JP3344334B2 - Internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an internal combustion engine.

[0002]

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

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

Therefore, conventionally, the EGR rate is set within a range not exceeding the maximum allowable limit. The maximum allowable EGR rate varies considerably depending on the type of engine and fuel, but is approximately 30 to 50%.
Therefore, in a conventional diesel engine, the EGR rate is at most 3
It is reduced from 0% to about 50%.

As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate.
If the R rate is within the range not exceeding this maximum allowable limit, NO
_It was set so that the amount of _x and smoke generated was as small as possible. However, in this way EGR
Rate that there is a limit to the reduction of the NO _x and the amount of generated NO _x and the amount of smoke produced also defined to be as small as possible of smoke, in fact still a significant amount of N
At present, O _x and smoke are generated.

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

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

Accordingly, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the fuel during combustion in the combustion chamber and its surroundings will not be generated. Can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system. An internal combustion engine employing this new combustion system has already been filed by the present applicant (Japanese Patent Application No. 9-305850).

[0009]

However, even when the required injection amount changes abruptly even under this new combustion, as in a conventional internal combustion engine, if the actual injection amount changes suddenly, the engine output torque suddenly increases. The shock occurs due to the change to. Therefore, it is necessary to gradually increase or decrease the actual injection amount when the required injection amount is increased or decreased even under this new combustion.

On the other hand, under this new combustion, there are optimum values for the air-fuel ratio and the EGR rate that change according to the operating state of the engine. The range of this optimum value is considerably narrow, and therefore, when performing new combustion, the air-fuel ratio and the EGR rate must be controlled within this narrow range. By the way, under this new combustion, the EGR rate increases as the injection amount increases, and the EGR rate decreases as the injection amount decreases.

As described above, when the required injection amount sharply increases or decreases, it is necessary to gradually increase or decrease the actual injection amount. Therefore, if the EGR rate is rapidly increased when the required injection amount is rapidly increased, the EGR rate becomes higher than the EGR rate suitable for the actual injection amount, causing misfire, and the required injection amount is rapidly reduced. If the EGR rate is suddenly decreased at this time, the EGR rate becomes lower than the EGR rate suitable for the actual injection amount, so that the combustion temperature rises and smoke is generated. Therefore, it is necessary to gradually change the EGR rate so that misfire does not occur under new combustion and smoke does not occur.

[0012]

Therefore, in the first invention, a recirculation exhaust gas control valve is arranged in a recirculation exhaust gas passage connecting the engine exhaust passage and the engine intake passage, and is supplied to the combustion chamber. It reached the peak As you increase the recirculated exhaust gas quantity generation amount of soot increases gradually fed into the combustion chamber
As the amount of recirculated exhaust gas is increased further,
Temperature of fuel and surrounding gas during combustion in
In an internal combustion engine in which soot is hardly generated because the temperature is lower than the formation temperature , the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas in which the amount of generated soot becomes a peak. When the required injection amount increases, the actual injection amount is gradually increased, and the recirculation exhaust gas control valve is gradually opened. When the required injection amount is reduced, the actual injection amount is gradually reduced and re-started. The circulating exhaust gas control valve is gradually closed.

In the second invention, in the first invention,
When the required injection amount increases, the opening of the recirculation exhaust gas control valve is gradually increased with an opening larger than the opening suitable for the actual injection amount, and when the required injection amount decreases, the recirculation exhaust gas control is performed. The opening of the valve is gradually reduced with an opening smaller than the opening suitable for the actual injection amount.

In a third aspect, in the first aspect,
The exhaust gas recirculation rate is approximately 55% or more. 4
According to a second aspect, in the first aspect, the engine exhaust passage
Is provided with a catalyst having an oxidation function. Fifth invention
Then, in the fourth invention, the catalyst is an oxidation catalyst, a three-way catalyst
Or NO _xConsists of at least one absorbent.

In a sixth aspect, in the first aspect,
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 is peaked and little soot is generated, and the recirculated exhaust gas at which the amount of soot is peaked There is provided 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 gas amount.

In the seventh invention, in the sixth invention,
When the required injection amount increases while the second combustion is being performed, the actual injection amount is gradually increased, and the recirculation exhaust gas control valve is immediately closed. The amount is gradually reduced and the recirculation exhaust gas control valve is gradually opened.

In the eighth invention, in the sixth 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 a first combustion is performed in the first operating region, and a second combustion is performed in the second operating region. Combustion is performed. In the ninth invention, in the first invention,
A throttle valve is arranged in the engine intake passage. When the required injection amount increases, the actual injection amount is gradually increased and the throttle valve is gradually opened. When the required injection amount is reduced, the actual injection amount is gradually reduced. And the throttle valve is gradually closed.

[0018]

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.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
1 and the exhaust turbocharger 15 via the exhaust pipe 22
The exhaust gas turbine 23 is connected to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function via an exhaust pipe 24. The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air suction pipe 17 downstream of the throttle valve 20 are connected to the EGR passage 2.
An EGR control valve 31 which is connected to each other via a motor 9 and driven by a step motor 30 is disposed in the EGR passage 29. Further, the EGR passage 29 is provided in the EGR passage 29.
An intercooler 32 for cooling the EGR gas flowing therein is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.

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

The electronic control unit 40 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the fuel pressure sensor 36 is input to the input port 45 via the corresponding AD converter 47. A load sensor 51 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . Also, input port 4
5 is connected to a crank angle sensor 52 that generates an output pulse each 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 EGR control valve control step motor 30, and the fuel pump 35 via a corresponding drive circuit 48.

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

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

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

The following can be said from the experimental results shown in FIGS. That is, first, the air-fuel ratio A / F is 1
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
As shown in ₍₁₎ , the generation amount of NOx is considerably reduced. N
That the generation amount of O _x produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 becomes low when the soot is hardly generated I can say. The same can be said from FIG. Immediately
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.
Emissions increase. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot production process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of generated soot becomes substantially zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a precursor of soot or a hydrocarbon in a state before it. .

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 study on this, if the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.

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

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

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

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

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

In this case, in order to suppress the temperature of the fuel and its 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, as the specific heat of the inert gas increases, the endothermic effect becomes stronger. Therefore, the inert gas preferably has a higher specific heat. In this regard, it can be said that it is preferable to use EGR gas as the inert gas since CO ₂ and EGR gas have relatively large specific heats.

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

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

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

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

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

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

When the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. Therefore, in FIG. 6, 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 In the region where the required load is larger than Lo, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.

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

In this case, the lower the temperature of the EGR gas, the wider the operating range in which low-temperature combustion occurs. Therefore, as shown in FIG. 1, the exhaust gas having a relatively low temperature flowing out of the exhaust turbine 23 is recirculated as the EGR gas, and the EGR gas is further cooled by the intercooler 32. In the embodiment shown in FIG. 1, 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 the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. 6, that is, the air-fuel ratio is made rich. 10p.p. the generation amount of the NO _x even while preventing generation of soot by
m or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. while the generation amount of the NO _x can be around or less 10 ppm.

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

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

By the way, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber can be suppressed to a temperature lower than the temperature at which the growth of hydrocarbons stops halfway, only during the low load operation in the engine where the calorific value due to combustion is relatively small. Can be Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In addition, the second combustion, that is, the combustion that is usually performed conventionally, is performed during the high load operation of the engine. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been performed normally in the past, is a combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot is peaked. Say that.

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 indicates 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) is the first
Shows the first boundary between the operating region I and the second operating region II, and Y (N) represents the first operating region I and the second operating region.
2 shows a second boundary with II. The determination of the change of the operation range from the first operation range I to the second operation range II is made based on the first boundary X (N), and the change from the second operation range II to the first operation range II is performed.
The determination of the change of the operation region to the operation region I of the second boundary Y
(N).

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

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

By the way, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, but the unburned hydrocarbon is replaced by 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. Catalyst 2
As 5, an oxidation catalyst, a three-way catalyst, or a NO _x absorbent can be used. _The NO _x absorbent absorbs NO _x when the mean air-fuel ratio in the combustion chamber 5 of the lean, the combustion chamber 5
The average air-fuel ratio in the internal has a function of releasing NO _x becomes rich.

This NO _x absorbent uses, for example, alumina as a carrier and, for example, potassium K, sodium N
a, lithium Li, at least one selected from alkali metals such as cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and noble metals such as platinum Pt. Is carried.

In addition to the oxidation catalyst, the three-way catalyst and the NO
_{The x} absorbent also has an oxidizing function, so that a three-way catalyst and a NO _x absorbent can be used as the catalyst 25 as described above. 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. 8 shows the throttle valve 2 with respect to the required load L.
0 indicates the opening degree, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount. As shown in FIG. 8, in the first operating region I where the required load L is low, the opening of the throttle valve 20 is gradually increased from almost fully closed to about 2/3 as the required load L increases. E
The degree of opening of the GR control valve 31 is gradually increased from almost fully closed to fully open as the required load L increases. Also,
In the example shown in FIG. 8, in the first operation region I, the EGR rate is set to approximately 70%, and the air-fuel ratio is set to a slightly lean air-fuel ratio. In other words, in the first operating region I, the opening of the throttle valve 20 and the EGR control valve 31 are adjusted so that the EGR rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio.
Is controlled. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

During the idling operation, the throttle valve 20 is closed until the valve is almost fully closed. At this time, the EGR control valve 31 is also closed almost completely. Throttle valve 2
If the valve is closed close to 0, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating region of the engine is the first operating region I.
From the second operating region II to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 8, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, the EGR rate at which the EGR rate generates a large amount of smoke
The engine operating range is the first because it jumps over the rate range (Fig. 5).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operating region II, the second combustion, that is, the conventional combustion is performed. In this combustion method generates little soot and NO _x, but the heat efficiency is higher than the low temperature combustion, thus as the operating region of the engine is shown in FIG. 8 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise. In the second operating region II, the throttle valve 20 is held in a fully open state except for a part, and the opening of the EGR control valve 31 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases.
In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 9 shows the air-fuel ratio A in the first operating region I.
/ F. In FIG. 9, A / F = 15.5,
Curves indicated by A / F = 16, A / F = 17, and A / F = 18 indicate when the air-fuel ratio is 15.5, 16, 17, and 18, respectively, and the air-fuel ratio between the curves is shown. Is determined by proportional distribution. As shown in FIG.
In the first operating region I, the air-fuel ratio A / F becomes leaner as the required load L decreases.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low-temperature combustion can be performed even if the EGR rate is reduced as the required load L decreases.
When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 9, as the required load L decreases, the air-fuel ratio A / F increases. As the air-fuel ratio A / F increases, the fuel consumption rate increases. Accordingly, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the air-fuel ratio A / F increases as the required load L decreases.

FIG. 10 shows the required injection amount in the first operation region I. As shown in FIG. 10, the required injection amount Q is stored in the ROM 42 in advance in the form of a map as a function of the depression amount L of the accelerator pedal 50 and the engine speed N. Note that the target opening ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 1A, a map is stored in advance in the ROM 42 as a function of the required load L and the engine speed N.

The target opening SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in (B), the ROM 42 is preliminarily stored in the form of a map as a function of the injection amount QR for EGR control and the engine speed N.
Is stored within. The injection amount QR for EGR control coincides with the required injection amount Q during steady operation of the engine, and becomes a value determined from the required injection amount Q and the actual injection amount QF during transient operation, as described later. Note that the EG shown in FIG.
The target opening SE of the R control valve 31 is the injection amount QR for EGR control.
Increases as the number increases.

FIG. 12 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 12, A / F = 24 and A / F = 3.
Curves indicated by 5, A / F = 45 and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. FIG. 13 shows the required injection amount in the second operation region II. As shown in FIG. 13, the required injection amount Q is stored in the ROM 42 in advance in the form of a map as a function of the depression amount L of the accelerator pedal 50 and the engine speed N.

The target opening degree ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 4A, a map is stored in advance in the ROM 42 as a function of the required load L and the engine speed N. Further, the target opening SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in (B), the ROM 42 is preliminarily stored in a map form as a function of the injection amount QR for EGR control and the engine speed N.
Is stored within. As described above, the injection amount QR for EGR control matches the required injection amount Q during steady operation of the engine, and has a value determined from the required injection amount Q and the actual injection amount QF during transient operation. The EG shown in FIG.
The target opening SE of the R control valve 31 is the injection amount QR for EGR control.
Decrease as the value increases.

Next, the injection amount and the control of the EGR control valve 31 during the transient operation will be described with reference to FIG. Note that, in FIG. 15, (A) shows a time when the first combustion is being performed, and (B) shows a time when the second combustion is being performed. FIGS. 15A and 15B
, A broken line Q indicates a required injection amount, and a solid line QF indicates an actual injection amount. From FIGS. 15A and 15B, when the required injection amount Q is rapidly increased, the actual injection amount QF is gradually increased, and the required injection amount Q
It can be understood that the actual injection amount QF is gradually reduced when the pressure is rapidly reduced.

By the way, when the first combustion, that is, the low temperature combustion is being performed, the optimum EG corresponding to the actual injection amount QF is determined.
There is an R rate. During steady operation, the injection quantity Q for EGR control
R coincides with the actual injection amount QF, and FIG. 11B shows the target opening SE of the EGR control valve 31 at which the EGR rate becomes optimum at this time. However, there is a delay in the opening and closing operation of the EGR control valve 31, and moreover, it takes time from when the opening degree of the EGR control valve 31 changes to when the EGR rate in the combustion chamber 5 changes. Therefore, even if the opening of the EGR control valve 31 is controlled to an opening suitable for the actual injection amount QF during the transient operation, the EGR rate deviates from the optimum EGR rate due to a delay in the change of the EGR rate in the combustion chamber 5. Become.

Therefore, in the present invention, even during the transient operation, E
FIG. 15 shows that the GR rate is maintained at the optimal EGR rate.
As shown by the solid line in (A), the EGR control valve 31
Is gradually increased or decreased. More specifically, in the embodiment according to the present invention, the average value of the required injection amount Q and the actual injection amount QF (= (Q + QF) /
2) is the EGR control injection amount QR, and the EGR control valve 3
1 based on the EGR control injection amount QR shown in FIG.
Control is performed based on the map shown in FIG. In this case, as shown in FIG. 15A, when the required injection amount Q increases, the opening degree SE of the EGR control valve 31 gradually increases with an opening degree larger than the opening degree suitable for the actual injection amount QF. When the required injection amount Q is decreased, the opening SE of the EGR control valve 31 is gradually decreased with an opening smaller than the opening suitable for the actual injection amount QF.

As described above, when the required injection amount Q is increased and the opening SE of the EGR control valve 31 is gradually increased with an opening larger than the opening suitable for the actual injection amount QF, the combustion chamber 5 The EGR rate within is maintained at the optimal EGR rate. Similarly, when the required injection amount Q decreases, the EGR
When the opening degree SE of the control valve 31 is gradually decreased by an opening degree smaller than the opening degree suitable for the actual injection amount QF, the EGR rate in the combustion chamber 5 continues to be maintained at the optimum EGR rate.

The method of changing the opening degree SE of the EGR control valve 31 shown by a solid line in FIG. 15A is an example, and for example, as shown by a broken line SE 'in FIG. When the Q changes, the opening of the EGR control valve 31 increases or decreases to an opening suitable for the required injection amount Q before the actual injection amount QF reaches the required injection amount Q.
The target opening degree SE ′ of the GR control valve 31 can also be controlled.

On the other hand, when the required injection amount Q increases during the second combustion, as shown in FIG. 15B, the opening degree SE of the EGR control valve 31 is immediately reduced, and the required injection amount is reduced. When Q decreases, the opening degree SE of the EGR control valve 31 is gradually increased. When the second combustion is being performed, if the EGR rate in the combustion chamber 5 is high when the injection amount increases, smoke is generated. Therefore, when the required injection amount Q increases in order to reduce the EGR rate in the combustion chamber 5 as soon as possible when the injection amount increases, the target opening SE of the EGR control valve 31 is immediately reduced. When the fuel injection amount decreases, the EGR control valve 31 prevents the EGR rate in the combustion chamber 5 from becoming too high and generating smoke.
Is gradually opened.

Next, the operation control will be described with reference to FIG. Referring to FIG. 16, first, Step 1
At 00, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, step 10
The program proceeds to 1 to determine whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 103, where the first combustion is performed.

That is, in step 103, it is determined whether or not the required injection amount Q is larger than the actual injection amount QF. Q
If> QF, the routine proceeds to step 104, where a constant value α is added to the actual injection amount QF, and then proceeds to step 107. Therefore, at this time, the actual injection amount QF is gradually increased. On the other hand, when Q ≦ QF, the routine proceeds to step 105, where it is determined whether the required injection amount Q is smaller than the actual injection amount QF. When Q <QF, step 106
Then, the constant value α is subtracted from the actual injection amount QF, and then the routine proceeds to step 107. Therefore, at this time, the actual injection amount QF is gradually reduced.

In step 107, the average value (= (Q + QF) / 2) of the required injection amount Q and the actual injection amount QF is set as the EGR control injection amount QR. Next, at step 108, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 11B based on the EGR control injection amount QR. Next, at step 109, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG.

On the other hand, in step 101, L> X
When it is determined that (N) has been reached, the routine proceeds to step 102, where the flag I is reset.
And the second combustion is performed. That is, in step 112, it is determined whether the required injection amount Q is larger than the actual injection amount QF. When Q> QF, the routine proceeds to step 113, where a constant value β is added to the actual injection amount QF, and then the routine proceeds to step 116. Therefore, at this time, the actual injection amount QF
Is gradually increased. On the other hand, when Q ≦ QF, the routine proceeds to step 114, where the required injection amount Q is set to the actual injection amount Q.
It is determined whether it is less than F. When Q <QF, the routine proceeds to step 115, where the constant value β is subtracted from the actual injection amount QF, and then the routine proceeds to step 116. Therefore, at this time, the actual injection amount QF is gradually reduced.

In step 116, the larger of the actual injection amount QF and the required injection amount Q is determined as the EGR control injection amount QR.
Then, at step 117, based on the EGR control injection amount QR, the map shown in FIG.
The target opening degree SE of the GR control valve 31 is calculated. Therefore Q
> QF, as shown in FIG.
The target opening SE of the control valve 31 is immediately reduced,
When Q <QF, as shown in FIG.
The target opening SE of the R control valve 31 is gradually increased as the actual injection amount QF decreases. Then step 1
In FIG. 18, the throttle valve 2 from the map shown in FIG.
A target opening ST of 0 is calculated.

When the flag I is reset, in the next processing cycle, the process proceeds from step 100 to step 110, where it is determined whether the required load L has become lower than the second boundary Y (N). Step L 112 when L ≧ Y (N)
And the second combustion is performed. On the other hand, step 110
When it is determined that L <Y (N), the routine proceeds to step 111, where the flag I is set. Then, the routine proceeds to step 103, where low-temperature combustion is performed.

In FIG. 11 (A) and FIG. 14 (A), the actual injection amount QF can be used instead of the required load L. That is, the target opening ST of the throttle valve 20 may be a function of the actual injection amount QF and the engine speed N. In this case, under the first combustion, the required injection amount Q
Is increased, the opening ST of the throttle valve 20 is gradually increased with the actual injection amount QF, and when the required injection amount Q is decreased, the opening ST of the throttle valve 20 is gradually decreased with the actual injection amount QF. Can be

[0076]

According to the present invention, it is possible to prevent generation of smoke and misfire during transient operation.

[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 view showing an opening degree of a throttle valve and the like.

FIG. 9 is a diagram showing an air-fuel ratio in a first operation region I.

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

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 in a second combustion.

FIG. 13 is a diagram showing a map of a required injection amount.

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

FIG. 15 is a time chart showing changes in the injection amount and the target opening degree SE of the EGR control valve.

FIG. 16 is a flowchart for controlling operation of the engine.

[Explanation of symbols]

 6. Fuel injection valve 20 Throttle valve 31 EGR control valve

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI F01N 3/24 F01N 3/24 U 9/00 9/00 Z F02D 41/04 360 F02D 41/04 360C 380 380B 380C 385 385C 43/00 301 43/00 301H 301N F02M 25/07 550 F02M 25/07 550D 570 570D 570J (72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Vehicle Co., Ltd. (72) Inventor Hiroki Murata Toyota, Aichi Prefecture No. 1, Toyota-cho, Toyota City (56) References JP-A-7-4287 (JP, A) JP-A 8-177654 (JP, A) JP-A 8-86251 (JP, A) JP-A-9-287527 (JP, A) JP-A-9-287528 (JP, A) JP-A-11-36923 (JP, A) JP-A-2000-27698 (JP, A) JP-A-2000-73837 (JP, A) A) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-41/40

Claims (9)

(57) [Claims] When a recirculation exhaust gas control valve is disposed in a recirculation exhaust gas passage connecting an engine exhaust passage and an engine intake passage to increase the amount of recirculation exhaust gas supplied to a combustion chamber. reached the peak generation amount of soot is gradually increased, combustion
Further increase the amount of recirculated exhaust gas supplied to the room
And surrounding gas during combustion in the combustion chamber
The temperature is lower than the soot generation temperature, soot is almost generated
In the internal combustion engine, the amount of recirculated exhaust gas supplied into the combustion chamber is made larger than the amount of recirculated exhaust gas at which the amount of generated soot becomes a peak, and when the required injection amount increases, the actual injection amount gradually increases. An internal combustion engine wherein the recirculation exhaust gas control valve is gradually opened, and when the required injection amount decreases, the actual injection amount is gradually reduced and the recirculation exhaust gas control valve is gradually closed. 2. When the required injection amount increases, the opening of the recirculation exhaust gas control valve is gradually increased with an opening larger than the opening suitable for the actual injection amount, and when the required injection amount decreases. 2. The internal combustion engine according to claim 1, wherein the opening degree of the recirculation exhaust gas control valve is gradually reduced with an opening degree smaller than an opening degree suitable for an actual injection amount. 3. The internal combustion engine according to claim 1, wherein the exhaust gas recirculation rate is approximately 55% or more. 4. The internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is arranged in the engine exhaust passage. 5. The catalyst according to claim 1, wherein said catalyst is an oxidation catalyst, a three-way catalyst or NO _x.
5. The internal combustion engine of claim 4, comprising at least one of the absorbent. 6. 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 amount of generated soot is at a peak and little soot is generated, and the amount of generated soot is at a peak. 2. The internal combustion engine according to claim 1, further comprising 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 recirculated exhaust gas. 7. When the required injection amount increases during the second combustion, the actual injection amount is gradually increased, and the recirculation exhaust gas control valve is immediately closed to decrease the required injection amount. 7. The internal combustion engine according to claim 6, wherein, when it is performed, the actual injection amount is gradually reduced and the recirculation exhaust gas control valve is gradually opened. 8. An operating region of the engine is divided into a first operating region on a low load side and a second operating region on a high load side, and a first combustion is performed in the first operating region. 7. The internal combustion engine according to claim 6, wherein the second combustion is performed in the region. 9. A throttle valve is disposed in the engine intake passage. When the required injection amount increases, the actual injection amount is gradually increased, and the throttle valve is gradually opened. When the required injection amount decreases, the throttle valve is opened. 2. The internal combustion engine according to claim 1, wherein the injection amount is gradually reduced and the throttle valve is gradually closed.