JP2002070620A - Operation controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control an air-fuel ratio to a target air-fuel ratio. SOLUTION: An operation controller is provided with a switching means performing a switch between first combustion, in which soot is hardly generated because a recirculation emission gas amount fed into a combustion chamber 5 is higher than a recirculation emission gas amount generating peak amount of soot, and second combustion, in which the recirculation emission gas amount fed to the combustion chamber is lower than that generating a peak amount of soot, an air-fuel ratio sensor 27a arranged in an engine exhaust passage for detecting an air-fuel ratio, and a controlling means performing feedback control of the air-fuel ratio on the basis of an output value of the air-fuel ratio sensor so that the air-fuel ratio becomes a target ratio. When a rich air-fuel ratio is attained during the first combustion, output value correcting processing is carried out for correcting the output value of the air-fuel ratio sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an operation control device for an internal combustion engine.

[0002]

Internal combustion engines, in particular the engine exhaust passage and the engine intake passage in order to suppress the generation of the NO _x connected by an exhaust gas recirculation passage in a diesel engine, the exhaust gas through the exhaust gas recirculation passage There is a known technique for recirculating oil into an engine intake passage. Since the exhaust gas has a relatively high specific heat and can absorb a large amount of heat, the combustion temperature in the combustion chamber increases as the amount of exhaust gas recirculated into the engine intake passage (hereinafter referred to as "recirculated exhaust gas amount") increases. reduced, thus the generation amount of the NO _x is reduced. Thus generation of the but recirculated exhaust gas amount may be to reduce the generation amount of the NO _x when increasing the recirculated exhaust gas amount exceeds the certain limit soot begins to increase rapidly. For this reason, it has conventionally been considered that the amount of recirculated exhaust gas must be limited to an amount before the amount of soot generation starts to increase sharply in order to keep the amount of soot generation below a certain limit.

However, recent studies have shown that when the amount of recirculated exhaust gas is further increased, the soot generation gradually decreases after a certain peak. Therefore, the first operation in which the internal combustion engine is operated by increasing the recirculated exhaust gas amount to be larger than the recirculated exhaust gas amount at which the generation amount of soot becomes a peak, and the generation amount of soot becomes the peak at the recirculated exhaust gas amount There has been proposed an internal combustion engine that selectively switches between a second operation in which the internal combustion engine is operated with a smaller recirculation exhaust gas amount (Japanese Patent Laid-Open No. 11-36923).

[0004]

When the first operation is performed, the amount of recirculated exhaust gas is large and the amount of intake air is small, so that the air-fuel ratio is relatively small and close to the stoichiometric air-fuel ratio. Here, in order to control the air-fuel ratio to the stoichiometric air-fuel ratio, an air-fuel ratio sensor is disposed in the engine exhaust passage, the air-fuel ratio of the exhaust gas is detected by the air-fuel ratio sensor, and based on the detected air-fuel ratio of the exhaust gas. It is preferable to control the fuel injection amount. However, when the air-fuel ratio becomes rich while the first operation is being performed (hereinafter, during the first combustion / rich operation), part of the fuel is not completely burned but becomes methane, and thus the exhaust gas is exhausted. The amount of oxygen remaining in the gas increases. That is, even if the air-fuel ratio is the same, the oxygen concentration in the exhaust gas during the first combustion / rich operation tends to be higher than the oxygen concentration in the exhaust gas other than during the first combustion / rich operation. Here, when the air-fuel ratio sensor is a sensor that outputs an output value corresponding to the oxygen concentration in the exhaust gas, the air-fuel ratio sensor outputs an output value corresponding to an air-fuel ratio leaner than the actual air-fuel ratio. Becomes That is, the air-fuel ratio detected by the air-fuel ratio sensor shifts to the lean side. Here, even if the fuel injection amount is controlled based on the output value of the air-fuel ratio sensor, the air-fuel ratio cannot be controlled to the stoichiometric air-fuel ratio.

Such a problem occurs not only when the air-fuel ratio is maintained at the stoichiometric air-fuel ratio but also when the output value of the air-fuel ratio sensor is used to maintain the air-fuel ratio at a specific target air-fuel ratio. It is. Therefore, an object of the present invention is to perform 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 at which the generation amount of soot becomes a peak and soot is hardly generated. An object of the present invention is to enable the air-fuel ratio to be accurately controlled to the target air-fuel ratio even when the air-fuel ratio becomes rich.

[0006]

In the first aspect of the present invention, when the amount of recirculated exhaust gas supplied to the combustion chamber is increased to achieve the above object, 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 fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, and soot is hardly generated. In the first combustion, in which the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas at which the amount of soot generation peaks, soot is hardly generated, and the first combustion at which the amount of soot generation peaks, Switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of circulated exhaust gas, and an air-fuel ratio sensor disposed in the engine exhaust passage for detecting an air-fuel ratio And the second Control means for performing feedback control of the air-fuel ratio based on the output value of the air-fuel ratio sensor so that the air-fuel ratio becomes the target air-fuel ratio when the combustion is performed. When the air-fuel ratio becomes rich during the operation, an output value correction process for correcting the output value of the air-fuel ratio sensor is executed. That is, when the air-fuel ratio becomes rich during the first combustion, the output value of the air-fuel ratio sensor is corrected, and the air-fuel ratio is feedback-controlled based on the corrected output value.

In the second invention, in the first invention, the output value of the air-fuel ratio sensor is corrected so that the richer the air-fuel ratio, the smaller the output value of the air-fuel ratio sensor. According to a third aspect, in the first aspect, the output value of the air-fuel ratio sensor is corrected in the output value correction process so that the output value is reduced over the entire output range of the air-fuel ratio sensor.

According to a fourth aspect of the present invention, in the first aspect, an exhaust purification catalyst is disposed downstream of the air-fuel ratio sensor, and an air-fuel ratio sensor is disposed separately from the air-fuel ratio sensor downstream of the exhaust purification catalyst. Controlling the amount of recirculated exhaust gas so that the amount of recirculated exhaust gas corresponds to the output value of the air-fuel ratio sensor on the upstream side of the exhaust purification catalyst when the first combustion is being performed; The recirculated exhaust gas amount is corrected based on a correction amount for the output value of the air-fuel ratio sensor downstream of the purification catalyst.

In a fifth aspect, in the fourth aspect, when the correction amount for the recirculated exhaust gas amount becomes larger than a predetermined amount, it is diagnosed that the exhaust purification catalyst has deteriorated.

[0010]

FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a supercharger, for example, an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Be linked. An inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17, and a throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17. A mass flow detector 21 for detecting the mass flow of the intake air is disposed in the air suction pipe 17 upstream of the throttle valve 20.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
The exhaust turbine 2 of the exhaust turbocharger 15 via the
3 and an outlet of the exhaust turbine 23 is connected via an exhaust pipe 24 to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function. Catalytic converter 26
An air-fuel ratio sensor (hereinafter, “upstream air-fuel ratio sensor”) 27a is disposed in the exhaust manifold 22 on the upstream side, and an air-fuel ratio sensor (hereinafter, downstream air-fuel ratio sensor) 27b is disposed downstream of the catalytic converter 26. Is done.

An exhaust pipe 28 connected to the outlet of the catalytic converter 26 and an air suction pipe 17 downstream of the throttle valve 20 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 29, and are connected to an EGR passage. An EGR control valve 31 driven by a step motor 30 is arranged in the inside 29. In the EGR passage 29, an intercooler 32 for cooling the EGR gas flowing in the EGR passage 29 is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water
The gas is cooled.

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

The electronic control unit 40 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the output signals of the upstream air-fuel ratio sensor 27a, the downstream air-fuel ratio sensor 27b, and the fuel pressure sensor 36 also correspond. AD converter 4
7 is input to the input port 45. 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 45 via the corresponding AD converter 47. . The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. on the other hand,
The output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EG via a corresponding drive circuit 48.
Step motor 30 for controlling R control valve and fuel pump 3
5 is connected.

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

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the EGR rate becomes 4
When the air-fuel ratio A / F becomes about 30% and the air-fuel ratio A / F becomes about 30, the amount of generated smoke starts to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of generated smoke rapidly increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more, and the air-fuel ratio A / F becomes about 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and N
The generation amount of O _x is considerably reduced. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3 (A) shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest. FIG. 3 (B) shows the air-fuel ratio A / F. The graph shows the change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) where the amount of generated smoke is almost zero, the amount of generated smoke is large.
It can be seen that the combustion pressure is lower than in the case shown in FIG.

The following can be said from the experimental results shown in FIGS. That is, first of all, the air-fuel ratio A / F is 1
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
Generation amount of the NO _x is considerably reduced, as shown in. NO
_The decrease in the generation amount of _x means that the combustion temperature in the combustion chamber 5 has decreased. Therefore, it can be said that the combustion temperature in the combustion chamber 5 is low when little soot is generated. . The same can be said from FIG.
That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low, and thus the combustion temperature in the combustion chamber 5 is low at this time.

Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, as shown in FIG.
O emission increases. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, so that a precursor of soot is formed. A soot consisting of a solid aggregate of atoms is produced. In this case, the actual soot generation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of soot generation becomes substantially 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 a state before the soot.

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

The temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature, depends on various factors such as the type of fuel and the compression ratio of the air-fuel ratio. Although the change can not be said that how many times since to define a certain degree from the amount of generated this certain temperature has a generation amount and the deep relationship between nO _x, therefore this certain temperature is nO _x be able to. That is, E
Fuel and gas temperature surrounding it at the time of combustion and higher GR rate increases is reduced, the amount of the NO _x is reduced. Generation amount at this time NO _x is soot is hardly generated when it is around or below 10 ppm. Therefore, the above certain temperature substantially matches the temperature when the amount of the NO _x becomes around or below 10 ppm.

Once soot has been produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with the catalyst having the oxidation function as described above, the hydrocarbon is discharged from the combustion chamber 5 in the state of the precursor of soot or in the state before it,
Alternatively, there is an extremely large difference as to whether to discharge from the combustion chamber 5 in the form of soot. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

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

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

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

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

FIG. 5 shows the relationship between the EGR rate and the smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, the curve A shows the case where the EGR gas is cooled strongly and the EGR gas temperature is maintained at approximately 90 ° C., and the curve B shows the case where the EGR gas is cooled by a small cooling device. Curve C shows 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 amount of soot generation peaks when the EGR rate is slightly lower than 50%, and in this case, the EGR rate becomes approximately 55%. Above a percentage, little soot is generated. On the other hand, when the EGR gas is slightly cooled as shown by the curve B in FIG.
The soot generation amount peaks at a level slightly higher than 0%, and in this case, soot is hardly generated when the EGR rate is set to approximately 65% or more.

As shown by the curve C in FIG. 5, when the EGR gas is not forcibly cooled, the amount of soot generation peaks near the EGR rate of 55%. If it is more than 70%, soot is hardly generated. FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load is reduced, the EGR rate at which the amount of soot is peaked slightly decreases, and the EGR rate at which soot is hardly generated is reduced. The lower limit also decreases slightly. Thus, soot is hardly generated.
The lower limit of the GR rate changes according to the degree of cooling of the EGR gas and the engine load.

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

Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is made lower than the temperature at which soot is formed. Necessary minimum EG
The R gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate, and is 70% or more in the embodiment shown in FIG. That is, the combustion chamber 5
In FIG. 6, the total amount of intake gas sucked into the fuel tank is indicated by a solid line X. When the ratio of the amount of air to the amount of EGR gas in the total amount of intake gas X is as shown in FIG. Gas temperature is lower than the temperature at which soot is generated, so that no soot is generated. In this case, the amount of generated NO _x is about 10 p.pm or less, and therefore, the amount of generated NO _x is extremely small.

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

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

However, as shown in FIG.
When the EGR gas is recirculated to the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15 through the line 9, the EGR rate is increased to 55% or more, for example, 70% in a region where the required load is larger than Lo. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which the soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the compressor 16 of the exhaust turbocharger 15
The EGR rate of the intake gas pressurized by the above also becomes 70%, so that the temperature of the fuel and the gas around it can be maintained at a temperature lower than the temperature at which soot is generated to the extent that the compressor 16 can pressurize the gas. Therefore, the operating range of the engine capable of causing low-temperature combustion can be expanded. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, the EGR control valve 31 is fully opened and the throttle valve 20 is slightly closed.

As described above, FIG. 6 shows the case where fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than that shown in FIG. 6, that is, the air-fuel ratio is made rich. Even so, while suppressing the generation of soot, the amount of generated NOx was reduced to 10 _p .
pm or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is lean from 17 to 18, the generation of soot is prevented. while the generation amount of the NO _x can be before, after, or less 10 ppm.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excess fuel does not grow to soot, and thus the soot is generated. Absent. The only occurs very little even at this time NO _x. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Further NO _x
Only very small amounts are generated.

As described above, when low-temperature combustion is performed, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. Sarezu, and the generation amount of the NO _x becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.

By the way, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, only when the engine is under low load operation where the calorific value due to combustion is relatively small. Can be Therefore, in the embodiment according to the present invention, during the low load operation in the engine, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas around it to a temperature lower than the temperature at which the growth of hydrocarbons stops halfway. In addition, at the time of engine high load operation, the second combustion, that is, the combustion that is conventionally performed normally is performed. Here, the first combustion, that is, the low temperature combustion, as is clear from the description so far, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the generation amount of soot is a peak, and almost no soot is generated. Combustion refers to combustion, which means that the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot generation peaks, which is the type of combustion that has been performed conventionally. Say

FIG. 7 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second operation region II in which the second combustion, that is, combustion by the conventional combustion method, is performed. I have. In FIG. 7, the vertical axis L represents the amount of depression of the accelerator pedal 50, that is, the required load, and the horizontal axis N
Indicates the engine speed. In FIG. 7, X (N)
Indicates a first boundary separating the first operating region I and the second operating region II, and Y (N) indicates a second boundary separating the first operating region I and the second operating region II. The border is shown. The determination of the change of the operation region from the first operation region I to the second operation region II is performed based on the first boundary X (N), and the change from the second operation region II to the first operation region I is performed. The determination of the change in the operating region is performed based on the second boundary Y (N).

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

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

By the way, when the operation region of the engine is in the first operation region I and low-temperature combustion is being performed, soot is hardly generated, and instead, the unburned hydrocarbon is converted into the precursor of soot or the state before it. It is discharged from the combustion chamber 5 in the form. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is oxidized well by the catalyst 25 having an oxidizing function. When the air-fuel ratio is feedback-controlled using two air-fuel ratio sensors as described later, it is preferable to use a three-way catalyst as the catalyst 25.

[0043] However it is also possible to use an oxidation catalyst or _the NO _x absorbent, as a catalyst 25. NO when the average air-fuel ratio is lean in _the NO _x absorbent is the combustion chamber 5
_It has a function of absorbing _x and releasing NOx when the average air-fuel ratio in the combustion chamber 5 becomes rich. This NO _x absorbent uses, for example, alumina as a carrier, and, for example, potassium K, sodium Na, lithium Li, cesium C
alkali metals such as s, barium Ba, calcium C
at least one selected from the group consisting of alkaline earths such as a, lanthanum La, and rare earths such as yttrium Y;
A noble metal such as t is carried. The oxidation catalyst as well, also having an oxidation function _the NO _x absorbent.

FIG. 8 shows the outputs of the air-fuel ratio sensors 27a and 27b. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 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. Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. FIG. 9 shows the opening degree of the throttle valve 20, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount with respect to the required load L. As shown in FIG. 9, in the first operation region I where the required load L is low, the throttle valve 20
The opening degree of the valve increases from almost fully closed to 2 as the required load L increases.
The opening degree of the EGR control valve 31 is gradually increased from near fully closed to fully open as the required load L increases. In the example shown in FIG. 9, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.

In other words, in the first operation region I, the EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

During the idling operation, the throttle valve 20 is closed to almost fully closed.
The valve 1 is also closed until it is almost fully closed. Throttle valve 20
When the valve is closed close to the fully closed state, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, when the operating state of the engine is in the first operating region I
From the second operation region II to the second operation region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, an EG that generates a large amount of smoke with an EGR rate
Since the engine jumps over the R rate range (see FIG. 5), a large amount of smoke does not occur when the operating state of the engine changes from the first operating area I to the second operating area II.

In the second operation region II, the conventional combustion is performed. In the second operating region II, the throttle valve 20 is held in a fully open state except for a part, and the opening of the EGR control valve 31 is gradually reduced as the required load L increases. In this operating region II, the EGR rate is equal to the required load L
Is higher, the air-fuel ratio is lower as the required load L is higher. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 10A shows the target air-fuel ratio A / F in the first operation region I. In FIG. 10A, A / F = 15.5, A / F = 16, A / F = 17,
Each curve indicated by A / F = 18 has a target air-fuel ratio of 15.
5, 16, 17, and 18, and the air-fuel ratio between the curves is determined by proportional distribution. FIG. 10 (A)
As shown in (1), the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the target air-fuel ratio A / F becomes leaner as the required load L decreases.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low-temperature combustion can be performed even if the EGR rate is reduced. When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 10A, as the required load L decreases, the target air-fuel ratio A / F increases. As the target air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the target air-fuel ratio A / F increases as the required load L decreases. . It should be noted that the target air-fuel ratio A / F shown in FIG. 10A is calculated in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.
It is stored in the OM42. The air-fuel ratio is shown in FIG.
The target opening ST of the throttle valve 20 required to obtain the target air-fuel ratio A / F shown in (A) is a function of the required load L and the engine speed N as shown in FIG. The target opening SE of the EGR control valve 31 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 10A is stored in the ROM 42 in advance in FIG. As shown, it is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.

FIG. 12A shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion according to the conventional combustion method is performed. Note that in FIG.
F = 24, A / F = 35, A / F = 45, A / F = 60
The curves indicated by are the target air-fuel ratios 24, 35, 45, and 6, respectively.
0 is shown. The target air-fuel ratio A / shown in FIG.
F is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. Further, the target opening ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 12A is equal to the required load L and the engine speed as shown in FIG. ROM in advance in the form of a map as a function of N
The EGR control valve 31 which is stored in 42 and is necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
As shown in FIG. 13 (B), the target opening degree SE is determined in advance in the form of a map as a function of the required load L and the engine speed N.
It is stored in the OM42.

When the second combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. Next, basic operation control of the internal combustion engine of this embodiment will be described with reference to FIG. Referring to FIG. 15, first, at step 100, it is determined whether or not a flag indicating that the operation state of the internal combustion engine is in the first operation region I is set. When it is determined in step 100 that the flag has been set, that is, when the operating state of the internal combustion engine is in the first operating state I, the routine proceeds to step 101, where the engine required load L exceeds the first boundary X (N). Is also larger (L> X (N)).

When it is determined in step 101 that L.ltoreq.X (N), the routine proceeds to step 103, where operation control I (ie, first combustion) is executed. That is, in step 103, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST, and the map shown in FIG. , The target opening SE of the EGR control valve 31 is calculated, and the opening of the EGR control valve 31 is set as the target opening SE. From the map shown in FIG.
F is calculated, and the target fuel injection amount Q is calculated based on the intake air amount Ga detected by the mass flow detector 21 so that the air-fuel ratio becomes the target air-fuel ratio A / F according to a fuel injection amount calculation method described later. The fuel of the target fuel injection amount Q is injected from the fuel injection valve 6.

When it is determined in step 101 that L> X (N), the routine proceeds to step 102, where the flag is reset. Then, the routine proceeds to step 106, where the operation control II (ie, the second combustion) is executed. That is, in step 106, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 20 is set to the target opening ST, and the map shown in FIG. , The target opening SE of the EGR control valve 31 is calculated, the opening of the EGR control valve 31 is set as the target opening SE, the target fuel injection amount Q is calculated from the map shown in FIG. , The fuel of the target fuel injection amount Q is injected.

Next, a method for calculating the fuel injection amount during the first combustion is described. In the following description, the exhaust air-fuel ratio means the air-fuel ratio of the exhaust gas,
The air-fuel ratio of the exhaust gas refers to the amount of air sucked into the combustion chamber 5 (including air supplied to the engine exhaust passage in a system capable of supplying air to the engine exhaust passage). (In a system in which fuel can be supplied to the engine exhaust passage, includes the fuel supplied to the engine exhaust passage).

When the upstream air-fuel ratio sensor 27a detects that the exhaust air-fuel ratio is leaner than the target air-fuel ratio, the air-fuel ratio is leaner than the target air-fuel ratio, and the fuel injection amount is gradually increased. The fuel ratio approaches the target air-fuel ratio. On the other hand, when the upstream air-fuel ratio sensor 27a detects that the exhaust air-fuel ratio is richer than the target air-fuel ratio, the air-fuel ratio is richer than the target air-fuel ratio, so that the fuel injection amount is gradually reduced, and the air-fuel ratio is reduced. To approach the target air-fuel ratio.

Further, in order to maintain the air-fuel ratio as a whole at the target air-fuel ratio, when it is detected that the air-fuel ratio has deviated from the target air-fuel ratio, the deviated air-fuel ratio should be made to approach the target air-fuel ratio as quickly as possible. Is preferred. Therefore, in this embodiment, the fuel injection amount to be reduced when the upstream air-fuel ratio sensor 27a detects that the air-fuel ratio has changed from lean to richer than the target air-fuel ratio, and the air-fuel ratio is richer than the target air-fuel ratio. And the fuel injection amount to be increased when the change from lean to lean is detected.
Correction is made based on the output value of 7b.

That is, the longer the period during which the downstream air-fuel ratio sensor 27b outputs lean than the stoichiometric air-fuel ratio (hereinafter, the lean output period), the longer the upstream air-fuel ratio sensor 2b.
At 7a, when it is detected that the air-fuel ratio has changed from rich to lean than the target air-fuel ratio, the fuel injection amount to be increased is increased. This is because the longer the lean output period, the more the air-fuel ratio deviates from the target air-fuel ratio toward the lean side. That is, the air-fuel ratio of the exhaust gas flowing out of the three-way catalyst should theoretically be the stoichiometric air-fuel ratio due to the oxygen absorption / release capability of the three-way catalyst. Still, when the lean output period is output for a long time, and when oxygen is supplied to the three-way catalyst that cannot be absorbed by the three-way catalyst,
That is, this is a case where the air-fuel ratio is largely shifted to the lean side from the target air-fuel ratio.

On the other hand, a period during which the downstream air-fuel ratio sensor 27b outputs rich (hereinafter, a rich output period).
The fuel injection amount to be decreased when the upstream air-fuel ratio sensor 27a detects that the air-fuel ratio has changed from lean to richer than the target air-fuel ratio is increased as the air-fuel ratio becomes longer. This is because the longer the rich output period, the more the air-fuel ratio deviates from the target air-fuel ratio to the rich side. That is, the air-fuel ratio of the exhaust gas flowing out of the three-way catalyst should theoretically be the stoichiometric air-fuel ratio due to the oxygen absorption / release capability of the three-way catalyst. Nevertheless, the case where the rich output period is still output for a long time means that the amount of oxygen supplied to the three-way catalyst is so small that all the oxygen absorbed by the three-way catalyst is released, that is, the air-fuel ratio is richer than the target air-fuel ratio. This is a case where it is greatly shifted to the side.

According to the present invention, by controlling the air-fuel ratio in this way, the air-fuel ratio can be maintained at the target air-fuel ratio as a whole. Next, an example of fuel injection control using the above-described fuel injection amount calculation method of the present invention will be described with reference to FIGS. Note that the flowcharts in FIGS. 16 to 18 show the case where the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

FIG. 16 is a flowchart for calculating the valve opening time TAU of the fuel injection valve necessary for injecting the target fuel injection amount. In FIG. 16, first, step 2
At 00, the intake air amount Ga / unit engine speed
N is calculated, and then in step 201, the basic fuel injection time TAUP is calculated according to the formula TAUP = α × Ga / N. Here, the basic fuel injection time TAUP is a fuel injection time required for setting a mixture of fuel and air supplied into the combustion chamber 5 to a target air-fuel ratio, and α is a constant.

Next, at step 202, the actual fuel injection time TAU is calculated by the formula TAU = TAUP × FAF × β × γ
Is calculated according to Here, FAF is an air-fuel ratio correction coefficient calculated according to a flowchart described later, and β,
γ is a constant determined according to the engine operating state.
Next, at step 203, the fuel injection time TAU is set, the fuel injection valve 6 is opened for the fuel injection time TAU, and the amount of fuel corresponding to the fuel injection time TAU is injected from the fuel injection valve 6.

FIG. 17 is a flowchart for calculating the air-fuel ratio correction coefficient FAF used in FIG. Referring to FIG. 17, first, at step 300, the air-fuel ratio feedback control is executed (F / B).
Is determined, that is, whether or not a condition that can execute the air-fuel ratio feedback control (hereinafter, a feedback execution condition) is satisfied. Here, the feedback execution conditions include, for example, that the air-fuel ratio sensor is activated, that the internal combustion engine has been completely warmed up, and that a predetermined time has elapsed since the fuel cut process for temporarily stopping fuel injection was canceled. And that it has passed. When it is determined in step 300 that F / B is being performed, the routine proceeds to step 301, where the output current IOM of the upstream air-fuel ratio sensor 27a is equal to or less than the reference output value I _R1 corresponding to the stoichiometric air-fuel ratio (IOM ≦ I _R1 ). Is determined. That is, it is determined whether the air-fuel ratio of the exhaust gas flowing into the catalyst 25 (hereinafter, the inflow exhaust air-fuel ratio) is leaner than the stoichiometric air-fuel ratio.

When it is determined in step 301 that IOM ≦ I _R1 , the routine proceeds to step 302, where it is determined whether or not the inflow exhaust air-fuel ratio has been reversed from rich to lean than the stoichiometric air-fuel ratio. When it is determined in step 302 that the inflow exhaust air-fuel ratio has just reversed from rich to lean than the stoichiometric air-fuel ratio, step 3
03, the air-fuel ratio correction coefficient FAF is increased by a skip increase amount R.
It is relatively large by SR and increases like a skip. On the other hand, if it is determined in step 302 that the inflow exhaust air-fuel ratio has not reversed from rich to lean than the stoichiometric air-fuel ratio, that is, if it is determined that the inflow exhaust air-fuel ratio has already been lean, the routine proceeds to step 305, where the air-fuel ratio correction coefficient FAF Is increased relatively small by a constant KIR. According to this, immediately after the inflow exhaust air-fuel ratio changes from rich to lean than the stoichiometric air-fuel ratio, the air-fuel ratio correction coefficient FAF is increased so that the lean degree of the inflow exhaust air-fuel ratio decreases in a skipping manner. The air-fuel ratio correction coefficient FAF is increased so that the lean degree of the exhaust air-fuel ratio decreases.

When it is determined in step 301 that IOM ≧ I _R1 , the routine proceeds to step 306, where it is determined whether or not the inflow exhaust air-fuel ratio has been inverted from lean to richer than the stoichiometric air-fuel ratio. When it is determined in step 306 that the inflow exhaust air-fuel ratio has just reversed from lean to richer than the stoichiometric air-fuel ratio, step 3
07, the air-fuel ratio correction coefficient FAF is set to the skip reduction amount R.
It is relatively large by SL and decreases like a skip. On the other hand, if it is determined in step 306 that the inflow exhaust air-fuel ratio has not been reversed from lean to rich than the stoichiometric air-fuel ratio, that is, if it is determined that the inflow exhaust air-fuel ratio has already been lean, the routine proceeds to step 308, where the air-fuel ratio correction coefficient FAF Is reduced relatively small by the constant KIL. According to this, immediately after the inflow exhaust air-fuel ratio becomes leaner to richer than the stoichiometric air-fuel ratio, the air-fuel ratio correction coefficient FAF is decreased so that the degree of enrichment of the inflow exhaust air-fuel ratio decreases in a skipping manner, and thereafter the inflow exhaust air-fuel ratio is reduced. The air-fuel ratio correction coefficient FAF is reduced so that the degree of richness of the exhaust air-fuel ratio is reduced.

In step 304, the air-fuel ratio correction coefficient F
Guard processing of the air-fuel ratio correction coefficient FAF is performed so that AF is between the allowable minimum value and the allowable maximum value. FIG. 18 shows the skip increase amount R used in the flowchart of FIG.
A flowchart for calculating the SR and the skip reduction amount RSL has been shown. Referring to FIG. 18, first, at step 400, it is determined whether or not F / B is being performed. The feedback execution condition here is a condition that the internal combustion engine is not in idle operation in addition to the condition in FIG. When it is determined in step 400 that the F / B is being performed, the process proceeds to step 401, where the output current IOS of the downstream air-fuel ratio sensor 27b is equal to or less than the output value I _R2 corresponding to the stoichiometric air-fuel ratio (IOS ≦ I _R2 ). It is determined whether or not it is.
That is, it is determined whether or not the air-fuel ratio of the exhaust gas flowing out of the catalyst 25 (hereinafter, the outflow exhaust air-fuel ratio) is leaner than the stoichiometric air-fuel ratio. In step 401, IOS ≦
If it is determined that it is I _R2 , the routine proceeds to step 402, where the skip increase amount RSR is increased by a predetermined amount ΔRS. On the other hand, the skip increase amount RSR is made to decrease by a predetermined amount ΔRS proceeds to step 405 when it is judged in step 401 IOS> is I _R2.

In step 403, the skip increment RSR
Is increased between the allowable minimum value and the allowable maximum value, and the skip increment RSR is guarded.
Then, the skip increase amount RSL is calculated by subtracting the skip increase amount RSR from 0.1. When the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio, I _R1 in the above-described flowchart is set to I _R1 + k, and when the target air-fuel ratio is richer than the stoichiometric air-fuel ratio, I _{R1 is set} to I If the above flowchart is executed with _R1 -k, the air-fuel ratio can be controlled to an air-fuel ratio different from the stoichiometric air-fuel ratio. Here, k is a positive value determined according to the lean degree or the rich degree of the target air-fuel ratio with respect to the stoichiometric air-fuel ratio.

By the way, recent research has revealed that if the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio during the above-described first combustion, some fuel does not completely burn and remains as methane. did. As described above, if the fuel is not completely burned, the amount of oxygen used for combustion decreases, and the oxygen concentration in the exhaust gas (hereinafter referred to as exhaust oxygen concentration) is higher than the exhaust oxygen concentration when the fuel is completely burned. Become. Therefore, when the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio during the first combustion (hereinafter, during the first combustion / rich operation), the output current value output from the air-fuel ratio sensor becomes the second current. It becomes larger than the output current value output from the air-fuel ratio sensor except during one combustion / rich operation. That is, the air-fuel ratio corresponding to the output current value I of the air-fuel ratio sensor is shifted to the lean side from the true air-fuel ratio as shown by the chain line in FIG. As described above, based on the output current value I of the air-fuel ratio sensor deviated to the lean side from the output current value I corresponding to the true air-fuel ratio according to the relationship shown by the solid line in FIG. 8 (the solid line in FIG. 19). Naturally, even if the fuel ratio is feedback controlled, the air-fuel ratio cannot be controlled to the target air-fuel ratio.

Therefore, in the present invention, during the first combustion / rich operation, the output current value I of the air-fuel ratio sensor is corrected so as to be reduced by a predetermined amount corresponding thereto, and based on the corrected output current value. The air-fuel ratio is determined according to the relationship shown in FIG. 8, and the above-described air-fuel ratio feedback control is executed based on the determined air-fuel ratio.
According to this, even during the first combustion / rich operation, the air-fuel ratio provided by the air-fuel ratio sensor represents the actual air-fuel ratio, so that the air-fuel ratio can be accurately controlled to the target air-fuel ratio.

According to another concept of the present invention, during the first combustion / rich operation, the air-fuel ratio is determined based on the output current value I of the air-fuel ratio sensor in accordance with the relationship shown by the chain line in FIG. The above-described air-fuel ratio feedback control is executed based on the air-fuel ratio. That is, FIG.
According to the relationship indicated by the chain line, the air-fuel ratio corresponding to the output current value I is calculated according to the relationship indicated by the solid line in FIG. 8 (solid line in FIG. 19) over the entire current value range that can be output by the air-fuel ratio sensor. The air-fuel ratio is corrected so as to be smaller than the calculated air-fuel ratio, that is, calculated so as to be shifted to the rich side.
According to this, even during the first combustion / rich operation, the air-fuel ratio provided by the air-fuel ratio sensor represents the actual air-fuel ratio, so that the air-fuel ratio can be accurately controlled to the target air-fuel ratio.

Further, by calculating the air-fuel ratio using the output current value of the air-fuel ratio sensor as described above, the air-fuel ratio range that can be detected by the air-fuel ratio sensor is widened to the rich side. That is, the air-fuel ratio sensor can also detect an air-fuel ratio having a greater richness. Therefore, even when the target air-fuel ratio is an air-fuel ratio having a large rich degree, the air-fuel ratio can be accurately controlled to the target air-fuel ratio. This can release the NO _x when a scene or a catalyst 25 for sulfur poisoning recovery process for recovering the poisoning of the catalyst 25 due to sulfur component S in the exhaust gas comprises a _the NO _x absorbent from _the NO _x absorbent there is an advantage to exhaust air-fuel ratio as a scene for performing _the NO _x releasing reduction treatment to reduce by at the scene to be rich. This is because, in such a case, the above-described processing must be performed in consideration of the following two points, and this is achieved because the air-fuel ratio sensor can detect an air-fuel ratio having a larger richness. .

That is, the first point to be considered is that the above two processes are not processes that are directly indispensable for improving the engine operation but are performed to maintain the purifying action of the catalyst 25, so that the engine operation is improved. period in terms of occupied shall executing the above two processes, i.e., the period that the exhaust air-fuel ratio rich is in that better short, second consideration is for the sulfur poisoning recovery and _the NO _x releasing reduction Even if fuel more than the minimum required amount is supplied to the catalyst 25, some of the fuel is wasted without being consumed by the catalyst 25. It is preferable to supply only a necessary amount of fuel. In order to satisfy these two considerations at the same time, it is necessary to supply the minimum necessary fuel to the catalyst 25 in the shortest possible time. To this end, the exhaust air-fuel ratio must be made richer and the exhaust air-fuel ratio must be accurately controlled to the target rich air-fuel ratio.
This can be achieved by the present invention in which the detectable range of the air-fuel ratio sensor is widened to a richer side. Thus to be able to secure and high fuel economy while maintaining the engine operation on favorable when executing a sulfur poisoning recovery process and _the NO _x releasing reduction treatment according to the present invention.

In the present invention, as described above, the first combustion
Using the phenomenon that the air-fuel ratio displayed by the air-fuel ratio sensor shifts to the lean side from the actual air-fuel ratio during the rich operation, the recovery completion timing of sulfur poisoning of the catalyst 25 is determined as follows. That is, as shown in FIG.
Sulfur (before time t ₁₎ before the step of recovering the poisoning, that is, in addition during the first combustion and the rich operation, or the output current of the second upstream-side air-fuel ratio sensor 27a in when combustion is being performed The value corresponds to the true air-fuel ratio, and the output current value of the downstream air-fuel ratio sensor 27b also corresponds to the true air-fuel ratio. Therefore, these air-fuel ratio sensors correspond to the output current value corresponding to the true air-fuel ratio. Of the output current value on the lean side (hereinafter referred to as lean-side deviation current amount) ΔI are substantially equal to zero.

Here, when the first combustion / rich operation is performed to recover the sulfur poisoning of the catalyst 25, the lean side deviation current ΔI of the upstream side air-fuel ratio sensor 27a becomes as shown by the solid line in FIG. Become larger. However, the lean side deviation current amount ΔI of the downstream side air-fuel ratio sensor 27b is
As shown by the dashed line in FIG. This is because the concentration of exhaust oxygen flowing into the catalyst 25 is high, but oxygen and methane in the exhaust gas
This is because the exhaust oxygen concentration consumed for the sulfur poisoning recovery reaction of No. 5 and thus flowing out of the catalyst 25 is not different from the exhaust oxygen concentration when the first combustion / rich operation is not performed. As long as the sulfur poisoning recovery reaction of the catalyst 25 continues, the lean-side deviation current amount ΔI of the downstream air-fuel ratio sensor 27b is substantially zero, and when the sulfur poisoning recovery reaction of the catalyst 25 ends, the oxygen in the exhaust gas is reduced. And the methane is no longer consumed, the lean side deviation current amount ΔI of the downstream air-fuel ratio sensor 27b also increases and becomes substantially equal to the lean side deviation current amount ΔI of the upstream side air-fuel ratio sensor 27a (time t ₂ ). Therefore, when the lean side deviation current amount ΔI of the downstream air-fuel ratio sensor 27b exceeds a predetermined value (for example, 70% of the lean side deviation current amount ΔI of the upstream side air-fuel ratio sensor 27a), the sulfur of the catalyst 25 is reduced. Judging that poisoning has been completed,
End rich operation.

In the present invention, as described above, the first combustion
Using the phenomenon that the air-fuel ratio displayed by the air-fuel ratio sensor shifts to the lean side from the actual air-fuel ratio during the rich operation, the deterioration of the catalyst 25 is diagnosed as follows. That is, as shown in FIG. 20B, when the catalyst 25 is deteriorated and the air-fuel ratio is made rich to recover the sulfur poisoning (at time t)
_{Also in 1} ), only a small amount of oxygen is consumed in the catalyst 25 to recover sulfur poisoning, and therefore, the lean side deviation current amount ΔI of the downstream air-fuel ratio sensor 27b is not maintained at zero, and FIG. B) As shown by the one-dot chain line, the current increases to, for example, about 50% of the lean side deviation current amount ΔI of the upstream air-fuel ratio sensor 27a. Therefore, when the air-fuel ratio is made rich to recover sulfur poisoning of the catalyst 25, the lean-side deviation current amount ΔI of the downstream air-fuel ratio sensor 27b
Is increased to a certain degree, it is diagnosed that the catalyst 25 has deteriorated.

As described above, in the present invention, when the first combustion is being performed, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 11B. Alternatively, the target opening degree SE of the EGR control valve 31 may be calculated as follows. That is, EGR is performed based on the output of the upstream air-fuel ratio sensor 27a.
The target opening SE of the control valve 31 is calculated, and the target opening SE is corrected based on the output of the downstream air-fuel ratio sensor 27b. At this time, the target opening degree SE is corrected so that the lean side deviation current amount ΔI of the downstream air-fuel ratio sensor 27b is maintained at a predetermined amount or a predetermined amount or more. Here, the fact that the lean side shift current amount ΔI is equal to or larger than the predetermined amount means that a sufficient amount of EGR gas is recirculated into the combustion chamber 5 and NO
It means that both _x generation amount and soot generation amount are small.
That is, if the target opening SE of the EGR control valve 31 is corrected so that the lean side deviation current amount ΔI of the downstream air-fuel ratio sensor 27b is maintained at a predetermined amount or more as in the present embodiment, NO _x
The amount of generation and the amount of soot generation can be extremely reduced.

In the present invention, when the target opening SE of the EGR control valve 31 is corrected so that the lean side deviation current amount ΔI of the downstream side air-fuel ratio sensor 27b becomes equal to or more than a predetermined amount, the correction amount is not limited. When it is larger than the fixed amount, it is diagnosed that the catalyst 25 is deteriorated. Here, when the correction amount is larger than the predetermined amount, the oxygen absorbing ability of the catalyst 25 is reduced, that is, the catalyst 25 is deteriorated, and thus the amount of oxygen consumed by the catalyst 25 is reduced. It means flowing out of the catalyst 25. Therefore, it can be diagnosed that the catalyst 25 has deteriorated because the correction amount has become larger than the predetermined amount.

In the present invention, the fact that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio means that, for example, the target air-fuel ratio is made richer than the stoichiometric air-fuel ratio, or the output current value of the air-fuel ratio sensor becomes higher than the stoichiometric air-fuel ratio. Is determined from a value corresponding to a rich air-fuel ratio. In addition, during the first combustion / rich operation, the air-fuel ratio is grasped in accordance with the relationship shown by the dashed line in FIG. 19 obtained by translating the chain line in FIG. 19 based on the output current value I of the air-fuel ratio sensor. The above-described air-fuel ratio feedback control is executed based on the air-fuel ratio thus obtained. That is, according to the relationship shown by the dashed line in FIG. 19, the air-fuel ratio corresponding to the output current value I over the entire current value range that can be output by the air-fuel ratio sensor is shown by the solid line in FIG. 8 (solid line in FIG. 19). The correction is performed so that the air-fuel ratio is calculated to be larger than the air-fuel ratio calculated according to the relationship, that is, the air-fuel ratio is calculated to be shifted to the lean side. According to this, even during the first combustion / rich operation, the air-fuel ratio provided by the air-fuel ratio sensor represents the actual air-fuel ratio, so that the air-fuel ratio can be accurately controlled to the target air-fuel ratio.

Further, by calculating the air-fuel ratio using the output current value of the air-fuel ratio sensor as described above, the air-fuel ratio range that can be detected by the air-fuel ratio sensor increases toward the lean side. That is, the air-fuel ratio sensor can also detect an air-fuel ratio having a greater lean degree. Therefore, even if the target air-fuel ratio is an air-fuel ratio having a large lean degree, the air-fuel ratio can be accurately controlled to the target air-fuel ratio. This has the advantage that the air-fuel ratio can be accurately set to the target air-fuel ratio when the air-fuel ratio is to be set to a large lean degree during the second combustion.

[0080]

The amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas at which the generation amount of soot is at a peak, and the first combustion in which soot is hardly generated is evacuated. When the fuel ratio becomes rich, an output value correction process for correcting the output value of the air-fuel ratio sensor is executed. Therefore, when the air-fuel ratio becomes rich during the first combustion, the output value of the air-fuel ratio sensor is corrected, and the air-fuel ratio is feedback-controlled based on the corrected output value.
If the air-fuel ratio becomes rich during the first combustion, the output value output by the air-fuel ratio sensor does not correspond to the actual air-fuel ratio, and the air-fuel ratio is not controlled to the target air-fuel ratio. If the output value of the sensor is corrected and the air-fuel ratio is feedback-controlled based on the corrected output value, the air-fuel ratio can be accurately controlled to the target air-fuel ratio.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing fuel molecules.

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

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

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

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

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

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

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

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

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

FIG. 14 is a diagram showing a map of a fuel injection amount.

FIG. 15 is a flowchart for controlling operation of the engine.

FIG. 16 is a flowchart for calculating a valve opening time of a fuel injection valve.

FIG. 17 is a flowchart for calculating an air-fuel ratio correction coefficient.

FIG. 18 is a flowchart for calculating a skip increase amount and a skip decrease amount.

FIG. 19 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 20 is a diagram showing a change in the output of the air-fuel ratio sensor during the execution of the sulfur poisoning recovery process of the exhaust purification catalyst.

[Explanation of symbols]

 6 Fuel injection valve 15 Exhaust turbocharger 20 Throttle valve 27a Upstream air-fuel ratio sensor 27b Downstream air-fuel ratio sensor 29 EGR passage 31 EGR control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301H 301N 45/00 314 45/00 314Z F02M 25/07 550 F02M 25 / 07 550F 550R 570 570J F-term (reference) 3G062 AA01 AA05 BA02 BA04 ED08 FA08 FA13 FA18 GA04 GA05 GA06 GA15 GA17 GA21 3G084 AA01 BA13 BA20 DA10 DA12 DA27 EA08 EB11 EB13 FA07 FA13 FA30 BA33 A03 DCA EA01 EA05 EA07 EA21 FB07 FB12 FC02 HA36 HA37 HA42 HB05 HB06 3G092 AA02 AA17 AA18 AB03 BB02 DB03 DC09 DE03Y EA05 EA07 EB02 EC01 FA44 GA14 HA01Z HD06Z HE03Z HF08Z 3G301 HA02 NE11 JA12 JA13 JA02 JA13 PA01Z PD09Z PD15Z PE01Z PE03Z PF03Z

Claims (5)

[Claims] As the amount of recirculated exhaust gas supplied to the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and the amount of recirculated exhaust gas supplied to the combustion chamber further increases. As the temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature and soot is hardly generated, the amount of soot generation peaks, The first combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is large and little soot is generated, and the recirculated exhaust gas supplied to the combustion chamber more than the amount of recirculated exhaust gas in which the amount of generated soot is peaked Switching means for selectively switching between a small amount of second combustion, an air-fuel ratio sensor disposed in an engine exhaust passage for detecting an air-fuel ratio, and an air-fuel ratio when the first combustion is performed. To achieve the target air-fuel ratio Control means for feedback-controlling the air-fuel ratio based on the output value of the air-fuel ratio sensor, and the output of the air-fuel ratio sensor when the air-fuel ratio becomes rich during the first combustion is performed. An operation control device for an internal combustion engine, wherein an output value correction process for correcting a value is executed. 2. The output value correction process according to claim 1, wherein the output value of the air-fuel ratio sensor is corrected such that the richer the air-fuel ratio, the smaller the output value of the air-fuel ratio sensor. An operation control device for an internal combustion engine according to claim 1. 3. The output value of the air-fuel ratio sensor is corrected in the output value correction process so that the output value is reduced over the entire output range of the air-fuel ratio sensor. An operation control device for an internal combustion engine according to the above. 4. An exhaust purification catalyst is arranged downstream of the air-fuel ratio sensor, and an air-fuel ratio sensor is arranged separately from the air-fuel ratio sensor downstream of the exhaust purification catalyst to perform first combustion. And controlling the amount of the recirculated exhaust gas so that the amount of the recirculated exhaust gas corresponds to the output value of the air-fuel ratio sensor on the upstream side of the exhaust purification catalyst, and the air-fuel ratio on the downstream side of the exhaust purification catalyst. 2. The operation control device for an internal combustion engine according to claim 1, wherein the recirculation exhaust gas amount is corrected based on a correction amount for an output value of the sensor. 5. The internal combustion engine according to claim 4, wherein when the correction amount for the recirculated exhaust gas amount becomes larger than a predetermined amount, it is diagnosed that the exhaust purification catalyst has deteriorated. Engine operation control device.