JP3061035B2 - 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]

The temperature of the fuel and the surrounding gas during combustion in the combustion chamber are affected by, for example, the temperature of the intake gas supplied into the combustion chamber and the temperature of the engine cooling water. The temperature of the fuel and its surrounding gas increases as the temperature of the intake gas supplied into the combustion chamber and the temperature of the engine cooling water rise. So in this case,
In order to suppress the temperature of the fuel during combustion in the combustion chamber and the surrounding gas temperature below the temperature at which the growth of hydrocarbons stops halfway, the higher the temperature of the intake gas supplied into the combustion chamber and the higher the engine cooling water temperature, the more the fuel It is necessary to increase the amount of heat absorbed by the surrounding gas.

[0010]

Therefore, in the first invention, an exhaust gas recirculation device for recirculating exhaust gas in the engine intake passage is provided, and the amount of recirculated exhaust gas supplied into the combustion chamber is reduced. In an internal combustion engine in which the amount of soot generation increases gradually and reaches a peak, the amount of recirculated exhaust gas supplied to the combustion chamber is made larger than the amount of recirculated exhaust gas where the amount of soot is peaked. Detecting means for detecting a representative temperature which influences the temperature of the fuel during combustion in the combustion chamber and the gas temperature around the fuel, and when the temperature increases, the gas temperature also increases. Is increased, the exhaust gas recirculation rate is increased.

That is, as the representative temperature such as the temperature of the intake gas supplied into the combustion chamber or the temperature of the engine cooling water increases, the exhaust gas recirculation rate increases, thereby increasing the amount of heat absorbed by the gas around the fuel. Can be In a second aspect based on the first aspect, the representative temperature is determined based on at least the temperature representing the temperature of the intake gas supplied into the combustion chamber.

In a third aspect, in the first aspect,
The representative temperature is determined based on at least the temperature representing the temperature of the intake gas supplied into the combustion chamber and the engine cooling water temperature. In a fourth aspect based on the first aspect, the exhaust gas recirculation device includes an exhaust gas recirculation control valve for controlling an amount of recirculated exhaust gas supplied to an intake passage downstream of the throttle valve. The exhaust gas recirculation rate is increased by increasing the opening of the circulation control valve.

In the fifth invention, in the fourth invention,
When the exhaust gas recirculation control valve is fully opened, the opening of the throttle valve is reduced. In a sixth aspect based on the first aspect, the exhaust gas recirculation rate is approximately 55% or more. In a seventh aspect based on the first aspect, a catalyst having an oxidation function is disposed in the engine exhaust passage.

In the eighth invention, in the seventh invention,
The catalyst is an oxidation catalyst, a three-way catalyst or NO _xAt least the absorbent
Consists of one. The ninth invention is the same as the first invention
The amount of soot generation is smaller than the amount of recirculated exhaust gas
The amount of recirculated exhaust gas supplied to the combustion chamber is large and soot is almost
The first combustion, which hardly occurs, and the soot generation peak
Recirculated exhaust gas supplied to the combustion chamber rather than recirculated gas volume
Switching means for selectively switching between the second combustion having a small amount of gas and the second combustion
It has a step.

In a tenth aspect based on the ninth aspect, the operating range of the engine is divided into a first operating range on the low load side and a second operating range on the high load side. Is performed, and the second combustion is performed in the second operation region.

[0016]

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. 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 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. A water temperature sensor 60 for detecting an engine cooling water temperature is arranged in the engine body 1, and an output signal of the water temperature sensor 60 is input to an input port 45 via a corresponding AD converter 47. In the surge tank 12, the intake air and EGR
A temperature sensor 61 for detecting the temperature of the mixed gas with the gas is provided, and the output signal of this temperature sensor 61 is
The data is input to the input port 45 via the D converter 47.

On the other hand, a mass flow detector 62 for detecting a mass flow rate of the intake air is disposed in the air suction pipe 17 upstream of the throttle valve 20, and an output signal of the mass flow detector 62 is a corresponding AD conversion. Input port 4 via the device 47
5 is input. The output signal of the fuel pressure sensor 36 is also input to the input port 45 via the corresponding AD converter 47. A load sensor 5 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50
1 is connected, and the output voltage of the load sensor 51 is
The data is input to the input port 45 via the D converter 47. The input port 45 has a crankshaft of, for example, 30.
A crank angle sensor 52 that generates an output pulse each time it rotates by an angle is connected. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 30, and the fuel pump 35 via a corresponding drive circuit 48.

FIG. 2 shows the throttle valve 2 when the engine is operating at a low load.
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 close to 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. 3A shows a change in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is the largest when the air-fuel ratio A / F is around 21, and FIG. 3B 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 ₍₂₎ , the generation amount of NOx is considerably reduced. N
That the generation amount of O _x produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 becomes low when the soot is hardly generated I can say. The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low.
The combustion temperature inside is low.

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

The consideration based on the experimental results shown in FIGS. 2 and 3 summarizes the fact that 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.

By the way, the temperature of the fuel and its surrounding 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 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 a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

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

That is, if there is only air around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel becomes extremely high locally. That is, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature locally becomes extremely high, the unburned hydrocarbons that have received the combustion heat 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, as the specific heat of the inert gas increases, the endothermic effect becomes stronger. Therefore, the inert gas preferably has a higher specific heat. In this regard, it can be said that it is preferable to use EGR gas as the inert gas since CO ₂ and EGR gas have relatively large specific heats.

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

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

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

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

When the fuel injection amount increases, the calorific value 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.

By the way, when supercharging is not performed,
The upper limit of the total intake gas amount X sucked into the firing chamber 5 is Y.
Therefore, in FIG.₀Territory greater than
In the region, the EGR gas ratio increases as the required load increases.
The air-fuel ratio can be maintained at the stoichiometric air-fuel ratio unless reduced.
Can not. In other words, it is necessary when there is no supercharging.
Load demand is L₀The air-fuel ratio is set to stoichiometric
When trying to maintain the fuel ratio, the required load increases.
As a result, the EGR rate decreases, and thus the required load becomes L ₀Than
In areas where the fuel and the surrounding gas temperature are
It will not be possible to maintain a temperature lower than the temperature produced.

[0040] However recirculating the required load is larger than L ₀ of the EGR gas into the air intake pipe 17 on the inlet side i.e. the exhaust turbocharger 15 via the EGR passage 29 supercharger as shown in FIG. 1 EGR rate of 5 in the region
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 cause low-temperature combustion can be expanded. E is when the required load is the EGR rate more than 55 percent in the region larger than L ₀
The throttle valve 20 is opened when the GR control valve 31 is fully opened.
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 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, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the surrounding gas temperature to a temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. During the high load operation of the engine, the second combustion, that is, the combustion that is usually performed conventionally, is performed. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been 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 operating region from the first operating region I to the second operating region II is made based on the first boundary X (N), and the determination of the change from the second operating region II to the first operating region 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 load side lower 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 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 operating region of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, but unburned hydrocarbons are instead replaced by the soot body 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.

The NO _x absorbent uses, for example, alumina as a carrier, and, for example, potassium K, sodium N
a, at least one selected from alkali metals such as lithium Li, cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. 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 EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

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

On the other hand, the operating range of the engine is the first operating range I.
From the second operating region II to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 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 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 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 target air-fuel ratio A / F in the first operation region I. In FIG. 9, A / F = 15.
5, A / F = 16, A / F = 17, and A / F = 18 indicate curves with target air-fuel ratios of 15.5, 16, 17,
18 indicates that the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 9, the air-fuel ratio is lean in the first operation region I, and in the first operation region I, the target air-fuel ratio A decreases as the required load L decreases.
/ F is made lean.

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 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. .

As described above, in the embodiment according to the present invention, when the first combustion is performed, the EGR rate is set to approximately 70%. However, for example, when the temperature of the intake gas supplied into the combustion chamber 5 increases, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 increases. Therefore, at this time, in order to suppress the temperature of the fuel during combustion in the combustion chamber 5 and the surrounding gas temperature to a temperature at which the growth of hydrocarbons stops halfway, that is, in order to prevent the generation of soot, the temperature of the intake gas is controlled. It is necessary to increase the amount of heat absorbed by the gas around the fuel as the pressure rises.

The same can be said when the engine cooling water temperature rises. That is, when the temperature of the engine cooling water increases, the amount of heat that escapes through the inner wall surface of the cylinder bore during the compression stroke decreases, so that the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 increases. Therefore, at this time, in order to suppress the temperature of the fuel during combustion in the combustion chamber 5 and the surrounding gas temperature to a temperature at which the growth of hydrocarbons stops halfway, that is, in order to prevent the generation of soot, the engine cooling water temperature must be increased. As the temperature rises, it is necessary to increase the amount of heat absorbed by the gas around the fuel.

In other words, the representative temperature which affects the temperature of the fuel and its surrounding gas during combustion in the combustion chamber 5 and increases as the temperature rises to the representative temperature at which the temperature of the fuel and its surrounding gas also increases. Accordingly, it is necessary to adjust the amount of heat absorbed by the gas around the fuel, and to increase the amount of heat absorbed by the gas around the fuel as the representative temperature increases.

Therefore, in the embodiment according to the present invention, when the representative temperature rises, the EGR rate is increased in order to increase the amount of heat absorbed by the gas around the fuel.
Next, this will be specifically described. FIG. 10 (A)
Is the EGR rate ΔE to be increased with respect to the reference EGR rate.
When G0 is zero, that is, when the EGR rate is the reference EGR rate, and when the EGR rate is to be increased with respect to the reference EGR rate Δ
When EG5 is 5%, when EGR rate ΔEG10 to be increased with respect to reference EGR rate is 10%, when EG5 is to be increased with respect to reference EGR rate
The case where the R rate ΔEG15 is 15% is shown. That is, for example, if the reference EGR rate is 70%, the curve ΔEG0 indicates the EGR rate of 70%, the curve ΔEG5 indicates the EGR rate of 75%, and the curve ΔEG10 indicates the EGR rate of 80%. The curve ΔEG15 shows that the EGR rate is 8
5 percent is indicated.

In FIG. 10A, the horizontal axis TG indicates the temperature of the intake gas supplied into the combustion chamber 5, and the vertical axis TW indicates the engine cooling water temperature. Therefore, the target EGR rate increases as the intake gas temperature TG increases, and the target EGR increases as the engine cooling water temperature TW increases.
It can be seen that the GR rate increases. EGR rate Δ to be increased
EG is stored in advance in the ROM 42 as a function of the intake gas temperature TG and the engine cooling water temperature TW, as shown in FIG.

Next, referring to FIG. 11, a change in the opening degree ST of the throttle valve 20 when the EGR rate ΔEG to be increased under the same required load and the same engine speed, and a change in the EGR control valve 31 The outline of the change in the opening degree SE, the change in the EGR rate, and the change in the air-fuel ratio will be described. As shown in FIG. 11, when the EGR rate ΔEG to be increased is relatively small, that is, in the region A, the EGR rate is increased as ΔEG increases while the air-fuel ratio A / F is kept constant. At this time, the opening degree ST of the throttle valve 20 and the opening degree SE of the EGR control valve 31 are determined by EG shown in FIG.
Control is performed so that the R rate and the air-fuel ratio A / F are obtained. In order to increase the EGR rate while maintaining the air-fuel ratio A / F constant, it is necessary to increase the opening SE of the EGR control valve 31 and the opening ST of the throttle valve 20 as the target EGR rate increases. The opening degree SE of the EGR control valve 31 and the opening degree ST of the throttle valve 20 change as shown in FIG. 11 as ΔEG increases.

On the other hand, the region B in FIG.
The region where the EGR control valve 31 is fully opened is shown. E
When the GR control valve 31 is fully opened, the EGR rate does not increase unless the opening of the throttle valve 20 is reduced, and therefore, in the region B, the EGR control valve 31 is maintained in a fully open state.
The throttle valve 20 is gradually closed as ΔEG increases. As a result, even in area B, E
The GR rate is increased as ΔEG increases.

On the other hand, when the throttle valve 20 is gradually closed, the air-fuel ratio A / F gradually decreases as shown in FIG. 11 because the amount of intake air decreases. As described above, when the air-fuel ratio A / F decreases, the amount of oxygen around the fuel decreases, so that the combustion becomes mild. That is, in the area B, E
The temperature of the fuel and the surrounding gas during combustion are suppressed to a temperature at which no soot is generated by the effect of increasing the GR rate and the effect of decreasing the air-fuel ratio.

FIG. 12 is a map of the target opening ST of the throttle valve 20 when the EGR rate to be increased is ΔEG0 (FIG. 1).
2 (A)), a map of the target opening degree SE of the EGR control valve 31 (FIG. 12 (B)), and a map of the target air-fuel ratio A / F (FIG. 12 (C)), and FIG. Is the EG to be increased
Target opening S of throttle valve 20 when R rate is ΔEG5
T (FIG. 13A), a map of the target opening SE of the EGR control valve 31 (FIG. 13B), and a target air-fuel ratio A.
/ F (FIG. 13 (C)), and FIG.
A map of the target opening ST of the throttle valve 20 when the EGR rate to be increased is ΔEG10 (FIG. 14A), and E
A map of the target opening SE of the GR control valve 31 (FIG. 14)
(B)) and a map of the target air-fuel ratio A / F (FIG. 14)
FIG. 15 shows the target opening ST of the throttle valve 20 when the EGR rate to be increased is ΔEG15.
15 (A), the map of the target opening SE of the EGR control valve 31 (FIG. 15 (B)), and the target air-fuel ratio A /
F (FIG. 15 (C)).

All the maps shown in FIGS. 12 to 15 are functions of the required load L and the engine speed N, and these maps are stored in the ROM 42 in advance. Δ
The intermediate value between EG0 and ΔEG5, the intermediate value between ΔEG5 and ΔEG10, and the intermediate value between ΔEG10 and ΔEG15 are calculated by interpolation. 12 to 15 show a region A in which the air-fuel ratio A / F is kept constant and a region B in which the air-fuel ratio A / F is smaller than the region A. 13, 14,
As can be seen from FIG. 15, the region B exists only in the operation region where the required load L where a large amount of EGR gas is required is high, and this region B expands toward the low load side as ΔEG increases. When ΔEG shown in FIG. 12 is ΔEG0, that is, when the EGR rate is the reference EGR rate, only the region A is set, and the target air-fuel ratio A / F at this time is the target air-fuel ratio shown in FIG.

FIG. 16 shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 16, A / F = 24, A / F
Curves indicated by F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. FIG. 17A shows the target opening degree ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
The EGR control which 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. 16 and is necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the valve 31 is as shown in FIG.
As shown in (1), a map is previously stored in the ROM 42 as a function of the required load L and the engine speed N. Further, 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, the operation control will be described with reference to FIG. Referring to FIG. 19, 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 low-temperature combustion is performed.

That is, in step 103, the temperature sensor 61
The EGR rate Δ to be increased from the map shown in FIG. 10B based on the intake gas temperature TG into the combustion chamber 5 detected by the engine and the engine cooling water temperature TW detected by the water temperature sensor 60.
EG is calculated. Next, in step 104, based on ΔEG, FIG. 12 (A), FIG. 13 (A), FIG.
The target opening ST of the throttle valve 20 is calculated from the map selected from FIG.
Is set as the target opening ST. Then step 1
In FIG. 12, based on ΔEG, FIGS.
(B), the target opening SE of the EGR control valve 31 is calculated from a map selected from FIG. 14 (B) and FIG. 15 (B), and the opening of the EGR control valve 31 is determined by the target opening SE. Is done.

Next, at step 106, based on ΔEG, FIGS. 12 (C), 13 (C), 14 (C),
From the map selected from (C), the target air-fuel ratio A /
F is calculated. Next, at step 107, the mass flow rate Ga of the intake air detected by the mass flow rate detector 62 is taken in. Next, at step 108, the air-fuel ratio is set to the target air-fuel ratio based on the mass flow rate Ga of the intake air and the target air-fuel ratio A / F. The fuel injection amount Q required for A / F is calculated.

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, step 111
In FIG. 18, the target fuel injection amount Q is calculated from the map shown in FIG. 18, and the fuel injection amount is set as the target fuel injection amount Q.
Next, at step 112, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 17A, and the opening of the throttle valve 20 is set to this target opening ST.

Next, at step 113, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 17B, and the opening of the EGR control valve 31 is set to this target opening SE. When the flag I is reset, in the next processing cycle, the process proceeds from step 100 to step 109, where it is determined whether or not the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the routine proceeds to step 111, where the second combustion is performed under a lean air-fuel ratio.

On the other hand, at step 109, L <Y
When it is determined that (N) has been reached, the routine proceeds to step 110, where the flag I is set. Then, the routine proceeds to step 103, where low-temperature combustion is performed.

[0075]

As described above, good low-temperature combustion can be ensured even when the temperature represented by the temperature of the intake gas supplied into the combustion chamber or the temperature of the engine cooling water changes.

[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 and the like in a first operation region I.

FIG. 10 is a diagram showing an EGR rate ΔEG to be increased.

FIG. 11 is a diagram showing a change in a throttle opening and the like.

FIG. 12 shows a target opening degree of the throttle valve at the time of ΔEG0,
It is a figure which shows the map of the target opening degree and target air-fuel ratio of an EGR control valve.

FIG. 13 shows a target opening degree of the throttle valve at the time of ΔEG5,
It is a figure which shows the map of the target opening degree and target air-fuel ratio of an EGR control valve.

FIG. 14 is a diagram showing a map of a target opening of a throttle valve, a target opening of an EGR control valve, and a target air-fuel ratio when ΔEG10.

FIG. 15 is a diagram showing a map of a target opening of a throttle valve, a target opening of an EGR control valve, and a target air-fuel ratio when ΔEG15.

FIG. 16 is a diagram showing an air-fuel ratio in the second combustion.

FIG. 17 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 18 is a diagram showing a map of a fuel injection amount.

FIG. 19 is a flowchart for controlling operation of the engine.

[Explanation of symbols]

 6. Fuel injection valve 20 Throttle valve 29 EGR passage 31 EGR control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/04 380 F02D 41/04 380C F02M 25/07 570 F02M 25/07 570C (72) Inventor Takekazu Ito Toyota-shi, Aichi 1 Toyota Town, Toyota Motor Corporation (72) Inventor Hiroki Murata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-8-218920 (JP, A) JP 7-4287 (JP, A) JP-A-9-287527 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/02 380 F02M 25/07 570

Claims (10)

(57) [Claims] An exhaust gas recirculation device for recirculating exhaust gas in an engine intake passage is provided, and as the amount of recirculated exhaust gas supplied to a combustion chamber increases, the amount of soot generated gradually increases. In an internal combustion engine that increases and reaches a peak, the amount of recirculated exhaust gas supplied to the combustion chamber is made larger than the amount of recirculated exhaust gas at which the generation amount of soot becomes a peak, and the fuel during combustion in the combustion chamber and its surroundings Detecting means for detecting a representative temperature that affects the gas temperature of the gas and increases with the rise of the gas temperature as the temperature rises, and the exhaust gas recirculation rate increases as the representative temperature increases. Internal combustion engine designed to be increased. 2. The internal combustion engine according to claim 1, wherein the representative temperature is determined based on at least a temperature representative of a temperature of the intake gas supplied into the combustion chamber. 3. The internal combustion engine according to claim 1, wherein the representative temperature is determined based on at least a temperature representative of a temperature of an intake gas supplied into the combustion chamber and an engine cooling water temperature. 4. The exhaust gas recirculation device according to claim 1, further comprising an exhaust gas recirculation control valve for controlling an amount of recirculated exhaust gas supplied to an intake passage downstream of the throttle valve. The internal combustion engine according to claim 1, wherein the exhaust gas recirculation rate is increased by increasing the opening. 5. The internal combustion engine according to claim 4, wherein the opening of the throttle valve is reduced when the exhaust gas recirculation control valve is fully opened. 6. The internal combustion engine according to claim 1, wherein the exhaust gas recirculation rate is approximately 55% or more. 7. The internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is disposed in the engine exhaust passage. 8. The catalyst according to claim 1, wherein said catalyst is an oxidation catalyst, a three-way catalyst or NO _x.
The internal combustion engine of claim 7, comprising at least one absorbent. 9. 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 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 a switching unit that selectively switches between a second combustion in which an amount of recirculated exhaust gas supplied to the combustion chamber is smaller than an amount of recirculated gas that becomes the second combustion. 10. The engine operating region 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. Second in the area
10. The internal combustion engine according to claim 9, wherein combustion of the internal combustion engine is performed.