio (that is, NO
In the case the air-fuel ratio of the exhaust gas flowing into the _x absorbent is lean), the percentage of certain of the generated amount of NO _x is NO _x
Is absorbed in the absorbent, the amount of the NO _x absorbed in _the NO _x absorbent increases in accordance with the NO _x generation amount of the engine. Further, when the engine is operated at a rich or stoichiometric air-fuel ratio, since the NO _x is released from the NO _x absorbent, NO
The amount of NO _x absorbed in the _x absorbent decreases with the time the engine is operating at rich or stoichiometric. In this internal combustion engine, when the operating air-fuel ratio is a lean air-fuel ratio, a predetermined amount is added at regular intervals, and when the engine operating air-fuel ratio is a rich or stoichiometric air-fuel ratio, the predetermined amount is subtracted according to the operating time. estimates the absorption of NO _x of _the NO _x absorbent by providing the absorption of NO _x amount counter.

[0014]

However, when the engine is operated at a rich or stoichiometric air-fuel ratio as in the above-described apparatus, the value of the NO _x absorbent absorption counter is decreased based only on the operation time. If it has, there is a problem of causing an error between the actual value of the NO _x amount and the absorption of NO _x amount counter which is absorbed in _the NO _x absorbent.

[0015] That amount of NO _x released from _the NO _x absorbent per unit time (NO _x release rate) is not always constant, non-contained in temperature or the exhaust gas of the NO _x absorbent as described below It changes according to the amount of components such as HC and CO. Therefore, reducing the value of the NO _x absorption amount counter based on only the operation time of the rich or stoichiometric air-fuel ratio (NO _x release speed assuming constant from Namely, absorption of NO _x agents) as in the above device If that is, in some cases, depending on the engine operating condition and _the NO _x absorbent temperature a large error is produced between the amount of released true NO _x from _the NO _x absorbent and the amount of decrease in the counter.

[0016] In the internal combustion engine, to determine the amount of the NO _x with the value of the absorption amount counter _the NO _x absorbent in the absorbed NO _x, the predetermined value of absorption of NO _x amount is increased during the lean air-fuel ratio operation NO _x fuel ratio of the forced engine if exceeded by switching to a rich air-fuel ratio from _the NO _x absorbent
Has been released. Therefore, when the error between the value of the NO _x amount and the absorption of NO _x amount counter which is absorbed in the reality in _the NO _x absorbent is caused actually less absorption of NO _x of _the NO _x absorbent is, NO _x deteriorates the fuel efficiency is performed switched to the rich air-fuel ratio operation to a value despite absorption of nO _x amount counter need not be released exceeds a predetermined value, actually _the nO _x absorbent in the opposite Despite the fact that the NO _x absorption amount of NOx needs to be increased to release NO _x ,
_Since the value of the _x absorption counter does not exceed the predetermined value, NO _x
May not be released, and there may be a problem that the absorption capacity of the NO _x absorbent is reduced and the NO _x in the exhaust gas cannot be absorbed.

An object of the present invention is to accurately estimate the amount of NO _x absorbed in _the NO _x absorbent.

[0018]

In order to achieve the above object, according to the first invention, as the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and peaks. And when the amount of inert gas supplied into the combustion chamber is further increased, the temperature of the fuel during combustion in the combustion chamber and the temperature of the surrounding gas become lower than the temperature at which soot is generated, so that the internal combustion engine hardly generates soot. When the air-fuel ratio of the inflowing exhaust gas is lean, N contained in the exhaust gas
NO _x to absorb O _x and the air-fuel ratio of the inflowing exhaust gas to release NO _x absorbed and becomes the stoichiometric air-fuel ratio or rich
The first combustion in which the absorbent is disposed in the engine exhaust passage, the amount of inert gas supplied into the combustion chamber is larger than the amount of inert gas at which the amount of generated soot reaches a peak, and soot is hardly generated; Switching means for selectively switching between the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas having a peak generation amount, and the internal combustion engine being operated at a lean air-fuel ratio. NO time to, said predetermined addition amount determined in accordance with the engine operating state at predetermined time intervals _the NO _x absorbent
_x is added to a NO _x absorption amount counter representing the amount of absorption, and when the internal combustion engine is operated at a rich or stoichiometric air-fuel ratio, a predetermined subtraction amount is subtracted from the NO _x absorption amount counter at regular intervals. by, NO of the _the NO _x absorbent
_x absorption amount estimating means for estimating the absorption amount; and NO _x when the internal combustion engine is operated at a rich or stoichiometric air-fuel ratio.
And _the NO _x releasing amount estimating means for estimating the amount of NO _x released from the absorbent, the internal combustion engine based on the _the NO _x releasing amount when it is operated at a rich or stoichiometric air-fuel ratio N
A subtraction amount determining means for determining the subtraction amount of the O _x absorption amount counter. That actually corresponds to the amount of released NO _x from the NO _x absorbent absorption of NO _x amount counter is caused to subtract.

According to the second invention, the first invention
NO_xThe emission amount estimating means is such that the engine is rich or
NO when operating at stoichiometric air-fuel ratio_xSupply to absorbent
NO based on the amount of fuel_xEstimate the release. 3
According to the first aspect, in the first aspect, the NO_xRelease
No output estimation means _xNO based on the temperature of the absorbent_xRelease
Estimate output.

According to a fourth aspect, there is provided the first aspect.
NO_xNO _xDeterioration of absorbent
NO based on_xEstimate the release. In the fifth invention
According to the first invention, the NO_xEmission estimation means
Is NO _xNO based on the amount of exhaust gas flowing into the absorbent
_xEstimate the release. According to the sixth invention, the first source
Exhaust gas from the combustion chamber
A recirculation device for recirculating in the passage;
The gas comprises recirculated exhaust gas.

According to a seventh aspect, in the sixth aspect, the exhaust gas recirculation rate is approximately 55% or more. According to an eighth aspect, in the first aspect, the operating region of the engine is divided into a first operating region on a low load side and a second operating region on a high load side. The combustion is performed, and the second combustion is performed in the second operation region.

[0022]

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 a supercharger, for example, an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Be linked. An inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17, and a throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17. The air suction pipe 17 upstream of the throttle valve 20
A mass flow detector 21 for detecting a mass flow rate of the intake air is disposed therein.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
The exhaust turbine 2 of the exhaust turbocharger 15 via the
3 and an outlet of the exhaust turbine 23 is connected via an exhaust pipe 24 to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function. Exhaust manifold 22
Inside, an air-fuel ratio sensor 27 is arranged. Exhaust pipe 28 connected to the outlet of catalytic converter 26 and throttle valve 2
The exhaust gas recirculation (hereinafter referred to as E)
(Referred to as GR) through a passage 29, and
E driven by a step motor 30 is provided in the passage 29.
A GR control valve 31 is provided. In the EGR passage 29, an intercooler 32 for cooling the EGR gas flowing in the EGR passage 29 is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.

On the other hand, the fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 34, via a fuel supply pipe 33. Fuel is supplied into the common rail 34 from an electric control type variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34, and the fuel pump 35 is controlled so that the fuel pressure in the common rail 34 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 36. Is controlled.

The electronic control unit 40 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the output signals of the air-fuel ratio sensor 27 and the fuel pressure sensor 36 are also input to the input port via the corresponding AD converter 47, respectively. 45 is input. A load sensor 51 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . Also,
The input port 45 has a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °.
Is connected. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 3 via the corresponding drive circuit 48.
0 and the fuel pump 35.

FIG. 2 shows the throttle valve 2 when the engine is under low load operation.
Change in the output torque when changing the air-fuel ratio A / F (abscissa in FIG. 2) by changing the opening and the EGR rate of 0, and smoke, HC, CO, a change in emission of the NO _x It shows the experimental example shown. As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the higher the EGR rate. When the air-fuel ratio A / F is smaller than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is 65% or more.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the smoke is reduced when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30. 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
The generation amount of O _x is considerably reduced. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3 (A) shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest. FIG. 3 (B) shows the air-fuel ratio A / F. The graph shows the change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. 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.
As shown in ₍₁₎ , the generation amount of NOx is considerably reduced. 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 becomes low when the soot is hardly generated 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. .

When these considerations based on the experimental results shown in FIGS. 2 and 3 are summarized, 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 and the compression ratio of the air-fuel ratio. Although the change can not be said that how many times since this certain temperature has a generation amount and the closely related of the nO _x, therefore 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. Generation amount at this time NO _x is soot is hardly generated when it is around or less 10 ppm. Therefore, the above certain temperature is NO
It almost coincides with the temperature when the amount of generated _x is about 10 p.pm or less.

Once soot has been produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed 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 removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 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 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 generated, 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, as the specific heat of the inert gas increases, the endothermic effect becomes stronger. 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 amount of 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 a mixture of EGR gas and air necessary to make the temperature of the fuel and the surrounding gas during combustion lower than the temperature at which soot is generated when EGR gas is used as the inert gas. A gas amount, a ratio of air in the mixed gas, and a ratio of EGR gas in the mixed gas are shown. The vertical axis in FIG.
The dashed line Y indicates the total amount of intake gas that can be drawn into the combustion chamber 5 when supercharging is not performed. The horizontal axis indicates the required load.

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. Further, the NO _x generation amount at this time is around 10 p.pm or less.
The amount of O _x generated is 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.

When the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. Therefore, in FIG. 6, the required load is larger in the region where the required load is larger than Lo. As the ratio increases, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced. In other words, when the supercharging is not performed and the required air-fuel ratio is maintained at the stoichiometric air-fuel ratio in an area where the required load is larger than Lo, the EGR rate decreases as the required load increases, and In the region where the required load is larger than Lo, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.

However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 to the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15, the required load is larger than Lo. In EGR rate 5
It can be maintained at 5% or more, for example 70%, so that the temperature of the fuel and its surrounding gas can be kept below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which soot is generated, to the extent that the pressure can be increased by the compressor 16. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, E
The GR control valve 31 is fully opened, and the throttle valve 20 is slightly closed.

As described above, FIG. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. 6, that is, the air-fuel ratio is made rich. Even so, while suppressing the generation of soot, the amount of generated NOx was reduced to 10 _p .
pm or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. while the generation amount of the NO _x can be around or less 10 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 excess fuel does not grow into 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, when low-temperature combustion is performed, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. Sarezu, the amount of the NO _x becomes 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 during combustion in the combustion chamber and the gas around it can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, only when the engine is operating at a low load and the calorific value due to combustion is relatively small. Can be Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In addition, the second combustion, that is, the combustion that is usually performed conventionally, is performed during the high load operation of the engine. 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 FIG. 7 shows a first operation region I in which the first combustion, that is, low-temperature combustion, is performed, and a second operation region, in which the second combustion, that is, combustion by the conventional combustion method, is performed.
II. In FIG. 7, the vertical axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load.
The horizontal axis N indicates the engine speed. In FIG. 7, X (N) indicates the first boundary between the first operating region I and the second operating region II, and Y (N) indicates the first operating region I and the second operating region. The second boundary with the area 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 determination from the second operating region II to the first operating region I is performed. The determination of the change in the operating region is performed based on 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.

The two boundaries of the first boundary X (N) and the second boundary Y (N) on the lower load side than the first boundary X (N) are provided as follows. For three reasons. The first reason is that the combustion temperature is relatively high on the high load side of the second operation region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not immediately start unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for a change in the operation range between the first operation range I and the second operation range II.

By the way, when the operating region of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and instead, the unburned hydrocarbon is converted into the precursor of soot or the state before it. It is discharged from the combustion chamber 5 in the form. At this time unburnt hydrocarbons exhausted from the combustion chamber 5 is caused to favorably oxidized by _the NO _x absorbent 25 to be described later. FIG. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 is
It changes according to F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.

Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. FIG. 9 shows the throttle valve 2 with respect to the required load L.
0 indicates the opening degree, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount. As shown in FIG. 9, in the first operating region I where the required load L is low, the opening of the throttle valve 20 is gradually increased from almost fully closed to about 2/3 opening as the required load L increases. E
The degree of opening of the GR control valve 31 is gradually increased from almost fully closed to fully open as the required load L increases. Also,
In the example shown in FIG. 9, in the first operation region I, the EGR rate is set to approximately 70%, and the air-fuel ratio is set to a slightly lean air-fuel ratio.

In other words, in the first operating region I, the EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is 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 20 is closed until the valve is almost fully closed. At this time, the EGR control valve 31 is also closed almost completely. Throttle valve 2
If the valve is closed close to 0, 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 20 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 to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, the EGR rate at which the EGR rate generates a large amount of smoke
The engine operating range is the first because it jumps over the rate range (Fig. 5).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operation area II, the conventional combustion is performed. In the second operating region II, the throttle valve 20 is held in a fully open state except for a part, and the opening of the EGR control valve 31 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. 10A shows the target air-fuel ratio A / F in the first operation region I. In FIG. 10A, A / F = 15.5, A / F = 16, A / F = 17,
Each curve represented by A / F = 18 has a target air-fuel ratio of 1
5.5, 16, 17, and 18, and the air-fuel ratio between the curves is determined by proportional distribution. FIG.
As shown in (A), the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the target air-fuel ratio A / F becomes leaner as the required load L decreases.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low-temperature combustion can be performed even if the EGR rate is reduced as the required load L decreases. When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 10A, as the required load L decreases, the target air-fuel ratio A / F increases. As the target air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, as the required load L decreases, the target air-fuel ratio A / F increases.
Is increased.

The target air-fuel ratio A / F shown in FIG. 10A is previously stored in a ROM 4 as a function of the required load L and the engine speed N as shown in FIG.
2 is stored. Also, the throttle valve 2 required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
The target opening ST of 0 is stored in the ROM 42 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.
EGR required to achieve target air-fuel ratio A / F shown in (A)
As shown in FIG. 11B, the target opening SE of the control valve 31 is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.

When the first combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 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. FIG.
(A) shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion by the conventional combustion method is performed.
In FIG. 13A, A / F = 24 and A / F = 3.
Curves indicated by 5, A / F = 45 and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. The target air-fuel ratio A / F shown in FIG.
As shown in (1), a map is previously stored in the ROM 42 as a function of the required load L and the engine speed N. In addition, the air-fuel ratio is set to a target air-fuel ratio A / A shown in FIG.
The target opening ST of the throttle valve 20 required to obtain F is stored in the ROM 42 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. The target opening degree S of the EGR control valve 31 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
E is stored in the ROM 42 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.

When the second combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 in advance as a function of the required load L and the engine speed N as shown in FIG. On the other hand, FIG.
In the above, the NO _x absorbent 25 is disposed in the casing 26. The NO _x absorbent 25 uses, for example, alumina as a carrier, and, for example, potassium K, sodium N
a, at least one selected from alkali metals such as lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. It is carried. Engine intake passage, combustion chamber 5 and NO
_x absorbent 25 upstream of the exhaust passage supplying air and fuel into _the NO _x absorbent 25 the ratio of Toko called air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 25 (hydrocarbon) is in the inflowing exhaust gas air absorbs 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 and becomes the stoichiometric air-fuel ratio or rich.

[0063] _the NO _x absorbent 25 be disposed the _the NO _x absorbent 25 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. 1, combustion is performed with the air-fuel ratio in the normal combustion chamber 5 being lean. Thus the oxygen concentration in the exhaust gas when the air-fuel ratio is performed is combusted in a lean state is high, these oxygen O ₂ as is shown in FIG. 16 (A) at this time O
₂ ^- or O ^2- shape is deposited on the surface of the platinum Pt. on the other hand,
NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2N).
O ₂ ). Then part of the generated NO ₂ while bonding with the barium oxide BaO is absorbed in the NO _x absorbent 25 while being oxidized on the platinum Pt 16 nitrate ions NO as shown in (A) ₃ ^- of It diffuses into the NO _x absorbent 25 in the form. In this way, NO _x is absorbed in the NO _x absorbent 25. As long as the oxygen concentration in the incoming exhaust gas is high, platinum P
At the surface of t, NO ₂ is generated, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- are generated.

On the other hand, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas decreases, and as a result, the amount of NO ₂ generated on the surface of the platinum Pt decreases. The amount of NO ₂ is lowered and the reaction is reverse (NO ₃ ^- → NO ₂₎
The process proceeds, thus to NO _x nitrate ions NO absorbent 25
₃ ^- is released from the NO _x absorbent 25 in the form of NO _2.
In this case NO _x released from _the NO _x absorbent 25 1
As shown in FIG. 6 (B), it is reduced by reacting with a large amount of unburned HC and CO contained in the inflowing exhaust gas. In this way, when NO ₂ no longer exists on the surface of the platinum Pt, NO ₂ is released from the NO _x absorbent 25 one after another. Therefore NO _x from the NO _x absorbent 25 in a short time when the air-fuel ratio of the inflowing exhaust gas is made rich is released,
Moreover, since the released NO _x is reduced, NO _x is not discharged into the atmosphere.

In this case, the air-fuel ratio of the inflowing exhaust gas is
NO even at stoichiometric air-fuel ratio_xNO from absorbent 25_xIs released
Is done. However, the air-fuel ratio of the inflowing exhaust gas is
NO if ratio_xNO from absorbent 25_xGradually
NO because only _xAbsorbed by the absorbent 25
All NO_xIt takes a slightly longer time to release.

As described above, the NO _x absorbent 25 is made of platinum P
includes a noble metal such as t, therefore _the NO _x absorbent 2
5 has an oxidation function. On the other hand, as described above, when the operation state of the engine is in the first operation region I and low-temperature combustion is being performed, soot is hardly generated, and instead, the unburned hydrocarbon is a precursor of soot or a soot. It is discharged from the combustion chamber 5 in the form of a state. However, as described above, the NO _x absorbent 25 has an oxidizing function, and therefore, the unburned hydrocarbons discharged from the combustion chamber 5 at this time are oxidized well by the NO _x absorbent 25.

[0068] Incidentally the absorption of NO _x capacity of the NO _x absorbent 25 is limited, absorption of NO _x capacity of the NO _x absorbent 25 needs to release the NO _x from the NO _x absorbent 25 before saturation. For this purpose it is necessary to estimate the amount of NO _x is absorbed in the NO _x absorbent 25. Therefore, in this embodiment of the present invention of a map as shown in FIG. 17 (A) as a function of the NO _x absorption amount A of the required load L and engine speed N per unit time when it is performed first combustion is previously obtained in the form of a map as shown in FIG. 17 (B) the absorption of NO _x amount B per unit time as a function of the required load L and engine speed N when the second combustion is being performed is previously obtained in the form, per these unit time of absorption of NO _x amount a, so that to estimate the absorption of NO _x amount ΣNOX being absorbed in the NO _x absorbent 25 by integrating the B.

[0069] In the embodiment according to the present invention N when exceeding the allowable maximum value that this absorption of NO _x amount ΣNOX reaches a predetermined
NO _x is released from the O _x absorbent 25. Next, this will be described with reference to FIG. Referring to FIG. 18, in the embodiment according to the present invention, two allowable maximum values, that is, an allowable maximum value MAX1 and an allowable maximum value MA,
X2 is set. The maximum allowable value MAX1 is NO _x
The maximum absorption amount MAX2 is about 30% of the maximum NO _x absorption amount that the absorbent 25 can absorb, and the allowable maximum value MAX2 is about 80% of the maximum absorption amount that the NO _x absorbent 25 can absorb. NO _x during the first combustion
NO fuel ratio in order to release the NO _x from _x absorbent 25 is made rich, NO _x absorption amount ΣNOX permissible maximum when the second combustion is being performed when the absorption amount ΣNOX has exceeded the allowable maximum value MAX1 When the value exceeds MAX1, the second
Air-fuel ratio in order to release the NO _x from the NO _x absorbent 25 when it is switched from the combustion to the first combustion is made rich,
Absorption of NO _x amount when the second combustion is being performed ΣNOX
_The NO _x absorbent 2 when but exceeding the maximum allowable value MAX2
5 in order to release the NO _x additional fuel late or during the exhaust stroke of the expansion stroke is injected.

That is, in FIG. 18, the period X is the required load L
Is lower than the first boundary X (N), indicating that the first combustion is being performed. At this time, the air-fuel ratio is a lean air-fuel ratio slightly leaner than the stoichiometric air-fuel ratio. Very little occurrence amount of the NO _x when the first combustion is being performed, thus absorption of NO _x amount ΣNOX as is shown in Figure 18 at this time rises very slowly. Absorption of NO _x amount ΣN when first combustion is being performed
OX is an air-fuel ratio A / F exceeds the allowable maximum value MAX1 is temporarily rich, whereby NO _x from the NO _x absorbent 25 is released. At this time, NO _x absorption amount ΣNOX
Is gradually reduced as described in detail below.

As described above, when the first combustion is being performed, no soot is generated regardless of whether the air-fuel ratio is lean, the stoichiometric air-fuel ratio, or rich, so that the first combustion is performed. and does not soot generated at this time is also the air-fuel ratio a / F in order to release the nO _x from the nO _x absorbent 25 is made rich when being. Then the required load L at time t ₁ is switched from the first combustion exceeds the first boundary X (N) to the second combustion. As shown in FIG.
When the combustion is performed, the air-fuel ratio A / F becomes considerably lean. When the second combustion is being performed _the amount of NO _x ΣNOX when the generation amount of the NO _x as compared with the case where the first combustion is being performed is large and therefore the second combustion is being performed relatively quickly To rise.

When the second combustion is being performed, the air-fuel ratio A
When / F is made rich, a large amount of soot is generated, and therefore, the air-fuel ratio A / F cannot be made rich during the second combustion. Thus the air-fuel ratio in order to release the NO _x from _the NO _x absorbent 25 as the second of the NO _x absorption amount ΣNOX when combustion is being performed has exceeded the allowable maximum value MAX1, as shown in FIG. 18 A / F is not made rich.
The required load L as at time t ₂ in FIG. 18 when the _the NO _x absorbent when is switched from the second combustion is lower in the first combustion than the second boundary Y (N) 25 air-fuel ratio a / F in order to release the NO _x is temporarily rich, whereby _the NO _x absorbent 25 from the NO _x is released from the. The time of absorption of NO _x amount ΣNOX is caused to gradually decrease as described in detail below.

[0073] Then the first combustion is switched to the second combustion at the time t ₃ in FIG. 18, the second combustion during interim pleasure continues. The time of absorption of NO _x amount ΣNOX exceeds the allowable maximum value MAX1. Next, as the required load L increases, the air-fuel ratio A / F decreases, and the time t in FIG.
_{At 4} , the air-fuel ratio A / F becomes rich. NO at this time
NO _x is released from the _x absorbent 25 and the NO _x absorption amount ΣN
OX is gradually reduced as will be described in detail later.

[0074] then the air-fuel ratio A at time t ₅ of FIG. 18
/ F becomes lean, and the second combustion continues for a while,
Then assuming that exceeds the allowable maximum value MAX2 at time t ₆ this time additional fuel late or during the exhaust stroke of the expansion stroke so as to release the NO _x from the NO _x absorbent 25 is injected in, flows into _the NO _x absorbent 25 The air-fuel ratio of the exhaust gas is rich. At this time, the NO _x absorbent 25
_x is released gradually caused to decrease as detailed later absorption of NO _x amount .SIGMA.NOX.

The additional fuel injected during the second half of the expansion stroke or during the exhaust stroke does not contribute to the generation of engine power, and therefore it is preferable to inject the additional fuel as little as possible. Thus when the absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1 when the second combustion is performed second
When the air-fuel ratio A /
Temporarily rich, F, and so as to inject additional fuel only if special where absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX2.

[0076] Incidentally HC of the air-fuel ratio A / F flowing into _the NO _x absorbent 25 along with the exhaust gas when the and the rich time becomes rich, the amount of CO component, from the amount of fuel supplied to the engine The amount of fuel required to operate the engine at the stoichiometric air-fuel ratio is reduced by the amount of fuel, that is, the amount of excess fuel is increased in proportion to the amount of excess fuel. Therefore, NO _x amount released from _the NO _x absorbent 25 per unit time (NO _x release speed),
It increases according to the amount of excess fuel supplied to the engine in this unit time.

When the additional fuel is injected in the latter half of the expansion stroke or during the exhaust stroke, the amount of the HC component flowing into the NO _x absorbent 25 together with the exhaust gas depends on the amount of the supplied fuel, that is, the amount of excess fuel. Increase in proportion to Therefore NO
_{The x} release rate increases with this excess fuel amount. Also _the NO _x absorbent 25 by the sulfur component contained in the exhaust gas in _the NO _x absorbent 25 is attached is deteriorated. Therefore, the amount of NO _{x that} the NO _x absorbent 25 can release per unit time is reduced. That is, the NO _x release speed decreases in accordance with the degree of deterioration of the NO _x absorbent 25.

[0078] Further _the NO _x releasing rate from _the NO _x absorbent is influenced by the temperature of the NO _x absorbent, the maximum value of the NO _x release rate by _the NO _x absorbent temperature substantially determined. That _the NO _x releasing rate in the presence of a sufficient excess fuel tends to increase as the temperature of the NO _x absorbent becomes high. The reason why the _the NO _x releasing rate as the temperature rises is increased,
It is considered that when the temperature of the NO _x absorbent is increased, nitrate ions bonded to BaO in the absorbent are easily separated.
Thus _the NO _x releasing rate A low temperature is excessive fuel amount is large even _the NO _x absorbent is reduced.

Further, the NO _x release rate is set to NO _x per unit time.
It is affected by the amount of exhaust gas flowing into the absorbent (hereinafter referred to as the amount of exhaust gas flowing in). That _the NO _x releasing rate decreases the more the amount of exhaust gas flowing. This early rate of the exhaust gas passing through the _the NO _x absorbent the more the inflow exhaust gas,
Sufficient time for the fuel in the exhaust gas to contribute to _the NO _x releasing action is can not be ensured.

[0080] Next, estimate of the NO _x release rate from _the NO _x absorbent in this embodiment will be described in detail. Is necessary to know the temperature and the inflowing exhaust gas amount of excess fuel amount and _the NO _x absorbent in the deterioration degree and _the NO _x absorbent in order to accurately determine the _the NO _x releasing rate from _the NO _x absorbent as described above is there.

FIG. 19 shows the excess fuel amount EF and NO_xRelease speed
V shows an example of the relationship with V_xRelease speed V is too high
It increases substantially in proportion to the increase in the surplus fuel amount EF. Also
FIG. 20 shows NO_xAbsorbent temperature T and NO_xRelation to release rate V
Shows an example of the person in charge, NO _xRelease speed V is NO_xabsorption
It increases as the agent temperature T increases. In this embodiment, the excess fuel
Quantity EF and NO_xBasic NO corresponding to absorbent temperature T_xRelease
As shown in FIG. 21, when the delivery speed VB is equal to the excess fuel amount EF and NO
_xROM in advance in the form of a map as a function of the absorbent temperature T
42.

[0082] A further 22 shows an example of the relationship between NO deterioration degree of _x absorbent D and NO _x release rate V, N
The _Ox release speed V decreases as the degree of deterioration D increases.
The 23 decreases the NO _x shows an example of the relationship between the amount AE and _the NO _x releasing velocity V of the exhaust gas flowing into the absorbent, _the NO _x releasing speed V inflow exhaust gas amount AE increases per unit time I do. Advance in the form of a map as a function of the deterioration degree D and the inflow exhaust gas amount AE corresponding _the NO _x releasing speed correction coefficient K1 is a degree of degradation D as shown in FIG. 24 in the inflow exhaust gas amount AE in this embodiment ROM42 Is stored within.

[0083] The amount C should reduce the absorption of NO _x amount ΣNOX when NO _x is released from _the NO _x absorbent in this embodiment
Basic _the NO _x releasing speed VB, which is calculated as described above
Formula C = CB × using the _the NO _x releasing speed correction coefficient K1 and
It is calculated according to VB × K1. Here, CB is a basic decrease amount. In this embodiment, the excess fuel amount when the air-fuel ratio A / F is set to or becomes rich or stoichiometric is calculated from the air-fuel ratio and the intake air amount. Also, the amount of excess fuel when additional fuel is injected during the second half of the expansion stroke or during the exhaust stroke is equal to the amount of additional fuel injected into the combustion chamber per unit time. The NO _x absorbent temperature is calculated based on the temperature detected by the exhaust gas temperature sensor 53 provided in the exhaust passage downstream of the NO _x absorbent 25. The output signal of the exhaust temperature sensor 53 is input to the input port 45 via the corresponding AD converter 47.

The degree of deterioration of the NO _x absorbent is calculated based on the total operating time of the internal combustion engine. The longer the total operating time, the greater the degree of deterioration. Further, the inflow exhaust gas amount is calculated based on the mass flow rate detected by the mass flow rate detector provided in the intake pipe. Figure 25 is _the NO _x absorbent 2
5 shows a processing routine of a NO _x release flag which is set when NO _x should be released from 5, and this routine is executed by interruption every predetermined time.

Referring to FIG. 25, first, in step 1
At 00, it is determined whether or not a flag I indicating that the operating region of the engine is the first operating region I is set. If the flag I is set, that is, if the operating region of the engine is in the first operating region I, step 10
Absorption of NO _x amount A per unit time from the map shown in FIG. 16 (A) is calculated proceeds to 1. Then step 102
In A is added to the absorption of NO _x amount .SIGMA.NOX. Next, at step 103 NO _x absorption amount ΣNOX permissible maximum value M
It is determined whether or not AX1 has been exceeded. ΣNOX> MAX
Becomes 1 when the process proceeds to step 104, NO _x releasing flag 1 indicating that it should release the NO _x is set when the first combustion is being performed.

On the other hand, in step 100, the flag I
When it is determined that the engine has been reset,
When the region is the second operation region II, step 107
To the map shown in FIG.
NO_xThe absorption amount B is calculated. Then at step 108
Is NO_xB is added to the absorption amount ΣNOX. Next,
NO at step 103_xAbsorption amount ΣNOx is allowable maximum value MA
It is determined whether or not X1 has been exceeded. ΣNOX> MAX1
Then, the routine proceeds to step 104, where the first combustion is performed.
NO when you are_xNO to indicate that_xRelease
The lug 1 is set. That is, in this case, the second combustion
NO when switching to the first combustion _xIs released
You.

In step 105, the NO _x absorption amountΣNO
It is determined whether X has exceeded the allowable maximum value MAX2.
.SIGMA.NOX> becomes the MAX2 proceeds to step 106, it is a set _the NO _x releasing flag 2 indicating that it should release the second half or NO _x in the exhaust stroke of the expansion stroke. Next, FIG.
The operation control will be described with reference to FIG. 27 and FIG.

Referring to FIG. 26, first, at step 200, 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, step 2
In step 01, it is determined whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 203, where low-temperature combustion is performed.

That is, in step 203, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 20 is set to this target opening ST. Next, at step 204, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Next, at step 205 NO _x releasing flag 1 is whether it is set or not. When the NO _x release flag 1 is not set, the routine proceeds to step 206, where fuel injection is performed so as to achieve the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.

On the other hand, when it is determined in step 205 that the NO _x release flag 1 is set, the routine proceeds to step 207, where the injection control I is performed. That is, the air-fuel ratio is set to a rich or stoichiometric air-fuel ratio. Step 20
When it is determined in 1 that L> X (N), the routine proceeds to step 202, where the flag I is reset, and then proceeds to step 212, where the second combustion is performed.

That is, in step 212, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 14A, and the opening of the throttle valve 20 is set to this target opening ST. Next, at step 213, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Then whether _the NO _x releasing flag 2 in step 214 is set or not. When the NO _x release flag 2 is not set, the routine proceeds to step 215, where fuel injection is performed so as to achieve the air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.

[0092] On the other hand, the injection control II is performed proceeds to step 214 when _the NO _x releasing flag 2 has been determined to have been set in step 214. That is, additional fuel is injected during the latter half of the expansion stroke or during the exhaust stroke. Next, at step 217 in FIG. 27, the subtraction amount C
Is calculated. The subtraction amount C is zero when the air-fuel ratio is lean. Then subtract the amount of C is subtracted from the absorption of NO _x amount ΣNOX in step 218. Then step 2
19 The absorption of NO _x amount ΣNOX is whether zero or more is discriminated. When ΣNOX ≧ 0, the process ends. On the other hand, if ΣNOX <0, step 22
Absorption of NO _x amount ΣNOX at 0 is zero, the processing is terminated.

[0093]

Since, according to the present invention by the amount of released NO _x from actually _the NO _x absorbent According from 1st eighth aspect of absorption of NO _x amount counter is subtracted, it is absorbed in _the NO _x absorbent The amount of NO _x present is accurately estimated.

[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 a first operation region I and a second operation region II.

FIG. 8 is a diagram showing an output of an air-fuel ratio sensor.

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

FIG. 10 is a diagram showing an air-fuel ratio and the like in a first operation region I.

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

FIG. 12 is a diagram showing a map of a fuel injection amount.

FIG. 13 is a diagram showing an air-fuel ratio and the like in a second operation region II.

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

FIG. 15 is a view showing a map of a fuel injection amount.

FIG. 16 is a view for explaining the NO _x absorption / release action.

FIG. 17 is a diagram showing a map of the NO _x absorption amount per unit time.

FIG. 18 is a diagram for explaining NO _x release control.

19 is a diagram showing the relationship between the excess fuel amount and _the NO _x releasing rate.

FIG. 20 is a diagram showing the relationship between the NO _x absorbent temperature and the NO _x release speed.

FIG. 21 is a diagram showing a map of a basic NO _x release speed.

22 is a diagram showing the relationship between the deterioration degree and _the NO _x releasing rate.

23 is a diagram showing the relationship between the inflow exhaust gas amount and _the NO _x releasing rate.

FIG. 24 is a diagram showing a map of a NO _x release speed correction coefficient.

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

FIG. 26 is a flowchart for controlling operation of the engine.

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

[Explanation of symbols]

 6 fuel injection valve 15 exhaust turbocharger 20 throttle valve 29 EGR passage 31 EGR control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 355 F02D 41/04 355 45/00 312 45/00 312R F02M 25/07 570 F02M 25/07 570D 570J (72) Inventor Yoshi ▲ Saki ▼ Koji 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72 ) Inventor Hiroki Murata 1 Toyota Town, Toyota City, Aichi Prefecture F-term in Toyota Motor Corporation (Reference) 3G062 AA01 AA05 AA06 BA04 BA05 BA06 DA04 EA10 GA01 GA04 GA06 GA09 GA17 3G084 AA01 AA03 AA04 BA05 BA09 BA13 BA15 BA20 BA24 DA07 FA07 FA10 FA26 FA27 FA33 FA38 3G091 AA02 AA10 AA11 AA18 AB06 BA14 BA15 BA33 CA07 CA08 CA13 CA18 CB02 CB03 CB07 C B08 DA01 DA02 DA05 DB06 DB07 DB10 EA00 EA01 EA03 EA05 EA07 EA17 EA31 EA34 FA12 FA13 FA14 FB10 FB11 FB12 GB01X GB02W GB03W GB04W GB05W GB06W GB10X GB16X HA36 HA37 HB05 HB06 3G301 JA03 HA11 HA02 HA11 HA03 HA11 NC02 NC04 NE01 NE06 NE13 NE14 NE15 PA01A PA11A PA18A PD02A PD11A PE01A PE03A PF03A

Claims (8)

[Claims] 1. The amount of inert gas supplied to a combustion chamber is increased.
As it increases, soot generation gradually increases and reaches a peak
And further increase the amount of inert gas supplied to the combustion chamber.
The fuel and the surrounding fuel during combustion in the combustion chamber
The gas temperature is lower than the soot generation temperature and soot is almost emitted
In an internal combustion engine that does not
NO contained in exhaust gas when the fuel ratio is lean_xTo
The air-fuel ratio of the exhaust gas that is absorbed and flows in is the stoichiometric air-fuel ratio or
NO absorbed when rich_xReleases NO_xAbsorbent
In the engine exhaust passage, soot generation peaks
The amount of inert gas supplied into the combustion chamber rather than the amount of inert gas
Combustion that generates little soot and generates soot
The amount of inert gas supplied into the combustion chamber
Switching to the second combustion with a small amount of inert gas
Switching means for operating the internal combustion engine at a lean air-fuel ratio.
Is determined according to the operating state of the engine when
The addition amount of_xAbsorbent NO_xabsorption
NO for quantity _xThe internal combustion engine adds
Is operating at rich or stoichiometric
The fixed subtraction amount is set to_xAbsorption counter
From the above, the NO_xAbsorbent NO_xabsorption
Absorption amount estimating means for estimating the amount, and the internal combustion engine is rich
Or NO when operating at stoichiometric air-fuel ratio_xAbsorbent
NO released from_xNO to estimate the amount of_xEmission estimation
Means for operating the internal combustion engine at a rich or stoichiometric air-fuel ratio
NO when_xNO based on release_xSucking
Subtraction amount determining means for determining the subtraction amount of the yield counter;
An internal combustion engine comprising: 2. The NO_xWhen the emission amount estimating means
NO when operating at rich or stoichiometric_x
NO based on the amount of fuel supplied to the absorbent _xRelease amount
The internal combustion engine according to claim 1, wherein the estimation is performed. 3. The internal combustion engine according to claim 1, wherein said NO _x release amount estimating means estimates the NO _x release amount based on the temperature of the NO _x absorbent. 4. The internal combustion engine according to claim 1, wherein said NO _x release amount estimating means estimates the NO _x release amount based on the degree of deterioration of the NO _x absorbent. 5. The internal combustion engine according to claim 1, wherein said NO _x emission amount estimating means estimates the NO _x emission amount based on an amount of exhaust gas flowing into the NO _x absorbent. 6. The 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. 7. The internal combustion engine according to claim 6, wherein the exhaust gas recirculation rate is approximately 55% or more. 8. An operation region of the engine is divided into a first operation region on a low load side and a second operation region on a high load side, and a first combustion is performed in the first operation region. The internal combustion engine according to claim 1, wherein the second combustion is performed in the region.