JP3405197B2 - Internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an internal combustion engine.

[0002]

2. Description of the Related Art In an internal combustion engine in which a lean mixture is burned, NO _x is absorbed when the inflowing exhaust gas has a lean air-fuel ratio, and NOx is absorbed when the inflowing exhaust gas has a rich or stoichiometric air-fuel ratio. NO releasing _x
The _x absorbent disposed in an engine exhaust passage, the NO _x generated when burned lean mixture is absorbed by _the NO _x absorbent, the combustion chamber before the absorption of NO _x capacity of the NO _x absorbent becomes saturated The air-fuel ratio of the air-fuel mixture supplied to the air is temporarily made rich or the theoretical air-fuel ratio to release NO _x from the NO _x absorbent and the released NO _x is reduced gas, that is, unburned HC contained in the exhaust gas. , CO are known to reduce the internal combustion engine (see Japanese Patent Laid-Open No. 6-294319).

[0003]

However, the internal combustion engine is provided with an exhaust gas recirculation device for recirculating exhaust gas into the engine intake passage, and NO _{x is} recirculated during exhaust gas recirculation.
When the air-fuel ratio in order to release the NO _x from the absorbent and from the lean air-fuel ratio is switched to a rich air-fuel ratio flows into _the NO _x absorbent by the lean degree of the lean air-fuel ratio immediately before the start air-fuel ratio switching action The air-fuel ratio of the exhaust gas changes considerably.

That is, when combustion is performed under a lean air-fuel ratio, the exhaust gas discharged from the engine contains excess air. Therefore, at this time, recirculation is performed in the engine intake passage. Excess air is also contained in the exhaust gas generated. The excess air contained in the recirculated exhaust gas is supplied again to the combustion chamber, so that the air-fuel ratio in the combustion chamber is affected by the excess air in the recirculated exhaust gas.

When the lean degree of the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation to release NO _x from the NO _x absorbent is small, the amount of excess air contained in the recirculated exhaust gas is reduced. Low, and therefore the air-fuel ratio in the combustion chamber is in this case almost unaffected by excess oxygen in the recirculated exhaust gas. Therefore, in this case, if the fuel injection amount is increased by an amount required to make the lean air-fuel ratio the predetermined rich air-fuel ratio, the air-fuel ratio of the exhaust gas immediately becomes the predetermined rich air-fuel ratio, and immediately NO _x is to be released from _the NO _x absorbent Te.

On the other hand, when the lean degree of the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action to release the NO _x from the NO _x absorbent is large, the excess amount contained in the recirculated exhaust gas is increased. There is a large amount of air, and in this case, therefore, even if the fuel injection amount is increased by an amount necessary to bring the lean air-fuel ratio to the predetermined rich air-fuel ratio, the air-fuel ratio of the exhaust gas immediately becomes the predetermined rich air-fuel ratio. ratio and not during the increase after interim pleasure of the fuel injection amount immediately nO _x from _the nO _x absorbent so is maintained at a lean air-fuel ratio is not released.

Therefore, when the lean air-fuel ratio immediately before the air-fuel ratio switching operation is large and when the lean air-fuel ratio immediately before the air-fuel ratio switching operation is small, the air-fuel ratio is changed from the lean air-fuel ratio at the same engine load and engine speed. increasing the amount of injected fuel to the amount of reducing gas to a predetermined required to release the NO _x as sent into _the NO _x absorbent even from _the NO _x absorbent when switching to a rich air-fuel ratio or It is necessary to change the time for continuing the increasing action of the injected fuel.

[0008]

Therefore, according to the first aspect of the invention, an exhaust gas recirculation device is provided for recirculating the exhaust gas discharged into the engine exhaust passage into the engine intake passage,
The _the NO _x absorbent air-fuel ratio of the inflowing exhaust gas to release the NO _x when the air-fuel ratio of the exhaust gas absorb and flowing the NO _x contained in the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich when the lean place the engine exhaust passage, and temporarily rich air-fuel ratio by increasing the amount of fuel injection when to release the NO _x from the NO _x absorbent when burning fuel under a lean air-fuel ratio has been performed, in whereby an internal combustion engine in which the predetermined amount of reducing gas required to feed the _the NO _x absorbent to be released the NO _x from the NO _x absorbent from _the NO _x absorbent in the recirculation of the exhaust gases increasing the amount of injected fuel based on the lean air-fuel ratio immediately before the start air-fuel ratio switching action when the air-fuel ratio in order to release the NO _x switching from the lean air-fuel ratio to a rich air-fuel ratio, time or injection to continue increasing effect of the injected fuel An air-fuel ratio having a predetermined lean air-fuel ratio immediately before the start of the air-fuel ratio switching action at a certain engine load and engine speed, is provided with an injection control means for controlling at least one of the start timings of the fuel increasing action. when greater than, as Okurikomeru the reducing gas in an amount which reduced speed is predetermined at the latest air-fuel ratio of the exhaust gas immediately after the start air-fuel ratio switching action to _the NO _x absorbent, above certain engine load and Continuing to increase the amount of injected fuel and increase the amount of injected fuel when the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation at the same engine load and engine speed as the engine speed is smaller than the predetermined air-fuel ratio Or at least one of the start time of the increasing action of the injected fuel is changed.

In the second invention, in the first invention,
When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation is smaller than the predetermined air-fuel ratio, the amount of fuel injection required to maintain the air-fuel ratio at the predetermined rich air-fuel ratio immediately after the start of the air-fuel ratio switching operation is performed. The amount is increased and the action of increasing the fuel injection amount is continued for the period required to deliver a predetermined amount of reducing gas to the NO _x absorbent.

In the third invention, in the first invention,
When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation at a certain engine load and engine speed is larger than a predetermined air-fuel ratio, the engine load and engine speed that are the same as the above-mentioned certain engine load and engine speed. The increase amount of the injected fuel is increased as compared with the case where the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action in is smaller than the predetermined air-fuel ratio.

In the fourth invention, in the third invention,
When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation is larger than the predetermined air-fuel ratio, the increase amount of the injected fuel is increased as the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation becomes larger. In a fifth aspect based on the first aspect, when the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action at a certain engine load and engine speed is larger than a predetermined air-fuel ratio, the above-mentioned certain engine load and engine are provided. Compared with the case where the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation at the same engine load and engine speed as the engine speed is smaller than the predetermined air-fuel ratio, the time for continuing the increasing action of the injected fuel is lengthened.

In the sixth invention, in the fifth invention,
When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action is larger than the predetermined air-fuel ratio, the larger the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action, the longer the time for continuing the action of increasing the injected fuel is. In a seventh aspect based on the first aspect, when the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action at a certain engine load and engine speed is larger than the predetermined air-fuel ratio, the air-fuel ratio is in a predetermined period. , A lean air-fuel ratio smaller than a predetermined air-fuel ratio, and then the air-fuel ratio is switched to rich.

In the eighth invention, in the seventh invention,
When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action is larger than the predetermined air-fuel ratio, the predetermined period is lengthened as the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action increases. In the ninth invention, in the first invention, when the internal combustion engine increases the amount of recirculated exhaust gas supplied into the combustion chamber, the amount of soot generated gradually increases and reaches a peak.
When the amount of recirculated exhaust gas supplied to the combustion chamber is further increased, the temperature of the fuel and the gas around it during combustion in the combustion chamber becomes lower than the temperature at which soot is produced, and soot is hardly generated. The first combustion, which consists of an internal combustion engine, has a larger amount of recirculated exhaust gas supplied to the combustion chamber than the amount of recirculated exhaust gas at which the amount of soot is peaked, and the air-fuel ratio is smaller than a predetermined air-fuel ratio. And second combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of recirculated gas at which the soot generation amount reaches a peak and the air-fuel ratio is larger than a predetermined air-fuel ratio. and switching means for switching to, comprising a determining means for determining whether or not to release the NO _x from the NO _x absorbent, release the NO _x from the NO _x absorbent when the second combustion is being performed When it is judged that it should be issued Is from the combustion air-fuel ratio is rich temporarily when it is switched to the first combustion is larger than the air-fuel ratio lean air-fuel ratio is predetermined in this case the air-fuel ratio switching action for immediately before the start.

[0014] In the ninth invention is a tenth invention, the fuel injection amount is made to increase when it is determined that it should release the NO _x from the NO _x absorbent when the first combustion is being performed The air-fuel ratio is temporarily made rich. In the eleventh invention, in the ninth invention, NO _x
The amount of NO _x absorbed in the absorbent comprises an estimation means for estimating a first maximum allowable value amount of NO _x estimated by the estimating means when the second combustion is being performed is a predetermined Is exceeded, the air-fuel ratio is temporarily made rich when the second combustion is switched to the first combustion, and the NO estimated by the estimating means when the second combustion is being performed.
Exhaust that flows into the NO _x absorbent by injecting additional fuel in the latter half of the expansion stroke or during the exhaust stroke when the _x amount exceeds the predetermined second allowable maximum value that is larger than the first allowable maximum value. The gas air-fuel ratio is set to the stoichiometric air-fuel ratio or rich.

According to the twelfth invention, in the ninth invention, the exhaust gas recirculation rate in the first combustion state is approximately 5
It is 5% or more. In the thirteenth invention, in the ninth invention, the operating region of the engine is divided into a first operating region on the low load side and a second operating region on the high load side, and the first combustion is performed in the first operating region. The second combustion is performed in the second operation area.

According to the fourteenth invention, in the ninth invention, a catalyst having an oxidizing function is arranged in the engine exhaust passage upstream of the NO _x absorbent.

[0017]

FIG. 1 shows the case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, and 9 is an intake port. Indicates an exhaust valve, and 10 indicates an exhaust port, respectively. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an outlet portion of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Compressor 16
The inlet part of is connected to an air cleaner 18 via an air suction pipe 17. On the other hand, the exhaust port 10 is the exhaust manifold 1
Exhaust turbine 2 of exhaust turbocharger 15 via 9
The exhaust turbine 20 has an outlet connected to a casing 23 containing a NO _x absorbent 22 via an exhaust pipe 21.

A step motor 24 is provided in the intake duct 13.
A throttle valve 25 driven by the air-fuel ratio sensor 26 is arranged in the exhaust manifold 19. The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 27, and an EGR control valve 29 driven by a step motor 28 is arranged in the EGR passage 27. . Also, EG
A cooling device 30 for cooling the EGR gas flowing in the EGR passage 27 is arranged around the R passage 27. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 30, and the engine cooling water cools the EGR gas.

On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 32, via a fuel supply pipe 31. Fuel is supplied into the common rail 32 from an electrically controlled variable fuel discharge pump 33, and the fuel supplied into the common rail 32 is supplied to the fuel injection valve 6 via each fuel supply pipe 31. A fuel pressure sensor 34 for detecting the fuel pressure in the common rail 32 is attached to the common rail 32, and the fuel pump 33 is arranged so that the fuel pressure in the common rail 32 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 34. Is controlled.

The electronic control unit 40 is composed of a digital computer and has a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45 and an input port 45 which are connected to each other by a bidirectional bus 41. The output port 46 is provided. The output signal of the air-fuel ratio sensor 26 is input to the input port 45 via the corresponding AD converter 47, and the output signal of the fuel pressure sensor 34 is also input to the input port 45 via the corresponding AD converter 47. A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 4 via the corresponding AD converter 47.
Input to 5. A crank angle sensor 52 that generates an output pulse each time the crankshaft rotates, for example, 30 ° is connected to the input port 45. On the other hand, the output port 46 is connected via the corresponding drive circuit 48 to the fuel injection valve 6,
The throttle valve control step motor 24, the EGR control valve control step motor 28, and the fuel pump 33 are connected.

Conventionally, in an internal combustion engine, for example, a compression ignition type engine, an engine exhaust passage and an engine intake passage are connected by an EGR passage in order to suppress generation of NO _x ,
Exhaust gas, that is, EGR gas, is recirculated through the EGR passage into the engine intake passage. In this case, since the EGR gas has a relatively high specific heat and can absorb a large amount of heat, the EGR gas amount increases, that is, the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)). Is increased, the combustion temperature in the combustion chamber decreases. When the combustion temperature decreases, the amount of NO _x generated decreases. Therefore, the higher the EGR rate, the lower the amount of NO _x generated.

As described above, it has been known that the amount of NO _x generated can be reduced by increasing the EGR rate. However, when the EGR rate is increased, when the EGR rate exceeds a certain limit, the amount of soot generated, that is, the smoke starts to increase rapidly. In this regard, it has been conventionally thought that if the EGR rate is further increased, the smoke will increase infinitely, and therefore the smoke will start to increase rapidly.
The GR rate is considered to be the maximum allowable limit for the EGR rate.

Therefore, conventionally, the EGR rate is set within a range not exceeding the maximum allowable limit. The maximum allowable limit of this EGR rate is approximately 30 to 50 percent, though it varies considerably depending on the engine type and fuel.
Therefore, in the conventional compression ignition type internal combustion engine, the EGR rate is suppressed to about 30% to 50% at the maximum.

As described above, the maximum allowable limit for the EGR rate was conventionally considered to exist, so that the EG
The R rate is NO within the range that does not exceed this maximum allowable limit.
_It was stipulated that the amount of _x and smoke generated should be as small as possible. However, this way there is a limit to the EGR rate to decrease of the NO _x and NO _x and the amount of smoke produced be determined so that the amount of generation is possible less smoke, actually still substantial amount of the NO _x
And the situation is that smoke is generated.

However, if the EGR rate is made larger than the maximum permissible limit in the process of studying the combustion of the compression ignition type engine, the smoke increases sharply as described above, but there is a peak in the amount of smoke generated, and this peak is present. Beyond EGR
When the rate is further increased, the smoke starts to decrease sharply this time. When the EGR rate is 70% or more during idling operation, and when the EGR gas is strongly cooled, the EGR rate is almost 55% or more. It was found that it was almost zero, that is, soot was hardly generated. At this time, N
It has also been found that the amount of O _x generated is extremely small.
After that, the reason why soot was not generated was examined based on this finding, and as a result, soot and NO
_This led to the construction of a new combustion system capable of simultaneously reducing _x . This new combustion system will be explained in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle of the process until the hydrocarbons grow into soot.

That is, as a result of repeated experimental research, it was found that when the temperature of the fuel and the gas around it during combustion in the combustion chamber is below a certain temperature, the growth of hydrocarbons stops at a stage before the soot is reached. However, if the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons will suddenly grow to soot. In this case, the temperature of the fuel and its surrounding gas is greatly affected by the endothermic action of the gas around the fuel when the fuel burns, and the endothermic amount of the gas around the fuel is adjusted according to the amount of heat generated during fuel combustion. Thus, the temperature of the fuel and the gas around it can be controlled.

Therefore, if the temperature of the fuel and the gas around it during combustion in the combustion chamber is suppressed below the temperature at which the growth of hydrocarbons stops midway, soot will not be generated, and the fuel and the surroundings during combustion in the combustion chamber will be eliminated. It is possible to control the gas temperature in the range below the temperature at which the growth of hydrocarbons stops halfway by adjusting the heat absorption amount of the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of the new combustion system.

FIG. 1 shows a compression ignition type internal combustion engine which employs this new combustion system. FIG. 2 shows that in the compression ignition type internal combustion engine shown in FIG. 1, the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree of the throttle valve 25 and the EGR rate during engine low load operation. Change of output torque at the time of smoke, HC, CO, NO
_It shows an experimental example showing the change in the emission amount of _x . As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the larger the EGR rate, and the theoretical air-fuel ratio (≈14.6)
In the following cases, 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 EGR rate becomes around 40%, and when the air-fuel ratio A / F becomes about 30, the smoke amount is increased. The amount of generation begins to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is made smaller, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke sharply decreases this time, the EGR rate is increased to 65% or more, and the smoke becomes almost zero when the air-fuel ratio A / F is around 15.0. . That is, soot is hardly generated. At this time, the output torque of the engine slightly decreases, and N
The amount of O _x generated is considerably low. On the other hand, at this time, HC,
The amount of CO generated starts to increase.

FIG. 3 (A) shows a change in combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 18 and the amount of smoke generated is largest, and FIG. 3 (B) shows the air-fuel ratio A / F. It shows a change in the combustion pressure in the combustion chamber 5 when F is around 13 and the amount of smoke generated is almost zero. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case shown in FIG. 3 (B) where the amount of smoke generated is almost zero, the amount of smoke generated is large.
It can be seen that the combustion pressure is lower than in the case shown in (A).

From the experimental results shown in FIGS. 2 and 3, the following can be said. That is, first of all, the air-fuel ratio A / F is 1
When the amount of smoke generated is 5.0 or less and the amount of smoke is almost zero,
As shown in (3), the amount of NO _x generated is considerably reduced. N
The decrease in the amount of generated O _x means that the combustion temperature in the combustion chamber 5 is decreased, and therefore, when the soot is hardly generated, the combustion temperature in the combustion chamber 5 is decreased. I can say. The same can be said from FIG. That is, the combustion pressure is low in the state shown in FIG. 3 (B) where almost no soot is generated.
The combustion temperature inside is low.

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

When these considerations based on the experimental results shown in FIGS. 2 and 3 are summarized, the soot generation amount becomes almost zero when the combustion temperature in the combustion chamber 5 is low, and at this time, the soot precursor or the precursor thereof. The hydrocarbons in this state are discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the gas around it in the combustion chamber 5 is below a certain temperature, the soot growth process stops halfway, that is, the soot is generated. It was found that soot was not generated at all and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 reached a certain temperature or higher.

By the way, the temperature of the fuel and its surroundings when the hydrocarbon production process is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. It cannot be said how many times it changes, but this certain temperature has a deep relationship with the amount of NO _x produced, and therefore this certain temperature is defined to some extent from the amount of NO _x produced. be able to. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas around it decreases, and the amount of NO _x generated decreases. At this time, soot is hardly generated when the amount of NO _x generated is about 10 p.pm or less. Therefore, the above certain temperature is NO
It is almost the same as the temperature when the amount of _x generation is around 10 p.pm or less.

Once soot is produced, this soot cannot be purified by a post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before it can be easily purified by a post-treatment using a catalyst having an oxidizing function. Considering the post-treatment with a catalyst having an oxidizing function as described above, it is extremely difficult to determine whether the hydrocarbon is discharged from the combustion chamber 5 in the state of the soot precursor or in the state before it, or is discharged from the combustion chamber 5 in the form of soot. There is a big difference. The new combustion system employed in the present invention allows hydrocarbons to be discharged from the combustion chamber 5 in the form of soot precursors or pre-presence conditions without producing soot in the combustion chamber 5 The core is to oxidize with a catalyst having an oxidizing function.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the gas around it in the combustion chamber 5 during combustion is set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that, in order to suppress the temperature of the fuel and the gas around it, the endothermic action of the gas around the fuel when the fuel burns has an extremely large effect.

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

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

In this case, in order to suppress the temperature of the fuel and the gas around it to a temperature lower than the temperature at which soot is produced, an amount of inert gas sufficient to absorb the amount of heat required to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas also increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action. Therefore, the inert gas is preferably a gas having a large specific heat. In this respect, since CO ₂ and EGR gas have relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.

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

As shown by the curve A in FIG. 5, when the EGR gas is strongly cooled, the soot generation amount reaches a peak when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Almost no soot is generated if the percentage is exceeded. On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the soot generation amount reaches a peak when the EGR rate is slightly higher than 50%. In this case, the EGR rate is approximately 65% or more. If so, soot is hardly generated.

Further, as shown by the curve C in FIG. 5, EG
When the R gas is not forcibly cooled, the EGR rate is 5
The soot generation amount peaks near 5%, and in this case, if the EGR rate is set to approximately 70% or more, soot is hardly generated. Note that FIG. 5 shows the amount of smoke generated when the engine load is relatively high, and the EGR rate at which the amount of soot generated peaks when the engine load decreases and the EGR rate at which soot almost does not occur decreases. The lower limit of is also slightly lowered. Thus, the lower limit of the EGR rate at which soot is hardly generated changes depending on the cooling degree of EGR gas and the engine load.

FIG. 6 shows a mixture of EGR gas and air required to bring the temperature of the fuel and its surrounding gas at the time of combustion to a temperature lower than the temperature at which soot is produced when EGR gas is used as the inert gas. The amount of gas, the ratio of air in this mixed gas amount, and the ratio of EGR gas in this mixed gas are shown. Note that, in FIG. 6, the vertical axis represents the total intake gas amount sucked into the combustion chamber 5, and the chain line Y represents the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. In addition, the horizontal axis represents the required load, and Z1 represents the low load operation region. Referring to FIG. 6, the ratio of air, that is, the amount of air in the mixed gas, indicates the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the theoretical air-fuel ratio. On the other hand, in FIG. 6, the ratio of EGR gas, that is, the amount of EGR gas in the mixed gas is set so that when the injected fuel is burned, the temperature of the fuel and its surrounding gas is lower than the temperature at which soot is formed. The minimum required EGR gas amount is shown. This EGR
The gas amount is approximately 55% or more in terms of EGR rate, and 70% or more in the embodiment shown in FIG.
That is, the total amount of intake gas sucked into the combustion chamber 5 is shown by the solid line X in FIG. 6, and the ratio of the amount of air to the amount of EGR gas in this total intake gas amount X is set as shown in FIG. The temperature of the fuel and the gas around it is lower than the temperature at which soot is produced, and thus no soot is generated. Also, the amount of NO _x generated at this time is around 10 p.pm,
Or less, and therefore the amount of NO _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 gas around it at a temperature lower than the temperature at which soot is generated, heat generated by the EGR gas is used. The amount of absorption must be increased. Therefore, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount is increased.
That is, the EGR gas amount needs to increase as the required load increases.

On the other hand, in the load region Z2 of FIG. 6, the total intake gas amount X required to prevent the generation of soot exceeds the total intake gas amount Y that can be inhaled. Therefore, in this case, in order to supply the total intake gas amount X required to prevent the generation of soot into the combustion chamber 5, both the EGR gas and the intake air, or EG
It is necessary to supercharge or pressurize the R gas. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intakeable gas amount Y in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the air amount is slightly decreased to increase the EGR gas amount and the fuel is burned under the rich air-fuel ratio.

As described above, FIG. 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 smaller than the air amount shown in FIG. Even _if the amount is small, that is, even if the air-fuel ratio is made rich, the generation amount of NO _x can be reduced to around 10 p.pm or less while preventing the generation of soot. Further, in the low load region Z1 shown in FIG. Even if the amount is made 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 generation amount of NO _x is 10 _p .
It can be around pm or less.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excessive fuel does not grow to soot, and soot is generated. There is no. Further, at this time, a very small amount of NO _x is generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature becomes high, but in the present invention the combustion temperature is suppressed to a low temperature, soot Not generated at all. Furthermore, NO _x
Also produces only a very small amount.

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. Therefore, the amount of NO _x generated is extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time. By the way, the temperature of the fuel and the gas around it in the combustion chamber can be suppressed below the temperature at which the growth of hydrocarbons stops halfway only when the calorific value due to combustion is small and the engine load is relatively low. Therefore, in the embodiment according to the present invention, when the engine load is relatively low, the temperature of the fuel and the gas around it during combustion are suppressed below the temperature at which the growth of hydrocarbons stops halfway, and the first combustion, that is, low temperature combustion is performed. Thus, when the engine load is relatively high, the second combustion, that is, the combustion that is more commonly performed than before is performed.
It should be noted that here, the first combustion, that is, low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generated peaks, and soot is almost generated. The second combustion, that is, the combustion that is normally performed in the past, is the combustion that does not have the amount of soot generated and the amount of the inert gas in the combustion chamber is smaller than the amount of the inert gas that does not reach the peak. Say that.

FIG. 7 shows a first operating region I in which the first combustion, that is, low temperature combustion is performed, and a second combustion region II in which the second combustion, that is, combustion by the conventional combustion method is performed. There is. In FIG. 7, the vertical axis L represents the depression amount of the accelerator pedal 50, that is, the required load, and the horizontal axis N represents the engine speed. Further, in FIG. 7, X (N) is the first
Shows the first boundary between the operating region I and the second operating region II, where Y (N) is the first operating region I and the second operating region.
The second boundary with II is shown. The determination of the change of the operating region from the first operating region I to the second operating region II is made based on the first boundary X (N), and the change from the second operating region II to the first operating region II is performed.
The determination of the change of the operating range to the operating range I of the second boundary Y
It is performed based on (N).

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

FIG. 8 shows the output of the air-fuel ratio sensor 24. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 24 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 24. Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. 9.

FIG. 9 shows the throttle valve 2 for the required load L.
5, the opening of the EGR control valve 29, the EGR rate, the air-fuel ratio, the injection timing and the injection amount are shown. As shown in FIG. 9, in the first operating region I where the required load L is low, the opening degree of the throttle valve 25 is gradually increased from near full close to half open as the required load L increases, and the EGR control valve 29 The opening degree of is gradually increased from near full close to full open as the required load L increases. Further, in the example shown in FIG. 9, the EGR rate is approximately 7 in the first operating region I.
The air-fuel ratio is set to 0% and the air-fuel ratio is slightly lean.

In other words, in the first operating region I, EGR
The opening of the throttle valve 25 and the opening of the EGR control valve 29 are controlled so that the ratio becomes approximately 70% and the air-fuel ratio becomes a lean air-fuel ratio which is slightly lean. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening degree of the EGR control valve 29 based on the output signal of the air-fuel ratio sensor 24. Further, in the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes late as the required load L becomes high, and the injection completion timing θE also becomes late as the injection start timing θS becomes late.

During the idling operation, the throttle valve 25 is closed to near full closure, and at this time, the EGR control valve 29 is also closed to near full closure. Throttle valve 2
When the valve 5 is closed to near full closure, the pressure in the combustion chamber 5 at the beginning of compression becomes low and the compression pressure becomes small. When the compression pressure becomes small, the compression work by the piston 4 becomes small, so that the vibration of the engine body 1 becomes small. That is, in idling operation, the throttle valve 25 is closed to close to the fully closed state in order to suppress the vibration of the engine body 1.

On the other hand, the operating region of the engine is the first operating region I.
When changing from the second operating region II to the second operating region II, the opening degree of the throttle valve 25 is increased stepwise from the half open state to the full open direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. Second
In the operation area II, the conventional combustion is performed. In the second operating region II, the throttle valve 25 is kept fully open except for a part, and the opening degree of the EGR control valve 29 is gradually reduced as the required load L increases. Also,
In this operating region II, the EGR rate becomes lower as the required load L becomes higher, and the air-fuel ratio becomes smaller as the required load L becomes higher. However, the air-fuel ratio is a lean air-fuel ratio even if the required load L becomes high. Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

As shown in FIG. 9, the injection amount is the required load L
Increases with increasing. This injection amount Q is stored in advance in the ROM 42 as a function of the required load L and the engine speed N as shown in FIG. FIG. 11 shows the first
The air-fuel ratio A / F in the operating region I of is shown. Figure 1
1, A / F = 15.5, A / F = 16, A / F
= 17, A / F = 18, the respective curves indicate the air-fuel ratios of 15.5, 16, 17, and 18, respectively,
The air-fuel ratio between each curve is determined by proportional distribution. Figure 11
As shown in (1), the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the air-fuel ratio A / F is leaner as the required load L is lower.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low temperature combustion can be performed even if the EGR rate is decreased.
When the EGR rate is reduced, the air-fuel ratio becomes large, so that as shown in FIG. 11, the air-fuel ratio A / F is made larger as the required load L becomes lower. The fuel consumption rate increases as the air-fuel ratio A / F increases. Therefore, in order to make the air-fuel ratio as lean as possible, the air-fuel ratio A / F is increased as the required load L decreases in the embodiment of the present invention.

It should be noted that the target opening degree ST of the throttle valve 25 required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 2 (A), the EGR is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N, and is required to set the air-fuel ratio to the target air-fuel ratio shown in FIG. The target opening degree SE of the control valve 29 is shown in FIG.
As shown in (4), it is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N.

FIG. 13 shows the target air-fuel ratio when the second combustion, that is, the normal combustion according to the conventional combustion method is performed. Note that in FIG. 13, A / F = 24, A / F = 3
5, each curve shown by A / F = 45 and A / F = 60 shows the target air-fuel ratios 24, 35, 45, 60, respectively. Throttle valve 2 required to set the air-fuel ratio to this target air-fuel ratio
The target opening degree ST of 5 is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 14 (A), and the air-fuel ratio is set to this target air-fuel ratio. Target opening SE of EGR control valve 29 required for
Is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N, as shown in FIG.

On the other hand, it is built in the casing 23.
NO_xThe absorbent 22 uses, for example, alumina as a carrier and
For example, potassium K, sodium Na, lithium L on the body
i, alkali metal such as cesium Cs, barium B
a, alkaline earth such as calcium Ca, lanthanum L
a, at least selected from rare earths such as yttrium Y
One and a noble metal such as platinum Pt are supported.
It Engine intake passage, combustion chamber 5 and NO_xOn the absorbent 22
Air and fuel (carbonized water) supplied in the exhaust passage of the flow
Ratio) to NO_xAir-fuel ratio of exhaust gas flowing into the absorbent 22
This is NO_xThe absorbent 22 is the air-fuel of the inflowing exhaust gas
NO when the ratio is lean_xAbsorbs the inflowing exhaust gas
NO absorbed when the air-fuel ratio becomes stoichiometric or rich_x
Releases NO _xIt absorbs and releases.

If this NO _x absorbent 22 is arranged in the exhaust passage of the engine, the NO _x absorbent 22 will actually perform the action of absorbing and releasing NO _x , but the detailed mechanism of this action of absorbing and releasing some parts is not clear. . However, it is considered that this absorbing and releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking the case where platinum Pt and barium Ba are supported on the carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

In the compression ignition type internal combustion engine shown in FIG. 1, combustion is normally performed in a state where the air-fuel ratio in the combustion chamber 5 is 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 is O as is shown in FIG. 15 (A) to the time
It attaches to the surface of platinum Pt in the form of ₂ ⁻ or O ²⁻ . on the other hand,
NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2N
O ₂ ). Then, a part of the generated NO ₂ is oxidized on the platinum Pt and absorbed in the absorbent to be barium oxide BaO.
As shown in FIG. 15 (A), it diffuses into the absorbent in the form of nitrate ions NO ₃ ⁻ while being bound with. In this way, NO _x is absorbed in the NO _x absorbent 22. As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is produced on the surface of platinum Pt, and unless the NO _x absorption capacity of the absorbent is saturated, NO ₂ is generated.
₂ is absorbed in the absorbent to produce nitrate ion NO ₃ ⁻ .

On the other hand, the air-fuel ratio of the inflowing exhaust gas becomes rich.
Oxygen concentration in the inflowing exhaust gas decreases, resulting in white
NO on the surface of gold Pt₂The production amount of is reduced. NO₂of
If the amount of production decreases, the reaction goes in the opposite direction (NO₃ ^-→ NO₂)
And thus the nitrate ion NO in the absorbent₃ ^-Is NO
₂Is released from the absorbent in the form of. NO at this time_xAbsorbent
NO released from 22_xIs shown in Figure 15 (B)
A large amount of unburned HC and CO contained in the inflowing exhaust gas
Reacted and reduced. In this way, the platinum Pt
NO on the surface₂When there is no longer any absorbent
Heto NO₂Is released. Therefore, the air-fuel ratio of the inflowing exhaust gas
Is made rich, it will be NO in a short time. _xAbsorbent 22
Et NO_xIs released, and this released NO_xIs returned
NO in the atmosphere to be sourced_xIs never emitted
Yes.

In this case, the air-fuel ratio of the inflowing exhaust gas is
NO even at the theoretical air-fuel ratio_xAbsorbent 22 to NO_xIs released
To be done. However, the air-fuel ratio of the inflowing exhaust gas is
NO in case of ratio_xAbsorbent 22 to NO_xGradually
NO because it is only released _xAbsorbed by the absorbent 22
All NO_xIt takes a little longer time to release.

As described above, the NO _x absorbent 22 is platinum P
It contains a noble metal such as t and is therefore a NO _x absorbent 2
2 has an oxidizing function. On the other hand, as described above, when the engine operating condition is in the first operating region I and the low temperature combustion is performed, soot is hardly generated, and instead, the unburned hydrocarbon is the precursor of soot or the soot precursor. It is discharged from the combustion chamber 5 in the form of a state. However, as described above, the NO _x absorbent 22 has an oxidizing function, and therefore the unburned hydrocarbons discharged from the combustion chamber 5 at this time are satisfactorily oxidized by the NO _x absorbent 22.

[0066] Incidentally the absorption of NO _x capacity of the NO _x absorbent 22 is limited, absorption of NO _x capacity of the NO _x absorbent 22 needs to release the NO _x from the NO _x absorbent 22 before saturation. For this purpose it is necessary to estimate the amount of NO _x is absorbed in the NO _x absorbent 22. Therefore, in the embodiment according to the present invention, the NO _x absorption amount A per unit time when the first combustion is being performed is plotted as a function of the required load L and the engine speed N on a map as shown in FIG. 16B, the NO _x absorption amount B per unit time when the second combustion is being performed is calculated as a function of the required load L and the engine speed N, and the map shown in FIG. The NO _x amount ΣNOx absorbed in the NO _x absorbent 22 is estimated by previously obtaining the NO _x absorption amounts A and B per unit time.

In the embodiment according to the present invention, when this NO _x absorption amount ΣNOX exceeds the predetermined allowable maximum value, N
From O _x absorbent 22 so that to release NO _x. Next, this will be described with reference to FIG. Referring to FIG. 17, in the embodiment according to the present invention, there are two allowable maximum values, that is, an allowable maximum value MAX1 and an allowable maximum value MA.
X2 and are set. The maximum allowable value MAX1 is NO _x
It is set to about 30% of the maximum NO _x absorption amount that the absorbent 22 can absorb, and the allowable maximum value MAX2 is set to about 80% of the maximum absorption amount that the NO _x absorbent 22 can absorb. NO _x when the first combustion is taking place
When the absorption amount ΣNOX exceeds the maximum allowable value MAX1, the air-fuel ratio is made rich in order to release NO _x from the NO _x absorbent 22, and when the second combustion is performed, the NO _x absorption amount ΣNOX is the maximum allowable value. Second when the value MAX1 is exceeded
Air-fuel ratio in order to release the NO _x from the NO _x absorbent 22 when it is switched from the combustion to the first combustion is made rich,
NO _x absorption amount ΣNOx when the second combustion is performed
Exceeds the maximum allowable value MAX2, NO _x absorbent 2
2 from 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. 17, the period X is the required load L.
Is lower than the first boundary X (N) and shows the case where the first combustion is performed. At this time, the air-fuel ratio is a lean air-fuel ratio that is slightly leaner than the stoichiometric air-fuel ratio. When the first combustion is being performed, the amount of NO _x generated is extremely small, and therefore, at this time, the NO _x absorption amount ΣNO _x rises extremely slowly as shown in FIG. 17. NO _x absorption amount ΣN when the first combustion is 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 22 is released. At this time, NO _x absorption amount ΣNOX
Is zero.

As described above, when the first combustion is performed, soot is not generated regardless of whether the air-fuel ratio is lean, the stoichiometric air-fuel ratio, or the rich, so that the first combustion is performed. Even if the air-fuel ratio A / F is made rich in order to release NO _x from the NO _x absorbent 22 during this time, soot is not generated at this time. Next, at time t ₁ , when the required load L exceeds the first boundary X (N), the first combustion is switched to the second combustion. Second as shown in FIG.
When the combustion is being performed, the air-fuel ratio A / F becomes considerably lean. The amount of NO _x generated is larger when the second combustion is being performed than when the first combustion is being performed. Therefore, when the second combustion is being performed, the NO _x amount ΣNOX is relatively rapid. Rise to.

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 while the second combustion is being performed. Thus the air-fuel ratio in order to release the NO _x from _the NO _x absorbent 22 as absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1 when the second combustion is being performed as shown in FIG. 17 A / F is not considered rich.
Required load L as at time t ₂ of FIG. 17 in this case is second of the NO _x absorbent 22 when it is switched from the second combustion is lower in the first combustion of the boundary Y (N) The air-fuel ratio A / F is temporarily made rich in order to release NO _x from.

Next, it is assumed that the first combustion is switched to the second combustion at time t ₃ in FIG. 17, and the second combustion is continued for a while. The time of absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1, then in the second half or the exhaust stroke of the expansion stroke so as to release the NO _x assuming that exceeds the allowable maximum value MAX2 at time t ₄ at this time from _the NO _x absorbent 22 Is injected with additional fuel to make the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 22 rich.

The additional fuel injected during the latter half of the expansion stroke or during the exhaust stroke does not contribute to the generation of engine output, so it is preferable to minimize the opportunity to inject the additional fuel. Therefore, when the NO _x absorption amount ΣNOX exceeds the allowable maximum value MAX1 when the second combustion is performed, the second
The air-fuel ratio A /
F is temporarily made rich, and additional fuel is injected only in a special case where the NO _x absorption amount ΣNOX exceeds the maximum allowable value MAX2.

Next, referring to FIG. 18, the first combustion is performed.
NO when_xAbsorbent 22 to NO_xShould release
No_xThe air-fuel ratio of the exhaust gas flowing into the absorbent 22
The injection control in the case of turning off will be described. Shown in FIG.
NO when the first combustion is being performed as_xSucking
When the air-fuel ratio of the exhaust gas flowing into the absorbent 22 is made rich
If the throttle opening and EGR rate are not changed,
The fuel injection amount is shown in Fig. 10, which is determined by the operating state of the engine.
By increasing the injection quantity Q to be injected into the combustion chamber 5.
The air-fuel ratio A / F is made rich. That is, the air-fuel ratio is
(A / F)_LThe target air-fuel ratio when operating at
Air-fuel ratio (A / F)_RWhen the injection amount should be [(A
/ F)_L/ (A / F) _R] ・ Q. Shown in FIG.
If it is, the injection amount is set to (17/12) · Q.

On the other hand, when the first combustion is being performed
When ΣNOX> MAX1, that is, NO_xAbsorbent 2
NO absorbed in 2_xAmount is NO_xMaximum of absorbent 22
NO _xWhen the air-fuel ratio reaches 30% of the absorbed amount,
It is considered rich. NO at this time_xTotal NO from absorbent 22
_xThe amount of reducing gas required to release
And the amount of this reducing gas is Q_NOXIf so, an increase in the injection amount
Time t to continue using _rIs expressed by the following equation.

_Tr = C · Q _NOX / (ΔQ · N) ΔQ = [(A / F) _L / (A / F) _R ] · Q-[(A /
F) _L / (A / F) _ST ] · Q where C is a constant, N is the engine speed, and (A / F) _ST is the theoretical air-fuel ratio. That is, ΔQ represents the excess fuel amount, and the greater the excess fuel amount, the more time t _r.
Becomes shorter. Further, as the engine speed N increases, the amount of excess fuel supplied per unit time increases, so the time t _r
Becomes shorter. Thus the time t _r should continue to increase the action of the injection amount and will be expressed as the above equation.

[0076] On the other hand, release the NO _x from the NO _x absorbent 22 when it is switched to the first combustion from the second combustion becomes the .SIGMA.NOX> MAX1 when the second combustion is being performed as described above The air-fuel ratio is made rich in order to get it out. FIG. 19
Shows a change in the air-fuel ratio A / F when the injection amount increase amount ΔQ and the injection amount increase time continuation time _tr are calculated by the same method as that shown in FIG.

More specifically, for example, if the required load L becomes L _o lower than the second boundary Y (N) shown in FIG. 11 when the engine speed is N _o , the air-fuel ratio A
/ F, throttle opening ST and EGR control valve opening SE
Is a value determined from the required load L _o and the engine speed N _o in FIGS. 11, 12A and 12B, respectively. If the target air-fuel ratio at this time is (A / F) _L ,
9 is the target rich air-fuel ratio (A / F) _L based on this target air-fuel ratio (A / F) _L
F) shows the case of obtaining the injection amount Q and the time t _r should continue to increase the action of the injection amount required for the _R.

[0078] injection quantity = _{[(A / F) L / (} A / F) R ] _{· Q t r = C · Q} NOX / (ΔQ · N) air-fuel ratio A as is shown in FIG. 19 in this case The air-fuel ratio A / F does not become rich unless A / F does not decrease easily and the injection amount is increased for a while. That is, when combustion is performed under a lean air-fuel ratio, excess air is included in the exhaust gas discharged from the engine,
Therefore, at this time, E is recirculated in the engine intake passage.
The GR gas also contains excess air. The excess air contained in the EGR gas is again supplied into the combustion chamber 5, and thus the air-fuel ratio in the combustion chamber 5 is affected by the excess air in the EGR gas.

[0079] If should be released NO _x from the NO _x absorbent 22 when the first combustion is being performed as shown in FIG. 18, that is, the air-fuel ratio in order to release the NO _x from the NO _x absorbent 22 When the lean degree of the lean air-fuel ratio immediately before the start of the switching operation of is small, the amount of excess air contained in the EGR gas is small. Therefore, in this case, the air-fuel ratio in the combustion chamber 5 is in the EGR gas. Almost unaffected by excess oxygen. Therefore, in this case, as shown in FIG. 18, if the injection amount is increased by an amount required to make the lean air-fuel ratio a predetermined rich air-fuel ratio, the air-fuel ratio of the exhaust gas immediately becomes a predetermined rich air-fuel ratio. It becomes an air-fuel ratio, thus NO _x
Immediately NO _x from the absorbent 22 is to be released.

[0080] In contrast, when to release the NO _x from the NO _x absorbent 22 when it is switched from the second combustion to the first combustion, that in order to release the NO _x from the NO _x absorbent 22 empty When the lean degree of the lean air-fuel ratio immediately before the start of the fuel ratio switching operation is large, the amount of excess air contained in the EGR gas is large. Therefore, in this case, the lean air-fuel ratio is set to a predetermined rich air-fuel ratio. Even if the injection amount is increased by an amount necessary to obtain the air-fuel ratio A /
F does not immediately become a predetermined rich air-fuel ratio,
The air-fuel ratio A / F will not become rich unless it is done for a while.

The hatching in FIGS. 18 and 19
Area shown is NO_xReduction gas sent to the absorbent 22
This is the amount of time, and in the case shown in FIG.
The original gas amount is NO shown in FIG._xAll from absorbent 22
NO_xConsiderably less than the amount of reducing gas required to release
You can see that it will be less. Therefore, the first embodiment according to the present invention
Then, for example, if the engine speed is N_oThe required load is L_o
And the second combustion is switched to the first combustion.
When NO_xAbsorbent 22 to NO_xAir-fuel ratio A to release
When temporarily making / F rich, in FIG.
The amount of reducing gas is approximately the same as the amount of reducing gas indicated by hatching.
NO _xShown in FIG. 20 for delivery to absorbent 22.
Engine speed is N_oAnd the required load is L_oBut
To increase the injection amount when the first combustion is being performed.
In comparison, the amount of increase in the injection amount is increased.

Specifically, when the second combustion is switched to the first combustion, the lean air-fuel ratio (A / F) _L and the target rich air-fuel ratio (A / F) _R immediately before the air-fuel ratio switching action is obtained. The injection amount is calculated by the following equation based on the ratio of Injection amount = [(A / F) _L / (A / F) _R ] .Q Next, the injection amount is gradually reduced so that the rich air-fuel ratio matches the target air-fuel ratio (A / F) _R as much as possible.

On the other hand, as described above, when ΣNOX> MAX2 while the second combustion is being performed, additional fuel is injected in the latter half of the expansion stroke or during the exhaust stroke.
Additional fuel quantity and injection period of additional fuel at this time is set to Okurikomeru necessary reducing gas to release all NO _x absorbed in _the NO _x absorbent 22 in _the NO _x absorbent 22 ing.

FIG. 21 shows a processing routine of the NO _x releasing flag which is set when NO _x should be released from the NO _x absorbent 22, and this routine is executed by interruption every fixed time. Referring to FIG. 21, first, at step 100, it is judged if the flag I indicating that the engine operating region is the first operating region I is set or not. When the flag I is set, that is, when the engine operating region is the first operating region I, the routine proceeds to step 101, where the NO _x absorption amount A per unit time is calculated from the map shown in FIG. 16 (A). It Next, at step 102, A is added to the NO _x absorption amount ΣNOX. Next, at step 103, it is judged if the NO _x absorption amount ΣNOX exceeds the allowable maximum value MAX1. ΣN
Becomes the OX> MAX1 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, when it is determined in step 100 that the flag I is reset, that is, when the engine operating region is the second operating region II, step 106 is executed.
Then, the NO _x absorption amount B per unit time is calculated from the map shown in FIG. 16 (B). Next, at step 107, the NO _x absorption amount ΣNOX is added to B. Next, at step 108, the NO _x absorption amount ΣNOX is the allowable maximum value MA.
It is determined whether or not X1 has been exceeded. ΣNOX> MAX1
Advances to become the step 109, NO _x releasing flag 2 indicating that it should release the NO _x is set when it is switched from the second combustion to the first combustion.

On the other hand, at step 110, it is judged if the NO _x absorption amount ΣNOX exceeds the allowable maximum value MAX2. Becomes a .SIGMA.NOX> MAX2 proceeds to step 111, is set _the NO _x releasing flag 3 indicating that it should release the NO _x late or during the exhaust stroke of the expansion stroke. Next, the operation control will be described with reference to FIG.

Referring to FIG. 22, first, at step 200, it is judged if the flag I indicating that the engine operating condition is the first operating region I is set or not. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, step 2
The routine proceeds to 01, where it is judged if 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, at step 203, the target opening degree ST of the throttle valve 25 is calculated from the map shown in FIG. 12 (A), and the opening degree of the throttle valve 25 is made this target opening degree ST. Next, at step 204, the target opening degree SE of the EGR control valve 29 is calculated from the map shown in FIG.
The opening degree of the EGR control valve 29 is set to this target opening degree SE.
Next, at step 205, it is judged if the NO _x releasing flag 1 is set. When the NO _x release flag 1 is not set, the routine proceeds to step 206, where N
It is determined whether the O _x release flag 2 is set. When the NO _x release flag 2 is not set, the routine proceeds to step 207, where fuel injection is performed so that the air-fuel ratio shown in FIG. 11 is obtained. At this time, low temperature combustion is performed under a lean air-fuel ratio.

On the other hand, when it is judged at step 205 that the NO _x releasing flag 1 is set, the routine proceeds to step 208, where the injection control I shown in FIG. 23 is performed. On the other hand, when it is determined at step 206 that the NO _x release flag 2 is set, the routine proceeds to step 209, where the injection control II shown in FIG. 24 is performed.

On the other hand, in step 201, L> X
When it is determined that (N) has been reached, the routine proceeds to step 202, where the flag I is reset, and then step 212
Then, the second combustion is performed. That is, step 212
Then, the target opening degree ST of the throttle valve 25 is calculated from the map shown in FIG. 14 (A), and the opening degree of the throttle valve 25 is set to this target opening degree ST. Next, at step 213, the target opening degree SE of the EGR control valve 29 is calculated from the map shown in FIG. 14 (B), and the opening degree of the EGR control valve 29 is made this target opening degree SE. Next, at step 214, it is judged if the NO _x releasing flag 3 is set or not. N
When the _Ox release flag 3 is not set, the routine proceeds to step 215, where fuel injection is performed so that the air-fuel ratio shown in FIG. 13 is obtained. At this time, the second combustion is performed under the lean air-fuel ratio.

On the other hand, when it is judged at step 214 that the NO _x releasing flag 3 is set, the routine proceeds to step 214, where the injection control III shown in FIG. 25 is performed. Next, the injection control 1 will be described with reference to FIG. Referring to FIG. 23, first, step 300
At, it is determined whether or not the rich flag is set. When the rich flag is not set, the routine proceeds to step 301, where the injection amount Q _o is calculated based on the following equation.

Q _o = [(A / F) _L / (A / F) _R ] · Q where (A / F) _L is the current lean air-fuel ratio, and (A / F) _R is the target It shows the rich air-fuel ratio, and Q
Shows the injection amount shown in FIG. 10 according to the operating state of the engine. Next, at step 302, the excess injection amount ΔQ is calculated based on the following equation.

ΔQ = [(A / F) _L / (A / F) _R ].
Q-[(A / F) _L / (A / F) _ST ] · Q where (A / F) _ST represents the theoretical air-fuel ratio. Next, at step 303, the time t _r for continuing the injection amount increasing action is calculated based on the following equation.

_Tr = C · Q _NOX / (ΔQ · N) where C is a constant, and Q _NOX is the NO _x absorbent 2
Shows 30% of the amount of NO _x maximum absorption of NO _x of 2, N shows the engine rotational speed. Next, at step 304, the rich flag is set. Rich flag whether the elapsed time t after injection control I start progressing when set from step 300 to step 305 exceeds the time t _r is determined. When t> t _r , step 30
6, the rich flag is reset, then the NO _x release flag 1 is reset in step 307,
Next, at step 308, ΣNOX is made zero.
Therefore NO When _x releasing flag 1 is set injection quantity as shown in FIG. 18 is made to increase over time t _r, the total NO which has been absorbed in the NO _x absorbent 22 during this time
_x is emitted.

Next, the injection control II will be described with reference to FIG. Referring to FIG. 24, first, step 4
At 00, it is determined whether or not the rich flag is set. When the rich flag is not set, the routine proceeds to step 401, where the injection amount Q _o is calculated based on the following equation. Q _o = [(A / F) _L / (A / F) _R ] ・ Q where (A / F) _L represents the lean air-fuel ratio immediately before the switching from the second combustion to the first combustion. , (A / F)
_R indicates the target rich air-fuel ratio, and Q indicates the injection amount shown in FIG. 10 according to the operating state of the engine.

Next, at step 402, the excess injection amount ΔQ is calculated based on the following equation. ΔQ = [(A / F) _L / (A / F) _R ] ・ Q-[(A /
F) _L / (A / F) _ST ] · Q where (A / F) _ST indicates the theoretical air-fuel ratio.

[0097] Then the time t _r should continue to increase the action of the injection quantity based on the following equation at step 403 is calculated. _{t r = C · Q NOX /} (ΔQ · N) where C denotes a constant, Q _NOX is _the NO _x absorbent 2
Shows 30% of the amount of NO _x maximum absorption of NO _x of 2, N shows the engine rotational speed.

Next, at step 404, the rich flag is set. Then constant-injection amount Q _b of the second half increased action shown in FIG. 20 is calculated based on the following equation at step 405. Q _b = _{[(A / F) L / (} A / F) R ] · Q where (A / F) _L is shows a lean air-fuel ratio after being switched to the first combustion from the second combustion There is.

When the rich flag is set, step 4
From 00 to step 406, the injection amount Q_oTo a constant value
α is subtracted. Next, at step 407, the injection amount Q_o
Is Q _bIt is determined whether or not it has become smaller than. Q_o<
Q_bWhen is, proceed to step 408 and Q_bIs Q
_oIt is said that Next, in step 409, injection control II starts
Later elapsed time t is time t_rIt is determined whether or not
It t> t_rIf so, proceed to step 410
Lag is reset, then N in step 411
O_xRelease flag 2 is reset, then step 41
At 2, ΣNOX is made zero. Therefore NO_xEmission
When the lug 2 is set, as shown in Fig. 20, the injection amount
Is rapidly increased and then gradually decreased,
Then increased constant injection quantity Q_bHeld in. injection
NO while the quantity is being increased_xAbsorbed in absorbent 22
All NO that had been done _xIs released.

Next, the injection control III will be described with reference to FIG. Referring to FIG. 25, first, at step 500, the injection amount Q shown in FIG. 10 is calculated,
At this time, combustion is performed with the lean air-fuel ratio shown in FIG. Next, at step 501, it is judged if the rich flag is set. When the rich flag is not set, the routine proceeds to step 502, where the additional injection amount Q _add is calculated based on the following equation.

Q _add = [(A / F) _L / (A / F) _R ] · Q where (A / F) _L represents the current lean air-fuel ratio, and (A / F) _R is the target It shows the rich air-fuel ratio, and Q
Shows the injection amount shown in FIG. 10 according to the operating state of the engine. Next, at step 503, the excess injection amount ΔQ is calculated based on the following equation.

ΔQ = [(A / F) _L / (A / F) _R ].
Q-[(A / F) _L / (A / F) _ST ] · Q where (A / F) _ST represents the theoretical air-fuel ratio. Then time should continue to increase the action of the injection quantity t _r is calculated based on the following equation at step 504.

T_r= C ・ Q_NOX/ (ΔQ ・ N) Where C is a constant and Q_NOXIs NO_xAbsorbent 2
2 maximum NO_x80% NO absorbed_xQuantity
And N indicates the engine speed. Then step
At 505, the rich flag is set. Rich flag
Is set, step 501 to step 506
The elapsed time t after the start of injection control III is the time t_rOver
It is determined whether or not it has been obtained. t> t _rThen step 5
07, the rich flag is reset, then
No in 508_xRelease flag 2 and NO_xRelease
The output flag 3 is reset, and then in step 509.
And ΣNOX is made zero. Therefore NO_xRelease flag 3
When is set time t_rFuel Q across_addBut
Injected, NO during this_xIt was absorbed by the absorbent 22
All NO_xIs released.

FIG. 26 shows the switching from the second combustion to the first combustion.
NO when replaced_x24 for performing the release action of
2 shows another embodiment of the injection control II shown in FIG. this
In the second embodiment, for example, the engine speed is N_oRequest when
Load is L_oAnd switch from the second combustion to the first combustion
And then NO_xAbsorbent 22 to NO _xShould release
When the air-fuel ratio A / F is temporarily made rich,
8 is almost the same as the amount of reducing gas indicated by hatching
NO amount of reducing gas_xSo that it can be sent to the absorbent 22,
Engine speed is N_oAnd the required load is L_oSo the first
The duration of the action of increasing the injection amount when combustion is taking place
t_rIs Δt_rCan only be increased.

This Δt _r represents the time until the air-fuel ratio becomes an intermediate value between the target rich air-fuel ratio and the stoichiometric air-fuel ratio after switching from the second combustion to the first combustion, and this time Δt _{r As} shown in FIG. 27, _r increases as the lean degree of the lean air-fuel ratio immediately before the air-fuel ratio is switched increases. Next, referring to FIG. 28, the second of the injection control II
Examples will be described.

Referring to FIG. 28, first, step 6
At 00, it is determined whether or not the rich flag is set. When the rich flag is not set, the routine proceeds to step 601, where the injection amount Q _o is calculated based on the following equation. Q _o = [(A / F) _L / (A / F) _R ] ・ Q where (A / F) _L represents the lean air-fuel ratio immediately before the switching from the second combustion to the first combustion. , (A / F)
_R indicates the target rich air-fuel ratio, and Q indicates the injection amount shown in FIG. 10 according to the operating state of the engine.

Next, at step 602, the excess injection amount ΔQ is calculated based on the following equation. ΔQ = [(A / F) _L / (A / F) _R ] ・ Q-[(A /
F) _L / (A / F) _ST ] · Q where (A / F) _ST indicates the theoretical air-fuel ratio. Next, at step 603 continues time t _r of increasing the action of the injection quantity based on the following equation is calculated.

_Tr = CQ _NOX / (ΔQN) where C is a constant, and Q _NOX is the NO _x absorbent 2
Shows 30% of the amount of NO _x maximum absorption of NO _x of 2, N shows the engine rotational speed. Then extension time Delta] t _r continuation time t _r of increasing the action of the injection amount is calculated from the relationship shown in step 604 FIG. 27. Then final continuing time t _r is calculated by adding the extension time Delta] t _r in step 605 continues time t _r. Next, at step 606, the rich flag is set.

Step 60 where the rich flag is set
From 0 to step 607, progress after injection control II starts
Time t is continuation time t_rIt is determined whether or not the value exceeds. t
> T _rIf so, the routine proceeds to step 608, where the rich flag is
Reset, then NO in step 609_xRelease
Output flag 2 is reset, and then step 610 is performed.
And ΣNOX is made zero. Therefore NO_xRelease flag 2
When is set, the injection amount becomes as shown in FIG.
Increase over a longer period than shown in
NO while the injection amount is being increased_xAbsorbent 2
All NO absorbed in 2_xIs released.

FIG. 29 is a graph for carrying out the NO _x releasing action when the second combustion is switched to the first combustion.
5 shows another embodiment of the injection control II shown in FIG.
In the third embodiment, the first combustion is performed once when the second combustion is switched to the first combustion, and the air-fuel ratio is made rich after the time Δt _r is exceeded after the first combustion is switched. I am trying to do it. This time Δt _r is almost the same as Δt _r shown in FIG. 26. Therefore, the time Δt _r shown in FIG. 29 also shows the lean degree of the lean air-fuel ratio immediately before the air-fuel ratio is switched as shown in FIG. The larger it gets, the bigger it gets.

Next, referring to FIG. 30, the third of the injection control II
Examples will be described. Referring to FIG. 30, first, at step 700, it is judged if the rich flag is set or not. When the rich flag is not set, the routine proceeds to step 701, where Δt _r is calculated from the relationship shown in FIG. Next, at step 702, it is judged if the elapsed time t after the start of injection control II has become larger than Δt _r . When t ≦ Δt, the routine proceeds to step 703, where the injection amount Q is calculated based on FIG.
At this time, the first combustion is performed.

When it is judged at step 702 that t> Δt _r , the routine proceeds to step 704, where the injection amount Q _o is calculated based on the following equation. Q _o = [(A / F) _L / (A / F) _R ] ・ Q where (A / F) _L is the current lean air-fuel ratio, and (A / F) _R is the target rich air-fuel ratio. And Q
Shows the injection amount shown in FIG. 10 according to the operating state of the engine.

Next, at step 705, the excess injection amount ΔQ is calculated based on the following equation. ΔQ = [(A / F) _L / (A / F) _R ] ・ Q-[(A /
F) _L / (A / F) _ST ] · Q where (A / F) _ST indicates the theoretical air-fuel ratio. Then time should continue to increase the action of the injection quantity t _r is calculated based on the following equation at step 706.

T_r= C ・ Q_NOX/ (ΔQ ・ N) Where C is a constant and Q_NOXIs NO_xAbsorbent 2
2 maximum NO_x30% NO of absorbed amount_xQuantity
And N indicates the engine speed. Then step
At 707, the rich flag is set. Rich flag
When is set, step 700 to step 708
The elapsed time t after the start of injection control II is the time t_rBeyond
Whether or not it is determined. t> t_rThen step 70
9, the rich flag is reset, then step
No in 710_xRelease flag 2 is reset,
Next, at step 711, ΣNOX is made zero.
Therefore NO_xWhen the emission flag 2 is set, it is shown in FIG.
Was switched from the second combustion to the first combustion as
Sometimes the first combustion takes place for some time, then the air-fuel ratio
The injection amount is increased to make the fuel rich. Injection quantity
NO while being increased_xAbsorbed by the absorbent 22
All NO _xIs released.

FIG. 31 shows another embodiment of the compression ignition type internal combustion engine. In this embodiment, in order to oxidize unburned hydrocarbons better, at the outlet of the exhaust manifold 19, that is, NO
A catalyst converter 36 having a catalyst 35 having an oxidizing function such as a three-way catalyst or an oxidation catalyst is arranged in the exhaust passage upstream of the _x absorbent 22.

[0116]

Effect of the Invention NO _x good absorbent air-fuel ratio in order to release the NO _x from the from _the NO _x absorbent regardless of the lean degree of the lean air-fuel ratio immediately before is switched to the rich NO _x
Can be released.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing a fuel molecule.

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

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

FIG. 7 is a diagram showing a first operating region I and a second operating region II.

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

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

FIG. 10 is a diagram showing a map of an injection amount.

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

FIG. 12 is a diagram showing a map of a target opening degree of a throttle valve or the like.

FIG. 13 is a diagram showing an air-fuel ratio in the second combustion.

FIG. 14 is a diagram showing a target opening of a throttle valve or the like.

FIG. 15 is a diagram for explaining the action of releasing NO _x .

FIG. 16 is a diagram showing a map of the amount of NO _x absorbed per unit time.

FIG. 17 is a diagram for explaining NO _x release control.

FIG. 18 is a diagram showing changes in the injection amount and changes in the air-fuel ratio when switching from the lean air-fuel ratio to the rich air-fuel ratio.

FIG. 19 is a diagram showing changes in the injection amount and changes in the air-fuel ratio when switching from the lean air-fuel ratio to the rich air-fuel ratio.

FIG. 20 is a diagram showing changes in the injection amount and changes in the air-fuel ratio when switching from the lean air-fuel ratio to the rich air-fuel ratio.

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

FIG. 22 is a flowchart for controlling the operation of the engine.

FIG. 23 is a flowchart for executing injection control I.

FIG. 24 is a flowchart for executing injection control II.

FIG. 25 is a flow chart for executing injection control III.

FIG. 26 is a diagram showing changes in the injection amount and changes in the air-fuel ratio when switching from the lean air-fuel ratio to the rich air-fuel ratio.

FIG. 27 is a diagram showing the relationship between the lean air-fuel ratio (A / F) _L and the time Δt _r immediately before switching to the rich air-fuel ratio.

FIG. 28 is a flow chart for executing a second embodiment of injection control II.

FIG. 29 is a diagram showing changes in the injection amount and changes in the air-fuel ratio when switching from the lean air-fuel ratio to the rich air-fuel ratio.

FIG. 30 is a flowchart for executing a third embodiment of injection control II.

FIG. 31 is an overall view showing another embodiment of the compression ignition type internal combustion engine.

[Explanation of symbols]

6 ... Fuel injection valve 22 ... NO _x absorbent 25 ... Throttle valve 29 ... EGR control valve

Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01N 3/08 F01N 3/08 B 3/24 3/24 C ER S 3/36 3/36 B F02D 21/08 301 F02D 21/08 301D 41/02 380 41/02 380E F02M 25/07 550 F02M 25/07 550R (56) Reference JP-A-8-218918 (JP, A) JP-A-6-294319 (JP, A) JP-A-7 -145725 (JP, A) JP-A-9-287527 (JP, A) JP-A-9-287528 (JP, A) JP-A-8-226332 (JP, A) JP-A-8-86251 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02B 1/00-23/06 F02D 41/00-45/00 F01N 3/00-3/36 F02M 25/07

Claims (14)

(57) [Claims] 1. An exhaust gas recirculation device for recirculating exhaust gas discharged into the engine exhaust passage into the engine intake passage, wherein the exhaust gas recirculates into the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean. A NO _x absorbent that absorbs the contained NO _x and releases the absorbed NO _{x when} the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich is arranged in the engine exhaust passage, and under the lean air-fuel ratio. temporarily rich air-fuel ratio and when to release the NO _x from the NO _x absorbent to increase the amount of fuel injection when the combustion is being performed, thereby required to release the NO _x from the NO _x absorbent In an internal combustion engine in which a predetermined amount of reducing gas is sent to the NO _x absorbent, NO _{x is} recirculated during exhaust gas recirculation.
To continue increasing the amount of injected fuel, the increase effect of the injected fuel on the basis of the lean air-fuel ratio immediately before the start air-fuel ratio switching action when switching the air-fuel ratio in order to release the NO _x from the absorbent from lean air-fuel ratio to a rich air-fuel ratio A lean air-fuel ratio immediately before the start of the air-fuel ratio switching action at a certain engine load and engine speed is provided, which is provided with injection control means for controlling at least one of the start time of the increasing action of time or injected fuel. If it is larger than the air-fuel ratio, the above-mentioned certain amount can be sent so that the predetermined amount of the reducing gas can be sent to the NO _x absorbent even if the decreasing speed of the air-fuel ratio of the exhaust gas immediately after the start of the air-fuel ratio switching action is slow. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation at the same engine load and engine speed as the engine load and engine speed is smaller than the predetermined air-fuel ratio, An internal combustion engine adapted to change at least one of an increasing amount of injected fuel, a time for continuing the increasing action of injected fuel, and a start timing of the increasing action of injected fuel. 2. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation is smaller than the predetermined air-fuel ratio, the air-fuel ratio is maintained at the predetermined rich air-fuel ratio immediately after the start of the air-fuel ratio switching operation. The fuel injection amount is increased by a necessary amount, and the action of increasing the fuel injection amount is continued for a period required for sending the predetermined amount of reducing gas into the NO _x absorbent. Internal combustion engine according to. 3. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action at a certain engine load and engine speed is larger than a predetermined air-fuel ratio, the certain engine load and the same engine load as the engine speed. The internal combustion engine according to claim 1, wherein the amount of increase in injected fuel is increased as compared with the case where the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action at the engine speed is smaller than the predetermined air-fuel ratio. 4. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation is larger than the predetermined air-fuel ratio, the increase amount of the injected fuel is increased as the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation becomes larger. The internal combustion engine according to claim 3. 5. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation at a certain engine load and engine speed is larger than a predetermined air-fuel ratio, the certain engine load and the same engine load as the engine speed. The internal combustion engine according to claim 1, wherein the time period for continuing the increasing action of the injected fuel is lengthened as compared with the case where the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action at the engine speed is smaller than the predetermined air-fuel ratio. organ. 6. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action is greater than the predetermined air-fuel ratio, the time for continuing the increasing action of the injected fuel as the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action increases. The internal combustion engine according to claim 5, wherein the length is increased. 7. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching operation at a certain engine load and engine speed is larger than the predetermined air-fuel ratio, the air-fuel ratio is predetermined for a predetermined period. The internal combustion engine according to claim 1, wherein the lean air-fuel ratio is made smaller than the fuel ratio, and then the air-fuel ratio is switched to rich. 8. When the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action is larger than the predetermined air-fuel ratio, the predetermined period is lengthened as the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action increases. The internal combustion engine according to claim 7, wherein 9. When the internal combustion engine increases the amount of recirculated exhaust gas supplied to the combustion chamber, the amount of soot generated gradually increases and reaches a peak, and the amount of recirculated exhaust gas supplied to the combustion chamber is increased. As the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it become lower than the soot generation temperature as it further increases, it consists of a compression ignition type internal combustion engine in which soot is hardly generated, and the soot generation peaks. The first combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is larger than the amount of recirculated exhaust gas and the air-fuel ratio is smaller than the predetermined air-fuel ratio and the soot generation amount reaches a peak. Switching means for selectively switching between second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of circulating gas and the air-fuel ratio is larger than the predetermined air-fuel ratio, and a NO _x absorbent To NO
and a determination means for determining whether or not _x should be released,
NO from the NO _x absorbent when the second combustion is taking place
When it is determined that _x should be released, the air-fuel ratio is temporarily made rich when the second combustion is switched to the first combustion, and at this time, the lean air-fuel ratio immediately before the start of the air-fuel ratio switching action is The internal combustion engine according to claim 1, wherein the internal combustion engine has a ratio greater than a predetermined air-fuel ratio. 10. NO when the first combustion is being performed
The internal combustion engine according to claim 9, wherein when it is determined that NO _x should be released from the _x absorbent, the fuel injection amount is increased and the air-fuel ratio is temporarily made rich. 11. NO_xNO absorbed in the absorbent_x
The second combustion is carried out with the estimation means for estimating the quantity.
NO estimated by the estimation means when _xQuantity in advance
When the first maximum allowable value is exceeded, the second fuel
When the combustion is switched to the first combustion, the air-fuel ratio is temporarily
Is considered to be rich in the
NO estimated by fixed means_xAmount is the first allowable maximum value
Greater than a predetermined second maximum allowable value greater than
Sometimes additional fuel is added later in the expansion stroke or during the exhaust stroke.
Inject and NO_xThe air-fuel ratio of the exhaust gas flowing into the absorbent is controlled.
10. The air-fuel ratio or the rich air-fuel ratio according to claim 9,
Internal combustion engine. 12. The internal combustion engine according to claim 9, wherein the exhaust gas recirculation rate in the first combustion state is approximately 55% or more. 13. The engine operating region is divided into a first operating region on the low load side and a second operating region on the high load side, and first combustion is performed in the first operating region to perform the second operating region. Second in the area
The internal combustion engine according to claim 9, wherein the combustion is performed. 14. The internal combustion engine according to claim 9, wherein a catalyst having an oxidizing function is arranged in the engine exhaust passage upstream of the NO _x absorbent.