JP3424563B2 - 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 NOx. Exhaust gas, that is, EGR gas, is recirculated into the engine intake passage through the 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 NOx generation amount decreases, and therefore, the higher the EGR rate, the lower the NOx generation amount.

As described above, it has been known that the amount of NOx produced 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 specified 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 NOx and smoke produced is as small as possible, there is a limit to the reduction in the amount of NOx and smoke produced, and in reality, a considerable amount of N 2 is still generated.
The present situation is that Ox and smoke are generated.

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
When the rate is further increased, the smoke starts to decrease sharply this time. When the EGR rate is 70% or more during idling operation, and when the EGR gas is strongly cooled, the EGR rate is almost 55% or more. It was found that it was almost zero, that is, soot was hardly generated. At this time, N
It has also been found that the amount of Ox 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.

[0009]

However, the new combustion system as described above has not been disclosed yet. Therefore, the conventional combustion system that has already been disclosed cannot exert the new effect based on the new combustion system described above.

Therefore, the present invention simultaneously prevents the emission of soot and NOx from the internal combustion engine, while avoiding the problem of vibration associated with the decrease in the rotational speed, An object of the present invention is to provide an internal combustion engine capable of reducing fuel wasted during idle operation and improving fuel efficiency.

Further, the present invention prevents the emission of soot and NOx from the internal combustion engine at the same time, and at the same time, when the first combustion is performed, the actual operation during idle operation is performed. An object of the present invention is to provide an internal combustion engine capable of rapidly increasing the rotation speed to a target rotation speed.

[0012]

According to the invention described in claim 1, when the amount of the inert gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak. When the amount of the inert gas supplied into the combustion chamber is further increased, the temperature of the fuel and the gas around it during combustion in the combustion chamber becomes lower than the soot generation temperature, and soot is hardly generated. In the engine, the amount of the inert gas supplied to the combustion chamber is larger than the amount of the inert gas at which the soot generation amount reaches a peak, and the first combustion in which the soot is hardly generated, and the soot generation amount is Idle operation in which the first combustion is performed is provided with switching means for selectively switching between the second combustion in which the amount of the inert gas supplied to the combustion chamber is smaller than the peak amount of the inert gas. The target combustion speed at the time when the second combustion is Internal combustion engine set to a lower rotational speed than the target rotational speed during idling dividing is provided.

In the internal combustion engine according to the first aspect of the present invention, the target rotation speed during idle operation in which the first combustion is performed is set to a rotation speed lower than the target rotation speed during idle operation in which the second combustion is performed. ing. By the way, the rotation at low engine speed has a more pronounced rotation unevenness due to the explosion than the rotation at high engine speed. Therefore, there is a background that the problem of vibration becomes large when the engine speed is reduced. On the other hand, the peak of the combustion pressure during the first combustion is lower than the peak of the combustion pressure during the second combustion, that is, the rotation unevenness during the first combustion is smaller than the rotation unevenness during the second combustion. Therefore, when the first combustion is being performed, the problem of vibration does not occur even if the rotational speed is reduced as compared to when the second combustion is being performed. Therefore, as described above, in the internal combustion engine according to claim 1, the target rotation speed during the idle operation in which the first combustion is performed is lower than the target rotation speed during the idle operation in which the second combustion is performed. Is set to a number. As a result, it is possible to reduce fuel wasted during idle operation and improve fuel efficiency, while avoiding the problem of vibration associated with a decrease in rotation speed.

According to the second aspect of the present invention, the internal combustion engine according to the first aspect performs the correction for increasing the target rotational speed during the idle operation in which the first combustion is performed when the engine temperature is low. Provided.

In the internal combustion engine according to the second aspect of the present invention, the correction is performed to increase the target rotational speed during the idle operation in which the first combustion is performed when the engine temperature is low, so that the flame is burned due to the low engine temperature. It is possible to prevent the engine from stopping due to the development being hindered and the combustion becoming unstable.

According to the third aspect of the present invention, the internal combustion engine according to the first aspect performs the correction for increasing the target rotational speed during the idle operation in which the first combustion is performed when the intake air temperature is low. Provided.

In the internal combustion engine according to the third aspect of the present invention, the correction is performed to increase the target rotational speed during the idle operation in which the first combustion is performed when the intake air temperature is low. It is possible to prevent the engine from stopping due to the development being hindered and the combustion becoming unstable.

According to the invention described in claim 4, when the external load increases, the internal combustion engine according to claim 1 is corrected so as to increase the target rotational speed during idle operation in which the first combustion is performed. Will be provided.

In the internal combustion engine according to the fourth aspect, when the external load increases, for example, when the air conditioner, the power steering, etc. are actuated, the target rotational speed during idle operation in which the first combustion is performed is increased. Since the correction is performed, it is possible to prevent the engine from stopping due to an increase in the external load applied to the engine.

According to the invention as set forth in claim 5, a catalyst having an oxidizing function is arranged in the engine exhaust passage for oxidizing the unburned hydrocarbons discharged from the combustion chamber, and the temperature of the catalyst is increased. The internal combustion engine according to claim 1, wherein a correction is performed to increase the target engine speed during idle operation in which the first combustion is performed when the engine speed is low.

According to the invention described in claim 6, there is provided the internal combustion engine according to claim 5, wherein the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst and a NOx absorbent.

In the internal combustion engine according to claims 5 and 6, unburned hydrocarbons discharged from the combustion chamber are oxidized in the engine exhaust passage, so that unburned hydrocarbons are discharged from the internal combustion engine. In addition to being able to prevent it, the catalyst warm-up property is improved because correction is performed to increase the target rotation speed during idle operation in which the first combustion is performed when the temperature of the catalyst is low, such as when the engine is started. You can

According to the invention described in claim 7, as the amount of the inert gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the soot is supplied into the combustion chamber. When the amount of the inert gas is further increased, the temperature of the fuel during combustion in the combustion chamber and the temperature of the gas around it become lower than the soot generation temperature, and soot is hardly generated. The first combustion in which the amount of the inert gas supplied to the combustion chamber is larger than the amount of the inert gas which causes the peak amount of soot and the soot is hardly generated, and the inert gas which causes the peak amount of the soot amount The amount of the inert gas supplied to the combustion chamber is less than the amount of the second combustion, and the switching means for selectively switching between the second combustion and the second combustion, and the actual rotation speed during idle operation is the target rotation speed during idle operation. Fuel injection when lower than A fuel amount increase correction for increasing the actual number of revolutions during idle operation is performed by increasing and correcting the fuel injection amount injected from the valve, and the amount increase correction amount for the fuel amount increase correction for performing the first combustion is set to the first amount. There is provided an internal combustion engine in which the value is set to a value larger than the increase correction amount at the time of the fuel increase correction in which the combustion of 2 is performed.

In the internal combustion engine according to the seventh aspect, the increase correction amount at the time of the fuel increase correction for performing the first combustion is set to a value larger than the increase correction amount for the fuel increase at the second combustion correction. Has been done. By the way, since the temperature during the first combustion is lower than the temperature during the second combustion, the fuel consumption during the first combustion is worse than the fuel consumption during the second combustion. Therefore, if the increase correction amount during the fuel increase correction for performing the first combustion is made equal to the increase correction amount for the fuel increase correction for performing the second combustion, it will be It takes a longer time to increase the actual rotation speed to the target rotation speed during the idle operation in which the first combustion is performed, compared to the case where the actual rotation speed is increased to the target rotation speed. Therefore, as described above, in the internal combustion engine according to claim 7, the increase correction amount at the time of the fuel increase correction in which the first combustion is performed is the second increase correction amount.
Is set to a value larger than the increase correction amount at the time of fuel increase correction in which combustion is performed. As a result, even when the first combustion is performed, the actual rotation speed during idle operation can be quickly increased to the target rotation speed.

According to the eighth aspect of the present invention, there is provided an exhaust gas recirculation device for recirculating the exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas is the engine intake passage. An internal combustion engine according to claim 1 or 7, comprising recirculated exhaust gas recirculated therein.

In the internal combustion engine according to the eighth aspect of the present invention, the recirculated exhaust gas recirculated into the engine intake passage by the exhaust gas recirculation device is used as the inert gas, so that the inert gas is introduced into the combustion chamber from the outside. It is possible to avoid the need to provide a special means for supplying

According to the invention described in claim 9, the first
9. The internal combustion engine according to claim 8, wherein the exhaust gas recirculation rate is changed stepwise when switching from the second combustion to the second combustion or from the second combustion to the first combustion. To be done.

In the internal combustion engine according to the ninth aspect, the exhaust gas recirculation rate is changed stepwise when switching from the first combustion to the second combustion or from the second combustion to the first combustion. As a result, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the amount of soot generated peaks.

According to the tenth aspect of the invention, the exhaust gas recirculation rate when the first combustion is performed is approximately 55% or more, and when the second combustion is performed. An internal combustion engine according to claim 9, wherein the exhaust gas recirculation rate of the engine is approximately 50% or less.

In the internal combustion engine according to the tenth aspect, the exhaust gas recirculation rate when the first combustion is performed is approximately 55.
By setting the exhaust gas recirculation rate at the time of the second combustion to be about 50% or less and the exhaust gas recirculation rate at which the soot generation amount peaks, You can avoid being set to a rate.

According to the eleventh aspect of the invention, the engine operating region is defined as a first operating region on the low load side and a second operating region on the high load side.
9. The operating region according to claim 8, wherein the first combustion can be performed in the first operating region, and the second combustion can be performed in the second operating region. Internal combustion engine is provided.

In the internal combustion engine according to the eleventh aspect, when the first combustion can be executed, that is, when the temperature of the fuel at the time of combustion in the combustion chamber and the gas temperature around it can be maintained lower than the soot generation temperature. However, because the amount of heat generated by combustion is limited during engine low load operation, which is relatively small, it is possible to execute the first combustion in the first operation region on the low load side and the second operation on the high load side. The second combustion is executed in the operating region of. Therefore, appropriate combustion can be executed according to the operating region.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment in which the present invention is applied to a 4-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
Is an exhaust valve, 10 is an exhaust port, and 60 is a water temperature sensor for detecting the engine cooling water temperature. 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. Further, in the air intake pipe 17 upstream of the throttle valve 20, a mass flow rate detector 21 for detecting a mass flow rate of intake air and an intake air temperature sensor 61 for detecting an intake air temperature are arranged. It

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2
Exhaust turbine 2 of exhaust turbocharger 15 via 2
3 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. Exhaust manifold 22
An air-fuel ratio sensor 27 is arranged inside.

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 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 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 mass flow rate detector 21 is input to the input port 45 via the corresponding AD converter 47, and 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 fuel The output signal of the pressure sensor 36 is input to the input port 45 via the corresponding AD converter (not shown), and the output signals of the water temperature sensor 60 and the intake air temperature sensor 61 are also input via the corresponding AD converter 47. It is input to the port 45. Accelerator pedal 50
A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the load sensor 5
The output voltage of 1 is input to the input port 45 via the corresponding AD converter 47. 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. The engine speed is calculated based on the input output signal from the crank angle sensor 52. 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 the corresponding drive circuit 48.

FIG. 2 shows the throttle valve 2 at the time of engine low load operation.
Changes in output torque and changes in smoke, HC, CO, and NOx emissions 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. Shows an experimental example. 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 reaches 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 Ox 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 21 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 18 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).
Although not shown, the same experimental result as in FIG. 3 indicates that the amount of EGR gas supplied to the combustion chamber 5 is larger than the amount of EGR gas at which the amount of soot is peaked, and soot is hardly generated. Maximum value (peak) of combustion pressure during combustion (low temperature combustion)
Is the maximum value of the combustion pressure during the second combustion (combustion by the conventional combustion method) in which the amount of EGR gas supplied to the combustion chamber 5 is smaller than the amount of EGR gas at which the amount of soot generated reaches a peak ( It is known to be lower than (peak). From this, it can be said that the engine rotational unevenness due to the explosion at the first combustion is smaller than the engine rotational unevenness due to the explosion at the second combustion.

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 NOx generated is considerably reduced. N
A decrease in the amount of generated Ox means that the combustion temperature in the combustion chamber 5 has decreased, and therefore, it can be said that the combustion temperature in the combustion chamber 5 is low when soot is hardly generated. . The same can be said from FIG. That is, the combustion pressure is low in the state shown in FIG. 3 (B) where almost no soot is generated.
The combustion temperature inside is low.

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

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 soot generation amount 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 and the compression ratio of the air-fuel ratio. It cannot be said how many times it changes, but this certain temperature has a deep relationship with the NOx generation amount, and therefore, this certain temperature can be defined to some extent from the NOx generation amount. it can. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas surrounding it decrease, and the amount of NOx generated decreases. At this time, soot is hardly generated when the NOx generation amount becomes around 10 p.pm or less. Therefore, the above certain temperature is NO
It almost coincides with 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 during combustion in the combustion chamber 5 is made 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 generated, 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 reaches a peak when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Almost no soot is generated if the percentage is exceeded.

On the other hand, as shown by the curve B in FIG.
When the R gas is slightly cooled, the soot generation peaks when the EGR rate is slightly higher than 50%,
In this case, if the EGR rate is set to about 65% or more, 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.

FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load becomes small, the EGR rate at which the amount of soot generated peaks is slightly lowered, and soot is almost generated. The lower limit of the EGR rate that disappears also decreases slightly. 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 which is necessary 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 proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the 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. The EGR gas amount is approximately 55% or more when expressed by the EGR rate, and is 70% or more in the embodiment shown in FIG. That is, the total amount of intake gas sucked into the combustion chamber 5 is shown by the solid line X in FIG. 6, and the ratio of the amount of air to the amount of EGR gas in this total intake gas amount X is set as shown in FIG. The temperature of the fuel and the gas around it is lower than the temperature at which soot is produced, and thus no soot is generated. Also, NOx at this time
The amount of NOx generated is around 10 p.pm or less, so the amount of NOx generated is extremely small.

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

By the way, when the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. Therefore, the required load is larger in the region where the required load is larger than Lo in FIG. 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. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, E
The throttle valve 20 in which the GR control valve 31 is fully opened
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 that shown in FIG. 6, that is, the air-fuel ratio is made rich. Even so, the amount of NOx generated is 10 p.p. while preventing the generation of soot.
It can be around m or less, and even if the air amount is made larger than that shown in FIG. 6, that is, even if the average value of the air-fuel ratio is lean from 17 to 18, the soot generation is prevented. Meanwhile, the amount of NOx generated can be reduced to about 10 p.pm or less.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excessive fuel does not grow to soot, and soot is generated. There is no. Further, at this time, only a very small amount of NOx 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, NOx
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 NOx 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 low load, where the calorific value of combustion is relatively small. To be Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion can be performed by suppressing the temperature of the fuel and the gas around it at the time of low load operation in the engine to the temperature at which the growth of hydrocarbons stops halfway or less. In this way, the second combustion, that is, the combustion that is more commonly performed than the conventional one, is performed during the engine high load operation. However, even during the low load operation in the engine, the second combustion is performed depending on the engine operating state. It should be noted that here, the first combustion, that is, low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generated peaks, and soot is almost generated. The second combustion, that is, the combustion that is normally performed in the past, is the combustion that does not have the amount of soot generated and the amount of the inert gas in the combustion chamber is smaller than the amount of the inert gas that does not reach the peak. Say that.

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

That is, the operating state 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 can be performed again.

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 operating region of the engine is in the first operating region I and low temperature combustion is performed, soot is hardly generated, and instead, unburned hydrocarbons are in the state of the soot precursor or the state before it. 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.

As the catalyst 25, an oxidation catalyst, a three-way catalyst, or a NOx absorbent can be used. The NOx absorbent is NOx when the average air-fuel ratio in the combustion chamber 5 is lean.
And has a function of releasing NOx when the average air-fuel ratio in the combustion chamber 5 becomes rich.

This NOx absorbent uses, for example, alumina as a carrier and potassium K, sodium N
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 NOx 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 operation region I and the second operation 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. 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 the idle operation, the throttle valve 2
0 is closed until it is almost completely closed. At this time, the EGR control valve 31
Is closed to near full closure. 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, in order to reduce the vibration of the engine body 1 by reducing the compression pressure, the throttle valve 20 is closed to the fully closed state during the idle operation. On the other hand, the rotation at low engine speed has a larger rotational unevenness due to the explosion than the rotation at high engine speed, and therefore there is a background that the problem of vibration of the engine body 1 becomes large when the rotational speed is reduced. Therefore, the target rotation speed during idle operation is set in consideration of the vibration associated with the compression pressure and the vibration associated with the uneven engine rotation.

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, and the air-fuel ratio is increased stepwise. That is, the EGR that produces a large amount of smoke with an EGR rate
The operating range of the engine is the first because the rate range (Fig. 5) is skipped.
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 area II, the combustion which is conventionally performed is performed. In the second 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 gradually reduced as the required load L increases. Further, in this operating region II, the EGR rate becomes lower as the required load L becomes higher, and the air-fuel ratio becomes smaller as the required load L becomes higher. However, the air-fuel ratio is a lean air-fuel ratio even if the required load L becomes high. Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 10A shows the target air-fuel ratio A / F in the first operating region I. In FIG. 10A, A / F = 15.5, A / F = 16, A / F = 17,
Each of the curves indicated by A / F = 18 has a target air-fuel ratio of 1
The values are 5.5, 16, 17, and 18, and the air-fuel ratio between the curves is determined by proportional distribution. Figure 10
As shown in (A), the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the target air-fuel ratio A / F 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 the target air-fuel ratio A / F becomes larger as the required load L becomes lower as shown in FIG. 10 (A). Target air-fuel ratio A /
The fuel consumption rate increases as F increases, and therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment of the present invention, the target air-fuel ratio A / F is increased as the required load L decreases.

The target air-fuel ratio A / F shown in FIG. 10A is a ROM 4 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. 10B.
It is stored in 2. In addition, the throttle valve 2 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
The target opening degree ST of 0 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.
EGR required to achieve the target air-fuel ratio A / F shown in (A)
The target opening degree SE of the control valve 31 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. 11 (B).

FIG. 12A shows the target air-fuel ratio A when the second combustion, that is, the normal combustion by the conventional combustion method is performed.
/ F is shown. In addition, in FIG.
= 24, A / F = 35, A / F = 45, and A / F = 60, the respective curves indicated by the target air-fuel ratios of 24, 35, 45, 6 respectively.
0 is shown. Target air-fuel ratio A shown in FIG.
/ F is a 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.
It is stored in. In addition, the throttle valve 20 required to set the air-fuel ratio to the target air-fuel ratio A / F shown in FIG.
The target opening ST of 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. 13 (A), and the air-fuel ratio is shown in FIG. 12 (A).
As shown in FIG. 13B, the target opening degree SE of the EGR control valve 31 required to achieve the target air-fuel ratio A / F shown in FIG. 13 is previously set in the form of a map as a function of the required load L and the engine speed N. It is stored in the ROM 42.

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. This fuel injection amount Q 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.

Next, the operation control of this embodiment will be described with reference to FIGS. 15 and 16. Referring to FIGS. 15 and 16, first, at step 100, a flag I indicating that the operating state of the engine is the first operating region I is set.
Is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 101, where it is judged if the required load L has become larger than the first boundary X (N). To be done. When L ≦ X (N), the routine proceeds to step 105. On the other hand, if it is determined at step 101 that L> X (N), the routine proceeds to step 102, where the flag I is reset, and then the routine proceeds to step 107.

In step 100, when the flag I is not set, that is, when the operating state of the engine is in the second operating region II, the routine proceeds to step 103, where the required load L is higher than the second boundary Y (N). It is determined whether or not it has become low. When L ≧ Y (N), the routine proceeds to step 107. On the other hand, when it is determined at step 103 that L <Y (N), the routine proceeds to step 104, the flag I is set, and then the routine proceeds to step 105.

In step 105, it is determined whether the low temperature combustion can be actually executed although the operating state of the engine is in the first operating region I. When low temperature combustion can be executed, the routine proceeds to step 106, where the target engine speed NTRG during idle operation is set to 650 rpm. On the other hand, although the engine is operating in the first operating region I, when low temperature combustion cannot be performed, such as when the temperature of the catalyst 25 has not yet risen to a sufficient temperature immediately after the engine is started, When the operating state of is in the second operating region II, the routine proceeds to step 107. In step 107, the target speed NTRG during idle operation is set to 700 rpm.

That is, step 106 and step 107
Thus, the target rotation speed NTRG (= 650 rpm) during the idle operation in which the first combustion (low temperature combustion) is performed is the target rotation speed NTRG (in the idle operation in which the second combustion (combustion by the conventional combustion method) is performed. = 700 rpm). As described above, the rotation at low engine speed has a larger rotational unevenness due to the explosion than the rotation at high engine speed, and therefore there is a background that the problem of vibration becomes large when the rotational speed is reduced. Nevertheless, since the peak of the combustion pressure during the first combustion is lower than the peak of the combustion pressure during the second combustion, that is, the rotation unevenness during the first combustion is the rotation during the second combustion. Since it is smaller than the unevenness, the problem of vibration does not occur even when the rotational speed is reduced when the first combustion is performed as compared with when the second combustion is performed. Therefore, step 106 and step 1 as described above.
At 07, the target speed NTRG (= 650 rpm) during the idle operation in which the first combustion is performed is equal to the target speed NTRG (= 70 rpm) during the idle operation in which the second combustion is performed.
By setting the rotation speed lower than 0 rpm,
It is possible to reduce wasteful fuel consumption during idle operation and improve fuel efficiency while avoiding the problem of vibration associated with a decrease in rotation speed.

Next, at step 108, it is judged if the air conditioner is on or not. If the air conditioner is on, the routine proceeds to step 109, and if the air conditioner is not on,
The process proceeds to step 110 as it is. In step 109,
50 rpm is added to the target engine speed NTRG during idle operation set in step 106 or step 107 (NTRG ← NTRG + 50 rpm).

Next, at step 110, it is judged if the power steering switch is on or not. If the power steering switch is on, the routine proceeds to step 111. If the power steering switch is not on, the step is kept as it is. 112
Proceed to. In step 111, the target engine speed NTRG during idle operation set up to this point is further increased by 30 rp.
m is added (NTRG ← NTRG + 30 rpm).

By the steps 108 to 111, the correction for increasing the target rotational speed at the time of idling operation in which the first combustion is performed when the air conditioner or the power steering is operated, that is, when the external load is increased. Done. Therefore, it is possible to prevent the engine from stopping due to an increase in the external load applied to the engine.

Next, at step 112, the water temperature sensor 60
It is determined whether the cooling water temperature THW detected by is lower than 40 ° C, that is, whether the engine temperature is low. When the engine temperature is low, the routine proceeds to step 113, and when the engine temperature rises, the routine directly proceeds to step 114.
In step 113, 30 rpm is further added to the target rotational speed NTRG during idle operation set up to this point (NTRG ← NTRG + 30 rpm).

Corrections are made in steps 112 and 113 so as to increase the target engine speed during idle operation in which the first combustion is performed when the engine temperature is low. Therefore, it is possible to prevent the engine from stopping due to the instability of combustion due to the inhibition of the development of flame due to the low engine temperature.

In the modification of this embodiment, step 1
Instead of 12, it is determined whether or not the intake air temperature detected by the intake air temperature sensor 61 is low, and step 11
Instead of 3, when the intake air temperature is low, 30 rpm may be further added to the target engine speed NTRG during idle operation set up to this point (NTRG ← NTRG + 3).
0 rpm). According to this modification, the correction is performed to increase the target rotation speed during the idle operation in which the first combustion is performed when the intake air temperature is low. Therefore, it is possible to prevent the engine from stopping due to the instability of combustion due to the inhibition of the development of flame due to the low intake air temperature.

In another modification, in addition to or instead of any of the steps described above, it is determined whether the elapsed time after the engine has started is short, and the progress after the engine has started. When the time is short, that is, when the temperature of the catalyst 25 has not yet risen, 30 rpm may be further added to the target rotational speed NTRG during idle operation set up to this point (NTRG ← NTRG +
30 rpm). According to this modification, the correction is performed to increase the target rotation speed during the idle operation in which the first combustion is performed when the temperature of the catalyst 25 is low. Therefore, the warm-up property of the catalyst can be improved.

Returning to the description of this embodiment, at step 114, the same determination as at step 105 described above is performed to determine whether or not low temperature combustion is to be executed. YE
When S, the process proceeds to step 115, and low temperature combustion (first combustion) is executed from step 115 to step 119. If NO, the process proceeds to step 120 and step 12
From 0 to step 129, combustion by the conventional combustion method (second combustion) is executed.

At step 115, the target opening degree ST of the throttle valve 20 is calculated from the map shown in FIG.
The opening of the throttle valve 20 is set to this target opening ST.
Next, at step 116, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening degree of the control valve 31 is set to this target opening degree SE. Next, at step 117, the mass flow rate of the intake air detected by the mass flow rate detector 21 (hereinafter, simply referred to as the intake air amount).
Ga is captured, and then in step 118, as shown in FIG.
The target air-fuel ratio A / F is calculated from the map shown in (B). Next, at step 119, the fuel injection amount Q required to bring the air-fuel ratio to the target air-fuel ratio A / F is calculated based on the intake air amount Ga and the target air-fuel ratio A / F.

When the required load L or the engine speed N changes during the low temperature combustion, the opening degree of the throttle valve 20 and the EGR control valve 31 immediately reach the required load L and the engine speed N. According to the target opening ST,
It is matched with SE. Therefore, for example, when the required load L is increased, the amount of air in the combustion chamber 5 is immediately increased, and thus the torque generated by the engine is immediately increased.

On the other hand, the opening of the throttle valve 20 or EGR
When the opening degree of the control valve 31 changes and the intake air amount changes, the change in the intake air amount Ga is detected by the mass flow rate detector 21, and the fuel injection amount Q is controlled based on the detected intake air amount Ga. To be done. That is, the fuel injection amount Q is changed after the intake air amount Ga actually changes.

On the other hand, at step 120, the target fuel injection amount Q is calculated from the map shown in FIG. 14, and the fuel injection amount is made this target fuel injection amount Q. Then step 12
1 shows the throttle valve 20 from the map shown in FIG.
The target opening degree ST of is calculated. Next, at step 122, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. 13 (B), and the opening degree of the EGR control valve 31 is made this target opening degree SE.

Next, at step 123, the intake air amount Ga detected by the mass flow rate detector 21 is taken in. Next, at step 124, the fuel injection amount Q and the intake air amount Ga
The actual air-fuel ratio (A / F) _R is calculated from this. Next, at step 125, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 126, it is judged if the actual air-fuel ratio (A / F) _R is larger than the target air-fuel ratio A / F. When (A / F) _R > A / F, the routine proceeds to step 127, where the throttle opening correction value ΔS
T is reduced by a constant value α, then step 12
Proceed to 9. On the other hand, when (A / F) _R ≤A / F, the routine proceeds to step 128, where the correction value ΔST is increased by the constant value α, and then the routine proceeds to step 129. In step 129, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20, and the opening of the throttle valve 20 is set to this final target opening ST. That is, the opening of the throttle valve 20 is controlled so that the actual air-fuel ratio (A / F) _R becomes the target air-fuel ratio A / F.

When the required load L or the engine speed N changes during the second combustion, the fuel injection amount immediately matches the target fuel injection amount Q corresponding to the required load L and the engine speed N. Be punished. Request load L
Is immediately increased, the fuel injection amount is immediately increased, and thus the torque generated by the engine is immediately increased.

On the other hand, when the fuel injection amount Q is increased and the air-fuel ratio deviates from the target air-fuel ratio A / F, the opening degree of the throttle valve 20 is controlled so that the air-fuel ratio becomes the target air-fuel ratio A / F. That is, the air-fuel ratio is changed after the fuel injection amount Q changes.

In the above-described embodiments, the fuel injection amount Q is open-loop controlled when the low temperature combustion is performed, and the air-fuel ratio changes the opening degree of the throttle valve 20 when the second combustion is performed. It is controlled by changing.
However, the fuel injection amount Q can be feedback-controlled based on the output signal of the air-fuel ratio sensor 27 when the low temperature combustion is being performed, and the air-fuel ratio can be EGR controlled when the second combustion is being performed. It can also be controlled by changing the opening degree of the valve 31.

The second embodiment of the internal combustion engine of the present invention will be described below. The configuration of this embodiment is almost the same as that of the first embodiment shown in FIG. 17 and 1
The operation control of the present embodiment will be described with reference to FIG.

Referring to FIGS. 17 and 18, first, at step 100, it is judged if the flag I indicating that the engine operating condition is the first operating region I is set or not. When flag I is set,
That is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 101, where the required load L is the first boundary X
It is determined whether or not it is larger than (N). L ≦ X
If (N), the process proceeds to step 1701. On the other hand, if it is determined at step 101 that L> X (N), the routine proceeds to step 102, where the flag I is reset, and then the routine proceeds to step 1703.

In step 100, when the flag I is not set, that is, when the operating condition of the engine is in the second operating region II, the routine proceeds to step 103, where the required load L is higher than the second boundary Y (N). It is determined whether or not it has become low. When L ≧ Y (N), the process proceeds to step 1703. On the other hand, when it is determined in step 103 that L <Y (N), the routine proceeds to step 104, the flag I is set, and then the routine proceeds to step 1701.

At step 1701, it is judged if the low temperature combustion can be actually executed although the operating state of the engine is in the first operating region I. When low temperature combustion can be executed, the process proceeds to step 1702, and at step 1702,
An increase amount for increasing or decreasing the fuel injection amount injected from the fuel injection valve 6 when the actual rotation speed during idle operation becomes lower or higher than the target rotation speed during idle operation Alternatively, the reduction correction amount QIIDL is set to 0.1 mm ³ / st. On the other hand, although the engine is operating in the first operating region I, when low temperature combustion cannot be performed, such as when the temperature of the catalyst 25 has not yet risen to a sufficient temperature immediately after the engine is started, When the operating state of is in the second operating area II, step 17
Go to 03. In step 1703, the fuel injection amount injected from the fuel injection valve 6 is increased or decreased when the actual rotation speed during idle operation becomes lower or higher than the target rotation speed during idle operation. Increase or decrease correction amount QIIDL for 0.08 mm ³ /
set to st. That is, the increase or decrease correction amount QIIDL during the fuel increase or decrease correction in which the first combustion is performed
(= 0.1 mm ³ / st) is an increase or decrease correction amount QIIDL at the time of fuel increase or decrease correction in which the second combustion is performed.
It is set to a value larger than (= 0.08 mm ³ / st).

Next, at step 1704, NTRG>
It is determined whether or not NE + 5 rpm, that is, whether or not the actual rotational speed NE during idle operation is lower than the target rotational speed NTRG during idle operation minus 5 rpm. When YES, the actual speed N during idle operation
It is determined that E becomes lower than the target rotational speed NTRG during idle operation, and in step 1705, the correction amount QIIDL is added to the fuel injection amount correction amount QII by the idle speed control (QII ← QII + QIID).
L). On the other hand, when NO is determined, it is determined that the actual rotation speed NE during the idle operation is not lower than the target rotation speed NTRG during the idle operation, and step 170 is performed as it is.
Go to 6.

Next, at step 1706, NTRG <
It is determined whether or not NE-5 rpm, that is, whether or not the actual rotational speed NE during idle operation is higher than the target rotational speed NTRG during idle operation plus 5 rpm. When YES, the actual speed N during idle operation
It is determined that E becomes higher than the target rotation speed NTRG during idle operation, and in step 1707, the correction amount QIIDL is subtracted from the fuel injection amount correction amount QII by the idle speed control (QII ← QII-QII.
DL). On the other hand, if NO, it is determined that the actual rotational speed NE during idle operation is not higher than the target rotational speed NTRG during idle operation, and the process proceeds to step 17 as it is.
Proceed to 06.

By the way, since the temperature at the time of the first combustion (low temperature combustion) is lower than the temperature at the time of the second combustion (combustion by the conventional combustion method), the fuel consumption at the time of the first combustion is at the time of the second combustion. Worse than fuel economy. Therefore, if the increase correction amount QIIDL during the fuel increase correction for the first combustion is made equal to the increase correction amount QIIDL during the fuel increase correction for the second combustion, the idle operation in which the second combustion is performed is performed. It takes a longer time to increase the actual rotation speed NE to the target rotation speed NTRG during the idle operation in which the first combustion is performed than to increase the actual rotation speed NE to the target rotation speed NTRG. I will end up. Therefore, as described above, in the present embodiment, from step 1701 to step 1707, the increase correction amount QIIDL during the fuel increase correction for the first combustion is the increase amount during the fuel increase correction for the second combustion. It is set to a value larger than the correction amount QIIDL. As a result, even when the first combustion is performed, the actual rotation speed NE during idle operation can be quickly increased to the target rotation speed NTRG.

Next, at step 1708, the same determination as at step 1701 described above is performed to determine whether or not low temperature combustion is to be executed. If yes, step 1
15, proceed to step 115 as in the first embodiment.
From step to step 119, low temperature combustion (first combustion) is executed. If NO, the routine proceeds to step 120, where the combustion by the conventional combustion method (second combustion) is executed from step 120 to step 129 as in the first embodiment.

[0112]

According to the first aspect of the present invention, it is possible to reduce the fuel wasted during idle operation and improve the fuel consumption while avoiding the problem of vibration associated with the decrease in the rotational speed. You can

According to the second and third aspects of the present invention, it is possible to prevent the engine from stopping due to the instability of combustion due to the inhibition of the development of flame due to the low engine temperature. You can

According to the invention described in claim 4, it is possible to prevent the engine from stopping due to an increase in the external load applied to the engine.

According to the fifth and sixth aspects of the present invention, it is possible to prevent the unburned hydrocarbons from being discharged from the internal combustion engine and to improve the warm-up property of the catalyst.

According to the invention as set forth in claim 7, it is possible to rapidly increase the actual rotation speed during the idle operation to the target rotation speed even when the first combustion is performed.

According to the eighth aspect of the present invention, it is possible to avoid the need for specially providing a means for supplying the inert gas from the outside into the combustion chamber.

According to the inventions of claims 9 and 10,
It is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the amount of generated soot peaks.

According to the eleventh aspect of the present invention, appropriate combustion can be executed according to the operating region.

[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 NOx generated, etc.

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 and the like 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 and the like 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 a fuel injection amount.

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

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

FIG. 17 is a flowchart for controlling the operation of the engine of the second embodiment.

FIG. 18 is a flowchart for controlling the operation of the engine of the second embodiment.

[Explanation of symbols]

5 ... Combustion chamber 6 ... Fuel injection valve 20 ... Throttle valve 29 ... EGR passage 31 ... EGR control valve 52 ... Crank angle sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F02D 21/08 301 F02D 21/08 301D 41/02 380 41/02 380E 41/16 41/16 DP 43/00 301 43 / 00 301H 301N F02M 25/07 550 F02M 25/07 550J 550K 570 570D 570G (72) Inventor Takekazu Ito Toyota City, Aichi Prefecture Toyota City 1 Toyota Motor Corporation (72) Inventor Hiroki Murata Toyota City, Aichi Prefecture Toyota Town No. 1 Toyota Motor Corporation (56) Reference JP-A-7-4287 (JP, A) JP-A-8-177654 (JP, A) JP-A-8-86251 (JP, A) JP Hei 9-287527 (JP, A) JP 9-287528 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/00-45/00

Claims (11)

(57) [Claims] 1. When the amount of the inert gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the amount of the inert gas supplied to the combustion chamber is further increased. In the internal combustion engine, the temperature of the fuel and the gas around it during combustion in the combustion chamber becomes lower than the soot formation temperature, and soot is hardly generated, and the soot generation peaks. The first combustion in which the amount of inert gas supplied to the combustion chamber is larger than the amount of gas and soot is hardly generated, and the amount of inert gas supplied to the combustion chamber is larger than the amount of inert gas at which the soot generation peaks. The second combustion is provided with a switching unit that selectively switches between the second combustion in which the amount of the inert gas that is generated is small and the second combustion in which the target rotation speed during the idle operation in which the first combustion is performed is performed. Times lower than the target speed during operation Internal combustion engine set to the number of revolutions. 2. The internal combustion engine according to claim 1, wherein when the engine temperature is low, correction is performed to increase the target rotational speed during idle operation in which the first combustion is performed. 3. The internal combustion engine according to claim 1, wherein when the intake air temperature is low, correction is performed to increase the target engine speed during idle operation in which the first combustion is performed. 4. The internal combustion engine according to claim 1, wherein when the external load increases, correction is performed to increase the target rotation speed during idle operation in which the first combustion is performed. 5. A catalyst having an oxidizing function is arranged in an engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber, and the first combustion is performed when the temperature of the catalyst is low. The internal combustion engine according to claim 1, wherein the correction is performed to increase the target engine speed during idle operation. 6. The catalyst is an oxidation catalyst, a three-way catalyst or NO.
An internal combustion engine according to claim 5, comprising at least one x-absorbent. 7. The soot generation amount gradually increases and reaches a peak when the amount of the inert gas supplied to the combustion chamber is increased, and the amount of the inert gas supplied to the combustion chamber is further increased. In the internal combustion engine, the temperature of the fuel and the gas around it during combustion in the combustion chamber becomes lower than the soot generation temperature, and soot is hardly generated, and the soot generation peaks. First combustion in which the amount of inert gas supplied to the combustion chamber is larger than the amount of gas and soot is hardly generated, and the amount of inert gas supplied to the combustion chamber is larger than the amount of inert gas at which the soot generation peaks. The fuel injection is provided when the actual rotation speed during idle operation becomes lower than the target rotation speed during idle operation, which is provided with a switching means for selectively switching between the second combustion in which the amount of the inert gas that is generated is small. The amount of fuel injected from the valve By increasing the amount of fuel, the fuel amount is increased to increase the actual number of revolutions during idle operation.
An internal combustion engine in which an increase correction amount at the time of fuel increase correction for performing the first combustion is set to a value larger than an increase correction amount at the time of fuel increase correction for performing the second combustion. 8. A recirculation exhaust system comprising an exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into an engine intake passage, wherein the inert gas is recirculated into the engine intake passage. The internal combustion engine according to claim 1 or 7, which is made of gas. 9. The exhaust gas recirculation rate is changed stepwise when switching from the first combustion to the second combustion or from the second combustion to the first combustion. Internal combustion engine according to item 8. 10. The exhaust gas recirculation rate when the first combustion is performed is approximately 55% or more, and the exhaust gas recirculation rate when the second combustion is performed is approximately 50%. The internal combustion engine according to claim 9, which is not more than a percentage. 11. 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 the first combustion can be executed in the first operating region. The internal combustion engine according to claim 8, wherein the second combustion is performed in the second operation region.