JP3424554B2 - Internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, for example, a diesel engine, an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation (hereinafter referred to as EGR) passage in order to suppress the generation of NO _x. Exhaust gas, that is, EGR gas, is recirculated into the engine intake passage via the EGR 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 decreases, the amount of NO _x generated decreases. Therefore, the higher the EGR rate, the lower the amount of NO _x generated.

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

Therefore, conventionally, the EGR rate is set within a range that does not exceed the maximum allowable limit. The maximum allowable limit of this EGR rate is approximately 30 to 50 percent, though it varies considerably depending on the engine type and fuel.
Therefore, in the conventional diesel engine, the maximum EGR rate is 3
It is suppressed from 0% to 50%.

As described above, in the past, it was considered that the maximum allowable limit exists for the EGR rate.
The R rate is NO within the range that does not exceed this maximum allowable limit.
_It was stipulated that the amount of _x and smoke generated should be as small as possible. However, in this way EGR
Even if the rate is set so that the amount of NO _x and smoke produced is as small as possible, there is a limit to the reduction in the amount of NO _x and smoke produced, and in reality, a considerable amount of N 2 is still left.
The O _x, and smoke is generated at present.

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

[0007] That is, as a result of repeated experimental research, it was found that when the temperature of the fuel and the gas around it during combustion in the combustion chamber were below a certain temperature, the growth of hydrocarbons stopped in the middle of the process before reaching soot. However, if the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons will suddenly grow to soot. In this case, the temperature of the fuel and its surrounding gas is greatly affected by the endothermic action of the gas around the fuel when the fuel burns, and the endothermic amount of the gas around the fuel is adjusted according to the amount of heat generated during fuel combustion. Thus, the temperature of the fuel and the gas around it can be controlled.

Therefore, if the temperature of the fuel and the gas around it during combustion in the combustion chamber is suppressed below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated and the fuel and the surroundings during combustion in the combustion chamber will be eliminated. It is possible to control the gas temperature in the range below the temperature at which the growth of hydrocarbons stops halfway by adjusting the heat absorption amount of the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of the new combustion system. The applicant has already applied for an internal combustion engine that employs this new combustion system (Japanese Patent Application No. 9-305850).

[0009]

By the way, in this new combustion system, the EGR rate needs to be approximately 55% or more. However, the EGR rate can be increased to about 55% or more when the intake air amount is relatively small, that is, when the engine load is relatively low, and when the intake air amount exceeds a certain amount, this new combustion is no longer performed. I can't. Therefore, when the intake air amount exceeds a certain amount, it is necessary to switch to the combustion that is conventionally performed.

When switching between new combustion and conventional combustion, EGR in the combustion chamber is performed.
You have to switch rates instantly. However, in practice, it is difficult to instantaneously switch the EGR rate in the combustion chamber.
The rate changes gradually. However, the form of combustion is different between this new combustion and the conventional combustion,
Therefore, the optimum fuel injection control under the new combustion and the conventional optimum fuel injection control under the combustion are considerably different. Therefore, when the new combustion is switched to the conventional combustion, if the fuel injection control is immediately switched from the fuel injection control suitable for the new combustion to the fuel injection control suitable for the conventional combustion, the torque fluctuation is changed. When a conventional combustion is switched to a new combustion, the fuel injection control is suitable for the conventional combustion and the fuel injection control is suitable for the new combustion. If the fuel injection control is switched to another, similarly, there arises a problem that torque fluctuations occur.

[0011]

In order to solve the above problems, in the first invention, as the amount of inert gas in the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak.
When the amount of inert gas in the combustion chamber is further increased, the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it becomes lower than the temperature at which soot is produced, and soot is hardly generated. With the fuel injection valve installed, the amount of inert gas in the combustion chamber is larger than the amount of inert gas that causes the soot generation peak, and soot is hardly generated. A switching means is provided for selectively switching between the second combustion in which the amount of the inert gas in the combustion chamber is smaller than the amount of the active gas, and the fuel injection is performed once and the second combustion is performed when the first combustion is performed. Fuel injection is performed at least twice during the combustion of
When the combustion is switched from the first combustion to the first combustion, the fuel injection is performed at least twice under the first combustion for a predetermined period, and the fuel injection is performed once after the predetermined period has elapsed. I am trying.

In the second invention, in the first invention,
When switching from the first combustion to the second combustion, the fuel injection is switched from once to twice under the first combustion, and then the first combustion is switched to the second combustion. Three
In the second invention, in the first invention, when the fuel injection is performed twice, the injection performed first is the pilot injection, and the injection performed later is the main injection.

In the fourth invention, in the first invention,
A recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage is provided, and the inert gas is recirculated exhaust gas. According to a fifth aspect, in the fourth aspect, the exhaust gas recirculation rate in the first combustion state is approximately 55% or more.

In the sixth invention, in the first invention,
A catalyst with an oxidizing function is placed in the engine exhaust passage.
It In the seventh invention, in the sixth invention, the catalyst is an acid.
Catalyst, three-way catalyst or NO _xFrom at least one of the absorbents
Become. In the eighth invention, in the first invention,
The operating region is the first operating region on the low load side and the second operating region on the high load side.
The first combustion range is divided into
Do the second combustion in the second operating region
There is.

[0015]

FIG. 1 shows the case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, and 9 is an intake port. Indicates an exhaust valve, and 10 indicates an exhaust port, respectively. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected via an intake duct 13 and an intercooler 14 to a supercharger, for example, an outlet portion of a compressor 16 of an exhaust turbocharger 15. Be connected. The 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 pipe 22 through the exhaust turbocharger 15
Of the exhaust turbine 23, and the outlet of the exhaust turbine 23 is connected via an exhaust pipe 24 to a catalytic converter 26 containing a catalyst 25 having an oxidizing function. An air-fuel ratio sensor 27 is arranged in the exhaust manifold 21.

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

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 electrically controlled variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 via each fuel supply pipe 33. A fuel pressure sensor 36 for detecting a fuel pressure in the common rail 34 is attached to the common rail 34, and a fuel pump 35 is arranged so that the fuel pressure in the common rail 34 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 36. Is controlled.

The electronic control unit 40 is composed of a digital computer, and has a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, and an input port 45 which are connected to each other by a bidirectional bus 41. The output port 46 is provided. The output signal of the air-fuel ratio sensor 27 is input to the input port 45 via the corresponding AD converter 47, and 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 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 4 via the corresponding AD converter 47.
Input to 5. A crank angle sensor 52 that generates an output pulse each time the crankshaft rotates, for example, 30 ° is connected to the input port 45. On the other hand, the output port 46 is connected via the corresponding drive circuit 48 to the fuel injection valve 6,
The throttle valve control step motor 19, the EGR control valve control step motor 30, and the fuel pump 35 are connected.

FIG. 2 shows the throttle valve 2 during engine low load operation.
The change in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree of 0 and the EGR rate, and the change in the amount of smoke, HC, CO, and NO _x emissions. It represents the experimental example shown. As can be seen from FIG. 2, in this experimental example, the EGR rate becomes larger as the air-fuel ratio A / F becomes smaller, and when the air-fuel ratio is equal to or less than the theoretical air-fuel ratio (≈14.6), the EGR rate becomes 65% or more.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the EGR rate becomes around 40%, and when the air-fuel ratio A / F becomes about 30, smoke is generated. The amount of generation begins to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is made smaller, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke sharply decreases this time, the EGR rate is increased to 65% or more, and the smoke becomes almost zero when the air-fuel ratio A / F is around 15.0. . That is, soot is hardly generated. At this time, the output torque of the engine slightly decreases, and N
The amount of O _x generated is considerably low. On the other hand, at this time, HC,
The amount of CO generated starts to increase.

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

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

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

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

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

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

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

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

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

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

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

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

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

FIG. 6 shows a mixture of EGR gas and air required to bring the temperature of the fuel and its surrounding gas at the time of combustion to a temperature lower than the temperature at which soot is produced when EGR gas is used as the inert gas. The amount of gas, the ratio of air in this mixed gas amount, and the ratio of EGR gas in this mixed gas are shown. Note that, in FIG. 6, the vertical axis represents the total intake gas amount sucked into the combustion chamber 5, and the chain line Y represents the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis shows the required load.

Referring to FIG. 6, the ratio of air, that is, the amount of air in the mixed gas, shows the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the theoretical air-fuel ratio. On the other hand, in FIG. 6, the ratio of EGR gas, that is, the amount of EGR gas in the mixed gas is set so that when the injected fuel is burned, the temperature of the fuel and its surrounding gas is lower than the temperature at which soot is formed. The minimum required EGR gas amount is shown. This EGR gas amount is approximately 55% or more when expressed by the EGR rate, and is 7 in the embodiment shown in FIG.
It is 0% or more. That is, the total intake gas amount sucked into the combustion chamber 5 is shown by a solid line X in FIG. 6, and the ratio of the air amount and the EGR gas amount in the total intake gas amount X is shown in FIG.
When the ratio is as shown in (1), the temperature of the fuel and the gas around it becomes lower than the temperature at which soot is generated, and thus soot is not generated at all. Further, the amount of NO _x generated at this time is around 10 p.pm or less, so N
The amount of O _x generated is extremely small.

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

By the way, when the supercharging is not performed, the upper limit of the total intake gas amount X drawn into the combustion chamber 5 is Y. Therefore, in FIG. 6, the required load is larger than Lo. The air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced as it becomes larger. In other words, when supercharging is not performed and the air-fuel ratio is maintained at the stoichiometric air-fuel ratio in a region where the required load is larger than Lo, the EGR rate decreases as the required load increases, thus In the region where the required load is larger than Lo, the temperature of the fuel and the gas around it cannot be maintained below the temperature at which soot is generated.

However, as shown in FIG. 1, when the EGR gas is recirculated to the inlet side of the supercharger, that is, the air suction pipe 17 of the exhaust turbocharger 15 through the EGR passage 29, the required load is larger than Lo. EGR rate at 5
It can be maintained above 5 percent, for example 70 percent, thus maintaining the fuel and surrounding gas temperatures 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 intake gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the gas around it can be maintained below the temperature at which soot is produced, up to the limit that can be boosted by the compressor 16. Therefore, the operating range of the engine capable of producing the low temperature combustion can be expanded.

In this case, when the EGR rate is set to 55% or more in the region where the required load is larger than Lo, the EGR control valve 31 is fully opened and the throttle valve 20
Is closed a little. 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 made smaller than the air amount shown in FIG. It is possible to reduce the amount of NO _x generated to around 10 p.pm or less while preventing the generation of air, and to make the air amount larger than that shown in FIG. Even if it is lean from 17 to 18, the generation amount of NO _x can be reduced to about 10 p.pm or less while preventing the generation of soot.

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

As described above, 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. However, the amount of NO _x generated is extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.

By the way, the temperature of the fuel during combustion in the combustion chamber and the temperature of the gas around it can be suppressed below the temperature at which the growth of hydrocarbons stops halfway only when the engine is operating at a low load, where the calorific value of combustion is relatively small. To be Therefore, in the embodiment according to the present invention, when the engine is operated at low load, the temperature of the fuel and the gas around it during combustion is suppressed below the temperature at which the growth of hydrocarbons stops halfway, and the first combustion, that is, low temperature combustion is performed. In addition, the second combustion, that is, the combustion normally performed from the conventional one, is performed during the engine high load operation. It should be noted that here, the first combustion, that is, low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generated peaks, and soot is almost generated. The second combustion, that is, the combustion that is normally performed in the past, is the combustion that does not have the amount of soot generated and the amount of the inert gas in the combustion chamber is smaller than the amount of the inert gas that does not reach the peak. Say that.

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

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

In this way, the two boundaries of the first boundary X (N) and the second boundary Y (N) on the lower load side of the first boundary X (N) are provided as follows. For one reason. The first reason is that the combustion temperature is relatively high on the high load side of the second operating region II, and at this time, even if the required load L becomes lower than the first boundary X (N), low temperature combustion cannot be immediately performed. Because. That is, the low temperature combustion does not start immediately unless the required load L becomes considerably low, that is, when it becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for changes in the operating region between the first operating region I and the second operating region II.

By the way, when the engine is operating in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and instead, unburned hydrocarbons are in a soot precursor or in a state before that. It is discharged from the combustion chamber 5 in shape. At this time, the unburned hydrocarbons discharged from the combustion chamber 5 are satisfactorily oxidized 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
It has a function of releasing NO _x when the average air-fuel ratio in the inside becomes rich.

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

Not only oxidation catalysts, but also three-way catalysts and NO
_{The x-} absorbent also has an oxidizing function, so that the three-way catalyst and the NO _x absorbent can be used as the catalyst 25 as described above. FIG. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.

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

In other words, in the first operating region I, EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled so that the ratio becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening degree of the EGR control valve 31 based on the output signal of the air-fuel ratio sensor 27, for example. Further, in the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes late as the required load L becomes high, and the injection completion timing θE also becomes late as the injection start timing θS becomes late. In addition, during idling, the throttle valve 20 is closed until it is almost fully closed.
At this time, the EGR control valve 31 is also closed until it is almost fully closed. When the throttle valve 20 is closed to near full closure, the pressure in the combustion chamber 5 at the beginning of compression becomes low, and the compression pressure becomes small. When the compression pressure becomes small, the compression work by the piston 4 becomes small, so that the vibration of the engine body 1 becomes small. That is, during idling operation, the throttle valve 20 is closed close to the fully closed state in order to suppress the vibration of the engine body 1.

On the other hand, the operating region of the engine is the first operating region I.
When changing from the second operating range II to the second operating range II, the opening degree of the throttle valve 20 is increased stepwise from about 2/3 opening degree toward the full opening direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less so that the EGR rate jumps over the EGR rate range (FIG. 5) where a large amount of smoke is generated, and the air-fuel ratio is stepped. Be made larger.

In the second operating region II, the second combustion, that is, the combustion which is conventionally performed is performed. Although some soot and NO _x are generated in this combustion method, the thermal efficiency is higher than that in low temperature combustion, so that when the operating region of the engine changes from the first operating region I to the second operating region II, as shown in FIG. In addition, the injection amount is reduced stepwise. Second operating area
In II, conventional combustion is performed. This second
In operating region II, the throttle valve 20 is kept fully open except for a part, and the opening degree of the EGR control valve 31 is equal to the required load L.
Becomes higher and smaller. Also, this operating area
In II, the EGR rate decreases as the required load L increases,
The air-fuel ratio becomes smaller as the required load L becomes higher. However, the air-fuel ratio is a lean air-fuel ratio even if the required load L becomes high. Further, in the second operation region II, the pilot injection Qp is performed prior to the main injection Qm. That is, fuel injection is performed twice in the second operation region II.

FIG. 10 shows the air-fuel ratio A / F in the first operating region I. In FIG. 10, A / F = 15.
5, each curve indicated by A / F = 16, A / F = 17, A / F = 18 has an air-fuel ratio of 15.5, 16, 17, 18 respectively.
And the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 10, the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the air-fuel ratio A / F is leaner as the required load L is lower.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low temperature combustion can be performed even if the EGR rate is decreased.
When the EGR rate is decreased, the air-fuel ratio becomes large, so that as shown in FIG. 10, the air-fuel ratio A / F is made larger as the required load L becomes lower. The fuel consumption rate increases as the air-fuel ratio A / F increases. Therefore, in order to make the air-fuel ratio as lean as possible, the air-fuel ratio A / F is increased as the required load L decreases in the embodiment of the present invention.

It should be noted that the target opening degree ST of the throttle valve 20 required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 1 (A), the EGR is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N, and is required to set the air-fuel ratio to the target air-fuel ratio shown in FIG. The target opening degree SE of the control valve 31 is shown in FIG.
As shown in (4), it is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N.

FIG. 12 shows the target air-fuel ratio when the second combustion, that is, the combustion by the conventional combustion method is performed.
In FIG. 12, A / F = 24, A / F = 35, A
The curves shown by / F = 45 and A / F = 60 show the target air-fuel ratios 24, 35, 45, 60, respectively. The target opening degree ST of the throttle valve 20 required to bring the air-fuel ratio to this target air-fuel ratio is the required load L as shown in FIG. 13 (A).
And RO in advance in the form of a map as a function of the engine speed N
The target opening degree SE of the EGR control valve 31 which is stored in the M42 and is required to bring the air-fuel ratio to this target air-fuel ratio is shown in FIG.
As shown in FIG. 3 (B), it is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N.

As shown in FIG. 9, when the first combustion is performed in the first operating region I, the fuel injection Q is performed only once at the end of the compression stroke, and the second fuel injection is performed in the second operating region II. When the combustion is being performed, the pilot injection Qp is performed prior to the main injection Qm as described above.
As shown in FIG. 9, the injection amount of the fuel injection Q, the injection amount of the main injection Qm, and the injection amount of the pilot injection Qp increase as the required load L increases.

Actually, the injection amount of the fuel injection Q is the required load L
And the engine speed N, and this injection quantity Q is shown in FIG.
As shown in FIG. 4 (A), it is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N. Similarly, the injection amount of the main injection Qm is also a function of the required load L and the engine speed N, and this injection amount Qm is also shown in FIG.
As shown in (B), required load L and engine speed N
Is previously stored in the ROM 42 in the form of a map as a function of. Further, the injection amount of the pilot injection Qp is also a function of the required load L and the engine speed N, and this injection amount Qp is also a map of the required load L and the engine speed N as shown in FIG. 14 (C). It is stored in the ROM 42 in advance in the form.

As described above, when the first combustion is switched to the second combustion, the throttle valve 20 is opened to reduce the EGR rate from 70% to 40% or less. However, at this time, the EGR rate does not instantaneously decrease due to a delay in the increase of the intake air amount or the like, and it takes a certain time until the EGR rate decreases from 70% to 40% or less. That is, when the first combustion is switched to the second combustion, the EGR rate suitable for the first combustion gradually changes to the EGR rate suitable for the second combustion. Therefore, when the fuel injection control is switched from the fuel injection control suitable for the first combustion to the fuel injection control suitable for the second combustion when the first combustion is switched to the second combustion, the output torque fluctuates. Etc. causes problems.

Therefore, in the embodiment of the present invention, when switching from the first combustion to the second combustion, first, the fuel injection is switched from once to twice under the first combustion, and a predetermined Δt1 time is set. The pilot injection is performed prior to the main injection, and the pilot injection is performed before the main injection, and the first combustion is switched to the second combustion. That is, when the first combustion is switched to the second combustion, the EGR rate is largely switched, and when the fuel injection method is also switched at the same time, the output torque easily varies.
However, as described above, when the first combustion is switched to the second combustion, if only the EGR rate is changed without changing the fuel injection method, the fluctuation of the output torque can be suppressed.

Since there is not sufficient air around the fuel during the first combustion, the output torque hardly changes even if the fuel injection amount or the fuel injection method changes. On the other hand, if the amount of air in the combustion chamber 5 changes during the first combustion, the combustion becomes active and the output torque changes. That is,
The output torque during the first combustion is insensitive to the fuel injection amount and the fuel injection method, but the combustion chamber 5
Sensitive to changes in the amount of air inside. Therefore, as described above, even if the fuel injection is changed from once to twice during the first combustion, the output torque hardly changes.

As described above, in the embodiment according to the present invention, when switching from the first combustion to the second combustion, the fuel injection is performed twice under the first combustion for a predetermined Δt1 time. In this case, in the embodiment according to the present invention, this Δ
The t1 time is a fixed time. On the other hand, even when the second combustion is switched to the first combustion, the EGR rate gradually changes from the EGR rate suitable for the second combustion to the EGR rate suitable for the first combustion. Also, the fuel injection control from the fuel injection control suitable for the second combustion to the first
Immediately switching to the fuel injection control suitable for the combustion of causes the problem that the output torque fluctuates.

Therefore, in the embodiment according to the present invention, pilot injection is performed prior to main injection while switching from the second combustion to the first combustion, and after a predetermined Δt2 time has elapsed, the fuel is burned under the first combustion. The injection is switched from twice to once. As described above, the output torque during the first combustion is insensitive to the fuel injection amount and the fuel injection method, but is sensitive to the change in the air amount in the combustion chamber 5. is there. Therefore, even if the fuel injection is changed from twice to once while the first combustion is being performed as described above, the output torque hardly changes.

On the other hand, when the second combustion is switched to the first combustion, the air-fuel ratio in the combustion chamber 5 is greatly reduced. However, in this case, it takes time until the air-fuel ratio becomes small due to the influence of the air contained in the EGR gas.
That is, since the second combustion is performed under a fairly lean air-fuel ratio, the exhaust gas discharged from the engine at this time contains a large amount of air, and thus the EGR gas also contains a large amount of air. Contains air. In such a state, the throttle valve 20 is closed, and the first combustion from the second combustion is performed.
Even if the combustion mode is switched to the combustion mode, the amount of air contained in the EGR gas does not immediately decrease, and as a result, the air-fuel ratio in the combustion chamber 5 does not easily drop to the target air-fuel ratio.

Therefore, in the embodiment according to the present invention, after the second combustion is switched to the first combustion, the fuel injection is performed twice for Δt2 hours until the air-fuel ratio in the combustion chamber 5 reaches the target air-fuel ratio. I am trying. By the way, in this case, E
The amount of air contained in the GR gas decreases in a shorter time as the engine speed increases, and thus, the higher the engine speed, the shorter the time until the air-fuel ratio in the combustion chamber 5 reaches the target air-fuel ratio. Become. Therefore, as shown in FIG. 15A, the Δt2 time is shortened as the engine speed N increases.

On the other hand, the required load immediately before the switching from the second combustion to the first combustion (hereinafter referred to as the immediately preceding required load) L
Is higher, the air-fuel ratio in the combustion chamber 5 is smaller. Therefore, the amount of air contained in the EGR gas is smaller as the immediately preceding required load L is higher. Therefore from the second combustion to the first
The higher the immediately preceding required load L when the combustion is switched to, the shorter the time until the air-fuel ratio in the combustion chamber 5 becomes the target air-fuel ratio. Therefore, as shown in FIG. 15B, the Δt2 time is made smaller as the immediately preceding required load L becomes higher.

As the immediately preceding required load L, it is possible to use the required load L before a fixed time when switching to the first combustion, or the average within a fixed period until the switching to the first combustion. Values can also be used. This Δt2 time is a function of the immediately preceding required load L and the engine speed N, as shown in FIG.
Are stored in advance in the ROM 42 in the form of the map shown in FIG.

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 the 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
In step 1, it is determined whether the required load L has become larger than the first boundary X (N). When L ≦ X (N), the routine proceeds to step 102, where low temperature combustion is performed.

That is, at step 102, fuel injection is performed once so that the air-fuel ratio shown in FIG. 10 is obtained. Next, at step 103, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG. 11 (A), and the opening degree of the throttle valve 20 is made this target opening degree ST. Next, at step 104, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. 11 (B), and the opening degree of the EGR control valve 31 is made this target opening degree SE.

On the other hand, in step 101, L> X
When it is determined that (N) has been reached, the routine proceeds to step 105, where it is determined whether or not Δt1 time has elapsed since L> X (N). When Δt time has not elapsed, the routine proceeds to step 106, where the main injection amount Qm is calculated from the map shown in 14 (B), and the pilot injection amount Qp is calculated from the map shown in 14 (C).
Based on p, pilot injection is performed prior to main injection. Then, it proceeds to step 103. That is, the fuel injection is performed twice under the first combustion before switching to the second combustion.

When it is determined in step 105 that Δt1 time has elapsed, the routine proceeds to step 107, where the flag I is reset, then the routine proceeds to step 109, where the second combustion is performed. That is, in step 109, as shown in FIG.
From the map shown in (A), the target opening S of the throttle valve 20
T is calculated, and the opening of the throttle valve 20 is set to this target opening ST. Next, at step 110, FIG.
The target opening degree SE of the EGR control valve 31 is calculated from the map shown in (1), and the opening degree of the EGR control valve 31 is set to this target opening degree SE. Next, at step 111, the main injection amount Qm is calculated from the map shown in 14 (B), and the pilot injection amount Qp is calculated from the map shown in 14 (C).
Based on Qp and Qp, pilot injection is performed prior to the main injection. That is, fuel injection is performed twice so as to achieve the lean air-fuel ratio shown in FIG.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 100 to step 108, where it is judged if the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 109
And the second combustion is performed under a lean air-fuel ratio.
On the other hand, if it is determined at step 108 that L <Y (N), then the routine proceeds to step 112, where FIG.
Δt2 is calculated from the map shown in (C), and L <Y
It is determined whether or not Δt2 time has elapsed since (N). When Δt2 hours have not elapsed, step 1
Proceed to 14, and from the map shown in 14 (B), the main injection amount Qm
Is calculated, the pilot injection amount Qp is calculated from the map shown in FIG. 14 (C), and pilot injection is performed prior to the main injection based on these Qm and Qp. Then, it proceeds to step 103. Therefore, at this time, the second combustion is switched to the first combustion, and the fuel injection is performed twice under the first combustion.

When it is determined in step 112 that Δt2 has elapsed, the routine proceeds to step 113, where the flag I is set, and then the routine proceeds to step 114. When the flag I is set, the process proceeds from step 100 to step 101 and then to step 102. Therefore, after the switching to the first combustion, the fuel injection is switched from twice to once when Δt2 time has elapsed.

[0075]

EFFECTS OF THE INVENTION It is possible to prevent the output torque from varying when switching between the first combustion and the second combustion.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing a fuel molecule.

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

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

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

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

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

FIG. 10 is a diagram showing an air-fuel ratio in a first operating region I.

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

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

FIG. 13 is a diagram showing a map of a target opening degree of a throttle valve or the like.

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

FIG. 15 is a diagram showing Δt2.

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

[Explanation of symbols]

6 ... Fuel injection valve 15 ... Exhaust turbocharger 20 ... Throttle valve 29 ... EGR passage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F02D 41/04 375 F02D 41/04 375 43/00 301 43/00 301G 301N F02M 25/07 550 F02M 25/07 550R 570 570J ( 72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Hiroki Murata, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (56) References 7-4287 (JP, A) JP 8-177654 (JP, A) JP 8-86251 (JP, A) JP 9-287527 (JP, A) JP 9-287528 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/00-45/00

Claims (8)

(57) [Claims] 1. When the amount of inert gas in the combustion chamber increases, the soot generation amount gradually increases and reaches a peak, and when the amount of inert gas in the combustion chamber further increases, combustion in the combustion chamber occurs. In an internal combustion engine in which the temperature of the fuel and the gas around it are lower than the temperature of soot generation and soot is hardly generated, a fuel injection valve is placed in the combustion chamber and the amount of soot generation reaches a peak. First combustion with a large amount of inert gas in the combustion chamber and almost no soot, and second combustion with a smaller amount of inert gas in the combustion chamber than the amount of soot generated at the peak. The fuel injection is performed once when the first combustion is being performed and at least twice when the second combustion is being performed. Switch from 2nd combustion to 1st combustion The internal combustion engine is configured to perform the fuel injection at least twice under the first combustion for a predetermined period during the predetermined time and to perform the fuel injection once after the predetermined period elapses. 2. When switching from the first combustion to the second combustion, the fuel injection is switched from once to twice under the first combustion, and then from the first combustion to the second combustion. The internal combustion engine according to claim 1. 3. The internal combustion engine according to claim 1, wherein when the fuel injection is performed twice, the injection performed first is the pilot injection and the injection performed later is the main injection. 4. The internal combustion engine according to claim 1, further comprising a recirculation device for recirculating exhaust gas discharged from the combustion chamber into an engine intake passage, wherein the inert gas is recirculation exhaust gas. 5. The internal combustion engine according to claim 4, wherein the exhaust gas recirculation rate in the first combustion state is approximately 55% or more. 6. The internal combustion engine according to claim 1, wherein a catalyst having an oxidizing function is arranged in the engine exhaust passage. 7. The catalyst is an oxidation catalyst, a three-way catalyst or NO _x.
7. An internal combustion engine according to claim 6, comprising at least one absorbent. 8. The engine operating region is divided into a first operating region on the low load side and a second operating region on the high load side, and first combustion is performed in the first operating region to perform the second operating region. The internal combustion engine according to claim 1, wherein the second combustion is performed in the region.